Recycled Water Too Clean?

I found this interesting article in The Age on Friday. It refers to concerns that have been raised regarding the suitability of using highly treated recycled water for enhanced river flows.

The concern is not that the water is contaminated, but rather that the water may be ‘too clean’.

After treatment by reverse osmosis, recycled water tends to contain only very low concentrations of important minerals such as calcium, magnesium and potassium, -all of which are essential to sustain aquatic life. Furthermore, there is none of the microscopic algae and other phytoplankton, which fish feed on, or nutrients required to grow such plants.

In most schemes, subsequent to reverse osmosis, water is ‘remineralised’, typically with calcium carbonate prior to transport or re-use. I would expect that in most environmental flow situations, further natural remineralisation and mixing with algae and nutrients would occur very quickly. But perhaps it is possible that if the water was not carefully adjusted prior to release, and then contributed (by far) the major portion of the environmental flow, then a waterway could indeed become deficient in some important chemical and microbial components.

There are a number of major environmental flow supplementation schemes currently under consideration or development around Australia (in Melbourne, Sydney and South East Queensland). Accordingly, I think this question warrants a closer look. The overall mineral and nutrient balance from various receiving waters to a river or reservoir is something that should be considered when assessing the environmental impacts of any proposed scheme.



Recycled Water 'Too Clean' for Yarra, Say Critics
By Peter Ker
The Age, April 18, 2008

A VICTORIAN Government proposal to divert billions of litres of recycled sewage into the Yarra River could hurt the waterway because the water could be "too clean", environmental groups have warned.

The Government is searching for the best way to use the 100 billion litres that will be recycled annually at the Eastern Treatment Plant plant at Bangholme once an upgrade is completed in 2012.

The Yarra proposal is one of two that have been under consideration since late last year. The second is piping the recycled water to the Latrobe Valley for use at power stations.

But Green groups have become concerned about the Yarra plan since briefings at which the Government made it clear that more water would be removed from the Upper Yarra for drinking if the recycled scheme went ahead.

That means the recycled water would be more of a substitute for river water rather than additional flows, with water diverted into Melbourne's dams just two kilometres upstream of where the recycled water would be piped into the river.

Those opposed to the plan include some of the most vocal campaigners for increased environmental flows in the river, with Environment Victoria spokeswoman Leonie Duncan saying that she had serious concerns.

"The purified recycled water that will be coming from the Eastern Treatment Plant will be the equivalent of distilled water," she said.

"It sounds bizarre, but it will actually be too clean for the Yarra. It will lack that real physical and chemical composition that is required to feed the chain of life in a river."

These claims were backed by Yarra Riverkeeper Ian Penrose, who said the idea of substituting recycled water for Yarra water was appalling.

"If it provides additional water to the Yarra and they take no more water out, we would be much more enthusiastic about this," he said.

"It's because they are going to do this as an excuse to take more water out that we are angry."

Despite being funded by Government-controlled bodies such as Melbourne Water and the Environment Protection Authority, Mr Penrose has been vocal in his criticism of the Brumby Government for failing to honour election promises to increase environmental flows in the Yarra.

He said recycled water was "better than no water" but was "a second choice to natural river water".

"The river needs the little bits and pieces in it as part of life," he said.

The Government is expected to decide how to use the recycled water when the two business cases are completed later this year.

Water Minister Tim Holding said he was aware of the argument that recycled water might not be ideal for river flows.

"That is why a business case is being done," he said.

"The purpose of having a multiple set of options is to give us the flexibility to select the superior option … that will address those issues as to what an environmental flow should look like."