Effect of Alkyl Benzyl Dimethyl Ammonium Chloride and Temperature on Nitrification

The inhibitory effect of alkyl benzyl dimethyl ammonium chloride (AB), a quaternary ammonium compound commonly used as a disinfectant, was assessed at room temperature (22 to 24°C) and AB concentrations between 2 to 20 mg/L using an enriched, mixed nitrifying culture. Ammonia oxidation was inhibited with increasing AB concentration and ceased at 15 mg AB/L. For all tested AB concentrations, AB was not degraded in the nitrifying culture within 4 days of testing because of the very low concentration of heterotrophic bacteria in the enrichment culture. Assuming non-competitive inhibition, the AB inhibition coefficient was estimated as 1.5 ± 0.9 mg AB/L, indicating that AB is a potent nitrification inhibitor. Nitrification tests were conducted at a temperature range of 24 to 10°C with and without AB at an initial concentration of 5 mg/L using an aerobic, mixed heterotrophic/nitrifying culture. In the absence of AB, short-term exposure of the culture at 10°C resulted in the slow removal of ammonia and the slow conversion of the resulting nitrite to nitrate. However, short-term exposure of a duplicate culture at 10°C amended with 5 mg/L AB resulted in even slower ammonia removal, while nitrite accumulated and less than 30% of the initial ammonia was converted to nitrate. Maintaining the aerobic mixed culture at 10°C for over one month and in the absence of AB, resulted in even slower nitrification kinetics compared to those measured when the culture was first exposed to 10°C. AB was degraded in all tests conducted with the heterotrophic/nitrifying culture, but the AB degradation rate decreased significantly as the temperature decreased to 10°C. These results confirm the negative impact of low temperature on the rate and extent of nitrification and the deleterious effect of quaternary ammonium compounds on the nitrification process.