Water-borne bacteria and viruses can cause serious health problems, but many places in Africa do not have access to clean drinking water. Mdori, in Tanzania, is one of those places. In addition, its natural spring water is too high in salt and fluoride. The new ROSI water filtration system could change this.

Due to high temperatures and a dry climate outside of the rainy season, water in Mdori is scarce. According to the Karlsruhe Institute of Technology (KIT), from where tests of the system are being run, a well in Mdori from which natural spring water can be extracted produces water that is both very high in salt content and has a fluoride content of 60 µg of per liter. This is 40 times the level that the World Health Organization (WHO) deems safe for human consumption.

In order to find a solution to this problem, Professors Andrea Schäfer and Bryce Richards developed ROSI (the Reverse Osmosis Solar Installation) and have been testing it in Mdori. ROSI is able to filter out undesirable substances, bacteria and viruses from water, as well as reduce fluoride levels to within WHO recommendations.

In order to do so, the system “combines ultrafiltration membranes of about 50 nm in pore size to retain macromolecular substances, particles, bacteria, and viruses with membranes for nanofiltration and reverse osmosis with pore sizes below 1 nm to remove dissolved molecules from the water.”

ROSI is designed to be robust, mobile and to be operated with solar and/or wind power. If there is too little power available, for example at night time or due to cloud cover, filtration cannot be carried out. This was one area that Schäfer and Richards were looking at in their tests.

“If less power is available, pressure decreases. As a result, less water passes the membranes. The fluoride concentration increases for a short term,” explains Schäfer. “The concentration of fluoride and other pollutants, however, is balanced as soon as more water passes the filter again. Hence, the water is completely safe.”

ROSI was initially developed by Schäfer and Richards in Australia, before further work on it was carried out in Scotland. Field tests for the system were planned at at the Nelson Mandela African Institution of Science and Technology in Tanzania, and test were carried out earlier this year in Mdori, amongst other places. The results of the tests are currently being analyzed at KIT. The next stage for the tests will be for ROSI to be installed at selected locations.

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