Biodegradation and Toxicity of Alkyl Benzyl Dimethyl Ammonium Chloride in a Mixed Aerobic Culture
Abstract:The aerobic degradation of alkyl benzyl dimethyl ammonium chloride (AB), a commonly used quaternary ammonium compound, was assessed with a mixed, aerobic culture developed from a contaminated aquatic sediment. Three cultures were maintained with dextrin and peptone which served as the main carbon source. A control culture was AB-free, while two cultures were amended with 20 or 50 mg/L AB. All cultures were maintained at room temperature (22 to 23°C). AB degradation took place without any lag. Complete AB degradation was observed without any accumulation of degradation products. AB at the levels tested in this study did not affect the rate and extent of degradation of the added carbon sources and the production of ammonia (ammonification). After a significant lag period, complete nitrification of the resulting ammonia took place at 20 mg AB/L. In contrast, complete inhibition of nitrification was observed at 50 mg AB/L. Another set of two cultures were developed from the AB-amended cultures, except that AB was the only externally added carbon and nitrogen source. AB at both 20 and 50 mg/L was completely degraded by these cultures without any accumulation of degradation products. The acute, 15-min Microtox® toxicity EC50 value of an AB solution was 0.15 mg/L (95% confidence range: 0.09 to 0.25 mg/L, R2 = 0.83). In contrast, the effect of a supernatant from a culture fed with 50 mg/L AB did not exceed a 17% effect even at a supernatant fraction as high as 45%. Based on the above results, it is concluded that the aerobic mixed culture was able to degrade AB to products which had insignificant toxic effects. However, the inhibitory effect of AB on nitrification at a concentration above 20 mg/L is a concern.
Document Type: Research Article
Publication date: October 1, 2007
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