A pilot-scale research on dealing with micro-polluted source water of 4.2 m 3 /h by biological aerated filter (BAF) with volcanic filler for pretreatment was carried out. Under the experimental condition of air/water ratio 1:1, and the ammonia nitrogen of raw water 1.57 to 2.72 mg/L, the ammonia nitrogen average removal rate was 95.8%, when water temperature was above 10°C; and the removal rate was still above 70%, when water temperature ranged from 5.5 to 10°C. At the same time, there was no

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... cumulation of nitrite nitrogen in the reactor. Moreover, the removal rate of Mn, COD Mn and UV 254 was 66.3, 14.1 and 3.2%, respectively. Backwashing process of the BAF had little influence on the biofilm, which could be recovered within 1 to 2 h after the backwashing. The experimental result show that the removal effect of ammonia nitrogen and organic matter was very significant in BAF, even in lower temperature, which could guarantee the treatment effect of the follow-up processing unit.