Enhancing Microbial Disinfection in Household Water Treatment by Combining a Silver–Ceramic Tablet with Copper and Chlorine Technologies

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-cost method for reducing the pathogen load in drinking water to decrease instances of diarrhea and sometimes death. This study developed and evaluated a new silver and copper water treatment product that meets WHO one-star performance criteria for household water treatment without using electricity: the $\mathrm{MadiDrop}+\mathrm{Cu}$. First, we tested different configurations of a copper mesh and a copper screen with the MadiDrop to evaluate the effects of their proximity to one another on copper and silver concentrations in water. Wrapping the copper mesh around the MadiDrop decreased silver concentrations in water compared with the MadiDrop alone. Folding the copper screen into smaller dimensions decreased the copper concentrations in water compared with the copper screen unfolded. The MadiDrop and copper screen, coined $\mathrm{MadiDrop}+\mathrm{Cu}$, provided an average of $125–415\mathrm{\mu g}/\mathrm{L}$ copper and $4–21\mathrm{\mu g}/\mathrm{L}$ silver daily for 150 days of use. When tested individually and in combination against E. coli, $\mathrm{MadiDrop}+\mathrm{Cu}$ removed the most bacteria together rather than separately after 8 h. A previous study found a prototypic chlorinated polymer gel removed more E. coli with the MadiDrop than either intervention alone after 8 h. This study tested the viral (MS2 Bacteriophage) disinfection from the chlorinated polymer and $\mathrm{MadiDrop}+\mathrm{Cu}$ by themselves and in combination with one another. The MadiDrop alone removed $<1\log$ (90%) of viruses, whereas $\mathrm{MadiDrop}+\mathrm{Cu}$ removed $>3\log$ (99.9%) after 24 h. The greatest viral disinfection occurred when the $\mathrm{MadiDrop}+\mathrm{Cu}$ and chlorine-charged polymer gel were used together, removing $>4\log$ (99.99%) after 24 h.

Low-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 low-cost water treatment: combining a silver-embedded ceramic tablet with a high specific-surface-area copper screen and a chlorine-charged polymer gel. $\mathrm{MadiDrop}+\mathrm{Cu}$ was found to consistently release sufficient levels of silver and copper over 150 days of use. The MadiDrop alone killed less than 90% of viruses, whereas the $\mathrm{MadiDrop}+\mathrm{Cu}$ killed over 99.9% of viruses after 24 h. The MadiDrop, copper screen, and the chlorine-charged polymer gel killed over 99.99% of viruses after 24 h. Although a 24 h wait time is not ideal for emergency settings, the findings suggest that this novel approach to combining silver, copper, and chlorine without electricity is a promising method for a low-cost, household water treatment.