Assessment of the potential energy and environmental benefits of solid waste recycling in China

Unraveling the spillover effects of socio-governance on circular transition: Does contract monitoring sand or grease the wheels of circular economy?

Governments worldwide have prioritized addressing global climate change by integrating the circular economy (CE) principles into public procurement practices. The driving force behind this study is to investigate the spillover effects of socio-governance factors on the CE transition, focusing on the role of contract monitoring. Panel data encompassing 16 EU countries that have made limited progress in meeting their greenhouse gas emission targets from 2010 to 2019 are utilized for the analysis. To estimate the spatial spillover effects, various models including spatial Durbin models, spatial lag regression models, spatial error models with spatial and time fixed-effects, spatial autocorrelation and mixed-effects ML and REML regression models are employed. Findings reveal that robust contract monitoring plays a significant role in enhancing CE, emphasizing that transparent public procurement and accountable decision-making are key drivers of the circular transition. Legal frameworks that protect property rights and promote regulatory quality further facilitate CE adoption, with positive spatial spillover effects suggesting that well-governed countries indirectly encourage CE implementation in neighboring countries. Conversely, stringent environmental policies lead to regulatory arbitrage, in line with the "pollution haven hypothesis," as waste-intensive industries relocate to jurisdictions with weaker enforcement, undermining collective CE efforts. The results highlight that governance structures not only act as domestic CE drivers but also as external factors influencing regional environmental outcomes. The study advocates for the harmonization of regulatory standards and enhanced contract monitoring mechanisms across the EU to prevent cross-border regulatory evasion. Strengthening social cohesion is also found to amplify these effects, underscoring the importance of multi-dimensional socio-political foundations for a successful and cooperative CE transition.

A survey and partial dependency analysis to assess residential solid waste recycling awareness in Saudi Arabia

Rapid industrialization, rise in population, and urbanization have led to severe environmental degradation and health concerns for inhabitants due to regular household waste (RHW). Implementing sustainable waste management practices, such as regular household waste recycling, is an imminent need in Saudi Arabia and other nations. Yet, the analysis of the awareness regarding RHW recycling and its influencing elements in the Kingdom of Saudi Arabia (KSA) has rarely been conducted. Efficient management of home waste is currently a major concern, particularly in economically developing countries, as inappropriate disposal of waste results in financial losses and detrimental effects on the environment and public health. The objective of this study is to assess the level of awareness among Saudi households on RHW, the environmental issues associated with improper waste disposal, and their readiness to participate in the recycling of RHW. Therefore, we conducted a two-stage analytic investigation that included a total of 909 households from different areas of Saudi Arabia. In addition to the analysis of questionnaire responses, partial dependency (PDP) analysis was also conducted using two supervised machine learning algorithms, Multi-Layer Perceptron (MLP) and Decision Tree (DT), to evaluate how sociodemographic factors influence waste recycling awareness. Based on the study results, most respondents are knowledgeable and worried about the adverse environmental effects of solid waste. Most respondents are motivated to support a large-scale recycling program, provided enough facilities are available. Also, the PDP analysis revealed that sociodemographic factors such as age, gender, salary, and marital status also significantly impact the awareness of waste recycling. Finally, considering the rising amount of waste produced by the Saudi population, the authorities must implement a recycling program to address this harmful waste and promote the development of a sustainable world.

Random Forest Algorithm for the Mechanical Strength Prediction of Green Cement-Based Materials Incorporating Waste Materials Under Fire Condition

High temperature treatment is a typical detrimental situation that may significantly influence the compressive strength of cement-based materials. It was reported that the incorporation of common waste materials as supplementary cementitious materials (SCMs) can improve high temperature resistance. In this work, fly ash (FA), granulated blast-furnace slag (GGBFS), and silica fume (SF) were used as SCMs to replace cement to produce green cement-based materials. The mechanical strengths of the samples being subjected to various elevated temperatures were measured and analyzed with different SCMs contents. Results showed that when the high temperature was above 500 °C, it caused significant loss of strength, and the use of SCMs can improve the high temperature resistance of the cement-based materials with higher residual strength, especially for the GGBFS and SF blended samples. Moreover, the random forest regression algorithm was used to predict the compressive strength for the cement-based material incorporating various waste materials, and exhibited high accuracy. This work presents a comprehensive study on the regularity of changes of mechanical strength and provides a specific algorithm for the precise prediction of this occurrence, which is helpful to understand and predict the influence of high temperature treatment on green cement-based materials with various waste materials.

Exploring the impact of circular economy practices on ecological footprint, inflation rate, and renewable energy consumption: evidence from G20 economies

The circular economy (CE) has acquired significant interest for its potential to contribute to sustainable development (SD). The present study utilizes empirical methodology, specifically panel data analysis, to examine the distinct effects and outcomes of the circular economy and its associated factors within a unified framework. The focus is on the G20 countries from 2008 to 2021. We evaluated the influence of various CE value sources (renewable energy consumption, composting rate, repair services availability, recycling rate) and a factor-analysis-derived measure of the CE on economic, environmental, and social aspects of SD. The objective was to assess the distinct effects and outcomes of CE and its components in a unified framework-the analysis utilized panel data from G20 countries from 2008 to 2021. Our findings show a substantial influence of CE in achieving SD, with positive implications for the economy, environment, and society. However, the impact of each CE value source on the SD dimensions shows variation. While renewable energy consumption (RENEC) and composting rate (CR) lessen environmental impact, recycling rate (RR) shows no significant effect, and repair services availability (RSA) increases the Ecological Footprint (EFP). Notably, RSA is the sole CE component, showing a positive economic impact at the national level. Additionally, RENEC, RSA, and RR contribute to reducing the inflation rate (INFR). Policymakers should undertake detailed impact assessments to develop effective, tailored strategies based on each country's unique goals. The findings of this study have important policy implications, particularly in terms of emphasizing targeted strategies for implementing CE practices to achieve sustainable development.

Do industrial solid waste recycling and technological innovation promote low-carbon development in China? New insights from NARDL approach

Recycling waste is crucial for consolidating resources and promoting sustainable development, serving a pivotal role in achieving the objectives of carbon peak and carbon neutrality. Nonetheless, most existing research has primarily focused on municipal solid waste (MSW) recycling, often neglecting the significant volume of industrial solid waste (ISW). This study aims to explore the asymmetric effects of industrial solid waste recycling and technological innovation on the low-carbon development. To this end, this study selects GDP and carbon intensity as indicators representing economic growth and environmental quality. A variable that can enhance GDP growth while reducing carbon intensity signifies its contribution to low-carbon development. By collecting data from China over the period of 1985-2020, non-linear autoregressive distributed lag (NARDL) models of GDP and carbon intensity are established to discover whether the low-carbon development can be achieved by enacting ISW recycling and technological innovation. The results show the asymmetric shocks of ISW recycling and technological innovation on economic growth and environmental quality. In the long run, both ISW recycling and technological innovation promote low-carbon development. In the short run, technological innovation proved to be detrimental to economic growth and environmental quality. This paper also highlights the inhibitory effect of the labor force on economic growth. The "pollution haven hypothesis" is supported by the finding that foreign direct investment reduces carbon intensity. Additionally, the Granger test revealed the direction of the variables' causality. Based on empirical findings, policymakers can protect the environment and create economic value simultaneously through waste recycling and technological innovation, thereby realizing low-carbon development.

Effect of Industrial Solid Waste as Fillers on the Rheology and Surface Free Energy of Asphalt Mastic

The continuous growth of industrial solid waste production has generated many environmental problems. We evaluated the potential of industrial solid waste as a substitute filler in asphalt mastic, with the aim of increasing the use of sustainable road construction materials. In this study, X-ray fluorescence spectroscopy (XRF) and scanning electron microscopy (SEM) were used to characterize the oxide composition and micromorphology of limestone (LS), red mud (RM), steel slag (SS), and ground granulated blast-furnace slag (GGBFS). Four asphalt mastics containing LS, RM, SS, and GGBFS with a filler-to-binder weight ratio of one were prepared. An evaluation of the rheology and wetting of the solid-waste-filler asphalt mastic was conducted using a frequency sweep, temperature sweep, linear amplitude sweep (LAS), multiple stress creep and recovery (MSCR), and surface free energy (SFE) methods. The results showed that SS increased the complex modulus, elastic component of the asphalt mastic and decreased the nonrecoverable creep compliance at stress levels of 0.1 and 3.2 kPa, which improved the rutting resistance of the asphalt mastic and reduced deformation under high-temperature conditions. The RM and GGBFS increased the fatigue performance of the asphalt mastic under strain loading, enhanced its fatigue life, and maintained good performance under long-term loading. The dispersive component of the SFE parameter of the solid-waste-filler asphalt mastic was larger than the polar component for the largest share of the surface energy composition. The SFE of the asphalt mastic prepared from the industrial solid-waste filler was reduced; however, the difference was insignificant compared to the limestone asphalt mastic. Solid-waste-filler asphalt mastic has performance characteristics, and its actual application can be based on different performance characteristics to select an appropriate solid-waste filler. The results of this study provide new technological solutions for solving the utilization rate of solid waste materials and sustainable road construction in the future.

Carbon feasibility of terminating plastic waste leakage by landfill mining: A case study based on practical projects in China

Over 900 million tons (Mt) of plastic waste (PW) are disposed in Chinese landfills, posing a permanent risk of migration through environmental media. Landfill mining has emerged as a promising solution to this problem but requires incineration and a substantial energy supply for the excavation, sorting and recycling processes, which themselves exert environmental impacts, particularly on climate change. Based on the life cycle assessment of pilot-scale demonstration projects, this study investigates the carbon feasibility of landfill mining followed by several PW treatments to quantify whether terminating PW leakage from landfills will produce unaffordable greenhouse gas emissions in the drive towards carbon neutrality. The changing trend of the carbon feasibility was deduced considering the decarbonization scenarios of electricity sector and petrochemical industries. When all the sorted PW is treated by incineration with power generation, the climate-change impact of mining is 134.10 kg CO2-eq per ton of aged refuse, projected to increase by 100.47 % in 2050. To completely eliminate the PW in Chinese landfills, the incineration pathway would generate a minimum of 2457.66 Mt CO2-eq emissions, equivalent to 17.69 % of the 2020 emissions in China by carbon flow analysis. In all scenarios, the most carbon-feasible solution was mechanical recycling of high-quality PW combined with chemical recycling of low-quality PW, although the industrial application of chemical recycling technologies remains uncertain. This study provides stakeholders with systematic guidance for balancing the trade-off between PW management and climate action.

Enhanced degradation of VOCs from biomass gasification catalyzed by Ni/HZSM-5 series catalyst

Volatile organic compounds (VOCs) evolved from biomass gasification plays a positive role in the formation of PM2.5 and odor pollution. In order to improve the removal rate of various VOCs produced by biomass gasification, a nickel-based supported HZSM-5 cataly st (Ni/HZSM-5 and Ni-Ca-Co/HZSM-5) was prepared by different auxiliary methods, Ni loadings, and pyrolysis temperatures. The catalytic cracking performance of Ni/HZSM-5 catalysts for different VOCs model compounds such as toluene, phenol, furan, acetic acid and cyclohexane were studied in a fixed-bed reactor. The catalysts were further characterized and analyzed by XRD, SEM, XPS and BET. The results showed that the Ni/HZSM--C-Co5 catalyst prepared by ultrasonic-assisted excess impregnation method with Ni loading of 8 wt%, Ca loading of 4 wt%, Co loading of 0.1 wt% had strong catalytic activity for VOCs degradation. With the increase of the cracking temperature, the conversion rate and gas yield of from model compound cracking improved significantly. At 800 °C, the conversion of each model compound was more than 90%, accompanied by the generation of cracking gases such as H2 and CH4. The selectivity of H2 and CH4 from toluene cracking reached 93%, and cyclohexane reached 98%. The models with higher oxygen content and lower bond energy were more likely to undergo reforming reaction to form small molecular gas. Model compounds with large molecular weight and high carbon content provided more carbon sources. Under the conversion degree towards the gas direction was high. This study provides a new idea on the removal of VOCs for the efficient utilization of biomass resources.

The current status and future of solid waste recycled building bricks

Solid waste (SW) has become a problem hindering the economic and social development. Achieving the full green cycle from raw material to production of recycled building bricks (RBB) using SW is the focus of future research. In this paper, the research results of RBB manufacturing using SW in recent years are reviewed. According to the consolidation principle of RBB, the effects of different types of SW on the physicochemical properties and microstructure of RBB are summarized based on the recycled unsintered brick (RUSB) and recycled sintered brick (RSB). By comparing and evaluating the two consolidation methods, it is proposed that RSB has good practicality due to its higher SW utilization rate, higher strength, and faster consolidation speed. Furthermore, the difference between MWS and conventional sintering (CS) is analyzed, and the research on the application of MWS in SW-RBB manufacturing in recent years is reviewed in detail. It is pointed out that microwave sintering (MWS) technology can solve many drawbacks in traditional sintering technology and has great prospects in manufacturing SW-RBB due to the low energy consumption, low pollution, and high efficiency. Finally, the shortcomings and possible challenges in the current research on manufacturing SW-RBB using MWS technology are discussed, which provides guidance for the future development of SW-RBB manufacturing.

Assessing the economic and ecological viability of generating electricity from oil derived from pyrolysis of plastic waste in China

The increased plastic waste generation worldwide poses ponderous issues for public health and the environment. China is the highest generator of plastic waste around the world. The current treatment process (incineration) of the increased plastic waste causes dangerous environmental consequences. Pyrolysis has recently surfaced as an ecologically friendly technique for energy and material recovery from plastic waste. The present study assesses the financial and ecological viability of power production from oil derived from the pyrolysis of mixed plastic wastes in China from 2009 to 2028. The prominent findings show that the amount of plastic waste collected in 2020 (24.16 Mt) increased by 53.19% in 2028.The pyrolysis of mixed plastic wastes during the project period yielded 359.29 Mt oil, which has a power potential of 1,060.86 GWh. The economic analysis indicated the project is viable and profitable with a positive net present value (US$8.80 million) and profitability index (1.26) greater than 1. The project has 10.6 y payback period, US$0.0752/kWh levelized cost of energy, 22.5% return on investment, and 13.0% internal rate of return. The life cycle assessment results show that conversion of mixed plastic waste to pyrolysis oil for electricity generation during the project period has a total global warming potential (GWP) of 1,311.4 kt CO2eq. The GWP is mainly from conversion of pyrolysis oil to electricity (73.42%), pyrolysis oil production (15.01%) and upgrading of pyrolysis oil (11.38%). The consumption of power from the project could avoid the combustion of 2,659.0 t coal, minimizing global warming by 11,278.8 kt CO2eq. Sensitivity analysis, which examines the influence of variation in sensitive factors on the success of the project, is presented. This paper provides scientific strategies for optimal investment and decision-making on the environmental sustainability of plastic waste-to-energy pyrolysis projects.

Exploring greenhouse gas emissions pathways and stakeholder perspectives: In search of circular economy policy innovation for waste paper management and carbon neutrality in Hong Kong

Waste paper disposed in landfills notably contributes to greenhouse gas (GHG) emissions and impedes more sustainable, circular alternatives, such as recycling. In Hong Kong, this unsustainable approach is currently dominant as 68% of waste paper products are treated in landfills in 2020. To contextualize the impact of local waste paper management and explore mitigation potentials of circular alternatives, this paper develops a quantitative assessment framework around GHG emissions development trajectories. Combining guidelines of the Intergovernmental Panel on Climate Change (IPCC), national GHG inventories, and local parameters from life cycle analysis, five GHG emissions projections were simulated along the Shared Socioeconomic Pathways (SSPs) until 2060. Most recent baselines indicate that Hong Kong's current waste paper treatment generated 638,360 tons CO₂-eq in 2020, comprising 1,821,040 tons CO₂-eq from landfill and 671,320 tons CO₂-eq from recycling, and -1,854,000 tons CO₂-eq from primary material replacement. Proceeding along a Business-as-Usual scenario under SSP5, GHG emissions will dramatically increase to a net 1,072,270 tons CO₂-eq by 2060, whereas a recycling-intensive scenario will lead to a net saving of -4,323,190 tons CO₂-eq. To complement the quantitative evidence on the benefits of waste paper recycling, field research was conducted to explore the feasibility of circular policy innovation from the perspective of recycling stakeholders. These empirical qualitative and quantitative findings from stakeholders' business routines and material transactions provide crucial indications for policy and institutional innovation: Essentially, for Hong Kong to improve waste paper recycling capacities and facilitate a circular economy (CE), local stakeholders require support via fiscal policy measures (financial subsidies or tax reductions) and infrastructure improvements (delivery access and material storage). In sum, this study employs a novel analytical framework combining original qualitative and quantitative evidence to provide policy innovation towards circular, GHG emission-saving waste paper management.

Evolutionary game analysis of WEEE recycling tripartite stakeholders under variable subsidies and processing fees

The standardization of formal recycling and rational subsidy plays an important role in waste electrical and electronic equipment recycling. In order to explore the tripartite decision and evolution path of waste electrical and electronic equipment recycling in different time periods, a tripartite evolutionary game model consisting of recyclers, manufacturers, and government are presented. Moreover, the evolution stability strategies and conditions in each period are calculated by replicating the dynamic equation and Jacobian matrix. Numerical simulations on tripartite evolution stability strategies corresponding to different stages of industry development are used to verify the rationality of the model. The results indicate that there is existed an indirect effect between tripartite decisions, and the indirect effect can expand the slack of tripartite decisions' thresholds of waste electrical and electronic equipment recycling. The variable subsidy in waste electrical and electronic equipment recycling proposed in this paper is useful to incentive recyclers to choose a formal recycling strategy, and manufacturers also choose production with recycled materials as subsidy varies. Besides, the appropriate waste electrical and electronic equipment processing fee is a conducive indirect effect for the tripartite decision to the optimal evolutionary stability strategy in waste electrical and electronic equipment recycling and can promote manufacturers to produce with the recycled materials. The research can assist in benefit coordination and behavior adjustment of waste electrical and electronic equipment recycling members and provide a theoretical basis for the government to formulate appropriate recycling subsidies to promote the formal recycling of electronic waste recycling.

Post-consumer plastic sorting infrastructure improvements planning: Scenario-based modeling of greenhouse gas savings with sustainable costs

With the increasing share of waste material recovery, household plastic waste is one of the biggest problems. In most countries, mainly manual sorting is used. Meanwhile, new automated technologies are being developed to expand the range of classifiable types to increase material recovery. The overall automation of the sorting process can help the EU's established recycling targets to be effectively met. However, the new technologies are feasible only in the case of large-capacity centers, which must be conveniently located in the existing infrastructure. This paper presents a two-stage model aiming to modernize the current sorting infrastructure for plastic waste. The approach uses multi-criteria optimization to minimize environmental impact at a reasonable price. The result is the optimal location of new automatic sorting centers, and waste stream flows using existing manual sorting facilities. The model is applied through an initial case study inspired by the Czech Republic data. Optimization output proposes four new automatic sorting lines with a total capacity of 158 kt per year. In most cases, manual sorting is used to reduce the transported weight of plastic waste, while automatic sorting lines separate the remaining, hardly recognized part. More than 60% of separately collected plastic is sorted and determined for material recovery.

Characteristics and health effects of particulate matter emitted from a waste sorting plant

Solid waste components can be recycled in waste paper and cardboard sorting plants (WPCSP) through a multistep process. This work collected 15 samples every six days from each of the 9 points selected to study the processes taking place in a WPCSP (135 particulate matter samples total). Examining the concentration and size fraction of particulate matter (i.e., PM₁, PM_2.5 and PM₁₀) in WPCSP is an essential issue to notify policy makers about the health impacts on exposed workers. The major activities for increasing of the concentration of PM in various processing units in the WPCSP, especially in hand-picking routes I and II were related to manual dismantling, mechanical grinding, mechanical agitation, and separation and movement of waste. The results of this work showed that a negative correlation between temperature and particulate matter size followed the order PM₁₀ > PM_2.5 > PM₁. Exposure to PM_2.5 and PM₁₀ in the WPCSP lead to possible risk (HI = 5.561 and LTCRs = 3.41 × 10^-6 to 9.43 × 10^-5 for PM_2.5 and HI = 7.454 for PM₁₀). The exposure duration and the previous concentrations had the most effect on the ILCRs and HQs for PM_2.5 and PM₁₀ in all sampling sites. Hence, because WPCSP are infected indoor environments (I/O ratio > 1), the use of control methods such as isolation of units, misting systems, blower systems equipped with bag houses, protective equipment, a mechanical ventilation system, and additional natural ventilation can reduce the amount of suspended PM, enhance worker safety, and increase the recycling rate.

Decomposition analysis of the decoupling and driving factors of municipal solid waste: Taking China as an example

As one type of debt 'borrowed' from nature, municipal solid waste (MSW) can be influenced by financing debt. Taking China as an example, an improved Logarithmic Mean Divisia Index (LMDI) model, together with the Tapio decoupling model, is developed to analyze the impact of private debt on MSW generation and the relationship between MSW and economic growth. The results show that the debt-income ratio promotes MSW generation and the output efficiency of debt inhibits MSW generation. Second, the linkage relationship between GDP growth and MSW shows three states: strong decoupling, expansion coupling and weak decoupling. The MSW generation per unit of GDP and the output efficiency of debt are the main contributors to the change of decoupling state. Third, implementing a MSW classification measure can greatly reduce the quantity of MSW removed and transported and improve the decoupling state. By 2035, deleveraging scenario and economic growth slowdown scenario can reduce MSW removal and transportation quantities by 765 and 1080 million tons, respectively. It is worth noting that negative population growth worsens decoupling while curbing MSW. The results provide a new perspective for the realization of MSW reduction and some sound policies are formulated to improve MSW management.

The potential energy and environmental benefits of global recyclable resources

Globally, the production of vast volumes of municipal solid waste impacts public health and the climate. Greening the solid waste sector could contribute to the achievement of the Sustainable Development Goals (SDGs). Therefore, this study assessed how the potential electricity and environmental benefits of recycling paper and plastic wastes could contribute to the achievement of the SDGs. The study used model equations methods to estimate the electricity consumption, diesel consumption, and greenhouse gas (GHG) emissions saved due to recycling. The key findings show that the 132.4 thousand toe/day of electricity saved globally in 2012 soared to 182.3 thousand toe/day in 2025. In 2012 and 2025, an average of 63.6% of electricity was saved. Globally, recycling saved a record of 1.4 million ktons CO₂eq/day of GHG emissions in 2012 and 1.9 million ktons CO₂eq/day in 2025. It was further realized that the overall volume of diesel fuel saved in 2012 grew from 511,146 to 703,887 million Liters/day in 2025, representing a rise of 37.7%. The sensitivity analysis shows an increase in the waste collection rate, the fraction of paper waste, the fraction of plastic waste, and the recycling rate in 2025 will boost recyclable resources' energy and environmental benefits. The findings of this study could offer scientific guidance for the achievement of the SDGs related to solid waste recycling and management.

Determinants of household food waste reduction intention in China: The role of perceived government control

About one third of food are wasted or lost globally every year which causes the problems of environmental degradation, food security issues, and economic inefficiency. With the new mandatory source separation policy implemented in China, the main objective of this research is to identify the variables that impact household food waste reduction intention and to understand the role of perceived government control and perceived policy effectiveness from the perspective of households. Using a PLS-SEM model design, a questionnaire with nine constructs including theory of planned behaviors variables, perceived policy effectiveness, perceived government control, perceived consumer effectiveness, and environmental concern were answered by respondents (n = 3037). Results showed that the less well-studied variables of perceived government control are important in shaping shareholder's food waste intention. As expected, the theory of planned behavior variables, perceived consumer effectiveness, and environmental concern are positively related to reducing food waste intention, while strong perceived government control was associated with lowering intention in food waste reduction. This paper then extends existing understanding of psychological determinants of food waste by identifying perceived government control as mediator.