The impact of different stages of water treatment process on the number of selected bacteria

Critical infrastructure facilities play an important role in ensuring the safety of human life. The present paper provides an overview of the legal framework for critical infrastructure facilities regarding protection against epidemiological risk. Based on test results for treated and raw water samples (n = 8973) and samples collected in water treatment plants at individual stages of the technological process, the effectiveness of water treatment processes used at the plants was assessed with regard to selected pathogens, i.e., Coliforms bacteria, Escherichia coli, Enterococcus faecalis and Clostridium perfringens. It was demonstrated that the level of bacteriological contamination of river water is mainly determined by the number of fecal bacteria Coliforms bacteria and Enterococcus faecalis, and the proportion of individual types of pathogens in water from both the river and infiltration wells does not change significantly throughout the year and presents the following order: Coliforms bacteria > Clostridium perfringens ≈ Enterococcos faecalis. It was shown that the process of soil infiltration is highly effective in removing pathogenic bacteria (99% on average) and may present an alternative to intermediate processes of water treatment, comparable to filtration on DynaSand filters. The level of microbial removal was high at the intermediate stage of water treatment, i.e., preliminary coagulation in settling tanks and filtration on sand filters. Following subsequent technological processes, namely disinfection with UV light and gas chlorine, or ozonation and filtration on activated carbon, there was a 100% reduction in microbiological pathogens in the water analyzed, which is an essential requirement to ensure the safety of drinking water.