Reductive biodegradation of 1,2-dichloroethane by methanogenic granular sludge in lab-scale UASB reactors

Abstract

Dechlorination of 1,2-dichloroethane (1,2-DCA) dosed to a model wastewater in lab-scale upflow anaerobic sludge blanket (UASB) reactors was examined. Anaerobic granular sludge was used as a biocatalyst. Ethanol served as the main methanogenic substrate. For 3 months, two types of UASB reactors were studied, the first type consisting of a sludge blanket and the second type containing an additional layer of activated carbon. When subjected to 1,2-DCA at an average volumetric loading rate of 87.6 mg l −1 day −1, the latter type obtained an average removal efficiency of 82%. Increasing the volumetric loading rate of ethanol from 5 to 15 g COD l −1 day −1 resulted in higher 1,2-DCA conversion rates. No chlorinated intermediates or residues were found. 1,2-DCA was converted mainly to ethene (65–80%) and ethane (<1%). Both autoclaved sludge and cell extracts were not able to degrade 1,2-DCA, which indicates the need for metabolic activity. The reactor effluents were less toxic relative to the influent when analyzed by Nitrox tests, indicating that such UASB treatments can protect a subsequent aerobic nitrifying system. The 1,2-DCA removal rates achieved, and the safe nature of the endproducts, warrant the combination of granular sludge and UASB technology for practical decontamination of waters containing such types of organochlorines.