Biodegradation Kinetics of Toluene, Ethylbenzene, and Xylene as a Mixture of VOCs

Abstract

Toluene, xylene and ethylbenzene constitutes more than 50% of the total VOC emissions from manufacturing and application processes of surface coatings. Although biodegradability of these compounds has been reported by many researchers, the biodegradation characteristics are mostly measured for their biodegradation as a single substrate. In industrial VOC emissions, these compounds are mostly emitted as mixture. Hence, it is important to study the biodegradation of these compounds as a mixture with different relative concentrations of individual VOCs. The present work focused on the biodegradation of toluene, ethylbenzene, and xylene by acclimatized mixed culture under aerobic condition. The experimental data were fitted into various biokinetic models to predict the individual biokinetic parameters, viz., maximum specific growth rate (µmax), half saturation constant (Ks), inhibition constant (Ki), and yield coefficient (YT). Monod's kinetic model, Monod's inhibition, and Haldane model were used for this purpose. The results indicated that for the same initial concentrations of the three mono-aromatic compounds, xylene degradation took longer time than ethylbenzene and toluene though its presence in the mixture did not have a significant inhibitory effect on the biodegradation of this two substrates. Four inhibition models, viz., no-interaction, competitive, uncompetitive, and noncompetitive models, were applied to study the nature of inhibition for different combinations of these compounds. The biodegradation of these VOCs was also studied in presence of easily biodegradable hydrocarbons like glucose.