Biological elimination of H2S and NH3 from wastegases by biofilter packed with immobilized heterotrophic bacteria

Biotreatment of various ratios of H2S and NH3 gas mixtures was studied usin g the biofilters, packed with co-immobilized cells (Arthrobacter oxydans CH 8 for NH3 and Pseudomonas putida CH11 for H2S). Extensive tests to determin e removal characteristics, removal efficiency, removal kinetics, and pressu re drops of the biofilters were performed. To estimate the largest allowabl e inlet concentration, a prediction model was also employed. Greater than 9 5% and 90% removal efficiencies were observed for NH3 and H2S, respectively , irrespective of the ratios of H2S and NH3 gas mixtures. The results showe d that H2S removal of the biofilter was significantly affected by high inle t concentrations of H2S and NH3. As high H2S concentration was an inhibitor y substrate for the growth of heterotrophic sulfur-oxidizing bacteria, the activity of H2S oxidation was thus inhibited. In the case of high NH3 conce ntration, the poor H2S removal efficiency might be attributed to the acidif ication of the biofilter. The phenomenon was caused by acidic metabolite ac cumulation of NH3. Through kinetic analysis, the presence of NH3 did not hi nder the NH3 removal, but a high H2S concentration would result in low remo val efficiency, Conversely, H2S of adequate concentrations would favor the removal of incoming NH3. The results also indicated that maximum inlet conc entrations (model-estimated) agreed well with the experimental values for s pace velocities of 50-150 h(-1). Hence, the results would be used as the gu ideline for the design and operation of biofilters. (C) 2001 Elsevier Scien ce Ltd. All rights reserved.