The effect of water velocity on nitrification rates in fixed bed biofilters was investigated in three freshwater pilot scale RAS with rainbow trout. Removal of total ammonia nitrogen (TAN) and nitrite-nitrogen were assessed by NH₄Cl spikes and tested at four different water velocities in the biofilters (1.4, 5.4, 10.8 and 16.2 m h⁻¹) under identical conditions. Water velocities below 10.8 m h⁻¹ significantly reduced TAN- and nitrite removal rates. The surface specific TAN removal rates correlated with the TAN concentrations at the water velocities 10.8 and 16.2 m h⁻¹, and the first order surface removal rate constant was estimated at 0.45 m h⁻¹. However, no correlations between TAN removal and TAN concentrations were found at the lowest velocities. Up to five-fold elevated nitrite levels were found in the RAS when biofilters were operated at 1.4 m h⁻¹ compared to the trials at other water velocities, substantiating the significant effect of water velocity on both nitrification processes. The importance of biofilter hydraulics documented in this pilot scale RAS probably have implications for design and operation in larger scale RAS.

在三个带虹鳟鱼的淡水中试规模RAS中，研究了水速对固定床生物滤池硝化速率的影响。通过NH ₄ Cl加标评估总氨氮（TAN）和亚硝酸盐氮的去除，并在相同条件下在生物滤池中的四种不同水速下（1.4、5.4、10.8和16.2 mh ^-1）进行测试。低于10.8 mh ^-1的水流速显着降低了TAN-和亚硝酸盐的去除率。在水速10.8和16.2 mh ^-1时，表面比TAN去除速率与TAN浓度相关，并且一阶表面去除速率常数估计为0.45 mh ^-1。但是，在最低流速下，TAN去除与TAN浓度之间没有相关性。与其他水流速下的试验相比，当生物滤池在1.4 mh ^-1下运行时，在RAS中发现亚硝酸盐水平升高了五倍，证实了水速对两个硝化过程的显着影响。在中试规模的RAS中记录的生物滤池液压系统的重要性可能会对大规模RAS中的设计和操作产生影响。