Transformation of Benzalkonium Chloride under Nitrate Reducing Conditions

Abstract

The effect and transformation potential of benzalkonium chlorides (BAC) under nitrate reducing conditions were investigated at concentrations up to 100 mg/L in batch assays using a mixed, mesophilic (35 degrees C) methanogenic culture. Glucose was used as the carbon and energy source and the initial nitrate concentration was 70 mg N/L Dissimilatory nitrate reduction to ammonia (DNRA) and to dinitrogen (DNRN) were observed at BAC concentrations up to 25 mg/L At and above 50 mg BAC/L, DNRA was inhibited and DNRN was incomplete resulting in accumulation of nitrous oxide. Long-term inhibition of methanogenesis and accumulation of volatile fatty acids were observed at and above 50 mg BAC/L Over 99% of the added BAC was recovered from all cultures except the one amended with 100 mg BAC/L where 37% of the initially added BAC was transformed during the 100 day incubation period. Abiotic and biotic assays performed with 100 mg/L of BAC and 5 mM (in the liquid phase) of either nitrate, nitrite, or nitric oxide demonstrated that BAC transformation was abiotic and followed the modified Hofmann degradation pathway, i.e., bimolecular nucleophilic substitution with nitrite. Alkyl dimethyl amines (tertiary amines) were produced at equamolar levels to BAC transformed, but were not further degraded. This is the first report demonstrating the transformation of BAC under nitrate reducing conditions and elucidating the BAC transformation pathway.