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 log(10) (90%) inactivation, 45 to 90 Wh m(-2) for 3 log(10) (99.9%), and 90 to 180 Wh m(-2) for 6 log(10) (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 log(10) (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 W m(-2) did not increase the inactivation constant. A synergistic effect of water temperatures below 50 degrees 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.