Context. Ozonation is a used for drinking water preparation and to reduce assimilable organic matter and remove hazardous ozonation byproducts, ozonation is frequently followed by biofiltration, such as passage through slow sand filters (SSFs). The disinfectant properties of the ozone causes shifts in the water prokaryote communities (Xu, et al. 2017) as well as increased relative abundance of antimicrobial resistance genes (ARGs) (Zhang, et al. 2019) and Mycobacterium (Li, et al. 2017). The increased bioavailability of organic matter due to ozonation has affected the prokaryotic community structure in biologically activate carbon filters (Li, et al. 2021).
Gap. The effects of pre-ozonation on the microbial communities of SSFs have not been studied in detail. Specifically, studies are lacking regarding changes in the non-prokaryotic microbiome and the relative abundance of genes related to metabolism and antimicrobial resistance.
Aim. Identifying changes in the microbiome and metagenome of slow sand filters caused by pre-ozonation of the influent water.
Methods. Flow cytometry and metagenomic sequencing were performed on the water and sand of two full-scale slow sand filters and one pre-ozonated pilot-scale (20 m2) filter treating the same raw water (Figure 1a). Water quality parameters were measured to guarantee the functionality and maturity of the pilot-scale setup.
Findings. Pre-ozonated influent had less than 1/200 of the total cell concentration of the non-ozonated influent, as expected, and the effluent cell concentration was also lower (Figure 1b). The percentage of intact cells was lower in the pre-ozonated influent but seemed to reach similar levels in all SSF effluents (Figure 1c). Sample DNA is currently being extracted for library preparation (SMARTer ThruPLEX DNA-seq) and sequencing (Illumina
NovaSeqS4-300) at NGI Sweden (https://ngisweden.scilifelab.se/).
Utilization. Pre-ozonation presents a potential method to engineer the microbial communities of SSFs.
