Effects of phenol feeding pattern on microbial community structure and cometabolism of trichloroethylene.

Cometabolism of trichloroethylene (TCE) by phenol-fed enrichments was evaluated in four reactors with distinct phenol feeding patterns. The reactors were inoculated from the same source, operated at the same average dilution rate, and received the same mass of phenol over time. Only the timing of phenol addition differed. Reactor C received phenol continuously; reactor SC5 received phenol semicontinuously--alternating between 5 h of feed and 3 h without feed; reactor SC2 alternated between 2 h of feed and 6 h without feed; and reactor P received a single pulse every 24 h. The structure of the enrichments and their capacity for TCE transformation were analyzed. In long-term operation, reactors C and SC5 were dominated by fungi, had higher levels of predators, were more susceptible to biomass fluctuations, and exhibited reduced capacity for TCE transformation. Reactors P and SC2 were characterized by lower levels of fungi, higher bacterial biomass, higher concentrations of TCE-degrading organisms, and higher rates of TCE transformation. After 200 days of operation, rates of TCE transformation increased 10-fold in reactor P, resulting in TCE transformation rates that were 20 to 100 times higher than the rates of the other reactor communities. The cause of this shift is unknown. Isolates capable of the highest rates of TCE transformation were obtained from reactor P. We conclude that cometabolic activity depends upon microbial community structure and that the community structure can be manipulated by altering the growth substrate feeding pattern.