EN
This paper presents investigation results which evaluate the role of biological processes in elimination of Mn (II) and NH4+ ions from groundwater. The raw water containing up to 1.4 mg/dm3 manganese and up to 2.9 mg N/dm3 ammonia nitrogen after aeration was treated using first and second stage sand filters at the "Letniki" water treatment plant near Elblag. Both ions were removed with high efficiency and the concentrations of these components after two stages of filtration were lower than the admissible values for drinking water in Poland (0.1 mg Mn/dm3 and 0.5 mg N-NH4/dm3). It was found that physico-chemical and biological processes were responsible for ammonia nitrogen elimination, while catalytic processes (physico-chemical and biological) contributed to manganese removal.