Field-scale study of co-processing dichlorodiphenyltrichloroethane-contaminated soil in a cement kiln

Controllable chemical redox reactions to couple microbial degradation for organic contaminated sites remediation: A review

Global environmental concern over organic contaminated sites has been progressively conspicuous during the process of urbanization and industrial restructuring. While traditional physical or chemical remediation technologies may significantly destroy the soil structure and function, coupling moderate chemical degradation with microbial remediation becomes a potential way for the green, economic, and efficient remediation of contaminated sites. Hence, this work systematically elucidates why and how to couple chemical technology with microbial remediation, mainly focused on the controllable redox reactions of organic contaminants. The rational design of materials structure, selective generation of reactive oxygen species, and estimation of degradation pathway are described for chemical oxidation. Meanwhile, current progress on efficient and selective reductions of organic contaminants (i.e., dechlorination, defluorination, -NO2 reduction) is introduced. Combined with the microbial remediation of contaminated sites, several consideration factors of how to couple chemical and microbial remediation are proposed based on both fundamental and practical points of view. This review will advance the understanding and development of chemical-microbial coupled remediation for organic contaminated sites.

Effects of increasing chlorine concentration in feedstock on the emission and distribution characteristic of dioxins in circular fluidized bed boiler

Field studies were conducted to study the emission and distribution characteristics of dioxins by elevating the chlorine concentration in feedstock in a circular fluidized bed boiler. The concentration and total equivalent quantity of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in all flue gas, electrostatic ash, bag filter ash, and bottom ash samples under blank condition (i.e., feedstock was normal coal) and chlorine labeling condition (i.e., feedstock mixed with coal and chlorine-containing labeling agent) were analyzed. Results illustrated that the concentration of PCDD/Fs in all gaseous and ash samples increased with the addition of chlorine in feedstock, with the largest and least increment in dioxin concentration observed in electrostatic ash and flue gas. PCDDs were the predominate congeners in flue gas, accounted for 50.1-60.4% of the total PCDD/F concentration under chlorine labeling and blank conditions, while PCDD/F distribution changed from PCDD- to PCDF-predominate by increasing chlorine content in feedstock under all field test conditions: 46.6-92.9%, 34.0-76.1%, and 47.0-53.1% of PCDFs were distributed in electrostatic ash, bag filter ash, and bottom ash, respectively. Highly chlorinated PCDD/F congeners such as O₈CDD/F and 1,2,3,4,6,7,8-H₇CDD/F were the primary contributors to dioxin concentration in flue gas and bottom ash samples, whereas low-chlorinated 2,3,7,8-T₄CDF and 1,2,3,7,8-P₅CDF congeners became critically dominating in electrostatic and bag filter ash.

Heavy metal and metalloid emissions during co-processing of waste in a sintering kiln: Migration characteristics in the kiln and long-term leaching from bricks

Heavy metals (HMs) in mixed hazardous waste can be volatilized in the kiln for preparing sintered bricks, which greatly increases the environmental risk. In this study, the volatilization, transformation, and leaching of HMs from bricks were evaluated. Field tests and laboratory leaching experiments were carried out. HM-contaminated soil was used to prepare sintered bricks at high-temperature in a tunnel kiln. Release of HMs from brick under rainfall conditions was investigated in laboratory simulation experiments. The field tests showed that the total amount of Pb, Zn, Cd distributed to the gas phase were all less than 2%, but the amount of Hg entering the gas phase 40.1%-60.5% in the particulate forms. The As leaching rate increased after sintering of bricks in the kiln, which was attributed to the increased formation of soluble arsenate and the reduced availability of sorption sites. The tank leaching test indicated that the release mechanism of trance elements (Cr, As, Zn, Cd, Pb and Ni) was mainly controlled by diffusion. This study provides useful knowledge for decreasing the volatilization and leaching of HMs from sintered bricks prepared using hazardous waste.

Dioxin emission and distribution from cement kiln co-processing of hazardous solid waste

Cement kiln collaborative disposal technology can not only dispose of hazardous waste but also provide energy for the cement industry. However, the addition of hazardous waste may promote the formation of dioxins in cement kilns. In this study, typical hazardous solid wastes, such as solidified fly ash, electroplating sludge, and industrial residue, were co-processed in a cement kiln with different feeding positions and different feeding amounts. The concentrations of dioxins in the flue gas, clinker, and precalciner furnace slag were investigated. The effect of adding mixed hazardous solid waste on the formation of dioxin was also studied. The results showed that the concentration of dioxin in the flue gas without added hazardous waste was 1.57 ng/m³, and the concentration varied from 1.03 to 6.49 ng/m³ after the addition of hazardous waste. In addition, the concentration of dioxin in the flue gas and solid samples increased substantially when the co-processing ratio doubled. The large amount of Cu in solidified fly ash promoted the formation of dioxins, while the higher S content in the electroplating sludge suppressed the formation of dioxins. Compared with the addition of single hazardous waste, the concentration of dioxin in precalciner furnace slag increases by about 300%. Furthermore, the distributions of isomers in the clinker and precalciner furnace slag were similar. 1,2,3,4,6,7,8-HpCDD and OCDD accounted for a large proportion of the mass concentration, and the contribution rate ranged from 48.7 to 82.0%. Most importantly, correlation analysis showed that the concentration of dioxin was closely related to the copper content, hazardous waste types and additive proportion, with correlation coefficients of 0.79, 0.83, and 0.89, respectively. This study provides a basis for exploring the high environmental benefits of disposing of hazardous solid waste by co-processing in cement kilns.