Three pilot scale anoxic biotrickling filters containing different packing materials were built and tested over an extended period in the municipal wastewater treatment plants (WWTP). Performance of biological beds containing polyethylene elements, ceramic Raschig rings, and keramzite particles was investigated at hydrogen sulfide concentrations in biogas ranging from 369 to 1733 mg/m(3). The dependence of the number of colony forming units on hydrogen sulfide concentration and location in the bed was determined. Microbial enumeration was performed for all three columns using cultivation methods. The best results of desulfurization were observed for polyethylene elements. For this material the optimum empty bed retention time was 12 min and the minimum concentration of nitrate ions in a nutrient solution was 50 mg/L. The hydrogen sulfide reduction over 99% was achieved at loading rates (LR) of 1.79-5.08 g/m(3)/h. The increase in LR to 8.45 g/m(3)/h reduced the removal efficiency to 96%. The results of kinetic analysis enabled characterization of biological systems immobilized in each biofilter.