Microbial dechlorination of carbon tetrachloride and biotreatment of carbon tetrachloride contaminated gases

Five microbial cultures have been developed for studying microbial carbon tetrachloride (CT) degradation. Four microbial cultures were fed with 1,2-propanediol, propionaldehyde, glucose and acetate plus nitrate, respectively and grown under alternative anaerobic/aerobic conditions, and one microbial culture was fed with 1,2-propanediol and grown under anaerobic-only conditions. Batch tests were carried out to study CT degradation and the kinetics with live cultures, autoclaved cultures, and culture liquid under various conditions.; Among all the cultures, the CT degradation was much faster for the propanediol fed culture than for the glucose fed culture, propionaldehyde fed culture and acetate/nitrate fed cultures. CF was the only chlorinated metabolite detected. About 5% to 10% of the CT was converted to CF, which degraded slowly. Nitrate inhibited CT degradation for the denitrifying culture.; The CT degradation rates were directly proportional to CT and biomass concentrations for all cultures. The first order rate constant (k) for each culture was obtained. The k value for the propanediol culture (3.7 L/g VSS-h) was three to six times greater than those for the other cultures grown under sequential anaerobic/aerobic conditions. The k value for CF degradation is less than that for CT degradation by about 150 times for the propanediol culture.; The cultures grown with these selected substrates contained various levels of vitamin B12. A nearly linear relationship was observed between the first-order rate constants (k) and the intracellular vitamin B12 contents among the five developed cultures with increased k values for higher vitamin B12 contents, suggesting the importance of vitamin B12 for CT degradation.; A bench-scale suspended growth system for treating CT-contaminated gases was established to study the CT degradation under continuous operation. A steady state and a nonsteady state mathematic models have been developed to describe the system, with model parameters and coefficients obtained using batch bottle tests. The model predicted values agreed with the experimental results very well. The steady-state model simulations showed that relatively high values of propanediol dosage, PAC dosage, VSS and SRT can improve CT removal efficiency. The steady state model was also used to help design and analyze a biotreatment system for an industrial CT-contaminated gas stream.