Source of water
200,000 L/hr (normal current flow 100,000 L/hr).
- Filtration at inlet (infiltration gallery).
- Coagulation (poly aluminium chloride).
- Mixing (static mixers).
- Flocculation (polyelectrolyte).
- Contact flocculation (pressure adsorption clarifiers).
- Filtration (pressure filters).
- Sterilisation (chlorine).
- pH correction (lime).
Two pressure adsorption clarifiers, media – granular MDPE (Medium Density Polyethylene), rise rate (at 100,000L/hr) is 10.7m/hour.
Two pressure filters, media – dual media (silicon sponge and sand), filter rate (at 100,000L/hr) is 10.7m/hour.
The water treatment process
The water for the Inglewood Water Treatment Plant is extracted from the Ngatoro Stream via an infiltration gallery. The infiltration gallery consists of two slotted pipes buried under the stream bed. The stream bed and filter material placed on top of the pipes act to filter gross solids from the raw water before it enters the plant. The two gallery pipe legs feed a pipeline that supplies the treatment plant.
At the entrance of the plant a small amount of a chemical called poly aluminium chloride is added. This enables the tiny particles in the water to clump together in a process called coagulation, which makes them easier to remove. A static mixer and large diameter detention pipe allow turbulence and time for this reaction to take place. Polyelectrolyte is also added to bind the clumps of particles.
The water flows upwards through two pressure adsorption clarifiers. Buoyant granular media in the clarifier further helps the clumping of solids in a process called contact flocculation, and traps the majority of these solids on the surface of the media. A regular wash sequence flushes the trapped solids from the media to waste.
The clean water flows out of the top of the clarifiers into two pressure filters and passes down through silica sponge and sand filtration media where any remaining particles are removed. The filters are also backwashed regularly to remove particles trapped in the media.
From the filter outlets, the treated water flows to the reservoirs. On the way, chlorine gas and hydrated lime (calcium hydroxide) are injected. Chlorine is added as a disinfectant to ensure there are no micro-organisms present in the water that is distributed to the reservoirs, and as a safeguard against accidental contamination of the reticulation system. Lime is added to raise the pH of the water to 8.0, making the acidity/alkalinity level healthy for consumers and non-corrosive to household plumbing.