- Kitale, Trans-Nzoia County
- info@transwasco.co.ke
Water supply is composed of the following treatment process as illustrated on the diagram below:
Water is abstracted from the river through the intake either by gravity or pumping. The Intake structures are essential to diversion works to allow water to the transmission for treatment processes.
The intake works consists of an intake chamber fitted with bar screens which removes large debris such as sticks, leaves, trash, and other large particles, which may interfere with subsequent filtration process. The intake is installed with a coarse and fine screens.
At this stage, there are a number of facilities that are used to make the first chemical treatment process to raw water after screening. This is achieved by dosing with Aluminium sulphate ( ALUM) which is a coagulants used in the formation of flocs.
Soda Ash can only be used for PH correction. The dosages can be determined from jar and PH tests done daily at 8:00 a.m and 6:00 p.m. At the back of the mixing tanks, there is a store to keep bags of Alum and soda Ash.
Alum dosages allow the formation of flocs to take place. This is done to ensure that there is enough time mixing of chemicals with raw water then a wedge is created along the channel after the dosing pipes which changes the lamina flow into turbulent flow .Water then flows into flocculation basins.
This is the process which clarifies the water, clarifying means removing any turbidity or colour so that water is clear and colorless. Clarification is done by causing a precipitate to form in the water which can be removed using simple physical method. This is achieved by passing water mixer into flocculation chamber that has a series of baffles that utilizes the principle of up and down flow from the first chamber to the third one to ensure thorough and homogenous mixer.
In the process the precipitate forms small particles. Small particles that where originally present in the raw water which is absorbed on the surface of these small precipitate particle which incorporate into the large particles that coagulation produces. In this way, the coagulated precipitate takes most of the suspended matter out of the water. The flocs formed is only be allowed to settle down by directing it to the sedimentation basins.
Water exiting the flocculation basin enters the sedimentation basin, also called a clarifier. It was located closer to the flocculation basin in such a way that the transit between does not permit settlement or flocs break up. The basins are three in number and are rectangular in shape such that water moved from one end to the other .The basins are deep enough to ensure that they retain water for a period of 8 hours, to reduce the horizontal velocity of water to give flocs time to settle as particles settle at the bottom of the basin , a layer of sludge is formed on the floor of the tank. This layer of the sludge is weekly removed and from each tank, through the process called disludging before it is rechanneled to the river. Sedimentation basin outflow is typically over a weir so that only a thin top layer furthest from the sediments exist.
Filtration is the process of passing the water through sand medium. After separation, most of the flocs water is filtered at the final stage to remove the remaining the suspended particle and unsettled flocs.The effective size of sand used is 0.45 mm to 0.7 mm. The sand is placed in three layers , the top layer is the fine sand ,the medium sand in the middle and course sand at the bottom. At this stage, filtration removes turbidity but not bacteria, color ,odour and tasteless water characteristics. Afterwards, water passes through the top most layer whereby the fine particles that escape from the sedimentation basin is trapped and also cleaning of rapid sand filters back washing is used.
Disinfection is the process of killing of pathogenic bacteria. At this stage, chlorine is added to the filtered water to disinfect the water free of virus ,bacteria (Escherichiacoli,campy /obacter and shigella), and protozoa. The filtered water is directed to the chlorine dosing chamber which has an open channel where dosing pipes from the chlorine mixing room is dozed depending on the chlorine demand tests results. Soda ash is dozed when the PH is below 6.5 to boost to about 7.5 this is to avoid the acidic effect that result in complications to consumers suffering from stomach problems.Residual chlorine of 0.2 mg/ liter is allowed to safeguard against contamination of water during distribution.
Filtered chlorinated water enters into the clear water tanks for storage before it is distributed to the consumers. The tank has been designed in a way that water drops through some height before it falls to the floor of the tank. Bacteria, colour, odour are removed. The water has tasteless required characteristics after the process of mixing the chemicals with water. The tank has several partitioning walls inside for maximum mixing of chlorine and soda ash and a retention contact / period of 30-45 minutes before it is pumped to a distribution tank.
The system of water distribution is can either be gravity or pumping system. The distribution system can be : Ring/Circular system to the town area or Dead End System to the extended areas away from the town.
