Effect of solar water disinfection (SODIS) on model microorganisms under improved and field SODIS conditions

SODIS is a solar water disinfection process which works by exposing untreated water to the sun in plastic bottles. Field experiments were carried out in Cochabamba, Bolivia, to obtain standard UV-A (320–405 nm) dose values required to inactivate non-spore forming bacteria, spores of Bacillus subtilis, and wild type coliphages. Inactivation kinetics for non-spore forming bacteria are similar under SODIS conditions, exhibiting dose values ranging between 15 and 30 Wh m⁻² for 1 log₁₀ (90%) inactivation, 45 to 90 Wh m⁻² for 3 log₁₀ (99.9%), and 90 to 180 Wh m⁻² for 6 log₁₀ (99.9999%) inactivation. Pseudomonas aeruginosa was found to be the most resistant and Salmonella typhi, the most sensitive of the non-sporulating organisms studied here. Phages and spores serve as model organisms for viruses and parasite cysts. A UV-A dose of 85 to 210 Wh m⁻² accumulated during one to two days was enough to inactivate 1 log₁₀ (90%) of these strong biological structures. The process of SODIS depended mainly on the radiation dose [Wh m⁻²] an organism was exposed to. An irradiation intensity exceeding some 12 Wm⁻² did not increase the inactivation constant. A synergistic effect of water temperatures below 50°C was not observed. Data plotting from various experiments on a single graph proved to be a reliable alternative method for analysis. Inactivation rates determined by this method were revealed to be within the same range as individual analysis.