He sells desal ...

The Age:

He sells desal...

15 June 2009

In the world of Australian higher education, the oddest connections are occurring between researchers in different universities in different states. One of the latest is between engineers at Victoria University in Melbourne and a PhD student at the University of Queensland who is studying salt uptake by marsh plants.

The research involves the design and installation of a solar-powered desalination plant at Brisbane's Botanic Gardens, coupled with a new method of disposing of the unwanted brine left by the process. The investigation could lead to portable desalination systems that could be easily moved and used in drought-affected regions across Australia.

VU engineering lecturer Dr Eric Peterson and his fourth-year civil engineering students designed and helped build the desalination system. The $500,000 project was financed by the Queensland Government in collaboration with Queensland University's centre for marine studies and VU's institute of sustainability and innovation.

Until last month, south-east Queensland had endured a seven-year drought that had forced the Botanic Gardens to truck in up to 200,000 litres of recycled water a week to ensure its plants survived. Dr Peterson says the gardens have the world's largest collection of Australian rainforest species and the only way to keep them alive was to have tankers deliver huge quantities of water.

A desalination plant was seen as a possible solution and it is now driven by solar panels that produce the electricity to pump brackish bore water from the Brisbane aquifer - some 80 metres beneath the gardens - and press it through reverse osmosis membranes to strip out almost all the salt ions. The desalinated water is then mixed with water held in the gardens' ponds to introduce minerals and nutrients needed for irrigation.

The desalination system has the potential to generate 64,000 litres of pure water a day. Once it becomes fully operational in the coming months, the project is expected to produce 10 million litres of recycled water a year using solar power by day and off-peak electricity at night.

One of the many remarkable features of the joint project is that the researchers expect to achieve a zero waste outcome by piping the brine that comes from the desalination plant through a series of terraced ponds in which salt-loving marsh plants are growing. They take up the water and in turn can be harvested and mixed with livestock fodder in a complete recycling process.

"Our hypothesis was that we could treat the brine and use solar energy to drive the system so we had two innovations - an engineering aspect using solar energy for power and the botany hypothesis that we could take care of the salt using marsh plants that Jock McKenzie, a UQ PhD student, is testing as part of his thesis on the subject," says Dr Peterson.

A mechanical engineer who earned his first degree in the US, Dr Peterson became interested in environmental engineering after migrating to Australia. He undertook a PhD in aquaculture engineering at James Cook University in northern Queensland and then taught at Queensland University's centre for marine studies before taking up his lectureship at Victoria University.

"When we were setting up the desalination plant, we had intended to pump the brine into a big lagoon but freeway construction work meant we had to pump the water uphill on to a series of terraces that the civil engineering students designed as if we were building rice paddies," he says.

"We originally thought all we had to do was engineer the desal plant and instead we ended up doing that and designing the terraced ponds as well. We also discovered there is a lot of pressure produced by the reverse osmosis in the desalination, so much so we could use it to push the brine up Mt Cootha - 20 metres uphill in fact."

As Dr Peterson says, the reverse osmosis in a desalination plant is an example of "bio-mimicry" in that it works rather like our kidneys in extracting salts from the blood stream and excreting the waste. The membranes in the desalination plant act as extremely fine molecular filters that allow only low molecular weight molecules such as water to pass through, but very few of the various salt ions.

"As with your kidneys, you explode if you can't pass the waste products so we have that pressure in the system and it just pushes the effluent uphill. As we don't need any additional pumps, we can discharge the brine uphill to the terraces. People don't realise that the brine from a desalination plant has all this energy in it and I've thought you could use it as a `green' roof on a building and have these salt marshes growing there and pump the desalinated water up to them."

The terraced areas, sown with salt-loving plants including species of sarcocornia that grow around Port Phillip Bay at Point Cook and in Geelong, have created a new display at the Botanic Gardens while allowing Mr McKenzie to calculate the uptake of salt. As well as monitoring what is happening on the terraces, he is also conducting trials in glass houses on the university campus and in big aquaculture tanks.

Dr Peterson says that eventually the marine beds will be mowed periodically to take the plant tips off so they can continue to be harvested. The nutritious fodder will then be fed to livestock at the university's animal research farm outside Brisbane.

Dr Peterson says he runs debates with his engineering students so they can consider the case for desalination versus dams or, in Victoria's case, piping water from the north of the state to Melbourne, or even across Bass Strait from Tasmania.

The plant in the Brisbane Botanic Gardens is strictly for inland desalination. The system would not service a capital city but would be sufficient for a small community or an agricultural enterprise on a property, he says.

As for Victoria's plans to build a massive desalination plant near Wonthaggi, Dr Peterson says before such decisions are made, it is essential that all the pros and cons be debated and the costs compared with alternative arrangements, which could include a do-nothing approach.

"With desal plants, you absolutely have to build a pilot plant: you cannot go to full-scale without first finding out what the problems are. It's much better to build a small plant, sort out the problems and then double the production with each evolution.

"Without that feedback you can't refine the process. That's what we've done with the Botanic Gardens scheme: throw a bit of money at it and see how it goes, but also look at the alternatives - including the do-nothing alternative; just leave things as they are and see what happens."

See - The Age - He sells desal.