Biotreatment of Ammonia in Air by an Immobilized Nitrosomonas europaea Biofilter

The chemoautotrophic microorganism Nitrosomonas europaea has been utilized to remove gaseous ammonia in a continuous reactor. Extensive tests including removal characteristics, metabolic products, and removal efficiencies of ammonia by N. europaea were conducted. The operational principles governing the biofilter and the question of the heterotroph contamination were also studied. The optimum pH value and operating temperature required to effectively remove ammonia were found to be pH 7.5 and 30°C, respectively. When the diluted inlet ammonia concentration was 10 or 20 ppm, the biofilter achieved a 99% removal efficiency after 4 days of operation. However, higher ammonia inlet concentrations and heterotroph contamination resulted in a lower removal efficiency. The results showed that the maximum removal rate and apparent saturation constant were 1.11 g-N/day/kg-bead and 63.67 ppm, respectively. The mainly metabolic product of ammonia oxidation was determined to be nitrite, but the conversion ratio was dependent on whether the contaminations by heterotrophic bacteria were present. From an operating perspective, if the ammonia emission limit (i.e., 1 ppm) was to be achieved, the maximum inlet concentration could not exceed 75 ppm. These results suggest that the immobilized Nitrosomonas europaea biofilter provides a significant potential for treating ammonia in the gaseous phase.