Biological degradation of 1,2-dichloroethane under groundwater conditions

Abstract

To gain a better understanding of the applicability of bacteria with special metabolic properties to purify polluted groundwaters, we have investigated the mineralization of low concentrations of 1,2-dichloroethane (DCA) in two different bioreactors which were inoculated with a mixture of two pure cultures capable of mineralizing DCA. Degradation experiments were continuously run at neutral pH at temperatures of between 10 and 30°C and in solutions of low conductivity (c. 1000 μS cm −1) thus simulating groundwater pumped from a polluted site. DCA concentrations in the feed ranged from 1 to 25 mg l −1. Oxygen was monitored in the reaction effluent and was added to the feed if required as a solution of H 2O 2. The fixed bed bioreactor with sintered glass beads as carrier was run in a flow-through mode with a hydraulic retention time of 2–3 h. DCA mineralization, determined by the disappearance of DCA, the consumption of oxygen, the decrease in pH and the formation of chloride ions, started 3 weeks after inoculation. After this time, at least 80% of DCA was mineralized with DCA feed concentrations of 20–25 mg l −1. DCA elimination efficiency increased up to 90% with increasing running time. With a feed concentration of 10 mg l −1 DCA. DCA effluent concentration decreased further to below 300 μg l −1. This degradation efficiency was independent of the different temperatures applied. Using granular activated carbon as carrier-material for the micro-organisms and running the reactor with a recycle at the same hydraulic residence time, mineralization started 5 weeks after inoculation. DCA effluent concentration was between 1 and 2 mg l −1 with feed concentrations of up to 20 mg l −1 DCA. The ability to mineralize DCA was kept without feeding the micro-organisms for 3 weeks.