Recycling, Volume 9, Issue 5 (October 2024) – 21 articles

The present study investigates the use of electric arc furnace (EAF) steel slag, a by-product of the steel industry, in asphalt pavement surface courses instead of virgin aggregates (VAs). Therefore, a general performance evaluation of such mixtures compared to conventional mixtures is carried out through laboratory and in situ tests, while both mixtures are environmentally assessed using the life cycle assessment (LCA) tool. The results of the laboratory and in situ tests show that asphalt mixtures containing granulated EAF slag aggregates perform as well as mixtures containing only VA. In addition, the LCA results show that the use of EAF slag aggregates in the asphalt surface course has a lower environmental impact than the exclusive use of VA when it comes to the impact categories of acidification, climate change, marine and terrestrial eutrophication, energy consumption and photochemical pollution. In summary, these results show that replacing virgin aggregates with a proportion of EAF slag aggregate is a viable and sustainable method for road pavement construction. Full article

Driven by population growth, rising living costs, and the urgent need to address climate change, sustainable food production and circular economy principles are becoming increasingly important. Conventional agriculture faces significant challenges, including land scarcity, water shortages, and disrupted supply chains. As a solution, cities are adopting vertical farming to enhance urban food security and promote circularity. This research introduces FLOAT (Farming Lab on a Trough), an innovative vertical farming system made from bio-polymers and recycled polyethylene terephthalate glyco (rPETG) pellets from plastic bottles. FLOAT’s design emphasizes sustainability and closed-loop material usage. The study showcases the versatility of additive manufacturing (AM) in creating complex geometries with fully functional 1:1 prototypes. These prototypes highlight FLOAT’s potential as a scalable and adaptable solution for sustainable food production in urban settings, contributing to improved food security and environmental sustainability. By integrating FLOAT with conventional practices, we aim to exceed Singapore’s 2030 food security targets and achieve lasting urban food resilience. FLOAT aims to scale sustainable food production, fostering community ties with food, and nurturing future responsibility. Full article

Direct Contact Membrane Distillation (DCMD) uses low heat sources to separate water from urea, which was then used as a plasticizer in regolith-based cement to make it more workable. The work investigated separating potable water and urea from artificial urine using DCMD and then characterizing the products. Water was successfully separated from the artificial urine solution as characterized by density, conductivity, pH, and substance concentrations. The concentrated urine solution was used in regolith-based cement cured under vacuum at temperatures that simulated temperatures that would be expected in construction on the Moon. Workability and other properties were improved by replacing water with concentrated urine solution in the mix. Full article

This work aims to evaluate how the particle size of a waste filler in the form of eggshells changes the mechanical properties of biopoly(ethylene terephthalate) (bioPET). BioPET was modified with three different waste fractions: 1.60–3 mm—large particles; 1.60–1 mm—medium particles; 1 mm–200 μm—small particles. Waste filler was added to the biopolymer matrix in the amount of 10 wt.%. Static tensile tests, as well as bending and impact tests, were carried out to assess the strength properties of the waste-enriched materials. Dissipation energy changes and relaxation processes were observed and evaluated by means of a low-cycle dynamic test. Waste particles were shown to be an effective modifier of bioPET by increasing its stiffness (all particle sizes) and strength (the smallest ones). Studies of the wetting angle and mechanical energy dissipation in the first hysteresis loops indicate the better adhesion of small particles to the biopolymer and their greater ability to dissipate mechanical energy. Full article

Understanding the composition of disposed municipal solid waste (MSW) and recyclables can lead to better waste management. New York State (United States) has never had a state-wide waste characterization sorting program. In 2021, sampling was conducted at 11 locations, representing 25% of the state population outside of New York City. Twenty-three tonnes from 173 discrete samples were sorted into 41 categories. The resulting data were analyzed by single constituent approaches and more novel multivariate distance techniques. The analyses found that disposed MSW was 22.8% paper, 20.5% food, and 16.8% plastics. Recyclable paper and glass–metal–plastic containers were 18.2% (11.7% paper, 6.5% containers) and yard waste was 6.5%, meaning about 25% of the disposed MSW could have been recovered. Multivariate analysis determined that the disposed MSW was similar to that from other United States jurisdictions such as Wisconsin, Pennsylvania, New York City, and Syracuse (NY), and different from California and United States Environmental Protection Agency model data. Recyclables composition was different from disposed MSW composition. Dual-stream recyclables were sorted better than single-stream recyclables. Corrugated cardboard was the most common paper recyclable and plastics were the most common container recyclable. The data are being used to help guide planning for an expected packaging extended producer responsibility law for the State. Full article

The investigation into the implementation and widespread adoption of oyster shell recycling methods aimed at restoring coastal ecosystems and enhancing water quality is currently limited. In this study, we investigated the utilization of oyster shell powder (OSP) as a cost-effective and environmentally sustainable method for treating high-fluoride-concentration wastewater, a byproduct of industrial processes. We conducted extensive laboratory testing to determine the optimal conditions for fluoride removal. This involved variations in OSP doses, particle sizes, and initial wastewater pH levels. The results of these tests showed that OSP achieved fluoride removal efficiencies exceeding 98% at an optimal dosage of 5 g/L. In addition, OSP effectively adjusted the wastewater pH from highly acidic (pH 2) to almost neutral (pH 6.87), demonstrating its effectiveness in real-world industrial wastewater treatment. OSP, derived from oyster shell waste, is rich in calcium carbonate and offers a novel approach to wastewater management by leveraging a natural waste product. This study demonstrates the potential of OSP as a waste management strategy and contributor to the circular economy by repurposing industrial byproducts. Full article

The substitution of virgin asphalt binder with reclaimed asphalt pavement (RAP) has environmental and economic merits, however, cracking susceptibility arises due to the aged asphalt binder within RAP. The objectives of this study are to (1) enhance the cracking resistance of asphalt mixtures containing 50% RAP utilizing recycling agents (RAs) derived from six petroleum-based and bio-based materials, (2) conduct an environmental impact assessment (represented by global warming potential “GWP”) for high-RAP mixtures including RAs, and (3) estimate the cost effectiveness of including high-RAP content in asphalt mixtures. Based on the RAP asphalt binder performance grade (PG), base asphalt binder PG, and RAP content, the RA contents were determined to achieve a target asphalt binder of PG 76-22. A control mixture was benchmarked for comparison, specified for high-traffic volume roads, and contained PG 76-22 polymer-modified asphalt binder. The engineering performance of studied asphalt mixtures was evaluated using the Hamburg wheel-tracking (HWT), semi-circular bend, Illinois flexibility index, Ideal cracking tolerance, and thermal stress-restrained specimen tensile strength tests. It was found that petroleum-derived aromatic oil, soy-based oil, and tall oil fatty acid-based RAs demonstrated a successful restoration of aged RAP asphalt binder without compromising the permanent deformation resistance. The 50% RAP mixtures emitted less GWP by 41% and 42.9% using petroleum- and bio-oil RAs, respectively, and achieved a 31% cost reduction compared to the control mixtures. Full article

Wastewater treatment must be proactive and sustainable to facilitate an increase in the circularity of water. Therefore, the current approach, based on a linear cycle, must be replaced with a circular economy concept that implements strategies to address the different byproducts in the wastewater treatment sector. In recent years, Nuevo León, Mexico, has encountered high water stress levels, with its main water bodies presenting their lowest levels ever recorded. This study was focused on the wastewater treatment plant Monterrey, which treats the largest volume at the state level. Throughout its operation process, it generates different potential byproducts that are yet to be harnessed to fully. This study developed three proposals using a circular economy approach: the treatment of water for the industrial sector, the use of residual sludge as an organic fertilizer, and the cogeneration of energy from biogas. These proposals can potentially generate benefits regarding the three pillars of sustainability, yielding a closed cycle in the wastewater treatment sector at the national level. Full article

Currently, less attention is paid to zinc–carbon batteries, although they are still widely used and are among the major types of batteries collected and recycled. The recycling technologies currently in use do not allow the complete recovery of resources, are not self-sufficient and require additional financing. Therefore, this paper aims to study the possibility of complete recycling of waste zinc–carbon batteries and to suggest the practical use of the final products generated in the recycling process. The possibility of complex processing of spent zinc–carbon batteries using mechanical separation and processing of the battery’s components (steel case, zinc electrode, graphite electrode, polypropylene and paper insulators) is justified. The separation of spent electrolytes from other components of batteries with hydrochloric acid was studied. It was shown that the extraction of Zn²⁺ and NH⁴⁺ cations takes place following the addition of an equivalent amount of Na₃PO₄ solution and water-insoluble NH₄ZnPO₄ salt sedimentation. Waste agglomerate (mixture of MnO₂, MnO(OH), and graphite) was regenerated to its initial composition (MnO₂, graphite) at a temperature of 300–325 °C; manganese (III) hydroxide was oxidized to manganese (IV) dioxide. Thermal destruction of polypropylene and paper insulators with additional introduction of polyethylene into the primary mixture produced pyrolysis liquid, pyrocarbon and pyrolysis gas as products. The practical use of the products obtained and compliance with the environmental requirements of the suggested method of waste batteries recycling were shown. Full article

This paper analyzes the relationship between urban waste recycling and innovation systems in Europe. Data from the Global Innovation Index for 34 European countries in the period 2013–2022 were used. To analyze the characteristics of European countries in terms of waste recycling capacity, the k-Means algorithm optimized with the Elbow method and the Silhouette Coefficient was used. The results show that the optimal number of clusters is three. Panel data results show that waste recycling increases with domestic market scale, gross capital formation, and the diffusion of Information and Communication Technologies (ICTs), while it decreases with the infrastructure index, business sophistication index, and the average expenditure on research and development of large companies. Full article

Polymer-bonded magnets are increasingly being used in terms of applications in drive technology and, more specifically, in new concepts based on reluctance motors. The increasing demand for polymer-bonded magnets, especially in the context of electromobility, is leading to a shortage of materials, mainly in terms of the finite resource neodymium–iron–boron (NdFeB). So far, the recycling strategy for polymer-bonded magnets based on thermosets is pyrolysis, which leads to either a massive reduction of the magnetic properties or a high energy requirement. Therefore, the paper investigates an alternative recycling strategy for polymer-bonded magnets based on thermosets based on the reusage of shreds. Several influencing factors such as the form of the carrier material and the temperature level were varied in order to find a suitable recycling method. It was found that the magnetic properties were reduced by at least 15% compared to the pure material. The required energy and the CO₂ emission were reduced by 90% compared to the pyrolysis. Thus, the strategy of recycling polymer-bonded magnets based on thermosets by the reusage of shreds leads to improved conditions compared to pyrolysis and is, therefore, a suitable alternative. Full article

This study investigates the potential of utilizing industrial by-products—mill scale (MS) and aluminum dross (AD)—as sources of Fe₂O₃ and Al₂O₃, respectively, for hercynite (FeAl₂O₄) production. Through combustion of MS-AD-graphite systems at 1550 °C under air atmosphere, hercynite-based refractory materials were synthesized. Results confirm the viability of this upcycling approach for hercynite synthesis. During the formation of hercynite, the development of a dendritic structure can be observed, which subsequently fuses into a grain shape. XRD phase analysis using the Rietveld method revealed that the major components of the product with a C/O ratio of 1 were 85.11% FeAl₂O₄, 10.99% Al₂O₃, and 3.9% C. For the product with a C/O ratio of 2, the composition was 82.4% FeAl₂O₄, 13.0% Al₂O₃, and 4.6% C. The combustion of raw pellets with a C/O ratio of 1 at 1550 °C for 1 h in a normal air atmosphere is economically viable for producing hercynite, yielding 85.11 wt%. This approach presents a sustainable and eco-friendly alternative to using commercial raw materials, potentially eliminating the need for virgin alumina and iron ore. By repurposing waste materials from the steel and aluminum industries, this study contributes to the circular economy and aligns with the goal of zero waste. Full article

Food waste and by-products are intricately linked to sustainable food production, as reducing waste can play a significant role in achieving a more sustainable and efficient food system. Sustainable utilization and recovery of by-products can significantly contribute by creating strategies that can lead to cost savings and increased efficiency across the food supply chain. Worldwide, more than 40% of whey from cheese production is discarded, resulting in the loss of valuable nutrients and potentially polluting the environment. Effective use of whey reduces environmental impact and enhances manufacturing sustainability. Thus, a circular approach to food waste management in the dairy industry supports sustainability goals and creates opportunities for innovation. Whey contains most of the soluble components of milk, including a large number of serum proteins and all the essential amino acids, making it suitable for producing beverages with high nutritional value. This study aims to produce whey-based beverages with different additions to obtain dairy products with high nutritional value. Three different ingredients, sea buckthorn, ginger, and cinnamon, were chosen for their numerous health benefits to the consumer. Six samples were prepared utilizing both unmodified and deproteinized whey in a 75% proportion, with the addition of 25% sea buckthorn juice, 0.75% ginger juice, and 0.2% cinnamon powder. The resultant samples were packaged in 200 mL bottles and maintained at a controlled temperature of 6 °C to ensure optimal preservation. Given the paramount importance of consumer acceptability in novel beverage development, a comprehensive evaluation was conducted to assess the sensory properties of the formulated beverages. In addition, physico-chemical properties and their evolution over 14 days of storage were examined. The sample containing whey, sea buckthorn juice, ginger juice, and cinnamon powder received the highest marks from the tasters. The values of the physico-chemical parameters varied depending on the type of whey used and the storage period. Thus, a pH of approximately 5 and an acidity between 30 and 80 °T were recorded. The average lactose content was 4%, the average protein content was 2.5%, and the total soluble solids content was 11.5 °Brix. The beverages developed in this study represent viable alternatives for diversifying food production through sustainable, environmentally friendly technological variants. By applying circular economy principles, these products contribute to reducing food waste in the dairy industry. Full article

This paper adopts a systems firm-centered perspective on the environmental assessment of recyclable glass and PET soft drink containers. We employ LCA and discrete-event simulation modeling for the environmental assessment of the two soft drinks packaging alternatives in operational terms over the entire supply chain over a period of three years. The assessment is based on real data collected from a large soft drink producer and its suppliers. The research and practice contribution of the paper is twofold: first, it introduces a methodological framework for environmental assessment of companies’ packaging environmental impact under different product and operations strategies; and secondly, it provides a holistic environmental assessment of the two packaging materials (PET and glass) taking into account specific operational issues, such as product mix and recycling and reuse options, as well as activity interdependences and stochasticity. The results of the simulation experiments confirm at the operations system level, for glass, the importance for sustainability, to increase the number of reuse cycles (for the particular case, for significant improvement, seven reuses) and the percentage of used bottles collected for refilling (80% recovery rate), whereas for PET, to increase the percentage of recycled PET in new bottles (towards 30%). Full article

The pollution of the environment by plastics is a global problem that is real and needs to be resolved urgently. The authors argue that banning the use of plastic is not a reasonable and rational solution for the problem because plastics have many useful applications. Solutions to the problem must involve developing scientific approaches as well as global efforts and strategies. The world’s approach needs to be guided by an economic model that eliminates or minimizes the amount of plastics in the waste stream. As long as most plastic materials are not made from a single polymer, then the idea of “recycling 100% of plastics” is so far an unrealistic solution. The development of biodegradable plastics is still far from being an effective solution because besides being expensive and having limitations in engineering applications when compared to petroleum-based ones, biodegradable plastics still require specific conditions for their biodegradation. Comprehensive studies on microplastic particles are needed, focusing mainly on the source of the particles, their distribution, transport, fate in different environments, and toxicological effects and mechanisms. Since plastic pollution is a global problem, its minimization will require an increased international cooperation platform and partnerships at a global level. While current technologies and strategies are not solving the environmental problem caused by waste plastic, the most effective solution would be to adopt the first two levels of the waste management hierarchy, which are “reduce” and “reuse”. Full article

The global shift towards sustainability is driving the electrification of transportation and the adoption of clean energy storage solutions, moving away from internal combustion engines. This transition significantly impacts lithium-ion battery production in the electric vehicle (EV) market. This paper summarizes specialized topics to highlight regional differences and specific challenges related to electric batteries, focusing on how pollution from gas consumption, distribution, usage, and lithium production affects society. EV batteries offer promising opportunities for a sustainable future, considering their economic and environmental impacts and the importance of understanding their lifecycle. This analysis delves into the recovery of materials and various methods for extracting lithium and manufacturing EV batteries. Efficient lithium recovery is crucial and globally significant, with liquid extraction presenting a more environmentally friendly option. By addressing these challenges, this paper provides an overview of the rationale behind supporting the future of EVs. Full article

In this study, we examined the correlation between the collected municipal waste (MW) and the tourism intensity (TI) in five of Croatia’s most popular tourist towns—Zagreb, Poreč, Rovinj, Split, and Dubrovnik—from 2015 to 2021. Furthermore, we conducted a comparative analysis of target scenarios for municipal waste reduction in these tourist towns based on population changes and the amount of separately collected and residual MW collected to achieve EU targets for processing MW for reuse and recycling. The TI indicator quantifies the population’s theoretical multiplication during tourist influx, providing a clear picture of the pressure exerted by tourism. Rovinj and Poreč have the highest TIs, while larger cities like Dubrovnik, Split, and Zagreb have lower average TI values. The correlation between the collected MW and the tourism intensity in Dubrovnik is very high and positive, in Zagreb and Rovinj it is high and negative, while Split has a higher positive correlation than Poreč. The results for the MW preparation rates for reuse and recycling from 2015 to 2021 and future projections for 2021–2035 suggest that, in five of Croatia’s leading tourist towns, the imperative must be to decrease residual MW, promote separation at the source, and separate MW collection to meet EU targets. Given the challenges of meeting all three—or even two or one—of the EU’s targets of 50% by 2025, 60% by 2030, and 65% by 2035, the current waste separation system must be improved. This study contributes to the scientific community by addressing the gap in the current knowledge on the effects of population changes caused by tourism on MW in tourist destinations. The findings could be relevant for practitioners and policymakers planning MW collection, processing, and recovery in tourism-oriented economies, particularly in Croatia’s top tourist destinations. Full article

The aluminum terephthalate (MIL-53) metal–organic framework (MOF) (MIL-53(Al)) was evaluated as an adsorbent for removing phosphates from aqueous solutions. XRD and FTIR were used to confirm the molecular structure. TGA/DSC was used to measure its stability. The green synthesizing MIL-53(Al) showed good performance as a highly efficient adsorbent. The adsorbed MIL-53(Al) nanoparticles still retain their original morphology according to SEM, allowing it to be easily separated from the aqueous solution via filtration. Additionally, the thermal stability of synthesized MIL-53(Al) is capable of withstanding temperatures up to 500 °C, as confirmed by TGA/DSC. Using different initial concentrations of Na₂HPO₄ and ICP-OES measurements, we determined the adsorption values of Na₂HPO₄ by MIL-53(Al) as a function of time. Three kinetic models (pseudo-first-order, pseudo-second-order, and Elovich) and three isotherm models (Langmuir, Freundlich, and Temkin) were used to evaluate the phosphate adsorption behavior of MIL-53(Al) powder in Na₂HPO₄ aqueous solution. Error functions are used to evaluate various kinetic and isotherm models related to different physical processes. From the analysis of the adsorption experiments, the Elovich model is the best-fitting kinetic model, showing that the adsorption rate decreases with increasing adsorption capacity. Furthermore, error function analysis identified the Freundlich model as the most suitable, indicating that complicated adsorption coexists with physisorption, and chemisorption synergistically drives the adsorption process. The module utilizing MIL-53(Al) hollow fibers also demonstrated preliminary attempts at phosphate adsorption and desorption for the first time. This work demonstrated that MIL-53(Al) is an exceptionally stable adsorbent for removing phosphate from contaminated wastewater. Full article

Geopolymer concrete, a cement-free concrete with recycled concrete aggregate (RCA), offers an eco-friendly solution for reducing carbon emissions from cement production and reusing a significant amount of old concrete from construction and demolition waste. This research on self-compacted, ambient-cured, and low-carbon concrete demonstrates the superior performance of one-part geopolymer concrete made from recycled materials. It is achieved by optimally replacing treated RCA with a unique method that involves coating the recycled aggregates with a one-part geopolymer slurry composed of fly ash, micro fly ash, slag, and anhydrous sodium metasilicate. The research presented in this paper introduces predictive models to assist researchers in optimising concrete mix designs based on RCA rates and treatment methods, including the incorporation of coated recycled concrete aggregates and basalt fibres. This study addresses the knowledge gap regarding geopolymer concrete based on recycled aggregate, various RCA rates, and novel RCA treatments. The novelty of the paper also lies in presenting the effectiveness of Artificial Neural Network (ANN) models in accurately predicting the compressive strength, splitting tensile strength, and modulus of elasticity for self-compacting geopolymer concrete with various rates of RCA replacement. This addresses a knowledge gap in existing research on ANN models for the prediction of geopolymer concrete properties based on RCA rate and treatment. The ANN models developed in this research predict results that are more comparable to experimental outcomes, showcasing superior accuracy compared to linear regression models. Full article

This paper examines the emissions tradeoffs of additive manufacturing (i.e., 3D printing) using plastic waste in fused granular fabrication (FGF) versus traditional fused filament fabrication (FFF) and injection molding (IM). A ‘cradle-to-gate’ life cycle assessment (LCA) was utilized to compare these methods, built in OpenLCA v1.11.0 with the Ecoinvent v3.9.1 database. Different scenarios were used to evaluate the impacts of varying transportation and material inputs, highlighting critical emission contributors in manufacturing plastic goods. FGF with waste plastic can significantly reduce climate impact by 82.1% relative to FFF and 70.6% relative to IM for a specified unit product. Even with varied transportation and materials, FGF is a lower CO₂-equivalent emitting method. Utilizing FGF with waste plastic as a manufacturing method could reduce emissions and divert plastic from landfills and the environment, thereby contributing to a circular plastic economy. Full article

This study explores the transition toward sustainable economic models through the circular economy (CE) in Mexico. Utilizing a mixed-methods approach, this research incorporates a comprehensive literature review and analyzes responses from 42 stakeholders, gathered through surveys and focus groups. These stakeholders comprise a diverse group including PhD students, professors, researchers, industry professionals in sustainability and the environment, and government advisors and coordinators from the Mexican Secretary of Environment. This representative sample provides a broad perspective on the barriers, opportunities, and societal perceptions regarding CE. The findings reveal significant challenges such as economic barriers, regulatory inadequacies, and a lack of awareness and education, all of which hinder the adoption of CE practices. Despite these challenges, there is a generally optimistic view among stakeholders about CE’s potential to positively impact societal needs, suggesting robust opportunities for innovation and policy enhancement to foster sustainable development. Key recommendations include intensifying educational programs to elevate public understanding and engagement, formulating supportive policies that facilitate CE adoption, and promoting intersectoral collaboration to leverage collective expertise and resources. Additionally, the research underscores the necessity of integrating CE principles into urban planning and policy frameworks to effectively address specific local challenges such as waste management, pollution, and urban sprawl. By providing a detailed analysis of the current state and potential of CE in Mexico, this paper contributes valuable insights to the global discourse on sustainability. It proposes strategic actions to overcome existing hurdles and capitalize on opportunities within the CE framework, charting a path forward for Mexico and serving as a model for other regions facing similar sustainability challenges Full article