Dissolved organic matter (DOM) was detected in MSWI plant: An investigation of DOM and potential toxic elements variation in the bottom ash and fly ash

Enhanced self-cementation of arsenic-contaminated soil via activation of non-thermal plasma-irradiated ferromanganese: A mechanistic investigation

The self-cementation characteristics of arsenic (As)-contaminated soil were comprehensively investigated in this study. Different non-thermal plasma-irradiated binary (hydro)oxides of polyvalent ferromanganese (poly-Fe-Mn) were synthesized and exploratorily dispersed to soil samples to activate solidification and stabilization during the self-cemented process. The maximum compressive strength of 56.35 MPa and the lowest leaching toxicity of 0.004 mg/L were obtained in the proof test under optimal conditions (i.e., the mass ratio of the poly-Fe-Mn to the soil sample of 0.05; the mass ratio of the composite alkali activator (NaOH + CaO) to the soil sample of 0.25; the mass ratio of CaO to NaOH of 1.5; the mass ratio of the DI water to the binder of 0.515). The composite alkaline activator primarily contributed to the strength formation of the self-cemented matrix while the poly-Fe-Mn significantly influenced the reduction of the As-leaching toxicities. The poly-Fe-Mn maintained diffusion-controlled polycondensation and strengthened the nucleation process during self-cementation. The amount of water and the dosage of poly-Fe-Mn caused an interactive influence on the self-cemented solidification of contaminated soils. The solidified samples with poly-Fe-Mn exhibited better thermal decomposition than their counterparts, reflecting the enhancement of poly-Fe-Mn to the matrix. Some minerals including C-S-H, kaolinite, gehlenite, diopside sodian, augite, and albite were matched in the samples, directly demonstrating the geopolymerization-steered self-cementation of the As soil. The employment of poly-Fe-Mn not only reinforced the immobilization of As pollutants in the matrix but also induced the self-cementation of soils by intensifying the composite alkaline-activated geopolymerization kinetics.

Chemical speciation and health risk assessment of potentially toxic elements in playground soil of bell metal commercial town of Eastern India

Contaminated playground soils can expose players to harmful pollutants, increasing the risk of respiratory, skin, and gastrointestinal issues and potentially impacting long-term health and development. This study investigated the chemical forms and the human health risks associated with potentially toxic elements (PTEs) found in playground soil samples from Khagra, a historic town known for its bell metal industry, located in the Murshidabad district of eastern India. Sequential extraction techniques were employed to analyze the distribution of PTEs such as As, Cd, Co, Cu, Mn, Pb, Ni, Sn, and Zn among different fractions: exchangeable (F1), bound to carbonate phase (F2), bound to iron and manganese oxides (F3), bound to organic matter (F4), and residual (F5). The playground soil showed the highest contamination with Sn, with an IPOLL value of 3.14, indicating moderate to heavy contamination, while Cd, Cu, Mn, Pb, and Zn exhibit moderate contamination. The mean concentration of PTEs in all fractions (F1-F5) follows the order: Fe > Zn > Cu > Mn > Pb > Sn > Ni > Co > As > Cd. The maximum affinity of PTEs and their percentages are as follows: Fe (F5, 80.6%), As (F5, 55.31%), Cd (F5, 48.8), Co (F5, 64.9%), Mn (F3, 44%), Ni (F5, 53.2%), Pb (F3, 44.7%), Zn (F3, -43.19%), Sn (F3, 55%), Cu (F5 -42.18). As, Cd, Co, Cu, Fe, and Ni have a high affinity for F5, indicating geogenic source, while Mn, Pb, Sn, and Zn have a high affinity for F3, indicating anthropogenic source. Fe-Mn oxide partition was dominant for nearly all PTEs due to elevated sorption of cations onto Fe-Mn oxides at high pH. The risk assessment code for Cd, Cu, Mn, Ni, Sn, and Zn in playground soil is categorized under moderate risk, below 30%, while other elements showed no risk. Also, mobility factors were calculated for each PTEs, suggesting the degree of mobility that PTEs can easily migrate and be taken up, absorbed, or adsorbed by the human body. The mobility factor in playground soil was higher for Sn (59.89%) followed by Mn (54.24%) > Pb (52.91%) > Zn (52.01%) > Cd (39.49%) > Ni (33.20%) > As (30.39%) > Co (26.56%) > Cu (21.24%) > Fe (11.20%). Risk hazard quotients for children and adults were found to follow the order: Pb (0.263; 0.040), Cu (0.098; 0.015) > As(0.056; 0.008) > Mn (0.045; 0.009) > Zn(0.36; 0.05) > Cd(0.006; 0.001) > Ni (0.004; 0.001) > Co (0.001; 0.0). PTEs detected in the environment result from atmospheric deposition from small-scale metallurgical industries (bell metal and brass), coal and oil combustion, civil works, municipal waste incineration, and fugitive emissions from road dust. The human non-carcinogenic health risk for PTEs from ingestion and dermal contact was higher than that from inhalation. In the context of carcinogenic risk, As shows the highest health risk of 2.51E-05, followed by Cd (1.02E-09) and Co (8.14E-09). This study uniquely assesses the chemical speciation of PTEs in playground soils, revealing their geogenic and anthropogenic sources, and evaluates associated health risks. Policy intervention is vital for monitoring and remediating PTEs in playgrounds to protect children's health.

Risk assessment for the long-term stability of fly ash-based cementitious material containing arsenic: Dynamic and semidynamic leaching

Fly ash from municipal solid waste incineration (MSWIFA) contains leachable heavy metals (HMs), and the environmental risk of contained HMs is an important concern for its safe treatment and disposal. This paper presents a dynamic leaching test of fly ash-based cementitious materials containing arsenic (FCAC) in three particle sizes based on an innovative simulation of two acid rainfall conditions to investigate the long-term stability of FCAC under acid rain conditions. As well as semi-dynamic leaching test by simulating FCAC in three scenarios. Furthermore, the long-term stability risk of FCAC is evaluated using a sequential extraction procedure (SEP) and the potential risk assessment index. Results showed that the Al3+ in the FCAC dissolved and reacted with the OH- in solution to form Al(OH)3 colloids as the leaching time increased. Moreover, the oxidation of sulfide minerals in the slag produced oxidants, such as H2SO4 and Fe2(SO4)3, which further aggravated the oxidative dissolution of sulfides, thereby resulting in an overall decreasing pH value of the leachate. In addition, due to the varying particle sizes of the FCAC, surface area size, and adsorption site changes, the arsenic leaching process showed three stages of leaching characteristics, namely, initial, rapid, and slow release, with a maximum leaching concentration of 2.42 mg/L, the cumulative release of 133.78 mg/kg, and the cumulative release rate of 2.32%. The SEP test revealed that the reduced state of HMs in the raw slag was lowered substantially, and the acid extractable state and residual state of HMs were increased, which was conducive to lessening the risk of FCAC. Overall, the geological polymerization reaction of MSWIFA is a viable and promising solution to stabilize mining and industrial wastes and repurpose the wastes into construction materials.

Concentration, speciation and risk effects of multiple environmentally sensitive trace elements in respirable fine-grained fly ash

Respirable fine-grained fly ash (RFA) is captured very inefficiently by existing air purification devices of power plant, leading to increasing concerns regarding their migration and subsequent interaction with body due to fine particle size and its complex toxic composition. Trace elements of RFA in three groups with five different sizes between 8-13 µm were analyzed in terms of available concentration, speciation and risk effects. The concentration, pollution level and ecological risk level of elements in RFA were related to particle sizes. Chronic non-carcinogenic effect risk (NER) and carcinogenic effect risk (CER) were negatively correlated with particle size. The individual weight of exposed subjects, corresponding trace elements concentration and ingestion rate in RFA were three significant variables influencing CER. NER and CER had a tenfold exaggerated effect when calculated using total element concentration of RFA. In addition to individual differences and exposure conditions, trace element properties, speciation and available concentration were the dominant factor responsible for ecological and environmental effects of trace elements in RFA, following the order As>Ni, Mn>Cr>Pb>Cu>Zn. Results of this work highlight the effects and differences of trace elements in RFA on ecology and health, and provide a basis for further pollution control and human health warning.

Novel process for organic wastewater treatment using aerobic composting technology: Shifting from pollutant removal towards resource recovery

In this study, an organic wastewater treatment process based on aerobic composting technology was developed in order to explore the transition of wastewater treatment from pollutants removal to resource recovery. The novelty of the process focuses towards the microbial metabolic heat that is often ignored during the composting, and taking advantage of this heat for wastewater evaporation to achieve zero-discharge treatment. Meanwhile, this process can retain the wastewater's nutrients in the composting substrate to realize the recovery of resources. This study determined the optimum condition for the process (initial water content of 50 %, C/N ratio of 25:1, ventilation rate of 3 m3/h), and 69.9 % of the total heat generated by composting was used for wastewater treatment under the condition. The HA/FA ratio of composting substrate increased from 0.07 to 0.53 after wastewater treatment, and the retention ratio of TOC and TN was 52.3 % and 61.7 %, respectively, which proved the high recycling value of the composting products. Thermoduric and thermophilic bacteria accounted for 44.3 % of the community structure at the maturation stage, which played a pivotal role in both pollutant removal and resource recovery.

Self-alkali-activated self-cementation achievement and mechanism exploration for the synergistic treatment of the municipal solid waste incineration fly ashes and the arsenic-contaminated soils

The feasibility and potential mechanisms of the self-alkali activation brought by municipal solid waste incineration (MSWI) fly ashes to the self-cementation of arsenic-contaminated soils were quantitatively evaluated and comprehensively analyzed to avoid the additional application of the alkali activators and binder materials traditionally. The employment of the two kinds of precursor materials achieved the self-alkali-activated self-cementation ('double self') under ambient conditions. The largest compressive strength (MPa) of 25.64 and lowest leaching toxicities (mg/L) of 21.05, 2.86, 0.08, 0.02, 2.05, and 0.34 for Zn, Cu, Cr, Cd, Pb, and As were obtained in the solidified matrix. Geopolymerization kinetics of the 'double self' cementation can be mathematically fitted by the Johnson-Mehl-Avrami-Kolmogorov model. CaClOH and halite in the MSWI fly ashes set up the self-alkali activation by reacting with the kaolinite and quartz in soils contaminated with arsenic by forming layered hydration and three-dimensional geopolymerization products to push for self-cementation.

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.

Spatial and temporal dynamic response of abundant and rare aerobic denitrifying bacteria to dissolved organic matter in natural water: A case study of Lake Baiyangdian, China

Revealing the responses of abundant and rare aerobic denitrifying bacteria to dissolved organic matter (DOM) composition is essential for understanding the aquatic N cycle ecosystems. In this study, fluorescence region integration and high-throughput sequencing techniques were used to investigate the spatiotemporal characteristics and dynamic response of DOM and aerobic denitrifying bacteria. The DOM compositions were significantly different among the four seasons (P < 0.001) without spatial differences. Tryptophan-like substances (P2, 27.89-42.67%) and microbial metabolites (P4, 14.62-42.03%) were the dominant components, and DOM exhibited strong autogenous characteristics. Abundant (AT), moderate (MT), and rare taxa (RT) of aerobic denitrifying bacteria showed significant and spatiotemporal differences (P < 0.05). The responses of α-diversity and niche breadth of AT and RT to DOM differed. The DOM explanation proportion for aerobic denitrifying bacteria exhibited spatiotemporal differences based on redundancy analysis. Foliate-like substances (P3) had the highest interpretation rate of AT in spring and summer, while humic-like substances (P5) had the highest interpretation rate of RT in spring and winter. Network analysis showed that RT networks were more complex than AT networks. Pseudomonas was the main genus associated with DOM in AT on a temporal scale, and was more strongly correlated with tyrosine-like substances (P1), P2, and P5. Aeromonas was the main genus associated with DOM in AT on a spatial scale and was more strongly correlated with P1 and P5. Magnetospirillum was the main genus associated with DOM in RT on a spatiotemporal scale, which was more sensitive to P3 and P4. Special operational taxonomic units were transformed between AT and RT with seasonal changes, but not between the two regions. To summarize, our results revealed that bacteria with different abundances utilized DOM components differently, and provides new insight on the spatiotemporal response of DOM and aerobic denitrifying bacteria in aquatic ecosystems of biogeochemical significance.

Agricultural waste to real worth biochar as a sustainable material for supercapacitor

Biochar made from agricultural waste is gaining more attention in energy field due to its sustainability, low cost, apart from having high supercapacitance performance. Also, it has a wide range of environmental applications, including wastewater treatment, upgrading soil fertility, contaminant immobilization, and in situ carbon sequestration. The existing thermo-chemical methodologies for converting agricultural waste into a sustainable material i.e. biochar and the role of activation agents in enhancing the performance of these materials were critically analyzed and discussed. An overview of recent trends in agricultural waste-derived biochar for supercapacitor electrodes is highlighted in this review that emphasizes green circular economy for encouraging net-zero utility of agriculture waste biomass. The roles of various newly prepared "green" electrolytes in reducing the negative consequences of supercapacitor is also reviewed. The trashing of agricultural waste and the depletion of energy supplies has become a global concern, hurting the world's ecosystem and economy through pollution and a fuel crisis and hence the concept of a green circular economic model is also highlighted.

Synergistic influence of diatomite and MoS2 nanosheets on the self-alkali-activated cementation of the municipal solid waste incineration fly ash and mechanisms

The solidification/stabilization technique recommended for the disposal of municipal solid waste incineration (MSWI) fly ashes in developed countries was inappropriate for the treatment in most developing counterparts. In this study, the diatomite and MoS₂ nanosheets were synergistically employed to activate the self-alkali-activated cementation of the MSWI fly ashes to achieve efficient solidification, the immobilization of heavy metals (HMs), and the inhibition of chloride release. The compressive strength of 28.61 MPa and the leaching toxicities (mg/L) of Zn, Pb, Cu, Cd, and Cr of 2.26, 0.87, 0.5, 0.06, and 0.22 were obtained from the hardened mortars. Diatomite significantly influenced the self-alkali-activated cementation of the MSWI fly ashes while MoS₂ nanosheets played both roles in intensifying the stabilization of HMs and strengthening the binding process by inducing the formation of sodalite and kaolinite, enhancing the growth rates of nucleation, and transforming the layered cementation to the partial and full three-dimensional cementation in the hardened matrix. This study not only verified the feasibility of diatomite and MoS₂ in activating the self-alkali-activated cementation of the MSWI fly ashes but also supplied a reliable technique for the harmless disposal and efficient utilization of MSWI fly ashes in developing countries.

Municipal Solid Waste Incineration Fly Ash: From Waste to Cement Manufacturing Resource

This study investigates the possibility of using municipal solid waste incineration fly ash as a supplementary cementitious material to replace part of the clinker in cement. Life cycle assessment has shown that the partial replacement of clinker with blast furnace slag (CEM III) reduces cement's global warming potential by ~30%, while replacing clinker with fly ash reduces it by up to 55%. When using CEM III as the control binder in cement in which 55 wt% of the clinker was replaced with hydrothermally treated fly ash, the flexural strength decreased by ~60% and the compressive strength by ~65%. When the fly ash was mixed with calcined and vitrified demolition materials, flexural strength decreased by ~30% and compressive strength by ~50%. The hardening of the hydraulic binders fixed the heavy metals in the municipal solid waste incineration fly ash.

Insights into the landfill leachate properties and bacterial structure succession resulting from the colandfilling of municipal solid waste and incineration bottom ash

Four simulated bioreactors were loaded with only MSW, 5 % BA + MSW, 10 % BA + MSW and 20 % BA + MSW to investigate the leachate property and bacterial community change trends during the colandfilling process. The results showed that with increasing BA addition proportion (5 %∼20 %), the leachate oxidation-reduction potential (ORP) was lower, the leachate pH quickly entered the neutral stage, and the chemical oxygen demand (COD), volatile fatty acids (VFA), NH₄⁺-N, Ca²⁺ and SO₄^2- presented faster downward trends. The leachate SUVA₂₅₄ and E_300/400 confirmed that BA can accelerate the leachate humification process. BA can quickly increase bacterial diversity, and the higher the addition proportion of BA, the more significant the change in microbial community structure during the landfilling process. The leachate pH and COD greatly influenced the bacterial community structure. A low BA proportion can increase metabolism pathway abundance during the initial stage, but a high BA proportion had an inhibitory effect on the metabolism pathway.