Removal of Ammonia from Air by a Peat Biofilter

Peat was studied as a filter material for removing ammonia from air. Since the peat itself contained no nitrifiers and had no nitrification potential, it was inoculated with nitrifying bacteria from nitrifying activated sludge. To achieve good nitrifying activity, the acid filter material had to be neutralized by Ca(OH)2. The addition of nutrients (P, K, Mg+ and micronutrients) increased the capacity of the filter to oxidize ammonia to nitrate. The removal of ammonia was effective (mean removal rate 95 %) when initial concentrations were less than 14 mg NH3 m−3 (1.8 g NH3 m−3 peat per hour). The biofilter became overloaded at a concentration of 45 mg NH3 m−3 (7.9 g NH3 m−3 peat per hour), which caused an accumulation of ammonium and nitrite, as the ammonium inhibited oxidation of the nitrite. The biofilter operated properly down to a temperature of 5°C, and the amounts of bacteria and fungi released from biofilter into the filtered air were low.