A comprehensive review of toxicity of coal fly ash and its leachate in the ecosystem.

Coal fly ash (CFA), a byproduct of coal combustion, is a hazardous industrial solid waste. Its excessive global production, coupled with improper disposal practices, insufficient utilization and limited awareness of its inherent hazards, poses a significant threat to both ecological environment and human health. Based on the physicochemical properties of CFA and its leachates, we elucidate the forms of CFA and potential pathways for its entry into the human body, as well as the leaching behavior, maximum tolerance and biological half-life of toxic elements present in CFA. Furthermore, we provide an overview of current strategies and methods for mitigating the leaching of these harmful elements from CFA. Moreover, we systemically summarize toxic effect of CFA on organisms across various tiers of complexity, analyze epidemiological findings concerning the human health implications resulting from CFA exposure, and delve into the biotoxicological mechanisms of CFA and its leachates at cellular and molecular levels. This review aims to enhance understanding of the potential toxicity of CFA, thereby promoting increased public awareness regarding the disposal and management of this industrial waste.

Evolution of physicochemical and leaching characteristics of municipal solid waste incineration fly ash in China under ultra-low emission standard.

The physical and chemical characteristics of fly ash has changed significantly under ultra-low emission system and the current leaching system is no longer suitable for high alkalinity fly ash. This work investigated the pH values and evolution of physical and chemical characteristics of fly ash from 24 typical municipal solid waste incineration plants in China. The pH value of the leaching solution obtained by HJ/T 300-2007 presented two different acid and alkali characteristics, where high and low alkalinity fly ash accounted for 54.17% and 45.83%, respectively. The alkali content in fly ash increased significantly after ultra-low emission standard, increasing by 18.24% compared with before the implementation of GB 18485-2014. The leaching behavior of high alkalinity fly ash showed the illusion that they could enter the landfill only by the addition of a small amount of chelating agent or even without stabilization treatment, and its long-term landfill risk is significant. The phase change of high alkalinity fly ash and pH value change of the leaching solution after carbonation were the key factors for the leaching concentration change of heavy metals. Therefore, it is recommended to improve the existing leaching system or conduct accelerated carbonization experiments to scientifically evaluate the long-term leaching characteristics of high alkalinity fly ash, and to reduce the risk of heavy metal release from high alkalinity FA after entering the landfill site.

Optimizing nutrients from fly ash-amended soil through microbial-assisted phytoremediation using response surface methodology.

Nutrients are vital ingredients to boost plant health. The availability of nutrients is limited in fly ash (FA) waste to properly implement phytoremediation. The research explored the integration of microbes and treated wastewater irrigation in phytoremediation to provide the necessary nutrients for plant growth in fly ash-amended soils. The Box-Behnken method was used to design the experimental layout for the pot study. Response surface methodology (RSM) was applied as the optimization approach to model predictions for nutrient accumulation. The implemented pot study attained the highest morphological indicators with a plastochron index of 33.40, an absolute growth rate of 2.63 cm/day, and a leaf area of 2681.68 cm2 and attained maximum biomass of 24.91 g for the treatments that included a mid-range of the variables. The combination of FA 14.98%, microbial dose 4.07 mL, and treated wastewater as the irrigation source was found to be the optimized combination for nitrogen and phosphorus accumulation of 212.4 and 8.867 mg/L.

Insights into Full-congener Profiles of Chlorinated Benzenes in Fly and Bottom Ash: Case Study in Vietnamese Industrial and Municipal Waste Incinerators.

Chlorinated benzenes (CBzs) are a group of organic pollutants, which have been industrially or unintentionally produced through various chemical and thermal processes. Studies on full congener profiles of CBzs in waste and environmental samples are relatively limited and not updated. In the present study, concentrations of 12 CBzs were determined in fly ash (FA) and bottom ash (BA) samples collected from one municipal waste incinerator (MWI) and one industrial waste incinerator (IWI) in northern Vietnam. Levels of Σ12CBzs were higher in bottom ash (median 25.3; range 1.59-45.7 ng/g) than in fly ash (median 7.30; range 1.04-30.0 ng/g). The CBz profiles were dominated by di- and tri-chlorinated congeners with the major congeners as 1,2,4-TCB, 1,2,3-TCB, 1,2-DCB, and 1,3-DCB. However, CBz profiles varied greatly between sample types and incinerators, implying differences in input materials, formation pathways, and pollutant behaviors. Incomplete combustion is possibly responsible for high levels of CBzs in industrial bottom ash. The emission factors of Σ12CBzs ranged from 21 to 600 µg/ton for fly ash and from 190 to 4570 µg/ton for bottom ash, resulting in annual emissions of about 6 and 3 g/year for the IWI and MWI, respectively. Our results suggest additional investigations on industrial emission and environmental occurrence of all 12 CBzs rather than solely focusing on regulated congeners like hexachlorobenzene and pentachlorobenzene.

Growth, biochemical, and antioxidant response of pot marigold (Calendula officinalis L.) grown in fly ash amended soil.

The present study was carried out to determine the impact of FA application on growth performance, biochemical parameters, and antioxidant defense activity of Calendula officinalis. The results revealed that under a low dose of FA (40%) amended soil, the plant growth performance and metal tolerance index (MTI) were increased compared to control plants and further decreased with increased FA application (60%, 80%, and 100% FA). In addition, the incorporation of 40% FA in soil not only improved the physicochemical properties of soil but also increased the biochemical parameters in the Calendula plant, however, these parameters declined under high FA applications. It was also observed that antioxidant enzyme activity (SOD, CAT, POD, and APX) in leaves of Calendula officinalis increased at high FA application (100% FA) to combat heavy metal stress from FA. The overall study suggests that 40% FA amended soil is the best suitable dose for growing Calendula officinalis and can be considered as metal tolerant species for phytoremediation of 40% FA amended soil.Novelty statement: Fly ash (FA) management is a major problem nowadays. The present study was carried out for FA utilization and to determine the impact of FA amended soil on growth performance, antioxidant properties, and biochemical attributes of Calendula officinalis. This is a sustainable approach in which waste (FA) utilization was done simultaneously with the enhancement in response of the medicinally potent Calendula species. The novelty of this study also suggests that Calendula has phytoremediation potential for remediation of heavy metal polluted soil. Further, the relationship between the growth, biochemical parameters, and antioxidant defense mechanism of Calendula grown on FA amended soil was studied which has not been studied so far. It was found that Calendula is a hyperaccumulator that can adapt to heavy metal stress from FA due to its ability to mitigate oxidative damage. Statistical analysis (ANOVA, Duncan's multiple range test, and PCA) was done for the results obtained using SPSS (11.5) and Origin 8 Pro software.

Evaluation of potential radiological hazards of unfired construction materials containing fly ash in Vietnam.

In this study, the specific activities of 226Ra, 232Th and 40K in the unfired construction materials (solid card bricks, 4-hole bricks, pavement bricks) containing fly ash and bottom ash from a coal-fired thermal power plant in Vietnam were measured using the low-level gamma-ray spectrometer with HPGe detector. Also, the 222Rn concentrations in these materials were analyzed using RAD7 radon monitor and then radon mass exhalation rate and emanation fraction of these materials were calculated. The potential radiological hazards for residents living in the model room made of these materials were evaluated. The average specific activity of 226Ra, 232Th and 40K were found as 67.7, 79.3 and 703.5 Bq kg-1, respectively. The total annual effective dose (due to external gamma exposure and internal radon exposure for resident living in the CEN model room made of the unfired brick samples) was found as 0.9 mSv y-1 which is lower than the worldwide average dose of 2.4 mSv y-1. Calculations from ResRad-Build code showed that the doses due to radon exposure account for from 62.3% (at the first year) to 98.8% (at the next 30 years) of the total gamma and radon dose. Under low air exchange to the outside environment, from the 6th year onwards, the total dose may exceed the average dose value from natural radiation exposure sources.

Seedling growth and physicochemical transformations of rice nursery soil under varying levels of coal fly ash and vermicompost amendment.

Fly ash is an inevitable by-product from the coal-fired power plants in many developing countries including India that needs safe, timely and productive disposal. The addition of fly ash alters physicochemical properties of soil and hence could be used as a soil conditioner or modifier along with the appropriate level of vermicompost to support plant growth. Several studies have focalized sole use of fly ash and vermicompost in agricultural production systems lacking information on combined application effects. This work was carried out at Chiplima in the district of Sambalpur, Odisha, India, to ascertain the best suited combination of native soil, fly ash and vermicompost (from farmyard manure) for rice nursery based on the changing physicochemical properties and seedling growth. The experiment consisting of 21 treatment combinations of soil, fly ash and vermicompost at 0%, 20%, 40%, 60%, 80% and 100% by weight was laid out in a factorial complete randomized design with three replications. Fly ash and vermicompost at moderate concentrations significantly ameliorated the physical properties, viz., porosity, bulk and particle densities, water holding capacity, infiltration rate and the capillary rise of water in rice nursery soil that ultimately resulted in vigorous rice seedlings at 40 DAS through beneficial soil biota as well as better root and shoot development. The porosity, water holding capacity and infiltration rate significantly increased with the addition of vermicompost while fly ash addition substantially reduced them. Fly ash and vermicompost in moderate quantities smothered soil chemical properties like electrical conductivity and organic carbon that increased the availability of N, P, K, B, S and Zn. The pH did not differ significantly due to treatment effects owing to a marginal difference in pH of the substrates, whereas electrical conductivity increased significantly with only marginal addition of fly ash to vermicompost. Considering the economic feasibility and environmental impacts, 40% soil + 20% fly ash + 40% vermicompost may be recommend to the farmers for wet rice nursery raising and also for remediating the coal fly ash in agricultural production system.

Chromium in Chinese coals: geochemistry and environmental impacts associated with coal-fired power plants.

Chromium (Cr), one of the prime hazardous trace elements in coals, may engender adverse effects on eco-environment and threaten human health during utilization of coal. Based on the samples obtained in our laboratory and published literature, the abundance and modes of occurrence of Cr in Chinese coals, and the environmental impacts associated with coal-fired power plants (CFPPs) were elucidated in this study. With a total of 1397 sets of data, the mean concentration of Cr in Chinese coals was calculated as 21.33 µg/g by the "reserve-concentration" weighted calculation method. Spatially, the average Cr contents increased gradually from North China to South China. Temporally, coals from T3, E-N and P2 were relatively enriched in Cr compared to the other geological time. The Cr concentration in coal varied with different coal ranks. The geological factors accounted for Cr enrichment in coals could be divided into the primary, secondary and epigenetic processes. Higher percentages of organically Cr occurred in low-rank coals, while inorganically associated Cr was mainly found in clay minerals. After coal combustion, most of Cr was enriched in solid wastes (e.g., fly ash and bottom ash). The leaching of Cr from solid wastes in the rainy season (especially acid rain) needs to be a concern for CFPPs. It was estimated that the atmospheric emission of Cr from CFPPs increased annually from 2015 to 2019 and reached approximately 159 tons in 2019.

Ecological risk assessment of heavy metals in bottom ashes generated by small-scale thermal treatment furnaces for domestic waste in villages and towns of China.

Small-scale Solid Waste Thermal Treatment (SSWTT) is prevalent in remote Chinese locations. However, the ecological threats associated with heavy metals in resultant bottom ash remain undefined. This research study scrutinized such ash from eight differing sites, assessing heavy metal content, chemical form, and leaching toxicity. Most bottom ash samples met soil contamination standards for development land (GB36600-2018). However, levels of As, Cd, Cr, Cu, Ni, Pb, and Zn in some samples exceeded agricultural land standards GB15618-2018) by 1591%, 64,478%, 1880%, 3886%, 963%, 1110%, and 2011% respectively. Additionally, the As and Cd contents surpassed the construction land control limit value by 383% and 13% respectively. The mean values of the combined oxidizable and residual fraction (F3 + F4) for each heavy metal in all samples exceeded 65%, with Cr, Cu, Ni, and Pb reaching over 95%. All sample leaching concentrations, obtained via the HJ/T 299 procedure, were less than limits set by the identification standards for hazardous wastes (GB5085.3-2007). However, only the leaching concentrations of three samples via the leaching procedure HJ/T 300 met the "Solid Waste Landfill Pollution Control Standard" (GB 16889-2008). The results indicate that the location and type of SSWTT equipment play a crucial role in determining an appropriate solution for bottom ash management.

Radioactivity of residues from waste incineration facilities in Finland.

Waste incineration in Europe has been increasing in the past few decades as there is a need to reduce the burden on landfills and their associated environmental concerns. While incineration reduces the volume of the waste, the volume of slag and ash is still substantial. To find out potential radiation risks that incineration residues could set to workers or the public, the levels of radioactive elements in these residues were investigated from nine waste incineration plants in Finland. Natural and artificial radionuclides were detected in the residues, but in general the activity concentrations were low. This study shows that the level of Cs-137 in the fly ash from municipal waste incineration follows the pattern of 1986 fallout zones in Finland, although the levels are significantly lower than in ash from bioenergy production from the same areas. Am-241 was also detected in many samples, although the activity concentrations were very low. Based on the findings in this study, the typical ash and slag residues from municipal waste incineration do not need radiation protection measures for workers or the public even in regions that received up to 80 kBq m-2of Cs-137 fallout in 1986. The further use of these residues need not be restricted due to radioactivity. Hazardous waste incineration residues and other special cases need to be considered separately, depending on the original waste composition.

Stabilization/solidification of heavy metal-contaminated marl soil using a binary system of cement and fuel fly ash.

The stabilization/solidification (S/S) method is one of the most effective remediation techniques for treating contaminated soils. Several stabilizers, mostly the cementitious materials, have been used for the S/S treatment. In this paper, the feasibility of utilizing fuel fly ash (FFA) as a partial replacement of ordinary Portland cement (OPC) for the S/S treatment of marl soil contaminated with heavy metals was investigated. Two industrial waste materials, namely steel and electroplating wastes, were used to synthetically contaminate the marl soil. The stabilizers comprising of OPC and FFA were mixed with the contaminated soil at different dosages ranging from 10 to 40%, by mass, and a total of 48 S/S-treated soil mixtures were prepared. A series of experiments, including density, porosity, permeability, unconfined compressive strength (UCS), and toxicity characteristics leaching procedure (TCLP), were carried out on the soil mixtures to evaluate the efficiency of the proposed S/S treatment. Test results showed that the incorporation of FFA at higher volumes reduced the density and increased the porosity and permeability of the treated mixtures. Although FFA addition resulted in reducing the UCS values by an average of 46%, and this reduction was more significant at higher FFA percentages, the UCS values of all mixtures were more than 0.35 MPa (350 kPa), which passed the minimum requirements set by USEPA. In addition, the metal immobilization ability of the proposed treatment was confirmed by the TCLP analysis. As compared to the negative effect of the contamination of the soil by the electroplating waste, the contamination of the soil by steel waste had a higher negative effect. The results of this study would contribute in selecting an environment-friendly treatment of the contaminated soils using industrial waste materials, such as FFA, as a partial replacement of OPC. Nevertheless, the present study is an initial attempt to explore the possibility of utilizing FFA as a partial replacement of OPC in S/S treatment of marl soil contaminated with heavy metals. It is recommended to conduct another study in future including analysis of the treated soil mixtures using XRD, SEM, and FTIR techniques to better understand the stabilization/solidification mechanism and its implications on the test results.

Chemical characteristics of bottom ash from biomedical waste incinerators in Ghana.

Biomedical waste (BMW) incineration is the most used alternative disposal method in developing countries, such as Ghana. The improper disposal of incinerator-generated bottom ash (BA) is a significant concern due to the hazardous nature of waste. A study was conducted at Tema Hospital (TGH) and Asuogyaman Hospital (VRAH) incinerator sites. The BA samples were sent to the Council for Scientific and Industrial Research, Institute of Industrial Research, Ghana. The BA samples were weighed with fisher analytical balance, ground, and sieved with standard grade meshes of 120, 100, and 80 to determine the BA particle size distribution. The chemical composition and heavy metals were analysed using X-ray fluorescence spectrometry (XRF) and atomic absorption spectroscopy (AAS) techniques. The results indicated the chemical composition of the analysed BA samples was CaCO3 (49.90%), CaO (27.96%) and MgCO3 (6.02%) for TGH and CaCO3 (48.30%), CaO (27.07%), and SiO2 (6.10%) for VRAH, respectively. The mean concentration (M) (kg m-3) and standard deviation (SD) for TGH in the BA were 7.082 ± 0.478 (Ti), 4.657 ± 0.127 (Zn) and 4.271 ± 1.263 (Fe), while that of VRAH consisted of 10.469 ± 1.588 (Ti), 7.896 ± 2.154 (Fe) and 4.389 ± 0.371 (Zn). Therefore, the heavy metals' mean concentration at the BA is above the WHO permissible limits of soil, i.e., 0.056 kg m-3 (Ti), 0.085 kg m-3 (Pb), 0.100 kg m-3 (Cr) and 0.036 kg m-3 (Cu). Furthermore, the heavy metal mean concentrations of TGH and VRAH present in the BA analysed samples were ranked in descending order: Ti > Zn > Fe and Ti > Fe > Zn, respectively. It is therefore recommended that BA must be properly disposed of because of the hazardous nature of heavy metals present in the analysed samples, which are able to cause environmental and public health issues.

Emission and transformation behaviors of trace elements during combustion of Cd-rich coals from coal combustion related endemic fluorosis areas of Southwest, China.

Long-term combustion of low-quality coal may release hazardous elements into the environment causing serious environmental problems. This phenomenon is particularly prevalent in the Three Gorges Region of Southwest (SW), China. Cadmium (Cd), as well as other harmful elements are found to be highly enriched in coals and supergene environments in this area. In the existing literature, the behavioral issue of emission and transformation of the elevated trace elements during simulated household stove combustion from Cd-rich inferior coal remains unknown. This study investigated the emission of toxic elements, mineral assemblages, and provided technical guidance for reducing pollution by means of optimization combustion tests on inferior coals. The research may improve the understanding of geochemical characteristics from toxic elements emission in coal combustion endemic diseased areas. For this purpose, a series of simulated coal combustion experiments were conducted to reveal the release, mobility, and distribution of elevated elements in Cd-rich coal combustion products. The results showed that Cd, Mo, Cr, Cu, Zn, As, and Sb were significantly enriched in the inferior coals of the study area. Furthermore, large amounts of toxic elements were released as fly ash into the environment during the combustion process. In particular, combustion conditions played an important role in the emission and transformation of elevated elements. For example, higher temperatures promoted the release of Cd, Sb, Zn, and Tl into the environment. Oxygen-deficient combustion was found to liberate more Cd, Sb, and Tl to the atmosphere and generated complex mineral assemblages of lizardite, calcite, dolomite, forsterite, and enstatite. Moreover, toxic elements were found to be absorbed in the fine particle matter of fly ash from the endemic fluorosis area of SW, China. The findings of this work may aid to control the emission of toxic elements from inferior coals and mitigate the effect of toxic elements in the environment to protect human health.

Migration behavior and leaching ability of radioactive uranium during incineration of uranium-containing strippable coating wastes.

It is currently thought that the incineration approach is an effective method to minimize the volume of radioactive wastes. In this paper, we used an incinerator to burn uranium-containing strippable coating waste. The migration behavior of radioactive uranium during the incineration process were investigated based on hierarchical sampling and mass spectrometry. Results shows that the radioactive uranium is more easily to adhere to the particles with smaller size. The leaching abilities of radioactive uranium in the bottom ash and the fly ash were analyzed. The leaching rate of the uranium from the fly ash and bottom ash were 1% and 6%, respectively, indicating that most of the radioactive uranium was fixed in the ash and the same storage/disposal methods can be used for both the fly ash and bottom ash. According to x-ray spectrometry and SEM-EDS, mineral compositions of the original uranium ore and the bottom ash were mostly the same. Calcium plays an important role in uranium fixation during incineration. The potential mechanism of the uranium special transformation during uranium-containing strippable coating waste combustion was revealed. Our research results can provide technical support for nuclear emergency waste treatment and disposal.

Hydrothermal oxidation degradation of dioxins in fly ash with water-washing and added Ce-Mn catalyst.

A comprehensive analysis of the effects of the temperature, reaction time, liquid-solid ratio (L/S), and initial pH on the hydrothermal degradation of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) (which are both PCDD/Fs) in municipal solid waste incineration (MSWI) fly ash is presented. Consequently, the hydrothermal degradation reaction is catalyzed using Ce-Mn catalyst under low-temperature conditions to study the effect of the catalyst on the degradation efficiency of PCDD/Fs. The experimental results show that temperature is the most critical factor for the reaction. When the hydrothermal oxidation temperature reaches 280 °C (reaction time = 120 min, original pH = 8.5, L/S = 4 mL/g), the toxicity equivalent (I-TEQ) of PCDD/Fs is only 5.4 ng TEQ/kg, and the degradation efficiency reaches 99.71%. Under these conditions, 2,3,4,7,8-P5CDF makes the highest contribution to I-TEQ degradation, reaching 37.4%. There are four main pathways for the reaction of 2,3,4,7,8-P5CDF with hydroxyl radicals. A comparison of the PCDD/F concentrations of different products shows that the addition of 0.5%, 1.0%, and 1.5% of the Ce-Mn catalyst reduces the degradation efficiency by 8.79%, 1.40%, and 0.07%, respectively, which indicates that the addition of a small quantity of Ce-Mn catalyst does not facilitate the degradation of PCDD/Fs. The addition of the catalyst significantly decreases the degradation efficiency of low-chlorinated homologs but has a relatively small effect on that of high-chlorinated homologs. Therefore, it is concluded that Ce-Mn catalysts are more likely to promote resynthesis than degradation of PCDD/Fs.

Effect of calcium oxide on chromium solidification during the melting of hazardous waste incineration fly ash.

Thermal treatment technology considerably affects the harmlessness of fly ash (FA), but highly toxic heavy metals, such as Cr, attract considerable attention. In this study, we investigated the influence of CaO dosage at 600°C-1200 °C on the curing effect of Cr during FA thermal treatment based on the combination effect of CaO. Static, dynamic, and continuous sequential leachings were performed for the sintered products. Results showed that the leaching concentration of Cr decreased by approximately 91% when CaO dosage was 8.57%, and the difference in the residual state was the main reason for the difference in the leaching behavior of Cr. The proportion of the residual state in the sintered products increased from 35.16% to 64.01%. The transition between Cr2O3, Cr5O12, and CaCr2O4 is the fundamental reason for the leaching behavior of Cr and the change in the residual state. This study provides a scientific basis for preventing and controlling heavy metal pollution and optimizing environmental supervision in the FA thermal treatment process.

A comparative study on characteristics and leaching toxicity of fluidized bed and grate furnace MSWI fly ash.

Grate furnace and fluidized bed are the most widely used technologies for municipal solid waste incineration (MSWI), which play significant roles in characteristics of MSWI fly ash. A comparative study of the physicochemical characteristics, microstructure morphology and leaching toxicity of fluidized bed and grate furnace MSWI fly ash was conducted in this work, and some resource utilization and disposal treatments were proposed. Results showed that calcium salt and chlorine salt formed the dominant components of MSWI fly ash. CaO-SiO2-Al2O3 ternary system indicated that MSWI fly ash had potential pozzolanic activity, similar to coal fly ash and blast furnace slag. The total Pb, Cd and Zn contents in fluidized bed MSWI fly ash was only 1/2, 1/3 and 2/3 of grate furnace MSWI fly ash, respectively. Leachability of Pb in MSWI fly ash collected from Dalian, Shanghai, Zhuji and Hangzhou was 4.25 mg/L, 3.83 mg/L, 3.84 mg/L and 3.68 mg/L, 28.3, 25.5, 25.6 and 24.5 times as much as the national standard limitation (GB16889-2008), respectively. However, grate furnace MSWI fly ash with high chloride and unstable chemical speciation distribution of heavy metals would pose more environmental risk toits immobilization and disposal. Fluidized bed fly ash is a promising candidate for preparing the Portland cement clinker, microcrystalline glass and ceramics due to its high Si and Al content. Grate furnace MSWI fly ash is more appropriate for Alinite cement preparation because of high chloride content.

Sustainable Recovery of Valuable Nanoporous Materials from High-Chlorine MSWI Fly Ash by Ultrasound with Organic Acids.

The new technology development for municipal solid waste incineration fly ash treatment and reuse is urgent due to landfill shortage and environmental effect of leached hazardous substances. Chlorine (Cl) is worth considering due to its high levels in fly ash. In this study, a treatment process of ultrasound combined with organic acid was used to eliminate Cl from fly ash to enhance its properties for reuse. Taguchi methodology was implemented to design the experiments by controlling four impact factors and the contribution of each factor was evaluated by the ANOVA analysis of variance. Following two treatment steps within 5 min with a solid/liquid ratio of 1:10 at 165 kHz, 98.8% of Cl was eliminated. Solid/liquid ratio was the most prominent factor that contributed to the Cl removal with more than 90%, according to the ANOVA analysis of variance. Tert-butyl alcohol (tBuOH), an •OH radical scavenger, was utilized to examine different effects of ultrasonic cavitation on Cl removal efficiency. A 20 kHz ultrasound was used to explore the influence of multi-frequency ultrasound with different mechanical and sonochemical effects on the fly ash dechlorination. This ultrasonic-assisted organic acid treatment was found to be a time and cost-effective pathway for fly ash Cl removal.

Anthropogenic arsenic menace in contaminated water near thermal power plants and coal mining areas of India.

Coal mining and coal combustion in thermal power plants (TPPs) are the major anthropogenic sources of arsenic (As) contamination in many different industrial regions. In this study of industrial regions of West Bengal and Singrauli, it is observed that there is an anthropogenic contribution to the contamination from As-bearing coal. Up to 14.53 mg/kg of As is obtained in coal of West Bengal which also has very high average Fe concentration (16,095 mg/kg) along with high concentration of Cu, Mn and Hg. Similar observations are also found in Singrauli Industrial Region where 3.14 mg/kg of As with very high concentration of Fe 43,867 mg/kg along with high Cu, Mn and Hg concentration is found in coal samples. This low-grade bituminous coal contains arsenopyrite as observed by SEM-EDX. Arsenopyrite is converted to arsenolite upon combustion in these TPPs as observed in XRD. The fly ash has average As concentration of 1.53 mg/kg for West Bengal and 2.38 mg/kg for Singrauli Industrial Region and high concentration of toxic elements. The soil near these TPPs and mining areas is enriched in As, Fe, Hg, Cu and Mn. Not only As but high concentrations of Fe, Hg, Mn are also observed from analysis of water which relates to the anthropogenic inputs. The dissolution of arsenolite in reducing environments caused by periodic flooding releases As into water. Hence, the As contamination in the study area also has anthropogenic origin from coal consumption in TPPs.

Profiling and occupational health risk assessment study on coal ashes in terms of polycyclic aromatic hydrocarbons (PAHs).

Profiling and cancer risk assessment on the polycyclic aromatic hydrocarbons (PAHs) content of coal ashes produced by the major coal combustion plants from the eastern coalfield region in India was conducted. Thirteen PAHs were detected on coal ashes collected from ash deposition sites of major thermal power plants and the profiling of the PAHs was done. Benzo[a]pyrene equivalents (BaPeq) for individual PAHs were calculated and applied to the probabilistic assessment model from US EPA (1989). Monte Carlo simulations were conducted to assess the risk of inhabitants exposed to PAHs through the dust of the coal ash deposition site. In fly ash, the range of total amount of carcinogenic PAHs was from 3.50 to 6.72 µg g-1 and for the bottom ash, the range was 8.49 to 14.91 µg g-1. Bottom ashes were loaded with ample amounts of 5- and 6-ring carcinogenic PAHs, whereas fly ashes were dominated by medium molecular weight PAHs. The simulated mean cancer risks from fly ashes were 2.187 E-06 for children and 3.749 E-06 for adults. For the case of bottom ash, the mean risks were 1.248 E-05 and 2.173 E-05 respectively for children and adults. Among all the three exposure routes, dermal contact was the major and caused 81% of the total cancer risk. The most sensitive parameters were exposure duration and relative skin adherence factor for soil, which contributed the most to total variation. The 90% risks calculated from the bottom ashes (2.617 E-05 for children and 4.803 E-05 for adults) are marginally above the acceptable limit (>1.000 E-06) according to US EPA. In this study, a comprehensive risk assessment on carcinogenic PAHs present in coal ashes was done for the first time that may be helpful to develop potential strategies against occupational cancer risk.