Kinetic Modeling of Styrene Biodegradation by Rhodococcus erythropolis PTCC 1767: Effect of Adaptation to Styrene and Initial Biomass Concentration

Abstract

Styrene is found at high concentrations in many petrochemical wastewaters and, due to its toxicity, has to be removed from these wastewaters before their discharge. Biological treatment of these wastewaters using pure or mixed microbial cultures that remove styrene through biodegradation has many advantages compared to physic-chemical processes. However, the growth of most of pure or mixed microbial cultures used previously for biodegradation of styrene is retarded at relatively low styrene concentration. In this study, the biodegradation of styrene by Rhodococcus erythropolis PTCC 1767 was considered. The effect of initial biomass concentrations (X), in the range 0.31 gL−1 and 2.2 gL−1, and exposure of R. erythropolis to styrene-containing media–on the kinetics of styrene biodegradation was studied.The results of kinetic showed that, for runs at X = 2.2 gL−1, the kinetic data were satisfactorily fitted to the Monod model although the Haldane model gave a better fit of the kinetic data at all initial values of X. The results of kinetic modeling also showed that, with increase in X, the maximum specific removal rate (qm) decreased whereas the threshold styrene concentration Sthreshold increased. On the other hand, the exposure of the bacterial population to successive media in which styrene concentration was increased in a stepwise manner resulted in increase in the values of both qm and Sthreshold. The results of the present study showed the good potential of R. erythropolis for biodegradation of styrene in petrochemical wastewaters, although studies with real petrochemical wastewaters are needed to confirm this potential.