Pretreatment adaptation for Namibian SWRO plant

A 400 m³/d seawater reverse-osmosis desalination plant in Walvis Bay, Namibia, is to be upgraded under a contract announced at the end of September by Aqua Services & Engineering (ASE).

To cope with the source water’s high organic content, ASE, a company of Veolia Water Solutions & Technologies, will adapt an air-flotation filtration system for use as pretreatment.

“Our engineers will introduce a vortex mixer to generate micro bubbles, which are fed into the flocculated raw seawater stream,” says Christian Stöck, managing director at ASE. “This will help lighter organic particles float to the surface, and allow for heavier particles to settle.”

These settled particles will then be filtered by an ultrafine filtration bed where, unlike with an additional pumping step, minimal break-up of the flocculated particles will occur. This pretreatment will ensure that the raw seawater, often affected by red tide and sulphur eruptions, meets the required standards for effective desalination in reverse-osmosis membranes.

The plant, which will include an energy-recovery system, should be operational within 5-6 months and will provide much needed relief to Walvis Bay, where water scarcity has been a longstanding problem.