It’s cheap as long as the sun shines

Could sunlight provide a cheap and effective means of purifying drinking water in India?

More than one billion people across the globe drink contaminated water, according to the World Health Organization, and 3.4 million people, mostly children, die every year of water-contracted diseases. There is therefore an urgent need for simple, effective, low-cost methods for producing safe drinking water.

Robert Reed at the University of Northumbria in Newcastle and Isaac Bright Singh at Cochin University in Kerala, India, are collaborating on a research project exploring the possibility of using sunlight to decontaminate water.

Previous experiments to test whether sunlight could inactivate bacteria and other microbes in water were inconclusive, until in 1997 Dr Reed discovered the vital ingredient: oxygen. ‘The action of the ultraviolet light from the sun on oxygen dissolved in the water creates temporary free radicals which inactivate fecal bacteria,’ explains Dr Reed. ‘It won’t work if you haven’t got oxygen there.’ Moreover, although the free radicals created are temporary, the results are permanent. ‘Once the pathogens in the water have been deactivated by this process of photo-oxidation, provided you keep the lid on the water container, they won’t reactivate.’

Oxygenating the water sounds complicated, but is actually simply a question of shaking the bottle. This creates air bubbles which restore the oxygen level to near saturation. ‘It only takes about a minute of shaking to put back the oxygen if the level is low, so you don’t have to worry about measuring it if you’re out in the field,’ explains Dr Reed.

Dr Reed has already tested the effectiveness of the method in preliminary trials in India and South Africa, treating locally drawn water with sunlight and oxygen. ‘After three or four hours of full-strength sunlight the water would pass the standard UK or US bacteriological tests for drinking water quality. It’s very cheap as long as the sun shines.’

The collaborative study with Dr Bright Singh now aims to establish the operational limits of this method in India under a range of climatic conditions. ‘We’re trying things out over an annual cycle, looking at the effects of different weather and climates to find out what the limits are. For example, will it still be effective during the monsoon season when there’s cloud cover? We also need to establish which organisms it works for. We know it inactivates fecal bacteria, but it’s going to work less and less well with organisms that are tougher.’

The study is particularly relevant to India which has high levels of sunlight and a significant problem with water-borne disease. India also has a history of using sunlight as a means of purifying water, which should aid implementation of the method there. ‘It goes back 2000 years,’ points out Dr Reed. ‘If you look at Sanskrit texts, they talk about putting water in a shallow bowl in the morning, praying to the water, leaving it all day in the sunshine, coming back in the evening, praying to it again and drinking it. It was the sunshine that was shining on it all day not the prayer that did the purifying.’

Pilot studies will be undertaken in three areas with radically different climates: the arid zone of Rajasthan, the flood-prone region of Uttar Pradesh (where cloud cover may be a problem), and the humid zone of Kerala.

During the first year, water in two sizes of plastic containers – one for an individual’s and one for a household’s daily drinking water needs – will be tested for pathogens before and after exposure to sunlight. They will actually be used during the second year, and the incidence of water-borne disease will be recorded and compared with that of the previous year.

At the end of the study, the users will be asked for their opinion on the practicalities of using the containers, and how easy and effective they found this method of water purification.

In parallel with these field trials, a microbiological analysis will be carried out at Cochin University and the University of Northumbria. The combined information from the field and laboratory work will be used to develop a mathematical model of the inactivation process, making it possible to specify the conditions under which solar water treatment will be effective.

‘We are trying to establish the conditions under which this method does and doesn’t work effectively,’ says Dr Reed. ‘There are bound to be limitations, but if the alternative is nothing, it’s got to be better.’

Source: Wellcome Trust

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