Effect of common rooftop materials as support base for solar disinfection (SODIS) in rural areas under temperate climates

Abstract Two common rooftop materials easily found in rural areas – zinc-coated metal sheet and bamboo cover – were studied to analyse their possible influence in the solar disinfection process by affecting the received UV radiation and water temperature in SODIS plastic bottles. The objective is to use available local materials to enhance the process while reducing the extra energy usage required for the manufacturing of new ad-hoc systems. Experiments were conducted at a temperate climate, 40 °N latitude, over different seasons of the year. Escherichia coli and total coliforms disinfection processes were studied. Results show that in most cases the bottles over the zinc-coated metal roofing material reached an inactivation level of 1-log higher than those on the bamboo cover. Maximum water temperatures differences in the bottles over the two materials were of about 2.5 °C in the best case. Higher inactivation in the zinc-coated metal sheet when water temperature is below 40 °C should be attributed to better material reflectivity. At water temperatures around 40 °C, the 2.5 °C difference can be significative and accelerate the disinfection process. Material heat transfer characteristics have been also found to be essential, especially when the solar disinfection starts at mid-day instead of early in the morning. In this case, as the support materials are already at higher temperatures because of solar irradiance absorption, the water temperature in the bottles increases more rapidly, contributing to the water disinfection process when it rises above 40 °C.