Speeding up solar disinfection : effects of hydrogen peroxide, temperature, and copper plus ascorbate on the photoinactivation of E. coli in Charles River water

Abstract

Sunlight efficiently disinfects drinking water in plastic bottles over two days, but simple additives may show promise for reducing this time to several hours. This study found that adding up to 500 [micro]M hydrogen peroxide accelerates the room-temperature inactivation of E. coli K12 by sunlight at a rate proportional to concentration, while temperatures of 35 and 45 degrees Celsius further enhance this effect. It was also found that both 25 [micro]M ascorbic acid in the presence of 2.5 [micro]M copper sulfate and solid copper metal in the presence of 200 [micro]M ascorbate synergistically increased the light-mediated inactivation rate with first-order dependence in both dissolved species, while the addition of hydrogen peroxide to this system exhibited further synergistic enhancement. Although solid copper and 1% lemon juice performed no better than lemon juice alone, the latter significantly accelerated inactivation in a light-dependent manner. Finally, at higher concentrations the copper-ascorbate system can also inactivate E. coli in the dark. These findings suggest possible directions for accelerating the rate of SODIS, with potential for the Cu + ascorbate system to act as a residual disinfectant and an alternative to SODIS on extremely cloudy days.