Interplay of Biologically Active Carbon Filtration and Chlorine-Based Disinfection in Mitigating the Dissemination of Antibiotic Resistance Genes in Water Reuse Distribution Systems

Appropriate
management approaches are needed to minimize the proliferation
of antibiotic resistance genes (ARGs) in reclaimed water distribution
systems (RWDSs). Six laboratory-scale RWDSs were operated over 3 years
receiving influent with or without biologically active carbon (BAC)
filtration + chlorination, chloramination, or no disinfectant residual.
Shotgun metagenomic sequencing was applied toward comprehensive characterization
of resistomes, focusing on total ARGs, ARG mobility, and specific
ARGs of clinical concern. ARGs such as aadA, bacA, blaOXA, mphE, msrE, sul1, and sul2 were
found to be particularly sensitive to varying RWDS conditions. BAC
filtration with chlorination most effectively achieved and maintained
the lowest levels of nearly all metagenomically derived antibiotic
resistance indicators. However, BAC filtration or addition of residual
disinfectants alone tended to increase these indicators. Biofilm and
sediment compartments harbored ARGs in disinfected systems, presenting
a concern for their release to bulk water. Relative and absolute abundances
of most ARGs tended to decrease with water age (up to 5 days), with
notable exceptions in BAC-filtered chloraminated and no residual systems.
Superchlorination of unfiltered water especially raised concerns in
terms of elevation of clinically relevant and mobile ARGs. This study
revealed that BAC filtration and disinfection must be carefully coordinated
in order to effectively mitigate ARG dissemination via RWDSs.