Recently, application of vapor-phase bioreactors to the treatment of volatile organic compounds (VOCs) from paint spray booths has drawn increased interest. Contaminated air streams from paint spray booths are characterized by transient loading conditions and chemical mixtures consisting of both hydrophobic (e.g., xylene and toluene) and hydrophilic compounds (e.g., ketones). The main objective of this study was to investigate the effect of VOC mixtures on the overall performance of a hybrid bioreactor.
Lab-scale experiments were conducted using a compost-based hybrid bioreactor subjected to a surrogate paint VOC mixture consisting of toluene, xylene, methyl propyl ketone, butyl acetate, and ethyl 3-ethoxy-propionate. A total inlet VOC concentration of approximately 100 ppmv and a gas residence time of 46 seconds were employed. During the initial start-up phase, a drop in pH was observed presumably due to incomplete biodegradation of the VOC components. Following pH neutralization, pseudo-steady state operation was observed with an overall VOC removal efficiency of approximately 80%. Hydrophilic components of the gas stream were degraded almost completely in the bioreactor, but minimal degradation of the hydrophobic compounds was observed. To improve the removal of the hydrophobic components, the bioreactor was inoculated with a microbial solution cultivated with toluene vapor as the sole carbon source. Following inoculation, the bioreactor was fed toluene for a 12-day period, and external nitrogen was supplied to achieve high toluene removal efficiencies. After the inlet feed was changed back to the VOC mixture, overall bioreactor performance stabilized at an overall VOC removal efficiency of 90% and a toluene removal efficiency of approximately 70%. These results combined with results of elimination capacity tests suggest that microbial population must be fully established to achieve higher degradation capacity, especially for hydrophobic compounds.
Volatile organic compounds (VOCs) emitted from paint spray booths are facing increasingly stringent regulations. Paint spray booths typically generate waste gas streams contaminated with low concentrations of VOCs at high flowrates.