1.4.4. Solar disinfection (SoDis)
Solar disinfection (SoDis) is a water treatment technique consisting of exposing water to sunlight, specifically
UVA radiation. Unlike conventional UV water treatment, where UVC radiation directly damages the DNA of
pathogen, SoDis utilizes UVA wavelengths in order to form reactive-oxygen species (ROS) in water. These ROS,
(which include monatomic oxygen, superoxide, hydrogen peroxide and hydroxyl radicals) damage the DNA of
pathogens and deactivate the microbes [15].
Cells have a number of DNA repair mechanisms [15]. Ubomba-Jaswa et al. [31] showed that following SoDis
treatment, microbe growth in contaminated water samples placed in the dark will continue if complete inactivation
of pathogens has not occurred. However, continued inactivation post treatment occurs if a sufficiently high UVA
dosage is applied [32]. It is proposed that the DNA repair mechanisms are overwhelmed and rendered inert. It is
therefore necessary that SoDis treatment is undertaken immediately prior to consumption or the UVA dosage is
sufficient to completely deactivate any pathogens.
Thermally enhanced SoDis occurs when water is exposed to UVA radiation and maintained at a temperature
above 45oC – 50oC [15,33]. The higher water temperatures improve the efficiency of the pathogen deactivation, with
an exponential relationship of efficiency to temperature. Thermal enhancement of SoDis improved efficiency by a
factor of 1.7 at 45oC, and an efficiency factor of 3 at 50oC [15].