Using high amounts of chlorine to disinfect contaminated natural waters for drinking purposes can produce an unpleasant taste and odor and contribute to the formation of toxic byproducts. These challenges can be addressed through the combined use of lower amounts of chlorine and silver. Several studies in well water or solutions inoculated with bacteria or viruses have demonstrated that this combination produces a synergistic effect in the inactivation of pathogens. This study investigated the synergistic inactivation of bacteria in natural waters (from a pond with 4.82 NTU and upstream with 11.9 NTU in Virginia) using low doses of silver (added as silver nitrate) and free chlorine (from Aquatabs). There was a significant synergistic effect at 3-h contact time, and the ${\log }_{10}$ reductions of E. coli and total coliform bacteria (TCB) were $\ge 1.44$ and $\ge 2.73$ , respectively, with the lower-turbidity water, and 0.87 and 1.29, respectively, with the higher-turbidity water. Chlorine effectiveness was significantly reduced by higher turbidity, whereas silver effectiveness was not. Thus, for waters with higher turbidity, silver alone or a combination of low doses of silver and chlorine may produce a higher bacteria inactivation than chlorine alone. In addition, bacteria inactivation by the MadiDrop+ (MD, a commercial silver-ceramic tablet that releases silver ions for point-of-use water disinfection), with low doses of free chlorine in water from a stream in South Africa, was tested. The MD alone at 8-h contact time obtained $\sim 1\text{-}{\log }_{10}$ reduction for E. coli and $\sim 2\text{-}{\log }_{10}$ reduction for TCB. However, some of the MD-free chlorine combinations achieved a similar bacteria reduction with a substantial reduction of contact time (between 6 and 7 h less). Overall, these results show that the silver–chlorine synergistic effect demonstrated in previous studies with solutions inoculated with pathogens is also present in the more realistic scenario of natural waters that contain more complex matrices.

The World Health Organization (WHO) estimates that microbiologically contaminated drinking water is estimated to cause 485,000 diarrheal deaths each year. Household water treatment is a low... Practical ApplicationsLow-cost and simple household water treatment products can be used in underresourced settings to prevent waterborne disease. This study designed and tested a novel approach to...

Combinations of metal disinfectants (i.e., silver and copper) with chlorine in doses that meet the World Health Organization guidelines for drinking water operate synergistically to provide superior drinking water disinfection across a wide range of pathogens. Moreover, the combination of disinfectants allows for lower chlorine levels and a less objectionable taste and odor to the treated water (some people can taste or smell chlorine at concentrations as low as 300 μg/L). Towards chlorine-releasing materials for combination with silver- or copper-releasing materials in point-of-use water disinfection, N-chloramine containing polymer gels were developed and their potential for E. coli bacteria inactivation was assessed in deionized water that contained salts to simulate groundwater. Following the chlorination of gels containing chloramine precursors, these gels capably inactivated E. coli, achieving log₁₀ reductions—depending on the gel mass—ranging from 1.1 to 4.5. While chlorine released from the gels was not spectroscopically detected, free chlorine solutions inactivated E. coli in a concentration-dependent way, with 5 and 20 μg/L Cl₂ yielding log₁₀ reductions of 0.43 and 1.69, respectively, suggesting that low levels of chlorine, below both the limit of detection of spectroscopic assays (ca. 40 μg/L Cl₂) and levels known to create adverse taste and smell, are sufficient to inactivate bacteria. Unchlorinated gels or chlorinated control styrene gels (without chloramine precursor) did not inactivate bacteria, suggesting that disinfection did not come from the precursor or from chlorine trapped in the gels after chlorination. In addition, these gels were evaluated together with the MadiDrop (MD, a commercial silver-ceramic tablet) and a copper screen that release silver and copper disinfectants, respectively. Combinations of the gel and MD produced E. coli inactivation close to 2-log₁₀ reduction, with the combination, gels alone, and MD alone achieving 1.86-, 1.10-, and 0.69-log₁₀ reduction, respectively. When the gels were combined with the copper screen, however, neither an increase nor a decrease in bacterial reduction was observed compared to that achieved with the gels alone. The laboratory results in this study are promising and suggest the potential for chloramine-functionalized gels to serve as an alternative to existing commercial chlorine-based POU technologies and in combination with silver-based POU technologies.