A cost-benefit analysis of landfill mining and material recycling in China

Air classification efficiency evaluation of landfilled municipal solid waste using experiments and a probabilistic method

The air classification efficiency of landfilled Municipal Solid Waste (MSW) is critical for resource recovery but remains challenged by the heterogeneity and non-spherical morphology of waste. In this study, a probabilistic framework that integrates spheroid modeling with the Monte Carlo procedure to predict and optimize the separation efficiency was developed, and the results were compared using orthogonal experiments. The morphological distributions (elongation, flatness, and size) of 381 landfill samples and the density distributions of 184 landfill samples were statistically characterized. For the numerical model, spheroidal particles were generated by randomly sampling from each parameter's distribution. Then, a numerical model that incorporates non-spherical drag coefficients was developed. The model achieved a Root Mean Square Error (RMSE) of < 0.13 in predicting separation indicators, compared to the experimental results. The experimental results demonstrated that, under the same airflow velocity conditions, the recovery of light substances (RL) in landfilled MSW was lower than that of fresh MSW, partially due to the increase in density resulting from the degradation of organic matter. The numerical model revealed that the separation efficiency (E) exhibited velocity-dependent unimodal trends. The model further identified the optimal performance of the effective separation interval for an airflow direction of 15° under 21.40 m/s (50 Hz), and the interval length was 21 % and 15 % longer compared to 0° and 30°, respectively, under equivalent velocities. The results of this work provide a reference for optimizing the air classification apparatus of landfilled MSW, and a basic method for use in more thorough simulation studies.

A systematic review of plastic recycling: technology, environmental impact and economic evaluation

In this systematic review, advancements in plastic recycling technologies, including mechanical, thermolysis, chemical and biological methods, are examined. Comparisons among recycling technologies have identified current research trends, including a focus on pretreatment technologies for waste materials and the development of new organic chemistry or biological techniques that enable recycling with minimal energy consumption. Existing environmental and economic studies are also compared. The findings highlight differences in the environmental characteristics of various recycling methods, including their ability to recover plastic resins, carbon footprint, electricity consumption and gas emissions. The comparisons also reveal the challenges associated with these methods: mechanical recycling often encounters economic barriers due to contamination and inefficiencies in sorting and cleaning processes; thermolysis is constrained by high energy demands and operational costs, whereas chemical and biological recycling faces limitations related to scalability and material costs. Additionally, current challenges, emerging research areas and future directions in plastic recycling are discussed. For example, the role of innovative techniques, such as artificial intelligence, in refining recycling processes is emphasized. The importance of incorporating circular economy principles in the integrated sustainable analysis of recycling processes is also highlighted. The innovative contribution of this review is to address both technological developments and their environmental and economic implications. The focus is placed on literature from the past 10 years to ensure coverage of the most recent advancements. Overall, the insights of this review article aim to guide researchers, policymakers and industry stakeholders in improving sustainable management practices for plastic waste.

Resource recovery from legacy waste dumpsites in India: A path towards sustainable waste management

Legacy waste dumpsites have been a significant environmental concern in India for many years. These dumpsites are characterized by the uncontrolled disposal of Municipal Solid Waste (MSW) and have led to various types of pollution and disease outbreaks. As India faces the challenges of rapid urbanization and increased waste generation and with over 3000 legacy waste dumpsites in the country, the need to address these legacy waste dumpsites has become paramount. As we continue to struggle extensively for waste management as well as space, landfill mining has been recognized as a promising way of recovering resources in our country by employing various technological and engineering advancements to extract valuable materials and energy from legacy waste streams. Unlike existing waste management approaches, this review explores the application of a novel Recovery Potential Index (RPI) for legacy waste dumpsites in India, which evaluates the feasibility of waste treatment facilities based on waste compositions and recovered material quantities. Depending on the RPI, recovered fine fractions can be sold as city compost or used as fill material, while recyclable, combustible, and inert fractions could be directed towards appropriate recycling or landfill uses. Unscientific and uncontrolled landfill mining practices could lead to unanticipated impacts on the nearby environment in the form of heavy contamination, thereby presenting this practice as a challenge in addition to the immense opportunities it provides.

Coastal plastic pollution: A global perspective

Coastal ecosystems have ecological importance worldwide and require control and prevention measures to mitigate human pollution. The objective of this study was to perform a systematic review to provide a comprehensive overview of the global issue of coastal plastic pollution. 689 articles were eligible for qualitative synthesis and 31 were considered for quantitative analysis. There was an exponential increase in articles addressing coastal plastic pollution over the past 50 years. Studies were mainly carried out on beaches, and plastic bottles were the most found item, followed by cigarette butts. Polyethylene was the predominant plastic polymer, and white microplastic fragments stood out. China published most articles on the topic and Brazil had the highest number of sites sampled. Meta-analysis had significant effect sizes based on the reported data. These findings carry significant implications for environmental policies, waste management practices, and targeted awareness campaigns aimed at mitigating plastic pollution.

Sulfate reduction behavior in response to landfill dynamic pressure changes

During the long-term stabilization process of landfills, the pressure field undergoes constant changes. This study constructed dynamic pressure changes scenarios of high-pressure differentials (0.6 MPa) and low-pressure differentials (0.2 MPa) in the landfill pressure field at 25 °C and 50 °C, and investigated the sulfate reduction behavior in response to landfill dynamic pressure changes. The results showed that the pressurization or depressurization of high-pressure differentials caused more significant differences in sulfate reduction behavior than that of low-pressure differentials. The lowest hydrogen sulfide (H2S) release peak concentration under pressurization was only 29.67% of that under initial pressure condition; under depressurization, the highest peak concentration of H2S was up to 21,828 mg m-3, posing a serious risk of H2S pollution. Microbial community and correlation analysis showed that pressure had a negative impact on the sulfate-reducing bacteria (SRB) community, and the SRB community adjusted its structure to adapt to pressure changes. Specific SRBs were further enriched with pressure changes. Differential H2S release behavior under pressure changes in the 25 °C pressure environments were mediated by Desulfofarcimen (ASV343) and Desulfosporosinus (ASV1336), while Candidatus Desulforudis (ASV24) and Desulfohalotomaculum (ASV94) played a key role at 50 °C. This study is helpful in the formulation of control strategies for the source of odor pollution in landfills.

Managing urban development could halve nitrogen pollution in China

Halving nitrogen pollution is crucial for achieving Sustainable Development Goals (SDGs). However, how to reduce nitrogen pollution from multiple sources remains challenging. Here we show that reactive nitrogen (Nr) pollution could be roughly halved by managed urban development in China by 2050, with NH3, NOx and N2O atmospheric emissions declining by 44%, 30% and 33%, respectively, and Nr to water bodies by 53%. While rural-urban migration increases point-source nitrogen emissions in metropolitan areas, it promotes large-scale farming, reducing rural sewage and agricultural non-point-source pollution, potentially improving national air and water quality. An investment of approximately US$ 61 billion in waste treatment, land consolidation, and livestock relocation yields an overall benefit of US$ 245 billion. This underscores the feasibility and cost-effectiveness of halving Nr pollution through urbanization, contributing significantly to SDG1 (No poverty), SDG2 (Zero hunger), SDG6 (Clean water), SDG12 (Responsible consumption and production), SDG14 (Climate Action), and so on.

Evaluating the Potential of Multi-Walled Carbon Nanotube-Modified Clay as a Landfill Liner Material

In this paper, the feasibility of multi-walled carbon nanotube (MWCNT)-modified clay as a landfill liner material is investigated. Experiments were conducted on the modified clay with 0.5%, 1%, and 2% MWCNTs. The effects of the MWCNTs on the compaction characteristics, permeability coefficient, stress-strain curve, peak deviation stress, shear strength parameters (internal friction angle and cohesion), microstructures, and adsorption performance of the clay were analyzed. The results showed that the optimum moisture content (OMC) increased from 16.15% to 18.89%, and the maximum dry density (MDD) decreased from 1.79 g/cm3 to 1.72 g/cm3 with the increase in MWCNTs. The permeability coefficients firstly fell and then gradually rose as the MWCNTs increased; the minimum permeability coefficient was 8.62 × 10-9 cm/s. The MWCNTs can also effectively increase the peak deviation stress of the clay, and at the maximum level, the peak deviation stress was increased by 286%. SEM images were processed using the Pore and Crack Analysis System (PCAS), and the results showed that the appropriate amount of MWCNTs could fill the pores and strengthen the clay structure. The effect of the MWCNT-modified clay on the adsorption performance of common heavy metal ions Cd2+, Mn2+ and Cu2+ in landfill leachate was analyzed by batch adsorption tests. The maximum adsorption capacities (Qmax) of Cu2+, Cd2+ and Mn2+ in the 2% MWCNT-modified clay were, respectively, 41.67 mg/g, 18.69 mg/g, and 4.97 mg/g. Compared with the clay samples without MWCNTs, the adsorption properties of Cu2+, Cd2+, and Mn2+ were increased by 228%, 124%, and 202%, respectively. Overall, the results suggest that MWCNT-modified clays have the potential to be suitable barrier materials for the construction of landfills.

Assessing the city-level material stocks in landfills and the landfill mining potential of China

Landfill mining has become an emerging issue in urban metabolism research and environmental remediation practices. Comprehensive understanding of the quantity and distribution of material stocks in landfills, as well as identifying hotspots of landfill mining potential, is of crucial importance. However, high-resolution datasets and systematic analytical tools remain insufficient. This study established a time-series landfill material stock inventory at prefecture level in China. An evaluation system for mining potential of landfills at prefecture level was then constructed using an integrated expert scoring and entropy weight method, based on ten indicators across five dimensions, including environmental impact, energy recovery, resource cycling, economic cost, and social aspect. The results show that over the past twenty years, the material stock in landfills was 2321.07 Tg (106 tons) in China, among which, soil-like materials, ash & stone and plastic & rubber were the three largest fractions, accounting for 61.06 wt%, 18.96 wt%, and 12.69 wt% of the total stock. Regional differences in landfill mining potential were found to be significant, with South China presenting the largest mining potential, while Southwest China showed the lowest. Cities with better economic development in China show the possibility to have greater landfill mining potential. This study established a methodology for the assessment of landfill mining potential for China or other countries, and provided scientific evidences for formulating regional-specific policies on landfill mining in China.

The waste ban in China: what happened next? Assessing the impact of new policies on the waste management sector in China

The 2017 ban on the waste import and new policies for the waste management sector in mainland China had wide-spread impact. After decades of poor environmental and public health impacts from the sector, a study is needed which focuses on policies updates and waste management. This provides a direction for the survival of local waste management industries and consider similarities with the ban promulgated in China on the restriction of waste import from other countries. We review the waste management situation in China before national legislation prevented the import of waste, highlight the status of landfill mining in China, and review the dynamics of domestic policies before and after the promulgation of the ban in China. The impact of the COVID19 pandemic on the waste management system is starting to emerge, providing both challenges and opportunities for the sector in China. We see the impact of the ban on the range of imported waste and domestically generated materials. The ban results in price increases for domestic recycling that forces companies to introduce more formal recycling processes and to drive the consumption behaviours to more reasonable and environmentally friendly options. The driver in China is to reduce pollution in the environment and improve health, but a negative impact has been from increased landfill mining which has impeded the original aim of the waste ban and requires further technological development. The dynamic of domestic policies in China shows higher level of activity of updates and revisions or introduction of new policies from 2015 onwards and the concept of 'zero waste cities' brings new hope for improvement of the Chinese waste management system. The pandemic also suggests an important step to establish sustainable management systems despite evidence of increased "fly-tipping". The rebound of the waste ban may have stimulated in the short term negative impacts on local environments both in China and internationally.

Potential health risk assessment of contaminants in soil-like material recovered from landfill mining

Landfill mining is an innovative technique to clear dumpsites and recover valuables from legacy waste. Bio-earth, referred here as soil-like material, constitutes a major portion of the legacy waste fraction. The characterisation of Soil Like Material from Ariyamangalam Dumpyard and estimation of pollution indices by comparing with the background soil helps in the identification of the contamination level. The potential health risk associated with the contaminants in Soil Like Material is highlighted. A statistical correlation was also done for various parameters of Soil Like Material to identify the indicator element through the Spearman rank correlation method. The degree of contamination based on eight heavy metals taken into account shows a value of 48.23, which is in the range of very high contamination. The major pollution is induced by the lead present in the Soil Like Material compared to the background soil, followed by chromium and zinc. Lead shows the maximum contamination factor of 19, pollution index of 23.3, geo-accumulation index of 4.2 and enrichment factor of 19. The hazard index is in the order of Cr > Pb > Cu > Ni > Cd > Zn > Hg > As for the heavy metals. Among all heavy metals, the cumulative cancer risk is more due to nickel (0.06 and 0.006 for children and adults, respectively) which is harmful to human health. Hexavalent chromium was found to be an indicator element by significantly correlating with four other parameters. The results of the health risk assessment (HRA) and pollution indices add value to the application of Soil Like Material fractions both onsite and offsite.

Flow and stock accumulation of plastics in China: Patterns and drivers

Plastic pollution has always been a hot issue of global concern. Previous studies have mainly focused on the flow of plastics. However, information on the patterns and characteristics of flow, stock, and waste in the plastic life cycle and their driving factors is limited in China, and effective waste reduction and sustainable strategies are missing. Therefore, this research established a flow model of polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET); further analyzed the driving factors; and proposed strategies for waste reduction and sustainable development. We found that the total consumption, stock, and waste of PET, PE, and PP in 2010-2017 reached 552.96, 292.70, and 257.18 Tg, respectively. Building and construction (B&C), packaging, and textiles were the sectors with the largest stock of PE, PP, and PET. From 2010 to 2013, the stock of PE increased by 440 %, which was mainly driven by the increase in material utilization intensity (MUI). Similarly, the growth of MUI was the main driving factor driving PP (351 %) and PET (367 %) stocks. Notably, from 2014 to 2017, economic growth was the main factor driving the plastic stock. These results will provide a scientific basis for promoting the sustainable utilization of PE, PP, and PET and be of great significance to achieve the strategic goal of a no-waste city.

Influence of dissolved organic matter and heavy metals on the utilization of soil-like material mined from different types of MSW landfills

Soil-like material (SLM) mined from municipal solid waste (MSW) landfills can be used as nursery cultivation soil, landfill cover, and as a building material. However, SLM utilization is restrained by heavy metal (HM) contents whose speciation and migration are influenced by their dissolved organic matter (DOM) content. Therefore, the properties of aged refuse and the correlation between DOM and HM forms were studied using samples from different types of MSW landfills. The dominant components of aged refuse were SLM (18.80%-83.51%) and plastics (11.17%-65.51%). The moisture, organic matter, and pH ranged from 29.55% to 57.92%, 15.70%-57.68%, and 7.84-8.51, respectively. The Zn content was highest (455.48-1379.27 mg/kg) in the SLM, followed by Cu (96.29-428.90 mg/kg), Cr (49.10-236.21 mg/kg), Pb (53.52-222.71 mg/kg), and Ni (20.92-39.10 mg/kg). The SLM cannot be used for agriculture because the HM contamination exceeds the multiple of 0.07-7.99. Zinc in the acid-soluble state and reducible state had the highest mobility in SLM. However, Cu and Pb, mainly in the oxidizable state, and Cr and Ni, in the oxidizable and residual states, were relatively stable. In the sanitary and simple MSW landfills, the average proportion of protein-like materials decreased from 84.44% to 82.61% and from 65.58% to 55.94%, respectively, as the landfill depth increased. Both the acid-soluble and oxidizable HM states and all forms of Zn in the SLM were significantly positively correlated with tyrosine-like materials (r = 0.58*-0.87**). Protein-like materials may enhance the mobility of HMs.

Biogas production from the landfilled easily degradable fraction of municipal solid waste: mining strategy for energy recovery

The growing demand for space and financial resources to manage current and new municipal solid waste (MSW) landfills has become a massive challenge for several countries. Additionally, landfills contribute to adverse environmental impacts such as pollution and CO2 (carbon dioxide) and CH4 (methane) emissions. This paper has analyzed the possibility of producing biogas from landfilled MSW. An easily degradable fraction of landfilled MSW with 8 years of landfilling was mined and subjected to chemical characterization and elemental composition analysis. The abbreviation for the study sample was called ED8 - Mined. The low values of lignin (24.5%) and nitrogen content (0.7%) and high values of holocellulose (75.9%) and C/N (46.1%) on dry basis were obtained resulting in materials with the potential to be used for biogas generation. Recalcitrant materials were found in greater amounts than easily biodegradable fresh MSW fractions. The reuse of energy from landfilled MSW can contribute positively to the country's environment and economy, reducing environmental liabilities and generating energy in a controlled way. In Delta A Sanitary Landfill, Southeastern Brazil, the recovery of the ED8 - Mined would reflect a significant recovery of about 100,000 tonnes of landfilled materials for annual MSW cells of about 450,000 tonnes, allowing recovery of materials and space expansion for rejects.

Graphical abstract

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Transformation of Solid Waste Management in China: Moving towards Sustainability through Digitalization-Based Circular Economy

In China, environmental pollution due to municipal solid waste (MSW) over-generation is one of the country’s priority concerns. The increasing volume and complexity of the waste poses serious risks to the environment and public health. Currently, the annual growth of MSW generation is estimated to be approximately 8–10% and will increase to 323 million metric tons (Mt) by 2030. Based on the secondary data collected from a literature survey, this article critically evaluates the recent progress of MSW management (MSWM) in China and offers new insights into the waste sector in the era of Industry 4.0. This helps decision makers in China to plan a smooth transition nationwide to a circular economy (CE) in the waste sector. It is evident that digitalization is a driving force for China to move towards low-carbon development strategies within the framework of CE. Through digitalization, the waste sector has promoted prevention, reduction, reuse, and recycling (3Rs) of waste before waste disposal in landfills. A proper implementation of digitalization-based waste recycling has contributed to an efficient cooperation between the government and private sector, increased job opportunities, and promoted the conservation of resources. It is anticipated that this work not only contributes to the establishment of an integrated MSWM system in China, but also improves local MSWM through digitalization in the framework of a CE.

Life cycle environmental and economic comparison of thermal utilization of refuse derived fuel manufactured from landfilled waste or fresh waste

This paper analyses environmental and economic performance of thermal utilization technologies of two different refuse derived fuel (RDF) manufactured from landfilled waste or fresh municipal waste, including incineration of landfilled RDF (I-LRDF), gasification of landfilled RDF (G-LRDF), replacement of partial coal by landfilled RDF for the cement industry (C-LRDF), incineration of municipal RDF (I-MRDF), and replacement of partial coal by municipal RDF for the cement industry (C-MRDF). The preference among the RDF utilization options is identified from the standpoints of various stakeholders by integrating the life cycle assessment (LCA) and techno-economic analysis (TEA) with the analytic hierarchy process (AHP) and technique for order preference by similarity to ideal solution (TOPSIS) approaches. RDF thermal utilization technologies bring an economic profit of $17.29∼$35.77 per ton of waste. Especially, I-LRDF has the worst effect on ecosystem quality and human health and can yield the greatest economic profit of $35.77 per ton of landfilled waste, while I-MRDF has the least impact on environment. In terms of the five RDF thermal utilization technologies, I-MRDF has the best comprehensive performance from the perspectives of different stakeholders. The improvement of the RDF thermal utilization efficiency is the most critical factor affecting the economic benefits for all cases.

Energy Potential Assessment of Excavated Landfill Material: A Case Study of the Perm Region, Russia

The paper presents results of field and laboratory studies of thermal characteristics to excavated landfill waste in Perm region, Russia. The peculiarity of the study includes the following aspects: waste composition with a high share of polymers, the climatic conditions of the territory and the lack of engineering infrastructure at the waste disposal facility. When determining the waste composition and thermal properties of waste, it is proposed to include a stage of removal of contamination from landfilled waste fraction, since their share of contamination can reach up to 33%. This stage will allow researchers to adjust the net calorific value of the excavated waste without overestimation, which may affect decision-making when implementing waste management technology. Among combustible components with the highest moisture content are waste paper (69.1%) and diapers (65.8%), whereas wood (11.2%), PET bottles (3.1%) and other 3D plastics (13.4%) have rather low ash content on a dry basis. Calculation of thermal properties and analysis of the energy potential of the waste samples was conducted based on the obtained data. The calorific value of the individual components and excavated waste depends not only on the moisture and ash content of the individual components, but also on the presence of contaminants. The average net calorific value of the excavated waste is 4.9 MJ/kg, and for the separate mixture of combustible components, it is 7.5 MJ/kg at a moisture content of 44%. Excavated landfill waste can be regarded as a resource for the manufacture of secondary fuel only after pretreatment that includes at least sorting and drying. The results of this study may be useful in developing technologies needed to eliminate old MSW dumps and old landfills, for the development of the concept of circular economy and prevention of environmental degradation problems.

A Non-Market Valuation Approach to Environmental Cost-Benefit Analysis for Sanitary Landfill Project Appraisal

Extensive non-engineered landfilling practice in developing countries has raised environmental concerns, but operating a sanitary landfill appears infeasible due to financial incapability. This study aims to determine the feasibility of a sanitary landfill project by including its environmental values into the project appraisal while simultaneously applying three policy-relevant methods—non-market valuation, benefits transfer, and cost-benefit analysis—in two study areas in Peninsular Malaysia. The non-market valuation study used choice modeling, a questionnaire-based technique, to elicit willingness to pay among 624 households toward the environmental attributes of the sanitary landfill. Their responses resulted in the monetary values of the environmental attributes by referring to implicit prices of leachate discharge, bad odor, disease vector and view. The implicit prices of bad odor (RM2.29 per month) and view (RM3.59 per month) in the two study areas were transferable and used as a proxy of additional solid waste disposal payment in environmental cost-benefit analysis. Positive net present value offers empirical evidence of the feasibility of the sanitary landfill project. The findings show that the inclusion of environmental values in project appraisals increases the chances of implementing sanitary landfills, providing a new approach to address the environmental concerns in developing countries. Future research should consider the external costs along with the external benefits to allow for a comprehensive comparison between environmental values in environmental cost-benefit analysis.

Dynamic flow and pollution of antimony from polyethylene terephthalate (PET) fibers in China

Antimony (Sb), a regulated contaminant, is added as a catalyst in the process of polyethylene terephthalate (PET) synthesis. Previously, Sb release from PET bottles and films was studied. However, Sb release from PET fibers (the most common form of PET) is limited. Therefore, a network model of material flow for PET fibers in China is developed, and the anthropogenic Sb flow and release entering into the hydrosphere, pedosphere, and atmosphere are studied based on microexperiments and macromodels. To compensate for the uncertainty caused by material flow analysis, Sb pollution in the surrounding areas (the drinking water of nearby residents and sediments of nearby river area) is further explored by combining field investigations and sample analysis. The results are as follows: 1) the manufacture stage of PET fibers is the main source of Sb release (2926 t), followed by the dyeing (2223 t) and weaving (908 t) stages; 2) Sb release (1108 t) from waste PET fibers subjected to landfill disposal is the highest. Sb release (872 t) from discarded fiber waste is second highest. Sb release from PET fibers subjected to mechanical recycling, incineration, and chemical recycling is 784, 284, and 25 t, respectively; and 3) an obvious source-sink relationship is found between anthropogenic Sb in the rivers and sediments and the intensity of the industries. This study suggests that Sb from PET fibers should be properly managed to prevent widespread dispersion in the hydrosphere, pedosphere, and atmosphere.

Enhancing anaerobic digestion of kitchen wastes via combining ethanol-type fermentation with magnetite: Potential for stimulating secretion of extracellular polymeric substances

Magnetite, a common mineral that is abundant in the soils and sediments, has been widely documented to enhance the anaerobic digestion of organic wastes, whereas the mechanisms of magnetite promoting interspecies electron transfer are still unclear. In this study, under the conditions (ethanol-type fermentation) employed, magnetite stimulated the secretion of extracellular polymeric substances (EPS). Analysis of three-dimensional excitation emission matrix revealed that these EPS secreted in the presence of magnetite were primarily comprised of the redox-active organic functional groups. Electrochemical analysis showed that the EPS secreted with magnetite had the higher electron-accepting and electron-donating capacity than the EPS without magnetite. Syntrophomonas species capable of extracellularly transferring electron were enriched with supplementing magnetite. Together with the increased abundance of Methanospirillum and Methanobacterium species that could proceed direct interspecies electron transfer (DIET), the anaerobic digestion was likely improved due to the establishment of DIET with supplementing magnetite. As a result, anaerobic digestion of kitchen wastes was evidently enhanced. With decreasing the solid retention time to 30 d, the methane production rate only slightly declined to 18 ± 0.8 mL/g-VSS/d in the magnetite-supplemented digester, while almost no methane was detected in the digester without magnetite.

Comprehensive Performance Evaluation of Green Infrastructure Practices for Urban Watersheds Using an Engineering–Environmental–Economic (3E) Model

Green infrastructure practices could provide innovative solutions for on-site stormwater management and runoff pollution control, which could relieve the stress of nonpoint pollution resulting from heavy rainfall events. In this study, the performance and cost-effectiveness of six green infrastructure practices, namely, green roofs, rain gardens, pervious surfaces, swales, detention basins, and constructed wetlands, were investigated. The comprehensive performance evaluation in terms of the engineering performance, environmental impact, and economic cost was determined in the proposed engineering–environmental–economic (3E) triangle model. The results revealed that these green infrastructure practices were effective for stormwater management in terms of runoff attenuation, peak flow reduction and delay, and pollutant attenuation. It was suggested that for pollution control, detention basins can efficiently reduce the total suspended solids, total nitrogen, total phosphorus, and lead. The implementation of detention basins is highly recommended due to their higher engineering performance and lower environmental impact and economic cost. A case study of a preliminary cost–benefit analysis of green infrastructure practice exemplified by the Pearl River Delta in China was addressed. It suggested that green infrastructure was cost-effective in stormwater management in this area, which would be helpful for sustaining healthy urban watersheds.

Dynamic flows of polyethylene terephthalate (PET) plastic in China

Polyethylene terephthalate (PET) is a widely used plastic material that may cause significant environmental pollution. China is a major global producer and consumer of PET. Previous studies have focused on the effects of toxic elements from PET (e.g., antimony leached from PET products) on the environment. However, detailed information about PET, particularly about the PET production, trade, use, and recycling in China, is limited. This study developed a network model of PET flows in China, including the production, market trade, manufacturing and use, and waste management and recycling stages. Based on this network model, the characteristics of PET flows during three periods of development for the PET industry were analyzed. The results show that the fiber and bottle manufacturing industries are the industries with the largest PET in-use stocks. The PET flows showed different characteristics in the terms of waste import, recycling, and disposal (mechanical recycling, chemical recycling, incineration, landfill, and discarding) in the different periods of PET industrial development. Notably, the amount of discarded PET was significant, and the treatment of waste PET would probably be a challenge in the future. Policies for improving the PET cycling system were provided on the basis of the study results to promote the management and sustainable utilization of PET materials.

Evaluating the physicochemical properties of refuse with a short-term landfill age and odorous pollutants emission during landfill mining: A case study

A field excavation of refusewitha short-termlandfillage from the Qingdao Xiaojianxi municipal solid waste (MSW) landfill was conducted. The physical composition and chemical properties of refuse with landfill ages of 1-4 years were studied, and the emission characteristics of odorous pollutants during the excavation period were monitored. The refuse aged 1-2 years has a higher proportion of combustible material than that the refuse aged 3-4 years, and the volatile content and calorific value in refuse aged 1-2 years were also higher than those in refuse aged 3-4 years, indicating that the refuse with a short-term landfill age was more suitable for incineration than refuse with a long-term landfill age. The pH and availablephosphorus (AP) gradually increased with increasing landfill age, while the total Kjeldahlnitrogen (TKN) and organic matter (OM) decreased. The contents of the heavy metals Cu, Zn, Ni, Pb and As generally decreased with landfill age, especially in refuse aged 2-4 years, whereas the Cr content showed no significant differences in refuse aged 1-4 years. The main odorous pollutants emitted during the excavation and screening periods were ammonia (NH₃) and carbon disulfide (CS₂), and the odor intensity of excavated refuse aged 1-3 years was higher than that of refuse aged 4 years. Under the condition of a small excavation area and continuous deodorization, the pollution intensity can meet the discharge standards of the factory boundary.

Cost-benefit analysis of waste photovoltaic module recycling in China

With the rapid development of renewable energy, the impact on environment and resource caused by waste photovoltaic modules has been realized gradually. To solve the problem, recycling becomes an effectual way. Therefore, the aim of this paper was to assess the economic feasibility of the photovoltaic modules recycling project in China by using cost-benefit analysis. It was found that, under the estimated treatment quantity will generate in China in 2020-2034, the recovery cost per kilowatt (kW) of photovoltaic modules will be 25.11 USD, the unit benefit is 25.68 USD/kW, and the unit net benefit is 0.57 USD/kW. The net present value (NPV) and benefit-cost ratio (BCR) are 21.14 million USD and 1.023. The sensitivity analysis indicated that the sale benefits of recycled materials and tax were the most sensitive factors affecting the project's economy. Finally, we proposed ways to improve the economy for the government and related enterprises.

Environmental and economic assessment of Enhanced Landfill Mining in Tehran

Landfilling brings many difficulties such as leaching of hazardous substances, methane gas production, loss of land, and natural resources such as groundwater, soil, and minerals. Enhanced landfill mining (ELFM) gives an opportunity to deal with such related problems. This study aimed to assess the environmental performance of ELFM through the application of life cycle assessment (LCA). SimaPro (v 8.5) was utilized to model the consequential life cycle assessment. Moreover, a comprehensive cost-benefit analysis was applied to assess the economic performance along with the Monte Carlo simulation to address the related uncertainties. In addition, the indicator of net present value (NPV) was adopted to understand the economic feasibility of the project. The case study landfill was the closed 55-hectare dumpsite of the municipality of Tehran in Kahrizak due to the need for further landfilling space in the future. The results of this study indicated that ELFM could lead to remarkable environmental benefits compared with the landfill's current status (the do-nothing scenario). The ELFM project reduced the impact of global warming by 1,759,790 ton CO2 eq, equaling to 134% reduction in comparison with the do-nothing scenario. Moreover, the potential profitability of the project was calculated to be 370 million $. Among the processes, recycling and thermal treatment of waste significantly dominated the environmental results of the project. Although the research was based on a case study landfill, the methodology can be applied to similar projects worldwide.

Cost-benefit analysis of rehabilitating old landfills: A case of Beiyangqiao landfill, Wuhan, China

A comprehensive approach for evaluating the feasibility of landfill rehabilitation should be developed to allow landfill owners to thoroughly examine the feasibility of a landfill soil remediation project in advance. With a view of contributing to the development of a common framework for the evaluation of landfill rehabilitation projects, this paper presents the results of a case study in which the issue of assessing the costs and benefits of rehabilitating the Beiyangqiao simple landfill is addressed. Based on the results of a survey, the cost-benefit assessment criteria and candidate remediation methods were selected. The alternatives included are, in-situ landfill closure; in-situ aerobic stabilization combined with in-situ screening and classification of recovered materials, transport for off-site disposal; and ectopic mining combined with recycling and incineration. Results show that the costs of landfill rehabilitation would range from 11.23 to 32.02 million United States dollars (USD). The key benefits would be land reclamation, heat, or electricity generation by incineration, and recycling of waste materials. The total benefits would range in value from 59.62 to 61.47 million USD. The net present value of the three scenarios would be positive and would range from 8.6 to 10.02 million USD. The results suggest that all three scenarios were positive. Nevertheless, "in-situ aerobic stabilization, in-situ screening, transportation, and off-site disposal" was most beneficial considering all parameters.Implications: This study applied a cost-benefit analysis model for assessing the economic feasibility of landfill rehabilitation, which is important to promoting landfill rehabilitation, and the market potential was assessed based on an actual project. The findings can be useful for providing landfill owners choices in a landfill rehabilitation project to achieve least quantified costs and overhead.

Assessment of Land Reclamation Benefits in Mining Areas Using Fuzzy Comprehensive Evaluation

Land reclamation plays a vital role in the ecological improvement and economic development of mining regions. This study aims to conduct a preliminary discussion on the evaluation content, evaluation methods, and evaluation indicators of land reclamation benefits in mining areas. Using fuzzy comprehensive evaluation (FCE) method, land reclamation was assessed. After compiling a model of the land reclamation influencing factors, an evaluation index of land reclamation benefit in the mining area was constructed using the land reclamation monitoring data for the northern part of the mining area over the last decade. In addition, an expert scoring method and a traditional evaluation model were used to estimate the comprehensive benefits of land reclamation at Hanjiawan coal mine in Shendong mining area. Land reclamation markedly improved the land type within the mining region and decreased the amount of damaged land, including subsided and occupied land. Moreover, land reclamation improved the available land area such as agricultural and construction land. The proposed model obtained an overall 63% increase in the land reclamation area. Different degrees of ecological, economic, and social benefits of Hanjiawan coal mine were observed; however, the ecological benefits were the most significant, with a growth rate of 56%. Based on the evaluation criteria, all benefits of the mining area after reclamation were good. Over time, land reclamation will offer greater comprehensive benefits to the mining area. Furthermore, this method can be used for precise evaluation of comprehensive benefits after land reclamation, and the assessment results will provide a reference basis for sustainable development of the mining area.

Fire Phoenix facilitates phytoremediation of PAH-Cd co-contaminated soil through promotion of beneficial rhizosphere bacterial communities

Pot experiments were conducted in a growth chamber to evaluate the phytoremediation efficiency and rhizosphere regulation mechanism of Fire Phoenix (a mixture of Festuca L.) in polycyclic aromatic hydrocarbon-cadmium (PAH-Cd) co-contaminated soils. Plant biomass, removal rates of PAHs and Cd, soil enzyme activity, and soil bacterial community were determined. After 150 days of planting, the removal rates of the total 4 PAHs and Cd reached 64.57% and 40.93% in co-contaminated soils with low-PAH (104.79-144.87 mg·kg^-1), and 68.29% and 25.40% in co-contaminated soils with high-PAH (169.17-197.44 mg·kg^-1), respectively. The polyphenol oxidase (PPO) activity decreased in soils having Fire Phoenix, while the dehydrogenase (DHO) activity increased as the changes of DHO activity had a strong positive correlation with the removal rates of PAHs and Cd in the low-PAH soils (r = 0.862 (P < 0.006) and 0.913 (P < 0.002), respectively). Meanwhile, successional changes in the bacterial communities were detected using high-throughput 454 Gs-FLX pyrosequencing of the 16S rRNA, and these changes were especially apparent for the co-contaminated soils with the low PAH concentration. The Fire Phoenix could promote the growth of Mycobacterium, Dokdonella, Gordonia and Kaistobacter, which played important roles in PAHs degradation or Cd dissipation. These results indicated that Fire Phoenix could effectively motivate the soil enzyme and bacterial community and enhance the potential for phytoremediation of PAH-Cd co-contaminated soils.

Assessment of a residual municipal solid waste landfill for prospective 'landfill mining'

Landfill mining is a prospective tool for the recycling of valuable materials (waste-to-material) and secondary fuel (waste-to-energy) from old, therefore more or less stabilised municipal solid waste landfills. The main target of Horizon 2020 'SMARTGROUND' R&D was improving the availability and accessibility of data and information from both urban landfills and mining dumps through a set of activities to integrate all the data - from existing sources and new information retrieved with time progress - in a single EU database. Concerning urban landfills, a new sampling protocol was designed on the basis of the current Hungarian national municipal solid waste analysis standards, optimised for landfill mining. This protocol was then applied in a sampling campaign on a municipal solid waste landfill in Debrecen, Hungary. The composition and parameters of the landfilled materials were measured as a 12-year timescale. The total wet and dry mass of the valuable components possible for utilisation was estimated.

Practical dechlorination of polyvinyl chloride wastes in NaOH/ethylene glycol using an up-scale ball mill reactor and validation by discrete element method simulations

To avoid the formation of undesired Cl compounds during polyvinyl chloride (PVC) wastes treatment and facilitate the recycling of valuable NaCl and dechlorinated hydrocarbons as feedstocks, advanced dechlorination (de-Cl) process should be developed. Here, an up-scale ball mill reactor was established for the de-Cl of real PVC wastes, including sealing strips from waste refrigerators and crushed cable coverings from waste cables. The effects of NaOH on de-Cl were validated with lab-scale studies and the influences of mechanical conditions were innovatively investigated. A maximum de-Cl degree of 99% was obtained with 1 M NaOH in ethylene glycol for sealing strips, whereas a maximum de-Cl degree of 92% was obtained with Φ1.27 cm stainless steel balls at a moderate rotation speed for cable coverings. The remaining Cl content in the sample residues was small and decreased with decreasing residue size, resulting in minimum contents of 0.49% and 0.61% for sealing strips and cable coverings, respectively. The de-Cl behavior was consistent with a shrinking-core model and the meaning of kinetic parameters was illustrated. The ball milling process was simulated by discrete element method (DEM). A positive correlation was observed between the apparent rate constant of the experimental de-Cl process and the specific impact energy calculated using DEM simulations. The combined experimental and simulation approach suggested that the surface of PVC is first dechlorinated and then crushed into fine particles by ball milling to expose the inner unreacted surface. For industrial application, the balance of chemical and mechanical conditions should be optimized.

Review on Indian Municipal Solid Waste Management practices for reduction of environmental impacts to achieve sustainable development goals

Open dumping is a common practice for MSW disposal in most of the Indian cities, apart from the metro-cities. This practice poses significant environmental and health risks due to toxic and greenhouse gases (GHGs) emission through direct combustion and/or decay of wastes. Therefore, integrated solid waste management (ISWM) using different methods viz., incineration, composting, anaerobic digestions, refuse derived fuel, material recovery facility and sanitary landfilling, is much needed. Accordingly, three waste management case scenarios were studied for year 2001-2051 by keeping weightage of sustainable development goals 2030 of India. Case I depicts Indian present scenario of waste management where 164-735 tonnes/year of wastes would be generated for year 2001-2051. Further, 60% of waste can be treated in case II that help in reducing the land requirement up to 40% from estimated conditions of 2031 i.e., 83.8 × 10⁷ m³. The case III is most ideal waste management condition for year 2031 to reduce 80% waste hence landfill requirement would minimize up to 16.76 × 10⁷ m³ where population is at controlled conditions. This article concludes the formal handling and treatment of ISWM would minimize the landfilling, where LCA can be an antidote to achieve sustainable development goals.

Eliciting stakeholder needs - An anticipatory approach assessing enhanced landfill mining

Landfill owners, governmental institutions, technology providers, academia and local communities are important stakeholders involved in Enhanced Landfill Mining (ELFM). This concept of excavating and processing historical waste streams to higher added values can be seen as a continuation of traditional landfill mining (LFM) and seems to be an innovative and promising idea for potential environmental and societal benefits. However, ELFM's profitability is still under debate, and environmental as well as societal impacts have to be further investigated. This study provides a first step towards an anticipatory approach, assessing ELFM through stakeholder integration. In the study, semi-structured interviews were conducted with various stakeholders, involved in a case study in Flanders, Belgium. Participants were selected across a quadruple helix (QH) framework, i.e. industrial, governmental, scientific, and local community actors. The research comprises 13 interviews conducted with an aim to elicit stakeholder needs for ELFM implementation using a general inductive approach. In total 18 different stakeholder needs were identified. The paper explains how the stakeholder needs refer to the different dimensions of sustainability, which groups of stakeholders they primarily affect, and what types of uncertainty could be influenced by their implementation. The stakeholder needs are structured into societal, environmental, regulatory and techno-economic needs. Results show additional economic, environmental, and societal aspects of ELFM to be integrated into ELFM research, as well as a need for the dynamic modeling of impacts.

A full-scale survey of sludge landfill: sludge properties, leachate characteristics and microbial community structure

In this study, a full-scale survey was conducted of a sludge landfill that had been sealed for 10 years to investigate sludge properties, leachate characteristics and microbial community structure. Vertical distribution of sludge and leachate pollutants in the landfill site showed that the sludge and soluble pollutants in the leachate were both distributed almost evenly even after long-term anaerobic digestion, and higher concentrations of soluble pollutants and richness of microbial community were observed at the middle layer. Compared to dewatered excess sludge generated from the activated sludge process before landfill, landfill sludge had a much lower organic content (28.1%), smaller particle size and worse dewaterability. Compared to municipal waste landfill, sludge landfill generated leachate with a lower concentration of organic substances, and comparable concentrations of nitrogenous and phosphorus pollutants. Bacterial community analysis by Illumina MiSeq sequencing showed that Proteobacteria, Firmicutes, Chloroflexi, Actinobacteria and Bacteroidetes were the major phyla, and some new genera (Methylocystaceae, Mariniphaga and Aminicenantes) were enriched in the sludge landfill. Archaeal community analysis showed that aceticlastic methanogenesis by Methanosaeta and Methanosarcina was the main pathway for methane production in the sludge landfill, in contrast to waste landfill with hydrogenotrophic methanogenesis as the main pathway.

Systematic assessment of critical factors for the economic performance of landfill mining in Europe: What drives the economy of landfill mining?

Landfill mining (LFM) is a strategy to mitigate environmental impacts associated with landfills, while simultaneously recovering dormant materials, energy carriers, and land resources. Although several case study assessments on the economy of LFM exist, a broader understanding of the driving factors is still lacking. This study aims at identifying generically important factors for the economy of LFM in Europe and understanding their role in developing economically feasible projects in view of different site, project and system-level conditions. Therefore, a set-based modeling approach is used to establish a large number (531,441) of LFM scenarios, evaluate their economic performance in terms of net present value (NPV), and analyze the relationships between input factors and economic outcome via global sensitivity analysis. The scenario results range from -139 Euro to +127 Euro/Mg of excavated waste, with 80% of the scenarios having negative NPVs. Variations in the costs for waste treatment and disposal and the avoided cost of alternative landfill management (i.e. if the landfill was not mined) have the strongest effect on the scenario NPVs, which illustrates the critical role of system level factors for LFM economy and the potential of policy intervention to incentivize LFM. Consequently, system conditions should guide site selection and project development, which is exemplified in the study for two extreme regional archetypes in terms of income and waste management standard. Future work should further explore the developed model to provide decision support on LFM strategies in consideration of alternative purposes, stakeholders, and objectives.

Scaling up the treatment of the fine fraction from landfill mining: Mass balance and cost structure

The treatment of the fine fraction (FF) obtained from landfill mining is necessary in order to reduce the amount of organic matter and biological activity in FF, thus increasing its potential to be utilized after landfill mining. This paper suggests the scaled up anaerobic and aerobic treatment of FF, with or without continuous irrigation, and presents the mass balance and cost structure of such treatment based on two hypothetical landfills. The physical treatment structure for the treatment of FF should prevent emissions, and in this paper, it includes suitable bottom and top liners as well as the collection and treatment of the gaseous and leachate emissions formed during the treatment. Methane produced in anaerobic treatments could either be utilized for energy recovery or be flared. The cost of the anaerobic and aerobic treatment of FF, including investments and operation costs, are 20-65 €/t FF, depending on size of the landfill. The costs of anaerobic treatment and passive aeration are similar, and active aeration is slightly more expensive, but the cost of the continuous irrigation is the most significant, as it multiplies the leachate treatment costs. The overall cost of treatment could be lowered by reducing the treatment time and utilizing existing landfill structures. The results of this paper can be used in planning and estimating the cost of the biological treatment of FF when evaluating landfill mining projects, as the fate of FF may have a major impact on the economics of landfill mining projects.

Urban mining demonstration bases in China: A new approach to the reclamation of resources

This paper aims to examine a key Chinese circular economy program, the Urban Mining Demonstration Base Construction (UMDBC) Program, for its successes, experiences and existing problems. Using publicly available data and detailed investigation and analysis, we discuss the details of the UMDBC Program. Although the whole program has been implemented and has made significant progress, some problems exist. Our findings suggest that it is more important for the Chinese government to provide an effective legal framework than merely provide financial support. The experiences and lessons from research into the UMDBC Program could serve as an example to other developing countries facing environmental and resource pressures.

Conversion of solid waste to activated carbon to improve landfill sustainability

Heterogeneous composite wastes from landfills were evaluated as precursors for the generation of activated carbon (AC). A single-step chemical activation process was applied involving irradiation with microwave energy and impregnation with KOH. The average percentage yield of AC from active landfill precursor was higher than that from closed landfill for all depths sampled. Increase in impregnation ratio and irradiation power decreased the average percentage yield for both landfill precursors (active: 38.1 to 33.1%; closed: 42.1 to 33.3%). The optimum pH range for adsorption of methylene blue was pH 6-7, while adsorption increased with increase in temperature over the range 30 to 50°C. Carbonyl and hydroxyl groups were the major functional groups on the surface of AC. The properties of the AC are potentially suitable for the removal of cationic dyes and pollutants. AC generated from the landfill composite was comparable to that from other biomass being managed through AC generation. This is the first report to demonstrate the possible reuse of landfill composite as AC. The reuse option of landfill composite could provide a means of sustainable management of landfilled municipal waste.

Decision making guidelines for mining historic landfill sites in Flanders

This study aims at showing how the United Nations Framework Classification for Resources (UNFC) can help to classify potential landfill mining projects with different levels of maturity, from exploration to production, under technical, socio-economic and project-planning aspects. Taking the example of three former landfill sites in Flanders general decision making guidelines regarding the future management of old landfills are provided. Using the ECLAR methodology for the evaluation (E) and classification (CL) of anthropogenic resources (AR), the individual projects, where clean land and/or materials are recovered, are mapped under the three-dimensional UNFC system. The Bornem project, yields a negative Net Present Value (NPV) of -17 Mio € (-44 €/t of excavated waste), i.e. the project is currently not economically viable. In case of changing key parameters the landfill has, however, reasonable prospects for future economic extraction. The Turnhout land development turned out to be economically viable with a NPV of 361,000 € (8 €/t of excavated waste). The Zuienkerke remediation project is at a too early stage to determine its socioeconomic viability. The main focus to compare and prioritize potential landfill mining projects in Flanders should be on (1) site specific conditions (e.g. landfill's composition, land prices), (2) project related factors (e.g. remediation required vs. resource/land recovery, selected technologies and project set-ups, private vs. public evaluation perspective) and (3) the timing of mining, considering future development of costs, prices, laws, available data and information.

A multiobjective optimization model and an orthogonal design-based hybrid heuristic algorithm for regional urban mining management problems

In this paper, a multiobjective mixed-integer piecewise nonlinear programming model (MOMIPNLP) is built to formulate the management problem of urban mining system, where the decision variables are associated with buy-back pricing, choices of sites, transportation planning, and adjustment of production capacity. Different from the existing approaches, the social negative effect, generated from structural optimization of the recycling system, is minimized in our model, as well as the total recycling profit and utility from environmental improvement are jointly maximized. For solving the problem, the MOMIPNLP model is first transformed into an ordinary mixed-integer nonlinear programming model by variable substitution such that the piecewise feature of the model is removed. Then, based on technique of orthogonal design, a hybrid heuristic algorithm is developed to find an approximate Pareto-optimal solution, where genetic algorithm is used to optimize the structure of search neighborhood, and both local branching algorithm and relaxation-induced neighborhood search algorithm are employed to cut the searching branches and reduce the number of variables in each branch. Numerical experiments indicate that this algorithm spends less CPU (central processing unit) time in solving large-scale regional urban mining management problems, especially in comparison with the similar ones available in literature. By case study and sensitivity analysis, a number of practical managerial implications are revealed from the model.

IMPLICATIONS

Since the metal stocks in society are reliable overground mineral sources, urban mining has been paid great attention as emerging strategic resources in an era of resource shortage. By mathematical modeling and development of efficient algorithms, this paper provides decision makers with useful suggestions on the optimal design of recycling system in urban mining. For example, this paper can answer how to encourage enterprises to join the recycling activities by government's support and subsidies, whether the existing recycling system can meet the developmental requirements or not, and what is a reasonable adjustment of production capacity.

Designing and examining e-waste recycling process: methodology and case studies

Increasing concerns on resource depletion and environmental pollution have largely obliged electrical and electronic waste (e-waste) should be tackled in an environmentally sound manner. Recycling process development is regarded as the most effective and fundamental to solve the e-waste problem. Based on global achievements related to e-waste recycling in the past 15 years, we first propose a theory to design an e-waste recycling process, including measuring e-waste recyclability and selection of recycling process. And we summarize the indicators and tools in terms of resource dimension, environmental dimension, and economic dimension, to examine the e-waste recycling process. Using the sophisticated experience and adequate information of e-waste management, spent lithium-ion batteries and waste printed circuit boards are chosen as case studies to implement and verify the proposed method. All the potential theory and obtained results in this work can contribute to future e-waste management toward best available techniques and best environmental practices.

Material flow-based economic assessment of landfill mining processes

This paper provides an economic assessment of alternative processes for landfill mining compared to landfill aftercare with the goal of assisting landfill operators with the decision to choose between the two alternatives. A material flow-based assessment approach is developed and applied to a landfill in Germany. In addition to landfill aftercare, six alternative landfill mining processes are considered. These range from simple approaches where most of the material is incinerated or landfilled again to sophisticated technology combinations that allow for recovering highly differentiated products such as metals, plastics, glass, recycling sand, and gravel. For the alternatives, the net present value of all relevant cash flows associated with plant installation and operation, supply, recycling, and disposal of material flows, recovery of land and landfill airspace, as well as landfill closure and aftercare is computed with an extensive sensitivity analyses. The economic performance of landfill mining processes is found to be significantly influenced by the prices of thermal treatment (waste incineration as well as refuse-derived fuels incineration plant) and recovered land or airspace. The results indicate that the simple process alternatives have the highest economic potential, which contradicts the aim of recovering most of the resources.

Cost-benefit calculation of phytoremediation technology for heavy-metal-contaminated soil

Heavy-metal pollution of soil is a serious issue worldwide, particularly in China. Soil remediation is one of the most difficult management issues for municipal and state agencies because of its high cost. A two-year phytoremediation project for soil contaminated with arsenic, cadmium, and lead was implemented to determine the essential parameters for soil remediation. Results showed highly efficient heavy metal removal. Costs and benefits of this project were calculated. The total cost of phytoremediation was US$75,375.2/hm(2) or US$37.7/m(3), with initial capital and operational costs accounting for 46.02% and 53.98%, respectively. The costs of infrastructures (i.e., roads, bridges, and culverts) and fertilizer were the highest, mainly because of slow economic development and serious contamination. The cost of phytoremediation was lower than the reported values of other remediation technologies. Improving the mechanization level of phytoremediation and accurately predicting or preventing unforeseen situations were suggested for further cost reduction. Considering the loss caused by environmental pollution, the benefits of phytoremediation will offset the project costs in less than seven years.

Monetizing the social benefits of landfill mining: Evidence from a Contingent Valuation survey in a rural area in Greece

Despite the emerging global attention towards promoting waste management policies that reduce environmental impacts and conserve natural resources, landfilling still remains the dominant waste management practice in many parts of the world. Owing to this situation, environmental burdens are bequeathed to and large amounts of potentially valuable materials are lost for future generations. As a means to undo these adverse effects a process known as landfill mining (LFM) could be implemented provided that economic feasibility is ensured. So far, only a few studies have focused on the economic feasibility of LFM from a private point of view and even less studies have attempted to economically justify the need for LMF projects from a social point of view. This paper, aiming to add to the limited literature in the field, presents the results of a survey conducted in a rural district in Greece, by means of the Contingent Valuation method (CVM) in order to estimate society's willingness to pay for LFM programs. According to the empirical survey, more than 95% of the respondents recognize the need for LFM programs. Nevertheless, only one-fourth of the respondents are willing to pay through increased taxes for LFM, owing mainly to economic depression and unemployment. Those who accept the increased tax are willing to pay about €50 per household per year, on average, which results in a mean willingness to pay (WTP) for the entire population under investigation of around €12 per household per year. The findings of this research work provide useful insights about the 'dollar-based' benefits of LFM in the context of social cost-benefit analysis of LFM projects. Yet, it is evident that further research is necessary.

Assessment of environmental and economic feasibility of Enhanced Landfill Mining

This paper addresses the environmental and economic performance of Enhanced Landfill Mining (ELFM). Based on life cycle assessment and life cycle costing, a detailed model is developed and is applied to a case study, i.e. the first ELFM project in Belgium. The environmental and economic analysis is performed in order to study the valorisation of different waste types in the landfill, such as municipal solid waste, industrial waste and total waste. We found that ELFM is promising for the case study landfill as greater environmental benefits are foreseen in several impact categories compared to the landfill's current situation (the 'Do-nothing' scenario). Among the considered processes, the thermal treatment process dominates both the environmental and economic performances of ELFM. Improvements in the electrical efficiency of thermal treatment process, the calorific value of refuse derived fuel and recovery efficiencies of different waste fractions lead the performance of ELFM towards an environmentally sustainable and economically feasible direction. Although the environmental and economic profiles of ELFM will differ from case to case, the results of this analysis can be used as a benchmark for future ELFM projects.

Characteristics of H2S emission from aged refuse after excavation exposure

Hydrogen sulfide (H2S(g)) emission from landfills is a widespread problem, especially when aged refuse is excavated. H2S(g) emission from aged refuse exposed to air was investigated and the results showed that large amounts of H2S(g) can be released, especially in the first few hours after excavation, when H2S(g) concentrations in air near refuse could reach 2.00 mg m(-3). Initial exposure to air did not inhibit the emission of H2S(g), as is generally assumed, but actually promoted it. The amounts of H2S(g) emitted in the first 2 d after excavation can be very dangerous, and the risks associated with the emission of H2S(g) could decrease significantly with time. Unlike a large number of sulfide existed under anaerobic conditions, the sulfide in aged municipal solid waste can be oxidized chemically to elemental sulfur (but not sulfate) under aerobic conditions, and its conversion rate was higher than 80%. Only microorganisms can oxidize the reduced sulfur species to sulfate, and the conversion rate could reach about 50%. Using appropriate techniques to enhance these chemical and biological transformations could allow the potential health risks caused by H2S(g) after refuse excavation to be largely avoided.