Recycling to help protect our rivers

Posted 26 February 2009

Macleay River, News South Wales

Dr John Radcliffe

Rivers have always been the first place to look when we wanted water. Access in the past has usually been 'first in, best dressed'. In some overseas countries, though not Australia, this is even enshrined in the regulatory framework of 'First to right'.

The Australian approach has more usually been accompanied by the philosophy 'she'll be right'. But over the past decade we have learned, sometimes quite dramatically, that our river water resources are over-allocated, the natural environment is being threatened and our groundwater is being directly or indirectly diminished.

These changes can have serious feedback effects on the ecosystem services that communities have obliviously taken for granted. Nowhere is this more evident than in the lower reaches of the Murray River.

Since the 1950s Adelaide has progressively accessed a higher proportion of its water directly from the Murray River, to the point where now it may constitute up to 90 per cent of Adelaide's supply. But reduced upstream flows are also impacting on quality, with the potential that the river water could exceed maximum recommended salinity standards for human consumption.

The river has largely ceased to flow. It is now operating below sea level, with no outflow to ocean. A fortune has been spent dredging the river mouth to keep it open for when flows may increase. The water resources of the lower lakes have receded beyond the reach of irrigators' pumps and their ability to grow crops with the water if they could reach it.

Perhaps not so dramatically, similar impacts are occurring in the rivers accessed by other cities. So how can we help preserve riverine environments by reducing our take of river water?

One alternative resource is stormwater. In most urban environments, with the possible exception of Perth, located on the Swan Coastal Sandplain, the runoff from the roofs, roads and hard-stand areas is greatly increased compared with the original undeveloped environment. Historically, this has been seen as a risk - a risk of flooding - much feared by local government, which has usually been saddled with the consequent liabilities. But this water is increasingly now being seen as a resource, albeit not always pristine. It usually needs treatment, but then becomes suitable at least for irrigation, industrial and some domestic uses.

Remediation with wetlands can be an effective treatment option. Space will be needed but, by using airports, golf courses and urban open spaces, wetlands can be combined with other land uses. In new subdivisions, developers are increasingly adopting the principles of water-sensitive urban design. Land blocks commanding a water frontage achieve higher prices. Golf courses need water hazards, which may also double as remediating wetlands before the water is later used to keep the fairways green.

The northern Adelaide group of local government councils is among the leading developers of capturing stormwater in remediating wetlands for permitted domestic and industrial use. Consumers like the water as it has half the salinity of Adelaide tap water.

Though climate-dependent, stormwater capture and recycling makes a small but significant reduction on water drawn from the Murray River. Current projects will take the savings to 18 gigalitres per year.

Effluent recycling from wastewater treatment plants represents another water source that can reduce demands on existing rivers which could be imperilled by more water being extracted from them for urban expansion. Effluent recycling systems are much more climate-independent, constrained only if access to the original water supply system is limited by water restrictions.

There has been a revolution in technology in recent years, with widespread adoption of reverse osmosis. Membranes are much cheaper and have a longer life if well managed. In 2006-07 Melbourne claimed to have recycled 23 per cent of its effluent, much of it being used for beef cattle pastures or for vegetable and horticulture crops near Werribee.

Adelaide achieved almost 30 per cent recycling for use by Northern Adelaide Plains vegetable growers, Mawson Lakes home gardeners and Southern Vales viticulturists. In the same year, Brisbane achieved seven per cent, Perth six per cent and Sydney only four per cent wastewater recycling.

However, Brisbane has by far the most innovative ambitions with its proposals to use 12 per cent recycled wastewater in its drinking-water system by 2012, something thus far only achieved to a comparable extent in Windhoek, Namibia. This drinking water will come from wastewater treatment plants at Luggage Point, Gibson Island and Bandamba. Construction is well advanced, with recycled water already being supplied from Bandamba to the Swanbank Power Station in place of drinking water. Although not without some muted controversy, operatives are fully confident that through adopting the Hazard Analysis and Critical Control Point (HACCP) management system, which has been so effective in the Australian food industry since the 1980s, quality assurance will be achieved.

Underpinning the processes is a comprehensive text Purified Recycled Water for Drinking: The Technical Issues, published by the Queensland Water Commission, and built upon the Australian Guidelines for Water Recycling, Phase 2 - Recycled Water for Drinking approved by Federal and state health, environment protection and water resources ministers in April 2008. Adoption of this technology will reduce the extent to which Brisbane, one of the fastest-growing areas in Australia, has to further access river systems for its drinking water. But it is absolutely essential that Brisbane consumers appreciate how any risks in the system are managed and have confidence in their water-supply system and the people who run it.

Though depending on location, the capital and operating costs of the reverse osmosis technology for recycling wastewater are likely to be lower than for desalination. However, they will be higher than for the biological remediation of stormwater through wetlands, although wetlands may need major maintenance periodically, perhaps at 20 to 30 year intervals.

For the use of recycled water to be successful, market demand must be matched with likely supply. Where the recycled water is being used for crops and amenity horticulture, including home gardens, the demand is likely to be seasonal. But where the water is being used for industrial purposes, the demand is likely to be relatively constant.

Where the source is stormwater, the supply will be erratic. Where the source is from urban wastewater treatment, the supply is likely to be constant. Therefore matching a constant supply to a constant demand will require little storage. Matching an erratic supply to any demand or a constant supply to a seasonal demand is likely to require significant storage capacity.

Above-ground storage is easy to manage, but may be limited by land availability or the value of the land for other uses. Unless covered, evaporation will reduce storage efficiency, though open storage does have the advantage of providing additional 'polishing' of the quality of the water, due to UV radiation falling on ponded surfaces.

A further set of issues to be addressed is the reticulation system to be used. Where the recycled water is fit for a specific purpose, for example industrial use as occurs from the Kwinana recycling plant to five nearby industries in Perth, or from the Wollongong Sewage Treatment and Recycling Plant to Bluescope Steel, specific reticulation can be provided.

But where the recycled water is to be used for domestic use - toilet flushing, garden use and car washing - a duplicate set of pipes will be required to all users. In Brisbane, by adopting drinking water standards, the need for a duplicate capital investment in retail water distribution is obviated, a process that would be especially difficult where retrofitting of older suburbs is required.

The provision of water for consumption is increasingly recognised as involving consideration of many 'trade-off' options in terms of source, processing, product quality, storage, distribution and costs. Increasingly, a mixed portfolio of supply sources is being adopted.

Recycled water options for both non-potable and potable (drinking water) use should be among the options considered on their merits as mechanisms that have potential to reduce the long-term demands on the resources of our river and groundwater systems.

Dr John Radcliffe AM FTSE, an agricultural scientist, authored the Academy's 2004 review Water Recycling in Australia. Previously he was Deputy Chief Executive of CSIRO, and earlier Director-General of Agriculture in South Australia and a Murray-Darling Basin Commissioner. In 2005-08 he served as a Commissioner of the National Water Commission, with specific responsibilities for urban water and groundwater.

Source:

Australian Academy of Technological Sciences and Engineering ATSE Focus web site.

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