The Kariobangi Treatment Plant is located at Nairobi City County Kamunde Road off Outering Road behind Kariobangi Light Industries.The Plant was built in 1961 and extended in 1963. It is a conventional treatment plant using biological filters known as trickling filters where organic waste is consumed or broken-down by microbial action.
The plant was constructed in several stages to finally treat a design DWF capacity of 32,000m3 waste water per day and hydraulic storm capacity of 96,000m3. It has a laboratory to analyze waste water for the purpose of process control and as per legal requirements in the Environmental Management Coordination Act (2012).
The treatment process involves two processes:
- Physical Treatment
(a)Removal of the largest solids (Coarse Screen)
(b)Fine Screen
(c) Grit Chamber.
- Biological Treatment
(a) Primary clarifies or sedimentation.
The wastewater or influent flows into the sedimentation tank where the waste water is clarified or sediment by using the difference of settling speeds or velocity of particles. The most liquid portion of the organic matter goes onto the trickling filter while the most solid (sludge) is pumped to the primary anaerobic digester.
(b) Secondary Sedimentation (Humus) Tank
The waste water consists of slime which is a waste which dies off and flows along with the treated waste water from the filters. It is removed at the humus tank by depositing and forming sediment at the bottom of the humus tank as sludge.
(c) Anaerobic Digesters
The anaerobic digester is a closed tank in which anaerobic organisms digest the organic matter in to sludge. The organisms produce methane, hydrogen sulphide and carbon dioxide in the process.
The solids are removed from the tank and sent to the sludge drying beds where they are sundried for eventual land application while the supernatant is drawn off and sent to the inlet works and recycled.
Effluent Disposal
The waste water on treatment is released to Nairobi River.The sludge is sold to farmers to apply in their farms at a very low price. The sludge is only suitable Treatment Works for growing of trees or flowers because it contains high amounts of heavy metals.