Metabolic pathways for biotransformation of benzalkonium compounds in fungal- and bacteria-based biofilm reactors

Benzalkonium compounds (BACs) are quaternary ammonium biocides widely used in healthcare and industrial animal production, resulting in high concentrations in manure and wastewater. While BAC biodegradation has been demonstrated in wastewater and soil, little is known about the relevant biodegradation pathways in multi-species biofilm systems. This study investigated BAC degradation pathways in three aerobic moving bed biofilm reactor (MBBR) systems: (1) a fungi (Trametes versicolor) inoculated reactor, and heterotrophic biofilm in (2) water, and (3) manure. We characterised transformation products and elucidated their fragmentation mechanisms to explain the spectra. ω-oxidation and β/α-oxidation dominated in the water-MBBR, whereas formation of benzyldimethylamine (BDMA), was observed only in the manure-MBBR, which was the only system hosting Pseudomonas and Aeromonas species. The water-MBBR microbial community showed a significant increase in abundance of Rhodococcus, known for ω- and β-oxidation, suggesting a role in BAC degradation. None of the five ARGs (sul1, sul2, qnrD, tetM, tetA) tested in this study were elevated in the systems by exposure to BAC. These results demonstrate that BACs are degradable in different aerobic biofilm systems via diverse pathways, influenced by microbial composition and matrix complexity. However, the different metabolites indicate towards complex risk assessments and bioremediation strategies.