Implementation of an Elevation-Driven Backwash System
In 2017, the first rapid sand filter, built in a 1000 L rain barrel, was field-tested in Kyamagemule. The initial concept was a continuous feed system using jerrycans. The concept proved effective (turbidity greater than 40 NTUs reduced to 9.5 NTUs), but not ideally suited to culture, as water was normally gathered mornings and evenings. The sand filter was converted to a batch reactor, filling the filter in the evening and recovering the filtrate the next morning. This had the effect of both being acceptable to culture and producing turbidity results 5-8 NTUs. The system has been successfully used for close to one and a half years prior to our return in August 2018.
During that time, the filter was not backwashed. Although the results remained favorable (2-5 NTUs), it is not expected to continue producing such results long- term. Precisely for this reason, WeDev developed a simplified backwash system based on a similar full-scale treatment plant design. The principal design uses gravity from a small, elevated tank producing upward flow from the bottom of the filter of sufficient pressure to lift the smaller dirt particles, but insufficient to carry away the fine filter sand. The prototype was built in Kaiserslautern and proved effective. It was implemented in Kyamagemule in August 2019.