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The importance of clean drinking water cannot be understated. Water is essential for life and maintaining good health, and yet, providing access to clean drinking water in developing countries continues to be a major global challenge. As a result, some communities must resort to consuming unsanitary water, which poses a variety of serious human health risks. Indeed, as stated by Sam Dorevitch and colleagues in their paper published on Gates Open Research, one such serious health risk is diarrhoea, of which, in 2017 alone, there was a staggering 357 million cases in children aged under 5 in low/middle-sociodemographic index (SDI) countries, leading to around 222,457 deaths. 93.5% of these deaths were attributable to the consumption of unsanitary drinking water.

Clearly, the development of more efficient and affordable water treatment systems in these countries has the potential to greatly improve quality of life and eliminate unnecessary health risks associated with drinking unsanitary water, and this was the aim of Dorevitch and colleagues in their paper; namely, the establishment of a decentralised solar-powered water treatment system.

As Sam Dorevitch of the University of Illinois, USA, says: “After addressing water quality issues in the US for nearly 15 years, I was struck by the fact that lake or river water considered to be unsafe for swimming would be higher quality than surface waters used for drinking in many parts of the world”.

This inspired his research on providing safe drinking water to communities using an entirely solar-powered approach for water treatment. Dorevitch sums up the benefits of this approach, as ‘neither “centralized” nor “point-of-use” but rather, intermediate: community-scale treatment’.

So what exactly do we mean by a “decentralised” water treatment system, and why did Dorevitch et al. seek to test a solar-powered decentralised system in Kisumu Country, Kenya? Read on to find out…

Conventional vs decentralized approaches to drinking water treatment

The conventional approach to drinking water treatment in urban areas, particularly in upper- and middle-income countries, is “centralized.” In such systems, a large facility treats water – often from a lake or a river – and distributes the water through a system of pipes, bringing treated drinking water to homes. Such systems are very costly to build and maintain, and for that reason, they are rarely found in rural areas of low- and middle-income countries. At the other end of the spectrum are “point of use” methods, in which families treat water that they fetch from local waters by adding chlorine or by filtering it. These are far less costly than centralized systems, but, in part because of adherence to regular application of these treatment methods, they do not seem to reduce the incidence of diarrhoea in small children. The decentralized approach used by Dorevitch’s team in Kenya has the advantage of being far less expensive than centralized drinking water treatment plants, while not requiring families to fetch water from a river or lake and then treat it at home.   

However, the challenge of providing clean drinking water to low/middle-SDI countries, even with decentralised systems, is compounded by the fact that many communities in these countries are unable to consistently access electricity. Because of this, even decentralised systems that normally require electricity to function cannot be used to reliably provide them with clean drinking water. This is exactly the benefit of the decentralised solar-powered water treatment system used by Dorevitch et al. – it runs on solar energy and so it works “off-the-grid” using sunlight, without needing to be connected directly to electricity. This makes the system much more flexible compared to conventional systems, allowing it to be brought to communities living in remote, hard-to-access areas. Air pollutants are also not produced as a by-product. And why was solar power particularly useful here? Because Kenya, like many countries where access to clean drinking water is limited, is an equatorial country and so sunlight is plentiful year-round.

Therefore, the decentralised solar-powered treatment system used by Dorevitch et al. kills two birds with one stone. Also, the effectiveness of decentralised, ‘ozone-based’ water treatment systems had not been tested in practice before, making their work even more important. So how does their system work, and how did they know it was effective?

Ozone-based water treatment and the results of Dorevitch et al.’s system

Dorevitch et al.’s water treatment system is ‘ozone-based’ – ozone water treatment has been used to purify water since 1904. Ozone (O₃) is a gas that can be produced in generators by passing a high voltage across a gas stream containing oxygen (O₂), causing oxygen molecules to split into oxygen atoms and then re-organise into ozone molecules. When ozone is dissolved in water, it produces a broadly-effective “biocide” that destroys bacteria, viruses and other contaminants in the water.

In the past, ozone-based systems have sometimes been energy intensive and costly to build but with the advent of new microplasma technology, it has become possible to develop modular microplasma systems that are small and, relative to conventional ozone systems (such as dielectric barrier discharge and corona ozone reactors) with a similar output, can have 3 times the efficiency of these systems.

In addition, the system’s ease of use is another important advantage, as it helped Dorevitch and colleagues in instructing local residents how to operate the system, further improving the system’s sustainability, and allowing it to become a “community-scale” treatment system which was one of Dorevitch and colleagues’ main goals. As Sam Dorevitch himself explains: “I was also inspired by the simplicity and efficacy of the solar-powered ozone generators. Although they use advanced microplasma technology they are simple to operate. We have trained community residents to operate the water treatment system and to market and manage water sales at the water kiosk. Thus, our off-grid system should be sustainable with only occasional input from the experts at the Safe Water and AIDS Project.”

Dorevitch et al. constructed their decentralised water treatment system at the site of a defunct water kiosk in the town of Ahero in Kisumu Country, Kenya. They collected samples of extremely turbid river water and over the course of 6 months, measured the turbidity, total coliform and E. coli levels in the water before and after passing them through the treatment system. During the first 4 trials, the ozonation system and pumps were powered by electricity from AC outlets while the “solarization” of the system took place. During the 5^th and 6^th trials, the solarization process was complete and the system could run solely on solar power, proving that solar energy was sufficient to power it.

Notably, the system was able to produce 1000 L of WHO safety standard-meeting drinking water a day (which has since been raised to 2000 L a day at a small extra cost). Following the water treatment  the water samples had experienced substantially reduced levels of E. coli, total coliforms and turbidity, with nearly 4 log-orders of magnitude reduced E. coli on average.

So, what next?

Dorevitch et al.’s results are clearly promising. The system was able to treat even highly turbid water and make it safe for drinking. Furthermore, the system is modular and highly transportable, but also cheap – the construction and material costs were only around $24,000. All things considered, the system has great potential in improving access to clean drinking water in low/middle-SDI countries.

However, this cost did not take into account the additional costs that would have been needed to build the kiosk structures and storage tanks that were already at the site in this case. Also, the system still needs to be tested in key locations, such as schools, hospitals and other health-care facilities.

As Sam Dorevitch stresses, to make any water treatment system viable for communities and become truly “community-scale”, no matter how efficient and intuitive the actual treatment system is, it must be made financially viable so that local governments can adopt them:“The next steps are to develop approaches to make the construction and operation of systems [financially] viable. This would require simplifications and standardization in the design and construction of the community-scale water treatment systems. It would likely also require partnerships among local governments, entrepreneurs, and community groups. We would also want to see this technology be applied to managing non-sewered sanitation systems at facilities such as schools and health care facilities. Finally, evaluating impacts on the health of children – by deploying more and larger systems that combine water treatment and onsite sanitation – would be a critical step in determining the public health/development value of this approach.”