Direct potable reclamation in Windhoek: a critical review of the design philosophy of new Goreangab drinking water reclamation plant

Abstract

Direct drinking water reclamation from the Goreangab reclamation plant, has been a reality in Windhoek, Namibia since 1968. Potable reclamation is a fixed part of the water supply and waste water has become an indispensible resource for the survival and continued growth of the city. The multi barrier concepts that were applied 40 years ago have been refined over many years. Improvements in water treatment technology have made it possible to improve the reliability and the drinking water quality of the reclamation treatment process. With the latest upgrade, which was designed 14 years ago and commissioned in 2002, a specific design philosophy was followed. This paper will assess whether the objectives of the design philosophy have been met in terms of removal efficiencies and safety of drinking water, which contains at present 25% reclaimed water. The basis and aims of the multi barrier design that was applied is discussed and with the aid of natural organic matter (NOM) and microorganism removal, the reliability of the philosophy is tested and compared with the goals set. Comparisons are drawn between the new plant and the previous plant and how the new plant is able to accommodate changes in raw water quality. It can be concluded that the water quality has been improved and the barrier principle does reduce the risk and improve the water quality.