Enhanced nitrobenzene removal and column longevity by coupled abiotic and biotic processes in zero-valent iron column

Nitrobenzene (NB) infiltrated in groundwater has caused serious threats to the safety of drinking water due to its persistence and high toxicity. In this study, abiotic zero-valent iron (ZVI) column and biotic ZVI column were employed to investigate abiotic and biotic effects between iron and microorganisms on NB removal and column longevity. Physical removal and kinetics analysis revealed that NB was largely removed through adsorption and/or co-precipitation and the reduction of NB to aniline (AN) via abiotic reaction in the abiotic column and via both abiotic and biotic reactions in the biotic column. Due to the interactive effect of ZVI and microorganisms, more effective iron consumption and more reactive minerals such as green rust and iron sulfide were found in the biotic column. This led to approximately 50% higher total NB removal and 6 times higher AN production in the biotic column as compared to the abiotic column during the entire operation. According to the NB breakthrough curves, longer stability and longer life-span of the column system could be maintained in regard of microbial activity. It indicated that additional microorganisms might improve the performance of iron-based permeable reactive barrier (PRB) for groundwater remediation.