Solar Pasteurization of Contaminated Water
Caleb
A.
6th
Grade, Challenger 7 Elementary, Cocoa Florida
Teacher: Michael Mugge
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Hypothesis: I hypothesized that if I used solar radiation to bring the temperature of naturally contaminated water to a temperature of 160o F for a short period of time, then the water will be pasteurized, which would destroy the waterborne pathogens.
Conclusion: Can solar radiation pasteurize naturally contaminated water?
I hypothesized that if I used solar radiation to bring the
temperature of naturally contaminated water to a temperature
of 160oF for a short period of time, then the water will be
pasteurized, which would destroy the waterborne pathogens.
Contaminated water samples were inoculated on multiple Petri
dishes. These plates grew from 39-46 colonies per plate over
a 96 hour period. Samples of the contaminated water were then
placed in a solar cooker and the temperature of the water brought
up to 100oF in 60 minutes and 160oF in 90 minutes and the water
kept at this temperature for a minimum of three minutes. Both
the different solar pasteurized water samples were inoculated
on Petri plates and incubated for up to 96 hours. The plates
were visually inspected. The 100oF plates grew 2-5 colonies
per plate over the 96 hour period. However, the nine petri
plates of the 160oF solar pasteurized water samples had zero
growth at the end of the 96 hour growth period.
These results supported my hypothesis. The water reached temperatures
high enough to pasteurize the water thus destroying all the
pathogens that were present in the contaminated water samples.
Field studies completed at the California State University along with data found in Applied and Environmental Microbiology provided me guidance in developing a simple and reliable method in the use of solar energy for water pasteurization.
Pasteurization can achieve the same result as boiling, but at a lower temperature. Data revealed that the temperature of the water needed to be >149oF (65oC) in order to destroy microbes such as E. coli, Salmonella, typhi, and Hepatitis A virus. To verify that sufficient water temperatures were obtained, a standard thermometer and a water pasteurization indicator (WAPI) were used. The soybean wax found within the clear tube melts at 156oF (69oC) and falls to the bottom of the tube, thus indicating that pasteurization conditions have been reached. The WAPI was used successfully in this experiment and is utilized as a safe, reliable, reusable device in measuring water temperatures during solar pasteurization.
The research obtained from the Solar Cooking Archive was important in the design, development and the required methods for use of the solar cooker. Using a blackened-lidded container in a reflective panel solar box produced the desired temperatures required for water pasteurization.
Solar water pasteurization units are proven to be efficient and affordable. They use no fuel or energy resources and create no pollution. This effective method of pasteurizing contaminated water could be provided at a low-cost to many sun-rich areas around the world, thus possibly contributing to improved health and reduction in childhood illness and death from waterborne pathogens.
This procedure may be inadequate to inactive all possible pathogens. A future question to investigate is can solar pasteurization cause inactivation of more resistant pathogenic microorganisms?
