SODIS
Marco Campos - Wednesday 10 May 2006
Boiling, chlorination and filtration are the most widely known technologies for disinfecting water. It is important to add another one: solar disinfection.
Solar disinfection of water is a proved safe and cheap technology available to all people that have access to 6 hours of sunshine (as a minimum).
People only need to clear water through any procedure to make it as clear as 30 NTUs and then put water into a clear plastic bottle to expose it to solar radiation.
Infrared as well as UV radiation kills all microbia contened into the water being exposed in the following 6 hours. For practical reasons (i.e. absense of a clock) is widely recommended to exposed water during the day and let it cool off during night.
SODIS
Foort Bustraan - Thursday 11 May 2006
I agree that SODIS can work very well. We are experimenting with it now, but the tricky part is to raise temperature enough (at least above 50 Celcius, even better > 60 Cel) and that for > 3 hours. This is possible if you paint bottles half black, put it on iron roofsheet, ideally protect it from wide and have sun all time...then E-Coli measurements show a 100% reduction in faecal coliform.
also bottles can not be oto large or else UV does not penetrate and water doesw not heat up enough; so we do this with 1.5 liter bottles, which means a family has to have space to put 10 on a roof....
Another advantage is that the bottles provide immediate safe storage in the house, as long as kids don't drink directly from the bottles...
SODIS
Kevin McGuigan - Thursday 11 May 2006
I have been involved with solar disinfection research for over 14 years now.
If you have strong local sunshine the basic protocol needs only be:
1. Fill the bottle.
2. Place it in direct sunlight for 6 hours.
3. Drink it as soon as possible afterwards.
Yes it's better to reduce the turbidity.
Yes it's better if you can boost the water temperature.
Yes It's even better if you give it a good shake at the start to maximise the dissolved O2 levels.
BUT
Too much emphasis is placed on including these additional steps to a simple protocol. If you have guaranteed levels of sunshine then there is no necessity for these steps in the procedure. If sunshine levels are not guaranteed or intermittent then by all means include them
We carried out the original controlled field trials of this technique in 1994 with the Kenyan Maasai using any old bottle that we could get our hands on, with no procedures for reducing turbidity or maximising dissolved O2 levels. We still saw an approximate 10% reduction in rates of diarrhoea among children under 5 years (see Lancet 1996;348:1695-97).
Since then we and other groups have shown that SODIS is effective against a wide range of waterborne pathogens including:
Vibrio cholerae
Polio virus
Cryptosporidium parvum (cyst stage)
Giardia (cyst stage)
Enterococcus sp.
Escherichia coli
Salmonella typhi
Salmonella typhimurium
Salmonella enteritidis
Shigella dysenteriae Type I
Shigella flexneri
Streptococcus faecalis
Pseudomonas aeruginosa
Solar disinfection has been approved by the WHO as an appropriate intervention against waterborne disease in the aftermath of natural disasters or other emergencies.
SODIS
Alan Spybey - Thursday 11 May 2006
A query to
Foort Bustraan re message of - Thursday 11 May 2006
"....This is possible if you paint bottles half black, put it on iron roofsheet, "
... which half would that be - so that the line of division is along the length, or around the circumference? Also, if the former, presumably the blackened part should be next to the roof, and the clear part exposed to the UV. Also does it help if the bottle is resting on a corrugated iron roof rather than on a fibre or mud roof?
Thanks
