Probing of maximal biodegradation rates of methylene chloride, carbon tetrachloride, and 1,1,1-trichloroethane in methanogenic processes

Computer controlled reactors were used to probe the maximal rate of anaerob ic biodegradation of methylene chloride, carbon tetrachloride, and 1,1,1-tr ichloroethane using three important methane precursors (formic, acetic and propionic acids) as primary substrates. Maximal biodegradation rate was def ined as that loading rate of the chlorinated aliphatic compounds which was achieved at a primary substrate removal rate of 50 % of the rate achieved w ith no chlorinated aliphatic present. The systems were controlled by a comp uter in response to the pH of the reactor in order to maintain an unlimitin g concentration of the primary substrate in the reactors. For methylene chl oride, carbon tetrachloride, and 1,1,1-trichloroethane 62 - 88, 96 - 99 and 93 - 97% respectively was biodegraded at maximal loading rates of 5.2 61, 19 - 79 and 31 - 110 mg l(-1) of reactor day(-1) for formate, acetate and p ropionate primary substrates respectively. Specific chlorinated organic rem oval rates, the most sensitive class of microorganisms, and the fate of the se three compounds also were examined. With acetate as the primary substrat e, the amount of methylene chloride, carbon tetrachloride and 1,1,1-trichlo roethane removed per acetate converted to methane was 0.0023, 0.0027 and 0. 045 mg mg(-1) respectively. Based upon the bacterial mass, the conversion r ate was 0.0085, 0.012 and 0.017 mg of methylene chloride, carbon tetrachlor ide and I,1,1-trichloroethane mg(-1) VSS day(-1) respectively.