Looking to the sea to solve problems
In response to the need to develop cost-effective means of providing fresh water for human consumption in regions where the availability of fresh water is limited, the volumes of seawater in oceans are increasingly considered a valuable resource to sustain the supply of fresh water through desalination.
"The desalination of seawater is becoming an increasingly popular option for the supply of fresh water," says Martin Pryor, GM: process and technology at Aveng Water.
He says Aveng Water designed, constructed and now operates southern Africa's largest desalination plant about 30km north of Swakopmund in Namibia. It began delivering water in mid-2010.
Pryor says the desalination plant uses a seawater reverse osmosis process, which is one of the best available technologies for desalination.
"The plant is the first significant desalination installation in southern Africa and is capable of delivering 20-million cubic metres a year - 60000m3 a day - of treated water that is pumped about 50km by pipeline to the Trekkopje mine.
"The intake system was designed to extract in excess of 360000m3 of seawater a day to cater for a possible future demand of 45-million cubic metres a year of fresh water, while the remainder of the desalination plant was built in a modular fashion to allow for future expansion.
"The project was delivered in record time, with less than four years elapsing from the point at which the idea of seawater desalination was mooted to the commissioning date," says Pryor.
The project was challenging in that it involved difficult seawater in a corrosive environment and a remote location with no resources nearby.
The seawater along the Namibian coast is nutrient rich, has high levels of plankton, and is subject to red tides, which necessitated the implementation of a robust technology.
The heart of the desalination process is high pressure reverse osmosis membrane filtration, which retains a large portion of the salt in the water and produces a permeate that meets drinking water standards.
In order for the process to work effectively Aveng Water had to implement certain pretreatment steps, which include fine screening and ultrafiltration.
Pryor says it was also vital to ensure that the plant was energy efficient, as the power required to drive the high pressure pumps is the largest component of the operating costs of seawater desalination systems.
Aveng Water chose pressure exchanger units that guarantee more than 95% efficiency.
"To this extent the power consumption achieved is only 2,58kWh a cubic metre of water produced, which is better than most of the recent desalination plants delivered worldwide in the past five years," says Pryor.
Source: Business Day
Source: I-Net Bridge
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