Desal drink at 0.03c a glass

Sunday Mail Adelaide
Sunday 16/9/2007 Page: 4

A GLASS of water from an Adelaide desalination plant would cost just 0.03c to produce, says one of Australia's top desalination experts. Former West Australian Water Corporation principal engineer desalination Gary Crisp said, if done right, desalination was cost-effective and environmentally friendly.

Mr Crisp worked on Perth's 144ML desalination plant and is now working on a 125ML plant in Queensland. He said the cost of producing 1kl of desalinated water was about $1.20, so a 250m1 glass of water would cost 0.03c. SA Water charges 50c/k1 up to 125k1, so a 250m1 glass of water costs 0.0125c. However, it then charges $1.16 for every kilolitre above 124k1.

Since Perth's desalination plant opened in November, water bills there have risen by $43 a year. A desalination plant in Adelaide is tipped to push water bills up by about $300. However, Mr Crisp said it was "absolutely" worth building a desalination plant here, which could be up and running in four years. "If you're using wind energy or renewable energy to produce seawater desalination, it's got the smallest environmental footprint of any water source," he said.

Desalination has been criticised for its high energy requirements, which Mr Crisp said were at least three times that of "conventional" water sources such as dams and ground water. He said a 100ML plant would run on 160,000 kilowatt hours a day - enough to power about 25 households for a year. Desalination plants draw water from the ocean, from between 200m and 400m offshore, at a depth of at least 10m.

Screens prevent animals and seaweed from being pulled into the plant and a filter removes smaller particles such as sand and plankton. A high-pressure pump pushes this water through a reverse-osmosis membrane where desalination occurs. "(The pump) is actually what uses all the energy," Mr Crisp said. "That's what puts all the pressure into the water so we get it through the membranes." During reverse-osmosis, about 40 per cent of the water passes through the membrane as fresh water while the remaining 60 per cent salt water flows over the top.

"The fresh water is literally pushed out of the salty water," Mr Crisp said. "The salt can't go through the membrane, the molecules are to big." Once the salt and fresh water are separated, minerals and chemicals including calcium, carbon dioxide, chlorine and fluoride are added to the fresh water, which can then be piped into the city's water supply ready to drink. The salty water is diverted through an energy recovery device to generate power which is put back into the plant.

The brine is returned to the ocean through a pipe, which extends at least 500m-600m from shore, and is dispersed by tides. It is this part of the process which scientists and the fishing industry have concerns with. Mr Crisp said brine was about 5.8 per cent salt while seawater was about 3.5 per cent salt.