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Recycling, Volume 9, Issue 3 (June 2024) – 20 articles

Cover Story (view full-size image): Manganese and rhenium share many of the chemical characteristics of transition metals, including multiple valency, the ability to form stable complex ions, paramagnetism, and catalytic properties. For this reason, Mn(ReO4)2·2H2O can potentially be used in the production of alloys, catalysts, or electrical components. The waste-free technology described in the publication enables the production of high-purity manganese(II) perrhenate dihydrate, a valuable material for future novel applications in alloys, catalysts, and electrical components. It is also in agreement with the principles of sustainable development and green transformation. The waste used in the research were scraps of Ni-based superalloys containing Re and scraps of Li–ion batteries containing Mn. View this paper
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12 pages, 2851 KiB  
Article
Study of the Mechanical and Electrochemical Performance of Structural Concrete Incorporating Recycled Polyethylene Terephthalate as a Partial Fine Aggregate Replacement
by Ana Cecilia Espindola-Flores, Michelle Alejandra Luna-Jimenez, Edgar Onofre-Bustamante and Ana Beatriz Morales-Cepeda
Recycling 2024, 9(3), 51; https://doi.org/10.3390/recycling9030051 - 20 Jun 2024
Viewed by 1318
Abstract
The extraction of materials, such as sand and gravel, required for the manufacture of concrete results in the overexploitation of natural resources and a large release of CO2 emissions into the environment. Therefore, the search for alternatives to partially replace these aggregates [...] Read more.
The extraction of materials, such as sand and gravel, required for the manufacture of concrete results in the overexploitation of natural resources and a large release of CO2 emissions into the environment. Therefore, the search for alternatives to partially replace these aggregates has become an important issue to solve. Nonetheless, the demand for producing sustainable yet high-strength and durable concrete using alternative materials has led concrete technologists to develop high-performance concrete. These novel concretes possess superior engineering properties, such as high durability and ductility, low maintenance costs, high mechanical strength, and prolonged service life. Currently, there is significant interest in the development of concrete–polymer compounds, primarily to improve the mechanical properties of the material. In this context, the present study explores the partial replacement of fine aggregate with recycled Polyethylene terephthalate (R-PET) in different proportions to produce green structural concrete, with the aim of studying its impact on the mechanical and electrochemical properties. The mechanical properties evaluated were the compressive and flexural strengths, while the electrochemical properties were evaluated through the open circuit potential and polarization curves. The results indicated that specimens containing different R-PET percentages as a replacement for fine aggregate showed higher increases in compressive and flexural strengths. It was also found that the presence of R-PET decreased the corrosion rate of the reinforcing steel when seawater was used as the electrolyte. Full article
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14 pages, 957 KiB  
Article
Optimization Production of an Endo-β-1,4-Xylanase from Streptomyces thermocarboxydus Using Wheat Bran as Sole Carbon Source
by Thi Ngoc Tran, Chien Thang Doan, Thi Kieu Loan Dinh, Thi Hai Ninh Duong, Thi Thuc Uyen Phan, Thi Thuy Loan Le, Trung Dung Tran, Pham Hung Quang Hoang, Anh Dzung Nguyen and San-Lang Wang
Recycling 2024, 9(3), 50; https://doi.org/10.3390/recycling9030050 - 9 Jun 2024
Cited by 1 | Viewed by 1739
Abstract
Xylanases, key enzymes for hydrolyzing xylan, have diverse industrial applications. The bioprocessing of agricultural byproducts to produce xylanase through fermentation approaches is gaining importance due to its significant potential to reduce enzyme production costs. In this work, the productivity of Streptomyces thermocarboxydus TKU045 [...] Read more.
Xylanases, key enzymes for hydrolyzing xylan, have diverse industrial applications. The bioprocessing of agricultural byproducts to produce xylanase through fermentation approaches is gaining importance due to its significant potential to reduce enzyme production costs. In this work, the productivity of Streptomyces thermocarboxydus TKU045 xylanase was enhanced through liquid fermentation employing wheat bran as the sole carbon source. The maximum xylanase activity (25.314 ± 1.635 U/mL) was obtained using the following optima factors: 2% (w/v) wheat bran, 1.4% (w/v) KNO3, an initial pH of 9.8, an incubation temperature of 37.3 °C, and an incubation time of 2.2 days. Xylanase (Xyn_TKU045) of 43 kDa molecular weight was isolated from the culture supernatant and was biochemically characterized. Analysis through liquid chromatography with tandem mass spectrometry revealed a maximum amino acid identity of 19% with an endo-1,4-β-xylanase produced by Streptomyces lividans. Xyn_TKU045 exhibited optimal activity at pH 6, with remarkable stability within the pH range of 6.0 to 8.0. The enzyme demonstrated maximum efficiency at 60 °C and considerable stability at ≤70 °C. Mg2+, Mn2+, Ba2+, Ca2+, 2-mercaptoethanol, Tween 20, Tween 40, and Triton X-100 positively influenced Xyn_TKU045, while Zn2+, Fe2+, Fe3+, Cu2+, and sodium dodecyl sulfate exhibited adverse impact. The kinetic properties of Xyn_TKU045 were a Km of 0.628 mg/mL, a kcat of 75.075 s−1 and a kcat/Km of 119.617 mL mg−1s−1. Finally, Xyn_TKU045 could effectively catalyze birchwood xylan into xylotriose and xylobiose as the major products. Full article
(This article belongs to the Special Issue Resource Recovery from Waste Biomass)
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18 pages, 5751 KiB  
Article
Adsorption of Eriochrome Black T on Pseudo Boehmite and Gamma Alumina Synthesized from Drinking Water Treatment Sludge: A Waste-to-Recycling Approach
by Ibtissam Ballou, Jamal Naja, Zineelabidine Bakher and Sanae Kholtei
Recycling 2024, 9(3), 49; https://doi.org/10.3390/recycling9030049 - 4 Jun 2024
Viewed by 1498
Abstract
Eriochrome black T is considered as one of the anionic dyes with potential harmful effects on human health and the environment. Among other processes, adsorption can contribute to the removal of these dyes. In the present study, two adsorbent materials, pseudo-boehmite (γ-AlOOH) and [...] Read more.
Eriochrome black T is considered as one of the anionic dyes with potential harmful effects on human health and the environment. Among other processes, adsorption can contribute to the removal of these dyes. In the present study, two adsorbent materials, pseudo-boehmite (γ-AlOOH) and gamma alumina (γ-Al2O3), were synthesized and tested in the removal of the Eriochrome black T molecule (EBT). γ-AlOOH and γ-Al2O3 were obtained by precipitation from NaAlO2 solution at pH = 7, at a temperature of 80 °C, and by the thermal transformation of γ-AlOOH at 800 °C, respectively. In order to gain insights into the structural, chemical, thermal and morphological properties of these materials, numerous analytical techniques were involved, including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), differential thermogravimetric–thermal analysis (TGA-DTA), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and specific surface area measurement using the Brunauer–Emmett–Teller (BET) method. Several adsorption parameters were studied, such as the adsorbent dose, initial concentration, pH, contact time and reaction temperature. The kinetic study showed that EBT adsorption follows the pseudo-second-order model. The Langmuir isotherm model revealed a maximum EBT adsorption capacity of 344.44 mg g−1 and 421.94 mg g−1 for γ-AlOOH and γ-Al2O3, respectively. A textural and structural analysis after adsorption highlighted the effective adsorption of the dye. Full article
(This article belongs to the Special Issue Sustainability of the Circular Economy)
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12 pages, 2923 KiB  
Article
An Innovative Magnetic Density Separation Process for Sorting Granular Solid Wastes
by Lin Wang, Peter Rem, Francesco Di Maio, Max van Beek and Gonçalo Tomás
Recycling 2024, 9(3), 48; https://doi.org/10.3390/recycling9030048 - 3 Jun 2024
Viewed by 1641
Abstract
Solid waste sorting is an important pre-treatment in recycling to improve the efficiency of material recovery and reduce costs. Motivated by the PEACOC project on metal recovery from solid wastes, an innovative magnetic density separation (MDS) process has been developed for solid waste [...] Read more.
Solid waste sorting is an important pre-treatment in recycling to improve the efficiency of material recovery and reduce costs. Motivated by the PEACOC project on metal recovery from solid wastes, an innovative magnetic density separation (MDS) process has been developed for solid waste sorting. It has intrinsic advantages over conventional gravity separation technologies and the previously industrialized MDS process. The new MDS process applies an inclined planar magnet and a horizontal basin containing a static magnetic fluid as the separation medium. A particle sliding phenomenon is identified as a feature that could help the separation. Experiments have been carried out to demonstrate the role of the MDS in concentrating valuable metals in shredded PCBAs and reducing metallic contaminants in plastic fractions of shredded wires. A pilot scale facility is introduced to show the design to achieve continuous production and to reduce the consumption of ferrofluid. Full article
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28 pages, 32642 KiB  
Article
Performance Evaluation of Self-Compacting Concrete Prepared Using Waste Foundry Sand on Engineering Properties and Life Cycle Assessment
by Ranjitha B. Tangadagi and P. T. Ravichandran
Recycling 2024, 9(3), 47; https://doi.org/10.3390/recycling9030047 - 1 Jun 2024
Cited by 2 | Viewed by 1348
Abstract
The primary objective of this research is to utilize an industrial waste byproduct such as waste foundry sand (WFS) as an alternative for fine aggregate in self-compacting concrete (SCC). This research focuses on the use of WFS in SCC to enhance durability and [...] Read more.
The primary objective of this research is to utilize an industrial waste byproduct such as waste foundry sand (WFS) as an alternative for fine aggregate in self-compacting concrete (SCC). This research focuses on the use of WFS in SCC to enhance durability and mechanical properties, to find an alternative for fine aggregate in SCC, to reduce the disposal challenges of WFS, and to make SCC lightweight and environmentally friendly. Initially, WFS was treated with chemical (H2SO4), segregating, and sieving to remove the foreign matter and clay content. For this study, WFS is considered in varying percentages such as 0, 10, 20, 30, 40, and 50. For this investigation, M60 grade SCC is considered as per Indian standards and EFNARC guidelines. After that, this research focuses on tests on various fresh properties of SCC in each batch to find the flowability and passing ability of various mixes prepared using WFS. Similarly, the mechanical properties of SCC such as compressive, flexural, and split tensile strength tests were performed at 7, 28, and 90 days curing periods, respectively. Likewise, durability properties of SCC were found in all the mixes prepared using WFS such as water absorption, sorptivity, resistance to chemical attack, and chloride ion penetration; tests of these properties were performed at 28 and 90 days curing periods, respectively. Based on the experimental investigation of SCC, it was found that WFS can be used in M60 grade SCC as an alternative for fine aggregate up to 30% without compromising much on its properties. Finally, this establishes that using treated WFS in SCC helps in reducing the generation of waste and prevails as a meaningful utilization method. This research will also establish that the use of treated WFS will reduce the density and make SCC a lightweight, green, and sustainable material. Full article
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12 pages, 2873 KiB  
Article
Development and Properties of Recycled Biomass Fly Ashes Modified Mortars
by Julien Hubert, Sophie Grigoletto, Frédéric Michel, Zengfeng Zhao and Luc Courard
Recycling 2024, 9(3), 46; https://doi.org/10.3390/recycling9030046 - 24 May 2024
Cited by 2 | Viewed by 1517
Abstract
The production of biomass fly ash has been increasing every year in Europe, reaching 5.5 million tons in 2020. Fly ash produced by burning biomass is not yet accepted in the standards as a substitute material for cement in mortar and concrete. In [...] Read more.
The production of biomass fly ash has been increasing every year in Europe, reaching 5.5 million tons in 2020. Fly ash produced by burning biomass is not yet accepted in the standards as a substitute material for cement in mortar and concrete. In a first approach, the substitution limit of biomass ash is determined by comparing the mechanical strengths (among others, compressive strength), fresh state properties and hardened properties of mortars produced with fly ash with those of mortars produced with coal fly ash (EN 450-1 and ASTM C618). Masonry and rendering mortars have been designed with different substitution rates of fly ashes from wood combustion in thermal power plants. Although there is an overall decrease in performance, mortars made with biomass ash retain properties that make them suitable for use in masonry (loss of 13% compressive strength for masonry mortars with 10% substitution rate after 90 days) or rendering (loss of 20% compressive strength for rendering mortars with 10% substitution rate after 90 days). Water absorption and porosity (24.1 and 23.7% for masonry and rendering mortars, respectively) are, however, not significantly modified, which potentially contributes to good durability properties. Full article
(This article belongs to the Special Issue Resource Recovery from Waste Biomass)
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25 pages, 6923 KiB  
Review
A Comprehensive Review on the Use of Wastewater in the Manufacturing of Concrete: Fostering Sustainability through Recycling
by Manjunath Maddikeari, Bibhuti Bhusan Das, Ranjitha B. Tangadagi, Suman Roy, Priyanka Bangalore Nagaraj and Manjunatha Lokanahally Ramachandra
Recycling 2024, 9(3), 45; https://doi.org/10.3390/recycling9030045 - 24 May 2024
Cited by 1 | Viewed by 1959
Abstract
The primary aim of this review article is to find the influence of wastewater and its characteristics on recycling as an alternative to potable water for concrete preparation. On the other hand, scarcity, and the demand for freshwater for drinking are also increasing [...] Read more.
The primary aim of this review article is to find the influence of wastewater and its characteristics on recycling as an alternative to potable water for concrete preparation. On the other hand, scarcity, and the demand for freshwater for drinking are also increasing day by day around the globe. About a billion tons of freshwater is consumed daily for concrete preparation for various operations such as mixing and curing, to name a few. The rapid development of certain industries such as textile, casting, stone cutting, and concrete production has caused the water supply to be severely affected. Recycling wastewater in concrete offers various potential benefits like resource conservation, environmental protection, cost savings, and enhanced sustainability. This article reviews the effect of various types of wastewater on various physical and chemical properties of wastewater, rheological characteristics, strength, durability, and microstructure properties of concrete. It also explores the potential effects of decomposing agents on enhancing concrete properties. Currently, limited research is available on the use of various types of wastewater in concrete. Hence, there is a need to develop various methods and procedures to ensure that the utilization of wastewater and treated wastewater is carried out in the production of concrete in a sustainable manner. Although wastewater can reduce the workability of fresh concrete, it can also increase its strength and long-term performance of concrete. The use of various types of wastewater, such as reclaimed water and tertiary-treated wastewater, was found to be superior compared to those using industrial- or secondary-treated wastewater. Researchers around the globe agree that wastewater can cause various detrimental effects on the mechanical and physical properties of concrete, but the reductions were not significant. To overcome limited scientific contributions, this article reviews all the available methods of using various types of wastewater to make concrete economically and environmentally friendly. This research also addresses possible challenges with respect to the demand for freshwater and the water crisis. Full article
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13 pages, 2152 KiB  
Article
Valorization of Spent Mushroom Substrate: Establishing the Foundation for Waste-Free Production
by Andrew Ravlikovsky, Maria Nazaré Coelho Pinheiro, Lucian Dinca, Vlad Crisan and Lyudmyla Symochko
Recycling 2024, 9(3), 44; https://doi.org/10.3390/recycling9030044 - 22 May 2024
Cited by 2 | Viewed by 2124
Abstract
Spent mushroom substrate (SMS), often disregarded as waste despite its abundance in organic matter and mineral micronutrients, has emerged as a valuable resource for diverse applications. While Europe and Asia have witnessed extensive research in this field over the past decade, Ukraine’s exploration [...] Read more.
Spent mushroom substrate (SMS), often disregarded as waste despite its abundance in organic matter and mineral micronutrients, has emerged as a valuable resource for diverse applications. While Europe and Asia have witnessed extensive research in this field over the past decade, Ukraine’s exploration remains limited. This study conducts a thorough investigation into SMS recycling and reutilization over a 4-year period. Employing experimental and comparative methods, this research unveils compelling insights into the potential of SMS for reintroduction into the primary production cycle and secondary activities. The main conclusions reveal the success of SMS valorization in the production of additives, fertilizers, and alternative fuels. Furthermore, the application of SMS in agroecosystems significantly enhances the soil biological activity. The integration of these methods into production chains not only yields economic benefits for companies but also fosters environmental stewardship, aligning with waste-free practices and the principles of bioeconomy and sustainability. Full article
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44 pages, 15051 KiB  
Review
Recent Advancements in Material Waste Recycling: Conventional, Direct Conversion, and Additive Manufacturing Techniques
by Mandar Golvaskar, Sammy A. Ojo and Manigandan Kannan
Recycling 2024, 9(3), 43; https://doi.org/10.3390/recycling9030043 - 21 May 2024
Viewed by 2264
Abstract
To improve the microstructure and mechanical properties of fundamental materials including aluminum, stainless steel, superalloys, and titanium alloys, traditional manufacturing techniques have for years been utilized in critical sectors including the aerospace and nuclear industries. However, additive manufacturing has become an efficient and [...] Read more.
To improve the microstructure and mechanical properties of fundamental materials including aluminum, stainless steel, superalloys, and titanium alloys, traditional manufacturing techniques have for years been utilized in critical sectors including the aerospace and nuclear industries. However, additive manufacturing has become an efficient and effective means for fabricating these materials with superior mechanical attributes, making it easier to develop complex parts with relative ease compared to conventional processes. The waste generated in additive manufacturing processes are usually in the form of powders, while that of conventional processes come in the form of chips. The current study focuses on the features and uses of various typical recycling methods for traditional and additive manufacturing that are presently utilized to recycle material waste from both processes. Additionally, the main factors impacting the microstructural features and density of the chip-unified components are discussed. Moreover, it recommends a novel approach for recycling chips, while improving the process of development, bonding quality of the chips, microstructure, overall mechanical properties, and fostering sustainable and environmentally friendly engineering. Full article
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25 pages, 3968 KiB  
Article
Investigating the Role of Municipal Waste Treatment within the European Union through a Novel Created Common Sustainability Point System
by Konstantinos Tsimnadis and Grigorios L. Kyriakopoulos
Recycling 2024, 9(3), 42; https://doi.org/10.3390/recycling9030042 - 20 May 2024
Cited by 1 | Viewed by 1589
Abstract
Over the last several decades, the European Union (EU) has championed recycling and sustainable waste management through Directives 2008/98/EC and 2018/851, shaping practices across its member states. Currently, 30% of the EU’s municipal waste is recycled, 19% composted, 23% incinerated, and 23% landfilled. [...] Read more.
Over the last several decades, the European Union (EU) has championed recycling and sustainable waste management through Directives 2008/98/EC and 2018/851, shaping practices across its member states. Currently, 30% of the EU’s municipal waste is recycled, 19% composted, 23% incinerated, and 23% landfilled. However, regional variations exist within the EU, with Greece and other Mediterranean/Balkan nations favoring landfilling, while Germany and other Western/Central EU nations prioritize recycling and composting, and Nordic countries lean toward incineration. To address these differences, a new sustainability point system was created in order to evaluate and compare all different municipal waste management strategies of EU members. Notably, countries like Germany, the Netherlands, and Sweden score the highest due to low municipal waste generation, high recycling rates (>35%), minimal landfilling (<1%), and significant incineration. In contrast, Cyprus, Malta, and Greece score lower due to landfill reliance and lower recycling rates. Therefore, this study introduces a novel sustainability point system to mitigate disparities, highlighting the need for targeted interventions and policy initiatives at the national and EU levels. By leveraging these insights, policymakers can allocate resources effectively, foster collaboration, and motivate citizens to achieve common environmental goals as well as the Sustainable Development Goals (SDGs). Full article
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29 pages, 8910 KiB  
Article
Effect of Recycled Concrete Aggregate Addition on the Asphalt Mixtures Performance: ITZ Area, Microstructure, and Chemical Analysis Perspectives
by Hanaa Khaleel Alwan Al-Bayati, Waleed Jadaa and Susan L. Tighe
Recycling 2024, 9(3), 41; https://doi.org/10.3390/recycling9030041 - 18 May 2024
Viewed by 1515
Abstract
The importance of environmental consciousness and sustainability is increasing among transportation governing bodies worldwide. Many government bodies are concerned with maximizing the usage of recycled substances in road construction. Therefore, assessing the effect of recycled materials consumption is essential, mainly when designing new [...] Read more.
The importance of environmental consciousness and sustainability is increasing among transportation governing bodies worldwide. Many government bodies are concerned with maximizing the usage of recycled substances in road construction. Therefore, assessing the effect of recycled materials consumption is essential, mainly when designing new ‘green’ pavement types. The primary objective of this study is to investigate the impact of different treatments on improving the interfacial transition zone (ITZ) of coarse recycled concrete aggregate (CRCA) and its application in asphalt mixes. Such an aim is accomplished by enhancing its physical and mechanical characteristics, as well as its microstructure. The surface morphology, chemical composition, and intermix phases of the ITZ area and calcium silicate hydrate (CSH) compounds for CRCA were evaluated using scanning electron microscopy (SEM), an energy-dispersive X-ray analyzer (EDAX), and X-ray diffraction analysis (XRD). The performance of asphalt mixtures that included treated and untreated CRCA was also examined using different tests. It was found that heat treatment is an effective technique for enhancing the ITZ. However, cracks were seen in the mortar of CRCA when exposed to high temperatures (500 °C), which adversely affects the characteristics of the mortar. Acid treatment appeared to be an effective approach for improving the ITZ area. Nevertheless, the treatment that used acetic acid, a weak acid, was more effective than HCl acid, a strong acid. The outcomes revealed that the ITZ microstructure is significantly enhanced under different treatment types; however, microstructure improvements mainly included increased surface homogeneity and CSH compounds and a reduced Ca/Si ratio. It was also found that the asphalt mixtures with different proportions of untreated CRCA exhibited enhanced resistance to rutting. Furthermore, their tensile strength ratio (TSR) values were above the minimal level requirements. Moreover, the asphalt mixture with 30% CRCA, which was treated with various treatment methods, demonstrated a significant improvement in the mixtures’ mechanical properties; therefore, its application is highly successful and an environmentally friendly solution. Full article
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24 pages, 1785 KiB  
Systematic Review
Valorizing Fruit and Vegetable Waste: The Untapped Potential for Entrepreneurship in Sub-Saharan Africa—A Systematic Review
by Grace Okuthe
Recycling 2024, 9(3), 40; https://doi.org/10.3390/recycling9030040 - 17 May 2024
Cited by 3 | Viewed by 2517
Abstract
Valorizing food waste (FW) in sub-Saharan Africa (SSA) can enhance the efficiency of limited resources, make healthy diets more affordable, and foster the creation of innovative enterprises. The vast quantities of FW from the agri-food chain significantly threaten food security. To address this [...] Read more.
Valorizing food waste (FW) in sub-Saharan Africa (SSA) can enhance the efficiency of limited resources, make healthy diets more affordable, and foster the creation of innovative enterprises. The vast quantities of FW from the agri-food chain significantly threaten food security. To address this issue and maximize potential environmental and socio-economic benefits, valorizing waste, a value-adding process for waste materials, has emerged as a sustainable and efficient strategy. Valorizing FW reduces greenhouse gas emissions, mitigates climate change, enhances resource efficiency, and improves planetary health. As a pivotal player in the transition toward the circular economy, this study investigates the potential of converting FW into value-added products, offering entrepreneurial opportunities for SSA’s unemployed youth. A systematic literature review is conducted to identify and filter relevant articles over five years by applying inclusion and exclusion criteria. A total of 33 articles were included for in-depth analysis to address the study’s aim. The findings highlight a range of value-added products derived from FW, including renewable energy sources, nutraceuticals, and heavy metal adsorbents. These products present promising entrepreneurial prospects within SSA. Nonetheless, overcoming barriers to FW valorization adoption is crucial for fully realizing its potential as a profitable business avenue. Full article
(This article belongs to the Special Issue Resource Recovery from Waste Biomass)
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12 pages, 3112 KiB  
Article
Rapid Waste Motor Oil Conversion into Diesel-Range Hydrocarbons Using Hydrochar as Catalyst: Kinetic Study and Product Characterization
by Herman A. Murillo, Evelyn Juiña, Karla Vizuete, Alexis Debut, Daniel Echeverría, Sebastian Taco-Vasquez and Sebastian Ponce
Recycling 2024, 9(3), 39; https://doi.org/10.3390/recycling9030039 - 17 May 2024
Viewed by 1628
Abstract
Herein, raw and alkali-treated hydrochars from biomass waste are prepared as a highly active catalyst for the conversion of waste motor oil into diesel-like fuels. Among all materials, hydrochar obtained at 250 °C and subsequent alkali activation with KOH showed a 600% improvement [...] Read more.
Herein, raw and alkali-treated hydrochars from biomass waste are prepared as a highly active catalyst for the conversion of waste motor oil into diesel-like fuels. Among all materials, hydrochar obtained at 250 °C and subsequent alkali activation with KOH showed a 600% improvement of the kinetic constant from 0.0088 to 0.0614 m−1. Conversion values at the same conditions were also improved from 66 to 80% regarding thermal and catalytic cracking, respectively. Moreover, the activation energy was also reduced from 293 to 246 kJ mol−1 for thermal and catalytic cracking, respectively. After characterization, the enhanced catalytic activity was correlated to an increased surface area and functionalization due to the alkali activation. Finally, the liquid product characterization demonstrated that catalytic cracking is more effective than thermal cracking for producing hydrocarbons in the diesel range. In particular, hydrochar-based catalysts are suggested to promote the formation of specific hydrocarbons so that the carbon distribution can be tailored by modifying the hydrothermal treatment temperature. Full article
(This article belongs to the Special Issue Resource Recovery from Waste Biomass)
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17 pages, 4714 KiB  
Article
Green Valorization of Waste Plastics to Graphene as an Upcycled Eco-Friendly Material for Advanced Gas Sensing
by Prince Oppong Amoh, Marwa Elkady, Mahmoud Nasr and Hassan Shokry
Recycling 2024, 9(3), 38; https://doi.org/10.3390/recycling9030038 - 13 May 2024
Viewed by 1878
Abstract
The valorization technique successfully transformed waste polyethylene terephthalate (PET) into valuable carbon nanomaterial (CN)/graphene, while doped and undoped ZnO nanopowders were synthesized via sol–gel methods. Utilizing XRD, BET, TEM, EDX, FTIR, and TGA analyses, the synthesis of sp2 2D sheet, pristine, and [...] Read more.
The valorization technique successfully transformed waste polyethylene terephthalate (PET) into valuable carbon nanomaterial (CN)/graphene, while doped and undoped ZnO nanopowders were synthesized via sol–gel methods. Utilizing XRD, BET, TEM, EDX, FTIR, and TGA analyses, the synthesis of sp2 2D sheet, pristine, and doped ZnO nanostructures was confirmed. Solid-state gas sensor devices, tested under 51% relative humidity (RH), 30 °C ambient temperature, and 0.2 flow rate, exhibited a 3.4% enhanced response to H2 gas compared to CO2 at 50 ppm concentrations over time. Notably, the ZnO/CN sensor surpassed CN and ZnO alone, attributed to CN dopant integration with decreasing order of response performance as ZnO/CN > CN > ZnO. This study underscores the efficacy of valorization techniques in generating high-value carbon nanomaterials and their efficacy in bolstering gas sensor performance, with ZnO/CN demonstrating superior response capabilities. Full article
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47 pages, 3426 KiB  
Review
Recent Trends of Recycling and Upcycling of Polymers and Composites: A Comprehensive Review
by Christina Podara, Stefania Termine, Maria Modestou, Dionisis Semitekolos, Christos Tsirogiannis, Melpo Karamitrou, Aikaterini-Flora Trompeta, Tatjana Kosanovic Milickovic and Costas Charitidis
Recycling 2024, 9(3), 37; https://doi.org/10.3390/recycling9030037 - 6 May 2024
Cited by 4 | Viewed by 5613
Abstract
This review article gathers the most recent recycling technologies for thermoset and thermoplastic polymers. Results about existing experimental procedures and their effectiveness are presented. For thermoset polymers, the review focuses mainly on fibre-reinforced polymer composites, with an emphasis on epoxy-based systems and carbon/glass [...] Read more.
This review article gathers the most recent recycling technologies for thermoset and thermoplastic polymers. Results about existing experimental procedures and their effectiveness are presented. For thermoset polymers, the review focuses mainly on fibre-reinforced polymer composites, with an emphasis on epoxy-based systems and carbon/glass fibres as reinforcement, due to the environmental concerns of their end-of-life management. Thermal processes (fluidised bed, pyrolysis) and chemical processes (different types of solvolysis) are discussed. The most recent combined processes (microwave, steam, and ultrasonic assisted techniques) and extraordinary recycling attempts (electrochemical, biological, and with ionic liquids) are analysed. Mechanical recycling that leads to the downgrading of materials is excluded. Insights are also given for the upcycling methodologies that have been implemented until now for the reuse of fibres. As for thermoplastic polymers, the most state-of-the-art recycling approach for the most common polymer matrices is presented, together with the appropriate additivation for matrix upcycling. Mechanical, chemical, and enzymatic recycling processes are described, among others. The use of fibre-reinforced thermoplastic composites is quite new, and thus, the most recent achievements are presented. With all of the above information, this extensive review can serve as a guide for educational purposes, targeting students and technicians in polymers recycling. Full article
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15 pages, 4531 KiB  
Article
Recycling of Rhenium from Superalloys and Manganese from Spent Batteries to Produce Manganese(II) Perrhenate Dihydrate
by Katarzyna Leszczyńska-Sejda, Arkadiusz Palmowski, Michał Ochmański, Grzegorz Benke, Alicja Grzybek, Szymon Orda, Karolina Goc, Joanna Malarz and Dorota Kopyto
Recycling 2024, 9(3), 36; https://doi.org/10.3390/recycling9030036 - 30 Apr 2024
Viewed by 1811
Abstract
This work presents the research results on the development of an innovative, hydrometallurgical technology for the production of manganese(II) perrhenate dihydrate from recycled waste. These wastes are scraps of Ni-based superalloys containing Re and scraps of Li–ion batteries containing Mn—specifically, solutions from the [...] Read more.
This work presents the research results on the development of an innovative, hydrometallurgical technology for the production of manganese(II) perrhenate dihydrate from recycled waste. These wastes are scraps of Ni-based superalloys containing Re and scraps of Li–ion batteries containing Mn—specifically, solutions from the leaching of black mass. This work presents the conditions for the production of Mn(ReO4)2·2H2O. Thus, to obtain Mn(ReO4)2·2H2O, manganese(II) oxide was used, precipitated from the solutions obtained after the leaching of black mass from Li–ion batteries scrap and purified from Cu, Fe and Al (pH = 5.2). MnO2 precipitation was carried out at a temperature < 50 °C for 30 min using a stoichiometric amount of KMnO4 in the presence of H2O2. MnO2 precipitated in this way was purified using a 20% H2SO4 solution and then H2O. Purified MnO2 was then added alternately with a 30% H2O2 solution to an aqueous HReO4 solution. The reaction was conducted at room temperature for 30 min to obtain a pH of 6–7. Mn(ReO4)2·2H2O precipitated by evaporating the solution to dryness was purified by recrystallization from H2O with the addition of H2O2 at least twice. Purified Mn(ReO4)2·2H2O was dried at a temperature of 100–110 °C. Using the described procedure, Mn(ReO4)2·2H2O was obtained with a purity of >99.0%. This technology is an example of the green transformation method, taking into account the 6R principles. Full article
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17 pages, 1282 KiB  
Article
Considering Grouped or Individual Non-Methane Volatile Organic Compound Emissions in Life Cycle Assessment of Composting Using Three Life Cycle Impact Assessment Methods
by Ben Joseph and Heinz Stichnothe
Recycling 2024, 9(3), 35; https://doi.org/10.3390/recycling9030035 - 29 Apr 2024
Viewed by 1898
Abstract
Composting is a waste management practice that converts organic waste into a product that can be used safely and beneficially as a bio-fertiliser and soil amendment. Non-methane volatile organic compounds (NMVOCs) from composting are known to cause damage to human health and the [...] Read more.
Composting is a waste management practice that converts organic waste into a product that can be used safely and beneficially as a bio-fertiliser and soil amendment. Non-methane volatile organic compounds (NMVOCs) from composting are known to cause damage to human health and the environment. The impact of waste management on the environment and workers is recognised as a growing environmental and public health concern. Measurements of NMVOCs emitted during composting have been carried out only in a few studies. NMVOC emissions are typically reported as a group rather than as species or speciation profiles. Recognising the need to investigate the issues associated with NMVOCs, the objective of this study is to estimate variation in life cycle assessment (LCA) results when NMVOCs are considered individual emissions compared to grouped emissions and to compare midpoint and endpoint life cycle impact assessment (LCIA) methods. In general, the ReCiPe 2016 LCIA method estimated the highest impact from the composting process in comparison to IMPACT World+ and EF 3.0 for the impact categories of ozone formation, stratospheric ozone depletion, and particulate matter formation. For ReCiPe 2016 and IMPACT World+, the NMVOC emissions were not linked to human toxicity characterisation factors, meaning that the contribution from NMVOC towards human health risks in and around composting facilities could be underestimated. Using individual NMVOCs helps to additionally estimate the impacts of composting on freshwater ecotoxicity and human carcinogenic and non-carcinogenic toxicity potential. If ecotoxicity or toxicity issues are indicated, then LCA should be accompanied by suitable risk assessment measures for the respective life cycle stage. Full article
(This article belongs to the Special Issue Feature Papers in Recycling 2023)
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18 pages, 3090 KiB  
Article
Recycling of Egyptian Shammi Corn Stalks for Maintaining Sustainable Cement Industry: Scoring on Sustainable Development Goals
by Fajr Qasem, Mahmoud Sharaan, Manabu Fujii and Mahmoud Nasr
Recycling 2024, 9(3), 34; https://doi.org/10.3390/recycling9030034 - 26 Apr 2024
Viewed by 1739
Abstract
This study focuses on recycling Shammi corn stalks in the cement industries, further avoiding air and soil pollution caused by their improper disposal. This crop residue was thermally treated at 700 °C for 2 h under an oxygen-rich environment to produce Shammi corn [...] Read more.
This study focuses on recycling Shammi corn stalks in the cement industries, further avoiding air and soil pollution caused by their improper disposal. This crop residue was thermally treated at 700 °C for 2 h under an oxygen-rich environment to produce Shammi corn stalk ash (SCSA). This SCSA was used as a cement replacement material (2–10%, w/w), whereas the control sample included only cement. The compressive strength values for the 4% (w/w) replacement ratio at 2-, 7-, and 28-day ages were greater than those for the control by 26.5%, 15.8%, and 11.4%, respectively. This 4% (w/w) also maintained a better flexural strength than other mixtures, with proper initial and final setting times (135 and 190 min), workability (18.5 cm), and water consistency (27.5%). These mechanical/physical properties were integrated with socio-enviro-economic data collected from experts through a pairwise comparison questionnaire, forming the inputs of a multi-criteria decision-making (MCDM) model. Recycling SCSA in the cement-manufacturing process attained positive scores in the achievement of the three pillars of sustainable development, revealing an overall score greater than the control. Hence, the study outcomes could be essential in developing green concrete, cement blocks, and mortar, based on the sustainable development goals (SDGs) agenda. Full article
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14 pages, 4039 KiB  
Article
Evaluation of Thermoplastic Starch Contamination in the Mechanical Recycling of High-Density Polyethylene
by Antonio Cascales, Cristina Pavon, Santiago Ferrandiz and Juan López-Martínez
Recycling 2024, 9(3), 33; https://doi.org/10.3390/recycling9030033 - 26 Apr 2024
Cited by 1 | Viewed by 1996
Abstract
This research highlights the importance of addressing bioplastic contamination in recycling processes to ensure the quality of recycled material and move towards a more sustainable circular economy. Polyethylene (PE) is a conventional plastic commonly used in packaging for which large amounts of waste [...] Read more.
This research highlights the importance of addressing bioplastic contamination in recycling processes to ensure the quality of recycled material and move towards a more sustainable circular economy. Polyethylene (PE) is a conventional plastic commonly used in packaging for which large amounts of waste are produced; therefore, PE is generally recycled and has an established recycling process. However, the contamination of biodegradable polymers in the PE waste stream could impact recycling. This study, therefore, focuses on polyethylene (PE) that has been polluted with a commercial thermoplastic starch polymer (TPS), as both materials are used to produce plastic films and bags, so cross-contamination is very likely to occur in waste separation. To achieve this, recycled PE was blended with small quantities of the commercial TPS and processed through melt extrusion and injection molding, and it was further characterized. The results indicate that the PE-TPS blend lacks miscibility, evidenced by deteriorated microstructure and mechanical properties. In addition, the presence of the commercial TPS affects the thermal stability, oxidation, and color of the recycled PE. Full article
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23 pages, 5999 KiB  
Article
Enhancing the Strength and the Environmental Performance of Concrete with Pre-Treated Crumb Rubber and Micro-Silica
by M. R. Rajagopal, Jyothikumari Ganta and Yashwanth Pamu
Recycling 2024, 9(3), 32; https://doi.org/10.3390/recycling9030032 - 24 Apr 2024
Cited by 5 | Viewed by 2229
Abstract
Dumped non-biodegradable tires present a significant environmental threat, with overflowing landfills and associated health risks highlighting the urgency of tire waste disposal. Current disposal methods, such as stacking tires in open spaces, exacerbate the problem. The large-scale recycling of tire rubber waste offers [...] Read more.
Dumped non-biodegradable tires present a significant environmental threat, with overflowing landfills and associated health risks highlighting the urgency of tire waste disposal. Current disposal methods, such as stacking tires in open spaces, exacerbate the problem. The large-scale recycling of tire rubber waste offers environmental benefits. This study examines the effects of pre-treatment using NaOH and micro-silica as a mineral admixture on the mechanical strength of crumb rubber concrete (CRC) with partial replacement of natural sand. Samples of M20 and M30 grade were prepared with varying levels of crumb rubber (CR) replacement and evaluated at 28 days. CRC prepared with pre-treated NaOH solution and micro-silica showed improved workability and strength compared to conventional concrete and untreated CRC, with the highest strength observed for 5% CR replacement using micro-silica. Predictive models and micro-structural analysis validated these findings. Life Cycle Assessment (LCA) using OpenLCA v2.10 software and the ecoinvent database revealed that incorporating micro-silica into CRC did not significantly increase environmental impacts, compared to conventional concrete across different mixes. Full article
(This article belongs to the Special Issue Recycling of Rubber Waste, 2nd Edition)
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