Effect of the radiation intensity, water turbidity and exposure time on the survival of Cryptosporidium during simulated solar disinfection of drinking water

The solar disinfection (SODIS) technique is a highly effective process that makes use of solar energy to inactivate pathogenic microorganisms in drinking water in developing countries. The pathogenic protozoan parasite Cryptosporidium parvum is often found in surface waters and is associated with waterborne outbreaks of cryptosporidiosis. In the present study, a complete multi-factorial mathematical model was used to investigate the combined effects of the intensity of solar radiation (200, 600 and 900 W/m2 in the 320 nm to 10 μm range), water turbidity (5, 100 and 300 NTU) and exposure time (4, 8 and 12 h) on the viability and infectivity of C. parvum oocysts during simulated SODIS procedures at a constant temperature of 30 °C. All three factors had significant effects (p < 0.05) on C. parvum survival, as did the interactions of water turbidity with radiation intensity and radiation intensity with exposure time. However, the parameter with the greatest effect was the intensity of radiation; levels ≥600 W/m2 and times of exposure between 8 and 12 h were required to reduce the oocyst infectivity in water samples with different degrees of turbidity.