Modeling competitive inhibition effects during biodegradation of BTEX mixtures

Abstract

A quantitative evaluation of the biodegradation rates of mixtures of volatile aromatic compounds (benzene, toluene, ethylbenzene, xylenes [BTEX]) was conducted. Three different mixed bacterial cultures grown on BTEX or benzene were used in batch biodegradation tests with individual and mixed BTEX compounds. The bacteria degraded each compound faster when it was present alone than when it was a component of a BTEX mixture. The biodegradation rates in the mixtures were predicted using a basic competitive inhibition model to account for the effects of up to five BTEX compounds. Under the limiting assumptions of similar individual half-saturation coefficients ( K s) for the multiple compounds and substrate concentrations significantly greater than K s, the competitive inhibition model could be simplified to demonstrate that the biodegradation rate of any individual compound in the multi-component mixture should be proportional to its individual maximum specific degradation rate and the concentration of the compound relative to the total mixture concentration. Comparison of measured BTEX mixture degradation to predictions from this simplified model showed this model yielded estimates of similar accuracy to the more rigorous competitive inhibition equation. This is the first report of a quantitative evaluation of the biodegradation of five-compound mixtures.