Influence of nitrogen supply and substrate interactions on the removal of paint VOC mixtures in a hybrid bioreactor

The study presented here was designed to investigate VOC degradation patterns as a function of nitrogen availability in a hybrid vapor-phase bioreactor column treating a surrogate paint VOC mixture. The mixture consisted of methyl propyl ketone, ethyl 3-ethoxy propionate, n-butyl acetate, toluene and p-xylene. In order to quantify nitrogen requirements, a series of experiments was conducted under various nitrogen-limited and nitrogen-rich conditions. Overall, increasing nitrogen availability improved the total VOC removal (efficiencies from approximately 70% to 99%. At the lowest available nitrogen condition, most of the ethyl 3-ethoxy propionate and n-butyl acetate, as well as approximately 75% of the methyl propyl ketone were removed in the bioreactor but toluene and p-xylene were not biodegraded. Increasing the nitrogen availability improved the biodegradation of methylpropyl ketone. Substantial degradation of toluene and p-xylene occurred in this study only after the molar ratio of the aromatic compounds to the other constituents in the waste gas stream increased above 2.0. Elimination capacity tests performed with the VOC mixture and each individual VOC indicated that the presence of other VOCs inhibited the biodegradation of toluene and p-xylene. These findings imply that substrate inhibitions limit the removal of aromatic hydrocarbons, particularly when the available nitrogen in the packing media is low.