A Comparison of Complex Electron Donors for Anaerobic Dechlorination of PCE

The potential of sugar, flour, corn steep liquor, molasses, non-fat milk, and whey to serve as electron donors for anaerobic dechlorination of tetrachloroethene (PCE) was examined. The electron donors were compared based on acclimation time, the extent of PCE dechlorination achieved, the minimum electron donor dose necessary to achieve PCE removal, and unit cost. The time required to achieve routine dechlorination of PCE (to any daughter product) for each donor was (in days): corn steep liquor (10), milk (10), whey (10), methanol (12), molasses (14), sugar (26), flour (30). Ethene production was achieved by milk-, whey-, and methanol-fed cultures, whereas the other donors did not facilitate ethene production over a 135-day period. Corn steep liquor-, whey-, molasses-, and sugar-fed cultures needed five times the stoichiometric amount (e.g., donor per eq PCE to ethene) to facilitate PCE conversion to dichloroethene (DCE). Cultures fed milk and flour needed 20 times the stoichiometric amount, and methanol-fed cultures required 50 times the stoichiometric amount, perhaps due to competition from methanogenic organisms. Minimum laboratory-scale electron donor costs to achieve stoichiometric conversion of PCE to DCE are ($ per pound lb] PCE) whey (0.04), molasses (0.07), milk (0.14), corn steep liquor (0.19), sugar (0.38), methanol (0.58), and flour (1.30).