http://www.sodis.ch/methode/faqs/index_EN
If the temperature is increased, the efficiency of the SODIS method can be improved. The germs are killed more quickly. In addition, amoebas are also rendered harmless above a temperature of 50°C. To increase the temperature, lay the bottles on a reflective surface, like a sheet of corrugated iron, and shield them from cooling by the wind.
http://web.mit.edu/watsan/Docs/Student%2...ns2002.pdf
SODIS works best between 35oS and 35o N. Outside of these regions, SODIS works sub-optimally because of the limited availability of solar radiation and the colder climate.
In order to assess the applicability of SODIS to colder climates, this study investigated two possible methods of ensuring that SODIS is effective under the conditions of lower temperatures and sunlight intensity: 1) enhancing the heating capacity of the bottle with black paint and 2) increasing the amount of radiation incident on the system using a solar reflector. Additionally, a mathematical model for predicting the expected bottle water temperature of each exposure regime, based on the ambient air temperature, wind, and available solar radiation, was developed. Such a model will be useful in future studies for assessing which type of exposure regime will be most effective.
Field studies were conducted in two locations in Haiti: Barasa and Dumay, and in Boston, Massachusetts, between the months of January through March, 2002. Analysis of the data collected showed that clear and half-painted bottles were most effective for microbial inactivation in non-tropical climates (Barasa and Boston). In Dumay, however, significant microbial inactivation was achieved in all bottles because the bottle water temperatures reached were much higher. There was no statistical significance between the amount of inactivation achieved by bottle on a reflector or without a reflector.
However, because of the limited amount of data, further studies on the use of solar reflectors are recommended to assess their actual effectiveness...
In order for thermal inactivation alone to be effective for microbial deactivation in the SODIS system, a bottle water temperature of 50o C must be exceeded for at least one hour. Additionally, reaching this temperature also causes synergistic effects between UV and temperature to be enabled. It has been shown that painting the bottom half of the bottles black can raise the water temperature 5o C, depending on the amount of radiation available. In order to test this technique under sub-optimal SODIS conditions, bottles in this study were painted half black so that UV inactivation of bacteria could also take
place within the bottle. Additional bottles were fully painted in hopes of absorbing more radiation than the half painted bottles and thus raising the temperature more.
Under sub-optimal conditions, there was no significant difference in the amount the bottle water temperature was raised in the half-painted or fully painted bottles. The bottle water temperature of the clear bottles was the same as that of the ambient air temperature. In Barasa, the peak temperature difference between the clear and painted bottles was 8o
C ñ greater than that expected from the literature. However, this only achieved a peak bottle water temperature of 38o
C, well below the thresholds mentioned above. In Dumay however, which has similar amounts of available solar radiation, a
temperature difference of almost 10o C was achieved, and the threshold temperature of 50o C was exceeded in both painted bottles. The difference in the peak temperature achieved can be mainly attributed to the difference in weather conditions, which were cooler and breezier in Barasa, which would cause cooler bottle water temperatures.
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