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close this bookAmaranth to Zai Holes, Ideas for Growing Food under Difficult Conditions (ECHO; 1996; 397 pages)
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View the documentAbout this book
View the documentAcknowledgements
Open this folder and view contents1: Basics of agricultural development
Open this folder and view contents2: Vegetables and small fruits in the tropics
Open this folder and view contents3: Staple crops
Open this folder and view contents4: Multipurpose trees
Open this folder and view contents5: Farming systems and gardening techniques
Open this folder and view contents6: Soil health and plant nutrition
Open this folder and view contents7: Water resources
Open this folder and view contents8: Plant protection and pest control
Open this folder and view contents9: Domestic animals
Open this folder and view contents10: Food science
Open this folder and view contents11: Human health care
Open this folder and view contents12: Seeds and germplasm
Open this folder and view contents13: Energy and technologies
Open this folder and view contents14: From farm to market
Open this folder and view contents15: Training and missionary resources
Open this folder and view contents16: Oils
Open this folder and view contents17: Above-ground (urban) gardens
View the document18: What is ECHO?
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Open this folder and view contentsECHO development notes - issue 52
close this folderECHO development notes: issue 53
View the documentFifty-one issues of edn in one book!
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View the documentThe nutritive value of chaya, one of the most productive green vegetables
View the documentSolar water disinfection
View the document"Why don't my tomatoes set fruit?"
View the documentInsights from a biogas project.
View the documentMalnutrition and child mortality
View the documentList of distance learning courses is available from ECHO.
View the documentFrom ECHO's seedbank
View the documentEchoes from our network
View the documentUpcoming events
View the documentBooks and other resources
Open this folder and view contents28 additional technical notes about tropical agriculture
Open this folder and view contentsPrinciples of agroforestry
Open this folder and view contentsGood nutrition on the small farm
 

Solar water disinfection

can be used to reduce bacteria counts in small volumes of drinking water at the individual household level. The simple technique of putting water in plastic bags or other containers and exposing it to the sun for 2-6 hours inactivated up to 100% of the bacteria in contaminated water. Scientists at Brace Research Institute in Quebec, Canada have been working with solar water disinfection since 1988. Several of their recent research reports are summarized below.

It was found that near ultraviolet (UV) radiation of 300- 400 nm had a bactericidal effect apart from temperature: "water temperatures from 12-43øC did not affect the inactivation of bacteria." The bactericidal effect of the radiation is affected by the turbidity of the water, the materials of the container, and the climate. Highly turbid and contaminated water is not easily disinfected by the sun, so it is best to settle and/or filter the water before putting it in the sun. On cloud cover: "The time for complete elimination of pathogenic bacteria was found to vary from 2 hours in hot arid areas to 5 hours in humid tropical regions or when clouds partly obscured the sun." "An average solar intensity of about 600 W/m2 over 4-6 hours must be maintained in order to permit the complete elimination of all bacteria in a water sample." Obviously, best results can be achieved around midday when the sun is strongest.

What is the best container to use? Many tests have been done with various materials. In general, clear containers are better than tinted ones. Transparent plastic bottles and glass jars, while they may be used, have many formulations and they can give inconsistent results and may transmit poorly in the required UV range. The two best containers were transparent plastic bags (disinfecting "to a level of zero coliforms on almost all occasions when the water was exposed for 6 hours or more") and open metal (aluminum) pans. The advantages of the pans over plastic bags are their greater capacity and durability. Containers should be capped or sealed with thin plastic wrap (usually with UV transmission levels 90%) to prevent contamination, especially in dusty areas.

For more information and publications from the Brace Research Institute, contact the Publications Department, Faculty of Engineering, P.O. Box 900, Macdonald College of McGill University, Ste. Anne de Bellevue, Quebec, CANADA H9X 3V9 phone 1-514-398-7833 fax 1-514-398-7767 email AE12000@Musica.McGill.CA. Return to Index.

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