The factors influencing ammonia removal of biological activated filter (BAF) and the mechanisms were discussed on pilot-scale basis by using modified settling tank effluent.The results showed that the organic content of influent and filter media size influenced ammonia removal of BAF significantly.When using the effluent of settling tank as the influent of BAF

the ammonia removal percentage of BAF-1 (filter media size range of carbon 0.8—1.2 mm) reached 97%;as 2 mg·L-1 of peptone

2 mg·L-1 of beef extract and 2 mg·L-1 of glucose were added to the influent

only 51.0% of influent ammonia was removed due to the competition of heterotrophic bacteria for oxygen and space.On the other hand

the ammonia removal efficiency of BAF-1 was 1.5%～16.7% higher than that of BAF-2 (filter media size range of carbon 1.0—2.0 mm).Almost complete ammonia removal was achieved by BAF-1 when influent ammonia concentration was less than 1.60 mg·L-1.As influent ammonia concentration increased gradually

the ammonia removal performance decreased because of the lack of dissolved oxygen.The ammonia removal of BAF-1 was enhanced as pre-aeration for the influent was performed.The influence of filter flow rate for ammonia removal was negligible.Backwashing was beneficial to ammonia removal of BAF-1 in this study.