Recycling doi: 10.3390/recycling11050094

Authors: Igor Cleyton Ferreira de Sousa Cláudio Henrique de Almeida Feitosa Pereira Yuri Sotero Bomfim Fraga

The excessive generation and improper disposal of Construction and Demolition Waste (CDW) represent one of the main environmental challenges in the sector. However, its potential for reuse and recycling enables the mitigation of these impacts through sustainable practices. In this context, the present study aimed to estimate reference values for the Federal District, Brazil, regarding the environmental impacts associated both with the transportation stage of CDW—from its point of origin to the processing facility—and with the operations involved in its conversion into recycled aggregates, through the application of a simplified Life Cycle Assessment approach. The analysis focused on quantifying the consumption of electricity, water, and fossil fuels, as well as carbon dioxide emissions and the generation of contaminant residues throughout the analyzed process. The system boundary adopted corresponds to a “cradle-to-gate” scope, with a declared unit of 1 tonne of recycled aggregate. Additionally, a survey of scientific studies providing life cycle inventory data related to aggregate production was conducted, enabling a consistency analysis with the data obtained in this study. Primary data related to the recycled aggregate production process were collected through direct field observations, in situ measurements, and the analysis of operational records from the studied facility. For the year 2024, the environmental indicators obtained showed that the production of 1 tonne of recycled aggregate required 1.23 kWh of electricity, 5.65 L of water, and 2.14 L of diesel, in addition to resulting in emissions of 6.64 kg CO2 eq and the generation of 2.3 kg of contaminant waste.

Recycling doi: 10.3390/recycling11050093

Authors: Jiani Tian Daohong Zhang Ning Jiang Chengze Yu Jiaqi Hou Chunming Hu Panpan Wang Chaocan Li

Effective management of organic wastes is essential for green and low-carbon development. Conventional technologies, including incineration, pyrolysis, hydrothermal carbonization (HTC), gasification, anaerobic digestion (AD), and composting, have supported waste reduction and basic resource recovery, but they remain limited in high-efficiency conversion and high-value utilization. This review comparatively evaluates these conventional routes together with advanced and intensified technologies, including microwave-assisted pyrolysis (MAP), plasma treatment, supercritical water gasification (SCWG), and flash joule heating (FJH), with emphasis on suitable feedstocks, performance characteristics, application boundaries, and integration potential. In general, wastes with high moisture content are more suitable for HTC, AD, and SCWG, whereas relatively dry wastes and wastes with high carbon content are more suitable for pyrolysis, gasification, plasma treatment, and FJH upgrading. The review also discusses representative integrated pathways, such as HTC-SCWG, pyrolysis and plasma coupling, AD and gasification coupling, and pyrolysis and FJH coupling, which may improve carbon conversion, broaden product portfolios, and reduce residual pollutants. However, large-scale implementation is still constrained by feedstock heterogeneity, heat and mass transfer limitations, catalyst deactivation, reactor corrosion, and system cost. Overall, no single technology is universally optimal; technology selection should depend on feedstock properties, moisture content, and target products.

Recycling doi: 10.3390/recycling11050092

Authors: Maria del Carmen Aragón-Duarte Hilda Esperanza Esparza-Ponce Lillian Vianey Tapia-Lopez Antonia Luna-Velasco Luis Fernando Jiménez-Tinoco Javier Servando Castro-Carmona

This study proposes the development of a recycling process for the reintegration of dental zirconia waste into CAD/CAM systems for rapid prototyping, with the objective of demonstrating the feasibility of manufacturing functional products from recycled zirconia obtained from a commercial dental laboratory. The proposed methodology aims to explore a simple and economically viable process, which involves the purification and processing of a heterogeneous zirconia powder, followed by the fabrication of pre-sintered blocks suitable for CAD/CAM applications. The recycled bulk ceramic was characterized and compared with commercial zirconia through density measurements, X-ray diffraction, scanning electron microscopy, Vickers hardness, flexural strength testing, and sintering shrinkage analysis. The results indicated that, although recycled zirconia exhibits lower property values than the commercial reference material, it retains adequate characteristics for specific practical applications. Consequently, to demonstrate industrial feasibility, four components were designed using CAD and machined using CAM from the recycled blocks, simulating a rapid prototyping process. The fabricated components exhibited a smooth and flawless surface, were mechanically robust and solid to the touch, and showed well-defined contours with sharp edges. Dimensional analysis demonstrated high accuracy, with an average percentage error of 0.53% ± 0.14. These findings demonstrate that high-value ceramic waste can be reintegrated into the production chain as functional industrial components through a process that is closely aligned with the real conditions of industrial recycling, while also mitigating environmental contamination from hazardous industrial waste.

Recycling doi: 10.3390/recycling11050091

Authors: Ivan Gaytán Aguilar María del Consuelo Hernández Berriel Federico del Razo López Everardo Efrén Granda Gutiérrez María del Consuelo Mañón Salas Roberto Alejo Eleuterio

Municipal solid waste management (MSWM) systems in Latin America are constrained by limited access to high-resolution operational data, compelling local authorities to depend on aggregated national statistics that are inadequate for behaviorally informed intervention design. This limitation is particularly evident in the State of Mexico, which generates about 16,187 tons of waste every day but only recycles only 11%. In this context, this study introduces a diagnostic data science framework to identify behaviorally grounded citizen segments and their defining attributes, supporting evidence-based decision-making in MSWM. Primary survey data from 560 households across three municipalities were used, and a three-stage analytical pipeline was implemented to account for contextual heterogeneity. First, k-means clustering was applied to identify behavioral segments. Second, random forest classifiers were used to validate cluster coherence and quantify feature importance. Third, the Apriori algorithm was used to extract association rules that capture recurrent material-mixing behaviors. The results revealed municipality-specific segmentation structures (Tequixquiac: K = 6; Tlalpujahua: K = 3; Xalatlaco: K = 2), with material-specific disposal behaviors emerging as stronger segmentation drivers. Random forest classifiers validated cluster coherence with 100% accuracy, confirming that segments represent behaviorally distinct archetypes. The proposed framework converts raw behavioral data into actionable municipal visions. This approach focuses on finding diagnostic patterns instead of making predictions by utilizing machine-learning-driven MSWM research.

Recycling doi: 10.3390/recycling11050090

Authors: Anayansi Estrada-Monje Sergio Alonso-Romero Anayansi Zaragoza-Estrada María Cristina Kantún-Uicab Claudia Ivone Piñón-Balderrama Claudia Alejandra Hernández-Escobar Erasto Armando Zaragoza-Contreras

The increasing use of biodegradable polymers, especially poly (lactic acid) (PLA), has raised concern about their entry into conventional post-consumer recycling streams. This review examines the technical and systemic consequences of PLA contamination in the high-density polyethylene (HDPE) circular economy through the “drop-in delusion,” defined here as the mistaken assumption that a sustainability-marketed polymer can enter an established recycling stream without compromising system compatibility. Focusing on contamination-sensitive conditions in which segregation, sorting, or stream purity are insufficient to prevent cross-contamination, the review discusses the immiscibility of HDPE/PLA blends and the resulting changes in stiffness, ductility, toughness, and aging behavior. It also analyzes mitigation routes such as improved sorting, compatibilization, and policy measures, while emphasizing that the practical severity of contamination depends on local infrastructure and contamination levels. In addition, it considers the risk that contaminated materials diverted into lower-value applications may become more vulnerable to interfacial damage, weathering, and secondary fragmentation. Overall, the review argues that circular-plastics strategies must distinguish biodegradability from recycling-system compatibility to protect the quality and value of HDPE recyclates.

Recycling doi: 10.3390/recycling11050089

Authors: Md Kaviul Islam Anirudha Karati Ikenna C. Nlebedim Pranav Shrotriya

The printed circuit board (PCB), a central component of most electronic devices, represents a significant fraction of the electronic product waste stream. The complex composition of PCBs, consisting of metals, polymers, and fiberglass, requires specialized recovery steps to reclaim valuable and critical materials and the safe disposal of brominated compounds. In this review paper, we describe the current state of critical material recovery and traditional recycling technologies and identify key obstacles to large-scale implementation. Metals present at high concentrations, such as copper, lead, and iron, are conventionally recovered from PCBs using hydrometallurgical, pyrometallurgical, or electrometallurgical processes. Hydrometallurgical methods achieve high selectivity through chemical leaching but pose significant challenges for effluent and reagent recovery. Pyrometallurgical methods facilitate rapid metal separation through smelting but require substantial energy and may release harmful gases. Electrometallurgical techniques produce high-purity metals but are constrained by pretreatment requirements and the consumption of energy. The non-metallic fraction of PCB waste is recycled using thermochemical conversion, microwave-aided heating, and direct recycling of epoxy–fiberglass composites, enabling material or energy recovery. The recovered polymer from direct recycling may have reduced mechanical strength and poor compatibility with new polymer matrices, and the resulting products from the thermal conversion suffer from incomplete conversion, degradation of quality, and residual contamination, as compared to synthetic polymers. Recent process developments have focused on extracting rare earth and supply-critical materials present at lower concentrations in the waste stream. The literature on existing and emerging approaches for recycling PCB wastes is reviewed to identify sustainable, economically viable, and environmentally responsible strategies for the recovery and reuse of critical materials from waste streams.

Recycling doi: 10.3390/recycling11050088

Authors: Wojciech Szymański Sonia Boczkal Dawid Kapinos Joanna Hrabia-Wiśnios Elżbieta Szymańska Lutz Stobbe Thomas Mager Marek Kościelski

Aluminum multifunctional housings can enhance circularity in electronics by replacing polymer enclosures while integrating heat sinking and electronic functions via laser direct structuring (LDS). Within the ALU4CED concept, we applied an IR-compatible LDS lacquer on aluminum, formed conductive tracks by electroless Cu/Ni/Au metallization, assembled components, and assessed end-of-life recyclability. Controlled remelting trials compared three disassembly levels: complete housings with PCBs and components, housings without PCBs, and housings with only integrated tracks. Metal yield rose from 81.4% for complete assemblies to 93.2% after PCB removal, while leaving integrated LDS tracks did not measurably penalize recovery. Only the complete electronics variant showed critical contamination (Cu = 1.64 wt.% vs. 0.25 wt.% limit for EN AC 4343); after PCB removal, composition remained close to the reference and major elements (Si, Mg, Fe) stayed within specification. Prefil testing indicated very low total inclusion content (0.006/0.001/0.002 mm2·kg−1), confirming high melt cleanliness despite coatings. Following remelting → billet casting → extrusion, tensile properties (Rm ≈ 120–123 MPa, Rp0.2 ≈ 59–61 MPa, A ≈ 29–33%) were comparable to the reference profile. These results demonstrate the technological feasibility of closed-loop recycling for LDS functionalized aluminum housings and inform clear Design-for-Recycling guidance: design for rapid PCB removal, allow LDS layers to remain during melting, and maintain compatibility with the 4343 family to enable efficient internal recycling.

Recycling doi: 10.3390/recycling11050087

Authors: Gavin E. Collis Renée L. Webster Aaron Seeber Chris Sheedy Sherman Wong Thomas J. Raeber Yanyan Zhao

Using strategies employed in synthetic chemistry, we investigated the chemicals found in lithium iron phosphate (LFP) spent battery via an initial dichloromethane (DCM) extraction of the individual cathode and anode. The pre- and post-treated electrodes and DCM extracts were examined using a range of analytical techniques. A total of 26 compounds were identified, which included the following: (1) some of the benchmark materials, LFP, lithium hexafluorophosphate (LIPF6), polyvinylidene fluoride (PVDF), graphite and carbon black; (2) NMR spectroscopy of DCM extract revealed five main chemicals, which were ethylene and propylene carbonate solvents, LiPF6, lithium tetrafluoroborate (LiBF4), and an unknown fluorochemical; (3) analysis of the water-treated DCM extract revealed 21 chemicals by GCMS, several fluorochemicals; (4) 12 chemicals were found in both cathode and anode and three only in the anode; (5) only 13 of the 21 chemicals could be properly named, whilst four had some notable functionality and three could not be identified; and (6) ICP analysis revealed high levels of Al, Cu, Fe, V, and Zn in both electrodes and spent electrolyte. The high number of chemicals present in the spent electrolyte and electrodes suggest battery manufacturers use many proprietary chemicals to enhance battery properties. This procedure allows insight and identification of chemicals present in waste LIBs which will require advanced chemical techniques to recover high yields and purity of recycled materials and the need to dispose of hazardous waste.

Recycling doi: 10.3390/recycling11050086

Authors: Wilfrido Campos Francisco Jonathan Villanueva Tavira Jonathan Jesús Carranza Vega Blanca Dina Valenzuela Robles Erik Rosado Tamariz Andrés Blanco Ortega

Municipal Solid Waste (MSW) is a common problem in all cities worldwide; it is expected to increase to 3400 billion tons by 2050. In Mexico, an average of 108,146 tons of MSW are generated daily. Artificial Intelligence (AI) is a computer tool that allows the development of systems that facilitate the recycling process. However, most AI programs focus on classifying paper, plastic, glass and metal; therefore, wood and textile waste have received little attention. Using texture techniques such as Local Binary Pattern (LBP), Gray-Level Co-occurrence Matrix (GLCM), Histogram of Oriented Gradients (HOG), Canny/Sobel edge detection, Fractal Dimension (FD), feature values were extracted and integrated from 4396 images belonging to wood and textile categories. Using the Random Forest Importance method, the most significant features were selected to train three Machine Learning (ML) algorithms. Multilayer Perceptron (MLP) achieved the best performance in accuracy with 96.70%, followed by Random Forest (RF) at 95.45% and Support Vector Machine (SVM) with 95.22%. The implementation of these comparisons will serve as a basis for the development of new technological tools with low computational cost that carry out a proper waste separation.

Recycling doi: 10.3390/recycling11050085

Authors: Samuel Alcoceba-Pascual Nicolás I. Villanueva-Martínez Abel Ortego Ricardo Magdalena Sofia Russo Marta Iglesias-Émbil Alicia Valero

The automotive sector is the third-largest consumer of plastics in Europe, after packaging and construction, and its demand is expected to grow. Plastic recycling at the end of vehicle life remains low, with 80% of plastics ending up in energy recovery or landfills. Three vehicle models (SEAT Ibiza Gen. IV and SEAT Leon Gen. II and III) with two trim versions (Reference and Formula Racing) were examined to identify the most critical plastic components from an exergy perspective. Ecodesign measures were defined by considering both the disassemblability of vehicle components and their recyclability potential as key criteria to evaluate end-of-life recovery pathways and guide material and design optimization strategies. The proposed methodology classified the measures into three types: (1) substitution of high-exergy plastics with lower-impact alternatives; (2) use of recycled plastics instead of primary materials, with substitution rates depending on the material; and (3) reuse of components in new models, evaluated by disassemblability and end-of-life condition. Results show that Type 1 measures achieved savings up to 70 MJ, mainly in the floor covering and engine compartment insulator, while Type 2 measures provided larger reductions, up to 1.7 GJ, mainly in bumpers and carpets. Type 3 measures showed reuse potential for paddings and insulators but faced limitations in carpets and dashboards. Findings highlight the importance of material selection and implementing disassembly and recycling strategies to reduce the exergy of vehicle plastics.

Recycling doi: 10.3390/recycling11050084

Authors: Nutcha Taneepanichskul

Urban plastic waste management in large metropolitan regions remains constrained by low recovery rates despite growing policy attention. This study adopts a sustainability-oriented innovation (SOI) perspective to examine how policy–technology integration reshapes system-level performance in urban plastic waste systems. Using Bangkok as a representative case, a system-level model integrates plastic waste generation growth, time-dependent behavioural adoption of separation at source, contamination-sensitive sorting efficiency, and mass-balance material flows. Three scenarios are assessed: Business-as-Usual, separation-at-source policy only, and an integrated policy–technology system with advanced sorting. Results show that the baseline system remains stagnant at approximately 3.1% recovery. Policy intervention alone increases recovery gradually, reaching around 20% by 2045 despite participation approaching an 85% ceiling. In contrast, integrating policy with advanced sorting generates non-linear gains, surpassing 20% recovery within two years and reaching approximately 47% by 2045, driven by substantial contamination reduction. A Monte Carlo sensitivity analysis extends the integrated pathway to 2060. The median recovery trajectory stabilises at 68%, while the probability of achieving more than 70% recovery rises to 28% by 2040 and plateaus at 33% thereafter. The findings demonstrate that circular economy performance is probabilistic and depends on system-level alignment between behavioural participation, material quality, and technological capability.

Recycling doi: 10.3390/recycling11050083

Authors: Thobile Zikhathile Harrison Atagana Joseph Bwapwa Taurai Mutanda

Healthcare waste management is a growing environmental and economic challenge due to increasing waste volumes, hazardous materials, and continued reliance on linear disposal methods such as incineration and landfilling. This review aims to examine how circular economy and zero-waste approaches can be applied to healthcare waste management to improve sustainability, resource efficiency, and system performance. A structured narrative review was conducted using peer-reviewed literature obtained from prominent scientific databases, concentrating on circular strategies, zero-waste initiatives, digital technologies, and policy frameworks relevant to healthcare waste systems. The reviewed studies indicate that practices such as improved waste segregation, recycling and material recovery, reusable product design, digital waste tracking, and Extended Producer Responsibility can significantly reduce waste generation, lower environmental impacts, and achieve cost savings, while maintaining infection control and patient safety. However, the review also identifies key barriers to implementation, including regulatory complexity, limited infrastructure, financial constraints, and weak coordination among stakeholders. The novelty of this review lies in its integrated analysis of circular economy and zero-waste strategies through the lens of digital enablement, offering a systems-based framework for transforming healthcare waste management beyond incremental improvements. The findings highlight that successful circular healthcare waste management requires strong institutional leadership, supportive policies, and the integration of digital technologies to enable monitoring, traceability, and decision-making. This review enhances the comprehension of how circular economy principles can facilitate the transition from linear to sustainable healthcare waste systems and provides guidance for policymakers, healthcare managers, and researchers. Future research should focus on evaluating real-world implementation, advancing recyclable and reusable medical materials, and developing standardised indicators to measure circular performance in healthcare settings.

Recycling doi: 10.3390/recycling11050082

Authors: Andrea Margheri Matteo Cordara Andrea Ballarino Carlo Brondi

Variability in life cycle assessment (LCA) results for metal recycling technologies arises from multiple sources, including allocation methods, recycling route, regionality of impacts, and type of waste treated. Among these factors, waste composition is particularly critical, as it directly influences process performance by affecting auxiliary material consumption and emissions. This work investigates four waste categories: metals from incineration bottom ash (MBA), waste-printed circuit boards (WPCBs), industrial waste from gold refining (GRA), and spent automotive and industrial catalysts (SCs). The Climate Change (CC) for 1000 kg of waste was estimated at 3251 × 103 kg CO2eq for WPCBs, 3923 × 103 kg CO2eq for MBA, 1569 × 103 kg CO2eq for GRA, and 2101 × 103 kg CO2eq for SCs. A sensitivity analysis was performed to assess the influence of allocation methods on results for 1kg of recycled metal. The highest variability in CC across waste categories was observed for gold (up to 8477%) with the black-box economic allocation method, while different allocation methods reached 21,700% for WPCBs. These results highlight the strong influence of methodological choices and waste characteristics, emphasizing the need for transparent and consistent LCA reporting.

Recycling doi: 10.3390/recycling11050081

Authors: Inês Costa Bruna Machado Bruno Silva Catarina Dias Luís Silva Isabel Carvalho Vera Sá Alexandre Pereira Catarina Basto-Silva

The European woodworking and furniture sector faces increasing sustainability challenges, including dependence on virgin raw materials and low recycling rates of furniture waste, highlighting the need for integrated environmental and economic assessments to support circular solutions. The purpose of this study is to evaluate and compare the environmental and economic performance of boards produced with different proportions of Polyethylene Recycling Waste (PRW) sourced from a Portuguese plastic recycling company, using an integrated Life Cycle Assessment and Life Cycle Costing approach. The environmental performance was assessed following ISO standards using the ReCiPe 2016 Midpoint (H) method, while the economic analysis included internal and external costs. First, the environmental and economic performance of PRW was assessed per 1 kg of material. Subsequently, four board formulations produced at pre-industrial scale, in a Portuguese company, were compared per 1 m3 of board: 100PRW; 80PRW20FW (with 20% furniture waste, FW); 80PRW20PE (with 20% virgin polyethylene, PE); and 80PRW20PU (with 20% virgin polyurethane, PU). Results show that waste-based boards (100PRW and 80PRW20FW) consistently present lower environmental impacts and improved cost-efficiency compared to formulations incorporating virgin polymers, particularly PU. Global warming and terrestrial ozone formation were the main contributing impact categories, largely driven by energy consumption. The dominant impact stage varied by formulation, with pressing prevailing in waste-based options and raw material production in virgin-polymer-based boards. These findings demonstrate that increasing the share of waste materials can significantly improve both environmental and economic performance, supporting the transition towards circular material solutions in the furniture sector. This study provides a novel contribution by integrating LCA and LCC in the assessment of pre-industrial PRW boards, offering practical insights for industry decision-making and sustainable material design.

Recycling doi: 10.3390/recycling11050080

Authors: Chin Mei Chan Amal Asheeba Romzi Linda Lim Biaw Leng Muhammad Raziq Rahimi Kooh

Developing practical low-cost adsorbents for dye-contaminated wastewater remains a critical challenge, especially for persistent cationic dyes such as crystal violet (CV). Here, raw rockmelon skin (RMS), an abundant fruit-processing residue, and its NaOH-modified derivative (NaOH-RMS) were investigated as adsorbents for CV adsorption. Alkaline treatment altered the biomass’s characteristics and affected its adsorption behaviour. Equilibrium was reached within 120 min, and the kinetic data were best fit by the pseudo-second-order model. Equilibrium analysis showed that the Freundlich model best described RMS. In contrast, NaOH-RMS was better represented by the Langmuir model, indicating that alkaline treatment altered the adsorption behaviour of the biomass surface. The Langmuir-derived maximum adsorption capacities were 343.7 mg g−1 for RMS and 295.2 mg g−1 for NaOH-RMS, indicating that NaOH modification did not increase the maximum adsorption capacity. Adsorption was spontaneous across 298–343 K, and both materials retained satisfactory removal performance over five regeneration cycles, particularly under basic desorption conditions. Overall, NaOH treatment altered the adsorption behaviour from heterogeneous adsorption on RMS to a more Langmuir-type adsorption pattern on NaOH-RMS, despite not increasing the maximum adsorption capacity. These findings support the valorisation of fruit-processing residues as practical adsorbents for dye-contaminated wastewater.

Recycling doi: 10.3390/recycling11040079

Authors: Inês Silva Graça Martinho Mário Ramos

The progression towards a circular economy in the construction sector has gained attention as a response to rising resource consumption and construction and demolition waste generation, with material reuse playing a central role. In this context, this study analyses the literature on reuse in the construction sector, examining its investigation over time and its relation to European regulatory frameworks and policy strategies. A systematic literature review was conducted using a structured search across the B-on, Scopus, and Web of Science databases. The search targeted peer-reviewed journal articles in English, published between 2008 and 2023, focusing on titles, abstracts, and keywords with predefined terms. A total of 78 articles met the inclusion criteria and were analysed. Research activity has increased in recent years, reflecting growing European policy attention, particularly the Waste Framework Directive, its 2018 amendment, and the Circular Economy Action Plan. Most studies address strategies to promote the circular economy, waste management practices, life cycle assessments, and the identification of barriers and opportunities to reuse. Despite the expanding literature, reuse remains insufficiently addressed. These findings underline the need for more targeted research and stronger integration between policy and practice to support effective reuse in the construction sector.

Recycling doi: 10.3390/recycling11040078

Authors: Dheeraja Winter Svea Ziegner Simone Krafft Markus Grömping Silvio Beier

The paper sector is characterised by high freshwater consumption and a strong need for improved resource efficiency. In this context, industrial digestates derived from short-fibre residues in paper recycling mills represent a promising substrate for water recovery within a circular economy framework. This study investigated the dewatering of short-fibre digestates as a pre-treatment for downstream membrane processes, aiming to maximise the liquid fraction (LF) recovery while minimising dry matter (DM) content. Seven scenarios were studied: sedimentation (S0); pre-sedimentation with chemical addition using iron(III) chloride (FeCl3) + polydiallyldimethylammonium chloride (polyDADMAC) (S1), FeCl3 + starch (S2), Nanofloc® (S3), and polyDADMAC (S4); and direct dewatering without pre-sedimentation using polyDADMAC with cloth filtration (S5) and centrifugation (S6). With reference to the sedimentation supernatant, S4 achieved the highest DM separation efficiency of 76%, followed by S1 (64%), whereas S2 and S3 were below 40%. However, LF recovery relative to the initial digestate was limited in scenarios S1–S4 to 17% (170 g/kgdigestate), with DM concentrations of 2.0–4.8 g/kgLF. In contrast, direct dewatering increased LF recovery substantially, with centrifugation (S6) achieving up to 690 gLF/kgdigestate and cloth filtration (S5) 420 g/kgdigestate, while maintaining a low DM (1.7 g/kgLF). Chemical oxygen demand (COD) and phosphorus (Ptot) were largely separated from the liquid fractions in all the scenarios. Nitrogen (Ntot) and ammonium (NH4-N) in the LF remained more variable, ranging from 22 to 153 and 5 to 22 mg/kgdigestate, respectively. These results indicate that centrifugation with polyDADMAC is the most effective approach, suggesting that mechanical force with a chemical additive can be used for the efficient dewatering of short-fibre digestates.

Recycling doi: 10.3390/recycling11040077

Authors: Noemi García-Gomez Roifer Pérez-Vásquez José Luis Pasquel-Reátegui Manuel Fernando Coronado-Jorge Enrique Navarro-Ramírez Karen Gabriela Documet-Petrlik Pierre Vidaurre-Rojas Keller Sánchez-Dávila Ángel Cárdenas-García

Orange waste, generally discarded, is a source of many bioactive compounds that could be used for the development of high-value-added products in the food, cosmetic, and pharmaceutical industries. The objective of this study was to evaluate the influence of extraction method (automated Soxhlet extraction and temperature-controlled maceration), solvent system, and extraction time on the recovery of bioactive compounds from Valencia orange (Citrus sinensis) by-products. Proximate characterization of the dried orange residue (DOR) was performed prior to extraction. The type of solvent (ethanol and methanol), solvent:water ratio (50, 75, and 100%), and extraction time (60 and 120 min) were evaluated in terms of total extraction yield (TEY), total phenolic content (TPC), and antioxidant capacity determined by ABTS and DPPH assays, for each extraction method. ASE generally provided higher extraction yield and total phenolic content, particularly with 75:25 ethanol:water at 120 min, whereas TCM combined with methanol produced the highest antioxidant capacity. Extracts with up to 46.32% TEY, 5.57 mg GAE/g dm, and antioxidant capacities of 66.49 and 11.10 µmol TE/g dm determined by ABTS and DPPH assays, respectively, were obtained. The results demonstrated that Valencia orange by-products are a source of phenolic compounds and antioxidants with potential for product development across different industrial sectors.

Recycling doi: 10.3390/recycling11040075

Authors: Pauls P. Argalis Kristers Gelzis Ralfs K. Valdovskis Laura Vitola

This preliminary study investigates the viability of substituting high-performance Aalborg white Portland cement (CEM I 52.5 R) with five diverse industrial byproducts: wood ash, silica waste, clay brick, glass fibre, and calcined sewage sludge ash. Sewage sludge ash was produced in a laboratory from two different sludges from wastewater treatment plants in the Latvian cities of Jelgava and Liepaja. The research evaluates the influence of substitution levels ranging from 5% to 20% on the rheology of fresh material and its early-age mechanical performance (day 7). Results indicate that particle morphology largely dictates workability; porous and angular materials, such as wood ash, clay brick, and sewage sludge ash, reduce flowability, whereas non-absorbent milled glass fibres unexpectedly improve spread diameter. Regarding mechanical performance, glass fibre and clay brick waste demonstrated the highest potential, exceeding the 48–62 MPa reference compressive strengths by achieving up to 69 MPa at a 10% substitution level. Conversely, wood ash and silica waste exhibited significant strength degradation at higher substitution levels, due to agglomeration and high water demand. This approach not only identifies viable waste streams for cement substitution but also diverts significant industrial waste from landfills, thereby reducing CO2e emissions and advancing more sustainable construction practices.

Recycling doi: 10.3390/recycling11040076

Authors: Rhudson Fellipy de Oliveira Almeida Ivaldo Itabaiana Maria Alice Zarur Coelho

Proteases are key biocatalysts widely applied in the food, pharmaceutical, detergent, and environmental industries. One of the most costly steps in large-scale enzyme production is the preparation of the culture medium, making agro-industrial wastes attractive as low-cost nutrient sources and potential inducers. The non-conventional yeast Yarrowia lipolytica stands out in bioprocess engineering due to its high secretion capacity, GRAS status, and ability to metabolize diverse industrial residues. In this study, Brazilian agro-industrial by-products, namely Corn steep liquor (CSL), brewer’s yeast residue (BYR), and okara, were evaluated as alternative nitrogen sources for protease production by Y. lipolytica IMUFRJ 50678. Enzyme activity was quantified by the azocasein method at optimized conditions (40 °C, 40 min, pH 5 and 8). After an initial exploratory screening (n = 1), brewer’s yeast residue (BYR) and okara were identified as promising candidates for protease production. These preliminary findings guided subsequent experiments performed in biological triplicate (n = 3), which confirmed the reproducibility and comparative performance of these substrates, showing higher acid protease (AXP) activity in the BYR medium ((5.4 ± 0.3) U/mL), whereas alkaline protease (AEP) activities were comparable between the BYR ((8.4 ± 0.6) U/mL) and okara ((7.5 ± 0.9) U/mL) media. CSL was associated with higher lipase activity ((11.7 ± 0.9) × 103 U/L), while esterase activity was higher in the BYR medium. These findings indicate that agro-industrial residues, particularly BYR and okara, can serve as effective nitrogen sources for protease production by Y. lipolytica IMUFRJ 50678, supporting their use in waste valorization and sustainable bioprocesses.

Recycling doi: 10.3390/recycling11040074

Authors: Daví Matos Lopes Monica Luci Oliveira de Brito Josiel Isaac Domingues de Almeida Danilo Corado de Melo Jhon Adno de Almeida Santana Manoel Ferreira Lima Neto Maico Chiarelotto

This study aimed to evaluate the effects of adding sludge generated in water treatment plants on the composting of sewage sludge, urban organic waste, and agroindustrial waste. Four treatments were conducted with different proportions of water treatment plant sludge (WTS). Four treatments were conducted with 0%, 10%, 20%, and 30% proportions of WTS. The different proportions allowed for the evaluation of the effects of WTS addition on composting. The study was carried out in composting reactors. Kinetic models were applied to study the degradation of organic matter. Physicochemical and microbiological parameters were analyzed. During the process, temperature variation and basal respiration exhibited similar patterns. Principal component analysis showed that the 30WTS (32.2% water treatment sludge) treatment presented higher values of cation exchange capacity (CEC)/total organic carbon (TOC) ratio (3.83), and germination index (94.35%), and lower values of TOC (23.67%) and C/N (carbon/nitrogen) ratio (14.45). The composts produced in all treatments complied with Brazilian regulations for the environmental and agronomic quality of organic composts. It was concluded that the inclusion of up to 30% of WTS in composting did not negatively affect the composting process and did not compromise the environmental or agronomic quality of the final organic composts.

Recycling doi: 10.3390/recycling11040073

Authors: Linda Y. Pérez-Morales Adriana Guzmán-López Rita Miranda-López Micael Gerardo Bravo-Sánchez José E. Botello-Álvarez

Latin America faces growing challenges in the management of municipal solid waste (MSW). This is particularly evident in medium-sized and metropolitan cities where rapid urbanization, limited infrastructure, and high proportions of organic waste (40–70%) converge. This review synthesizes the most recent advances in organic waste management, valorization strategies, environmental performance, and policy frameworks in Mexico and Latin America. To provide a comprehensive overview, evidence from studies on informal recycling systems, route optimization, sustainable landfill siting, food waste valorization, life cycle assessments (LCAs), and biogas production is integrated. Techno-economic analyses of energy recovery from organic fractions are specifically reviewed. This review highlights that valorization of organic waste through composting, anaerobic digestion, food supplementation, and bioproduct generation can reduce greenhouse gas emissions by 40–70% compared to landfilling, with AD–composting hybrids achieving the highest reductions of 60–70%. Community composting achieved moderate reductions, 30–50%, but at significantly lower cost and with greater social co-benefits. These alternatives for valorizing the organic fraction extend the lifespan of both confined and open landfills. It also contributes to mitigating the public health impacts related to open dumping, disease vectors, and contaminated leachate. In short, this review also highlights shortcomings in policy coherence, financial mechanisms, source separation, and technology adoption. A strategic framework is proposed that prioritizes decentralized treatment systems, the integration of informal recyclers, tax incentives, community-based waste separation, and planning based on Life Cycle Assessment (LCA). The findings point to a viable strategy for transitioning from landfill dependency to circular waste management systems that improve the quality of life for the population of Latin America and the Caribbean.

Recycling doi: 10.3390/recycling11040072

Authors: Denis Miroshnichenko Yurii Parkhomov Yurii Lypko Vladislav Reivi Yurii Rohovyi Mariia Shved Bohdan Korchak Serhiy Pyshyev

The effective utilization and effective valorization of various organic industrial wastes have become increasingly important issues. One significant area for enhancing the circular economy is the processing of waste generated from vegetable oils and animal fats. This article focuses on the processing and use of soapstocks, which result from the chemical reaction between fatty acids and alkali. These soapstocks represent the most significant portion (approximately 70–90 wt% by weight) of waste produced by the oil and fat industry. The raw material for this study was soapstock obtained from the neutralization of sunflower oil at the PJSC “Zaporizhzhya Oil and Fat Plant,” designed by the Belgian company “De Smet.” The soapstock yield was found to be 9.95 wt% based on 100 wt% oil. Through a series of treatments involving water, acid, and multiple washes, a low-sulfur fuel component was produced that nearly meets the standards for boiler fuels as outlined in DSTU 4058-2001 and PN-C-96024:2020, except for the heat of combustion. It fully complies with the requirements specified in ISO 8217:2024. The sulfur content of the final product was determined to be 0.12 wt%. Additionally, the fuels produced contained 75.33 wt% carbon, 11.64 wt% hydrogen, and 12.00 wt% oxygen. Due to the relatively low oxygen content, the resulting product exhibits approximately twice the heat of combustion of similar fuels derived from other waste streams in the oil and fat industry.

Recycling doi: 10.3390/recycling11040071

Authors: Placide Uwizeyimana Tania Lopes Rodolphe Sonnier Anthony Burlet Mohammed Rakkane Wissal Bouamri Marc Potin

The building sector is a major source of CO2 emissions and construction waste, motivating the development of sustainable materials and end-of-life recycling strategies. Bio-concretes, combining mineral binders with plant-based aggregates, offer low density and favorable hygrothermal performance but remain insufficiently studied with respect to recyclability, particularly for gypsum-based materials. This study experimentally investigates the thermal recycling of gypsum–hemp bio-concrete, in which gypsum acts as the binder and hemp shiv as the aggregate. Thermogravimetric analysis of individual constituents and the bio-concrete was conducted to identify a temperature range enabling gypsum dehydration without hemp degradation. Controlled oven treatments at selected temperature–time couples were then applied to determine optimal recycling conditions, followed by the bio-concrete remanufacturing using 100% recycled constituents. Physical, thermal, and mechanical properties were evaluated before and after recycling under controlled conditions. Results show that a treatment at 180 °C for 60 min enables effective gypsum dehydration (18–20% mass loss) while preserving hemp integrity. Recycled gypsum–hemp bio-concrete exhibits increased density (368 to 587 kg·m−3) and compressive strength (0.05 to 0.52 MPa), accompanied by a moderate increase in thermal conductivity (0.081 to 0.096 W·m−1·K−1). These findings demonstrate the feasibility of 100% thermal recycling of gypsum–hemp bio-concrete without constituent separation.

Recycling doi: 10.3390/recycling11040070

Authors: Zunaida Zakaria Arif Rochman Paul Refalo

In recent years, plastic recycling has emerged as a critical concern in environmental protection and waste management. Among the various techniques for repurposing plastic waste into valuable products, extrusion of filaments for 3D printing has proven to be a highly effective method. A thorough understanding of the crystallization behavior of recycled plastics used in 3D printing is essential, as it significantly influences their final performance. This review provides an in-depth analysis of the crystallization behavior and crystallinity of recycled semi-crystalline polymers, with particular emphasis on recycled commodity plastics such as recycled polyethylene terephthalate (rPET), recycled polypropylene (rPP), and recycled high-density polyethylene (rHDPE). Recent research published between 2015 and 2025 was systematically synthesized and provides information on sources of plastic waste, additives employed, and recycling processes involved, with the findings summarized in a table that highlights their effects on polymer crystallinity. Furthermore, the key factors impacting the crystallinity of 3D-printed recycled plastics were examined, including the influence of additives, multiple processing cycles, printing parameters, and thermal treatments. Research gaps and the challenges faced during the printing process were also identified and discussed. By consolidating recent findings, this review provides a comprehensive understanding of the crystallization behavior of recycled plastics in 3D printing, thereby providing guidance for future research and developing strategies to optimize the performance of these materials.

Recycling doi: 10.3390/recycling11040069

Authors: Diana Meza-Rojas James Holliman David Penney Anthony R. Lewis Peter J. Holliman

A method has been developed to delaminate the organic components (paint, foam) from the steel skins of composite polyisocyanurate (PIR) steel insulation panels at ambient temperature and in 20 min using selected solvents combined with ultrasonication. Using this method, polyisocyanurate foam can be selectively delaminated from polymer-based paint (PVC plastisol) and, in turn, the polymer paint can be selectively delaminated from the galvanised steel. Both the foam and paint are removed as intact layers, leaving the galvanised steel intact for the next steps of recycling, enabling the subsequent individualised recycling of each sub-component or layer. Several solvents have been tested, and the data show that H-bonding solvents (e.g., H2O, alcohols) are less effective at delaminating these polymers. Whilst high polarity, medium H-bonding acetonitrile and DMSO remove PVC paint and some PIR foam, the most effective solvent for both PIR foam and PVC paint removal is medium polarity, medium H-bonding acetone.

Recycling doi: 10.3390/recycling11040068

Authors: Megan Wagaman Brendan Derrick Taff Jeremy Shellhorn Haven Everhart Jennifer Carrigan Melissa Jung Elizabeth A. Himschoot

The Grand Canyon National Park (GRCA) attracts roughly five million visitors annually, creating immense pressure on the waste stream managed in the park. To reduce environmental impacts, the National Park Service, collaborating organizations and concessionaires are in the process of implementing large-scale reusable foodware systems, replacing single-use plastics. This pilot study aimed to engage visitors in the design process to inform preferences and attitudes to further support management decision-making regarding the design and implementation of reusable foodware systems in the park. During September 2025, park visitors were intercepted at key concessionaire food vending locations and asked to complete a brief survey. The survey contained attitudinal questions, persuasive phrases, and potential logos and graphic designs that could be used with program implementation, which were evaluated via Likert scales by n = 164 respondents. Results suggest that respondents have overwhelmingly positive attitudes and norms towards reusing foodware at the park. Results highlight phrases and graphic designs that will be most effective as the program launches and can be used to inform future research.

Recycling doi: 10.3390/recycling11040067

Authors: Dimitrios-Aristotelis Koumpakis Dimitrios Christoforidis Vasileios Diamantis Alexandra V. Michailidou Christos Vlachokostas

The lack of centralized waste management infrastructure in certain regions makes plastic waste an escalating environmental and economic problem. This research investigates how modular portable pyrolysis systems function as sustainable decentralized solutions. A standard shipping container houses a custom-designed pyrolysis unit which demonstrates flexibility and adaptability. The system contains a batch rotary kiln reactor with a processing capacity of 750 kg per batch which is fed with urban plastic waste, to produce pyrolytic oil, syngas and char. The produced pyrolytic oil exhibits an energy content comparable to that of conventional diesel fuel. Additionally, the integration of biomass briquettes and recycled pyrolytic gas can reduce to a big extent the external energy requirements, improving the system’s overall energy autonomy. Therefore, the system becomes economically reliable due to its low operational expenses and the short cycle of approximately 7-h operation. The unit’s mobility enables on-site treatment operations which reduces both transportation emissions and expenses. The analysis includes technical design elements together with performance metrics for different plastics. This conceptual study demonstrates the feasibility of containerized pyrolysis as a practical method to enhance plastic waste chemical recycling rates while presenting a scalable framework for industrial symbiosis and local waste-to-energy conversion.

Recycling doi: 10.3390/recycling11040066

Authors: Aleksandr B. Stefaniak Lauren N. Bowers Callee M. Walsh Sonette Du Preez Elizabeth D. Brusak Jason E. Ham Ryan F. LeBouf M. Abbas Virji Johan L. Du Plessis

Distributed recycling of high-density polyethylene (HDPE) into filament for use in material extrusion 3D printing has been proposed as part of a circular economy. There is a gap in the understanding of the potential for HDPE to release contaminants that are potentially hazardous to human health during reuse. Herein, HDPE from post-consumer packaging waste was sorted into food and non-food (NF) streams and virgin HDPE was taken as a benchmark material. All materials were extruded into filaments and recycled multiple times while monitoring emissions. In general, particle and organic chemical emissions decreased by 93 to 99% and 73 to 99%, respectively, with increased reprocessing cycle without appreciable decline in mechanical (Young’s modulus decreased by 5 to 16%), processability (melt flow index stable from 0.2 to 0.7 g/10 min for waste plastics), and thermal properties (crystallinity ranged from a 6% decrease to a 9% increase) of plastics. An exception was a sub-stream of NF plastic that had increased particle emissions (up to 3100%) with reprocessing cycle. Reductions in emissions during filament extrusion appeared to be more influenced by reprocessing cycle than by any specific process step (grinding, etc.). The progressive decline in emissions without appreciable loss of polymer integrity could be exploited to pre-condition HDPE to reduce potential hazardous emissions prior to extruding into filament. This work helps fill the knowledge gap on approaches to recycling plastics in distributed settings such as home-based businesses, which is critical for developing effective recommendations for controls to enable safe work practices such as the use of ventilation to minimize exposures.

Recycling doi: 10.3390/recycling11040065

Authors: Luca Taglieri Pietro Romano Francesco Vegliò Alberto Gallifuoco Luciano Fratocchi

Rare earth elements (REEs) are essential to many low-carbon and digital technologies, yet the primary supply is geographically concentrated; waste electrical and electronic equipment (WEEE) could act as an “urban mine”, but recovery pathways remain fragmented. We synthesize the evidence through a structured literature review of Scopus and Web of Science indexed studies focusing on WEEE-derived feedstocks for REE recovery: 148 records were screened and 51 papers met the inclusion criteria. Reporting of the search and study selection process follows PRISMA 2020. We coded each study by WEEE source/fraction, core technology family, and process configuration, target REEs, performance reporting, environmental proxies, and maturity, and discussed gaps against circularity goals. Results show an intense concentration on a few feedstocks, permanent magnets (22 studies), fluorescent lamps (16), and batteries (6), with only limited attention to multi-source streams. Hydrometallurgical routes dominate, while biometallurgical options are less explored. Recovery is more frequently reported than selectivity and environmental indicators, and most solutions remain at proof-of-concept maturity. Due to the heterogeneity of feedstocks, process configurations, and reported metrics, the findings were synthesized qualitatively (no meta-analysis). This review highlights priorities for future work: multi-source and heavy rare earth elements focused feedstocks, more selective and intensified flowsheets, harmonized performance reporting, and scale-up supported by life-cycle and cost assessments.

Recycling doi: 10.3390/recycling11040064

Authors: Pauls P. Argalis Laura Vitola

The escalating production of sewage sludge presents a significant environmental challenge, while the construction industry simultaneously seeks sustainable raw materials to improve its circularity. This review analyses the technical and regulatory landscape for valorizing SS within the Latvian construction sector, set against the divergent strategies of its Baltic neighbours. While global research confirms the technical viability of using SS in fired-clay bricks and as a supplementary cementitious material (SCM), national management approaches differ starkly. Lithuania has adopted widespread incineration, and Estonia has focused on advanced composting. In contrast, Latvia’s national strategy is failing, with 51% of its 2024 sludge production diverted to “temporary storage”. This review identifies this crisis as a unique opportunity, arguing that incorporating dewatered digestate into fired-clay bricks is the most logical and economically viable pathway for Latvia, as it leverages existing industrial infrastructure. The primary obstacle to this circular solution is not technical but legal, specifically the lack of a national “End-of-Waste” (EoW) criterion for sludge-derived construction materials. Therefore, this article proposes a strategic roadmap for Latvia, centred on developing this essential legal framework, creating a national sludge characterization map, and initiating a pilot project to bridge the research-to-industry gap. Although Latvia is the primary focus of this review, the regulatory, infrastructural and material constraints analysed here are common in many small and mid-sized countries, making the insights applicable beyond the Latvian context.

Recycling doi: 10.3390/recycling11030063

Authors: Abderrazzak El Hafiane Abdelali En-nadi Mohamed Ramadany

Integrating Lean Construction (LC), the Circular Economy (CE), and Construction 5.0 (C5.0) remains challenging in emerging delivery contexts. This difficulty increases when procurement routines determine which practices become enforceable across tendering, contracting, and site execution. This study prioritized barriers to LCCE5.0 implementation in Morocco and translated expert judgments into actionable recommendations. A structured literature review informed the barrier inventory and conceptual framing. The study proposed a three-layer, life-cycle LCCE5.0 framework that links governance, operational routines, and digital enablers. It operationalized 40 critical barrier factors across six dimensions and five life-cycle macro-phases. A two-round Delphi study was conducted with 22 Moroccan experts using a 7-point Likert scale. Barriers were ranked using Round 2 (T2) medians with ties resolved using the interquartile range. Top-box agreement (ratings of 6–7) and consensus tiers were reported. The ranking showed strong stability across rounds, with 92.5% of barrier factors remaining stable. Kendall’s W at T2 equaled 0.817 (p < 0.001), indicating high panel consensus. Results indicated that constraints clustered in upstream governance. Three procurement-centered regulatory and contractual barriers topped the ranking (Mdn_T2 = 7). These barriers reflected missing CE procurement guidelines, limited weighting of environmental criteria, and the absence of circularity and digital requirements in tenders. Six additional barriers reinforced this procurement bottleneck. They included limited owner commitment, weak enforcement authority, limited top-management commitment, and regulatory instability. They also included low interorganizational trust, limited risk-sharing contracts, and tool-centered deployment of LCCE5.0 practices. These findings support procurement-focused recommendations to institutionalize auditable circular requirements and data-enabled verification in tendering and contracting routines. The proposed LCCE5.0 mechanism and the resulting recommendations require empirical validation beyond this Delphi-based prioritization.

Recycling doi: 10.3390/recycling11030062

Authors: Siti Nurkomariyah Dodik Ridho Nurrochmat Dikky Indrawan Harianto

Indonesia, as a major global textile exporter, faces substantial sustainability challenges due to its linear production model, which generates massive volumes of post-industrial polyester waste (PIPW). However, reliable data and recycling pathways remain critically lacking. This study quantifies the volume, composition, and textile-to-textile (T2T) recyclability potential of PIPW across Indonesia’s national textile and clothing production chain, employing a mixed-methods approach that integrates material flow analysis (MFA), site visits, and stakeholder interviews. The results indicate that 572 kilotonnes of PIPW were generated in 2023, with garment manufacturing identified as the most waste-intensive. Nineteen waste types were identified; 61% comprise fibre blends, which significantly constrain closed-loop recycling. A novel five-tier waste typology was developed to classify waste streams based on material characteristics, technological availability, and economic feasibility. The circularity map reveals that Indonesia is trapped in pseudo-circularity. Scenario analysis suggests that up to 184 kilotonnes of PIPW could be feasibly redirected towards higher-value chemical recycling. The research recommends mandatory source segregation, fiscal incentives, investment in chemical recycling infrastructure, and the integration of circular design into national standards. The study provides the first national-level MFA of PIPW in Indonesia and establishes an empirical baseline to advance T2T recycling in emerging economies.

Recycling doi: 10.3390/recycling11030061

Authors: Gidalti García Cabrera José Aurelio Sosa Olivier Guadalupe Hernández Gerónimo José Ramón Laines Canepa Alejandro Padilla Rivera Gabriel Núñez-Nogueira María del Carmen Cuevas Díaz

Greenhouse gas (GHG) emissions from sanitary waste (SW) are not usually quantified in institutional inventories, which limits the ability to assess its management and associated carbon footprint. This study establishes emission factors (EF) for SW generated in a higher education institution (HEI), focusing on toilet paper. In 2022, 19 sanitary waste sources were monitored, obtaining a per capita generation of 3.02 g person−1 day−1 and an annual total of 356.87 kg of SW. Samples were characterized through proximate and elemental analyses, applying stoichiometric calculations for two disposal-site degradation pathways: Aerobic: 841.95 kg (total climate indicator) t−1 SW, and Anaerobic: 7041.97 kg (total climate indicator) t−1. The arithmetic mean of the aerobic and anaerobic EFs was 3941.96 kg (total climate indicator) t−1 SW. Based on an estimated annual mass of 1.12 t yr−1, emissions ranged from 0.35 to 6.71 t yr−1 (total climate indicator: CO2 + CH4-derived CO2e) depending on the scenario. Emissions could be reduced by over 90% when aerobic degradation or controlled methane capture predominates. The results suggest that separating SW at its point of generation and ensuring that it undergoes aerobic or energy-recovery treatment processes can limit its contribution to institutional GHG inventories. Having material-specific EF enables quantitative comparison among management strategies and guides continuous-improvement decisions.

Recycling doi: 10.3390/recycling11030060

Authors: Tendai Tawonezvi Anele Sinto Mihle N. Qhina Dorcas Zide Emihle Mlotha Bernard J. Bladergroen

The strong adhesion between cathode materials and aluminium (Al) foil substrates presents a significant challenge in the recycling of spent lithium-ion batteries (LiBs). Conventionally, high temperatures and high concentrations of costly organic solvents such as N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAC), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) are used to enhance ultrasonication-based delamination. In this study, a novel, eco-efficient approach was demonstrated for delaminating cathode materials from Al foil using a low-concentration organic citric-acid-assisted low-power ultrasonic treatment coupled with a gentle, low-power-per-volume mechanical mixing system at room temperature. The separation mechanism was attributed to the structure disruption, possibly swelling, of the polyvinylidene fluoride (PVDF) binder using low-concentration citric acid and the cavitation effects induced by ultrasound. Key parameters influencing the delamination efficiency included the solvent type, temperature, ultrasonic power, and treatment duration. Under optimised conditions, citric acid was used as the sonication reagent, with a process temperature of 20 °C, 60 W ultrasonic power, and 80 min of ultrasonication; a delamination efficiency of approximately 92% was achieved. The recovered cathode materials exhibited low agglomeration, favouring subsequent leaching processes. This work proposes an environmentally friendly and effective method for cathode and Al foil recovery from spent LiBs, integrating manual dismantling, ultrasonic treatment, and material separation.

Recycling doi: 10.3390/recycling11030059

Authors: Ruijiao Zhai Kui Huang Shanjin Mao Rugui Li Haili Dong Xi Zhai

Amid growing environmental pressure and increasing demand for resource sustainability, the efficient recovery of valuable metals from spent lithium-ion batteries (LIBs) has become a critical challenge in the field of resource recycling. Therefore, a novel approach is presented for selective lithium (Li) and manganese (Mn) separation from LiNixCoyMn1−x−yO2 by combining carbothermic reduction roasting and selective leaching. Low-cost glucose (C6H12O6) was selected as the reduction roasting reductant, which converts the cathode materials into water-soluble lithium carbonate (Li2CO3), water-insoluble cobalt (Co), nickel (Ni), and manganese oxide (MnO). Wet magnetic separation was employed to preferentially extract Li while simultaneously removing excess carbon from Ni, Co, and MnO. Under optimal roasting conditions at 600 °C for 90 min followed by wet magnetic separation with a liquid–solid ratio of 30 mL/g for 30 min, 95.42% of Li was preferentially extracted. Subsequently, at a formic acid (HCOOH) concentration of 1.6 mol/L, liquid–solid ratio of 6 mL/g, and leaching time of 30 min, 94.29% of Mn was selectively extracted from the wet magnetic separation products, whereas Ni and Co were leached at 6.13% and 7.22%, respectively. The acid-leaching residue can be recycled as a Ni-Co alloy.

Recycling doi: 10.3390/recycling11030058

Authors: Zhiji Gao Jin’an Xu Hanjie Qiu Maoxin Shi Siyao Li Rusheng Qian Jingchen Luo Fanli Wu Haibo Nie Tengfei Ma

Granite sawdust is a by-product in the process of stone processing, which is usually piled up, thus easily causing environmental pollution. To achieve resource utilization, granite sawdust was used as a partial substitution of cement in this work. The effects of different sawdust contents (10–50%) were systematically studied on the pore structure and the mechanical properties of its dry powder mortar. Combined with the grey correlation theory, the correlation between pore size distribution and compressive strength was analyzed. The results showed that the consistency and mechanical properties of the mortar gradually decreased along with the increasing sawdust content, while its critical pore-diameter decreased. The mortar performance was the best when its sawdust content is 10%, which meets the M25 technical requirements. When content reaches up to 30%, the mortar still met the strength standard of M20. Compared to fly ash, the mortar with 30% sawdust as the substitution has a higher water retention rate but lower mechanical strength. The grey correlation analysis indicated that the pores with diameters less than 10 nm and greater than 1000 nm had the most significant impact on the compressive strength.

Recycling doi: 10.3390/recycling11030056

Authors: Harrison Appiah Paul Asamoah Armando Gabriel McDonald

Rising global municipal solid waste (MSW) generation poses severe environmental and resource challenges, necessitating sustainable management strategies beyond landfilling. This review critically synthesizes thermochemical waste-to-energy (WtE) technologies, including incineration, pyrolysis, gasification, and hydrothermal carbonization, as viable pathways for converting heterogeneous MSW into energy (electricity, heat, syngas, bio-oil) and valuable materials (biochar, ash for construction). Drawing on recent literature, it highlights their superior greenhouse gas reductions, energy recovery efficiencies, and residue valorization potential compared to traditional disposal, while addressing persistent limitations such as feedstock variability, tar formation, high capital costs, and stringent emission controls. Advanced variants and integration with circular economy principles enhance feasibility, particularly in diverse regional contexts. Despite technical and economic barriers, thermochemical WtE offers a transformative approach to resource-efficient waste management, supporting zero-waste goals and renewable energy transitions when combined with optimized pre-treatment, policy incentives, and ongoing innovation in process efficiency and pollutant mitigation.

Recycling doi: 10.3390/recycling11030057

Authors: Ma. Guadalupe Plaza Maria Luisa Mendoza López José de Jesús Pérez Bueno Edain Belén Pérez Mendoza Martha Elva Pérez Ramos

Injection-molding purges are heterogeneous, bulky residues whose uncertain composition and irregular geometry hinder direct reinsertion, making cold shredding costly and maintenance-intensive. This work develops a low-infrastructure solar-assisted pre-processing route using a PMMA Fresnel lens to induce controlled sub-onset softening and enable clean shear cutting without destructive thermal histories. The sub-onset softening is here defined into a viscoelastically active range (at or above Tg for the amorphous phase) while remaining below the melting onset (Tm, onset) and below the onset of thermal degradation (Td, onset). The station was engineered via QFD and risk-oriented design tools, while a weighted Pugh matrix selected shear cutting over saw-based alternatives. A screening factorial DOE showed that lens height, angle, and their interaction significantly govern focal-spot diameter and receiver temperature, yielding linear relations for conservative set-point selection. Receiver benchmarking further indicated that copper reaches substantially higher temperatures than graphite under identical exposure conditions, supporting copper as the simplest, rapid-heating receiver. Under DOE-calibrated operation, tear-free shear cutting was achieved across representative purge families (PP–ABS, PC–ABS–PP, PA66, PA66-filler, and POM) without forced convection. From a recycling and waste-management perspective, the approach converts bulky purge scrap into mill-compatible feedstock with reduced mechanical resistance, lowering tool wear and fines generation, accelerating downsizing, and limiting stockpiling that elevates combustible-inventory fire risk. Overall, the proposed DOE-calibrated, operator-friendly framework improves recycling feasibility by enabling safer handling, more stable preprocessing throughput, and reduced reliance on disposal or long-term storage for heterogeneous industrial purges.

Recycling doi: 10.3390/recycling11030055

Authors: Jinzhao Li Xin Zuo Changchun Xin

The large-scale dredging activities in port areas generate substantial quantities of dredged soil, leading to land occupation and disposal challenges, while industrial wastes such as fly ash and desulfurization gypsum remain underutilized. In this study, industrial wastes were employed as a curing agent to stabilize dredged soil, aiming to achieve both mechanical performance improvement and cost-effective recycling. In total, 100 g of curing agent was added to 1 kg of sludge. The optimal strength-maximizing formulation comprised 4.5% activator 1 #, 4.5% fly ash, 4.5% mineral powder, and 0.5% desulfurization gypsum. It achieved an unconfined compressive strength of 0.794 MPa. For enhanced cost-effectiveness, a modified binder blend (1.88% activator 1 #, 4.5% fly ash, 4.5% mineral powder, and 0.5% desulfurization gypsum) delivered 0.63 MPa at 28 days, satisfying mechanical construction specifications. Results demonstrate that unconfined compressive strength increases with solid wastes; however, with the extension of solidification time, the unconfined compressive strength of dredged soil gradually slows down.

Recycling doi: 10.3390/recycling11030054

Authors: Javier Rodrigo Nahuat-Sansores Karla del Carmen García-Uitz Julio César Cruz-Argüello Carlos Andrés Ramírez-Pinto Ricardo Enrique Vega-Azamar Danna Lizeth Trejo-Arroyo Yazmin Vidal Valdez

Sugarcane bagasse ash (SCBA) has been widely studied as a partial supplementary cementitious material; nonetheless, its hydration behavior and performance when combined with nanoscale modifiers remain insufficiently understood. The aim of this study is to assess the pozzolanic potential of SCBA, the hydration behavior of binary SCBA–cement composites and the mechanical performance of ternary mortars with silica nanoparticles (Si-NPs). SCBA reactivity was confirmed by a Chapelle index of ~300 mg Ca(OH)2/g, while hydration development in binary pastes (5–20 wt% SCBA) was quantified using TG/dTG and semi-quantitative XRD. Low SCBA replacement levels (5–10 wt%) enhanced the hydration degree by up to ~12% at 28 days compared with the reference paste. Ternary mortars incorporating 5 wt% SCBA and Si-NPs exhibited significant strength gains, with the optimal blend (2.5 wt% Si-NPs) achieving a 42% increase in 28-day compressive strength relative to the reference mortar. A sustainability assessment showed concurrent reductions in clinker intensity and CO2 intensity of approximately 33% and 32%, respectively. These findings support the sustainable and technical viability of combining agro-industrial waste and nanotechnology as complementary strategies for reducing clinker content while enhancing eco-efficiency in alternative cementitious composites.

Recycling doi: 10.3390/recycling11030053

Authors: Pengfei Li Jie Ji Daiyue Wang Chuan Qiu Ran Zhang Yanling Li

The durability characteristics of inorganic mixtures incorporating recycled aggregates from rural residential construction and demolition waste with high red brick content remain inadequately elucidated. To illuminate their long-term serviceability, two types of recycled aggregate inorganic mixtures (RAIMs) were formulated and implemented in a test road section, with their mechanical properties and fatigue resistance systematically monitored and assessed. Comparative analysis indicated that RAIMs exhibit comparable resistance to permanent deformation and analogous fracture failure mechanisms to natural aggregate inorganic mixtures (NAIMs), yet their elastic deformation recovery capability is compromised. Specifically, RAIMs attained parity with NAIMs in terms of unconfined compressive strength, indirect tensile strength, flexural tensile strength, and static compressive resilient modulus. However, their dynamic compressive resilient modulus, indirect tensile resilient modulus, and flexural tensile resilient modulus were lower than those of NAIMs by over 30%. Furthermore, probabilistic fatigue prediction models for RAIMs were established, facilitating reliable estimation of the service life of RAIMs under various stress intensity levels. This study holds considerable significance for dispelling the inherent perception of RAIMs’ inferior service performance and augmenting the theoretical foundation for their resourceful utilization in road engineering.

Recycling doi: 10.3390/recycling11030052

Authors: Boris Kulikov Nikolay Dombrovskiy Aleksandr Kosovich Evgeniy Partyko Yulbarskhon Mansurov Pavel Yuryev Nikita Stepanenko Yuriy Baykovskiy Alexander Durnopyanov Ruslan Balanev Maxim Baranov

The depletion of natural resources remains an acute global problem, highlighting the importance of developing sustainable technologies that enable the simultaneous extraction of metals and recycling of waste. This paper describes a study of a technology for recycling aluminum slag from foundries to produce secondary aluminum alloy and regenerated flux. Research and processing methods include X-ray phase and spectral analysis of slag composition, multi-stage grinding in a jaw crusher and planetary mill, screening for fraction separation, and selective dissolution of the oxide–salt phase in water or hydrochloric acid followed by filtration and evaporation; obtaining regenerated flux based on phase diagrams of chloride systems; and briquetting and remelting of the extracted aluminum. The technology ensures the extraction of up to 85% of the metallic aluminum from slag and the production of regenerated flux based on the NaCl–KCl–MgCl2 system with a low melting point.

Recycling doi: 10.3390/recycling11030051

Authors: Ramona Giurea Ionela Gavrila-Paven Elena Cristina Rada

This paper analyzes the evolution of packaging waste recycling rates in four Central and Eastern European EU Member States—Bulgaria, Hungary, Poland, and Romania—in comparison with the EU-27 average over the period 2014–2023. The analysis is based on Eurostat data on total packaging waste recycling rates (percentage of generated waste recycled) and employs a linear trend model estimated for the EU-27, which is used as a reference trajectory. This reference trend does not aim to predict future recycling rates or to validate absolute national performance levels; rather, it serves as an analytical benchmark for assessing the relative convergence or divergence of national trajectories over time. Descriptive statistics and linear regression techniques are applied to characterize long-term tendencies and year-to-year dynamics, including potential disruptions during the 2020–2021 period. The results indicate that the EU-27 recycling rate remains high and relatively stable (average 78.7%), albeit with a slight downward trend (−0.44%) across the analyzed interval. Poland and Bulgaria record overall improvements relative to their initial levels, while Hungary—and particularly Romania—exhibit declining trends and persistent negative gaps compared to the EU-27 benchmark. Poland stands out by surpassing the EU-27 average after 2019, reporting exceptionally high recycling rates in several years, whereas Romania consistently records the largest deviation, with an average gap exceeding 20% in the later period. These findings reveal substantial heterogeneity in the implementation of EU packaging waste policies and highlight the need for targeted, country-specific interventions in Member States facing structural constraints in recycling capacity and collection systems.

Recycling doi: 10.3390/recycling11030050

Authors: Ameni Ben Salah M. Mirari Antxustegi Eriz Corro María González Alriols

This study explores the valorisation of apple pruning (AP) residues into sustainable carbonaceous adsorbents for dye-contaminated wastewater. Activated biochars (ABCs) were produced via single-step (ABC-1S) and two-step (ABC-2S) KOH activation, while activated hydrochar (AHTC) was obtained through hydrothermal carbonization followed by H3PO4 activation. The materials were comprehensively characterized using proximate analysis, FTIR spectroscopy, SEM imaging, and N2 adsorption–desorption to evaluate surface chemistry, morphology, and textural properties. Batch adsorption experiments using MB (5–100 mg/L) demonstrated the superior performance of ABCs compared to AHTC. At low dye concentrations, adsorption on ABCs was partially influenced by external mass transfer, while kinetic data were best described by the Avrami model, indicating complex adsorption mechanisms. Isotherm analysis showed that ABC-2S exhibited heterogeneous adsorption behaviour, whereas AHTC poorly conformed to conventional isotherm models. The Langmuir model indicated higher monolayer capacities for ABCs (up to 22.9 mg/g) relative to AHTC (9.7 mg/g), reflecting a greater density of accessible adsorption sites induced by alkaline activation. Notably, nearly complete methylene blue (MB) removal was maintained over three regeneration cycles, confirming the stability, reusability, and practical potential of AP-derived ABCs and AHTC for sustainable wastewater treatment.

Recycling doi: 10.3390/recycling11030049

Authors: Priscila Thalita Barros de Lima Rafael dos Santos Macedo Maurício Guimarães Bergerman Anette Müller Carina Ulsen

Mineral processing may decisively influence recycled aggregate (RA) production, yet it is systematically underreported. This critical review screened 338 Scopus-indexed publications (2004–2024) and retained 204 studies after eligibility assessment. Reporting on comminution was limited: ~52% (105 studies) of studies did not explicitly mention crushing, while ~26% (53 studies) identified the crusher type, and only about 1% (two articles) reported operating conditions, which undermines reproducibility and cross-study comparability. RA quality is application-/market-dependent. The literature was classified into cement-based materials (46.1%), pavement applications (44.6%), and fundamental studies without application (9.3%). For cement-based materials, water absorption and compressive strength were the most frequently reported primary and secondary properties, respectively. For pavement applications, particle-size distribution and optimum moisture content predominated. Overall, mineral processing directly governs the primary attributes of recycled aggregates (RAs) and indirectly influences their secondary performance outcomes. The main gap identified in the literature is the lack of clear recommendations for processing procedures, which limits the reproducibility and comparability of reported results. To address this limitation, this article proposes a mineral-processing framework intended to standardize both RA processing and reporting practices, thereby improving crosslink study comparability, experimental reproducibility, and evidence-based specification according to end-use requirements.

Recycling doi: 10.3390/recycling11030048

Authors: Takaaki Wajima

This study investigated a feasible recycling and detoxification process for waste tire ash containing hazardous Zn and Al using acid leaching, followed by layered double hydroxide (LDH) synthesis. The novelty of this work is the direct conversion of a Zn/Al/Fe/Ca-rich real waste system into a phosphorus removal material, in which LDH-related uptake and secondary hydroxyapatite formation cooperatively immobilize phosphorus. Waste tire ash mainly consists of Zn, Al, Fe, Ca, and Si, most of which can be effectively leached with hydrochloric acid (HCl). The optimum leaching conditions for high extraction efficiency involved treatment with 10 M HCl for 10 min at 20 °C (solid–liquid ratio: 50 g/L). Under these conditions, the elution concentrations of Zn and Al from the residue decreased to 0.3 and 0.17 mg/L, respectively, meeting the Japanese leaching standards, whereas the raw ash showed significantly higher values. From the leached solution, LDH-containing products with high phosphorus removal capacity were synthesized at 40 °C for 2 h by adjusting the pH to 11.5. A phosphorus removal performance of 2.0 mmol/g was obtained owing to the formation of hydroxyapatite. The combined process of HCl leaching and LDH synthesis enables the detoxification of waste tire ash and the production of an environmental purification material.

Recycling doi: 10.3390/recycling11030047

Authors: Catherine Cabrera-Escobar Juan Moreno-Gutiérrez Rubén Rodríguez-Moreno Emilio Pájaro-Velázquez Fátima Calderay-Cayetano Vanesa Durán-Grados

Used lubricating oils (ULOs) represent one of the largest hazardous liquid waste streams globally and pose significant environmental risks if improperly managed. This study presents a structured review of ULO management pathways, including regeneration, reprocessing, and energy recovery technologies, within a sustainability and circular economy framework. The review systematically categorizes treatment options based on recovery efficiency, waste generation, environmental performance, and technical feasibility. To contextualize environmental risk, a conceptual numerical spill dispersion analysis using the SIMOIL model is included as an illustrative case study under simplified marine conditions. The simulation highlights the rapid dispersion potential of ULOs in coastal environments, reinforcing the need for preventive management strategies. The analysis indicates that refining technologies generally offer higher material circularity potential, while thermochemical processes provide viable alternatives for heavily contaminated oils. The study identifies critical gaps in technoeconomic comparability, regulatory harmonization, and source segregation practices. Strengthening integrated management systems is essential to minimize environmental impact and enhance resource recovery.

Recycling doi: 10.3390/recycling11030046

Authors: Nataliya Alfimova Kseniya Levickaya Ivan Nikulin Mikhail Lebedev Natalia Kozhukhova

Phosphogypsum is one of the most widely produced gypsum-containing wastes. Therefore, researchers worldwide are exploring ways to recycle them. It is most often considered as an alternative to natural gypsum in the production of calcium sulfate hemihydrate. There are also isolated studies aimed at producing insoluble anhydrite (CaSO4 II) from phosphogypsum. Compared to hemihydrate, anhydrite is characterized by greater strength and water resistance, and compared to Portland cement, it demonstrates lower energy consumption and CO2 emissions during production. This study examined the possibility of phosphoanhydrite binder (CaSO4 II) synthesis by calcination at 600, 800, and 1000 °C of phosphogypsum from four different industrial plants. Phosphoanhydrite binders capable of self-hardening, without the use of special additives, were synthesized. Their maximum strength at 28 days reached 57 MPa, and 69 MPa at 90 days. New data have been obtained regarding the influence of initial phosphogypsum characteristics and calcination temperature on the properties of CaSO4 II and the hardened phosphoanhydrite paste.

Recycling doi: 10.3390/recycling11030045

Authors: Tetsuo Takayama Syunsuke Oneda

This study investigates the material recycling potential of discarded wind instrument reeds (Arundo donax), which are conventionally incinerated, by compounding them with thermoplastics (thermoplastic polyolefin, TPO; polybutylene succinate, PBS). After recovered reeds were pulverized and injection-molded at 10 and 30 wt% concentrations, their mechanical and interfacial properties were evaluated. Experimentally obtained results indicate that waste reeds function as effective reinforcing agents, particularly when combined with biodegradable PBS. Incorporating 30 wt% reed flour into PBS enhanced flexural strength by approximately 1.7 times and flexural modulus by 2.8 times compared to the neat resin. This superior performance relative to TPO composites is attributed to robust interfacial hydrogen bonding among PBS carbonyl groups and the hydroxyl groups on the reed surface. Additionally, thermal and spectroscopic analyses revealed that these strong interactions elevate the crystallization temperature and generate a “Rigid Amorphous Phase” (RAF) that facilitates efficient stress transfer. These research findings demonstrate the feasibility of creating high-quality, bio-based composites, offering a sustainable method to reduce petroleum reliance and carbon dioxide emissions by upcycling musical waste.

Recycling doi: 10.3390/recycling11030044

Authors: Oluwatobi Elijah Akindele Jinfeng Zhang Yuxin Liu Uttandaraman Sundararaj

This study evaluates the pyrolysis of recycled linear low-density and low-density polyethylene (rLLDPE/rLDPE) blends for producing wax suitable as a precursor for corrosion-resistant coatings. Experiments were performed in a horizontal quartz tubular reactor under argon, and we investigated different pyrolysis temperature (400, 450, 500 °C), residence time (45, 60, 75 min), and heating rate (3, 5, 10 °C min−1). Factorial design and response surface methodology (RSM) were applied to quantify factors and optimize wax yield. Analysis of Variance (ANOVA) indicated statistically significant models (p < 0.05), with heating rate having the highest standardized effect. The highest measured yield was 82% at 400 °C, 75 min, and 3 °C min−1; the DOE optimizer predicted an 84% yield at 400 °C, 45 min, and 3 °C min−1. Product quality was assessed by GC-MS analysis, which showed that the waxes were predominantly composed of 1-alkenes and n-alkanes (C9–C32), consistent with the literature and closely matching compositions of commercial waxes. Overall, slow heating at low temperature with short residence time maximized wax yield without compromising quality, confirming that pyrolysis of recycled PE is a viable route to produce high-yield, specification-consistent waxes suitable for protective coating applications.

Recycling doi: 10.3390/recycling11030043

Authors: Giuseppe Bonifazi Giuseppe Capobianco Roberta Palmieri Silvia Serranti

Glass is a highly recyclable material that provides substantial environmental benefits, including savings in raw materials and energy as well as a reduction in CO2 emissions. To ensure the production of high-quality secondary raw materials, container glass from municipal waste separate collection must be accurately separated by color in recycling plants, where only minimal color mixing is tolerated. Color sorting is therefore a key step in glass recycling, as it directly affects both the quality and the market value of recycled cullet. Given the increasingly stringent color quality requirements for recycled glass and the high fraction of cullet used in container glass, advanced technological solutions are needed to improve sorting accuracy. In this study, a visible–near-infrared (VIS-NIR: 400–1000 nm) hyperspectral imaging (HSI) approach integrated with machine learning (ML) is proposed for the automated classification of post-consumer glass fragments from bottles and jars into five color categories: brown, dark green, light green, half-white and white. A hierarchical Partial Least Squares-Discriminant Analysis (PLS-DA) model combined with an object-based analysis strategy was developed to optimize color recognition. The proposed system achieved sensitivity and specificity values between 0.910 and 1.000, demonstrating excellent robustness and predictive capability. Validation on independent datasets confirmed the model’s reliability, with all color glass fragments correctly classified at the object level. The results highlight the potential of HSI-ML systems to enhance color sorting accuracy and process efficiency in recycling plants, contributing to improved material recovery and the advancement of sustainable, circular glass production.

Recycling doi: 10.3390/recycling11020042

Authors: Yi Xu Chang Xuan Zaien Ying Changjiang Wan Huifang Zhang Weimin Shi

Despite the enormous amounts of waste textiles produced by the world’s textile industry’s explosive growth, resource utilization rates are still poor. Cotton/polyester blended waste fabrics make up a sizable share, and sorting them precisely is essential to increasing recycling value and promoting the circular economy in the textile industry. Traditional mechanical and human sorting techniques are ineffective and inaccurate; current spectral analysis algorithms mainly concentrate on quantitative composition prediction and are insufficiently capable of differentiating between waste fabrics with comparable content gradients. To address these challenges, this paper proposes an improved 1DCNN model (Dual-1DCNN-Residual-SE) integrated with Near-Infrared (NIR) hyperspectral imaging technology. This model takes raw spectral data and Savitzky-Golay (SG) smoothing data as dual-channel inputs, introducing residual connections to capture subtle spectral differences between similar fabric categories, and employs SE attention mechanisms to adaptively enhance key features. Comparative experiments with four traditional algorithms—KNN, RF, SVM, and PLS—demonstrate that the proposed model achieves a classification accuracy of 95.94%, surpassing the best traditional algorithm SVM (88.12%) by 7.82%. Ablation experiments confirm each enhanced module’s efficacy. This study achieves high-precision classification of cotton/polyester blended waste fabrics, providing technical support for intelligent sorting of industrial waste fabrics.

Recycling doi: 10.3390/recycling11020041

Authors: Anzhelika M. Eremeeva Anastasia R. Marinets Ivan L. Oleynik Vladimir G. Povarov

The quantity of waste produced by the food industry is on the rise annually. Among the most prevalent types of waste classified as Class I hazardous substances, posing a significant threat to the environment, is used cooking oils, necessitating proper disposal methods. Concurrently, the combustion of petroleum resources generates substantial greenhouse gas emissions, acting as a primary driver of global warming and associated climatic disruptions. To address the issues mentioned above, food industry waste has been processed into biodiesel fuel. The production involved transformation of sunflower and waste cooking oils with ethanol, with the reaction duration incrementally adjusted between 2 and 7 h in 30 min intervals to determine its effect on biofuel yield. The analysis revealed a pronounced disparity in ester yield between the feedstocks, with the primary component derived from sunflower oil exhibiting a yield 5,81% lower than that obtained from waste oil. For the waste oil substrate, the total ester yield varied from 77.45% (at a 3 h reaction duration) to a maximum of 95.49% (observed at 6.5 h). The temporal evolution of ester release demonstrated a complex, non-monotonic trend, characterized by periodic oscillations superimposed upon a parabolic profile. The confidence interval for the temporal yield data was determined to be ±10%.

Recycling doi: 10.3390/recycling11020040

Authors: Christine Blanchard Esther Landells Peter Harris Bernadette K. McCabe

Management of food organics and garden organics (FOGO) has emerged as a critical policy priority due to methane emissions from landfilled organics in Australia. Here, the responsibility for organics recovery rests with state and local governments, resulting in fragmented implementation, differing regulatory settings, and variable landfill levy designs. This study examines the viability of FOGO systems by drawing on three Queensland regional case studies: Lockyer Valley, Rockhampton, and Bundaberg. The study uses qualitative document analysis and comparative case study methods, supported by systems mapping, to examine interactions between policy, governance, infrastructure, and community factors. Seven key domains were identified as being central to system performance: (1) government waste strategy, (2) waste regulation, (3) political acceptance, (4) collection systems, (5) cost and funding, (6) community acceptance, and (7) compost processing. Examining these components collectively demonstrated that effective FOGO delivery relies on their alignment, with each layer reinforcing or constraining the others. To highlight waste regulation tools, the study compared landfill levies as a central economic and governance instrument in two contrasting Australian jurisdictions. In Queensland, the levy operates primarily as a fiscal tool rather than as a behavioural driver, limiting councils’ ability to invest in new services. By contrast, New South Wales’s mandatory FOGO implementation and a more mature regulatory framework have driven widespread service rollout but have also revealed the complexities of enforcing a universal policy in diverse regional contexts. The paper offers new insights into the financial and governance dynamics shaping regional waste policy, demonstrating how whole-of-system coherence is essential for advancing circular economy transitions in dispersed local contexts.

Recycling doi: 10.3390/recycling11020039

Authors: Natalya Kulenova Ruslan Sapinov Marzhan Sadenova Zhanserik Shoshay Nail Beisekenov Stanislav Boldyryev Olga Rudenko Murat Yeleukenov

This article discusses possible approaches to recycling electronic waste, with a focus on the main components of a personal computer (PC) system unit (SU). The study makes a significant contribution to solving the problem of natural resource depletion and environmental pollution. The article evaluates the possibility of commercial extraction of valuable metals without the use of reagents, complex processes, and equipment, as well as the utilization of plastic electronic waste (e-waste) in the construction industry. The proposed scheme for recycling the main components of printed circuit boards (PCBs) allows aluminum and copper alloys to be extracted from metal elements. Recycled PCBs provide raw materials containing more than 35.5% copper and other valuable metals. The plastic used in the production of control printed circuit boards is proposed to be used as an additive for construction concrete. When 40–50% of plastic is added to the mass of sand, concrete samples of grades M250–M200 can be obtained. And with a plastic content of 10–20% of the sand mass, concrete grades M350–M300 are obtained, which can be used for foundations and monolithic construction of low-rise buildings. A preliminary assessment of the toxicity of concrete has shown that it is safe. A preliminary assessment of the concrete’s toxicity revealed that it is safe. An initial evaluation of the commercial feasibility of processing the main components of the SU PC revealed the possibility of obtaining funds of approximately $3183.7 per 1000 SUs, without the use of complex processing schemes. The use of secondary metals will significantly reduce CO2 emissions. The need for this study is driven by the high relevance of the issue of electronic waste disposal. Despite numerous studies in this area, the amount of waste worldwide is growing, which indicates the low effectiveness of existing methods.

Recycling doi: 10.3390/recycling11020038

Authors: Ana Carolina Valdevieso Buzzo Maria Eliana Camargo Ferreira Willian Luís de Oliveira José Eduardo Gonçalves Luiz Fernando Belchior Ribeiro Natália Ueda Yamaguchi

This study aimed to evaluate the technical and environmental feasibility of producing concrete paver blocks and pervious concrete paver blocks by incorporating marble waste to evaluate its filler effect within the cementitious matrix. The methodology included the characterization of marble waste, the production of test specimens with the control (0%), 10%, 20%, and 30% of cement replacement, and the execution of performance tests, supplemented by statistical analyses. The results indicated that marble waste replacement significantly impacted the properties. In terms of pervious concrete paver block permeability, the highest rates were observed in the control and 30% treatments. For water absorption, concrete paver blocks showed higher values at a maximum of 20%, while pervious concrete paver blocks maintained statistically analogous values for 10% and 20%. Regarding compressive strength, the concrete paver block formulation with 10% marble waste was statistically compatible with the control. It is concluded that the incorporation of marble waste into concrete and pervious concrete paver blocks is environmentally advantageous as it valorizes an industrial waste. However, mix design optimization is essential, given that excessive replacement (above 10%) resulted in a reduction in compressive strength.

Recycling doi: 10.3390/recycling11020037

Authors: Matheus Silva de Oliveira Leila Lea Yuan Visconte Elen Beatriz Acordi Vasques Pacheco

Mechanochemical regeneration aims to selectively cleave the crosslinked network of vulcanized rubber. In this study, a tire-grade styrene–butadiene rubber (SBR) compound was vulcanized and then subjected to mechanochemical regeneration using a zinc (II) dithiocarbamate complex (ZNIBU) at 6, 8, and 10 phr. The regenerated materials were subsequently revulcanized, and their properties were assessed before and after both processing steps. The regenerated (non-revulcanized) samples exhibited reduced crosslink density and increased swelling, indicating effective network cleavage by the regenerator. After revulcanization, the compounds presented higher hardness (23%) but lower tensile strength (75%) and tear strength (25%) compared to the virgin vulcanizate. Overall, ZNIBU proved highly effective for the mechanochemical regeneration of SBR, with optimum performance observed at 8 phr.

Recycling doi: 10.3390/recycling11020036

Authors: Elaine Meireles Senra Ana Carolina da Silva Guimarães Renan Henriques Gonçalves de Almeida Ana Lúcia Nazareth da Silva José Carlos Costa da Silva Pinto Christine Rabello Nascimento Elen Beatriz Acordi Vasques Pacheco

This study investigated the chemical recycling of poly(ethylene terephthalate) (PET) fiber residues from two sources—high-molar mass mooring ropes and low-molar mass textile-grade fibers—to produce functional oligomers. Glycolysis was carried out using polyethylene glycol (PEG400) as the depolymerizing agent, and two catalysts were assessed, zinc acetate and lithium octoate, with the latter reported on for the first time in this application. Reactions were performed for 180 min under mechanical stirring, inert atmosphere, reflux, and controlled heating. The resulting oligomers were characterized by Fourier-transform infrared spectroscopy (FTIR), hydroxyl and acidity indices, and thermogravimetric analysis (TGA). Both PET feedstocks showed high reactivity toward glycolysis. Monitoring the reactions by acidity index indicated that conversion reached equilibrium at approximately 120 min. ATR-FTIR confirmed the formation of ester and hydroxyl groups, consistent with oligomer structures. Glycolysis of PET derived from mooring ropes produced oligoesters with hydroxyl values of 228 and 242 mgKOH/g for zinc acetate and lithium octoate, respectively, and molar masses of 1296 and 1338 g/mol for zinc acetate and lithium octoate, respectively. These values are suitable for subsequent syntheses such as polyester polyol production.

Recycling doi: 10.3390/recycling11020035

Authors: Alexander Pletl Roman-David Kulko Andreas Hanus Benedikt Elser

Plastic recycling represents an essential element of strategies aimed at lowering global carbon emissions while supporting a circular plastics economy. However, the effectiveness of current plastic sorting systems remains limited by data scarcity, spectral variability, and the complexity of real world waste streams. This study introduces a CNN-based polymer classification framework that integrates physics-informed spectral simulation, adaptive data augmentation, and Bayesian hyperparameter optimization to enable robust classification under data limited conditions. Our framework combines near-infrared (NIR) spectral data from technical scale measurements with synthetically generated spectra. With only 100 measured spectra per polymer, the proposed framework achieves average balanced accuracies of 0.9739 in multi-target polymer classification tasks. By using technical scale spectral data, this study bridges the gap between laboratory model development and real sorting conditions.

Recycling doi: 10.3390/recycling11020034

Authors: Douglas Lamounier Faria Tamires Galvão Tavares Pereira Danillo Wisky Silva Mário Vanoli Scatolino Julio Soriano Thiago de Paula Protásio Lourival Marin Mendes

The pursuit of alternatives to nonrenewable materials has stimulated the development of sustainable materials with improved performance, particularly polymer composites reinforced with plant-based fibers. In this study, eucalyptus fibers were thermally treated and evaluated as eco-friendly reinforcements for polyester composites, aiming to enhance their physical and mechanical properties. The fibers were subjected to heat treatments between 140 and 230 °C in a Macro-ATG oven, followed by analyses of anatomical characteristics and chemical composition. Composites containing 25% fiber reinforcement were produced using an orthophthalic unsaturated polyester matrix catalyzed with methyl ethyl ketone peroxide, with untreated fibers used as references. Thermal treatment induced significant modifications in fiber morphology and composition, including increases in cell wall fraction at 170 and 200 °C and higher cellulose contents at 140 and 170 °C. Mechanical performance was assessed through tensile, flexural (modulus of rupture—MOR), modulus of elasticity (EB), and impact tests. Composites reinforced with heat-treated fibers exhibited lower apparent density and, notably, those treated at 230 °C showed markedly reduced water absorption and enhanced tensile strength compared with the control. Overall, treatment at 230 °C proved most effective, highlighting the potential of thermally modified eucalyptus fibers as viable reinforcements for high-performance, bio-based polymer composites.

Recycling doi: 10.3390/recycling11020033

Authors: Xiao Yuan Chen Denis Rodrigue

Bicycle tires and inner tubes constitute a growing waste stream mainly composed of natural rubber, butyl rubber, synthetic elastomers, carbon black, and reinforcing materials. Their multi-material structure and highly crosslinked networks make their recycling challenging, yet efficient recovery is essential for advanced circular economy practices. This review summarizes the current and emerging strategies for recycling bicycle tires and inner tubes. It first outlines the materials and additives present in tire casings and butyl inner tubes, which determine their recycling behavior. Mechanical pre-processing methods, including shredding, grinding, and fiber/steel separation, are presented as essential feedstock preparation steps. Thermochemical approaches, such as pyrolysis and thermolysis, are discussed with emphasis on producing value-added fractions, including pyrolysis oil, recovered carbon black, and fuels. Solvent-based feedstock recycling and chemical dissolution are highlighted as promising routes for selective recovery of rubber polymers and additives. Physical, chemical, and biological devulcanization methods are also reviewed for their potential to restore partial processability to reuse reclaimed rubber. Finally, current and prospective applications of recycled materials are discussed, and key challenges with future research needs are identified, including improving devulcanization efficiency, expanding collection systems, and increasing the value of recovered products.

Recycling doi: 10.3390/recycling11020031

Authors: Ulyana A. Frolova Khoshim Kh. Urazov Nikita N. Sviridenko Ekaterina N. Kolobova

This study examines the effect of different heat treatment conditions on different mixtures of plastic waste to produce fuel fractions. The mixtures included polypropylene, polystyrene, polyethylene terephthalate, low-density polyethylene, and high-density polyethylene in various ratios. The experiments revealed optimal process parameters, including the heating rate, process temperature, process duration, and environment, as well as the composition of the plastic waste mixture. This made it possible to extract more than 80% of the liquid, while gasoline and diesel fractions amounted to 35.7 and 30.5% wt., respectively. A detailed analysis of the gasoline fraction and diesel fuel obtained by cracking has demonstrated favorable properties confirming their potential as alternative sources of hydrocarbons or fuel components. A detailed study of the characteristics of the initial coke, as well as coke after alkaline treatment and calcination, revealed conditions conducive to the formation of porous carbon structures with a high specific surface area. The use of coke obtained from a mixture of plastic waste as a cracking additive slows down gas formation (by 1–5 ± 0.2% wt.) and increases the yield of low-boiling fractions (by 8.4 ± 0.4% wt.). Alkaline treatment of coke slows down its formation by increasing the specific area of micropores (from 154.8 to 219.1–286.5 m2/g) and decreasing the specific area of mesopores (from 311.2 to 76.4–187.3 m2/g), and also increases the yield of gasoline fractions. The results indicate effective ways to recycle plastic waste into valuable fuels and carbon materials, contributing to the development of technologies for sustainable waste management and resource recovery.

Recycling doi: 10.3390/recycling11020032

Authors: Cecilia Solís Armin Kriele Borja Oliver-Tomas Martin Hitzl Juan Carlos Guerrero Ramos José Luis Millá Tamarit Alicia Marco Aleixandre Rosa Maria Pérez Campos Arturo Valero Michael Renz

Residual lignocellulosic biomass represents a major resource to be incorporated into the circular economy, with up to 1400 Mt/y in EU27. Due to its complex composition of three biopolymers (cellulose, hemicellulose and lignin) combined with its seasonal and regional variability and high water content, its valorization involves manifold challenging aspects. Herein a three-step procedure is presented to transform this type of biomass into solid composite panels: hydrothermal carbonization (HTC), dry thermal treatment and curing a phenolic resin. HTC triggers chemical dehydration of the polysaccharide part of the lignocellulose and breaks up the cell structure of the plants. This facilitates the diffusion of the water and its separation by filtration, which is more energy efficient than evaporation. HTC and thermal treatment induce chemical changes that concentrate the carbon content and make the material suitable for crosslinking with a phenolic resin, achieving a 90% renewable content. The composite panels are competitive with products of the particle and fiberboard sector with respect to tensile strength and screw withdrawal resistance. Hence, the products can be employed for construction or in the furniture industry.

Recycling doi: 10.3390/recycling11020030

Authors: Catarina Nobre Santa Margarida Santos José Copa Rey Andrei Longo Bruna Rijo Roberta Panizio Paulo Brito Cecilia Mateos-Pedrero

Mobile pyrolysis systems offer a practical pathway for the decentralized valorization of biomass waste, addressing the high logistical and economic burdens of transporting low-density, moisture-rich feedstocks to centralized facilities. By operating directly at the source, these systems convert diverse agricultural and forestry residues into biochar, bio-oil, pyrogas, and wood vinegar, while reducing transport volumes and associated emissions. Reported mobile reactors process between 4 kg per batch and 10 t/day, achieving biochar yields of 33–44 wt.% at 400 °C and bio-oil yields of 55–68 wt.% in fast pyrolysis at 500–550 °C, demonstrating performance comparable to stationary installations. This review synthesizes current mobile pyrolysis technologies, including reactor configurations, feedstock suitability, operational constraints, and recent advances in automation, real-time monitoring, and machine learning-based optimization. The agricultural and industrial applications of pyrolysis products are examined, with emphasis on soil health enhancement, biopesticide activity, renewable gas generation, and carbon sequestration. Emerging international projects and commercial efforts are highlighted, illustrating growing interest in flexible, low-carbon pyrolysis solutions for rural waste management and distributed bioresource utilization, while outlining the technological gaps that remain to be addressed.

Recycling doi: 10.3390/recycling11020029

Authors: Inês Silva Nuno Lapa Henrique Ribeiro Elizabeth Duarte

Anaerobic digestion (AD) is a proven and promising technology for recovering energy from biowastes, such as pig slurry (PS) from the fattening/finishing phase. The mechanisms of AD are widely studied, and nowadays, it is of the utmost importance to investigate strategies that give end-users the confidence to choose this technology and to adapt it to their reality, promoting the energy transition and circular economy. This study investigated how collection and storage period affect PS samples, and how hydraulic retention time (HRT) (15 versus 20 days) influences AD performance and stability. Seasonality was the primary factor influencing feedstock characteristics. Samples presented no significant differences during the storage period. A 20-day HRT led to higher digestate pH, total ammonia nitrogen (TAN), and free ammonia nitrogen (FAN) concentrations, which can cause process instability and methanogenesis inhibition. However, 20-day HRT led to a specific methane production that was 7% higher and to a methane quality (expressed in % v/v CH4) that was 6% higher than 15-day HRT. Overall, methane quality, digestate pH, TAN, and FAN values may be considered key points that need to be monitored to prevent the AD system from being compromised. Nevertheless, these results provide the operational freedom to choose either HRT, allowing reduced reactor volume and investment.

Recycling doi: 10.3390/recycling11020028

Authors: Florian Teuffo Xavier Trivelli Stéphane Menuel Loubna Firdaous Muriel Bigan Rénato Froidevaux

The recycling of industrial biomass waste, such as black liquor rich in lignin from the pulp and paper industry, represents a sustainable strategy to reduce environmental impact and promote resource valorization. Enzymatic depolymerization of lignin is considered a promising approach due to the high specificity of lignin-degrading enzymes. However, lignin’s poor solubility in aqueous and acidic conditions, combined with its structural complexity and recalcitrance, limits its enzymatic reactivity. In this study, Trametes versicolor laccase was used to depolymerize lignin following a sonication pretreatment designed to improve its solubility and reactivity. Response surface methodology (RSM) identified lignin concentration and sonication time as the most influential parameters for optimizing pretreatment efficiency. The enzymatic depolymerization process revealed a competition between condensation and depolymerization reactions. Characterization of the reaction products using GPC, FTIR, and NMR confirmed the formation of lignin-derived aromatic compounds. These findings highlight the effectiveness of sonication as a pretreatment method to enhance enzymatic lignin degradation. Future research will focus on integrating depolymerization and product separation processes to limit lignin repolymerization and increase the yield of depolymerized aromatic products.

Recycling doi: 10.3390/recycling11020027

Authors: Natalya Kulenova Marzhan Sadenova Stanislav Boldyryev

The rapid increase in e-waste has become a significant global concern, influenced by swift technological advancements, shorter product lifecycles, and rising consumer demand. This situation leads to considerable environmental and health hazards, primarily due to the presence of toxic materials, energy demands, and the inadvertent loss of valuable resources when waste is not adequately managed. This review synthesises contemporary theories related to sustainable e-waste management, featuring concepts such as principles of the circular economy, energy efficiency and innovative recycling technologies. The review explores a range of actions, including regulatory strategies, mechanical pre-treatment methods, focusing on reagent-free recovery techniques, and the utilisation of digital solutions to enhance traceability and operational efficiency. The findings indicate substantial improvements in formal e-waste collection rates in areas with strong legislative frameworks, enhanced metal recovery efficiencies through refined hydrometallurgical and pyrometallurgical techniques and minimised environmental footprints through reagent-free and energy-conserving practices. The review emphasises the importance of viewing e-waste recycling not just as a waste management issue but as a fundamental element of resource security and sustainable industrial practices. By assessing recent developments, this work advocates for closed-loop recycling as an essential driver in the global shift towards a resilient, low-carbon, energy-efficient and circular economy.

Recycling doi: 10.3390/recycling11020026

Authors: Yamila V. Vazquez Cristina Pavon Juan Vicente Miguel Guillem Juan López-Martínez María Dolores Samper

This study investigates the processability and performance limits of high-density polyethylene (HDPE) recovered from mixed polyolefin waste under realistic mechanical recycling conditions. The waste stream was processed by extrusion and injection molding, with parameters actively adapted. ATR-FTIR and DSC analysis confirmed HDPE as the matrix, contaminated with minor fractions of polypropylene (PP), PET, and polyurethane (PU). The reprocessed material exhibited a single melting peak at 132 °C and a melt flow rate (MFR) of 9.9 ± 0.6 g 10 min−1, indicative of moderate degradation. Mechanical testing revealed reduced tensile strength and elongation at break compared to virgin HDPE, indicating compositional heterogeneity and poor interfacial adhesion. Field emission scanning electron microscopy (FESEM) revealed dispersed inclusions and microvoids acting as stress concentrators, consistent with reduced ductility. Crucially, progressive reduction of back pressure during processing optimization was essential for stabilizing melt flow and minimizing shear-induced degradation. This adjustment enabled consistent mold filling despite the material’s variability. The results demonstrate that mixed HDPE waste can be successfully valorized for non-structural applications such as plastic lumber or pallets, providing a sustainable pathway for recycling heterogeneous streams without costly pre-treatment or compatibilization.

Recycling doi: 10.3390/recycling11020025

Authors: Bruno Machini Diogo Simões Pedro Humbert Julieta António João Almeida

The urgent need to reduce greenhouse gas emissions and enhance resource circularity is driving the cement and construction industry to explore alternatives to clinker-based binders. Electric arc furnace slag (EAFS), a major steelmaking by-product, is currently underutilised as a binder due to its low intrinsic reactivity. This study provides a comparative evaluation of three distinct valorisation pathways for the same EAFS—use as a supplementary cementitious material (SCM), as a precursor for alkali-activated binders, and as a component in accelerated carbonation systems—thereby highlighting its multifunctional and more ecological binding potential. A comprehensive physicochemical characterisation was conducted, followed by mechanical performance assessment under different curing regimes. When used as an SCM, partial cement replacement resulted in no loss of mechanical performance and a compressive strength increase of up to 8.9% at 10% replacement, demonstrating its suitability for structural applications. Under accelerated carbonation, specimens with 50% replacement of cement and sand achieved compressive strengths of 46.7 MPa, comparable to the non-carbonated reference (47 MPa), indicating full strength recovery despite high substitution levels. Full replacement systems based on alkali activation or carbonation of EAFS achieved moderate compressive strengths (~10 MPa), suitable for non-structural applications, with clear potential for improvement through optimisation of activation and curing conditions. Overall, this work demonstrates that EAFS can be effectively valorised through multiple reaction routes, supporting its role as a versatile and low-carbon resource for sustainable cementitious materials.

Recycling doi: 10.3390/recycling11020024

Authors: Lingli Wang Xiaoqi Hu Tianzhi Wang Fawei Lin Yuehua Li Xiangqi Meng Manuel Fiallos

Oily sludge is a complex emulsified waste consisting of water, oil, and solid particles. Conventional treatments are often inefficient, energy-intensive, and prone to causing secondary pollution. This study proposes a green demulsification technology based on ozone micro–nanobubbles (O3MNBs) by constructing an experimental system to analyze its effects and mechanisms of action on oily sludge treatment. The O3MNBs exhibited a mean particle size of 831 nm and generated a substantial amount of hydroxyl radicals (·OH, 250.4 μmol·L−1) in situ. Compared with conventional aeration, the dissolved ozone concentration and residence time in water of O3MNBs increased by 192% and 213%, respectively. During bubble collapse, intense pressure waves and high-speed microjets were generated to disrupt sludge aggregates, promoting the dispersion of sludge particles while simultaneously stripping oil films. Thus, the oil removal rate reached 41.5%, demonstrating the high demulsification efficiency of O3MNBs. Furthermore, ozone and ·OH attacked alkane C-H bonds in the oil phase, oxidizing hydrophobic films into hydrophilic products and decomposing surfactants that stabilize emulsions. This process promoted oil droplet coalescence and degradation into small organic molecules. After O3MNB treatment, the absorption peak of alkane C-H bonds gradually reduced, while a new C=O absorption peak appeared. This study provides a theoretical foundation and technical support for environmentally sustainable treatment of oily sludge by O3MNB application, offering an effective alternative to chemical demulsification without secondary pollution.

Recycling doi: 10.3390/recycling11020023

Authors: Roman Stetsiuk Mustafa A. Aldeeb Hossam A. Gabbar

Waste management remains a major challenge worldwide, as rapidly expanding urban populations put greater pressure on traditional disposal methods such as landfilling and incineration. Plasma-based waste treatment offers an innovative, sustainable waste-to-energy solution capable of converting a wide range of waste types. Although plasma technologies provide significant environmental benefits, such as greatly reducing waste volume and emissions compared to conventional approaches, their widespread adoption faces notable economic hurdles. Primary among these is high operational cost due to system inefficiencies. These costs mainly arise from energy losses within the plasma torch, energy consumed during plasma torch tuning with the plasma reactor, and power inefficiencies when processing unsuitable waste loads. These issues not only increase costs but also impact process stability, which can influence stakeholder support and the technology’s commercial potential. Optimizing the process through simulation presents an effective approach to overcoming this inefficiency. However, relying solely on these advanced tools can be time-consuming and requires substantial domain expertise, creating a bottleneck in design and optimization. This paper introduces a new integrated platform combining COMSOL Multiphysics v6.2, Ansys Fluent 2024 R1, and Aspen Plus v12.1 to address these challenges. Using a genetic algorithm, the platform automates the complex task of designing an optimal plasma torch, optimizes it for peak performance, and dynamically adjusts plasma conditions. This intelligent optimization system aims to maximize energy output and process efficiency, directly tackling key cost-related issues.

Recycling doi: 10.3390/recycling11010022

Authors: Pedro Adrián Martínez-Montoya Mónica Corea-Téllez Ricardo Gerardo Sánchez-Alvarado Teresita del Refugio Jiménez-Romero Jorge Luis Gutiérrez-Estrada Margarita García-Hernández Angel de Jesús Morales-Ramírez

Growing demand for rare earth elements (REEs) necessitates the development of efficient recycling strategies from secondary sources. This work presents a complete hydrometallurgical process for recovering yttrium (Y) from spent fluorescent lamps, emphasizing the efficient coupling of a conventional acid leaching with a solid–liquid extraction system. Multi-stage sulfuric acid leaching (2 M, 65 °C, an S/L ratio of 0.25 g/L) achieved a cumulative yttrium dissolution of 71.11% over four stages, with individual stage recoveries (based on initial yttrium content) of 44.2%, 21.56%, 7.19%, and 0.68%. Kinetic and spectroscopic analyses (FTIR, SEM-EDS) revealed that the leaching rate is controlled by diffusion through an in situ formed sulfate-rich layer (CaSO4, Na2SO4), as described by the Z-L-T (Zhuravlev–Leshokin–Templeman) model (Ea = 35.5 kJ mol−1). The resulting leachate was subjected to solid–liquid extraction using Amberlite XAD-7 resin impregnated with D2EHPA. Under optimal conditions, the extraction process was highly efficient, yielding over 99% yttrium recovery at an optimal pH of 0.75 with a low resin dosage of 0.1 g/L. Furthermore, the solvent-impregnated resins exhibited excellent reusability over five consecutive extraction–stripping cycles, maintaining a single-cycle stripping efficiency above 70% and a cumulative recovery exceeding 97%. This study validates the technical feasibility of an integrated leach–extract–strip process based on impregnated resins as an alternative approach for yttrium recycling from electronic waste, potentially supporting the development of a circular economy.

Recycling doi: 10.3390/recycling11010021

Authors: Quan Liu Huanting Lei Jiangyu Liu Yuting Han Jiantao Wu

Temperature homogeneity assumes a crucial role in the manufacture of asphalt mixtures due to its impact on mechanical formation and mixing homogeneity. The existence of reclaimed asphalt pavement (RAP) exacerbates its impact on temperature inhomogeneity. To address this, the RAP contents of 20%, 40%, and 60%, combined with RAP preheated temperatures of 353 K, 373 K, and 393 K, were taken into consideration to examine the thermal transition and evolution of temperature for the recycled asphalt mixtures in the mixing. Thermal images captured within the range of 30 s to 120 s were used to monitor the temperature evolution of the recycled asphalt mixtures during the mixing. To quantitatively assess the level of thermal non-uniformity, a Relative Thermal Equilibrium Temperature Index (RETI) was introduced. This index reflects the degree of deviation from ideal thermal equilibrium within the recycled mixtures. Based on the RETI calculation, complete temperature homogeneity cannot be attained until the end of the mixing of hot recycled asphalt mixtures. However, a prolongation of the mixing time or an elevation in the RAP preheated temperature can expedite the thermal equilibrium process of recycled asphalt mixtures. Additionally, the RAP contents also exerted a crucial influence on the thermal equilibrium process of the recycled asphalt mixtures.

Recycling doi: 10.3390/recycling11010020

Authors: Dionella Jitka B. Quinagoran James Albert Narvaez Joy Marisol Maniaul John Kenneth A. Cruz Djoan Kate T. Tungpalan Eduardo R. Magdaluyo Karlo Leandro D. Baladad

Mine waste remains a persistent challenge for the minerals industry, posing significant environmental concerns if not properly managed. The 1996 Marcopper Mining Disaster in Marinduque, Philippines, left a legacy of mine tailings that continue to threaten local ecosystems and communities. This study investigates the valorization and stabilization of Marcopper river sediments laden with mine tailings using a combined geopolymerization and cement hydration approach. Hybrid mortar samples were prepared with 7.5%, 15%, 22.5%, and 30% mine tailings by weight, utilizing potassium hydroxide (KOH) as an alkaline activator at concentrations of 1 M and 3 M, combined with Ordinary Portland Cement (OPC). The mechanical properties of the hybrid geopolymer cement mortars were assessed via unconfined compression tests, and their crystalline structure, phase composition, surface morphology, and chemical bonding were also analyzed. Static leaching tests were performed to evaluate heavy metal mobility in the geopolymer matrix. The compression tests yielded strength values ranging from 24.22 MPa to 53.99 MPa, meeting ASTM C150 strength requirements. In addition, leaching tests confirmed the effective encapsulation and immobilization of heavy metals, demonstrating the potential of this method for mitigating the environmental risks associated with mine tailings.

Recycling doi: 10.3390/recycling11010019

Authors: Anna Nocivin Camil Tudor Constantin Ilie Doina Raducanu Lucia Violeta Melnic

The automotive industry’s use of aluminum alloys continues to rise, driven by efforts to reduce vehicle weight—and thus fuel consumption—amid growing demand for larger vehicles such as SUVs, as well as the accelerating shift to electric vehicles and the expanding global vehicle fleet. These trends create major challenges for the aluminum sector. This paper provides a narrative literature review of available and published data, primarily from the period 2020–2025, examining new trends, challenges and opportunities regarding the implementation of recycled aluminum as a substitute for primary aluminum in the European automotive industry. The goal is to develop a discussion based on the answer to the following three issues: (1) What opportunities exist for increasing the production of recycled aluminum, given the imperative to conserve diminishing raw materials required for primary aluminum production? (2) What methods could enhance the obtaining of recycled aluminum over primary aluminum? (3) How might the technological barriers that hinder the wider use of recycled aluminum be overcome? This review finds that recycled aluminum availability in the EU automotive sector is improving due to rising demand for recycled material over primary aluminum—supported by a steadily growing scrap supply—alongside the development of advanced recycling strategies capable of producing high-purity recycled alloys.

Recycling doi: 10.3390/recycling11010018

Authors: Gözde Alkan Peter Mechnich Tim Giessmann Srecko Stopic Bernd Friedrich

The enormously increasing demand for rare earth elements (REE), due to their wide high tech-application areas and their limited and unproportioned reserves across the globe, induced the utilization of secondary resources to provide more robust REE supply chains. In several studies, hydrometallurgical/pyrometallurgical routes have been employed to recover REE’s from secondary resources such as industrial residues, end-of-life magnets, batteries, and catalysts. In this pioneer study, we investigate the feasibility to use end-of-life RE-silicate environmental barrier coatings (EBCs) of turbine engine components as a secondary Yb resource. For this purpose, state-of-the-art EBC materials, ytterbium monosilicate (Yb2SiO5), and ytterbium disilicate (Yb2Si2O7), were exposed to a fictional aeroengine scenario involving in service contamination by airborne mineral dusts, commonly referred to as CMAS corrosion. CMAS-corroded Yb-silicate pellets were exposed to sulfuric acid leaching. Phase and microstructural analyses were conducted on starting materials and leaching residues, in a comparative manner, to explain the leaching mechanism. Leaching solutions were analyzed by ICP-OES indicating a very promising preliminary leaching efficiency and selectivity for Yb2SiO5, whereas Yb2Si2O7 displayed a very low leachability. Further prospects were suggested to enhance process efficiency and implications on repair/overhaul end-of-life Yb-silicate EBCs are discussed.

Recycling doi: 10.3390/recycling11010017

Authors: Martha Sumba Carlos Amador Diego Portalanza Jorge Amaya Omar Ruiz Malena Torres Narcisa Gorotiza Barbara Guerrero Juan D. Cabrera Eduardo Álava

The growing generation of organic solid waste from small-scale agriculture poses major environmental challenges in developing countries like Ecuador, where rural areas often lack waste management infrastructure. Residues from livestock rearing and traditional brewing such as poultry manure (PM), bovine manure (BM), and barley by-product (BB) are often discarded untreated. This study evaluated the bioconversion potential of Hermetia illucens (black soldier fly larvae (BSFL), using a local Ecuadorian strain reared on these substrates under natural conditions and three feeding rates (50, 100, and 150 mg·larva−1·day−1). Larval growth and process efficiency were analyzed on a dry-matter basis. Both substrate and feeding rate significantly influenced performance (p < 0.05). PM and BB produced the highest larval dry weights (37.4 and 35.9 mg, respectively) at 100 mg·larva−1·day−1, with development completed in 35 days. BM-fed larvae reached only 17.6 mg and required up to 91 days. Bioconversion peaked at 4.6% (PM100) and 4.2% (BB50), while all BM treatments showed very low efficiency (<0.8%). Waste reduction was highest in BB100 (52.9%) and PM100 (43.5%). These results demonstrate the potential of BSFL as a biological treatment option for rural organic waste streams; however, performance strongly depended on substrate quality and feeding rate, indicating that not all locally available residues are equally suitable for larval bioconversion.

Recycling doi: 10.3390/recycling11010016

Authors: Na Lin Hao Liu Ruixia Duan Jinzhou Chen Wentao Liu

Polyethylene terephthalate (PET) recycling technology has developed into a mature system, providing a key paradigm for the circular utilization of polyester waste. Its pathways are primarily divided into mechanical recycling and chemical recycling. Mechanical recycling converts waste PET into rPET through physical processes such as efficient sorting, deep cleaning, and melt extrusion. However, the resulting product often faces issues of decreased intrinsic viscosity and thermal oxidative degradation. Chemical recycling, particularly depolymerization techniques like saccharification, hydrolysis, and methanolysis, can reduce PET waste back to monomers. After purification, these monomers can be repolymerized into virgin-quality PET, achieving a closed-loop cycle. However, this approach faces challenges related to cost and process complexity. Against this backdrop, this paper further explores potential recycling methods for polyethylene terephthalate-1,4-cyclohexanedimethyleneterephthalate (PETG). This paper argues that the experience of PET recycling provides a crucial foundation for addressing PETG challenges but is not a direct solution. Future development directions include: developing intelligent sorting technologies, creating highly efficient selective catalysts to optimize depolymerization reactions, and other initiatives. These measures are essential for establishing an efficient recycling system for complex polyester waste.

Recycling doi: 10.3390/recycling11010015

Authors: Jianzhong Luo Jie Yao Chunhua Zhu Feihong Guo

The rapid expansion of China’s photovoltaic (PV) industry has led to a significant increase in decommissioned PV modules. To address the high energy consumption and environmental impact of traditional recycling techniques, this study proposes a novel method that integrates DMPU solvent recycling with pyrolysis for recovering PV cell sheets. DMPU, an organic solvent with low volatility, non-toxicity, and excellent recyclability, was used in this study. The effects of temperature and treatment duration on the structural integrity of silicon cell sheets were systematically evaluated, establishing optimal parameters: immersion in DMPU at 200 °C for 60 min, followed by pyrolysis at 480 °C for 60 min. A case study was conducted on a small-scale recycling facility with a daily processing capacity of 200 standard PV panels, encompassing system boundaries such as transportation, pretreatment, and pyrolysis. The recycling process consumed 2.14 × 109 kJ of energy annually, reducing CO2 emissions by 9357.2 tons. Compared to conventional methods such as pyrolysis, mechanical dismantling, and chemical dissolution, the proposed approach employing a green, recyclable solvent markedly reduces energy consumption and carbon emissions, offering notable environmental benefits.

Recycling doi: 10.3390/recycling11010014

Authors: Bruna F. Oliveira Teresa I. Gonçalves Marcelo M. Sousa Liane Ferreira Victor Lourenço Flávia V. Barbosa

Circular economy and Industry 4.0 principles are increasingly shaping industrial practices. In the textile sector, environmental impacts and low recyclability make circularity a critical priority. This study focuses on enhancing both circularity and operational efficiency in a Portuguese manufacturer of labels and trimmings. Achieving this requires the collection of relevant data and identification of the factors that most influence operational performance, while linking these to circularity outcomes. To support this effort, the paper presents two complementary methodologies: Multi-layer Stream Mapping (MSM) for evaluating manufacturing efficiency and the Overall Circularity Index (OCI) for assessing circularity performance. MSM provides a detailed analysis of process efficiency, identifying sources of waste and summarizing results through user-friendly scorecards that highlight high-impact improvement areas. The OCI measures a company’s circularity on a scale from 0 to 1—where 1 represents full circularity—using strategic indicators across environmental, material, economic, and social dimensions. The MSM revealed an overall efficiency of 71%, whereas the OCI resulted in a final score of 0.516. When applied together, MSM and the OCI form a straightforward, iterative, and effective framework for diagnosing strengths and weaknesses in the manufacturing process, supporting evidence-based decision-making and guiding the company’s transition toward more circular and efficient operations.

Recycling doi: 10.3390/recycling11010013

Authors: Giovanni Marmora Carmen Ferrara Vittorio Roselli Giovanni De Feo

Packaging plays a crucial role in product preservation and distribution but also constitutes a major source of environmental burden. In the beverage sector, where unit value is low, secondary and tertiary packaging significantly influence the environmental profile of the final product. This study quantifies the environmental trade-offs between conventional single-use and reusable packaging systems for aluminum cans, identifying the operational thresholds that justify a transition to circular models. A standardized Life Cycle Assessment (LCA) approach is applied to five packaging configurations: three current market scenarios and two alternative solutions based on reusable plastic crates (RPCs). System boundaries include production, distribution, end-of-life, and, where applicable, reverse logistics. A functional unit of one fully packaged 0.33 L aluminum can is adopted. Results reveal that while single-use cardboard solutions achieve favorable performance under certain impact categories, reusable systems outperform them when a sufficient number of reuse cycles is achieved and reverse logistics are efficiently managed. Sensitivity analyses highlight the critical influence of transport distances and reuse frequency on overall impacts, with performance deteriorating for reusable systems beyond 200 km or below 50 reuse cycles. These findings offer concrete, evidence-based guidance for supply-chain and logistics decision-makers to optimize packaging choices and distribution network design. The study also provides robust quantitative insights for policymakers and industry stakeholders by defining the precise operational conditions under which reusable systems deliver real environmental benefits. By presenting a comprehensive, system-level comparison of complete packaging systems, this research closes a critical gap in LCA studies and sets out a practical pathway for implementing circular, low-impact packaging strategies consistent with emerging EU regulations.

Recycling doi: 10.3390/recycling11010012

Authors: Songcheng Wang Xue Zong Xiaotang Du Sven H. Behrens J. Carson Meredith

Froth flotation is a widely used method for the selective separation of particulates from aqueous dispersions or slurries. This technology is based on the attachment of sufficiently hydrophobic particles to the air–water interface of gas bubbles. However, when the target particles are strongly hydrophilic, the requirement of hydrophobicity limits the effectiveness of conventional froth flotation. A prominent example is the deinking step in paper recycling, where modern hydrophilic inkjet inks are difficult to remove by flotation. In this study, we evaluated oil-coated bubble flotation as an alternative to conventional air flotation for removing inkjet ink from pulped newsprint. We examined the effects of oil type, salt type and concentration, and pH on deinking efficiency. Compared with traditional air flotation, oil-coated bubble flotation produced substantial improvements in standard performance metrics, including ISO brightness, effective residual ink concentration (ERIC), and the fiber retention of recycled paper pads.

Recycling doi: 10.3390/recycling11010011

Authors: Steffen Fischer Jannik Guido Born Martin Wolke Timo Hölter Klaus Dröder Stephan Scholl Harald Zetzener Arno Kwade

With rising efforts to enable a circularity of valuable resources of lithium-ion batteries, a growing number of recycling companies in Europe are expanding their capacities and developing new recycling technologies. The European Union (EU) has set a benchmark for battery recycling by publishing recycling targets. These targets require precise mass determination of the individual battery components, making disassembly of the battery mandatory for characterization. The paper puts forth a semi-automated disassembly procedure for determining the composition of the components at the module and cell levels across a range of designs. Our analysis incorporates the introduction of TGA as a novel, direct method for determining the cathode active material with an accuracy above 99%. This approach is intended to define the recycling input for all extant recycling routes by providing quantitative experimental results with statistical significance. The results indicate a black mass proportion of 61.6% at the module level and 53–74% at the cell level. Additionally, there are significant differences in value creation, ranging from 0.80 to 1.81 USD kg−1 black mass, depending on the cell chemistry. The procedure can be used for EoL and scrap material, and enables greater transparency and comparability in battery recycling, opening up new perspectives for the resource-efficient and targeted use of various recycling technologies.

Recycling doi: 10.3390/recycling11010010

Authors: Chunle Yuan Zuoxiu Zhang Wanqing Wang

In light of the persistently mounting pressure on urban and rural waste management, developing efficient, low-carbon, and resource-oriented waste treatment technologies represents a critical challenge demanding urgent breakthroughs. Thermophilic anaerobic digestion (TAD), possessing these advantages, demonstrates unique application prospects in food waste treatment. However, its inherent instability constrains its engineering-scale implementation. This paper systematically reviews existing laboratory and pilot-scale research, focusing on: (1) Thecomplex interactions and synergistic effects of primary inhibitory factors; (2) The dynamic characteristics of microbial communities and their adaptive restructuring mechanisms under thermophilic stress; (3) The efficacy and underlying mechanisms of co-digestion, process control, and two-phase system strategies. This study aims to establish a clear pathway from mechanistic understanding to engineering optimisation, providing a theoretical framework for enhancing the operational stability and scalability of the TAD process.

Recycling doi: 10.3390/recycling11010009

Authors: Siti Mutia Mawaddah Mochamad Chalid Azizah Intan Pangesty Muhammad Ghozali Yora Faramitha Firda Dimawarnita Annisa Rifathin Zarlina Zainuddin Muhammad Hanif Ainun Azhar Adam Febriyanto Nugraha

Wood polymer composite (WPC), composed of polymer matrices reinforced with natural fibers, is increasingly used in structural and non-structural applications due to its sustainability and performance. Although teak and rice husk are common natural reinforcements, the use of oil palm empty fruit bunches (OPEFB) remains underexplored despite their abundance as agricultural waste. This study investigates the potential of OPEFB as an alternative reinforcement for recycled polyethylene-based WPC containing 20 wt% fiber and compares its morphology and performance with teak and rice husk. Compositional analysis shows that OPEFB exhibits lignin and cellulose contents as well as crystallinity comparable to teak, while exceeding rice husk in several structural parameters. These characteristics contribute to the highest tensile strength observed among the composites (37.45 MPa). Although its Shore D hardness is the lowest (58.8), the value remains within the acceptable range for construction applications. Combined with its favorable production costs, OPEFB emerges as a viable, resource-efficient alternative to conventional natural fibers, expanding the options for sustainable WPC development.

Recycling doi: 10.3390/recycling11010008

Authors: Hongren Su Bin Zhang Rencan Yang Jingyi Shi Shichun He Sifan Dai Dongwang Wu Zhiyong Zhao

The valorization of food waste through bioconversion using black soldier fly larvae (BSFL, Hermetia illucens) represents a promising pathway for sustainable waste management. However, the efficiency and safety of this process when using low-quality food waste substrates remain insufficiently characterized. This study investigated the adaptive responses, nutrient conversion efficiency, and product safety of BSFL reared solely on food waste (moisture 78.4%, crude protein 42.98%, pH 3.62) under controlled conditions (28 °C, 55% RH). Larval growth followed a logistic model (R2 = 0.96), with an inflection point at 13.14 days and a maximum daily weight gain of 0.0153 g/larva. Crude protein content increased significantly to 64.21%, while crude fat peaked at 26.42% by day 6 before declining. Larvae accumulated essential amino acids and functional fatty acids effectively. Notably, BSFL demonstrated a strong ability to exclude arsenic and chromium, with over 90% of these heavy metals retained in the frass. The frass itself exhibited high organic matter content (up to 61.57%) and an alkaline pH, meeting general standards for organic fertilizers. These findings underscore the resilience of BSFL and its potential for safe, high-value biomass production from challenging food waste streams, contributing to advanced circular economy strategies.

Recycling doi: 10.3390/recycling11010007

Authors: Noori M. Cata Saady Alejandro Vázquez Hernández Karla Lucia Flores Servin Jose Zuniga Rodriguez Md Ariful Haque Michael Kwaku Owusu Sohrab Zendehboudi Carlos Bazan Juan Enrique Ruiz Espinoza

Valorizing fruit and vegetable residues as renewable sources of bioactive compounds (BCs) is critical for advancing sustainable biotechnology. This review (i) assesses the occurrence, diversity and functionality of BCs in 20 edible plant residues; (ii) compares and classify them by botanical family and residue type; (iii) reviews and evaluates the efficiency of conventional and green extraction and characterization techniques for recovering phytochemical and isolating phenolics (e.g., flavonoids and anthocyanins), carotenoids, alkaloids, saponins, and essential oils; and (iv) examines the BCs’ environmental, medical, and industrial applications. It synthesizes current knowledge on the phytochemical potential of these crops, highlighting their role in diagnostics, biomaterials, and therapeutic platforms. Plant-derived nanomaterials, enzymes, and structural matrices are employed in regenerative medicine and biosensing. Carrot- and pumpkin-based nanoparticles accelerate wound healing through antimicrobial and antioxidant protection. Spinach leaves serve as decellularized scaffolds that mimic vascular and tissue microenvironments. Banana fibers are used in biocompatible composites and sutures, and citrus- and berry-derived polyphenols improve biosensor stability and reduce signal interference. Agro-residue valorization reduces food waste and enables innovations in medical diagnostics, regenerative medicine, and circular bioeconomy, thereby positioning plant-derived BCs as a cornerstone for sustainable biotechnology. The BCs’ concentration in fruit and vegetable residues varies broadly (e.g., total phenolics (~50–300 mg GAE/g DW), anthocyanins (~100–600 mg C3G/g DW), and flavonoids (~20–150 mg QE/g DW)), depending on the crop and extraction method. By linking quantitative food waste hotspots with phytochemical potential, the review highlights priority streams for the circular-bioeconomy interventions and outlines research directions to close current valorization gaps.

Recycling doi: 10.3390/recycling11010006

Authors: Monica Pivetti Francesca Giorgia Paleari Mariangela Vespa Maristella Tutolo

This study examines the psychosocial factors predicting municipal solid waste separation in Italy, applying and extending a model originally developed for Southern regions. The model integrates the Theory of Reasoned Action and the Value-Belief-Norm framework to explain how values, norms, and attitudes shape waste separation intentions and behaviours. Using data from 321 online survey respondents, this study tests the model’s validity in Northern Italy. Additionally, the study examines the relationships among the variables under investigation in people residing in the Northern and Southern regions of Italy. Findings confirm the model (χ2 (10) = 28.118, p = 0.002, CFI = 0.956; RMSEA = 0.075; AIC = 8.118): bio-altruistic values and social norms significantly predict positive attitudes, which in turn determine behavioural intentions. Perceived distributive unfairness is negatively associated with attitudes toward waste separation. Separation behaviour is mainly influenced by internal attributions and knowledge, while egoistic values show a negative relationship. The multi-group analysis indicates a good model fit for both Northern and Southern samples (χ2 (31) = 45.059, p = 0.049, CFI = 0.969; RMSEA = 0.053; AIC = −16.941), suggesting consistent psychosocial mechanisms. By integrating psychosocial insights with behavioural data, this research highlights the importance of knowledge, fairness, and social norms in promoting sustainable waste management. The findings provide practical guidance for policymakers and practitioners to design regionally communication and participation strategies that enhance the long-term sustainability of waste separation systems in Italy.

Recycling doi: 10.3390/recycling11010005

Authors: Juliene Maria da Silva Amancio Kelly Alonso Costa Welington Kiffer de Freitas Givanildo de Gois Paulo Miguel de Bodas Terassi Francisco Santos Sabbadini Josimar da Silva Freitas Juaneza Barroso Falcão Marco Antonio Conejero Ana Paula Martinazzo

This study compares the carbon footprints of two municipal solid waste treatment technologies—anaerobic digestion and a gas recovery system—with the aim of evaluating their potential for biogas recovery and greenhouse gas (GHG) mitigation. The analysis applies the 2006 IPCC model to real operational data from the Paracambi Waste Treatment Complex (Rio de Janeiro, Brazil), integrating carbon footprint estimation and environmental compensation modeling through tree planting. From a different perspective, this work evaluates the replacement of biogas recovery with a biologically controlled system based on material segregation. Within the limits and parameters defined for the system, anaerobic digestion achieved net emissions of 0.0029 tCO2eq per ton of organic waste, compared to 1.14 tCO2eq per ton for the biogas recovery system. This represents a potential 393-fold reduction in GHG emissions. However, this result is specific to the modeled conditions and does not consider the full life cycle impacts of non-organic waste fractions. The results suggest that anaerobic digestion, when integrated into an efficient selective collection system, can significantly improve energy recovery and mitigate the carbon footprint of waste management systems.

Recycling doi: 10.3390/recycling11010004

Authors: Gloria Abigail Martinez-Rodriguez Juan Antonio Rojas-Contreras Perla Guadalupe Vázquez-Ortega Damián Reyes-Jáquez Hiram Medrano-Roldán Norma Urtiz-Estrada Marcelo Barraza-Salas Grisel Fierros-Romero Ernesto Rodríguez-Andrade David Enrique Zazueta-Álvarez

The growing demand for lithium, driven by its key role in rechargeable batteries and its use in electric vehicles, highlights the need for sustainable and environmentally friendly recovery strategies. Conventional methods, such as pyrometallurgy and hydrometallurgy, are effective but costly and harmful as they emit toxic compounds. Biohydrometallurgy has emerged as a promising alternative, as it uses microorganisms and their metabolites to solubilize metals under milder conditions. Biohydrometallurgy has emerged as a promising alternative, as it relies on microorganisms and their metabolites to solubilize metals under mild operating conditions. Nevertheless, challenges related to process efficiency and selectivity remain, particularly for lithium recovery. In this context, recent advances in metal-binding peptides have attracted increasing attention due to their inherent selectivity and the possibility of rational design and heterologous expression in well-established microbial hosts such as Escherichia coli, Bacillus subtilis, and Saccharomyces cerevisiae. This review critically analyzes current biotechnological strategies and explores the integration of microbial bioleaching with peptide-based approaches as a complementary and environmentally friendly framework for the selective recovery of lithium and other metals from spent batteries and waste electrical and electronic equipment. Overall, this review provides an integrative conceptual framework that highlights the potential of combining microbial processes with metal-binding peptides to guide the development of more selective and sustainable biotechnological strategies for lithium recovery from secondary sources.

Recycling doi: 10.3390/recycling11010003

Authors: Israel Arzate-Vázquez Juan Vicente Méndez-Méndez Ruth Nohemí Domínguez-Fernández Mayra Beatriz Gómez-Patiño Daniel Arrieta-Baez José Jorge Chanona-Pérez Nayeli Vélez-Rivera Germán Anibal Rodríguez-Castro

Mechanical milling is a relevant preliminary processing operation that is widely used for the reuse of various types of agro-industrial waste. The objective of this study was to conduct milling experiments of hazelnut (Corylus avellana L.) shell waste at different times (0.5, 1 and 1.5 min) and subsequently evaluate the particle size distribution (PSD) of the powders obtained by sieving methodology. In addition, flowability parameters were determined for the particles retained on the sieves, and their morphology and microstructure were examined using several microscopy techniques. The results demonstrated that the hazelnut shells were successfully fractionated under the milling conditions investigated (short milling times ≤ 1.5 min), and the histograms of the PSD exhibited a wide dispersion of sizes (≤1.7 mm). The particles retained from sieve100 to residue exhibited poor or no flow, attributable to the high degree of cohesion between them. Morphological analysis based on optical microscopy and image analysis revealed that there was an increase in the aspect ratio parameter when the particle size decreased, meaning that the particles had elongated shapes. Microscopic analysis (SEM, AFM and CLSM) showed that the particles exhibited complex shapes and a comparable microstructure, comprising tightly packed clusters of sclerenchyma cells. From the microscopy images obtained (SEM and AFM), it was inferred that the cracks generated during blade impacts propagate along the middle lamella of the cells, allowing the cluster-like arrangement to be preserved. The CLSM results demonstrated that as the size of hazelnut shell particles decreases, the exposure of lignin on its surface is favored. The findings of this study demonstrate that hazelnut shell waste can be readily pre-processed using a blade grinder, thereby facilitating its reuse in applications that demand fine particle sizes (e.g., bioadsorption of pollutants and the production of biocomposite materials). Likewise, the results concerning the flowability parameters, microstructural arrangement, and morphological features of the different particle fractions obtained are crucial variables that must be considered. These variables significantly influence the possible applications for the revalorization of this type of agro-industrial waste.

Recycling doi: 10.3390/recycling11010002

Authors: Giovanni De Feo

This paper presents Greenopoli, an innovative framework for sustainability and waste management education that has engaged over 600 schools and 90,000 students since 2014. Greenopoli is founded on the idea that children and youth can grasp environmental issues as well as adults and act as agents of change within their families and communities. The Greenopoli approach combines scientific accuracy with playful, creative pedagogy to simplify complex topics and stimulate peer-to-peer learning. It includes storytelling, games, field visits, and “green raps” (original environmental songs co-created with students). The framework is adaptive, with content and activities tailored to education stages from kindergarten through university. Educators adopt the role of moderators or facilitators, encouraging students to discuss and discover concepts collaboratively. Greenopoli’s participatory method has been implemented across all age groups, yielding enthusiastic engagement and tangible outcomes in waste sorting and recycling behaviors. The program’s reach has extended beyond schools through collaborations with national recycling consortia, NGOs, municipalities, and media (TV programs, social media, TEDx talks). Numerous awards and recognitions (2017–2025) have highlighted its impact. A comparative analysis shows that Greenopoli’s use of peer-led learning, gamification, and creative communication aligns with global best practices while offering a unique blend of tools. Greenopoli is a novel best-practice model in environmental education, bridging theory and practice and contributing to the goals of Education for Sustainable Development and a circular economy. It demonstrates the effectiveness of engaging youth as change-makers through interactive and creative learning, and it can inspire similar initiatives globally.

Recycling doi: 10.3390/recycling11010001

Authors: Juana María Nájera-Ibarra Francisco Raúl Carrillo-Pedroza Ma. De Jesús Soria-Aguilar Nallely Guadalupe Picazo-Rodríguez Antonia Martínez Luévanos Simón Alberto Pedroza-Figueroa Isaías Almaguer-Guzmán Josué Cháidez-Félix Manuel Flores-Favela

The depletion of natural resources remains a major global challenge, emphasizing the need to develop sustainable processes that enable both metal recovery and waste recycling. This study investigates the leaching of valuable metals from lead smelting slag using methanesulfonic acid (MSA), a biodegradable and environmentally benign reagent. Batch experiments were performed under different MSA concentrations (0.35–1.4 M) and temperatures (22–80 °C). Metal dissolution increased nearly linearly with acid concentration up to 1 M, with maximum recoveries after 60 min of 85% Zn, 64% Pb, 75% Cu, and 68% Fe. Copper dissolution was governed by the oxidation of Cu2S, while Fe leaching was affected by pH variations that promoted re-precipitation. Kinetic modeling indicated mixed chemical–diffusion control mechanisms, with activation energies of 22.6 kJ mol−1 for Zn and 31–33 kJ mol−1 for Pb, Cu, and Fe. Beyond efficient metal extraction, the process generated a leach residue with reduced concentrations of base metals and a mineralogical composition dominated by stable calcium-silicate phases, improving its potential suitability for reuse in construction or mining backfill applications. Overall, methanesulfonic acid proved to be an effective and sustainable lixiviant, combining high metal recovery with the generation of recyclable slag, thereby contributing to circular metallurgical practices.

Recycling doi: 10.3390/recycling10060225

Authors: Kyle Parnell Abigail Rolston Brian Hilton Allen Luccitti

Rapid expansion of the global textile industry has accelerated both resource consumption and the scale of associated waste streams. An emerging body of recycling technology research aims to mitigate these impacts by enabling more circular material supply chains. While technologies are well described in a technical sense, literature focuses heavily on chemical methods and provides limited assessment of their physical and practical potential in the context of contemporary textile market conditions. This paper reviews these technologies in technical terms, and then establishes a qualitative framework for material value retention and waste avoidance potential with which to evaluate their efficacy. Analysis highlights that few recycling technologies are demonstrably compatible with either the attributes of post-consumer textile waste streams or the pace and scale of deployment necessary to address consumption and disposition patterns. We also highlight that both mechanical and chemical recycling are capacity constrained, and generally yield low material retention and solid waste avoidance potential per unit mass relative to other circularity strategies. Given these constraints, we posit that systems-level shifts in product and business model design may be useful as strategies to both reduce impacts upstream and mitigate waste volume, in turn supporting improved recycling rates.

Recycling doi: 10.3390/recycling10060224

Authors: María Ángeles García-Fortes Patricia Esteve-Guirao Isabel Banos-González Magdalena Valverde-Pérez Ana Ruiz-Navarro

This study explores how 130 future teachers (FTs) perceive and address massive waste generation when it is framed through two socio-environmental contexts: waste export from affluent to vulnerable countries and microplastic pollution in natural environments. Using a mixed-methods design, we examine how each context shapes problem perception, attribution of responsibility, and proposed teaching activities. Both contexts foster a systemic understanding of waste issues. Economic drivers are identified as the main cause (means = 3.2/4), while institutional factors are downplayed in the export scenario and individual factors in the microplastics scenario. Proposed solutions center on institutional and economic measures. Ecological impacts are prioritized in both contexts; however, the export case elicits broader multi-sphere interpretations, whereas microplastics are viewed primarily as ecological–sanitary risks. Perceived responsibility is moderate (mean = 2.6/4) in both contexts, though waste export is interpreted more individually and microplastics more collectively. A disengaged profile predominates, particularly for microplastics (76.92%), with most FTs showing limited intention to change personal habits. In terms of didactic design, only 20% of activities in the export context and 50% in the microplastics context are action-oriented. Findings highlight the importance of carefully selected socio-environmental contexts in teacher education to promote systemic reasoning, shared responsibility, and action-oriented learning.

Recycling doi: 10.3390/recycling10060223

Authors: Kazi Arafat Helmut Yabar Takeshi Mizunoya

Bangladesh generates approximately 3000 tons of plastic waste daily, and high mismanagement leads to substantial discharge into soils, rivers, and oceans. Limited research exists on plastic pollution along Cox’s Bazar in southeastern Bangladesh, with no studies spanning the entire coast; this study provides the first comprehensive assessment of the full coastline. This study investigates the abundance, types, and distribution of macro-, meso-, and microplastics in sediments from 23 stations covering Tourism, Active, and Less Active areas. Plastics were classified by size, shape, color, and polymer composition using stereomicroscopy and Fourier Transform Infrared Spectroscopy (FTIR), while spatial patterns of microplastic polymers were analyzed using Inverse Distance Weighted (IDW) interpolation. A total of 11,558 plastic particles were identified, with microplastics dominating (409.04 particles/m2), followed by mesoplastics (60.7 particles/m2) and macroplastics (32.8 particles/m2). Expanded polystyrene (EPS) and fragments were the most prevalent shapes, while transparent-white particles dominated in color. Polystyrene (PS), polypropylene (PP), and polyethylene (PE) comprised over 95% of polymers. IDW mapping highlighted Tourism, urban, and industrial zones as microplastic hotspots, with higher abundances in tourism areas. These findings provide a baseline for monitoring coastal plastic pollution and emphasize improved plastic management and recycling, contributing globally to understanding contamination in rapidly urbanizing, tourism-driven developing regions.

Recycling doi: 10.3390/recycling10060222

Authors: Dimitris Folinas Konstantinos Rotsios Chrysa Agapitou Maria-Theodora Folina Thomas Fotiadis

Deposit Refund Systems (DRS) are widely adopted in many European countries as effective mechanisms for increasing recycling rates and promoting circular-economy practices. Greece is currently preparing for the introduction of a national DRS for beverage containers, a transition expected to reshape existing waste-management structures. This study investigates the systemic challenges that may hinder the successful implementation of the upcoming Greek DRS. Focusing exclusively on polyethylene terephthalate (PET), aluminum, and glass beverage containers, this study adopts a multi-stakeholder qualitative approach involving 28 semi-structured interviews with beverage producers, retailers, recyclers, logistics actors, consumer representatives, and regulatory authorities. Thematic analysis reveals four interdependent barriers: restricted consumer accessibility due to uneven distribution of return infrastructure; fragmented governance and unclear institutional responsibilities; weak coordination and operational misalignment among supply-chain actors; and low consumer participation shaped by behavioral and cultural factors. These findings underscore that Greece’s DRS readiness is constrained not by technological limitations but by systemic gaps in governance, infrastructure planning, and stakeholder collaboration. This study contributes to the DRS literature by providing one of the first pre-implementation, multi-actor assessments in a Southern European context and offers policy-relevant insights to support an effective, equitable, and transparent rollout of the national DRS.

Recycling doi: 10.3390/recycling10060221

Authors: Julian Aberger Lena Brensberger Jesús Pestana Georgios Sopidis Benedikt Häcker Michael Haslgrübler Renato Sarc

Innovations in manual waste sorting have stagnated for decades, despite the increasing global demand for efficient recycling solutions. The recAIcle system introduces an innovative AI-powered assistance system designed to modernise manual waste sorting processes. By integrating machine learning, continual learning, and projection-based augmentation, the system supports sorting workers by highlighting relevant waste objects on the conveyor belt in real time. The system learns from the decision-making patterns of experienced sorting workers, enabling it to adapt to operational realities and improve classification accuracy over time. Various hardware and software configurations were tested with and without active tracking and continual learning capabilities to ensure scalability and adaptability. The system was validated in initial trials, demonstrating its ability to detect and classify waste objects and providing augmented support for sorting workers with high precision under realistic recycling conditions. A survey complemented the trials and assessed industry interest in AI-based assistance systems. Survey results indicated that 82% of participating companies expressed interest in supporting their staff in manual sorting by using AI-based technologies. The recAIcle system represents a significant step toward digitising manual waste sorting, offering a scalable and sustainable solution for the recycling industry.

Recycling doi: 10.3390/recycling10060220

Authors: Michelângelo Vargas Fassarella Izabella Luzia Silva Chaves Pedro Gutemberg Alcântara Segundinho Juarez Benigno Paes Roberto Carlos Costa Lelis Michel Picanço Oliveira Emilly Soares Gomes Silva Fabricio Gomes Gonçalves

Wastes, biomasses, and nanoparticles have motivated reformulations of adhesives in the wood-based-panel industry. This study investigated the incorporation of glass wool (GW) waste as a filler material in urea–formaldehyde (UF) adhesive, evaluating its effects on the adhesive properties as well as on the physical, mechanical, fire-retardant, and acoustic properties of particleboards. Panels with a target density of 700 kg m−3 were produced with different proportions of glass wool in the adhesive (T1: 0%; T2: 3.34%; T3: 4.93%; T4: 6.52%; T5: 9.49%; T6: 12.35%). The adhesive-coated particle mat was pressed in a hydraulic press at 160 °C under a compression force of 72 tons for 10 min. The panels were subjected to analyses of their physical, mechanical, fire-retardant, and acoustic properties, as well as scanning electron microscopy (SEM) analyses. Statistical analysis involved regression, analysis of variance, and a Scott–Knott test (p < 0.05). The results indicated that adding 3.34% GW to the adhesive improved the modulus of rupture, internal bond strength, screw withdrawal resistance, and acoustic efficiency of the panels. A glass wool content of 12.35% enhanced the hardness and the damping factor. These findings highlight the potential of glass wool as a functional filler material in UF adhesive, promoting the development of stronger and more sustainable particleboards.