Recycling

The construction, demolition, and renovation industries are among the largest contributors to global carbon emissions and waste. With decreased landfill capacities, increased waste diversion targets, resource shortages, and the recognition that material waste is critical to climate change, diverting demolition waste is now a significant priority in waste management. Deconstructing a structure and reusing its building components can significantly reduce the environmental burdens imposed. However, to optimize the reuse of building materials and components for their environmental, societal, and economical benefits, the reclamation procedure must be undertaken in a more rational and robust manner. There are currently gaps in frameworks and tools that involve the assessment of reusable building components in demolition projects. This paper develops a reclamation framework to assess the viability of recovering and reusing building components. The framework first describes a process for conducting a technical audit and uses an assessment tool to suggest a level of deconstruction based on the physical parameters of the building circumstances. The framework complements this initial outcome by then assessing additional comprehensive parameters, such as the cost, the heritage value, and the available timeframe to arrive at a suggested outcome of actions, which can range from complete demolition and basic material recovery to deliberately removing salvageable items. The framework is then applied to an older, detached office building as a conceptual case study for demonstration. The recommended level of deconstruction appears appropriate based on the visual assessment of the structure. The result of this paper promotes the circular economy and supports the United Nations Sustainable Development Goals (UN SDGs) by presenting a notably more insightful and guided approach to capturing deconstruction waste. Full article

Solid waste disposal methods within indigenous communities present unique challenges and opportunities for sustainable development. However, the current knowledge on solid waste management focuses on formal waste collection systems, neglecting the practices and sustainability aspects of solid waste management in indigenous communities. Thus, it becomes imperative to undertake research studies that evaluate the sustainability of these practices as they play a pivotal role in ensuring sustainable development. The current study systematically evaluates the views and judgments associated with the sustainability aspects of indigenous waste management practices in the rural communities of South Africa using the Analytic Hierarchy Process (AHP) model. The data analysis was carried out using the AHP model. The findings of this study showed that the rural communities of Bushbuckridge Local Municipality prioritize the sustainability of the environment (weight: 0.590) over the economic (weight: 0.240) and social sustainability (weight: 0.165) based on the AHP evaluative framework. The validity of the priorities was tested through the computed degree of consistency (<10%) and an eigenvalue of 5.107. Furthermore, according to the assessment in the current study, the AHP evaluative framework dominantly prioritizes the sub-criteria of environmental sustainability (composting) at a responding rate of over 70% almost across all indigenous communities except for Acornhoek (30%), Casteel (25%), and Mambumbu (24%). Likewise, the sub-criterion of social sustainability, which is associated with communal cleaning labor, was found to be of extreme importance (60%), outperforming taboos (10%) that are anchored in cultural and spiritual beliefs. With a response rate > 50%, waste trading proved to be of economic efficacy. Using the AHP model to evaluate the sustainability aspects associated with indigenous solid waste management practices addresses a substantial gap in the comprehension of the role of indigenous knowledge towards sustainability in the discipline of solid waste management. However, it also offers a valuable sustainability perception that is associated with indigenous waste disposal methods that local governments and policymakers should include for consideration in integrated waste management plans. This can lead to the development of waste disposal programs that are well-coordinated and in accordance with indigenous sustainable waste management practices that advance the circular economy and promote environmental protection. Full article

This study investigates the effects of aging and recycling on the optical properties of paperboard, which is key to advancing circular economy practices in packaging. Methods included deinking flotation of cardboard made from sea algae and eco-conventional cardboard of unexposed and exposed samples in a xenon test chamber. Optical measurements were performed on the obtained laboratory paper sheets. Measurements for the chromatic coefficients ΔL*, Δa* and Δb*, as well as the CIE whiteness from comparison of the fluorescent component in the cardboard, were carried out under two light sources, D65 and UV. Regression analysis was used to quantify the statistical significance of these changes over time, i.e., in the aging process. The results revealed significant effects of both aging and recycling on the chromatic coefficients, with ΔL* and Δa* decreasing, while Δb* initially increased before decreasing. The influence of the fluorescent component is reduced by recycling the samples. Opacity measurements showed an initial increase in values that decreased with the aging of the samples, which indicates structural changes in the material. This research contributes to the circular economy by providing insight into the durability and optical properties of recycled cardboard, helping to develop sustainable packaging solutions. Full article

As more countries emphasize the importance of the circular economy, recycling resources from waste has become increasingly crucial. This study proposes a novel separation process for SmCo magnets, which can separate and recover metals by precipitation, thus reducing the amount of solvent used. The precipitation process involved the use of Na₂SO₄, NH₄OH, and H₂C₂O₄ to separate Sm, Fe, Cu, and Co, resulting in high precipitation efficiencies of 96.11%, 99.97%, 93.81%, and 98.15%, respectively. Moreover, the recovered metals can be directly used to create magnets after calcination, making this process a step towards achieving a circular economy. Full article

Municipal solid waste (MSW) is a growing problem worldwide posing a variety of environmental and human health impacts. Despite recycling being one major strategy to alleviate MSW production, the effectiveness of recycling has been equivocally dependent on local policy implementation and citizen environmental behavior. To enhance recycling effectiveness in Hong Kong, the government has established Green@Community, a unified community-based network for recycling and public environmental education. Since its establishment, the number of visitors to and the amount of recyclable materials collected at the network increased steadily over time. Our study is the very first to investigate the effectiveness of this territory-wide recycling network. Through a questionnaire survey, we found that respondents’ recycling traits were stronger if they have accrued gift tokens through participating in recycling activities. Visiting a Green@Community facility could also enhance knowledge of the types of acceptable recyclables, and respondents who had visited a Green@Community facility agreed that education and publicity could increase the recycling rate in Hong Kong. These findings highlighted the effectiveness and uniqueness of this community-based recycling network, its role in raising recycling knowledge, and its implications for policymakers and urban planners of densely populated cities to leverage society’s recycling participation, but also called for more efforts on developing, promoting, and incentivizing the usage of such a network to further enhance recycling and alleviate MSW production in Hong Kong. Full article

The global tuna canning industry generates substantial volumes of by-products, comprising 50% to 70% of the total processed material. Traditionally, these by-products have been utilized in low-value products such as fish oils and fishmeal. However, there is significant potential to extract high-value compounds from these by-products, such as calcium phosphates (CaP), which can have pharmaceutical, agricultural and biotechnological applications. This work explores the potential of tuna canning by-products, particularly mineral-rich fractions (central skeleton, head and fish bones) as sources of calcium phosphates (CaP), offering a sustainable alternative to conventional synthetic derivatives within a circular bioeconomy framework. By-products from two of the most exploited species (yellowfin and skipjack) were subjected to enzymatic hydrolysis and chemical extraction, followed by controlled calcination to obtain CaP. The content of organic matter, nitrogen, total proteins, lipids and amino acids in the cleaned bones, as well as the main chemical bonds, structure and elemental composition (FT-Raman, XRD, XRF) were evaluated. Results indicated that the highest recovery yield of wet bones was achieved using the chemical method, particularly from the dorsal and caudal fins of yellowfin tuna. The proximal composition, with ash content ranging from 52% to 66% and protein content varying between 30% and 53%, highlights the potential of tuna skeleton substrates for plant growth formulations. Furthermore, variations in crystalline structures of the substrates revealed significant differences depending on the by-product source and species. XRD and Raman results confirmed a monophase calcium phosphate composition in most samples from both species, primarily based on hydroxyapatite (central skeleton, caudal and dorsal fin) or whitlockite/β-tricalcium phosphate (viscera), whereas the heads exhibited a biphasic composition. Comparing the species, yellowfin tuna (YF) exhibited a hydroxyapatite structure in the branchial arch and scales, while skipjack (SKJ) had a biphasic composition in these same regions. Full article

Over the last two decades, the use of bioreactors filled with aged refuse extracted from closed areas of landfills has proven to be a viable alternative for the treatment of different types of wastewater. This study presents the results obtained during the evaluation of aged refuse used as filling material for a downflow bioreactor during the removal of the organic load present in wastewater generated in the wet processing of coffee. The tests were carried out over a period of 120 days, with 15 days to start up and stabilize the bioreactor and 105 days to perform treatability tests. The aged refuse, once extracted, was dried and sifted to a particle size of less than 50 mm. The bioreactor used had a cylindrical geometry (Ø = 0.20 m, and h = 3.40 m), and it was fed with hydraulic loads of 50, 100, and 150 L m⁻³ d⁻¹. The analysis of the data obtained shows that the system studied achieves the removal of 98.3% of the initial organic load when fed with 150 L m⁻³ d⁻¹. This showcases recycling aged refuse as a technically viable alternative to treat the wastewater generated during coffee processing. Also, the evaluated system has the advantage of needing a short period of time to achieve its stabilization, which turns out to be of great value, especially in its possible use in the treatment of residual water generated in the harvest of agricultural products where the period of harvest is very short. Full article

This study addresses the global issue of recycling used vehicle tires, typically burned out or trimmed to be reused in playground floors or road banks. In this study, we explore a novel environmentally responsive approach to decomposing and recovering the carbon black particles contained in tires (25–30 wt.%) by vacuum pyrolysis. Given that carbon black is well known for its UV protection in plastics, the objective of this research is to provide an ecological alternative to commercial carbon black of fossil origin by recycling the carbon black (rCB) from used tires. In our research, we create a composite material using rCB and high-density polyethylene (HDPE). In this article, we present the environmental aging studies carried out on this composite material. The topographic evolution of the samples with aging and the oxidation kinetics of the surface and through the thickness were studied. The Beer–Lambert law is used to relate the oxidative index to the characteristic depth of the samples. The UV photons are observed to penetrate up to 54% less with the addition of 6 wt.% of rCB compared to virgin HDPE. In this work, the addition of rCB as filler for HDPE used for outdoor applications has demonstrated to be an antioxidant for UV protection and a good substitute for commercial carbon black for industrial goods. Full article

In order to be able to recycle composite components made of polymer and metal, which are used in the automotive industry, the joints must be broken. The success of the separation is influenced by the stress and also by the joining mechanism between the polymer and the metal. Here, force-fit and form-fit connected components are produced and crushed in a rotor impact mill with two different rotors. The results show that the crushing results differ significantly for the different rotors and for the various joining processes. In short, the hammer-type rotor provides much finer and better-separated fragments and the force-fit joints enable a better separation of metal and polymers. The additional cooling of the samples also changes the result in a way, where deep cooling significantly improves the separation of the metal and the polymer. Different types of polymers also led to a different separation result with both rotors. Full article

The discharge of metal-loaded mining-influenced waters can significantly pollute downstream water bodies for many kilometers. Addressing this issue at the earliest discharge point is crucial to prevent further contamination of the natural environment. Additionally, recovering metals from these discharges and other sources of contamination can reduce the environmental impacts of mining and support the circular economy by providing secondary raw materials. This study focused on optimizing zinc recovery from mining-influenced water in the Freiberg mining region in Germany, where significant loads of zinc are released into the Elbe River. By employing pretreatment techniques, conducting 100 mL scale ion-exchange column experiments, and refining the regeneration process, we aimed to identify optimal conditions for efficient zinc removal and recovery. Initial tests showed that aminophosphonic functionalized TP 260 resin had a high affinity for aluminum, occupying 93% of the resin’s capacity, while zinc capacity was limited to 0.2 eq/L. To improve zinc recovery, selective precipitation of aluminum at pH 6.0 was introduced as a pretreatment step. This significantly increased the zinc loading capacity of the resin to 1 eq/L. Under optimal conditions, a concentrated zinc solution of 18.5 g/L was obtained with 100% recovery. Sulfuric acid proved more effective than hydrochloric acid in eluting zinc from the resin. Further analysis using SEM-EDX revealed residual acid on the resin, indicating a need for additional study on long-term resin performance and capacity variation. The research also highlighted the environmental impact of the Freiberg mining area, where three drainage galleries currently contribute nearly 85 tons of zinc annually to the Elbe River. This study underscores the feasibility of efficient zinc recovery from these point sources of pollution using advanced ion-exchange processes, contributing to circular economy efforts and environmental conservation. Full article

Pressmud, a by-product of sugarcane processing, is typically disposed of through incineration or landfilling, though it has considerable potential in organic agriculture. This study explored the composting of pressmud through bioaugmentation using specific bacterial strains. Two experimental setups were created: E2 with a cellulolytic and phosphorus-solubilizing strain, Bacillus amyloliquefaciens-ASK11, and E3 with a nitrogen-fixing strain, Bacillus megaterium-ASNF3. A control setup (E1) was also maintained without bacterial augmentation. Results indicated that the Bacillus-enhanced composts in E2 and E3 showed significant increases of 129% and 83% in nitrogen and of 49% and 91% in phosphorus contents, respectively, after 60 days. Additionally, organic matter decomposition improved by 49–50% in the bioaugmented setups after 60 days. FTIR analysis revealed organic phosphate peaks and P-O-C stretching bands at 1025 cm⁻¹ in the E2 compost, while a nitrogen vibration band at 3849 cm⁻¹ in E3 indicated significantly higher nitrogen content compared to the control. The Bacillus-enriched pressmud compost not only accelerated the composting process but also enhanced nutrient levels, positioning it as a promising biofertilizer for rehabilitating barren lands. Full article

The palm oil industry (POI) generates significant amounts of waste, including calcium carbonate (CaCO₃) from the clay bath system used for the separation of palm kernels from shells. This CaCO₃ waste is often discarded, leading to environmental issues. However, the CaCO₃ can potentially be reused in the clay bath separation process to improve efficiency and reduce waste. To obtain PKO, the kernel is separated from the palm shell using a clay bath unit, where natural CaCO₃ acts as a decanting agent and adsorbent. This wet separation method, involving a mixture of water and CaCO₃ with a density of 1.12 g/mL, generates substantial amounts of saturated CaCO₃ waste that is often discarded into the environment. Therefore, this research aimed to regenerate oil-bound CaCO₃ waste for reuse as a decanter and adsorbent. Three treatments were tested, with CaCO₃ waste-to-water ratios of 1:1, 1:3, and 1:6, under varying pH levels (8, 10, 11, 12) and temperatures (28 °C, 80 °C, 100 °C). The regeneration process was conducted in an open reactor at 450 rpm with a volume of 0.0054 m³, followed by drying and grinding the waste for analysis. The results showed approximately 75.75% oil removal and CaCO₃ regeneration rates between 94.50% and 99.26%, with an increase in density from 1.687 g/mL to 2.467 g/mL. The efficiency of reusing regenerated CaCO₃ waste is 96.87%. When mixed with 25% natural CaCO₃, the efficiency increases to 99.24%. Additionally, a mixture of 50% regenerated CaCO₃ waste and 50% natural CaCO₃ achieves an average efficiency of 99.46% over five consecutive feed additions. This showed that the reuse of CaCO₃ waste regeneration results for the separation of palm shells and kernels has a high potential for application. These findings suggest that regenerated CaCO₃ waste can be effectively reused, offering a sustainable solution for palm oil mills. Full article

As a versatile metal, nickel will experience increased demand in the coming years, with a specific focus on its importance in the battery industry and its role in achieving net-zero emissions. Recognizing the need to ensure sustainable resource management, this study analyses the flow dynamics of nickel’s supply and demand by employing a modelling approach. This is done with a focus on understanding how recycling can contribute to meeting the growing nickel demand. By considering the interaction between mining production, product applications, and recycling rates, this study contributes to a better understanding of the long-term prospects for meeting the nickel demand. It can assist policymakers, industry stakeholders, and investors in making informed decisions regarding resource management and developing sustainable practices in the nickel industry. The results revealed that mining would still play an important role in the supply of nickel for at least the next 40 years. Nickel mining and recycling practices are sufficient to meet future nickel demand if sufficient recycling practices are (rapidly) implemented. Modelling results show that nickel recycling will account for 90% of the total demand (primary nickel mining accounts for the remaining 10%) between the years 2062 and 2096. Full article

The use of post-consumer recycled (PCR) plastic materials in sensitive packaging applications, such as for cosmetic products and detergents, requires a clear understanding of the identities and quantities of chemical substances, which they may release into packed products. With many potential sources of and thus different types of potentially releasable substances, a reliable non-targeted screening method is required to assess these materials. Such a method should be readily applicable in industrial practice and provide a realistic estimation of substance release. This investigation focused on the use of gas chromatography/coupled mass spectrometry (GC/MS) to analyze substances, which recycled HDPE (rHDPE) plastic pellets release into 95% ethanol under accelerated testing conditions. The results of the repeated testing of reference samples clearly demonstrated the good reproducibility of the described methodology, with standard deviations of repeated determinations of the total released substance amounts of 6.8–8.1%. The application to several production batches of three commercial rHDPE grades additionally demonstrated that the batch-to-batch variation of substances which rHDPE materials release can be confined to less than 10% of variation of the total detectable substance amount. The described methodology is therefore seen as a pragmatic, repeatable assessment of recycled HDPE plastic batches with a view to substance release. Full article

Reclaimed Asphalt Pavement (RAP) materials are used as substitutes for new materials in asphalt pavement construction, leveraging the engineering and commercial benefits of the aged binders and aggregate matrixes in RAP. These asphalt mixtures impart significant variations in volumetric properties and asphalt mixture characteristics. The current study investigates the Marshall properties, moisture susceptibility, and rutting behavior of 24 recycled asphalt mixtures developed with nanosilica and nanoclay. RAP material percent, nanomaterial content, binder grade, and extra binder were considered the factors influencing asphalt mixture performance. The above factors were analyzed using the Response Surface Methodology (RSM) to predict the Marshall and volumetric properties. Also, this investigation covers the moisture susceptibility and rut characteristics of recycled nanomaterial-modified Hot Mix Asphalt (HMA) and Warm Mix Asphalt (WMA) mixes developed with Viscosity Grade 30 (VG-30) and Polymer-Modified Bitumen-40 (PMB-40). The chemical additive Zycotherm was used to develop WMA mixes. The test results indicate that adding RAP material at higher percentages and modifying the binder with nanomaterials affected moisture susceptibility with reduced moisture damage. Recycled nanosilica-modified HMA mixes developed with PMB-40 at higher RAP percentages reported higher tensile strength ratio (TSR) values in contrast with VG-30 mixes, indicating their greater susceptibility toward moisture-induced damage. The rutting potential of all of the recycled asphalt mixture combinations was enhanced by densely packed aggregate structures optimized with nanomaterials, total binder content, and RAP materials developed using the Marshall method. Overall, the nanosilica-modified recycled asphalt mixes developed with PMB40 at higher RAP percentages showed better performance in terms of strength and durability. Full article

Durable building materials are essential for sustainability in construction projects, aiming to reduce environmental damage from the start to the end of a building’s life. Reducing the use of Portland cement in concrete production is essential because of the significant CO₂ emissions generated globally during its production process. This study investigates the workability, compressive strength, and water absorption of concrete when Portland cement is partially substituted with waste glass powder (WGP) and recycled concrete powder (RCP). These two waste powders can be used to partially substitute Portland cement in order to produce environmentally friendly concrete. The activity of the particles in concrete made from these two waste powders is mostly determined by the type and rate of the powders, as well as the curing methods. Therefore, the current research examines how different curing conditions impact the workability, compressive strength, and water absorption characteristics of this innovative eco-friendly concrete that includes the abovementioned waste powders. According to the experimental results obtained, adequate strength can be achieved using an appropriate replacement level of the powders and curing methods. Therefore, the application of these two recycled mineral admixtures in concrete can save Portland cement and has certain environmental and economic benefits. Full article

The use of solid waste such as ceramic sludge, ceramic rollers, and magnesite was studied to obtain cheap refractory ceramics at temperatures of 1300 °C based on XRF, XRD SEM, EDX, bending strength, and dielectric properties. The prepared samples were examined. The results showed that the significant crystalline phases formed were mullite, spinel, and corundum. They also showed that mullite hindered the formation of cordierite and enhanced spinel formation. With increased cordierite content, the microstructure varied from fine grained to coarse grained. Bending strength increased with increasing mullite content and bulk density, ranging from 10.80 to 13.50 MPa. Bulk density increased with the increase in mullite content and sintering temperature and ranged from 1.99 to 1.94 g/cm³, while the percentage of porosity and water absorption decreased and ranged from 29.40 to 38.83, respectively. To examine the effect of the produced phases on the dielectric characteristics, the permittivity (ε′), dielectric loss (ε″), and AC conductivity (σ_ac) were measured in the frequency range of 10⁻¹ Hz to 10⁶ Hz. As the concentration of cordierite increased, there was a noticeable drop in ε′ from 35.6 to 8.2 and σ_ac from 10⁻⁸ s/cm to around 10⁻¹¹ s/cm and high values of resistivity from 10⁸ cm/s to about 10¹⁰ cm/s, suggesting that this material might be an excellent insulator. Full article

Sewage sludge (SS), a byproduct of wastewater treatment plants, poses significant environmental and health risks if not properly handled. Conventional approaches for SS stabilization often involve costly and energy-consuming processes. This study investigated the effect of promoting native microalgae growth in SS on its stabilization, pathogen bacteria removal, and valuable biomass production. The effect on settleability, filterability, and extracellular polymeric substances (EPSs) was examined as well. Experiments were conducted in photobioreactors (PBRs) without O₂ supply and CO₂ release under controlled parameters. The results show a significant improvement in SS stabilization, with a reduction of volatile solids (VSs) by 47.55%. Additionally, fecal coliforms and E. coli were efficiently removed by 2.25 log and 6.72 log, respectively. Moreover, Salmonella spp. was not detected after 15 days of treatment. The settleability was improved by 71.42%. However, a worsening of the sludge filterability properties was observed, likely due to a decrease in floc size following the reduction of protein content in the tightly bound EPS fraction. Microalgae biomass production was 16.56 mg/L/day, with a mean biomass of 0.35 g/L at the end of the batch treatment, representing 10.35% of the total final biomass. These findings suggest that promoting native microalgal growth in SS could be sustainable and cost-effective for SS stabilization, microalgal biomass production, and the enhancement of sludge-settling characteristics, notwithstanding potential filtration-related considerations. Full article

Excessive use of plastic mulches has triggered a series of environmental problems, primarily due to the large volumes generated and their low or non-existent degradability. For this reason, materials with similar characteristics to synthetic mulches but with a biodegradable character were sought. In this work, mulch films were produced from gelatin/glycerol/cellulose (GelC) and chitosan/glycerol/cellulose (ChiC). Their biodegradation time in soil and photographic analysis using scanning electron microscopy (SEM) were determined. The GelC sample presented a weight loss of 80% at 25 days, compared to 58% for the ChiC sample in the same exposure time. However, the latter was the only sample that could be evaluated up to 70 days, during which it presented its greatest weight loss (97%). The SEM results for both mulch films showed some color changes after 30 days; complete fracturing, growth of mycelium on the surface, and the presence of pores were observed. FTIR spectra revealed a decrease in hydroxyl groups, amides, and carbonyl bands as the number of degradation days increased. Obtaining polymers from waste materials, such as mango, represents an important task to obtain cellulose that can both reinforce and provide biodegradable properties to biobased materials, which can be degraded by microorganisms present in the soil. Full article