Hydrogen sulfide and partially carbon dioxide can be absorbed into alkaline washing, liquid with nitrates for upgrading a quality of biogas. Sulfides captured into the washing liquid are consequently biologically oxidized in an anoxic bioreactor by autotrophic denitrifying bacteria. Nitrates in the washing liquid serve as electron acceptors for sulfide bio-oxidation. Washing of hydrogen sulfide from biogas was examined in a lab-scale countercurrent scrubber that was packed with plastic carriers and operated at different biogas and washing liquid flows. The hydrogen sulfide concentration in treated biogas was investigated in the range from 3 to 12.3 g m(-3). The influence of the hydrogen sulfide volumetric loading rate on required scrubber wetting S-w was determined. The anoxic bioreaetor packed with the same plastic carriers for immobilization of bacteria was operated long term at the sulfide loading rate in the range from 21 g in day(-1) during the start-up period to 400 g m(-3) day(-1) at the end of the operation to determine the maximum value for sufficient sulfide removal efficiency. On the basis of results, it was concluded that the sulfide loading rate of 160 g m(-3) day(-1) can ensure stable operation and sufficient desulfurization efficiency. The nitrate loading rate was set up according to molar ratio S/N, which must be lower than the stoichiometric value of 0.625 for stable and sufficient sulfide removal, with the maximum of about 0.55. Possibilities of the process application are suggested and discussed.