Biodegradation kinetics of carbon tetrachloride by Pseudomonas cepacia under varying oxidation-reduction potential conditions

Abstract

In recent years, considerable interest has been given to the in situ degradation of hazardous contaminants by stimulating indigenous microorganisms. Optimization of environmental conditions, especially oxidation-reduction potential (ORP), for metabolism of hazardous constituents by indigenous microorganisms may assist in cost-effective mitigation by enhanced bioremediation. Pseudomonas cepacia, the predominant species, was selected as the microorganism of study to evaluate ORP effects on biodegradation of carbon tetrachloride (CT), a common contaminant in many sites. Titanium till) citrate was used as a reducing agent to poise ORP at desired levels. Results indicate that initial ORP appears to be critical for initiating the CT degradation process. Substantial CT degradation occurred when cultures were poised at negative ORP conditions, while negligible CT removal was observed at oxidative ORP conditions. Accumulation of chloroform (CF) produced by CT metabolism was not observed, which may be attributed to its metabolism by P. cepacia and another pathway that preclude CF generation. The maximum biodegradation rate was found to occur at approximately-150 mv 2 and an overall substrate removal rate constant, K, of 6.9 x 10 -3 h -1 was observed at an initial CT concentration of 323 μg/L.