The Olifantsfontein works, situated in the northern Drainage District (DD3), serves the majority of the communities and industries in Tembisa, Olifantsfontein and Ivory Park, as well as sections of Kempton Park and Midrand. It is designed to treat some 65 megalitres of wastewater per day.
The original phase 1 of the works, based on the conventional biological filtration process, was built in 1972 to treat an inflow of 4.5 Mℓ/d. The works was expanded in 1976 to a treatment capacity of 9 Mℓ/d.
An increase in flow and loading resulted in a further expansion (phase 2) to a capacity of 38 Mℓ/d in 1985, based on an integrated biological filtration and activated sludge process. The economic and industrial growth in the district resulted in the construction and commissioning of the 70 Mℓ/d phase 3 extension by ERWAT in 1995, equipped with a semi-automatic process control via a Supervisory Control and Data Acquisition (SCADA) system.
The phase 3 works consists of a mirrored system, with two identical 35 Mℓ/d. Biological Nutrient Removal (BNR) process units, incorporating common preliminary and tertiary treatment units. The preliminary treatment includes screening in three sets and degritting in three vortex degritters, as well as automated screenings dewatering and grit classification. After flow measurement and division, primary treatment takes place in two in-line prefermenter primary settling tanks (36 m diameter). The settled sewage is treated in two 25000 m3 BNR reactors, designed as 3rd stage Bardenpho configurations, with flexibility to allow custom processes such as the University of Cape Town (UCT) or Modified UCT arrangements. A standby chemical phosphate removal dosing system is available to ensure nutrient removal can be accomplished continuously. Each reactor contains eight mixers (11 kW) and sixteen dual speed surface aerators (110 kW). Biomass settling, recirculation and final clarification take place in four secondary settling tanks (38 m diameter). Final effluent chlorination takes place in a flash mixer, after which a 3-leg contact basin (2200 m3) provides the required disinfection contact time. The disinfected effluent discharges into the Kaalspruit in quaternary catchment A21B which eventually flows to the Hartebeestpoort Dam.
Primary sludge is treated in four 2750 m3 anaerobic digesters before dewatering. Waste activated sludge is thickened in two Dissolved Air Flotation (DAF) units, before it is combined with the digested primary sludge for conditioning and final dewatering in three Filter Belt Presses (FBP). The dewatered sludge is used for agricultural land application.
The works is designed to contain and recover all waste liquid process water on-site, with a network of internal recirculation systems to allow for retreatment.
