Improving Silver-Ceramic-Based Point-of-Use Water Treatment with Novel Copper Addition and Commercial Water Filters

In 2020, 1 out of 4 people did not have safely managed drinking water in their homes. Household water treatment is a low-cost method to decrease the pathogen load in drinking water to reduce instances of waterborne disease. A household water treatment product, the MadiDrop+, uses silver to achieve a 4-log reduction of bacteria, but requires 8 hours of contact time and does not remove turbidity from the water. Additionally, silver only achieves around a 1-log reduction of viral pathogens. This research addresses the shortcomings of the MadiDrop+ technology with two approaches: (1) combining the MadiDrop+ with household water filters and (2) incorporating copper into the MadiDrop+.
For the first part of this research, the bacterial reduction of several water filters with and without a silver-embedded ceramic tablet (MadiDrop+) in both the laboratory and household settings was evaluated. In laboratory tests, after 24 hours, Kohler Clarity filters with MadiDrop+ halves split between upper and lower reservoirs removed 6.0-log E. coli compared to filters alone that removed 2.7-log E. coli. After 2 hours, Rama Water carbon filters with MadiDrop+ halves split between reservoirs removed 3.3-log E. coli compared to filters alone that removed 1.7-log E. coli. After 2 hours, ceramic pot filters with a MadiDrop+ in the lower reservoir removed 3.9-log TCB compared to filters alone that removed 2.8-log TCB. In households, effluent TCB (CFU/100 mL) was between 0 – 12, 1 – 36, and 509 – 5,916 when the MadiDrop+ was in the lower reservoir, split between reservoirs, and not present in Kohler Clarity filters, respectively. Silver levels were ≤ 100 µg/L, the drinking water limit set by the U.S. EPA. The addition of silver via MadiDrop+ either wholly in the lower reservoir or split between upper and lower reservoirs of household water filters improved bacterial reduction in both laboratory and household settings.
In tandem, this dissertation developed and evaluated several approaches to achieving sustained release of copper into water. Copper has been shown to have antibacterial, antiviral, and antifungal effects in drinking water to combat microbial contamination and thus decrease instances of waterborne disease. Studies have shown 2.5- and 1.8-log reductions of E. coli and MS2 bacteriophage, respectively, after 6 hours of contact time with 300 µg/L copper. This is well below the drinking water limit of 1,300 µg/L. This research sought to develop a copper-based household water treatment product that could consistently release ~300 µg/L copper into 10 L of water daily for at least 1 week. The first approach was to embed copper into ceramic tablets. We varied the copper salt, mass of copper, firing temperature, and firing environment. Copper-embedded ceramic tablets generally released high amounts of copper in the first few days of use followed by gradual or drastic declines over the following days. The second approach was immersing copper metal in water. We evaluated copper release from 3 copper metal products that vary in surface area: a sheet (lowest surface area), a mesh, and a screen (highest surface area). Unlike the copper-embedded tablets, none of the metallic copper interventions had initial spikes or drastic drops in copper release over 8 days of use. The copper sheet consistently released 70-129 µg/L copper over 8 days but was more than 3 times the cost of other interventions. The copper mesh and copper screen released 145-256 µg/L and 188-333 µg/L copper, respectively, over 8 days of use and cost $0.75 and $2.00 per 10 grams, respectively. Given consistency of copper release, target range of copper concentrations, and low cost, the copper mesh and copper screen were further evaluated in combination with the MadiDrop+.
We found that wrapping copper mesh around the MadiDrop+ decreased daily silver concentrations from 47 - 82 µg/L to 1 - 6 µg/L. Folding the copper screen into a 2x2 inch area reduced daily copper concentrations in the water from 203 - 293 µg/L to 20 - 31 µg/L. Placing ten grams of unfolded copper screen and the MadiDrop+ in the same container but not wrapped around each other provided an average of 174 - 325 µg/L copper and 60 - 141 µg/L silver daily for the first 15 days of use. Copper concentrations remain between 149 - 365 µg/L for 92 days of use.
Lastly, the MadiDrop+ and copper screen, coined MadiDrop+Cu, removed >6-log E. coli and >3-log MS2 Bacteriophage after 8 and 24 hours of contact time, respectively. Combining the MadiDrop+Cu with chlorinated polymer gels achieved the greatest viral disinfection, reaching 4.1-log removal of MS2 Bacteriophage. MadiDrop+Cu achieves 1-star performance of the World Health Organization scheme for household water treatment. The results collected in this dissertation support the feasibility and benefit of commercializing MadiDrop+Cu which achieves greater disinfection of drinking water than the MadiDrop+ alone. The next steps in this research are to continue testing longevity of the copper screen, how long-term use affects the disinfection properties, and a practical design for using the MadiDrop+Cu.