Electrolytic Release of Metal Cations in Water

Introduction. The final step in water treatment processes is disinfection, which inactivates disease-causing organisms in a water supply. This is accomplished through two mechanisms: the provision of primary disinfection that removes or deactivates pathogens in the water and the supply of a residual disinfectant in distribution systems. Inadequate disinfection of drinking water results in a variety of water-borne diseases such as cholera, typhoid, schistosomiasis, and diarrhea.

This is important in the context of diarrheal disease being the leading cause of mortality in children under the age of 5 and is particularly prevalent in low- and middle-income countries that lack the access to adequate water treatment. Effective water disinfection also has implications on providing safe water for medical, food safety, recreational purposes such as swimming pools and even reducing corrosion-inducing bacteria in cooling systems.

Chlorine is widely used to achieve both primary and residual disinfection of pathogenic microorganisms. However, while it is highly effective, it possesses an unappealing taste and odor for some consumers, an inability to disinfect certain resistant microorganisms, and contributes to the formation of hazardous products such as chloroform. In addition, the concentrations of hypochlorites required to effectively inactivate Legionella could cause corrosion in plumbing systems.

Chlorine also has security issues with storage and handling, a high toxicity to nontargeted microorganisms during disinfection, an efficiency dependent on pH and temperature, and a reactivity with ammonia and nitrogen to form chloramines and organic chlorine compounds, reducing potential for disinfection. These issues also affect chlorine’s efficiency and safety in disinfecting water for recreational purposes, as organics and bodily fluids from swimmers affect levels of free chlorine in the water, and trihalomethane compounds formed have the potential to absorb through skin.

Due to these concerns, various disinfection alternatives to chlorination have been developed.

Electrolytic water disinfection has been developed as one of these alternatives and has been examined for a variety of water treatment applications, as it is a promising tool to treat water without detrimental environmental effects. Specifically, copper and silver electrodes have previously been studied as viable electrode materials as a means for electrolytic disinfection. Ionic copper and silver are slower than chlorine in deactivating microorganisms, but they disinfect in smaller concentrations and are safe, odorless, and provide residual effect.

Copper has been shown to more severely harm coliform than does chlorine and cause longer recovery times. Silver ions have the potential to be recovered, rendering electrolytic silver disinfection both economical and environmentally friendly. Silver has also been incorporated into point-of-use water treatment technologies such as ceramic water filters that treat water in the home when households lack access to a continuous, reliable water source. Both metals have the potential to adsorb to materials’ surfaces to potentially provide contact residual against the formation of biofilms that could contain pathogens. There may be ways to treat water in a developing-world setting using electrolytic silver/copper alone or in combination with chlorine to provide resilient and sustainable treated water.

While there may be some hesitation about the health effects of ingesting copper and silver, the Environmental Protection Agency (EPA) has established copper and silver maximum of 1000 and 100 parts per billion to be safe in drinking water, respectively. To date, the only detrimental health effect discovered due to silver is argyria, irreversible skin discoloration that occurs due to the administration of high concentrations to individuals, which would require more than 10 g of silver to be ingested over a lifetime.