不同pH条件下三氯乙烯及其脱氯产物对苯或甲苯厌氧生物降解的影响

Influence of trichloroethene and its dechlorination byproduct on the anaerobic biodegradation of benzene or toluene under different pH conditions

将零价铁渗透反应格栅和生物降解格栅联用,先利用氯代烃易还原脱氯的性质通过零价铁渗透反应格栅去除氯代烃,后利用BTEX易生物降解的性质通过生物降解格栅去除BTEX,可以有效去除地下水中由氯代烃和BTEX这两种性质迥异的污染物形成的混合污染羽.但在联合格栅技术中,零价铁渗透反应格栅后的强碱性环境(pH>9)、氯代烃脱氯还原中间产物(cis-1,2-DCE)的积累和可能出现的TCE穿透均可对生物降解格栅中BTEX的生物降解产生影响.针对上述问题,本文研究了不同pH条件下TCE和cis-1,2-DCE对苯或甲苯厌氧生物降解的影响.结果发现,碱性pH条件有利于苯或甲苯的生物降解,但不同pH条件下TCE或cis-1,2-DCE的加入对苯或甲苯的生物降解均产生抑制(除pH=7.9,cis-1,2-DCE=100μg·L-1时的甲苯),且TCE对苯和甲苯生物降解的抑制要明显强于cis-1,2-DCE;不同pH条件下,TCE 100和500μg·L-1对苯生物降解的抑制作用没有明显差异,但对甲苯生物降解的抑制却随着TCE浓度的增加而增加;pH=7.9时,cis-1,2-DCE的加入有利于甲苯的生物降解,之后随着pH的增加又转变为抑制.另外,在苯或甲苯厌氧生物降解过程中,可能存在cis-1,2-DCE与苯或甲苯的共代谢生物降解,且甲苯更有利于cis-1,2-DCE的共代谢降解.

To effectively treat the mixed contaminant plume composed by chlorinated hydrocarbons and benzene,toluene,ethylbenzene and xylenes（BTEX）,combined zero valent iron permeable reactive barrier（ZVI PRB） and biodegradation permeable reactive barrier（bio-PRB） are used to reduce the chlorinated hydrocarbons through dechlorination and biodegrade the BTEX by microorganisms.However,during the application of the combined PRBs,the increased pH（pH9）,accumulation of dechlorinated intermediates（cis-1,2-DCE） and possible penetration of chlorinated carbon downgradient from ZVI PRB are likely to affect the anaerobic biodegradation of BTEX in bio-PRB.In this study,the influence of trichloroethene and cis-1,2-dichloroethene on the anaerobic biodegradation of benzene or toluene in groundwater under different pH conditions were investigated.It was found that the alkaline pH could improve the biodegradation of benzene or toluene,but biodegradation of benzene or toluene was always inhibited by TCE and cis-1,2-DCE underdifferent pH conditions（except for the biodegradation of toluene under pH = 7.9 with cis-1,2-DCE = 100 μg·L-1）,and the higher adverse effect of TCE was observed than cis-1,2-DCE.Under different pH conditions,similar inhibition effect of 100 and 500 μg·L-1TCE on benzene biodegradation was found;however,the adverse effect of TCE on toluene biodegradation was enhanced with increasing TCE concentration.Adding 100 μg·L-1cis-1,2-DCE would increase the biodegradation of toluene at pH 7.9,but inhibitory effect immediately appeared when pH increased to 10.5.Moreover,the cometabolism of cis-1,2-DCE during the anaerobic biodegradation of benzene or toluene was also observed,and the presence of toluene likely accelerates the co-metabolic degradation of cis-1,2-DCE.