Windhoek, Namibia's Direct Potable Reuse System
The wastewater reclamation system introduced in Windhoek, Namibia in 1968 was the first of its kind, and is currently the only place in the world to directly reuse its municipal wastewater as a drinking water source (National Research Council, 1998). The direct potable reuse system is used intermittently by the city to supplement an inconsistent and unreliable supply from both surface and groundwater sources. It used only during times of peak summer demand or during emergencies (Haarhoff & Van der Merwe, B., 1996). The systems is only used intermittently because of the high cost of reclaimed water. The city uses conservation methods as much as possible in order to alleviate as much of the costs of water as possible. Reclaimed water unit costs are approximately double that of the conventional supply (Haarhoff & Van der Merwe, B., 1996).
The uncertainty of using reclaimed water has created a very thorough monitoring program, of which approximately 20% of the total production costs can be attributed. It includes the following: chemical, virological, bacteriological, and algal monitoring, toxicity testing, on-line biomonitoring, and studies on mortality patterns in the city.
The system involves a lot of city planning, as industries are located based on the expected composition of their wastewater (Haarhoff & Van der Merwe, B., 1996). The wastewater from the industrial area is then diverted into a smaller, more conventional treatment plant, and not used for the drinking water supply.
The wastewater from the rest of the city is treated in two separate plants, containing several advanced treatment technologies. The treatment process has been slowly been changed over the course of the system’s life in response to increasing technology, and problems with specific contaminants. The current process train is shown in Figure 1. There are also two blending steps involved in the system, where reclaimed water is blended with a conventional source. They are located between the two treatment plants, and after the second plant. Pictures of the plant are available at the City of Windhoek website.
Figure 1 : Process Train for Windhoek, Namibia's Direct Potable Reuse System (City of Windhoek, 2004)
City of Windhoek. (2004). Water Reclamation. Retrieved May 7, 2004, 2004 from http://www.windhoekcc.org.na/default.aspx?page=117
Haarhoff, J., & Van der Merwe, B. (1996). Twenty-five years of wastewater reclamation in Windhoek, Namibia. Water Science and Technology Proceedings of the 1995 IAWQ 2nd International Symposium on Wastewater Reclamation and Reuse, Oct 17-20 1995, 33(10-11TY - JOUR), 25-35.
National Research Council. (1998). In Dobbs D. (Ed.), Issues in potable reuse : the viability of augmenting drinking water supplies with reclaimed water. Washington, D.C.: National Academic Press.