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Chemical Destruction
Published in Domenic Grasso, Hazardous Waste Site Remediation, 2017
Dechlorination is a destruction process that uses a chemical reaction to remove chlorine atoms from chlorinated molecules. The purpose of dechlorination in remediation is to make a toxic substance less toxic and more water soluble in order to expedite the remediation process. Several U.S. patents may be applicable to the technology. Key factors involved in dechlorination design include: type of contaminantgradation of soilreagent used
Chlorination
Published in Glenn M. Tillman, Wastewater Treatment, 2017
Dechlorination is the removal of all traces of residual chlorine remaining after the disinfection process and prior to the discharge of the final effluent to the receiving waters.This is commonly accomplished by the use of sulfur compounds such as sulfur dioxide, sodium sulfite, or sodium metabisulfite.Sulfur dioxide is the most popular method for dechlorination because it uses existing chlorination equipment.
Secondary Treatment
Published in David H.F. Liu, Béla G. Lipták, Wastewater Treatment, 2020
Wastewater treatment facilities should keep the maximum chlorine residuals in undiluted effluents at 0.1–0.5 mg/l to protect receiving surface water systems. Consequently, dechlorination can be required to reduce chlorine residual toxicity. Sulfur dioxide added at the end of the chlorination tank oxidizes both free chlorine and chlo-ramines to chloride. Activated-carbon adsorption of free-and combined-chlorine residuals is effective but expensive.
Nanoscale zero-valent iron for remediation of toxicants and wastewater treatment
Published in Environmental Technology Reviews, 2023
Kang et al. [150] synthesized nZVI activated on PS for the removal of para-chloronitrobenzene (p-CNB), a chlorinated organic compound used to manufacture pesticides, dyes, gasoline additives, explosives, and corrosion inhibitors in different sectors. The PS-nZVI had an 88% removal rate, while the PS and nZVI alone had removal rates of 36.5% and 60.2%, respectively. The removal of the p-CNB via the degradation mechanism was carried out under acidic and neutral conditions, rather than alkaline conditions. Because SO4•- is dominant at lower pH (3), both SO4•- and *OH coexisted and played important roles in the degradation process at pH 6.8. At a pH of 10, the *OH is dominant. The MS identified p-CNB degradation products as p-chloroaniline, 1, 4-benzoquinone, and (5-chloro-2-(3-chlorophenyl) polystyrene) phenol. The removal of pentachlorophenol (PCP), one of the priority pollutant pesticides, from the water was studied using nZVI. The degradation of the PCP using the heterogeneous Fenton catalyst of nZVI in the presence of H2O2 was completed within a 1 h reaction. Using 0.5% of H2O2 in the nZVI, 57% of the degradation (dechlorination) has been achieved. A continuous increase in chloride ion concentration was observed for 6 h, which indicates the dechlorination of PCP [151].
A review on biological occurrence, bioaccumulation, transmission and metabolism of chlorinated paraffins
Published in Critical Reviews in Environmental Science and Technology, 2023
Weifang Chen, Jiyan Liu, Xingwang Hou, Guibin Jiang
SCCP congeners (1,2,5,6,9,10-HexCD, 1,1,1,3,8,10,10,10-OctaCD, 1,1,1,3,10,11-HexCU, and 1,1,1,3,12,13-HexCT) were reported to be metabolized by pumpkins and soybeans via dechlorination, chlorine rearrangement, and carbon chain decomposition reactions. Soybeans transformed these SCCPs more easily than pumpkins. Congeners with more chlorine or carbon atoms were least metabolized by plants, which does not fit with the biotransformation behavior of LinA2-expressing bacteria (Heeb et al., 2019; Li, Hou, et al., 2019). This result was consistent with the quantum calculation theory which states that congeners with weak dispersibility of chlorine atoms are transformed more easily than others (Li, Hou, et al., 2019; Sun et al., 2016). Moreover, our previous work provided the first evidence of the improved transformation of SCCP congener (1,1,1,3,8,10,10,10-C10Cl8) by volatile active compounds emitted from plants, which hinted at the possible participation of plants in the release and transformation of CPs in the atmosphere (Li et al., 2020). In rice cells and seedlings, SCCPs and MCCPs were metabolized via multi-hydroxylation, dechlorination, HCl elimination, acetylation, sulfation, glycosylation, and amide acid conjugation pathways. These findings fill the gap in the information on biotransformation by food plants to some extent and provide indispensable information to assess the ecotoxicological risks of CPs (Chen, Hou, et al., 2022; Chen et al., 2020). Results also showed that MCCPs were less biotransformed than SCCPs in plants (Chen et al., 2020).
Municipal solid waste incineration (MSWI) fly ash washing pretreatment by biochemical effluent of landfill leachate: a potential substitute for water
Published in Environmental Technology, 2018
Yunfeng Xu, Yu Fu, Wei Xia, Dan Zhang, Da An, Guangren Qian
According to the leaching concentration of Cl− and fly ash dose, it could be calculated that 193.92–217.19 and 184.41–219.79 mg Cl− were washed away from 1 g raw fly ash by RW and BEL (chloride content in the BEL matrix was excluded before calculation), respectively, which suggested that the dechlorination ability of BEL was nearly equivalent to RW. Furthermore, according to other researches, the simple water-washing process as a pretreatment for MSWI fly ash can remove most of the chlorides, leachable salts, resulting in the washed ash having a lowered chlorine content [32]. This illustrated that the BEL treatment could also get lower chlorine content and better dechlorination ability.