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

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-D CA at an average volumetric loading rate of 87.6 mg l(-1) day(-1), the latt er type obtained an average removal efficiency of 82%. Increasing the volum etric 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 w ere 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 we re less toxic relative to the influent when analyzed by Nitrox tests, indic ating that such UASB treatments can protect a subsequent aerobic nitrifying system. The 1,2-DCA removal rates achieved, and the safe nature of the end products, warrant the combination of granular sludge and UASB technology fo r practical decontamination of waters containing such types of organochlori nes. (C) 2001 Elsevier Science Ltd. All rights reserved.