Effect of long-term operation of biofilters on biological removal of ammonia
生物滤塔处理含氨气体的长期运行研究

Long-term operation of biofilters for biological removal of ammonia was investigated using compost (BG1) and sludge (BG2) as packing materials. At the beginning of the experiment, during the low ammonia load period, the elimination capacities of both biofilters were high and the ammonia removal efficiencies could reach more than 99%. With the increase of ammonia load, at the end of the experiment when the inlet concentration of ammonia was higher than 190 mg·m-3, the removal efficiencies of both biofilters decreased to 50%. The maximum elimination capacities of BG1 and BG2 were 288 and 243 g (NH3)·m-3·d-1, respectively. Most of the NH3 removal was performed in the bottom layers of the reactors. Ammonia was mainly oxidized to nitrate. After long time operation and high load of ammonia, deactivation occurred in both biofilters. There are two possible reasons: First, with the increase of the inlet concentration of ammonia, large amounts of ammonium were adsorbed and accumulated in the packed bed, thus causing inhibition of nitrifying bacteria due to free ammonia accumulation. Second, the accumulation of ammonium and its products caused high salt concentrations, and the increased osmotic pressure due to the high salt concentration inhibited the activity of nitrifying bacteria.