Cometabolic Biodegradation of Trichloroethylene in a Biofilm Reactor

Cometabolic degradation of trichloroethylene (TCE) in an aerobic biofilm system with toluene as primary substrate was investigated. TCE degradation rate was first-order, giving an average first-order surface removal rate constant, k{sub 1,a}, of 0.26 m/d. TCE was probably degraded by a toluene-induced enzyme. However, if toluene was provided in high concentrations, degradation of TCE was inhibited. Furthermore, it appeared that TCE inhibited toluene degradation. This inhibition increased with the TCE concentration in the reactor, but it decreased with an increasing toluene concentration. The authors conclude that these interactions could be the result of a competitive inhibition between TCE and toluene. Practically, this shows that degradation of TCE can be maximized if an optimum concentration of toluene is provided. An example presented in this paper reveals that the optimum toluene concentration was in the range of 200 to 500 {micro}g/L for a TCE inlet concentration of 135 {micro}g/L. Under these optimal conditions, the TCE degradation rate was 0.045 g m{sup {minus}2} d{sup {minus}1}, leading to a first-order surface removal rate constant of 0.4 m/d and a transformation yield of 0.05 g TCE/g toluene degraded.