Conclusions of SODIS efficiency in the field The data collected during almost a decade of field research, demonstration workshops and monitoring at user level confirmed that SODIS is a reliable method for drinking water disinfection at household level. Figure 18 compares the SODIS efficiency for removing faecal coliforms in the laboratory with the SODIS efficiency under less optimal conditions such as a demonstration workshop in Latin America and at user level in Nicaragua. We can conclude that SODIS proved to be efficient not only under laboratory conditions, but also at user level, provided that the basic technical requirements are fulfilled.
Figure 18: Comparison of SODIS efficiency at different levels
However, SODIS will probably never supply 100% safe water to the whole population. Poor handling practices and inadequate application of the method lead to a reduced SODIS efficiency, or the treated drinking water is subject to secondary contamination. The objective of SODIS therefore is to significantly reduce the risk of microbiological infection. After years of research and field testing, the challenge of reducing the incidence of water-borne diseases through SODIS use is now lying in the hands of the institutions and field workers in charge of hygiene education and sanitation programs. Through appropriate diffusion of the information, intensive training of users and follow-up, people will have access to a simple and affordable alternative to improve the microbiological quality of their drinking water at household level.
3.3. Lessons learnt from the application in the field • Appropriate containers are transparent PET-bottles of up to 2 litres volume. • In warm climatic conditions, where water temperatures reach 50°C during exposure, half-blackened bottles may be used, as the water temperature increases quicker in such bottles. • In high altitude regions, where the water temperature remains cold, fully transparent bottles should be used in order to optimise the effect of UV-A. • The efficiency of SODIS will be increased if bottles are placed on a reflective surface such as for example aluminium or CGI-sheets. • The bottle needs to be exposed to the sun for 6 hours if the sky is clear or up to 50% cloudy. The bottle needs to be exposed to the sun for 2 consecutive days if the sky is 100% cloudy. During days of continuous rainfall, SODIS does not perform satisfactorily. Rainwater harvesting is recommended during these days. If a water temperature of at least 50°C is reached, 1 hour exposure time is sufficient. • Water with a turbidity of more than 30 NTU needs to be filtrered before it is filled into the SODIS bottle. • The SODIS efficiency is increased at higher levels of oxygen in the water. Aeration of the water can be achieved by shaking the 3/4 filled bottles for about 20 secondes before they are filled completely.
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