Underestimated Methane Emissions from Solid Waste Disposal Sites Reveal Missed Greenhouse Gas Mitigation Opportunities

1.Introduction Cities are responsible for approximately 70%of all anthropogenic greenhouse gas(GHG)emissions and about 60%of all anthropogenic methane(CH4)emissions[1,2].Solid waste disposal sites(including landfills and dumpsites),which are prevalent in global cities,emit CH4 generated from the anaerobic biodegradation of municipal solid waste(MSW).Notably,the proportions of CH4 emissions from disposal sites surpass 50%of the total CH4 emissions in some megalopolises[3].CH4 has a high global warming potential(GWP),being 28 times stronger than carbon dioxide(CO_(2))over a 100-year period and 80 times stronger over a 20-year period[4].Understanding and mitigating CH4 emissions from solid waste disposal sites is particularly pertinent and pressing,considering that the latest Synthesis Report from the Intergovernmental Panel on Climate Change(IPCC)emphasizes that the current pace of mitigation and adaptation policies and measures falls short of restraining global temperature rise to under 1.5℃ within the 21st century[4].More than 150 countries signed the Global Methane Pledge at the United Nations Climate Change Conference in Glasgow(COP26),which aims to reduce global annual CH4 emissions by 30%by 2030,compared with emissions in 2020[5].

Health risk assessment of municipal solid waste incineration emissions based on regression analysis

This study examined the potential health risks posed by the operation of 96 waste-to-energy(WtE)plants in 30 cities in the Bohai Rim of China.Utilizing a sophisticated simulation approach,the Weather Research and Forecasting(WRF)model coupled with the California Puff(CALPUFF)model,we obtained the spatial distribution of pollutants emitted by WtE plants in the atmosphere.Hazard indices(HI)and cancer risks(CR)were calculated for each plant using the United States Environmental Protection Agency's recommended methodologies.The results indicated that both HIs and CRs were generally low,with values below the accepted threshold of 1.0 and 1.0×10^(-6),respectively.Specifically,the average HI and CR values for the entire study area were 2.95×10^(-3)and 3.43×10^(-7),respectively.However,some variability in these values was observed depending on the location and type of WtE plant.A thorough analysis of various parameters,such as waste composition,moisture content,and operating conditions,was conducted to identify the factors that influence the health risks associated with incineration.The findings suggest that proper waste sorting and categorization,increased cost of construction,and elevated height of chimneys are effective strategies for reducing the health risks associated with incineration.Overall,this study provides valuable insights into the potential health risks associated with WtE plants in the Bohai Rim region of China.The findings can serve as useful guidelines for law enforcement wings and industry professionals seeking to minimize the risks associated with municipal solid waste(MSW)management and promote sustainable development.

The acceleration degradation processes of different aged refuses with the forced aeration for landfill reclamation

Forced aeration is one of the promising ways to accelerate landfill reclamation,and understanding the relation between aeration rates and waste properties is the prerequisite to implementing forced aeration under the target of energy saving and carbon reduction.In this work,landfill reclamation processes with forced aeration were simulated using aged refuses(ARs)of 1,4,7,10,and 13 disposal years,and the potential of field application was also investigated based on a field project,to identify the degradation rate of organic components,the O_(2)consumption efficiency and their correlations to microbes.It was found that the removal rate of organic matter declined from 20.3%(AR_(1))to 12.6%(AR_(13)),and that biodegradable matter(BDM)decreased from 5.2%to 2.4%at the set aeration rate of 0.12 L O_(2)/kg waste(Dry Matter,DM)/day.A linear relationship between the degradation rate constant(K)of BDM and disposal age(x)was established:K=−0.0002193x+0.0091(R^(2)=0.854),suggesting that BDM might be a suitable indicator to reflect the stabilization of ARs.The cellulose/lignin ratio decrease rate for AR1(18.3%)was much higher than that for AR13(3.1%),while the corresponding humic-acid/fulvic-acid ratio increased from 1.44 to 2.16.The dominant bacteria shifted from Corynebacterium(9.2%),Acinetobacter(6.6%),and Fermentimonas(6.5%),genes related to the decompose of biodegradable organics,to Stenotrophomonas(10.2%)and Clostridiales(3.7%),which were associated with humification.The aeration efficiencies of lab-scale tests were in the range of 5.4–11.8 g BDM/L O_(2)for ARs with disposal ages of 1–13 years,and in situ landfill reclamation,ARs with disposal ages of 10–18 years were around 1.9–8.8 g BDM/L O_(2),as the disposal age decreased.The increased discrepancy was observed in ARs at the lab-scale and field scale,indicating that the forced aeration rate should be adjusted based on ARs and the unit compartment combined,to reduce the operation cost.

Smart 6S roadmap for deciphering the migration and risk of heavy metals in soil and groundwater systems at brownfield sites nationwide in China

Rapid industrialization and economic development have left a great amount of industrial facilities,such as chemical,smelting and mining industries,throughout the country over the past few decades.As a result,a wide range of toxic pollutants are generated and discharged directly or indirectly into the soil environment[1].

Chemical and olfactive impacts of organic matters on odor emission patterns from the simulated construction and demolition waste landfills

The explosive increase of construction and demolition waste(CDW) caused the insufficient source separation and emergency disposal at domestic waste landfills in many developing countries. Some organic fractions were introduced to the CDW landfill process and resulted in serious odor pollution. To comprehensively explore the impacts of organic matters on odor emission patterns, five CDW landfills(OIL), with organic matters/inert CDW components(O/I) from 5% to 30%, and the control group only with inert components(IL) or organics(OL) were simulated at the laboratory. The chemical and olfactive characters of odors were evaluated using the emission rate of 94 odorants content(ER_(total)), theory odor concentration(TOC_(total)), and e-nose concentration(ER_(ENC)), and their correlations with waste properties were also analyzed. It was found that the main contributors to ER_(total)(IL: 93.0% NH_(3);OIL: 41.6% sulfides, 31.0% NH_(3), 25.9% oxygenated compounds) and TOC_(total)(IL: 64.1% CH_3SH, 28.2% NH_(3);OIL: 71.7% CH_(3)SH, 24.8% H_(2)S) changed significantly. With the rise of O/I, ER_(total), TOC_(total), and ER_(ENC) increased by 10.9, 20.6, and 2.1 times, respectively. And the organics content in CDW should be less than 10%(i.e., DOC < 101.3 mg/L). The good regressions between waste properties(DOC, DN, pH) and ER_(total),( r = 0.86, 0.86,-0.88, p < 0.05), TOC_(total),( r = 0.82, 0.79, -0.82, p < 0.05) implied that the carbon sources and acidic substances relating to organics degradation might result in that increase. Besides, the correlation analysis results( ER_(ENC) vs. TOC_(total,, r = 0.96, p < 0.01;vs. ER_(ENC), r = 0.86, p < 0.05) indicated that e-nose perhaps was a reliable odor continuous monitoring tool for CDW landfills.

Greenhouse gas emission and its potential mitigation process from the waste sector in a large-scale exhibition

As one of the largest human activities, World Expo is an important source of anthropogenic Greenhouse Gas emission（GHG）, and the GHG emission and other environmental impacts of the Expo Shanghai 2010, where around 59,397 tons of waste was generated during 184 Expo running days, were assessed by life cycle assessment（LCA）. Two scenarios, i.e., the actual and expected figures of the waste sector, were assessed and compared, and 124.01 kg CO2-equivalent（CO2-eq.）, 4.43 kg SO2-eq., 4.88 kg NO-3-eq., and 3509 m3 water per ton tourist waste were found to be released in terms of global warming（GW）, acidification（AC）,nutrient enrichment（NE） and spoiled groundwater resources（SGWR）, respectively. The total GHG emission was around 3499 ton CO2-eq. from the waste sector in Expo Park, among which 86.47% was generated during the waste landfilling at the rate of 107.24 kg CO2-eq.,and CH4, CO and other hydrocarbons（HC） were the main contributors. If the waste sorting process had been implemented according to the plan scenario, around 497 ton CO2-eq.savings could have been attained. Unlike municipal solid waste, with more organic matter content, an incineration plant is more suitable for tourist waste disposal due to its high heating value, from the GHG reduction perspective.

Environmental impacts of a large-scale incinerator with mixed MSW of high water content from a LCA perspective

Large-scale incinerators are applied widely as a result of the heavy burden of municipal solid waste（MSW） generated, while strong opposition is arising from the public living nearby. A large-scale working incineration plant of 1500 ton/day was chosen for evaluation using life cycle assessment. It was found that the corresponding human toxicity impacts via soil（HTs）, human toxicity impacts via water（HTw） and human toxicity impacts via air（HTa）categories are 0.213, 2.171, and 0.012 personal equivalents（PE）, and global warming（GW100）and nutrient enrichment（NE） impacts are 0.002 and 0.001 PE per ton of waste burned for this plant. Heavy metals in flue gas, such as Hg and Pb, are the two dominant contributors to the toxicity impact categories, and energy recovery could reduce the GW100 and NE greatly. The corresponding HTs, HTw and HTa decrease to 0.087, 0.911 and 0.008 PE, and GW100 turns into savings of- 0.007 PE due to the increase of the heating value from 3935 to5811 k J/kg, if a trommel screener of 40 mm mesh size is used to pre-separate MSW. MSW sorting and the reduction of water content by physical pressure might be two promising pre-treatment methods to improve the combustion performance, and the application of stricter standards for leachate discharge and the flue gas purification process are two critical factors for improvement of the environmental profile identified in this work.

Bioaerosol emissions variations in large-scale landfill region and their health risk impacts

Landfills are widely complained about due to the long-term odor and landfill gas emissions for local residents,while the bioaerosols are always neglected as another threat to on-site workers.In this study,bioaerosols samples were collected from the typical operation scenes in the large-scale modern landfill,and the emission levels of airborne bacteria,pathogenic species,and fungi were quantified and co-related.The corresponding exposure risks were assessed based on the average daily dose via inhalation and skin contact.It was found that the levels of culturable bacteria and fungi in all landfill samples were around 33–22778 CFU/m3 and 8–450 CFU/m3,and the active-working landfill area and the covered area were the maximum and minimum emission sources,respectively,meaning that the bioaerosols were mainly released from the areas related with the fresh waste operation.Acinetobacter sp.,Massilia sp.,Methylobacterium-Methylorubrum sp.and Noviherbaspirillum sp.were the main bacterial populations,with a percentage of 42.56%,89.82%,70.24%and 30.20%respectively in total bioaerosols measured.With regards to the health risk,the health risks via inhalation were the main potential risks,with four orders of magnitude higher than that of skin contact.Active-working area showed the critical point for non-carcinogenic risks,with a hazard quotient of 1.68,where 80 m protection distance is recommended for on-site worker protection,plus more careful protection measures.

Indicating landfill stabilization state by using leachate property from Laogang Refuse Landfill

Variation and evolution process of leachate can be applied as a reference for landfill stabilization phase. In this work, leachates with different ages were collected from Laogang Refuse Landfill, and characterized with 14 key parameters. Simultaneously, principal component analysis （PCA） was applied to develop a synthetic parameter-F based on these 14 parameters, and a logarithm equation was simulated for the landfill stabilization process finally. It was predicted that leachates would meet Class I and Class II in standard for pollution control on the landfill site of municipal solid waste （GB 16889-1997） after 32 years and 22 years disposal under the natural attenuation in the humid and warm southern areas of China, respectively. The predication of landfill state would be more accurate and useful according to the synthetic parameter F of leachate from a working landfill.