The project involves the process design, supply and erection of all the civil and electro-mechanical equipment for the final production of Phase 3 (240 Mld) and Phase 4 (240 Mld) water treatment plants. The new treatment plants will be located next to the existing Phase 1 and 2 water treatment plants. Water will be sourced from the existing Lower Usuma Dam, which supplies existing Phase 1 and 2 water treatment plants, and the new Gurara dam. Biwater's scope is to connect into the newly laid φ3 metre Gurara feed pipeline to supply water to the existing Phase 1 and 2 and Phase 3 and 4 water treatment plants. This φ3 metre pipeline will also be used to augment the Lower Usuma dam.
A new raw water feed pipeline from Lower Usuma dam with a pumping station is also to be incorporated to supply the new Phase 3 and 4 water treatment plants.
Treatment Plant
Each treatment plant (Phase 3 and 4) will consist of the following components: -
- Aeration
- Drum screen
- Clarification (sludge blanket clarifier with lamella)
- Rapid gravity filtration
- Disinfection within chlorine contact tank
- Balance tank
- Chemical dosing (aluminum sulphate, lime, polyelectrolyte and chlorine)
- Filter backwash return to head of works system
- Sludge treatment comprising: - Collection tank
- Sludge thickening Sludge filter pressing
- Administration building
- Workshop
- Electrical sub-station with standby
- generation
- SCADA
The source of water for the water treatment plants will be from either the Lower Usuma or Gurara Dam. The raw water from the Lower Usuma Dam will be delivered to the water treatment plants either by gravity or pumping. Raw water from Gurara will be by gravity only.
The raw water will enter the water treatment plants at the aeration stage. Aeration is used to remove odour and oxidise the soluble ferrous iron to insoluble ferric iron for removal in the clarifiers. Alum, lime and pre-chlorine is dosed at the aeration stage.
From the aerators the water will be channelled to sludge blanket type lamella clarifiers, where on entry polyelectrolyte is dosed to aid coagulation. Flocculation of the water is carried out in the base of the clarifier by water jetting. The formed floc particles rise within the lamella clarifier and form a sludge blanket. This sludge blanket is removed periodically during the day via desludging pipe system.
From the clarifiers the clarified water will be channelled to rapid gravity filters for final treatment. The filters will include a filter washing system.
The filtered water will then be carried by pipeline to the chlorine contact tank. Disinfection by chlorination will be carried out prior to entry into the chlorine contact tank.
At the exit of the chlorine contact tank, pH adjustment by lime will be carried out prior to water entry into the balance tank.
From the balance tank the water will gravitate into supply.
The Phase 3 and 4 works will be operated by a SCADA system. Sludge from the Phase 1 to 4 clarifiers will be treated in a sludge plant located on the Phase 3 and 4 works.