Degradation of N-methylbenzylamine and N,N-dimethylbenzylamine in anaerobic biological reactors and formation of N-nitrosomethylbenzylamine and N-nitrosodimethylamine during subsequent chloramination.

As water reuse demand increases, wastewater treatment plants must manage byproducts effectively while ensuring safety. The excessive use of benzalkonium chloride disinfectants can lead to the accumulation of benzylamines, such as N-methylbenzylamine (MBA) and N,N-dimethylbenzylamine (DMBA). Biological anaerobic treatment is becoming more popular due to concerns over energy consumption and carbon emissions. Our study examined the biodegradation of MBA and DMBA during anaerobic treatment and their effects on toxic byproduct formation during subsequent chloramination, as well as their impact on bioreactor performance, degradation pathways, and microbial communities. Our results showed that anaerobic bioreactors had minimal impact on overall treatment performance despite the presence of MBA and DMBA. MBA proved resistant to biodegradation, whereas DMBA underwent significant biodegradation. Notably, during chloramination, MBA effluent formed nitroso-MBA with a 1 % molar yield, whereas DMBA effluent had significant N-nitrosodimethylamine formation, with molar yields reaching 10 ± 1 % and 97 ± 7 % of the influent and residual DMBA concentrations. We observed significant differences in microbial communities between the DMBA reactor and the MBA and control reactors. Proposed degradation pathways and the involvement of specific microbial communities were detailed. These findings highlight the importance of thoroughly evaluating biologically treated effluent to manage the risks of toxic byproducts in water reuse.