Sewage recycling plant in Windhoek

Otjomuise sewage treatment plant phase 1 on the northern outskirts of Windhoek was constructed at the cost of  N$ 28 million easing increasing problem of recycling sewage in the capital.

Recent improvement in employment opportunities in Windhoek has led to influx of people from rural areas. To avoid the establishment of informal settlements, the City Council of Windhoek proclaimed 26 320 fully serviced new erven in and around Windhoek.
The resulting raw sewerage generated by these formal settlements necessitated the construction of a new sewage treatment plant as a matter of extreme urgency.
City Council of Windhoek decided to design a cost-effective sewerage treatment plant to produce treated water for re-use by the inhabitants of the capital.
It has been responsibility of Namibian company Africon to coordinate and supervise the many elements of the project, including the civil, structural, mechanical and electrical engineering services; documentation; quantity surveying and construction of the project.
Phase 1 consists of a 7,5 Kl/d activated sludge plant comprising elements such as a 30Ml/d capacity inlet works with manually cleaned screens, a grit removal system and a flume for flow measurement, a 7,5 Ml/d capacity biological reactor which can be upgraded to 15Ml/d capacity with modifications to the mechanical equipment, and a 35m diameter secondary settling tank with a Coanda Tulip inlet system - the first in southern Africa.

A total of 4 200m³ of rock has been excavated from the site, and 4 200m³ of concrete poured during construction.
The dolomite aggregate used for the construction was transported from Outjo, more than 300km from the site. The trucks transporting the aggregate accumulated 230 000km in just over a year.
Bateman Water Treatment was contracted for the supply and installation of mechanical equipment.
It also comprises sludge drying beds with a total surface area of 5 700m², a 16m diameter waste-activated sludge thickener, and a UV-treatment plant to produce an effluent to meet terminal needs.

The plant was designed for phased upgrading to a maximum capacity of 30Ml/d by the year 2008.
The project also involves the construction of a number of sludge and scum pumping stations, a wash water system, two motor control centre buildings, an operator's office, and a laboratory.
The civil contractor GMI construction - a joint venture between Grinaker Namibia, Murray & Roberts and International Construction - took possession of the site in March 1996.
The electrical contractor is ABB Windhoek Electrical Works.

Africon Namibia's Engineering Materials Laboratory was responsible for control testing, crushing more than 1 500 concrete test cubes during the course of the project.

In addition to the sewerage treatment plant itself, Africon Namibia was also appointed to design and supervise the construction of a 90m long pipe bridge to support the 800mm diameter glass reinforced polyester main sewage feed pipe to the works over the Gammams River. The triangular space frame superstructure, constructed from hollow circular steel sections, consists of three continues 30m spans, making the bridge unique in Namibia.

The project was financed by the European Investment Bank and completed in 1997.

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