Removal of xylene from off-gas using a bioreactor containing bacteria and fungi

Volatile organic compounds (VOCs) such as benzene, toluene and xylene, which are major constituents of petroleum and fine chemical industries, are possible carcinogens and can cause offensive odors, so that their release into the environment must be strictly controlled. A bench-scale combined-bioreactor consisting of two zones, one containing a bacterial suspension and the other packed with material for the attached growth of fungi, was used to treat VOCs of different water solubilities. The average elimination capacity for xylene, with its three isomers, in steady state was 62 g m−3 h−1. The total removal rate was >90%–24.0% in the first zone and 67.6% in the second. The ratio of the liquid and gas flows (Ql/Qg) influenced the removal efficiencies of the isomers o-, m- and p-xylene in the two zones. Increasing the Ql/Qg ratio led to increased removal of both o-xylene and m-/p-xylene in the first zone and decreased removal in the second. When the Ql/Qg ratio was >0.15, more o-xylene was removed in the first zone than in the second. The microbial populations were found in the two zones of the reactor differed, so that the xylene was degraded by different kinds of microorganisms in these zones.