Development and evaluation of small-scale systems for solar disinfection of contaminated drinking water in India

Abstract

The global magnitude of morbidity and mortality makes waterborne diarrhoeal disease one of the major environmental health threats to humanity, especially in the developing world. The burden of disease in developing countries also affects the potential of future generations. Simple, low-cost household water treatment has considerable potential to reduce this burden. The present research project has extended and developed knowledge and understanding of the practical application of solar photo-oxidative disinfection of water; the aim of the present study was to optimise the solar water treatment process by developing a custom-made system and then assessing its value as a small-scale, point-of-use approach for contaminated drinking water in several rural locations across India in field evaluation trials. Studies on the dynamics of solar disinfection in terms of the inactivation of bacteria over a range of weather conditions were carried out at the laboratory level in Kochi, Kerala using pure cultures of the faecal indicator bacterium Escherichia coli (E. coli). A novel solar disinfection system has been produced, consisting of a robust custom-made polyethylene terephthalate (PET) batch reactor of one-litre capacity with a flattened, rectangular profile together with a durable, reflective stainless steel backing as a rear casing to the reactor. This system was designed to optimise the capture of solar UV and visible radiation and was evaluated across a range of weather/sunlight conditions, proving to be more effective than earlier systems with black-backed, absorptive rear surfaces. While the newly developed small-scale solar disinfection system gave enhanced inactivation of E. coli during sub-optimal weather conditions (weak sunlight conditions, at <300 W m super(-2)), it did not always achieve the target of a minimum of 99.9% inactivation of E. coli within a single day of exposure during overcast/foggy days. The three regions (and locations) identified for field evaluation of the novel solar disinfection system were: Indo-Gangetic plain (Gorakhpur); arid region (Jodhpur); and coastal region (Alappuzha). These locations represented three distinct zones across the Indian continent with unique climatic conditions. The implementation of solar water treatment was found to be effective in reducing the number of cases of diarrhoea/gastro-enteritis in all field locations, substantiating the laboratory findings for the inactivation of E. coli, though the extent of the reduction varied across the different field sites. The acceptance of the effectiveness of the solar disinfection system was clearly demonstrated, with positive feedback from participants across all three regions and a perceived reduction in diarrhoea as well as an observed enhancement in overall well-being. The latter observation is significant, since it is an aspect that has not been fully appreciated in earlier studies, which have focussed on epidemiological evidence. However, the large number of one-litre batch rectors needed for a household to provide an adequate supply of treated water created some problems with managing the process. The development and application of larger volume containers could solve this limitation, as was evident when this was trialled with five-litre containers in Kerala. The findings of the present study clearly demonstrate the technical feasibility of solar disinfection in rural India, with evidence that sustained transfer to the grass-roots level now requires a co-ordinated approach to health education and knowledge dissemination beyond that used in the current research.