Resistance of bacterial pathogens to calcium hypochlorite disinfectant and evaluation of the usability of treated filter paper impregnated with nanosilver composite for drinking water purification.

Objectives: Innovative techniques are urgently required to remove pathogenic bacterial contamination of drinking water. This study aimed to evaluate the biocidal activity of calcium hypochlorite [Ca(OCl)], silver nanoparticles (AgNPs) and Ca(OCl)/AgNPs composite against bacteria isolated from drinking water supplies (tap and hand pump water). A field trial was subsequently performed to evaluate the efficacy of a biocidal filter paper containing Ca(OCl)/AgNPs composite against existing pathogenic bacteria and indicator coliform bacteria.

Methods: A total of 100 water samples were collected from the main source and water troughs used for cattle drinking and were examined for the presence of pathogenic bacteria. The susceptibility of 60 isolated strains to Ca(OCl), AgNPs and Ca(OCl)/AgNPs was evaluated by the broth macrodilution method. The field trial examined different water samples collected from water supplies (pre- and post-treatment) using filter paper impregnated with Ca(OCl)/AgNPs.

Results: Ca(OCl) loaded on AgNPs at a concentration of 1.5mg/L showed a lethal effect (100%) on Escherichia coli, Staphylococcus aureus and Klebsiella pneumoniae following 180min of exposure. Furthermore, filter paper impregnated with Ca(OCl)/AgNPs exhibited a biocidal effect (100%) against existing pathogenic bacteria, bacterial total viable count, total coliform count and faecal coliform count.

Conclusions: Use of the disinfectant Ca(OCl) against isolated bacteria revealed the existence of bacterial resistance. Enhancement of the biocidal effect of Ca(OCl) using AgNPs was reliable, proving that Ca(OCl)/AgNPs composite had a biocidal effect against isolated bacteria at 1.5mg/L as well as inactivation of coliforms and pathogenic bacteria during percolation through bactericidal filter paper.