Facilitation of cometabolic degradation of 4-chlorophenol using glucose as an added growth substrate

Abstract

This paper reports on the feasibility of using glucose as an added substrate for cometabolic transformation of 4-chlorophenol (4-cp). When glucose was fed as the added growth substrate, only 78% and 43% of the initial 4-cp concentrations of 100 and 200 mg l-1, respectively, were transformed before the pH dropped to below 4.5 and stopped all reactions. By maintaining the medium pH, complete removal of 4-cp was achieved even at the high initial concentration of 200 mg l-1. Phenol induction prior to inoculation was not a prerequisite to ensure transformation of 4-cp when glucose was the added growth substrate. Compared with phenol as the added growth substrate, cells grown on glucose displayed a longer acclimation phase and, in general, a lower specific transformation rate. The volumetric transformation rate of 4-cp, however, was greatly enhanced due to the increased cell density. The results of this work suggest that 4-cp itself induced the enzymes necessary for its cometabolism. With NADH regenerated effectively through metabolism of glucose, 4-cp was transformed in the absence of added phenol. Consequently, the competitive inhibition involved in cometabolism was avoided and the risks associated with addition of toxic growth substrates such as phenol were eliminated.