User:Pgallert/Goreangab Water Reclamation Plant

The Goreangab Water Reclamation Plant is the longest running direct potable reuse water reclamation plant in the world. It is situated in Windhoek, next to the Goreangab Dam in the Otjomuise suburb. It produces drinking water from the effluent of sewage of the City of Windhoek, without intermediate storage. Commissioned in 1968 it was the only plant of its kind. It retained that status for more than three decades.

Background
Namibia is the most arid country in sub-Saharan Africa. More than 80% of its landmass are desert or semi-desert. Its capital Windhoek, situated in the central Khomas Highland, has an average annual precipitation of 360 mm and an average annual evapotranspiration of 3400 mm. Potable water resources within 500 km distance are all already utilised, and the city's population is growing annually by 5%. Okavango, the closest perennial river, is over 700 km away. With the transportation of water economically not feasible, decreasing rainfall and increasing evaporation, extracting more and more water from the Windhoek Aquifer led to its overuse and consequently a dropping water level. By 1957 aquifer overuse had reached 57%, and a water crisis was looming.

Obtaining drinking water from domestic sewage and particularly its blackwater components - human faeces, urine, and toilet paper - meets a psychological barrier in its users. This is even more prevalent in a direct potable reuse ("Toilet-to-tap" ) plant, where reclaimed water is immediately being fed into the potable water system. An indirect potable reuse plant is the more common procedure. In this case, treated wastewater is used to recharge an aquifer or fed into a river. This makes the water lose its "sewage identity", even if the water is ultimately (e.g. downstream) used as potable water again. For the plant in Windhoek, though, negative public perception was never a problem.

When it was commissioned in 1968 the Goreangab Water Reclamation Plant was the only direct potable reuse plant in the world, and it remained that way for decades. In 2011 a second plant of this kind was built in in Beaufort West, South Africa, and there are three such plants in the United States and a plant in Malaysia, too. There is also a plant in Sydney, Australia, but did not start to operate due to public protests.

History
The plant was built in 1968 to a capacity of 4800 m3 per day. Opened in 1969, it was not in daily use but operated about 8 months per year. Ammonia removal by adding chlorine and the use of active charcoal led to high operational cost in its initial years. By 1973 the utilisation had already dropped to 70 days per year.

A redesigned process was started in 1976. Intended to make running the reclamation plant more economical, an ammonia stripping tower was added, the chemical dosage control was improved, and facilities were added to regenerate on site the active charcoal used. Still, the cost of the reclaimed water far succeeded that of any other water source.

In 2002 a second plant was built alongside the first as upgrading the old one would not have been economical. Since then, the maximum capacity is 21000 m3 per day. To distinguish the new plant from the old, it is referred to as the New Goreangab Water Reclamation Plant (NGWRP).

Technical description
Since the commissioning of the new plant, the original plant only processes water from the Goreangab Dam. Its effluent of around 1.3 e6m3/a is grey water, due to the dam's heavy pollution. It is used for the irrigation of the city's parks and sports fields.

The capacity of the new plant is 7.5 e6m3/a. the plant supplied 5.5 e6m3 of potable water, more than a quarter of Windhoek's demand.

The entire process from inlet to outlet takes four days.

Business structure
The Goreangab Water Reclamation Plant is operated by the Windhoek Goreangab Operating Company (WINGOC), whose business premises are on site. WABAG, the designer of the 2002 plant, holds 30% of WINGOC.