Solar Thermal Destruction of Cryptosporidium and Bilharzia in Water - Zinga Island, Lake Victoria

Many pathogens show strong resistance to disinfection with chlorine. Two such species are Cryptosporidium and Bilharzia. Bilharzia is prevalent in Lake Victoria water. The primary mode of transmission is through the skin. Infection by drinking primarily takes place through the skin of the lips. The most observable symptom of a bilharzia infection is the bloated bellies seen in children.

Cryptosporidium is contracted by drinking contaminated water. Cryptosporidium is very prevalent in Lake Victoria water. The symptoms of a Cryptosporidium infection are very similar to those of malaria. While both species are chlorine resistant, they are susceptible to heat treatment. Much like Legionella, heating water to 60°C for 30 minutes or 70°C for one minute appears, from literature research, to be sufficient for disinfection.

A solar collector with supplemental heat in the form of a 300 W - 12 V heating element, was installed at Zinga. Initial calculations indicate that two 300 W - 12 V heating elements would be needed to achieve 70°C on cloudy days. The apparatus was limited by local conditions. The solar collector had only a single port and larger 12-volt heating elements were unavailable locally.

On sunny days, the solar collector achieved temperatures as high as 53°C without supplemental heat energy. On cloudy days, similar results were achieved using three 150 W solar panels and three 100-Ah batteries (56°C), each connected in parallel, through a charge controller to the heating element

The undersized system required a day of recharge after use before reintroduction into the thermal system. A smaller system was chosen because of the aforementioned heating element limitation and a lack of funds. With these limitations, the goal was revised to “proof of concept”. By achieving 53°C under worst-case conditions it is clear that adding a second heating element (or larger one) would be sufficient to achieve the necessary temperatures.

Additionally, for test purposes, the water temperature of 70°C was achieved using traditional methods (charcoal fire). The lake water sample was treated for roughly ½ hour (additional time to allow for the sample temperature to reach 70°C). The sample was incubated at approximately 45°C under anaerobic conditions for 18 hours. After 18 hours, the sample was clean; no growth had occurred.

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