Development of water reclamation technology in South Africa

In South Africa, full-scale research on the technology of reclamation of drinking-water from wastewater was focused on two 4,500 m3/d plants. The Stander water reclamation plant (SRP), Pretoria, served as a research demonstration facility, initially treating biofilter humus tank effluent, which necessitated high lime treatment and ammonia stripping. Research findings and process development at the SRP were implemented to modify the Windhoek water reclamation plant (WRP), which was originally designed for maturation pond effluent after conventional biofilter treatment. High ammonia concentrations as a result of progressive overloading of the sewage works hampered continuous production of reclaimed water. Activated sludge secondary effluent which became available at both sites ensured low residuals of ammonia and a higher quality effluent more suitable for reclamation purposes. The high lime process was successfully replaced by coagulation with metal salts at both plants, with the application of interstage chlorination between the two clarification stages. This process modification significantly improved operating costs and simplified operational control. Results obtained over a 12-month period for the Windhoek plant form the main subject of this paper.