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Walvis improves waste water treatment

An aerial view of the plant showing the new trickling filter media [centre] and the existing stone media [right].

An aerial view of the plant showing the new trickling filter media [centre] and the existing stone media [right].

Walvis Bay has upgraded significantly its waste water treatment plant increasing capacity three-fold. The harbour town’s upgrade of its sewage treatment capacity follows that of  Swakopmund where a new plant was constructed. Both plants were installed by Aqua Services & Engineering, a subsidiary of the multi-national Veolia Water Solutions & Technologies.
Aqua Services & Engineering has also, earlier this year, upgraded the Katima Mulilo purification plant that feeds drinking water into the Caprivi pipe system.

The Walvis Bay Municipality contracted Aqua Services & Engineering to upgrade existing stone-media biofilters to the company’s flagship trickling filter technology, for improved waste water treatment.
This upgrade, costing about N$15 million, significantly improves the quality of final effluent from this portion of treatment, amounting to about 6.5 megalitres per day. Existing civil works in the form of the old trickling filters’ superstructures were rejuvenated to house the new generation treatment process.
“It’s the first time in Namibia that the new-generation trickling filter technology was used to replace old stone filter media,” said Chris Stöck, Managing Director at Aqua Services. “Trickling filters give far fewer operational problems and with regard to blockages and ponding, are decades more advanced.”
At full operation, the new polypropylene media will host the micro-organisms that, in stage one, remove carbonaceous material such as COD and BOD (chemical oxygen demand and biochemical oxygen demand). In stage two, the micro-organisms perform nitrification.
The effluent is continuously recirculated through the polypropylene media at a high rate, increasing the biofilters’ aeration by three times which, in turn, multiplies the biological treatment’s efficiency also by a factor of three.
“Aqua Services upgraded two of the three existing biofilters by packing the larger 45-metre diametre filter to heights of 3, 6-metres with new polypropylene media that is designed specifically for stage one processing.
The smaller 30-metre diameter biofilter was packed 1.8-metres high with polypropylene media suitable for stage two processing, for an effective total of 7000 cubic metres of PP filter media,” said Stöck. The newly constructed plant and pump station is currently receiving in excess of 500 m³ per hour of raw sewage at peak flows, and the total continuous recirculation flow through the filter media is approximately 1240 m³ per hour. The system is undergoing performance testing to ensure acceptable effluent quality.

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