Effects of fluctuations in biodegradable organic matter on nitrification filters

In these experiments, three completely mixed biofilm reactors were fed ammonium nitrogen (NH₄⁺-N) at a constant concentration of 1.5 or 2.5 mg/L. Acetate was added to the feed media at concentrations ranging from 0 to 10 mg C/L. Sudden increases in the acetate loading led to temporary deterioration of the nitrification efficiency and to formation of nitrite nitrogen (NO_2--N). The incomplete nitrification occurred because of the suddenly high growth rate of the heterotrophic bacteria, which outgrew the nitrifiers and temporarily swept them out of the biofilm. Establishment of a new steady state for the heterotrophic bacteria allowed the nitrifiers to regrow in the biofilm and achieve nearly 100 percent nitrification. These results demonstrate that fluctuations in the input loading of biodegradable organic matter can adversely affect nitrification performance through competition by fast-growing heterotrophic bacteria but that long-term stable nitrification is possible.