An Anaerobic/Aerobic Biological Permeable Reactive Barrier For The Remediation Of PCE-contaminated Groundwater

Tetrachloroethylene(PCE)is among the most ubiquitous chlorinated compounds found in groundwater contamination,thus the remediation of PCE-contaminated groundwater is attracting increased attention.Combined with the characteristics of PCE biodegradation and the features of PRB,in this study,an in situ anaerobic/aerobic fourlayer permeable reactive barrier system consisting of four different functional layers was designed to evaluate the remediation effectiveness of PCE-contaminated groundwater.The first layer(oxygen-capturing layer)filling with granular oxygencapturing materials is designed to provide nutrients,such as carbon and phosphorus,for the normal metabolism of immobilized anaerobic dechlorinating microbe filled in the second layer(anaerobic biodegradation layer).More importantly,the oxygen-capturing materials are used to capture dissolved oxygen(DO)in groundwater in order to create an anaerobic condition for the microbial dechlorination of PCE.The third layer(oxygen-releasing layer)filling with granular oxygen-releasing materials is proposed to provide enough oxygen and nutrients for the immobilized aerobic microbes in the fourth layer(aerobic biodegradation layer)in order to aerobically biodegrade the lesschlorinated compounds degraded from PCE to harmless coompounds.In this study,adsorbtion experiments to find the features of PCE and TCE adsorbtion in clays,enrichment and acclimation of experimental anaerobic microbes to biodegrade PCE and aerobic microbes to biodegrade less-chlorinated compounds,preparations of oxygen-capturing materials and oxygen-releasing materials,microbial immobilization,and column experiments were conducted respectively.The first column filled with oxygen-capturing materials.The second column filled with immobilized anaerobic microbes.The third column filled with oxygen-releasing materials.The fourth column filled with immobilized aerobic microbes.Simulated PCE-contaminated groundwater(PCE 1012 ?g/L,DO 6.34 mg/L,pH 7.2)was pumped into this system by a peristaltic pump at a flow rate of 250 mL/d.Samples from the anaerobic and aerobic biodegradation columns were analyzed for pH,DO,and PCE and less-chlorinated compounds every 24 hours.Results show that up to 99.3% of PCE removal efficiency was obtained in this passive system,and its toxic byproducts,less-chlorinated compounds,could also be biodegraded further in aerobic biodegradation column of this passive system.Further study is necessary in order to evaluate performance of its field application.