hydraulic design to optimise treatment capacity of multi-stage filtration units: a pilot plant study at moi university water treatment works, eldoret, kenya

Abstract

Access to potable water in Kenya is reported as 46% in rural areas and 89% for the urban areas. Rural areas in Kenya often rely on surface water for their drinking water, which more often than not is contaminated. As a result, numerous water-related outbreaks have led to a growing need for alternative but simple, reliable, and sustainable treatment technologies for use in such areas. Multi-Stage Filtration (MSF) can provide a robust treatment alternative for surface water sources of variable water quality in rural communities at low operation and maintenance costs. MSF is a combination of Slow Sand Filters (SSF) and Pre-treatment systems. The general objective of this research was to optimize the treatment capacity of MSF. Three main stages of MSF namely: The Dynamic Gravel Filter (DyGF), Horizontal-flow Roughing Filter (HRF) and SSF were identified, designed and built. The response of the respective MSF units in removal of selected parameters guiding drinking water quality such as Faecal and Total coliform, Suspended Solids, Turbidity, pH, Temperature, Iron and Manganese was investigated. The bench mark was KEBS and WHO standards for drinking water. The performance of the MSF unit was measured against the existing Conventional System (Moi University Water Treatment) with respect to microbiological water quality improvement. On average, DyGF achieved 59% Turbidity removal and 63% Suspended Solids (SS) removal. HRF unit registered 86% Turbidity removal and 85% SS removal. With respect to microbiological raw water quality improvement, MSF units achieved on average 98% Faecal and 96% Total coliform removal in comparison with the conventional system which registered average values of 75% Faecal and 78% Total coliform removal before chlorination. MSF units registered an average value of 70% removal of Iron and 64% removal of Manganese respectively. The pilot plant study results obtained indicate that implementation of MSF in rural communities has the potential to increase access to potable water to the rural populace with a probable consequent decrease in waterborne diseases. With a reduced down time due to illness, more time would be spent in undertaking other economic activities. Further research is recommended targeting development of a design manual for a population size as a function of raw water quality.