Kinetics of BTEX Degradation by a Nitrate‐reducing Mixed Culture^a

A culture enriched from a xylene-contamined, groundwater aquifer degraded m- and p-xylene, toluene, and ethylbenzene completedly within 5 days and o-xylene to 55% of its original concentration under nitrate-reducing conditions. The culture did not degrade benzene. The mixed culture had a maximum growth rate of 0.017 h-1 and a yield of 0.66 g dry cell weight/g toluene consumed. Substrate limitation and then inhibition were observed with increasing concentrations of toluene. The Ks and Ki for toluene were found to be 516 microM and 332 microM, respectively, when fitted to the Andrews model for substrate limitation and inhibition and 410 microM and 492 microM, respectively, when fitted to a multiplicative model for substrate limitation and inhibition. A Monod-type dependence of toluene degradation on the nitrate concentration was observed with a Ks for nitrate of 0.21 mM. Nitrate was not inhibitory to growth or to toluene degradation at concentrations up to 10 mM.