Enhanced dechlorination of tetrachloroethene by anaerobic granular sludge using different electron donors

ABSTRACT Tetrachloroethene (PCE) is a common groundwater pollutant, and bioremediation is an effective method for removing PCE. This study investigates the biodegradation of PCE by methanogenic granular sludge for groundwater bioremediation. Batch tests were conducted using six primary substrates – acetate, propionate, butyrate, lactate, methanol, or ethanol – as electron donors for reductive dechlorination. The results revealed that the addition of propionate and butyrate increased PCE biodegradation by 43% with complete dechlorination to ethene. The highest recorded dechlorination rate was 0.34 μg PCE per g volatile solids per day, which was achieved with the addition of 20 mM butyrate. Propionate and butyrate degraded more slowly than other electron donors, resulting in a lower hydrogen partial pressure. These substrates facilitated a gradual release of limited quantities of hydrogen and acetate, favoring dechlorination over methanogenesis. During tests in which lactate was added, propionate was formed by lactate fermentation, ensuring continuous PCE dechlorination after lactate depletion. Acetate, methanol, and ethanol were rapidly consumed and primarily generated significant amounts of methane, which did not support dechlorination. The use of anaerobic granular sludge in combination with propionate is recommended for the bioremediation of PCE-contaminated groundwater.