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.

Highly Reactive Peroxide Species Promoted Soot Oxidation over an Ordered Macroporous Ce0.8Zr0.2O2 Integrated Catalyzed Diesel Particulate Filter.

Particulate matter, represented by soot particles, poses a significant global environmental threat, necessitating efficient control technology. Here, we innovatively designed and elaborately fabricated ordered hierarchical macroporous catalysts of Ce0.8Zr0.2O2 (OM CZO) integrated on a catalyzed diesel particulate filter (CDPF) using the self-assembly method. An oxygen-vacancy-enriched ordered macroporous Ce0.8Zr0.2O2 catalyst (VO-OM CZO) integrated CDPF was synthesized by subsequent NaBH4 reduction. The VO-OM CZO integrated CDPF exhibited a markedly enhanced soot oxidation activity compared to OM CZO and powder CZO coated CDPFs (T50: 430 vs 490 and 545 °C, respectively). The well-defined OM structure of the VO-OM CZO catalysts effectively improves the contact efficiency between soot and the catalysts. Meanwhile, oxygen vacancies trigger the formation of a large amount of highly reactive peroxide species (O22-) from molecular oxygen (O2) through electron abstraction from the three adjacent Ce3+ (3Ce3+ + Vö + O2 → 3Ce4+ + O22-), contributing to the efficient soot oxidation. This work demonstrates the fabrication of the ordered macroporous CZO integrated CDPF and reveals the importance of structure and surface engineering in soot oxidation, which sheds light on the design of highly efficient PM capture and removal devices.

Functionalization of cellulose acetate nanofibrous membranes for removal of particulate matters and dyes.

Particulates and organic toxins, such as microplastics and dye molecules, are contaminants in industrial wastewater that must be purified due to environmental and sustainability concerns. Carboxylated cellulose acetate (CTA-COOH) nanofibrous membranes were fabricated using electrospinning followed by an innovative one-step surface hydrolysis/oxidation replacing the conventional two-step reactions. This approach offers a new pathway for the modification strategy of cellulose-based membranes. The CTA-COOH membrane was utilized for the removal of particulates and cationic dyes through filtration and adsorption, respectively. The filtration performance of the CTA-COOH nanofibrous membrane was carried out; high separation efficiency and low pressure drop were achieved, in addition to the high filtration selectivity against 0.6-µm and 0.8-µm nanoparticles. A cationic Bismarck Brown Y, was employed to challenge the adsorption capability of the CTA-COOH nanofibrous membrane, where the maximum adsorption capacity of the membrane for BBY was 158.73 mg/g. The self-standing CTA-COOH membrane could be used to conduct adsorption-desorption for 17 cycles with the regeneration rate as high as 97.0 %. The CTA-COOH nanofibrous membrane has excellent mechanical properties and was employed to manufacture a spiral wound adsorption cartridge, which exhibited remarkable separation efficiency in terms of treated water volume, which was 5.96 L, and retention rate, which was 100 %.

Effect of long-term dry-wet circulations on the Solidification/stabilization of Municipal solid waste incineration fly ash using a novel cementitious material.

Solidification/stabilization (S/S) is a typical technique to immobilize toxic heavy metals in Municipal solid waste incineration fly ash (MSWI FA). This study utilized blast furnace slag, steel slag, desulfurization gypsum, and phosphoric acid sludge to develop a novel metallurgical slag based cementing material (MSCM). Its S/S effects of MSWI FA and long-term S/S effectiveness under dry-wet circulations (DWC) were evaluated and compared with ordinary Portland cement (OPC). The MSCM-FA block with 25 wt.% MSCM content achieved 28-day compressive strength of 9.38 MPa, indicating its high hydration reactivity. The leaching concentrations of Pb, Zn and Cd were just 51.4, 1895.8 and 36.1 µg/L, respectively, well below the limit standard of Municipal solid wastes in China (GB 16889-2008). After 30 times' DWC, leaching concentrations of Pb, Zn and Cd for MSCM-FA blocks increased up to 130.7, 9107.4 and 156.8 µg/L, respectively, but considerably lower than those for OPC-FA blocks (689, 11,870.6 and 185.2 µg/L, respectively). The XRD and chemical speciation analysis revealed the desorption of Pb, Zn and Cd attached to surface of C-S-H crystalline structure during the DWC. The XPS and SEM-EDS analysis confirmed the formation of Pb-O-Si and Zn-O-Si bonds via isomorphous replacement of C-A-S-H in binder-FA blocks. Ettringite crystalline structure in OPC-FA block was severely destructed during the DWC, resulting in the reduced contents of PbSO4 and CaZn2Si2O7·H2O and the higher leachability of Pb2+ and Zn2+.

Preparation of geopolymer based on municipal solid waste incineration fly ash-phosphorus slag and its function for solidification of heavy metals.

Municipal solid waste incineration fly ash (MSWIFA) contains potential contaminants and needs to be efficiently solidified/stablized and so should be managed properly. To achieve this goal, alkali-activated MSWIFA and phosphorus slag (PS) based geopolymer solidified bodies were investigated. Therefore, the mechanical properties of the solidified body, heavy metal leaching characteristics, heavy metal chemical forms, and heavy metal solidification/stabilization mechanisms were also analyzed. The results show that: The addition of an appropriate amount of PS can promote the strength development of a solidified body. When the mass ratio of MSWIFA to PS is 7:3, the strength of the solidified body reaches 22.8 MPa at 90d curing age, which is 5.3 times higher than that of the unmodified material. The MSWIFA/PS immobilized Zn 99.9 %, Pb 99.4 % and Cd 99.8 % in 60 day leaching tests. Meanwhile, PS can significantly increase the proportion of chemically stabilized forms of heavy metals in the solidified body. PS affects on the hydration process of the solidified body. When the mass fraction of PS doping was 30 %, the main hydration products of the solidified body were calcium silicate hydrate (C-S-H) and calcium alumina (AFt). When the mass fraction of PS is 50 %, the main hydration products are calcium aluminosilicate hydrate (C-A-S-H), sodium aluminosilicate hydrate (N-A-S-H), and AFt. These hydration products have good solidification effects on heavy metals. Therefore, it can be concluded that the MSWIFA/PS solidified body is an environmentally friendly and efficient binder.

Sunlight-Driven Self-Cleaning Ultrafine Particulate Matter Filter with Antibacterial Activity.

Air pollution by particulate matter (PM) and airborne pathogens causes severe health problems in the human body. Presently, popular disposable air filters yield huge waste and have a fatal impact on the environment. Postuse cleaning of air filters also leads to secondary air and water pollution. Here, we report a sunlight-driven self-cleaning PM filter by coupling a full-solar-spectrum-active photocatalyst comprising up-conversion nanoparticles (UCNPs) decorated with semiconductor iron(III) oxide (UCNP@α-Fe2O3) shells stabilized upon graphene functionalized borosilicate fibrous membrane (rGO-BF). While rGO-BF ensures high PM adsorption, UCNP@α-Fe2O3 (NP) enables self-photodegradation of adsorbed PM under abundant sunlight and subsequent membrane regeneration, while preventing secondary air or water pollution. Rational surface chemistry and optimal microstructure enable our filters to remove >99% of PM2.5 under deplorable air-quality conditions. Moreover, our filter shows excellent antibacterial activity toward E. coli and S. aureus, demonstrating its potential for practical utilization in face masks, air filtering devices, and protective medical wear. This work successfully suggests an intriguing design platform for self-sustainable zero-waste air filter membranes.

Assessment of toxicological validity using tobacco emission condensates: A comparative analysis of emissions and condensates from 3R4F reference cigarettes and heated tobacco products.

The tobacco emission condensate, henceforth referred to as "tobacco condensate," plays a critical role in assessing the toxicity of tobacco products. This condensate, derived from tobacco emissions, provides an optimized liquid concentrate for storage and concentration control. Thus, the validation of its constituents is vital for toxicity assessments. This study used tobacco condensates from 3R4F cigarettes and three heated tobacco product (HTP) variants to quantify and contrast organic compounds (OCs) therein. The hazard index (HI) for tobacco emissions and condensates was determined to ascertain the assessment validity. The total particulate matter (TPM) for 3R4F registered at 17,667 µg cig-1, with its total OC (TOC) at 3777 µg cig-1. HTPs' TPM and TOC were 9342 ± 1918 µg cig-1 and 5258 ± 593 µg stick-1, respectively. 3R4F's heightened TPM likely arises from tar, while HTPs' OC concentrations are influenced by vegetable glycerin (2236-2688 µg stick-1) and propylene glycol (589-610 µg stick-1). During the condensation process, a substantial proportion of OCs in 3R4F smoke underwent significant concentration decreases, in contrast to HTPs, where fewer than half of the examined OCs exhibited notable concentration declines. The HI for tobacco emissions exhibited a marginally higher value compared to tobacco condensate, with variations ranging from 7.92% (HTPs) to 18.6% (3R4F), denoting a minimal differential. These observations emphasize the importance of accurate OC recovery techniques to maintain the validity and reliability of toxicity assessments based on tobacco condensates. This study not only deepens the comprehension of chemical behaviors in tobacco products but also establishes a novel benchmark for their toxicity evaluation, with profound implications for public health strategies and consumer protection.

Density functional theory study on the formation mechanism of CaClOH in municipal solid waste incineration fly ash.

Municipal solid waste incineration (MSWI) fly ash is defined as a kind of hazardous waste because of its high levels of multiple pollutants. The main component of MSWI fly ash is CaClOH, and the characteristics have not achieved consensus. And density functional theory (DFT) was used to calculate the formation process of CaClOH in this study, which mainly included HCl adsorption on CaO (0 0 1) surface and Ca(OH)2 (0 0 1) surface and the surface reaction process. The reaction mechanism was investigated. The results showed that the maximum adsorption energies of HCl on CaO and Ca(OH)2 surfaces reached - 195.17 kJ/mol and - 83.48 kJ/mol, respectively, representing strong chemisorption. The chemisorption process was shown as the adsorption of H atom on O site, and the adsorption capacity was reflected in the adsorption range of O site. The significant electron density overlap between O site and H atom meant that a new chemical bond formed, which made the adsorption structure stable. The adsorption energy of multi-HCl adsorption on the crystal surfaces was not proportional to the number of HCl molecule, indicating that the adsorption processes were influenced by each other. After surface reaction, the H-Cl bond was broken completely, and the structure of CaO and Ca(OH)2 changed to new structures. According to transition state (TS) search, the formation of CaClOH had a higher priority, easier than that of CaCl2, explaining the presence of CaClOH in fly ash. The study provides helpful information for the solidification treatment of fly ash.

The contribution of wildfire to PM2.5 trends in the USA.

Steady improvements in ambient air quality in the USA over the past several decades, in part a result of public policy1,2, have led to public health benefits1-4. However, recent trends in ambient concentrations of particulate matter with diameters less than 2.5 µm (PM2.5), a pollutant regulated under the Clean Air Act1, have stagnated or begun to reverse throughout much of the USA5. Here we use a combination of ground- and satellite-based air pollution data from 2000 to 2022 to quantify the contribution of wildfire smoke to these PM2.5 trends. We find that since at least 2016, wildfire smoke has influenced trends in average annual PM2.5 concentrations in nearly three-quarters of states in the contiguous USA, eroding about 25% of previous multi-decadal progress in reducing PM2.5 concentrations on average in those states, equivalent to 4 years of air quality progress, and more than 50% in many western states. Smoke influence on trends in the number of days with extreme PM2.5 concentrations is detectable by 2011, but the influence can be detected primarily in western and mid-western states. Wildfire-driven increases in ambient PM2.5 concentrations are unregulated under current air pollution law6 and, in the absence of further interventions, we show that the contribution of wildfire to regional and national air quality trends is likely to grow as the climate continues to warm.

Ambient PM2.5 and its components associated with 10-year atherosclerotic cardiovascular disease risk in Chinese adults.

BACKGROUND: Exposure to particulate matter with aerodynamic diameters less than 2.5 µm (PM2.5) may increase the risk of 10-year atherosclerotic cardiovascular disease (ASCVD) risk. While PM2.5 is comprised of various components, the evidence on the correlation of its components with 10-year ASCVD risk and which component contributes most remains limited. METHODS: Data were derived from the baseline assessments of China Multi-Ethnic Cohort (CMEC). In total, 69,722 individuals aged 35-74 years were included into this study. The annual average concentration of PM2.5 and its components (black carbon, ammonium, nitrate, sulfate, organic matter, soil particles, and sea salt) were estimated by satellite remote sensing and chemical transport models. The ASCVD risk of individuals was calculated by the equations from the China-PAR Project (prediction for ASCVD risk in China). The relationship between single exposure to PM2.5 and its components and predicted 10-year ASCVD risk was assessed using the logistic regression model. The effect of joint exposure was estimated, and the most significant contributor was identified using the weighted quantile sum approach. RESULTS: Totally 69,722 participants were included, of which 95.8 % and 4.2 % had low and high 10-year ASCVD risk, respectively. Per standard deviation increases in the 3-year average concentration of PM2.5 mass (odds ratio [OR] 1.23, 95 % confidence interval [CI]: 1.12-1.35), black carbon (1.21, 1.11-1.33), ammonium (1.21, 1.10-1.32), nitrate (1.25, 1.14-1.38), organic matter (1.29, 1.18-1.42), sulfate (1.17, 1.07-1.28), and soil particles (1.15, 1.04-1.26) were related to high 10-year ASCVD risk. The overall effect (1.19, 1.11-1.28) of the PM2.5 components was positively associated with 10-year ASCVD risk, and organic matter had the most contribution to this relationship. Female participants were more significantly impacted by PM2.5, black carbon, ammonium, nitrate, organic matter, sulfate, and soil particles compared to others. CONCLUSION: Long-term exposure to PM2.5 mass, black carbon, ammonium, nitrate, organic matter, sulfate, and soil particles were positively associated with high 10-year ASCVD risk, while sea salt exhibited a protective effect. Moreover, the organic matter might take primary responsibility for the relationship between PM2.5 and 10-year ASCVD risk. Females were more susceptible to the adverse effect.

Oxidation 1-methyl naphthalene based on the synergy of environmentally persistent free radicals (EPFRs) and PAHs in particulate matter (PM) surface.

Studies of the environmental fate through the interactions of particle-associated polycyclic aromatic hydrocarbons (PAHs) with environmentally persistent free radicals (EPFRs) are presented. The formation of PAHs and EPFRs typically occurs side by side during combustion-processes. The laboratory simulation studies of the model PAH molecule 1-Methylnaphthalene (1-MN) interaction with model EPFRs indicate a transformational synergy between these two pollutants due to mutual and matrix interactions. EPFRs, thorough its redox cycle result in the oxidation of PAHs into oxy-/hydroxy-PAHs. EPFRs have been shown before to produce OH radical during its redox cycle in aqueous media and this study has shown that produced OH radical can transform other PM constituents resulting in alteration of PM chemistry. In model PM, EPFRs driven oxidation process of 1-MN produced 1,4-naphthoquinone, 1-naphthaldehyde, 4-hydroxy-4-methylnaphthalen-1-one, and various isomers of (hydroxymethyl) naphthalene. Differences were observed in oxidation product yields, depending on whether EPFRs and PAHs were cohabiting the same PM or present on separate PM. This effect is attributed to the OH radical concentration gradient as a factor in the oxidation process, further strengthening the hypothesis of EPFRs' role in the PAH oxidation process. This finding is revealing new environmental role of EPFRs in a natural degradation process of PAHs. Additionally, it points to implications of such PM surface chemistry in the changing mobility of PAHs into an aqueous medium, thus increasing their bioavailability.

Long-term exposure to ambient PM2.5 constituents is associated with dyslipidemia in Chinese adults.

BACKGROUND: Ambient particulate matter with aerodynamic diameter ≤ 2.5 µm (PM2.5) consists of various toxic constituents. However, the health effect of PM2.5 may differ depending on its constituents, but the joint effect of PM2.5 constituents remains incompletely understood. OBJECTIVE: Our goal was to evaluate the joint effect of long-term PM2.5 constituent exposures on dyslipidemia and identify the most hazardous chemical constituent. METHODS: This study included 67,015 participants from the China Multi-Ethnic Cohort study. The average yearly levels of PM2.5 constituents for all individuals at their residences were assessed through satellite remote sensing and chemical transport modeling. Dyslipidemia was defined as one or more following abnormal blood lipid concentrations: total cholesterol (TC) ≥ 6.22 mmol/L, triglycerides (TG) ≥ 2.26 mmol/L, high-density lipoprotein cholesterol (HDL-C) < 1.04 mmol/L, and low-density lipoprotein cholesterol (LDL-C) ≥ 4.14 mmol/L. The logistic regression model was utilized to examine the single effect of PM2.5 constituents on dyslipidemia, while the weighted quantile sum regression model for the joint effect. RESULTS: The odds ratio with a 95 % confidence interval for dyslipidemia positively related to per-SD increase in the three-year average was 1.29 (1.20-1.38) for PM2.5 mass, 1.25 (1.17-1.34) for black carbon, 1.24 (1.16-1.33) for ammonium, 1.33 (1.24-1.43) for nitrate, 1.34 (1.25-1.44) for organic matter, 1.15 (1.08-1.23) for sulfate, 1.30 (1.22-1.38) for soil particles, and 1.12 (1.05-1.92) for sea salt. Stronger associations were observed in individuals < 65 years of age, males, and those with low physical activity. Joint exposure to PM2.5 constituents was positively related to dyslipidemia (OR: 1.09, 95 %CI: 1.05-1.14). Nitrate was identified as the constituent with the largest weight (weighted at 0.387). CONCLUSIONS: Long-term exposure to PM2.5 constituents poses a significant risk to dyslipidemia and nitrate might be the most responsible for the risk. These findings indicate that reducing PM2.5 constituent exposures, especially nitrate, could be beneficial to alleviate the burden of disease attributed to PM2.5-related dyslipidemia.

Composition and sources of suspended particles in the Pacific Arctic region.

During the 6th (2014) and 7th (2016) Chinese Arctic Expedition (CHINARE), samples of suspended particulate matter (SPM) were collected from both surface (depth: <1.0 m) and subsurface (depth: approximately between 10 and 150 m) waters over the northern shelf of the Bering Sea and in the western Arctic Ocean. To investigate the distribution and sources of organic matter in both the surface water and the vertical profile, the concentration and stable carbon isotopic composition of SPM, particulate organic carbon (POC), and particulate nitrogen (only in surface water samples) were determined, and some particle samples were selected for examination using scanning electron microscopy. Results showed apparent geographical partitioning and temporal variation in both the concentration and the composition of SPM. Higher SPM concentrations were observed in nearshore, shelf break, and sea ice edge areas; the distribution of POC concentration displayed a similar pattern, with higher values found from the northern part of the Bering Shelf to southern parts of the Chukchi Shelf. In surface water, SPM mainly comprised clay and detrital minerals with higher POC contents, lighter δ13C values, and higher POC/PN ratios, indicating organic matter predominantly derived from terrestrial sources in areas south of St. Lawrence Island and north of 73°N. The downward trend of heavier δ13C values, together with reduction in clay and detrital minerals, suggests that vertical transport of SPM is hindered by stratification, resulting in transport of terrestrial materials toward northern basin areas. In the Chukchi Slope and Canada Basin areas, extremely light δ13C values (as low as -33.41‰ PDB) were mainly observed at depths of 20-60 m, where the Polar Mixed Layer (PML) intersects with the Upper Halocline Layer (UHL). Under the condition of low sea ice extent in 2016, the POC-δ13C values were heavier in the PML than in the UHL in the Chukchi Slope and Canada Basin areas. These findings provide insights into the sources, transport, and fate of organic matter in the Pacific Arctic region, which have important implications for understanding the biogeochemical cycles and ecosystem dynamics in this remote and rapidly changing environment.

The physical encapsulation and chemical fixation of Zn during thermal treatment process of municipal solid waste incineration (MSWI) fly ash.

Thermal treatment is a promising treatment technology of municipal solid waste incineration (MSWI) fly ash because of its detoxication and volume reduction. However, the relationship between immobilization of heavy metals and mineral transformation during thermal treatment remains unclear. In this study, the immobilization mechanism of Zn during thermal treatment process of MSWI fly ash was investigated by experiment and calculation. The results show that addition of SiO2 facilitates transition of dominant minerals from melilite to anorthite during sintering, increases liquid content during melting and improves liquid polymerization degree during vitrification. ZnCl2 tends to be physically encapsulated by liquid phase, and ZnO is mainly chemically fixed into minerals at high temperature. Increase in both liquid content and liquid polymerization degree favors the physical encapsulation of ZnCl2. The decreasing order of chemical fixation ability of minerals to ZnO is spinel > melilite > liquid > anorthite. To better immobilize Zn during sintering and vitrification process chemical composition of MSWI fly ash should be located in melilite and anorthite primary phases of pseudo-ternary phase diagram, respectively. The results are helpful to understand immobilization mechanism of heavy metals and avoid volatilization of heavy metals during thermal treatment process of MSWI fly ash.

Chemical characteristics, leaching, and stability of the ubiquitous tire rubber-derived toxicant 6PPD-quinone.

We here report chemical characteristics relevant to the fate and transport of the recently discovered environmental toxicant 6PPD-quinone (2-((4-methylpentan-2-yl)amino)-5-(phenylamino)cyclohexa-2,5-diene-1,4-dione or "6PPDQ"). 6PPDQ is a transformation product of the tire rubber antioxidant 6PPD that is ubiquitous in roadway environments, including atmospheric particulate matter, soils, runoff, and receiving waters, after dispersal from tire rubber use and wear on roadways. The aqueous solubility and octanol-water partitioning coefficient (i.e. log KOW) for 6PPDQ were measured to be 38 ± 10 µg L-1 and 4.30 ± 0.02, respectively. Within the context of analytical measurement and laboratory processing, sorption to various laboratory materials was evaluated, indicating that glass was largely inert but loss of 6PPDQ to other materials was common. Aqueous leaching simulations from tire tread wear particles (TWPs) indicated short term release of ∼5.2 µg 6PPDQ per gram TWP over 6 h under flow-through conditions. Aqueous stability tests observed a slight-to-moderate loss of 6PPDQ over 47 days (26 ± 3% loss) for pH 5, 7 and 9. These measured physicochemical properties suggest that 6PPDQ is generally poorly soluble but fairly stable over short time periods in simple aqueous systems. 6PPDQ can also leach readily from TWPs for subsequent environmental transport, posing high potential for adverse effects in local aquatic environments.

New insights into the mechanism of phosphate release during particulate organic matter photodegradation based on optical and molecular signatures.

Phosphate release from particulate organic matter (POM) dominates phosphorus (P) cycling in aquatic ecosystems. However, the mechanisms underlying P release from POM remain poorly understood because of complex fractionation and analytical challenges. In this study, the release of dissolved inorganic phosphate (DIP) during POM photodegradation was assessed using excitation-emission matrix (EEM) fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). POM in suspension was significantly photodegraded under light irradiation, concomitantly with the production and release of DIP in the aqueous solution. Chemical sequential extraction revealed that organic phosphorus (OP) in POM participated in photochemical reactions. Moreover, FT-ICR MS analysis revealed that the average molecular weight of P-containing formulas decreased from 374.2 to 340.1 Da. Formulas containing P with a lower oxidation degree and unsaturation were preferentially photodegraded, generating oxygen-enriched and saturated formula compounds, such as protein- and carbohydrate-like P-containing formulas, benefiting further utilization of P by organisms. Reactive oxygen species played an important role in the photodegradation of POM, and excited triplet state chromophoric dissolved organic matter (3CDOM*) was mainly responsible for POM photodegradation. These results provide new insights into the P biogeochemical cycle and POM photodegradation in aquatic ecosystems.

A novel method of calcium dissolution-crystallization-polymerization for stabilization/solidification of MSWI fly ash.

Municipal solid waste incineration fly ash (MSWI FA) stabilization/solidification using calcium carbonate (CaCO3) oligomer is an efficient, low-carbon disposal method. The insoluble Ca in FA was converted to free-Ca, utilizing for CaCO3 oligomer preparation, which was crystallized and polymerized by thermal induction to develop continuous cross-link or bulk structures for stabilization/solidification of potentially toxic elements (PTEs, e.g., lead (Pb) and zinc (Zn)). Experimental results showed that the weakly alkaline acid-leaching suspension provided an excellent condition for the generation of CaCO3 oligomers, with Pb and Zn immobilization reaching over 99.4%. With the acid strengthening of the suspension, H+ took the lead in protonating with TEA and limiting the capping action of TEA, which was harmful to the synthesis of CaCO3 oligomers. Ethanol with a low dielectric constant was considered an ideal solvent for oligomer production, and triethylamine (TEA) as a capping agent established hydrogen bonds (N⋯H) with protonated CaCO3. H2O molecules competed with the protonated CaCO3 molecules for TEA with ethanol concentration decreasing, resulting in erratic precipitation of CaCO3 molecules and significantly elevated leaching risk of Pb and Zn. The sequential extraction procedure, pH-dependent leaching, and geochemical analysis results revealed that the dissolution/precipitation of Ca, Pb, and Zn in treated FA was mostly controlled by the carbonate mineral phases. Moreover, the low boiling points of ethanol and TEA can be recovered for recycling. The gel-like, flexible combination of CaCO3 oligomers and FA particles formed by FA offers great resource utilization potential via a controlled crystallization polymerization process.

Water washing and acid washing of gasification fly ash from municipal solid waste: Heavy metal behavior and characterization of residues.

Gasification fly ash (GFA) is a hazardous solid residue generated in the slagging-gasification of municipal solid waste (MSW). GFA contains higher amounts of heavy metals such as Pb and Zn than incineration fly ash (IFA), which increases the difficulty of heavy metal immobilization but simultaneously makes it a potential feedstock for metal recovery. Water washing and acid washing are conventional and economic methods to treat wastes with high heavy metal and chloride contents. However, the research on the effects of such methods in treating GFA is still blank. Hence, in this study, water washing and acid washing of GFA were investigated in detail. Heavy metal behaviors at different time points during the washing processes were studied in a wide pH range and comprehensive characterizations of washed GFAs were also conducted. The results show that different re-precipitates could be identified in washed GFAs depending on different pH conditions. After water washing for 24 h, more than 60% of Zn in GFA would dissolve and re-precipitate into calcium zincate. It is also revealed that the precipitation effect could in turn influence the pH during the washing process. After acid washing with a low-concentration acid, heavy metal leachabilities were found reduced due to the pH and precipitation effect. High-concentration acid washing could effectively extract Zn and Cd with extraction ratios exceeding 90%. Applying 1.2 M-HCl washing, a short washing period of 15 min could realize a Pb extraction ratio of 81.2%, much higher than 53.2% when extending the washing period to 24 h.

Environmental filling materials based on phosphogypsum powder with municipal solid waste incineration ash.

A new building filling materials (NBFM) using phosphogypsum and municipal solid waste incineration (MSWI) fly ash is prepared in this paper. The effects of MSWI fly ash dosage and MSWI fly ash water washing pretreatment on mechanical properties, setting time, metal leaching, hydration products and microstructure of NBFM are analyzed by a range of experimental studies. The results indicate that the mechanical properties, setting time and the density of micro interface of NBFM are optimal when the MSWI fly ash dosage is 3%. The mechanical properties of NBFM rise and the condensation time and leaching concentration of heavy metals decline after washing the MSWI fly ash. With the increase of the curing age, the metal element leaching of NBFM decreases, and when the curing age is 7 days, the solidification effect of NBFM on most metal elements meets the standard of Chinese code (GB5085.3-2007). The feasibility of MSWI fly ash and phosphogypsum as filling materials for building engineering is verified, and the change of macroscopic properties of NBFM is explained as well.

Chemical composition characteristics and source analysis of PM2.5 in Jiaxing, China: insights into the effect of COVID-19 outbreak.

Jiaxing is a medium-sized city in the Yangtze River Delta (YRD), which showed complex local and surrounding pollution sources. To study the COVID-19 impact on the ambient PM2.5 in Jiaxing, we collected the PM2.5 samples from 2 January to 25 April 2020 and analysed their chemical compositions (including carbon components, water-soluble ions (WSIs), and inorganic elements). The concentration of PM2.5 was 83.13 ± 30.93 µg/m3 before COVID-19 pandemic and then remarkably decreased with COVID-19 outbreak due to the suspension of mobility and industrial activities. Meanwhile, the concentrations of main chemical species (carbon components, water-soluble ions and inorganic elements) of PM2.5 all decreased from period A (2-20 January 2020) to period B (23 January to 10 February 2020). Moreover, Trajectory clustering analysis showed that close-range transport was one of the dominant factors throughout all the periods, except for period D (1-25 April 2020). In addition, the PSCF model indicated that the COVID-19 outbreak resulted in a significant decrease of WPSCF value. This study highlighted the differences in chemical compositions and sources of PM2.5 since COVID-19 pandemic was reported and provided a better understanding of its outbreak on PM2.5.