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:
“Whether our feet are compressed in iron shoes, our faces hidden with veils and masks; whether yoked with cows to draw the plow through its furrows, or classed with idiots, lunatics and criminals in the laws and constitutions of the State, the principle is the same; for the humiliations of the spirit are as real as the visible badges of servitude.”
—Elizabeth Cady Stanton (1815–1902)
“The mode of founding a college is, commonly, to get up a subscription of dollars and cents, and then, following blindly the principles of a division of labor to its extreme,—a principle which should never be followed but with circumspection,—to call in a contractor who makes this a subject of speculation,... and for these oversights successive generations have to pay.”
—Henry David Thoreau (1817–1862)
“In case I conk out, this is provisionally what I have to do: I must clarify obscurities; I must make clearer definite ideas or dissociations. I must find a verbal formula to combat the rise of brutality—the principle of order versus the split atom.”
—Ezra Pound (1885–1972)