"With the new plant, Windhoek is able to incorporate the allowed maximum 35% reclaimed water into its potable water mix at all times. (...) The City of Windhoek is indeed proud of what it has achieved against the odds of natural adversity."

Introduction

The City of Windhoek

Innovations in an arid land

The new Goreangab Water Reclamation Plant The multiple barrier system Selection of the processes

Public perception

References

Author information

Additional web resources Introduction (Back to top)

In any discussion on direct reclamation of water for potable reuse, the names of Windhoek and its Goreangab Reclamation Plant enjoy a fair amount of recognition; see for example Law (2003). The City of Windhoek, the capital of Namibia, was indeed the pioneer in direct potable reuse. Located in the southwestern part of Africa, Namibia has a number of distinguishing features, such as natural beauty and wildlife. With a surface area of 825,000 km2 (318,534 mi2) and a total population of 1.8 million, it is one of the most sparsely populated countries in Africa. It is also the most arid country in sub-Saharan Africa. The total length of Namibia's western coastline, on the Atlantic Ocean, is covered by the Namib Desert, one of the oldest deserts on Earth. In the southeast, Namibia shares the Kalahari Desert with South Africa and Botswana. Although the desert has major advantages in terms of tourism, because of its rare beauty, it is also indicative of the prevailing climatic conditions. The only perennial rivers to be found in Namibia are on the northern and southern borders of the country, respectively 750 and 900 km (~466 and 560 miles) from Windhoek. In the interior of the country, there are only ephemeral rivers--that is, rivers that run for only a few days at a time, after heavy rainfall events. The City of Windhoek (Back to top)

The population of Windhoek is approximately 250,000, which makes it the country's largest city. It is situated almost in the center of the country and utilizes approximately 90% of the water consumed in Namibia's central region. The average annual rainfall is 360 mm (~14.4"). The annual evaporation averages 3,400 mm (~136"). The city currently relies for 70% of its water on three surface reservoirs built on ephemeral rivers. The Omatako, Von Bach, and Swakopoort Dams that create these reservoirs are between 70 and 160 km (~43.5 and 99 miles) distant from Windhoek and are operated by a para-statal water utility called Namwater. They were built from 1978 to 1993 to supply water to central Namibia. Only three of the last 10 rainy seasons yielded above-average inflow into these reservoirs. The efficiency of these reservoirs is also such that the main "consumer" of water is evaporation, which accounts at times for twice as much water as that utilized by consumers. Security of water supply to central Namibia and the City of Windhoek is therefore a major challenge, both for the bulk water supplier, Namwater, and the City of Windhoek. Innovations in an arid land (Back to top)

Windhoek was originally settled because of the presence of both hot and cold water springs. As the settlement grew, so did exploitation of these sources with the added digging of wells in the area. The water table subsided as a result, and the first municipal borehole was drilled around 1912. From 1912 to 2004, some 60 municipal boreholes were developed, in an aquifer with a safe assured yield of 1.73 million cubic meters (Mm3; ~467 million U.S. liquid gallons [MG]) per annum. Groundwater remained the sole source of water for Windhoek until 1933 when the Avis Dam, with a capacity of 2.4 Mm3 (~634 MG), was constructed. This dam has a small catchment area and therefore a very small assured yield. From 1962 to 1973 its maximum contribution amounted to only 2.4% of Windhoek's consumption; often, it could not supply any water at all. Thus, Avis Dam is currently used exclusively for recreational purposes. During 1958, a second small surface reservoir, the Goreangab Dam, with a capacity of 3.6 Mm3 (~951 MG), was built downstream from Windhoek, and a conventional treatment plant was constructed to treat the surface water from this reservoir to potable standards. During 1960, the City commissioned its new 6,800 m3 (~1.8 MG) per day Gammams Sewage Purification Plant on a site adjacent to the Goreangab Dam, to deal with the city's domestic and industrial effluents. Until 1963, these two waste streams were treated together; in 1963, a series of anaerobic and aerobic oxidation ponds were added to Gammams, and the bulk of the industrial effluent load was diverted to these ponds for treatment. Throughout the 1960s, these waste streams, following treatment, were mingled and discharged to a dry river bed; the reclaimed water was not used for potable or other purposes. By 1967, however, the City was seriously considering potable reuse of reclaimed water, and the Gammams Works were extended to provide 14 days retention time in the maturation ponds, thereby improving the quality of final effluent for eventual use as influent to a water reclamation plant. In 1969, the conventional Goreangab treatment plant was converted to treat not only the surface water from the Goreangab Dam, but also the final effluent from what was by this time called the Gammams Wastewater Treatment Plant (WWTP) in two separate treatment trains (the bulk of the city's industrial effluents were still being diverted from domestic effluents and treated separately). Thus, the Goreangab Reclamation Plant was born. It had an initial capacity of 4,300 m3 (~1.1 MG) per day. This reclaimed water was blended with water from the city's well field and was delivered as drinking water to the city's residents. At this initial stage, reclamation could account for up to 25% of the City's water consumption. After Independence in 1990, however, the population of Windhoek started growing at a more rapid rate, currently accepted as 5% per annum. This, together with increased investment and development in the City, placed ever increasing pressure on the supply of water. As one way to cope with this pressure, the City instituted progressive water pricing structures and educational programs aimed at reducing average consumption; these met with considerable success. On the technical side, the Goreangab Reclamation Plant went through a series of upgrades, the latest being completed during 1997. The ultimate capacity of this "Old" Goreangab Plant was 7,500 m3 (~2 MG) of potable water per day. The process train in its ultimate configuration comprised the following steps: