During the 1990s, there was growing concern about the environmental effects of the large volumes of secondary-treated sewage effluent discharged into the sensitive Gulf St Vincent. The considerable quantities of the nutrients nitrogen and phosphorous were leading to the destruction of seagrasses and mangrove forests, as well as annual blooms of toxic algal species. The initial response was a plan to upgrade the sewage treatment process by the construction of a biological nutrient removal (BNR) plant.
However, at the same time it was recognised that horticultural farmers on the Northern Adelaide Plains were withdrawing unsustainable volumes of groundwater from local aquifers for irrigation. The cone of depression thus caused was resulting in salt water being drawn in from the Gulf St Vincent and the aquifers were becoming saline. The reduced availability and quality of groundwater was expected to cause reduced future horticultural production and, subsequently, reduced employment in an area which was already economically depressed.
It was realised that with suitable treatment, the effluent from a sewage treatment plant (STP) could be used as an alternative irrigation resource on the Northern Adelaide Plains.
Adelaide has four metropolitan STPs. The largest of these is Bolivar STP, just to the north of the city. Bolivar STP was converted from a trickling filter plant to an activated sludge plant, and then further upgraded by the addition of a Dissolved Air Flotation Filtration (DAFF) process. DAFF involves injecting the effluent with billions of very fine air bubbles that carry small particles and suspended matter to the surface for skimming off. Further multi-media filtering and chlorination then take place in preparation for reuse of the water.
A large proportion of reclaimed water from Bolivar is transported via an 18 kilometre pipeline to Virginia, which is an important agricultural area on the Northern Adelaide Plains. Currently, this is around 15,000 megalitres per year, which is about 15% of the total of Adelaide’s wastewater from its four STPs.
The reclaimed water is then distributed via 120 kilometres of pipeline network to horticultural irrigators. It serves more than 240 irrigators who produce root and salad crops, brassicas (cauliflower, broccoli, cabbage, etc), wine grapes and olives. No special labelling or marketing restrictions are required for the produce. No health problems have been reported and export of Adelaide Plains produce such as wine does not appear to have suffered in any way.
The water is metered as it is delivered to dams on individual grower's properties. The growers then pump out the water through their own irrigation systems. The dams are required to hold three days supply in case maintenance is required for the supply system.
For the development of the scheme, the South Australian Government negotiated a public-private partnership in the form of a build, own, operate and transfer (BOOT) arrangement. The funds for the $22 million pipeline network came partially from the successful private tenderer Euratech (subsequently acquired by EarthTech), SA Water, and the Commonwealth Government. EarthTech will transfer ownership of the pipeline network to SA Water in 2018.
The Virginia Pipeline has been operational since 2000 and in October 2005, the South Australian Government and the Commonwealth Government agreed to co-fund an extension of the scheme via the National Water Commission. The extension project involves an additional 18 km of pipelines to be laid, extending into neighbouring Angle Vale. This will allow up to a further 3000 megalitres of treated water to be supplied to the region every year.
However, a major limitation to the quantities of water that can be beneficially reused is the highly seasonal nature of the demand for irrigation water. On average, the Bolivar DAFF plant produces about 110 megalitres a day of effluent. During summer, most of this is used by growers at Virginia. However, in winter, when most growers do not need the water, the effluent is discharged to the sea.
If the effluent that is not required during winter could be efficiently stored, the scheme could be significantly expanded to other areas. A research program- funded by a consortium of government and private bodies including SA Water, CSIRO and United Water – is now underway to examine the possibility of storing water in an underground aquifer for seasonal use.
This research has involved the winter injection of recycled water diverted from the Virginia Pipeline scheme into a brackish limestone aquifer for subsequent reuse during the summer irrigation season. I hope to have a closer look at this aspect of the project when some results become available.
Adelaide may bask in the glory of being home to Australia’s largest water reuse scheme...at least until the end of 2008!
6 comments:
hmmm it will be interesting to see how much the price of water will go up in south east qld. although really the qld gov has only it self too blame for the water problem if u ask me. there in a panic because they realise there too late. i wonder what was the go with the bettie appearently getting warning in 2000 about the water crises in south east qld? does anyone else know anything about it?? i would love too see this report if it exist??
yes the water grid will be huge when it is built but i know of alot of backlash in south east qld about water at the moment. one just has too read todays courier mail too find out. some i do belive is with good reason thou. the one thing that really has me worried about is the price of water. i mean if water is too skyrocket in price it will become a luxury that only the rich can afford. i do belive there should be a cap on the price of water. I have noticed the price of homes have gone up something ridiculus in the last 10 years. If this is too happen with water the aussie dream of owning a house will become a nightmare
I think what Beattie is doing is a disgrace and anybody who supports it severely lacks any sort of social and moral intelligence!
G’day Mick,
Lots of interesting thoughts there. The executive summary of the report you refer to is available from here. It was commission by the Department of Natural Resources and identified a number of strategies for preserving South East Queensland’s water resources.
These included subsidised audits of water efficiency for households and businesses, rebates for water-efficient products, a reformed water pricing structure and a program to reduce leakages from water distribution pipes. As you know, many of these measures are now either in place or about to come in place in South East Queensland.
I do agree with you that Governments should have been working harder on this issue earlier. With the benefit of hindsight, that seems to be stating the absolute obvious. However, I also sympathise with a point that was made by Beattie/Bligh, that is that the urgency of the situation was not as obvious six years ago as it is today. Governments do have to prioritise how they spend money and in doing so, are answerable to the community.
I don’t recall significant community pressure to direct funds away from areas such as health and education towards water infrastructure. Furthermore, when a looming problem is not obvious to the community, it is much more difficult for a Government to introduce expensive or painful measures. The community first needs to be convinced that they may actually run out of water before they are likely to support introducing tough measures. Nonetheless, it would be fair to say that many of the measures in the report are not all that tough and not necessarily very expensive.
As you suggest, water pricing is likely to be the most controversial of all. Judging by the huge response to the Courier Mail article this week, this issue is likely to generate more outrage than any water recycling, seawater desalination or new dams proposals. I have discussed the issue of water pricing previously (but with a primary focus on recycled water). We should take some time to consider some of the more equitable approaches to water pricing in further detail soon.
Thanks Greg,
Are you referring primarily to the proposed pricing reforms or are there other issues about which you are more concerned?
Stuart: this seems like a good example of how recycled water can be used for agricultural purposes instead of forcing people to drink the stuff. Why can’t the same approach be used to free up drinking water supplies in Toowoomba and Brisbane???
Hello Anonymous,
The Virginia Pipeline was devised to address a number of problems (as described in the post), but freeing up potable water for Adelaide was not one of them. The scheme was never intended to do this and does not achieve this. Adelaide does not source potable water from aquifers in Virginia and thus does not compete for the alternative supply that the irrigators previously relied upon. For all its merits, the Virginia Pipeline does nothing to resolve potable water shortages in Adelaide. The current ‘drivers’ for water recycling in Toowoomba and Brisbane are simply different to those for Adelaide in the 1990s.
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