A review on the evaluation models and impact factors of greenhouse gas emissions from municipal solid waste management processes.

The total amount of global municipal solid waste (MSW) will reach 3.5 billion tons by 2050, thereby bringing tremendous environmental pressure, especially global warming. Large amounts of greenhouse gases (GHGs) have been released during MSW management (MSWM). Accounting for GHG emissions is a prerequisite for providing recommendations on appropriate treatment options to mitigate emissions from MSWM systems. There are many methods involved in estimating emissions. This paper summarizes the computing models commonly used in each process of the integrated MSWM system and emphasizes the influence of parameters and other factors. Compared with other disposal methods, landfilling has the highest emissions, commonly estimated using first-order decay (FOD) methods. Emission reduction can be realized through waste to energy (WtE) and resource recovery measures. IPCC is commonly used for calculating direct emissions, while LCA-based models can calculate emissions including upstream and downstream processes, whose results depend on assumptions and system boundaries. The estimation results of models vary greatly and are difficult to compare with each other. Besides, large gaps exist between the default emission factors (EFs) provided by models and those F measured in specific facilities. These findings provide a systematic view for a bettering understanding of MSW emissions as well as the estimating methods and also reveal the key points that need be developed in the future.

Unraveling the effect of phenolic extract derived from olive mill solid wastes on agro-physiological and biochemical traits of pomegranate and its associated rhizospheric soil properties.

Agricultural waste management poses a significant challenge in circular economy strategies. Olive mill wastes (OMW) contain valuable biomolecules, especially phenolic compounds, with significant agricultural potential. Our study evaluate the effects of phenolic extract (PE) derived from olive mill solid wastes (OMSW) on pomegranate agro-physiological and biochemical responses, as well as soil-related attributes. Pomegranate plants were treated with PE at doses of 100 ppm and 200 ppm via foliar spray (L100 and L200) and soil application (S100 and S200). Results showed increased biomass with PE treatments, especially with soil application (S100 and S200). Proline and soluble sugar accumulation in leaves suggested plant adaptation to PE with low-level stress. Additionally, PE application reduced malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents. Higher doses of PE (S200) significantly improved net photosynthesis (Pn), transpiration rate (E), water use efficiency (WUEi), and photosynthetic efficiency (fv/fm and PIabs). Furthermore, PE treatments enhanced levels of chlorophylls, carotenoids, polyphenols, flavonoids, and antioxidant activity. Soil application of PE also increased soil enzyme activities and microbial population. Our findings suggest the beneficial impact of PE application on pomegranate agro-physiological responses, laying the groundwork for further research across various plant species and soil types to introduce nutrient-enriched PE as an eco-friendly biostimulant.

Mechanism of soot and particulate matter formation during high temperature pyrolysis and gasification of waste derived from MSW.

This research investigates the formation mechanism of soot and particulate matter during the pyrolysis and gasification of waste derived from Municipal Solid Waste (MSW) in a laboratory scale drop tube furnace. Compared with CO2 gasification atmosphere, more ultrafine particles (PM0.2, aerodynamic diameter less than 0.2 µm) were generated in N2 atmosphere at 1200℃, which were mainly composed of polycyclic aromatic hydrocarbons (PAHs), graphitic carbonaceous soot and volatile alkali salts. High reaction temperatures promote the formation of hydrocarbon gaseous products and their conversion to PAHs, which ultimately leads to the formation of soot particles. The soot particles generated by waste derived from MSW pyrolysis and gasification both have high specific surface area and well-developed pore structure. Compared with pyrolysis, the soot generated by gasification of waste derived from MSW had smaller size and higher proportion of inorganic components. The higher pyrolysis temperature led to the collapse of the mesoporous structure of submicron particles, resulting in a decrease in total pore volume and an increase in specific surface area. Innovatively, this research provides an explanation for the effect of reaction temperature/ CO2 on the formation pathways and physicochemical properties of soot and fine particulate matter.

Mechanistic study on the promotion of Ca2+ leaching in steel slag through high-temperature solid waste modification.

Indirect carbonation of steel slag is an effective method for CO2 storage, reducing emissions, and promoting cleaner production in the steel industry. However, challenges remain, such as low Ca2+ leaching rates and slag management complexities arising from variations in mineral compositions. To address this, a high-temperature modification process is proposed to alter the mineral composition and facilitate the synergistic utilization of calcium and iron. This study delves into the effects of various solid waste modifications on the leaching of Ca2+ and the total iron content within steel slag. Results show that high-basicity modified slag forms Ca2(Al, Fe)2O5, reducing calcium leaching. Low-alkalinity modified slag produces calcium-rich aluminum minerals and also reduces the leaching of Ca2+ ions. At a basicity of 2.5, coal gangue, fly ash, and blast slag achieve maximum Ca2+ leaching rates of 88.93%, 89.46%, and 90.17%, respectively, with corresponding total iron contents of 41.46%, 37.72%, and 35.29%. Upgraded coal gangue exhibits a 50.02% increase in calcium leaching and a 15.58% increase in total iron content compared to the original slag. This enhances CO2 fixation and iron resource utilization. Overall, the proposed indirect carbonation and iron enrichment modification offer a novel approach for the resource utilization and environmental stability of steel slag.

Solid waste management practices and challenges in Besisahar municipality, Nepal.

This study is a comprehensive assessment of the waste management system in Besisahar municipality. Information and some data have been collected from the municipality of Besisahar, followed by interviews with municipal officials responsible for waste management, stakeholders, waste workers, and residents. A total of 230 households, 20 schools, 10 government and private offices, 10 financial institutions, 60 commercial hotels, restaurants, and shops, and 20 medical shops and healthcare institutions, were selected in this study by random sampling. An extensive field study was conducted within all municipal wards and at dump sites. The results indicated that 42.14% of solid waste was collected through door-to-door collection services, 5.87% was mismanaged in open public places, 11.21% was used as compost manure, and the rest was discarded on riverbanks, dug up, and burned. A large component of the characterization of household waste consisted of organic waste (68.03%), followed by paper/paper products (8.13%), agricultural waste (5.5%), plastic (5.21%), construction (3.81%), textile (2.72%), metals (0.54%), glass (1.01%), rubber (0.10%), electronic (0.05%), pharmaceutical (0.1%) and others (4.78%) in the Besishahar municipality. Solid waste generation was found to be at 197.604 g/capita/day, as revealed by cluster sampling in 230 households. Around 4.285 tons-solid waste/day were generated in urban areas, while 16.13 tons-solid waste/day was estimated for the whole municipality. An important correlation between the parameters of solid waste was found by statistical analysis. Currently, solid waste is dumped on riverbanks, open fields, and springs, creating environmental and health hazards. The findings of this study will be useful to Besisahar municipality and its stakeholders in forming policies that facilitate waste management practices in this region and promote sustainable waste management systems.

Consumer behavior in the model of the circular economy in the field of handling discarded items.

The circular economy is a way of eliminating the shortage of raw materials that Europe is currently facing. However, it is necessary to explicitly identify the problems that prevent greater involvement in the CE. This article is focused on consumers and how they treat discarded or non-functional items. The aim was to fill the research gap, i.e. to compile a suitable CE model and define a methodology that would ensure the efficient disposal of non-functional or unsuitable items by consumers. An original methodology was drawn up to conduct the representative research, designed to lead to the practical application of the proposed CE model. The research explored how consumers treat non-functional or unsuitable items, the costs they incur in discarding, renovating, reusing, and recycling such items, and the alternative costs of unsorted municipal waste. After the data had been implemented into the model the circular economy was proven to have an economic benefit for the national economy in all groups. However, the economic disadvantage for consumers was also calculated, where the cost of involvement in the CE is higher than the cost of unsorted municipal waste. This means that people are motivated to play a part in the CE more by their own responsible approach to life, or social pressure from those around them. Based on this research it may be said that economic aspects are one reason that consumers tend to be reluctant to get more involved in the CE. Unless there is a significant rise in the cost of municipal waste that would motivate consumers to move towards the CE for financial reasons, in order to support the CE consumers need to be better stimulated, educated and informed as much as possible through the media.

Effect of oxide interactions on chromium speciation transformation during simulated municipal solid waste incineration.

Chromium released during municipal solid waste incineration (MSWI) is toxic and carcinogenic. The removal of chromium from simulated MSWI flue gas by four sorbents (CaO, bamboo charcoal (BC), powdered activated carbon (PAC), and Al2O3) and the effects of four oxides (SiO2, Al2O3, Fe2O3, and CaO) on chromium speciation transformation were investigated. The results showed that the removal rates of total Cr by the four sorbents were Al2O3 < CaO < PAC < BC, while the removal rates of Cr(VI) by the four sorbents were Al2O3 < PAC < BC < CaO. CaO had a strong oxidizing effect on Cr(III), while BC and PAC had a better-reducing effect on Cr(VI). SiO2 was better for the reduction of Na2CrO4 and K2CrO4 above 1000°C due to its strong acidity, and the addition of CaO significantly inhibited the reduction of Cr(VI). MgCrO4 decomposed above 700°C to form MgCr2O4, and the reaction between MgCrO4 and oxides also existed in the form of a more stable trivalent spinel. Furthermore, when investigating the effect of oxides on the oxidation of Cr(III) in CrCl3, it was discovered that CaO promoted the conversion of Cr(III) to Cr(VI), while the presence of chlorine caused chromium to exist in the form of Cr(V), and increasing the content of CaO and extending the heating time facilitated the oxidation of Cr(III). In addition, silicate, aluminate, and ferrite were generated after the addition of SiO2, Al2O3, and Fe2O3, which reduced the alkalinity of CaO and had an important role in inhibiting the oxidation of Cr(III). The acidic oxides can not only promote the reduction of Cr(VI) but also have an inhibitory effect on the oxidation of Cr(III) ascribed to alkali metals/alkaline earth metals, and the proportion of acidic oxides can be increased moderately to reduce the generation of harmful substances in the hazardous solid waste heat treatment.

The impact of chronic and acute problems on sea turtles: The consequences of the oil spill and ingestion of anthropogenic debris on the tropical semi-arid coast of Ceará, Brazil.

Sea turtle mortality is often related to materials that reach the coast from different anthropic activities worldwide. This study aimed to investigate whether sea turtle mortality was related to older marine problems, such as solid waste, or one of the largest oil spill accidents on the Brazilian coast, that occurred in 2019. We posed three questions: 1) Are there solid residues in the digestive tract samples, and which typology is the most abundant? 2) Can meso­ and macro-waste marine pollutants cause mortality? 3) Is the dark material found really oil? A total of 25 gastrointestinal content (GC) samples were obtained, of which 22 ingested waste of anthropogenic origin and 18 were necropsied. These 22 samples were obtained during or after the 2019 oil spill, of which 17 specimens were affected, making it possible to suggest oil ingestion with the cause of death in the animals that could be necropsied. Macroscopic data showed that the most abundant solid waste was plastic (76.05 %), followed by fabrics (12.18 %) and oil-like materials. However, chemical data confirmed only three specimens with oil levels ranging from remnants to high. It was possible to infer possible causes of death in 16 of the total 18 necropsied cases: Most deaths were due to respiratory arrest (62.5 %), followed by pulmonary edema (12.5 %), cachexia syndrome (12.5 %), circulatory shock (6.25 %), and head trauma (6.25 %), which may have been caused by contact with solid waste, oil, or both. The study showed that not all dark material found in the GCs of turtles killed in oiled areas is truly oil, and in this sense, a chemical analysis step to prove the evidence of oil must be added to international protocols.

Methacrylic acid in situ modified steel converter slag/natural rubber composites: Resourceful utilization of steelmaking solid wastes.

As a by-product of the steelmaking industry, the large-volume production and accumulation of steel converter slag cause environmental issues such as land occupation and dust pollution. Since metal salts of unsaturated carboxylic acid can be used to reinforce rubber, this study explores the innovative application of in-situ modified steel slag, mainly comprising metal oxides, with methacrylic acid (MAA) as a rubber filler partially replacing carbon black. By etching the surface of steel slag particles with MAA, their surface roughness was increased, and the chemical bonding of metal methacrylate salt was introduced to enhance their interaction with the molecular chain of natural rubber (NR). The results showed that using the steel slag filler effectively shortened the vulcanization molding cycle of NR composites. The MAA in-situ modification effectively improved the interaction between steel slag and NR molecular chains. Meanwhile, the physical and mechanical properties, fatigue properties, and dynamic mechanical properties of the experimental group with MAA in-situ modified steel slag (MAA-in-situ-m-SS) were significantly enhanced compared with those of NR composites partially filled with unmodified slag. With the dosage of 7.5 phr or 10 phr, the above properties matched or even exceeded those of NR composites purely filled with carbon black. More importantly, partially replacing carbon black with modified steel slag reduced fossil fuel consumption and greenhouse gas emission from carbon black production. This study pioneered an effective path for the resourceful utilization of steel slag and the green development of the steelmaking and rubber industries.

Probabilistic human health risk assessment of PCDD/Fs near municipal solid-waste incinerator using Monte Carlo analysis coupled with triangular fuzzy numbers.

PCDD/Fs are dioxins produced by waste incineration and pose risks to human health. We aimed to detail the health risks of airborne and soil PCDD/Fs near a municipal solid-waste incinerator (MSWI) for the surrounding population and develop a new model that improves upon existing methods. Thus, we conducted field sampling and then investigated a MSWI in the Pearl River Delta (2016-2018). Our results showed that the carcinogenic and non-carcinogenic risk values of PCDD/Fs exposed to residents in nearby areas were acceptable, with hazard index (HI) values lower than 1.0 and a total carcinogenic risk lower than 1.0E-6. Notably, the results raised concerns regarding higher non-carcinogenic risks in children than in adults. Comparative analysis of the frequency accumulation diagram, accumulated probability risk, and the absolute value of error (δ) between the 95% confidence interval (CI) and the 90% CI of the Monte Carlo stochastic simulation-triangular fuzzy number (MCSS-TFN) and the MCSS model, respectively, demonstrated that the MCSS-TFN exhibited less uncertainty than the MCSS model, regardless of the health risk value of PCDD/Fs in ambient air or in soil. This observation underscores the superiority of the MCSS-TFN model over other models in assessing the health risks associated with PCDD/Fs in situations with limited data. Our new method overcomes the limited dataset size and high uncertainty in assessing the health risks of dioxin substances, providing a more comprehensive understanding of their associated health risks than MCSS models.

Assessment of emissions and potential occupational exposure to carbon monoxide during biowaste composting.

To date, only a few studies focused on the carbon monoxide (CO) production during waste composting; all targeted on CO inside piles. Here, the CO net emissions from compost piles and the assessment of worker's occupational risk of exposure to CO at large-scale composting plants are shown for the first time. CO net emissions were measured at two plants processing green waste, sewage sludge, or undersize fraction of municipal solid waste. Effects of the location of piles (hermetised hall vs. open yard) and turning (before vs. after) were studied. Higher CO net emission rates were observed from piles located in a closed hall. The average CO flux before turning was 23.25 and 0.60 mg‧m-2‧h-1 for hermetised and open piles, respectively, while after- 69.38 and 5.11 mg‧m-2‧h-1. The maximum CO net emissions occurred after the compost was turned (1.7x to 13.7x higher than before turning). The top sections of hermetised piles had greater CO emissions compared to sides. Additionally, 5% of measurement points of hermetised piles switched to 'CO sinks'. The 1-h concentration in hermetised composting hall can reach max. ~50 mg CO∙m-3 before turning, and >115 mg CO∙m-3 after, exceeding the WHO thresholds for a 1-h and 15-min exposures, respectively.

A comprehensive investigation of geoenvironmental pollution and health effects from municipal solid waste landfills.

This study investigates human health risks associated with heavy metals (HMs) occurrence in municipal solid waste (MSW) landfills. For testing of selected MSW landfills steps were involved, including site characterization, soil sampling and chemical testing, statistical analysis, as well as health risk assessment, carcinogenic and non-carcinogenic effects. For the Polish landfill (Radiowo) the average HMs concentrations were found in the following order: Zn (52.74 mg/kg DM) > Pb (28.32 mg/kg DM) > Cu (12.14 mg/kg DM) > Ni (4.50 mg/kg DM) > Cd (3.49 mg/kg DM), while for the Czech landfill (Zdounky): Zn (32.05 mg/kg DM) > Cu (14.73 mg/kg DM) > Ni (4.73 mg/kg DM) > Pb (0.10 mg/kg DM) = Cd (0.10 mg/kg DM). Strong positive correlations between selected HMs demonstrated identical origins. Principal component analysis (PCA) performed for the Radiowo landfill transferred the soil parameters into three principal components (PCs), accounting for 87.12% of the total variance. The results of the PCA analysis for the Zdounky landfill revealed three PCs responsible for 95.16% of the total variance. The exposure pathways of HMs for landfills were in the following order: ingestion > dermal absorption > inhalation. For both landfills, the values of hazard quotient were lower than 1, indicating no potential negative health effects. In terms of the hazard index (HI), for both landfills, no adverse human health effects occur (HI < 1). The incremental lifetime cancer risk (ILCR) values indicated negligible or acceptable carcinogenic risk of HMs (average ILCR in the range from 5.01E-10 to 5.19E-06).

Sustainable assessment and synergism of ceramic powder and steel slag in iron ore tailings-based concrete.

Solid waste management is a critical issue worldwide. Effectively utilizing these solid waste resources presents a viable solution. This study focuses on Iron ore tailings (IOTs), a solid waste generated during iron ore processing, which can be used as supplementary cementitious materials (SCMs) but have low reactivity, hindering their large-scale application in concrete production. To address this, ternary SCMs were prepared using ceramic powder (CP) and steel slag (SS) to enhance the performance of concrete incorporating IOTs. The study found that the synergistic effect of CP and SS significantly improved the compressive strength of concrete, with a notable increase of up to 21% compared to concrete with IOTs alone. Mercury intrusion porosimetry (MIP) and backscattering electron (BSE) analyses revealed that the ternary SCMs significantly optimized the characteristics of the interfacial transition zone (ITZ), which in turn enhanced the compressive properties of the concrete. This contributed to maintaining the structural integrity of the concrete, even amidst variations in the pore structure. Importantly, the incorporation of ternary SCMs led to a 23% reduction in carbon emissions, from 400.01 kg CO2/m3 to 307.48 kg CO2/m3, and elevated eco-strength efficiency from 0.1 to 0.14. The study highlights the role of multi-material synergy in developing composite SCMs systems, fostering the sustainable advancement of green building materials.

Optimization of organic solid waste composting process through iron-related additives: A systematic review.

Composting is an environmentally friendly method that facilitates the biodegradation of organic solid waste, ultimately transforming it into stable end-products suitable for various applications. The element iron (Fe) exhibits flexibility in form and valence. The typical Fe-related additives include zero-valent-iron, iron oxides, ferric and ferrous ion salts, which can be targeted to drive composting process through different mechanisms and are of keen interest to academics. Therefore, this review integrated relevant literature from recent years to provide more comprehensive overview about the influence and mechanisms of various Fe-related additives on composting process, including organic components conversion, humus formation and sequestration, changes in biological factors, stability and safety of composting end-products. Meanwhile, it was recommended that further research be conducted on the deep action mechanisms, biochemical pathways, budget balance analysis, products stability and application during organic solid waste composting with Fe-related additives. This review provided guidance for the subsequent targeted application of Fe-related additives in compost, thereby facilitating cost reduction and promoting circular economy objectives.

Highly efficient carbonation and dechlorination using flue gas micro-nano bubble for municipal solid waste incineration fly ash pretreatment and its applicability to sulfoaluminate cementitious materials.

Cement production is a primary source of global carbon emissions. As a hazardous waste, municipal solid waste incineration fly ash (MSWI-FA) can be pretreated as a cementitious and effective carbon capture material. This study proposes an efficient carbonation dechlorination pretreatment and resource recovery strategy using flue gas micro-nano bubble (MNB) to wash MSWI-FA. The results showed that the flue gas MNB water washing reaction solution inhibited CaCO3 boundary layer blocking and adsorption on NaCl and KCl leaching. Under low water-to-solid ratio and CO2 concentration conditions, two-step washing reduced the MSWI-FA chlorine content to <1%, improving the dechlorination effect by 19.72% compared to conventional carbonation. The flue gas MNB water accelerated the precipitation of Ca2+ and Ca(ClO)2 in the form of calcite. The higher the CO2 concentration in the flue gas MNB, the better the fragmentation and purification of the MSWI-FA shell, leading to improved dechlorination and CO2 fixation. Under optimized conditions, the mean particle size of MSWI-FA decreased by 47.82%, and the CO2 fixation rate reached 73.80%, with a 58.35% increase in the washing carbonation rate. MSWI-FA pretreated by flue gas MNB washing was used as both the raw material and supplementary cementitious material for sulfoaluminate cementitious (SAC) material, exhibiting excellent compressive strength and heavy metal stabilization. The maximum compressive strength of the MSWI-FA-based SAC material cured for 28 d reached 130 MPa. Cr leaching was inhibited with increased hydration time, and the leaching concentration was far below the standard limit.

Characterization and mechanical removal of metallic aluminum (Al) embedded in weathered municipal solid waste incineration (MSWI) bottom ash for application as supplementary cementitious material.

Municipal solid waste incineration (MSWI) bottom ash, due to its high mineral content, presents great potential as supplementary cementitious material (SCM). Weathering, also known as aging, is a treatment process commonly employed in waste management to minimize the risk of heavy metal leaching from MSWI bottom ash. Using weathered MSWI bottom ash to produce blended cement pastes is considered as a high-value-added and sustainable waste disposal solution. However, a critical challenge arises from the metallic aluminum (Al) in weathered MSWI bottom ash, which is known to induce detrimental effects such as volume expansion and strength loss of blended cement pastes. While most metallic Al in weathered MSWI bottom ash can be removed with eddy current separators in metal recovery plants, the residual metallic Al, owing to its small particle size, cannot be removed with the same technique. This study is dedicated to addressing this issue. An in-depth analysis was conducted on residual metallic Al embedded in weathered MSWI bottom ash particles, aiming to guide the removal of this metal. This analysis revealed that mechanical removal was the most suitable method for extracting metallic Al. The specific processes and mechanisms underlying this method were elucidated. After reducing metallic Al content in weathered MSWI bottom ash by 77 %, a significant improvement in the quality of blended cement pastes was observed. This work contributes to the broader adoption of mechanical treatments for removing residual metallic Al from weathered MSWI bottom ash and facilitates the application of treated ash as SCM.

Periodic injection of liquefied kitchen and food waste in municipal solid waste: Effects on leachate and gas generation.

With continuous advancements in the zero-waste strategy in China, transportation of fresh municipal solid waste to landfills has ceased in most first-tier cities. Consequently, the production of landfill gas has sharply declined because the supply of organic matter has decreased, rendering power generation facilities idle. However, by incorporating liquefied kitchen and food waste (LKFW), sustainable methane production can be achieved while consuming organic wastewater. In this study, LKFW and water (as a control group) were periodically injected into high and low organic wastes, respectively. The biochemical characteristics of the resulting gas and leachate were analyzed. LKFW used in this research generated 19.5-37.6 L of methane per liter in the post-methane production phase, highlighting the effectiveness of LKFW injection in enhancing the methane-producing capacity of the system. The release of H2S was prominent during both the rapid and post-methane production phases, whereas that of NH3 was prominent in the post-methane production phase. As injection continued, the concentrations of chemical oxygen demand, 5-d biological oxygen demand, total organic carbon, ammonia nitrogen, total nitrogen, and oil in the output leachate decreased and eventually reached levels comparable to those in the water injection cases. After nine rounds of injections, the biologically degradable matter of the two LKFW-injected wastes decreased by 8.2 % and 15.1 %, respectively. This study sheds light on determining the organic load, controlling odor, and assessing the biochemical characteristics of leachate during LKFW injection.

The synergistic regulation of sewage sludge biodrying and greenhouse gas reduction by additives.

As a dewatering method of high moisture solid waste sludge, biodrying still faces environmental problems such as material loss and greenhouse gas emission in the process of treatment. In this study, biochar and magnesium chloride were used to explore the synergistic effect of enhancing sludge biodrying and reducing greenhouse gas emissions. The highest temperature of biodrying was raised to 68.2 °C within 3 days, extending the longest high-temperature period to 5 days, which reduced the water content to 28.8 % in the single addition of biochar treatment. The complex addition increased the NH4+-N content of materials by 57.49 % and decreased the NO3--N content of materials by 40.62 %. The use of additives significantly reduced the emissions of CO2, CH4, and N2O compared to the no-addition treatment. The increase in dominant Actinomycetes and Chloroflexibacter was the main reason for the reduction in gas emissions.

Greenhouse gas mitigation scenarios in the solid waste sector for compliance with the Brazilian NDC: Case study of the Recife metropolitan area, Brazil.

The Intergovernmental Panel on Climate Change (IPCC) indicates that the waste sector is a potential emitter of methane gas (CH4), which has a greenhouse effect up to 28 times greater than that of carbon dioxide (CO2). The management of municipal solid waste (MSW) generates greenhouse gases (GHG) directly through emissions from the process itself as well as indirectly through transportation and energy consumption. The objective of this study was to evaluate the GHG emissions contributed by the waste sector in the Recife metropolitan region (RMR) and to define mitigation scenarios to comply with the Brazilian Nationally Determined Contribution (NDC), a result of the Paris Agreement. To achieve this, an exploratory study was carried out, including a literature review, collection of data, estimation of emissions using the IPCC model (2006), and comparison between the values assumed by the country in 2015 and those estimated in the adopted mitigation scenarios. The RMR is composed of 15 municipalities, has an area of 3,216,262 km2 and a population of 4,054,866 inhabitants (2018), generating approximality 1.4 million t-year of MSW. It was estimated that, in the period from 2006 to 2018, 25.4 million tCO2e were emitted. The comparative analysis between the absolute values defined in the Brazilian NDC and the results from the mitigation scenarios showed that approximately 36 million tCO2e could be avoided through the disposal of MSW in the RMR, equivalent to a 52% reduction in emissions estimated for 2030, a percentage greater than the 47% reduction assumed in the Paris Agreement.

Thermodynamic model of MSWI flue gas cooling path: Effect of flue gas composition on heavy metal binding forms.

In the context of circular economy and heavy metal (HM) recovery from municipal solid waste incineration (MSWI) fly ash (FA), detailed knowledge of HM binding forms is required for achieving higher extraction rates. The FA mineralogy is still poorly understood due to its low grain size and low metal concentration. To investigate the HM binding forms, a sophisticated thermodynamic reactive transport model was developed to simulate ash-forming processes. The stability of different binding forms was investigated at different flue gas conditions (varying ratios of HCl, SO2, O2) by simulating the gas cooling path in closed system and dynamic open system, where the gas composition is changing upon cooling due to precipitation of solids. The simulations predict that at flue gas conditions of molar ratio S/Cl < 1, Cu and Zn precipitate as oxides (and Zn silicates) at approximately 650°C. At temperatures <300°C, Zn, Cu, Pb and Cd are predicted to precipitate as easily soluble chlorides. In flue gas with molar ratio S/Cl > 1, the HM precipitate as less soluble sulphates. The results indicate that the less soluble HM fraction in the electrostatic precipitator ash represent oxides and silicates that formed in the boiler section but were transported to the electrostatic precipitator. The model provides insight into the physical-chemical processes controlling the metal accumulation in the flue gas and FA during the cooling of the flue gas. The obtained data serve as valuable basis for improving metal recovery from MSWI FA.