Circular economy life cycle cost for kerbside waste material looping process.

Rapid expansion in urban areas has engendered a superfluity of municipal solid waste (MSW) stemming from contemporary civilization, encompassing commercial sectors and human undertakings. Kerbside waste, a type of MSW, has the potential for recycling and reuse at the end of its first life cycle, but is often limited to a linear cycle. This study aimed to assess the life cycle costs of different separation and recycling methods for handling kerbside waste. A new life cycle cost model, drawing from the circular economy's value retention process (VRP) model, has been created and applied to assess the continuous recycling of kerbside glass. The study investigates two key separation techniques, kerbside recycling mixed bin recycling (KRMB) kerbside glass recycling separate bin (KGRSB) and analyses their impact on the life cycle cost of the recycling process. Additionally, the research explores two approaches of recycling and downcycling: closed-loop recycling, which pertains to the recycling of glass containers, and open-looped recycling, which involves the use of recycled glass in asphalt. The results showed when use annually collected waste as the functional unit, the KRMB model incurred lower costs compared to the KGRSB model due to its lower production output. However, when evaluated over a 1-ton production of glass container and asphalt, the KGRSB method demonstrated superior cost performance with a 40-50% reduction compared to the KRMB method. The open-loop recycling method (asphalt) incurred a higher cost compared to the closed-loop recycling method due to its larger production volume over a 21-year period.

Climate impacts of landfill gas emissions: Analysis for 20-year and 100-year time horizons.

Climate impacts of landfill gas emissions were investigated for 20- and 100-year time horizons to identify the effects of atmospheric lifetimes of short- and long-lived drivers. Direct and indirect climate impacts were determined for methane and 79 trace species. The impacts were quantified using global warming potential, GWP (direct and indirect); atmospheric degradation (direct); tropospheric ozone forming potential (indirect); secondary aerosol forming potential (indirect) and stratospheric ozone depleting potential (indirect). Effects of cover characteristics, landfill operational conditions, and season on emissions were assessed. Analysis was conducted at five operating municipal solid waste landfills in California, which collectively contained 13% of the waste in place in the state. Climate impacts were determined to be primarily due to direct emissions (99.5 to 115%) with indirect emissions contributing -15 to 0.5%. Methane emissions were 35 to 99% of the total emissions and the remainder mainly greenhouse gases (hydro)chlorofluorocarbons (up to 42% of total emissions) and nitrous oxide. Cover types affected emissions, where the highest emissions were generally from intermediate covers with the largest relative landfill surface areas. Landfill-specific direct emissions varied between 683 and 103,411 and between 381 and 37,925 Mg CO2-eq./yr for 20- and 100-yr time horizons, respectively. Total emissions (direct + indirect) were 680 to 103,600 (20-yr) and were 374 to 38,108 (100-yr) Mg CO2-eq./yr. Analysis time horizon significantly affected emissions. The 20-yr direct and total emissions were consistently higher than the 100-yr emissions by up to 2.5 times. Detailed analysis of time-dependent climate effects can inform strategies to mitigate climate change impacts of landfill gas emissions.

DFT simulated Quercetin imprinted polymer: Selective recovery of Quercetin from onion solid waste.

Onion peels (OP) are byproduct of food processing industries that poses economic and environmental challenges. However, being rich source of bioactive compounds like Quercetin (Qt), a polyphenolic antioxidant with potential health benefits, harnessing value from such waste can imbibe sustainable practices and protect environment. With this view, the present study targets selective recovery of Qt from OP waste using rationally designed molecularly imprinted polymer (MIP). Density Functional Theory (DFT) was used for the theoretical selection of the best conformer of Qt (template), methacrylic acid (MAA) as functional monomer, ratio of Qt-MAA for getting stable pre-polymerization complex, and to avoid hit and trial experiments. The theoretical results were validated experimentally by synthesizing MIP/ control polymer (NIP) using MAA as functional monomer, EGDMA as a cross-linker and AIBN as initiator. Synthesized MIP/NIP were characterized using various characterization techniques to confirm successful imprinting. Prepared MIP and NIP could effectively rebind the Qt molecule with binding capacity of 46.67 and 20.89 mg g-1 respectively. Furthermore, synthesized MIP could selectively recover 62.81 % of Qt from 1 g of dry onion peel powder. This study can be effectually used for sustainable recovery of Qt in large scale for various foods, cosmetic and pharmaceutical applications.

Impact of solid waste dumping on soil quality and its potential risk on human health and environment.

The soil, comprising minerals, organic matter, and living organisms, serves as a critical component of our environment. However, anthropogenic activities, such as uncontrolled sewage disposal and industrial waste, have led to pervasive soil pollution, impacting ecosystems and human health. This comprehensive study scrutinizes the intricate dynamics of soil pollution resulting from open waste dumping, specifically examining its impact on the health of local communities and the environment in Haridwar municipality. In this study, four solid waste dumping sites were meticulously surveyed, with soil samples analyzed for 19 parameters through statistical tools like one-way ANOVA, Kruskal-Wallis tests, soil pollution indices, and potential health risk assessment. The Geo-accumulation Index (Igeo) and contamination factor (CF) followed the heavy metals in the order of Zn > Mn > Fe > Cu in all selected sites. Additionally, a potential health risk assessment considered ingestion, inhalation, and dermal exposure pathways, revealing a high non-carcinogenic risk of metals (Mn > Fe > Zn > Cu) for both children and adults. In the ingestion pathway, the hazard quotient indicated a high risk of metals for both children and adults in the range of 1192.73 to 2066.94 for child and 191.98 to 312.16 for adults. Crucially, the HQ revealed potential health risks, emphasizing the urgency of addressing metal contamination. However, the findings indicate that dumping sites directly or indirectly affects the local people of Haridwar municipality. Therefore, this study provides a baseline framework for minimizing the impact of dumping sites on local population and the environment.

Plastics and plastic-bound toxic metals in municipal solid waste compost from Sri Lanka.

This study examined plastics and toxic metals in municipal solid waste compost from various regions in Sri Lanka. Plastics were extracted using density separation, digested using wet peroxidation, and identified using Fourier Transform Infra-Red Spectroscopy in Attenuated Total Reflection mode. Compost and plastics were acid-digested to quantify total Cd, Cu, Co, Cr, Pb, and Zn concentrations and analyzed for the bioavailable fraction using 0.01 M CaCl2. Notably, plastics were highly abundant in most compost samples. The main plastic types detected were polyethylene, polypropylene, and cellophane. However, the average Cd, Cu, Co, Cr, Pb, and Zn levels were 0.727, 60.78, 3.670, 25.44, 18.95, and 130.7 mg/kg, respectively, which are well below the recommended levels. Zn was the most bioavailable (2.476 mg/kg), and Cd was the least bioavailable (0.053 mg/kg) metal associated with compost. The Contamination factor data show that there is considerable enhancement of Cd and Cu, however, Cr, Cu, Co, and Pb are at low contamination levels. Mean geo accumulation index values were 1.39, 1.07, - 1.06, - 0.84, - 0.32, and 0.08 for Cd, Cu, Co, Cr, Pb, and Zn. Therefore, the contamination level of compost samples with Cd and Cu ranges from uncontaminated to contaminated levels, whereas Co, Cr, Pb, and Zn are at uncontaminated levels. Despite no direct metal-plastic correlation, plastics in compost could harm plants, animals, and humans due to ingestion. Hence, reducing plastic and metal contamination in compost is crucial.

Facing the solid waste of cotton straw and plastic mulch film mixture in China: Centralized or decentralized pyrolysis facility?

The widespread use of plastic mulch film (PMF) has led to significant environmental pollution, with PMF residues dispersed and mixed with straw and soil, posing challenges for recycling. Here, we proposed the mobile pyrolysis facility for the cotton straw and mulch film mixture (CMM) to mitigate the collection, storage, and transportation costs, while the application of co-pyrolysis technology for CMM conversion could improve the added value of products. Additionally, centralized combustion power generation and centralized pyrolysis systems were also established to evaluate and compare their sustainability from economic and environmental perspectives. Results showed that mobile pyrolysis has better economic performance than the centralized scenarios, due to its high internal rate of return (31 %) and significant net present value (29.21 M USD). Meanwhile, the mobile pyrolysis facility achieved a GWP of -1.298 kgCO2-eq/kg, reducing emissions by 70.79 % and 38.82 % compared to the two centralized scenarios. In conclusion, mobile pyrolysis technology provides a promising solution for PMF residue recycling because of its economically competitive approach with a lower carbon footprint.

Characterization of solid waste deposit using electrical resistivity tomography and time domain induced polarization.

The whopping increase in solid waste landfills poses serious threats to the environment. Compared to the drilling method, geophysical methods are effective, non-invasive techniques for delineating the contaminant distribution. In this study, electrical resistivity tomography (ERT) and induced polarization (IP) were used to investigate a solid waste deposit. The results of ERT/IP imaging illustrate the potential of the method in environmental studies. Based on the results of 21 survey lines, geo-electrical signals can be summarized as three types: with only high resistivity for construction & demolition wastes (CDWs) areas (RO type), contaminated soil for high chargeability (CO type), and contaminants under CDWs layer have both high resistivity and chargeability (RC type). Chargeability values over 10.2 mV/V correspond to contaminated soil with an overall concentration larger than 75 mg/kg. With the three-dimensional interpolation results and the determined chargeability criteria, the total volume of contaminated soil is 40,555 cubic meters. Finally, comparing the efficiency, cost and results of IP and drilling sampling methods shows that the IP is an efficient, low-cost and high-resolution contamination characterization. The results support that ERT/IP information can fulfill rapid and initial identification as a reliable tool in engineering and environmental investigations.

Recognition of screening out hierarchical toxic contaminants tuned by quantified pseudo-components from complex engineering co-combustion.

Co-combustion of industrial and municipal solid wastes has emerged as the most promising disposal technology, yet its effect on unknown contaminants generation remains rarely revealed due to waste complexity. Hence, six batches of large-scale engineering experiments were designed in an incinerator of 650 t/d, which overcame the inauthenticity and deviation of laboratory tests. 953-1772 non-targeted compounds were screened in fly ash. Targeting the impact of co-combustion, a pseudo-component matrix model was innovatively integrated to quantitatively extract nine components from complex wastes grouped into biomass and plastic. Thus, the influence was evaluated across eight dimensions, covering molecular characteristics and toxicity. The effect of co-combustion with biomass pseudo-components was insignificant. However, co-combustion with high ratios of plastic pseudo-components induced higher potential risks, significantly promoting the formation of unsaturated hydrocarbons, highly unsaturated compounds (DBE≥15), and cyclic compounds by 19 %- 49 %, 17 %- 31 %, and 7 %- 27 %, respectively. Especially, blending with high ratios of PET plastic pseudo-components produced more species of contaminants. Unique 2 Level I toxicants, bromomethyl benzene and benzofuran-2-carbaldehyde, as well as 4 Level II toxicants, were locked, receiving no concern in previous combustion. The results highlighted risks during high proportion plastics co-combustion, which can help pollution reduction by tuning source wastes to enable healthy co-combustion.

Regulatory compliance of PCDD/F emissions by a municipal solid waste incinerator. A case study in Sant Adrià de Besòs, Catalonia, Spain.

Despite incineration is an important emission source of toxic pollutants, such as heavy metals and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), it is still one of the most widely used methods for the management of municipal solid waste. The current paper summarizes the results of a 20-year follow-up study of the emissions of PCDD/Fs by a municipal solid waste incinerator (MSWI) in Sant Adrià de Besòs (Catalonia, Spain). Samples of ambient air, soils and herbage were periodically collected near the facility and the content of PCDD/Fs was analyzed. In the last (2017) survey, mean levels in soil were 3.60 ng WHO-TEQ/kg (range: 0.40-10.6), being considerably higher than the mean concentrations of PCDD/Fs in soil samples collected near other MSWIs in Catalonia. Moreover, air PCDD/F concentrations were even higher than those found in a previous (2014) survey, as they increased from 0.026 to 0.044 pg WHO-TEQ/m3. Ultimately, the PCDD/F exposure would be associated to a cancer risk (2.5 × 10-6) for the population living in the surrounding area. Globally, this information indicates that the MSWI of Sant Adrià de Besòs could have had a negative impact on the environment and potentially on public health, being an example of a possible inappropriate management for years. The application of Best Available Techniques to minimize the emission of PCDD/Fs and other chemicals is critical.

Impacts of advanced metals recovery on municipal solid waste incineration bottom ash: aggregate characteristics and performance in portland limestone cement concrete.

The optimization of alternative materials in concrete production continues to garner considerable attention in order to meet sustainability goals and supplement natural materials. Portland limestone cement (PLC) and municipal solid waste incineration (MSWI) bottom ash (BA) have been proposed separately as green cement and coarse aggregate supplement in low-strength concrete production, creating sustainable products and alternative disposal scenario for a waste material. This study discusses the impact of advanced ash processing techniques on aggregates and presents the performance of concrete incorporating both of these products with PLC for the first time. Two sources of MSWI BA were investigated, one as-produced (TMR) and one processed with novel advanced metals recovery (AMR). The AMR process reduced total Al content in ash compared to TMR (20,500 vs 17,000 mg/kg), though not aluminum oxide content, as the AMR process targets metallic aluminum. A composition study on both aggregates supports a reduction in ferrous and non-ferrous metals following the AMR process. All control and test mixes met 28-day compressive strength requirements (17 Mpa). Both AMR and TMR MSWI BA-amended concretes yielded compressive strengths below control specimens (no ash) ranging from 17 to 23 MPa, with little to no difference observed dependent on MSWI BA processing. The life-cycle discussion supports benefits deriving from supplementing naturally mined materials and recovering ferrous and nonferrous metals with the AMR process.

The reduction of the carbon footprint of municipal solid waste management via source classification and supporting strategies: An analysis for the megacity of Shenzhen.

Municipal solid waste (MSW) management is a critical concern in megacities that depend heavily on external material and energy inputs but lack space for waste disposal. MSW treatment is a significant contributor to carbon emissions. The implementation of source classification improved the overall MSW management system and enhanced resource recovery from MSW. However, the precise contribution of source classification to carbon emissions reduction remains unclear. This study aimed to analyze the carbon emissions evolution in the MSW management of Shenzhen, a prototypical megacity in China, using data from 2006 to 2020 and employing carbon footprint assessment methodologies. The results demonstrated that source classification reduced the carbon emissions from 0.19-0.25 to 0.14-0.18 t CO2-eq/t MSW when considering the contribution of the urban environmental sanitation management department. The entire MSW management system becomes a carbon sink when considering recyclables collected by commercial enterprises. Although the source classification complicated the collection and transportation of MSW, the carbon offset effect of recycling food waste and recyclables was more significant than that of carbon emissions from collection and transport. Moreover, the landfill gas recovery rate critically influenced the carbon emissions of landfill-based MSW management systems. In contrast, the recovery of plastics was crucial for determining carbon emissions from incineration-based MSW management systems.

Quantification and forecast of GHG emissions from municipal solid wastes by multi-expression programming method.

The municipal solid waste (MSW) management is significantly contributing to global greenhouse gas (GHG) emissions. Analyzing the emission pattern of GHGs from MSW is essential for formulating appropriate carbon mitigation policies. Based on IPCC Models, GHG emissions from MSW were calculated in Chinese provinces from 2004 to 2021 by landfilling and incineration operations, separately. Landfilling and incineration generated approximately 1271 MtCO2-eq and 198 MtCO2-eq from 2004 to 2021, respectively. GHG emissions from landfilling increased from 2004 to 2020 and declined in 2021, while GHG emissions from incineration demonstrated an increasing trend with three distinct growth stages. A panel regression model was then employed to identify the key factors influencing GHG emissions. GDP and population are positively related to GHG emissions from landfills, while PCCE is negatively related to GHG emissions from landfills. GDP and PCCE have a positive impact on GHG emissions from incineration, while population showed no significant impact. Multi-expression programming was used to develop an explicit model, forecasting GHG emissions from MSW by 2030. From 2022 to 2024, GHG emissions from landfills will quickly decrease, while GHG emissions from incineration will rapidly increase. Subsequently, the GHG emission rate of incineration will slow down, and GHGs from landfilling will slowly decrease due to no MSW for landfill disposal. The methods and results provide insightful information for policy-makers and waste management sector.

Reuse potential of municipal solid waste incinerator bottom ash as secondary aggregate: Material characteristics, persistent organic pollutant content and effects of pH and selected environmental lixiviants on leaching behaviour.

Increasing municipal solid waste (MSW) production poses challenges for sustainable urban development. Modern energy-from-waste (EfW) facilities incinerate MSW, reducing mass and recovering energy. In the UK, MSW incineration bottom ash (MSW IBA) is primarily reused in civil engineering applications. This study characterizes UK-produced MSW IBA, examining its pH-dependent leaching behaviour and response to environmental lixiviants. Results show predominant components include a melt phase, primary glass and fine ash aggregations, and a chemical composition dominated by SiO2 (30-50 %), CaO (∼15 %), Fe2O3 (∼10 %), and Al2O3 (∼8%). X-ray absorption near edge structure (XANES) analysis shows that Zn and Cu are most likely oxygen-bound (adsorbed to oxy-hydroxides and as oxides) with some sulphur bound. Polychlorinated biphenyls (PCBs) and polychlorinated dibenzodioxins/furans (PCDD/Fs) are well below regulatory limits, and polycyclic aromatic hydrocarbons (PAHs) were undetectable. Leaching tests indicate trace elements mobilize at pHs ≤ 6. With a natural pH of 11.3 and high buffering capacity, significant acid inputs to the MSW IBA are required to reach this pH, which are improbable in the environment. Wood chip additions increase leachate's dissolved organic carbon (DOC) and reduce pH, but had minimal impact on metal-leaching behaviour. Synthetic plant exudate solutions minimally affect metal leaching at realistic concentrations, only enhancing leaching at ≥ 1500 mg l-1 DOC. This work supports MSW IBA's low-risk in specified civil engineering applications.

Comparison and mechanism analysis of MgO, CaO, and Portland cement for immobilization of heavy metals in MSWI fly ash.

The significant production of municipal solid waste incineration fly ash (MSWI FA) underscores the importance of developing efficient solidification materials. This study employed MgO and CaO for immobilizing MSWI FA (with a 70% fly ash incorporation), and the immobilization effect was compared with that of Portland cement (PC). Experimental findings revealed that MgO exhibited the most effective stabilization for heavy metals (Cd, Cu, Pb, and Zn) compared to CaO and PC. XRD, FTIR, TG, and SEM analysis indicated that the principal hydration products in MSWI FA binders solidified with MgO, CaO, and PC were Mg(OH)2, CaCO3, and C-S-H gel, respectively. Mg(OH)2 efficiently immobilized heavy metals through chemical complexation and surface adsorption mechanisms. The MgO-treated MSWI FA demonstrated the highest residual fractions and the lowest easily leachable fractions. Moreover, the leaching characteristics of heavy metals were significantly influenced by the pH level, so MgO-treated MSWI FA with a leachate pH of 9.18 achieved the precipitation and stabilization of most heavy metals. In summary, this study provided an effective material selection for MSWI FA immobilization and presented a novel strategy for MSWI FA management.

Multi-criteria sustainability assessment of solid waste management in Jordan.

This study comprehensively evaluates Jordan's municipal solid waste (MSW) management sector from 2022 to 2030, in alignment with Jordan Vision 2030. This study introduces new sustainability indicators and innovative waste management alternatives to address the challenges of rapid industrialization and population growth. Four strategic scenarios-1) recycling, composting, and sanitary landfilling; 2) recycling, anaerobic digestion, and sanitary landfilling; 3) incineration and sanitary landfilling; and 4) sanitary landfilling alone-were assessed against the business-as-usual scenario. Using multi-criteria decision analysis (MCDA) and sensitivity analysis, this study evaluates net greenhouse gas emissions, annual operating expenses, revenue streams, and employment rates to measure environmental, economic, and social sustainability. The results indicate that Scenario 1 is the optimal scenario for integrating a material recovery facility (MRF) with a composting plant and sanitary landfill, achieving the lowest greenhouse gas emissions, annual costs, and employment opportunities. This study offers practical and sustainable solutions to Jordan's waste management challenges, provides novel insights through the developed MCDA and sensitivity analysis, and significantly contributes to sustainability research.

New insight into the spatio-temporal patterns of functional groups of hotspot inside the composting aggregates by synchrotron-based FTIR in hyperthermophilic composting.

Hyperthermophilic composting (HTC) is a recently developed and highly promising organic fraction of municipal solid waste (OFMSW) treatment technology. Investigation of organic matter (OM) dynamics in compost particle is thus crucial for the understanding of humification of HTC process. Herein, this work aimed to study the chemical and structural changes of OM at the molecular level during HTC of OFMSW using EEM and SR-FTIR analyses. Additionally, two-dimensional correlation spectroscopy (2D-COS) was also utilized to probe and identify the changes in chemical constituents and functional groups of organic compounds on the surface of compost particles during different composting periods. Results show that SR-FTIR can detect fine-scale (~µm) changes in functional groups from the edges to the interior of compost particles during different composting periods by mapping the particles in situ. In the hyperthermophilic stage (day 9), the extracted µ-FTIR spectrum reveals a distinct boundary between anaerobic and aerobic regions within the compost particle, with a thickness of anaerobic zone (1460 cm-1) of approximately 30 µm inside the particle's core. This provides direct evidence of anaerobic trends at compost microscales level within compost particles. 2D-COS analysis indicated that organic functional groups gradually agglomerated in the order of 1330 > 2930 > 3320 > 1600 > 1030 > 895 cm-1 to the core skeleton of cellulose degradation residues, forming compost aggregates with well physicochemical properties. Overall, the first combination of SR-FTIR and EEM provides complementary explanations for the humification mechanism of HTC, potentially introducing a novel methodology for investigating the environmental behaviors and fates of various organic contaminants associated with OM during the in-situ composting biochemical process.

Quantification and polymeric characterization of microplastics in composts and their accumulation in lettuce.

Organic fertilizers have become a vector for the transport of microplastics (MPs), which pose human health concerns through the food chain. This study aimed to quantify and characterize MPs in eight different compost samples of various raw materials and their subsequent translocation to lettuce (Lacuta sativa) grown on contaminated composts. The results revealed that the MP abundance ranged from 3810 to 16530 MP/kg. Municipal solid waste compost (MSWC) had highest abundance (16082 ± 632 MP/kg), followed by leaf compost (LC) and organic compost (OC) (6299 ± 1011 and 3680 ± 419 MP/kg, respectively). MPs of <100 µm in size were most dominant in MSWC and LC. Fragments and fibers were the prevalent shape types, with white/transparent colored MPs being more abundant. Polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET) were the dominant polymers. MPs accumulation in the lettuce leaves was greatest in the lettuce plants grown on MSWC, followed by those grown on LC and OC, indicating that MSWC grown lettuce is not suitable for human consumption. The decrease in the growth (leaf length, number of leaves, leaf fresh and weights) and physiological (membrane stability index, relative water contents) parameters of lettuce was in line with the trend of MP accumulations. Hence, it is highly important to regulate the plastic contents in compost because it is a threat to ecosystems and human health.

Linking microbial population dynamics in anaerobic bioreactors to food waste type and decomposition stage.

A key question in anaerobic microbial ecology is how microbial communities develop over different stages of waste decomposition and whether these changes are specific to waste types. We destructively sampled over time 26 replicate bioreactors cultivated on fruit/vegetable waste (FVW) and meat waste (MW) based on pre-defined waste components and composition. To characterize community shifts, we examined 16S rRNA genes from both the leachate and solid fractions of the waste. Waste decomposition occurred faster in FVW than MW, as accumulation of ammonia in MW reactors led to inhibition of methanogenesis. We identified population succession during different stages of waste decomposition and linked specific populations to different waste types. Community analyses revealed underrepresentation of methanogens in the leachate fractions, emphasizing the importance of consistent and representative sampling when characterizing microbial communities in solid waste.

Investigation of U.S. landfill GHG reporting program methane emission models.

As part of its commitment to the United Nations Framework Convention on Climate Change, the U.S. annually develops a national estimate of methane emissions from municipal solid waste (MSW) landfills by aggregating activity data from each facility. Since 2010, the U.S. has reported a 20 % decrease in MSW landfill emissions despite a 21 % increase in tons disposed. Operator-submitted data were investigated to understand the causes of this decline. In the U.S., operators of landfills with a gas collection and control system (GCCS) calculate their facility's emissions via two separate approaches - (1) first-order decay (FOD) and (2) collection efficiency assumption (CEA) - and select either result to feed into the annual inventory. The FOD model predicts methane generation proportional to waste disposal and that approach calculated a 19 % increase in total methane generated from 2010 to 2022, whereas generation via the CEA approach decreased by 8.9 %. The amount of measured methane collected has increased 7.5 % for the same years. Discrepancies between the two models' generated methane, assumed gas collection efficiencies, and oxidized methane compound into substantive differences in national estimates. Operators more frequently select the CEA method, which results in decreased national estimates. If only the FOD method was used, U.S. MSW landfill emissions would be 1.3-1.7 times greater than current estimates which is similar to recent extrapolations from remote sensing campaigns in the U.S. Both models contain parameters with large inherent uncertainty. Without measurement methods that continuously quantify both point-source and diffuse emissions, an assessment of either equation's accuracy cannot be made.

Metal(loid)s in urban soil from historical municipal solid waste landfill: Geochemistry, source apportionment, bioaccessibility testing and human health risks.

Landfills, especially those poorly managed, can negatively affect the environment and human beings through chemical contamination of soils and waters. This study investigates the soils of a historical municipal solid waste (MSW) landfill situated in the heart of a residential zone in the capital of Slovakia, Bratislava, with an emphasis on metal (loid) contamination and its consequences. Regardless of the depth, many of the soils exhibited high metal (loid) concentrations, mainly Cd, Cu, Pb, Sb, Sn and Zn (up to 24, 2620, 2420, 134, 811 and 6220 mg/kg, respectively), classifying them as extremely contaminated based on the geo-accumulation index (Igeo >5). The stable lead isotopic ratios of the landfill topsoil varied widely (1.1679-1.2074 for 206Pb/207Pb and 2.0573-2.1111 for 208Pb/206Pb) and indicated that Pb contained a natural component and an anthropogenic component, likely municipal solid waste incineration (MSWI) ash and construction waste. Oral bioaccessibility of metal (loid)s in the topsoil was variable with Cd (73.2-106%) and Fe (0.98-2.10%) being the most and least bioaccessible, respectively. The variation of metal (loid) bioaccessibility among the soils could be explained by differences in their geochemical fractionation as shown by positive correlations of bioaccessibility values with the first two fractions of BCR (Community Bureau of Reference) sequential extraction for As, Cd, Mn, Ni, Pb, Sn and Zn. The results of geochemical fractionation coupled with the mineralogical characterisation of topsoil showed that the reservoir of bioaccessible metal (loid)s was calcite and Fe (hydr)oxides. Based on aqua regia metal (loid) concentrations, a non-carcinogenic risk was demonstrated for children (HI = 1.59) but no risk taking into account their bioaccessible concentrations (HI = 0.65). This study emphasises the need for detailed research of the geochemistry of wastes deposited in urban soils to assess the potentially hazardous sources and determine the actual bioaccessibility and human health risks of the accumulated metal (loid)s.