the mortality of the microorganisms increases when they are exposed to both temperature and UV-A light at the same time.

Water temperature affects disinfection

A warmer water temperature speeds up the process. However, bacteria, viruses, giardia and cryptosporidia are killed by UV-A radiation even when water is cooler.

* UV-A interferes directly with the metabolism and destroys cell structures of bacteria.
* UV-A (wavelength 320-400 nm) reacts with oxygen dissolved in the water and produces highly reactive forms of oxygen (oxygen free radicals and hydrogen peroxides), that are believed to also damage pathogens.
* Infrared radiation heats the water. If the water temperatures rises above 50°C, the disinfection process is three times faster.

At a water temperature of about 30°C (86°F), a threshold solar radiation intensity of at least 500 W/m2 (all spectral light) is required for about 5 hours for SODIS to be efficient. This dose contains energy of 555 Wh/m2 in the range of UV-A and violet light, 350 nm-450 nm, corresponding to about 6 hours of mid-latitude (European) midday summer sunshine.

At water temperatures higher than 45°C (113°F), synergistic effects of UV radiation and temperature further enhance the disinfection efficiency.