By Rosalind Cairncross, P.Eng.
What Goes Around, Comes AroundEngineering
The largest city on the earth's driest continent is supplying treated wastewater as non-potable water to over 15,000 properties....
The largest city on the earth’s driest continent is supplying treated wastewater as non-potable water to over 15,000 properties.
Most of us agree that pollution prevention is a good thing. To that end, recycling water may be a very good thing. But not so good that it inspires us to rip out the plumbing at home to recycle water by connecting the shower drain to the toilet tank. For the residents of the Rouse Hill residential development on the outskirts of Sydney, Australia, the job of recycling water has been done for them. Every house boasts two sets of pipes. One carries potable water for drinking and bathing. The other carries recycled water for flushing toilets and watering gardens, both great water guzzling uses. The project was years in the making and the path from idea to successful implementation is both interesting and instructive.
The Hawkesbury-Nepean River is a major waterway in the state of New South Wales, Australia. With its source in the Blue Mountains west of Sydney, the river has plenty of opportunity to gather pollution on its way to the sea. The sewage treatment plants of more than 20 towns discharge treated effluent into its tributaries. Agricultural runoff and other contaminants find their way into its waters. The river reaches the sea at Broken Bay near Sydney, the country’s largest city on the world’s driest continent.
During the 1980s pollution of water bodies became a topic of growing concern in Australia. State authorities decided that no more treated effluent would be discharged into the Hawkesbury-Nepean River. This decision prompted Sydney Water, the crown corporation responsible for water management in the greater Sydney area, to embark on an integrated water cycle management program.
One of the key features of the program was the installation of a second — recycled — water supply system for domestic use to reduce the discharge of treated effluent to the receiving waters and to reduce the demand for potable water. Under the program, the effluent from new sewage treatment plants in all future greenfield development areas would undergo further processing and be reused for domestic non-potable purposes. The program was a bold step that required not only technical expertise, but also legal and social research.
The corporation sought legal advice from independent consultants to establish the legal status of water. The vital question: Was water a good? Apparently no one had asked the question before. The legal team confirmed that water was indeed a good. It was therefore subject to the Trade Practices Act (TPA), a very powerful Act in Australia and one that is stringently applied to the providers of services and goods. In order to avoid the wrath of the TPA, Sydney Water had to take all precautions that other producers of goods must.
One of the key precautions involved the area of risk. Corporation staff were counselled to be careful not to underplay the problems or to pretend that there weren’t any. Without causing undue anxiety, they had to advise the end users of any potential risk, explain how to use the product to safeguard themselves and how not to misuse it. In other words, they had to demonstrate due diligence.
A risk management study included workshops with the Environment Protection Agency (EPA) and the Department of Health. The risk management program that emerged identified risk control measures as well as infrastructure and operational safeguards. At the higher risk level end were the consequences of cross-connection between potable and recycled water, the uncertainty of product liability issues and the community acceptance of recycled water. Some 90 risks were listed and ranked, and each had to be addressed before the board of directors of Sydney Water would give the go-ahead.
The Rouse Hill residential development on the outskirts of Sydney was the first beneficiary of the decision to recycle treated sewage effluent. The subdivision’s environmental impact study required that the “after development” impact on the receiving water quality at the Hawkesbury River was no worse than the “pre-development” situation. As a greenfield site, the new development was ideal for the project. Laying pipes for new infrastructure and new houses was far more cost effective than retrofitting existing homes. Here contractors could co-locate pipes in the same trenches on the same site at the same time, and builders could install dual house plumbing during construction.
The Rouse Hill sewage treatment plant was designed for 35,000 properties, some 100,000 people. It had the usual EPA environmental discharge requirements of very high quality tertiary effluent. This tertiary effluent is the influent for the recycled water system, but first a number of technical considerations needed attention.
Since this was a new endeavour, there were no guidelines to follow. A committee was established to develop guidelines loosely based on the American (California Title 22) model. To transform the effluent from the sewage treatment plant into quality recycled water, additional processes were added, namely dual media filtration, micro-filtration and ozonation. Micro-filtration was considered the best disinfection process. Later, heavy chlorination was used because ozonation, as installed, proved problematic. The guidelines proposed a multi-barrier treatment process train, which would produce water of the required quality.
Rouse Hill’s Recycled Water project went on line in 2001, as soon as enough residents had moved into the area to ensure a base load for the pumps of the highly automated plant. The Sydney Water website (www.sydneywater.com.au) describes special features of the water system. Houses in the recycled water area require a dual-plumbing arrangement. Special recycled water taps must be used on the recycled water system. These taps are purple coloured, have a removable handle and a reverse thread hose fitting. All new homes in the recycled water area must have approved recycled water plumbing.
How has the project fared since its inception? The answer appears to be ‘very well’ with over 16,000 properties now connected to the system and over 1800 mL per year of drinking water use substituted. However, making sure that there are no household cross connections — one of the least desirable scenarios identified during risk management studies — remains an effort. Since September 2001, there have been four separate incidents of cross-connection. In one case, 80 households were affected. In each, the families had unwittingly drunk recycled water instead of drinking water. But the tale has a happy ending. The families came to no harm at all with no ill health reported. The recycled water survived a stringent though unintended test.
Measured against its prime objective: pollution control by keeping treated sewage effluent out of the Hawkesbury-Nepean River, the project has been a success. That first object has long been overtaken by another environmental priority: drinking water conservation. With ongoing drought, conservation/augmentation schemes are being pursued for the Sydney Water area including expanded water recycling. On the parched continent the conservation of water may be an even higher environmental priority than pollution control.
The recycled water project has also been a public success. Early concerns about the acceptance of recycled water were laid to rest. Sydney Water conducted extensive surveys and found that there was overwhelming support for the project. It seems that people who get recycled water see themselves as pioneers. They feel quite proud that they are at the leading edge of pollution prevention and water conservation.CCE
Rosalind Cairncross, P.Eng. is a contributing editor of Canadian Consulting Engineer. She lives and works in Toronto. More information about the Sydney water recycling program is at www.sydneywater.com.au
Sydney’s recycled water facts
* Across Greater Sydney there are now 14 recycled water schemes that recycle 15 billion litres of treated wastewater a year
* The schemes provide recycled water for residential, industrial and commercial use, including for golf courses, racecourses, university grounds and other irrigation purposes, and the operation of Sydney’s sewage treatment plants
* The Rouge Hill Recycled Water Scheme is the largest scheme in Australia, supplying 1,370 million litres each year, servicing more than 15,400 properties
* More residential recycled water schemes are being constructed in new development areas in western Sydney
Allowable residential uses for recycled water
* watering lawns and gardens * ornamental ponds * flushing toilets
* recreation not involving contact with water* construction and industry
* washing cars and houses* fire fighting
Uses for recycled water NOT allowed
* drinking* laundry
* cooking* household cleaning
* personal washing* irrigation of fruit trees or crops eaten raw or unprocessed
* swimming pools * evaporative coolers
Source: Sydney Water newsletter, January 2006