Biofilter study was carried out on 1.2 L gas phase filter for the removal of ammonia at inlet concentr ation around 250 ppmV. Removal efficiency (RE) of biofilter rema ined in the range of 90–99% during the stable perio d of operation (80 days) at empty bed residence time (EB RT) of 20 s whereas RE of biofilter dropped to 65% when the EBRT was 10s. Metabolites were observed as ammoniac al nitrogen, hydrazine, nitrite and nitrate were fo rmed during the degradation pathway in biofilter bedding material of a mixture of agricultural residue. It was inoculated with mixed microbial cultures of nitrifying and ana mmox bacteria were isolated from the active sludge of ETP of different industries.