Insights into the microbiology of selected drinking water treatment plants and sludge

Abstract

Drinking water treatment plants (DWTPs) play a crucial role in treating raw water sources to potable quality. Contaminants in drinking water can pose serious health concerns. The study evaluated the microbial diversity of raw water, the treatment stages, treated water, and the sludge of three DWTPs in the Northwest and Gauteng provinces over a 12-month monitoring period. Microbial and physicochemical parameters of the were analysed. Enumeration of E. coli and Enterococcus spp. was conducted using Colilert-18 and Enterolert Quanti-Tray/2000 IDEXX. Heterotrophic plate counts (HBC) were performed to quantify heterotrophic bacteria. Antibiotic resistance of the bacteriological indicators was assessed using the disc diffusion method. Microbial diversity and functional metagenomic profiles were analysed using the shotgun metagenomics sequencing approach. Correlation analysis was conducted to determine relationships between bacterial communities, treatment stages, raw water and the physicochemical parameters. All DWTPs achieved approximately 90% reduction in bacteriological indicator across the seasons. Most of the isolated bacteriological indicators showed resistance to beta-lactams class of antibiotics. Based on metagenomic analysis, Euryarchaeota and Nitrososphaerota (Archaea phyla), Pseudomonadota (Bacterial phyla), Ascomycota and Basidiomycota (Eukaryota phyla), were abundant in the water and sludge samples. Correlation analysis showed that pH, temperature, nitrates, sulphate, EC, TDS, and Fe were associated with the proliferation of the bacteria. Metabolism functional genes were abundant across the sampling points.