The zero order removal rate constants of ammonia and nitrite increased significantly with long-term loading until loading level 3(207 g feed/d), increasing no further at higher loadings (Table 2).The “threshold” level corresponds to a calculated loading of69 g feed/m2filter media/d and 2.70 mg TAN plus urea-N/l. First order removal rate constants of urea, ammonia and nitrite were not affected by loading in any consistent manner (Table 2).The first order removal rate constants were generally highest for ammonia and lowest for urea.