No abstract

Greywater often contains microorganisms carrying antimicrobial resistance genes (ARGs). Reuse of greywater thus potentially facilitates the enrichment and spread of multidrug resistance, posing a possible hazard for communities that use it. As water reuse becomes increasingly necessary, it is imperative to determine how greywater treatment impacts ARGs. In this study, we characterize ARG patterns in greywater microbial communities before and after treatment by a recirculating vertical flow constructed wetland (RVFCW). This greywater recycling method has been adopted by some small communities and households for greywater treatment; however, its ability to remove ARGs is unknown. We examined the taxonomic and ARG compositions of microbial communities in raw and treated greywater from five households using shotgun metagenomic sequencing. Total ARGs decreased in abundance and diversity in greywater treated by the RVFCW. In parallel, the microbial communities decreased in similarity in treated greywater. Potentially pathogenic bacteria associated with antimicrobial resistance and mobile genetic elements were detected in both raw and treated water, with a decreasing trend after treatment. This study indicates that RVFCW systems have the potential to mitigate antimicrobial resistance-related hazards when reusing treated greywater, but further measures need to be taken regarding persistent mobile ARGs and potential pathogens.

The reuse of household greywater is increasing globally. Wastewater and greywater treatment processes are not fully effective in removing all contaminants, such as emerging micropollutants, antimicrobial-resistant bacteria, and antibiotic resistance genes. The dynamics between emerging micropollutants and antibiotic resistance genes in greywater treatment systems are complex. Thus, this review aims to analyze the current knowledge on sources, spread, and the fate of emerging micropollutants, antibiotic-resistance genes, and antimicrobial-resistant bacteria in microbial communities of greywater and downstream recipients. The fate of antimicrobial resistance and emerging micropollutants from greywater in the environment has not been determined. More studies are needed to identify the mechanism/s involved in the degradation of emerging micropollutants and the presence of transformation pathways in the microbial metagenome. In the review, we aim to describe the link between the persistence of emerging micropollutants and the emergence of antimicrobial resistance. We showed that the effect of irrigation with treated wastewater was variable. In addition, we tried to summarize the impact of emerging micropollutants on bacteria and their fate in the soil microbiome, demonstrating that emerging micropollutants induce changes in the diversity of soil bacteria. The fate and transport of emerging micropollutants, antimicrobial-resistant bacteria, and antibiotic resistance genes can vary with soil properties. It is, therefore, necessary to better understand how widely antibiotic-resistance genes are disseminated.