Feasibility of sludge deep dewaterability improvement for incineration disposal by combined conditioning of freeze-thaw and sawdust.

Sludge incineration is the main strategy for sludge reduction in China. The combined conditioning of lime and chemical agents has been proven to achieve sludge dewatering by disrupting the extracellular polymeric substances (EPS) of sludge and reducing its compressibility. However, when incineration is the intended disposal purpose, this method poses challenges such as incomplete combustion, equipment corrosion, secondary pollution, and decreased calorific value of sludge cake. In contrast, freeze-thaw conditioning, coupled with sawdust as a high-calorific-value bio-waste, emerges as an efficient and clean alternative. The research investigates the synergistic effects of freeze-thaw and sawdust co-conditioning on various sludge properties, including dewaterability, compressibility, consolidation, permeability, microscopicity, and calorific value. The study reveals that the combined conditioning significantly reduces water content and compressibility while increasing void ratio, consolidation, permeability, and enhancing the calorific value of the sludge cake. Specifically, sludge cake conditioned with 60% dried solids (DS) sawdust and freeze-thaw achieved a water content (Wc) of 49.07% and a calorific value of 1422.3 kcal/kg, meeting standards for self-sustained incineration. With heat recovery, the combined conditioning generates an economic revenue of 25.1 $/t DS after deducting costs, thereby reducing the overall cost of sludge reduction treatment. This research offers a clean and practical solution for sludge incineration and reduction, demonstrating great economic value and application potential.

Enhanced effect of EDDS and hydroxylamine on Fe(II)-catalyzed SPC system for trichloroethylene degradation.

This study presents a performance comparison of Fe(II)-catalyzed sodium percarbonate (SPC), Fe(II)-EDDS-catalyzed SPC, and of the innovative hydroxylamine hydrochloride (HA)-Fe(II)-EDDS-catalyzed SPC for the degradation of trichloroethylene (TCE) in water. TCE degradation was greater in the Fe(II)-EDDS-catalyzed SPC system compared to the Fe(II)-catalyzed SPC system, indicating the effectiveness of adding EDDS as an enhancement factor for the removal of TCE. Moreover, TCE degradation was faster in the HA-Fe(II)-EDDS-catalyzed SPC system compared to the Fe(II)-EDDS-catalyzed SPC system, illustrating that HA can play a synergistic role in TCE degradation. Analysis of iron distribution in the three systems demonstrated that EDDS addition maintained iron in soluble form, and that the generation of soluble ferrous from ferric iron was expedited with addition of HA. Studies using nitrobenzene and carbon tetrachloride probes provided insights on the generation of hydroxyl radical (HO•) and superoxide anion radical (O2•-) in the three systems. A gradual increasing contribution of O2•- to TCE removal in Fe(II)-catalyzed SPC, Fe(II)-EDDS-catalyzed SPC, and HA-Fe(II)-EDDS-catalyzed SPC systems was verified through free-radical scavenger tests. Finally, monitoring of Cl- concentrations manifested the complete dechlorination of TCE. A possible mechanism of TCE degradation involving two pathways of HO• oxidation and O2•- reaction was proposed.

Enhanced effect of HAH on citric acid-chelated Fe(II)-catalyzed percarbonate for trichloroethene degradation.

This work demonstrates the impact of hydroxylamine hydrochloride (HAH) addition on enhancing the degradation of trichloroethene (TCE) by the citric acid (CA)-chelated Fe(II)-catalyzed percarbonate (SPC) system. The results of a series of batch-reactor experiments show that TCE removal with HAH addition was increased from approximately 57 to 79% for a CA concentration of 0.1 mM and from 89 to 99.6% for a 0.5 mM concentration. Free-radical probe tests elucidated the existence of hydroxyl radical (HO•) and superoxide anion radical (O2•-) in both CA/Fe(II)/SPC and HAH/CA/Fe(II)/SPC systems. However, higher removal rates of radical probe compounds were observed in the HAH/CA/Fe(II)/SPC system, indicating that HAH addition enhanced the generation of both free radicals. In addition, increased contribution of O2•- in the HAH/CA/Fe(II)/SPC system compared to the CA/Fe(II)/SPC system was verified by free-radical scavengers tests. Complete TCE dechlorination was confirmed based on the total mass balance of the released Cl- species. Lower concentrations of formic acid were produced in the later stages of the reaction for the HAH/CA/Fe(II)/SPC system, suggesting that HAH addition favors complete TCE mineralization. Studies of the impact of selected groundwater matrix constituents indicate that TCE removal in the HAH/CA/Fe(II)/SPC system is slightly affected by initial solution pH, with higher removal rates under acidic and near neutral conditions. Although HCO3- was observed to have an adverse impact on TCE removal for the HAH/CA/Fe(II)/SPC system, the addition of HAH reduced its inhibitory effect compared to the CA/Fe(II)/SPC system. Finally, TCE removal in actual groundwater was much significant with the addition of HAH to the CA/Fe(II)/SPC system. The study results indicate that HAH amendment has potential to enhance effective remediation of TCE-contaminated groundwater.

Degradation of carbon tetrachloride in aqueous solution in the thermally activated persulfate system.

Thermal activation of persulfate (PS) has been identified to be effective in the destruction of organic pollutants. The feasibility of carbon tetrachloride (CT) degradation in the thermally activated PS system was evaluated. The experimental results showed that CT could be readily degraded at 50 °C with a PS concentration of 0.5M, and CT degradation and PS consumption followed the pseudo-first order kinetic model. Superoxide radical anion (O2(*-)) was the predominant radical species responsible for CT degradation and the split of CCl was proposed as the possible reaction pathways for CT degradation. The process of CT degradation was accelerated by higher PS dose and lower initial CT concentration. No obvious effect of the initial pH on the degradation of CT was observed in the thermally activated PS system. Cl(*-), HCO3(*-), and humic acid (HA) had negative effects on CT degradation. In addition, the degradation of CT in the thermally activated PS system could be significantly promoted by the solvents addition to the solution. In conclusion, the thermally activated PS process is a promising option in in-situ chemical oxidation/reduction remediation for degrading highly oxidized organic contaminants such as CT that is widely detected in contaminated sites.

Trichloroethylene oxidation performance in sodium percarbonate (SPC)/Fe2+ system.

In this study, in-situ chemical oxidation technique employing Fe(II) catalytic sodium percarbonate (SPC) to stimulate the oxidation of trichloroethylene (TCE) in contaminated groundwater remediation was investigated. The effects of various factors including the SPC/TCE/Fe2+ molar ratio, the initial solution pH and the widely found constituents in groundwater matrix such as Cl(-), HCO3(-), SO4(2-) and NO3(-) anions and natural organic matters were evaluated. The experimental results showed that TCE could be completely oxidized in 5 min at 20 degrees C with a SPC/TCE/Fe2+ molar ratio of 5:1:10, indicating the significant effectiveness of the SPC/Fe2+ system for TCE removal. The initial solution pH value (from 3 to 11) has less influence on TCE oxidation rate. In contrast, Cl(-) and HCO3(-) anions had a negative effect on TCE removal in which HCO3(-) possesses a stronger influence than Cl(-), whereas the effects of both SO4(2-) and NO3(-) anions appeared to be negligible. With the 1.0-10 mg/L concentrations of humic acid in solution, slightly inhibitive effect was observed, suggesting that dissolved organic matters consumed less SPC and had a negligible effect on the oxidation of TCE in SPC/Fe2+ system. From the intermediate products' analyses and the released Cl(-) contents from TCE parent contaminant in solution, all the decomposed TCE had completely dechlorinated and led to carbon dioxide and hydrocarbon. In conclusion, Fe(II) catalytic SPC oxidation is a highly promising technique for TCE-contaminated groundwater remediation, but some complex constituents such as HCO3(-), in in-situ groundwater matrix should be carefully considered for its practical application.