| Chlorinated aliphatic solvent contamination of groundwater is of concern because many of these contaminants are known or suspected carcinogens. Biological treatment using aerobic cometabolism is one potential remedy. This study employed the mutant methanotroph, M. trichosporium OB3b PP358, which constitutively expresses soluble methane monooxygenase (sMMO). The non-specificity of sMMO permits a broad range of chlorinated solvents to be degraded. However, this creates the potential for inhibition of degradation rates as several compounds may compete for and saturate sites on the enzyme. Because groundwater contamination rarely consists of a single compound, the effect of more than one compound on degradation rates was studied.; The degradation kinetics for six chlorinated solvents and the effect of enzyme competition in binary mixtures was investigated. M. trichosporium OB3b PP358 degraded trichloroethylene (TCE), chloroform (CF), cis-1,2-dichloroethylene (c-DCE), trans-1,2-dichloroethylene (t-DCE) and 1,1-dichloroethylene at rapid rates, with pseudo-first order rate constants of 1.7, 0.9, 5.1, 3.7, and 2.4 L/mg-d respectively. Competition experiments using binary mixtures of TCE with CF, c-DCE, and t-DCE were carried out at concentrations ranging from 0.5 to 5 mg/L with 20 mM of formate and no growth substrate. No significant competition was observed at any of these concentrations. In addition, 7 mg/L of 1,1,1-trichloroethane did not inhibit TCE degradation in binary mixtures. Decreased rates were observed for a mixture of c-DCE and TCE without formate, indicating that reducing power limitations may be more inhibitory than enzyme competition. Additional competititon experiments, using binary mixtures of t-DCE with TCE and t-DCE with c-DCE, were conducted at higher concentrations to elicit enzyme competition. In binary mixtures containing TCE, TCE was more likely to be inhibited than vice versa. This was consistent with TCE having the highest half saturation coefficient of all the solvents investigated. Predictions from a competitive inhibition model compared well with experimental data for most mixtures.; The kinetic parameters reported for these frequently-occurring solvents will permit the continued development of a hollow fiber membrane reactor for groundwater treatment. The results of a reactor experiment treating 500 {dollar}mu{dollar}g/L of TCE and t-DCE showed that no competitive inhibition occurred as expected from batch competition experiments. |
