Point-of-Use Disinfection of Household Drinking Water with Copper/Zinc Ions and Oxide Nanoparticles: a Proof-of-Concept Lab Study

Water in households of the developing world is often microbially unsafe and the cause of waterborne disease. Therefore, simple, effective and convenient treatment methods are needed to disinfect such household water. Disinfecting water with antimicrobial metals as ions or nanoparticles has been inadequately studied for this application. This research quantified the disinfecting efficacy of low (0.2 mg/L) and high (2 mg/l) doses of combinations of ionic copper and zinc and copper and zinc oxide nanoparticles in model buffered water that are considered safe for consumption. Kinetics of disinfection were quantified for three test microorganisms: Bacillus cereus spores, Escherichia coli, and MS-2 coliphage in pH 7.3, 0.04M HEPES-buffered water with and without 10 mg/L added natural aquatic organic matter (NOM); concentrations of culturable microorganisms were assayed at 0, 20, 60, 180, and 360 minutes of contact time. Disinfection conditions that could meet the World Health Organization (WHO) “protective” performance guideline levels of 2 log10 bacteria and parasite reduction (for E. coli and spores of B. cereus, respectively) and 3 log10 virus reduction (for MS-2 coliphage) within 12 hours were investigated for kinetic modeling. Several test conditions of metal form (ion or nanoparticle oxide) and concentrations were efficacious against virus, bacteria and protozoan parasite surrogates within the 12 hour contact time specified. Both copper and zinc ions and nanoparticles oxides were effective in achieving microbial reduction targets in buffered test water lacking added NOM. None of the test conditions were effective in meeting microbial reduction targets in test water lacking added NOM. Additional studies are needed to better document the effect of NOM and other water quality parameters (such as turbidity, pH and chemical behavior of dissolved solids) on the ability of these metal ions and nanoparticles to disinfect drinking water.