Synergistic effect of solar radiation and solar heating to disinfect drinking water sources

Abstract

Waterborne diseases are still common in developing countries as drinking water sources are contaminated and feasible means to reliably treat and disinfect these waters are not available. Many of these developing countries are in the tropical regions of the world where sunlight is plentiful. The objective of this study was to evaluate the effectiveness of combining solar radiation and solar heating to disinfect contaminated water using a modified Family Sol*Saver System (FSP). The non-UV transmittable cover sheet of the former FSP system was replaced with an UV transmittable plastic cover sheet to enable more wavelengths of sunlight to treat the water. Disinfection efficiency of both systems was evaluated based on reduction of the natural populations of faecal coliform, E. coli, enterococci, C. perfringens, total heterotrophic bacteria, hydrogen sulphide producing bacteria and FRNA virus. The results showed that under sunny and partly sunny conditions, water was heated to critical temperature (60 degrees C) in both the FSP systems inactivating more than 3 log (99.9%) of the concentrations of faecal coliform and E. coli to undetectable levels of < 1 CFU/100 mL within 2-5 h exposure to sunlight. However, under cloudy conditions, the two FSP systems did not reduce the concentrations of faecal indicator bacteria to levels of < 1 CFU/100 mL. Nonetheless, sufficient evidence was obtained to show that UV radiation of sunlight plus heat worked synergistically to enhance the inactivation of faecal indicator bacteria. The relative log removal of indicator microorganism in the FSP treated water was total heterotrophic bacteria < C. perfringens < F RNA virus < enterococci < E. coli < faecal coliform. In summary, time of exposure to heat and radiation effects of sunlight were important in disinfecting water by solar units. The data indicated that direct radiation of sunlight worked synergistically with solar heating of the water to disinfect the water. Thus, effective disinfection was observed even when the water temperature did not reach 60 degrees C. Finally, the hydrogen sulphide test is a simple and reliable test that householders can use to determine whether their water had been sufficiently disinfected.

Optimizing the solar water disinfection (SODIS) method by decreasing turbidity with NaCl

“…The inactivation of select bacteria, viruses, and protozoa due to UV-A radiation and heat has been studied extensively in studies under both simulated and natural conditions (Berney et al 2006;Boyle et al 2008;Dejung et al 2007;Heaselgrave et al 2006;Joyce et al 1996;Méndez-Hermida 2007;McGuigan et al 1998;Rijal & Fujioka 2001). It has been shown that a synergistic effect in low-turbidity water is observed when water temperature exceeds 45 o C, at which point the combined inactivation effectiveness is greater than the individual contributions of radiation and heat (McGuigan et al 1998).…”

Drinking Water Disinfection by Solar Radiation

“…E. coli can be reduced by 3 logs with pasteurization at 65 o C within 3 hours. The same reductions can be achieved in a combination of solar disinfection and pasteurization within 2 hours at 56°C [37].…”

Untitled

“…This necessity was made evident by the results found by Rijal and Fujioka (2001), who demonstrate that a disinfection system based on the synergistic effect of solar radiation and temperature, for the purpose of disinfecting drinking water, suffered reduced efficiency on cloudy days. Further, the factors mentioned by Balladin et al (1999) and Hanson et al (2004) as having influenced the microbiological quality of treated water in their studies highlight the need for adequate operation and maintenance of the equipment in order to avoid any future failures.…”