Co-treatment of H2S and toluene in a biotrickling filter

Biological treatment is an emerging technology for the treatment of publicly owned treatment works (POTWs) off-gases. Most of POTWs off-gases contain H2S and a wide range of volatile organic compounds (VOCs). Since co-treatment of odors and VOCs in biotrickling filters is a relatively unexplored area, the simultaneous biotreatment of H2S and toluene (as the model VOC) was investigated. The experimental setup included two identical biotrickling filters, one operated at pH 4.5 and the other one was operated at pH 7.0. High concentrations of H2S (up to 170 ppm(v)) and toluene (up to 2.2 g m(-3)) were supplied to determine the influence of the pH on the maximum performance. A rapid startup (a few days) was observed for both toluene and H2S removal in the neutral-pH biotrickling filter. In the acidic biotrickling filter, toluene degradation also started immediately but at a lower rate. However, after several weeks of operation, the toluene elimination capacity (EC) at low pH reached a steady value identical to this found in the neutral-pH biotrickling filter. H2S did not affect toluene degradation at concentrations up to 170 ppm, at either pH. At a volumetric load of 100 m(3) m(-3) h(-1), maximum elimination capacities of 70 g toluene m(-3) h(-1) (at 1.7 g m(-3) toluene) and 20 g H2S m(-3) h(-1) (at 170ppm, H2S, the highest concentration tested) were observed. Microbial counting and activity measurements indicated the development of different microbial populations in the reactors. In the neutral-pH biotrickling filter, a population developed which had a limited tolerance to low pH. The population in the acidic biotrickling filter showed a broader pH range for removal of H2S and toluene. Overall. the results presented indicated that effective co-treatment of H,S and VOCs can be obtained in a single-stage biotrickling filter. (C) 2002 Elsevier Science B.V. All rights reserved.