Principle
Exposure to sunlight has been shown to deactivate diarrhea-causing organisms in polluted drinking water. Three effects of solar radiation are believed to contribute to the inactivation of pathogenic organisms:
- 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.
- Cumulative solar energy (including the infrared radiation component) heats the water. If the water temperatures rises above 50 °C (122 °F), the disinfection process is three times faster.
At a water temperature of about 30 °C (86 °F), a threshold solar irradiance 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, 350–450 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.
Read more about this topic: Solar Water Disinfection
Famous quotes containing the word principle:
“Thus it seemed that this one hillside illustrated the principle of all the operations of Nature. The Maker of this earth but patented a leaf. What Champollion will decipher this hieroglyphic for us, that we may turn over a new leaf at last?”
—Henry David Thoreau (1817–1862)
“The principle of fashion is ... the principle of the kaleidoscope. A new year can only bring us a new combination of the same elements; and about once in so often we go back and begin again.”
—Katharine Fullerton Gerould (1879–1944)
“The principle of the Gothic architecture is infinity made imaginable.”
—Samuel Taylor Coleridge (1772–1834)