Testing the Efficiency of Solar Disinfection in Removal of Escheria Coli from Contaminated Water

It is estimated that 900 million people lack access to improved water supplies and many more are forced to rely on sources that are microbiologically unsafe. While piped-in- water supplies are the ultimate goal for the provision of water in developing countries, low cost point-of –use disinfection treatments could help to significantly reduce the incidence of water- borne diseases.

Solar Disinfection has been known for more than 30 years. It is a simple water treatment method using natural solar radiation to inactivate pathogens commonly found in drinking water. During exposure, the UV and thermal energy of the sun act to inactivate the pathogenic microorganisms; however, the recommended protocol is 6 hours under direct sunlight. The efficiency depends on the environmental factors, and some pathogens are more resistant to solar disinfection. This technique involves filling transparent PET bottles with contaminated water and exposing the bottles to direct sunlight. SODIS inactivates pathogens through three mechanisms: DNA alteration by UV, Production of photo oxidative species and thermal inactivation.

 

SODIS works best between 35-45°с. At less than these temperatures, SODIS works sub-optimally because of the limited availability and the cold climate. In order to access the applicability of SODIS, this study investigated the level of disinfection of E- coli in two environmental conditions i.e. during the rainy season and during the dry season. In both a SODIS enhancement technology was applied and results compared with SODIS method. It involved the use of Zinc oxide which acted as a semiconductor photo catalyst.

 

Field studies were carried out for the Nairobi River water between the month of October 2013 and February 2014. Raw water was collected from the river and immediately tested for initial E- coli concentration using the 3M Petri films.  Water was then filled in duplicate in PET bottles. A set of the sample water was treated with 10 mg Zinc oxide and another set left untreated. They were then exposed to sunlight under the same conditions. In addition, physio-chemical characterization of the sample water was carried out including pH, Total suspended solids, Total solids, Total Dissolved solids Conductivity   and Temperature recorded.

 

Analysis of the data collected clearly showed that pure sunlight and the photo catalyst were effective for E-coli inactivation in both seasons. However, bottles treated with the photo catalyst took less time to completely inactivate E- coli than it took pure sunlight. In the control experiment, the level of inactivation was minimal clearly identifying sunlight as the main inactivating agent. Also time was a factor in this study and it was seen that the optimal exposure time was 6 hours for the dry season and 10 hours for the rainy season.

 

Further studies should be conducted to check whether the photo catalyst used is toxic to the human body and if so, come up with a less costly method of removing it to render water safe for drinking. Also since immobilized catalysts are more efficient than the mobile ones, studies should be carried out to investigate a way the Zinc Oxide photo catalyst can be immobilized for optimal results.

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