高级氧化技术矿化水中三氯甲烷和二氯甲烷理论极限浓度分析

Theoretical limiting concentration for mineralization of trichloromethane and dichloromethane in aqueous solutions by AOPs

对环境安全性尤其是饮用水安全而言,通常认为的高级氧化技术(AOPs)"彻底降解"大多数有毒有机污染物的观点需应用化工热力学分析来检验.本文分别以三氯甲烷(CHCl3)和二氯甲烷(CH2Cl2)为模型体系,分析了不同氯代甲烷初始浓度、pH值和羟基自由基(·OH)浓度下,AOPs矿化水中氯代甲烷的平衡浓度(即矿化理论极限浓度).结果表明,CHCl3和CH2Cl2与·OH矿化反应的理论极限浓度均随着初始浓度的增加而增加,随着·OH浓度的增加而明显减小;CHCl3与·OH矿化反应的理论极限浓度随着pH值的增加而明显减小(pH3.0～3.5除外),CH2Cl2与·OH矿化反应的理论极限浓度在文献报道的·OH浓度下随着pH值的增加无明显变化,而在·OH浓度分别增至文献值的10和100倍时,CH2Cl2与·OH矿化反应的理论极限浓度随着pH值由2.0增至3.0和由3.5增至4.5而不断减小,由3.0增至3.5和由4.5增至5.0而增加.较高的·OH浓度,较高pH值(pH4.0～5.0)的酸性环境以及较低的初始浓度对氯代甲烷的彻底矿化更有利.

It is widely stated that most organic contaminants could be completely mineralized by AOPs.This statement means that the concentration of the organic contaminant at equilibrium （limiting concentration,LC） is low enough to be neglected.However,for environmental safety,especially drinking water safety,this statement needs to be verified from chemical engineering thermodynamic analysis.In this paper,trichloromethane （CHCl3） and dichloromethane （CH2Cl2） are selected as the model systems,and the equilibrium concentration （theoretical limiting concentration,TLC） for the mineralization of chlorinated methanes in aqueous solutions at the different initial concentrations of chlorinated methanes,pH values and ·OH concentrations by Advanced Oxidation Processes （AOPs） are investigated by thermodynamic analysis.The results in this paper show that the TLC for the mineralization of CHCl3 and CH2Cl2 with ·OH increases with increasing initial concentrations of CHCl3 and CH2Cl2,decreases with increasing concentration of ·OH.And the TLC for the mineralization of CHCl3 decreases with increasing pH values except that the pH value changes from 3.0 to 3.5.For the mineralization of CH2Cl2 with ·OH,at the concentrations of ·OH obtained from the literature,there is no obvious change of the TLC with pH values,while as the concentrations of ·OH increase by 10 and 100 times,the TLC decreases with the increasing pH values from 2.0 to 3.0 and from 3.5 to 4.5,and increases with the increasing pH values from 3.0 to 3.5 and from 4.5 to 5.0.The investigations in this paper imply that high concentration of ·OH,a bit higher pH values （4.0？5.0） in acid environment and low initial concentrations of the organic contaminants are beneficial for the complete mineralization of chlorinated methanes by AOPs.