Electrochemical reduction of trichloroethylene using zero- valent iron bipolar packed- bed electrodes

Abstract

Bipolar electrode system has been known to be more efficient than monopolar electrode system in electrolytes of low electrical conductivity. In this study, the bipolar packed-bed electrodes system was investigated to degrade trichloroethylene (TCE) in groundwater which has a poor inherent conductivity of groundwater. Direct current was supplied to columns packed with sand and zero-valent iron (ZVI). The external current makes the ZVI granules in the column act as bipolar electrodes. As a result, TCE was reduced up to 72% with HRT of 62min. On average, the TCE reduction in 0.13mM lasted for the experiment period of 1100h with the electric current of 20mA. The dominant by-product was ethane, which is a final product of TCE reduction pathways. However, in the column without supplied current, TCE was barely reduced during the experiment. Low concentrations of dechlorinated hydrocarbons were detected compared with the column with current supply, with acetylene showing the highest concentration. No significant changes in chloride concentrations and pH were observed. The total dissolved iron concentration increased with decreasing TCE and vice versa for both columns.