Sustainability Report 2006/07Recycling west of Melbourne
Melbourne Water is using recycled water to lubricate and cool eight large pumps following a $750,000 upgrade of the Hoppers Crossing pumping station. This is saving more than 100 million litres of drinking water a year, and reducing the site’s drinking water demand by 85%.
The upgrade, completed in December, followed extensive testing to ensure the operating efficiency of the pumping station was not compromised by the use of recycled water.
The recycled water comes from the Western Treatment Plant via a distribution network built by City West Water to supply customers in the Werribee Technology Precinct.
The pumping station is the largest recycled water user in the technology precinct, which also includes the Melbourne University Veterinary School.
The precinct will initially use 300 million litres of recycled water a year for industrial purposes, irrigation and commercial washdown.
Works have begun on a new interface point for the Werribee Tourist Precinct. Melbourne Water currently supplies tourist precinct customers directly but they will soon be transferred to Southern Rural Water after the interface point works are completed. Flow monitors at the interface point will be solar powered.
Tourist precinct customers include the Werribee Park Golf Club, the National Equestrian Centre, the Werribee Open Range Zoo and Werribee Park and Mansion.
Managing and improving water quality
HACCP certification
The quality management framework for the supply of Class A recycled water from the Western Treatment Plant introduced in 2006/07 was third party certified under Lloyds Register HACCP (Hazard Analysis and Critical Control Point) assessment criteria following a detailed audit.
The HACCP system identifies potential risks to recycled water quality and the critical points in the treatment process at which these risks must be controlled. It covers all aspects of the sewage and recycled water treatment processes, transparently assessing, monitoring and verifying control points and validating water quality limits. A similar system was introduced at the Eastern Treatment Plant in 2004/05.
The certification provides further assurance of water quality to meet the stringent requirements of customers and Government legislation and guidelines. As part of the ongoing third party certification of the system, Lloyds will conduct process surveillance audits every six months to ensure the systems are being maintained and optimised. The latest audits, conducted in April, found no issues of concern.
Managing salinity
Significant work has been undertaken by the retail water businesses in the past few years to reduce the level of salt in recycled water produced at the Western Treatment Plant.
Salt-reduction treatment is at this stage prohibitively expensive, so it is important to actively manage the discharge of salt into sewage entering the plant. The retail water businesses have made significant efforts to implement cleaner production programs to reduce the salt entering the treatment plant in sewage from trade waste customers. Despite these efforts, the salinity of untreated sewage and recycled water at the Western Treatment Plant has increased over the past three years.
This is primarily a result of a reduction in sewage inflows of about 12%, caused by the drought, water conservation measures and water restrictions. This has led to a reduction in the dilution of salt in the recycled water previously achieved from higher domestic (low salt) sewage inflows.
The EPA Victoria licence limit of 1250 milligrams per litre for the salt concentration in untreated sewage entering the plant will be reduced to a median of 1000 milligrams per litre in 2009.
Southern Rural Water is working with growers in the Werribee Irrigation District to examine options for mitigating the impacts of salinity in recycled water as part of the Western Irrigation Futures Study, which will be carried out over the next two years.
Melbourne Water will support Southern Rural Water during the study, which aims to develop a long-term strategy for the Werribee and Bacchus Marsh irrigation districts.
Supplying salt-reduced water to West Werribee
Melbourne Water is working closely with City West Water on the early stages of its design of a small treatment plant to supply salt-reduced Class A recycled water from the Western Treatment Plant to residential customers in the West Werribee dual pipe scheme.
City West Water is considering the use of reverse osmosis membrane technology to reduce salt levels in the recycled water. This design work will continue in 2008/09. Once complete, the scheme will enable 9000 homes to use recycled water for garden watering and toilet flushing. Water will also be supplied for some open space irrigation in the area.
Algal blooms interrupt supply
Class A recycled water produced at the Western Treatment Plant begins as Class C water sourced from the 25 West and 55 East lagoons and is then further treated (disinfected) with UV and chlorine.
For the UV disinfection plant to operate properly, the turbidity of the Class C source water must be very low. The supply of Class A water also requires low levels of algal cells to ensure water quality standards required for irrigation are maintained.
Algal blooms have been an annual problem at the Western Treatment Plant and in late December, blooms developed in both lagoons at the same time. Blue-green algal cell counts in 25 West were above the toxicity-based threshold for Class A recycled water. Green algal cell counts in 55 East, while not toxic, caused the turbidity threshold of the UV plant to be exceeded. Recycled water could not be supplied for four days, and supplies were intermittent in the following six days.
Management protocols were put in place, including targeted sampling and customer notifications. As turbidity and blue-green algae levels continued to improve, uninterrupted supply of Class A recycled water was resumed.
It is believed the blue-green algal bloom was caused by a combination of high nutrient loads, warm weather and periods of stagnation in the lagoon water, and the green algal bloom by high ammonia levels in the lagoon water and warm weather.
Melbourne Water and Southern Rural Water are working on contingency plans as part of mitigating the risk of blue-green algal blooms including:
- Increased monitoring of algae levels to investigate the correlation between algal growth and other water treatment quality parameters
- Installation of online ammonia monitoring to improve treatment process stability
- Field trials of ultrasonic algae control devices to prevent algal growth.
Melbourne Water, City West Water and Southern Rural Water established a recycled water reliability working group to prepare supply contingency plans for the 2008/09 season, and develop long-term reliability improvements.
A risk assessment of the recycled water system was performed, including an assessment of operational events at the Western Treatment Plant that could interrupt recycled water supplies, combined with contingency planning for summer periods when the demand and supply risk are both at their highest.
Expanded monitoring program
Monitoring of Class A recycled water at the Western Treatment Plant has been expanded to about 240 water quality parameters. A wide range of metals, synthetic and natural organic chemical contaminants, disinfection by-products and pharmaceuticals and personal care products were included in the monitoring program this year. Many of these are not traditionally monitored in recycled water.
The program forms part of a two-year quantitative risk assessment being managed by Melbourne Water. Results are being analysed by technical experts and will improve our understanding of the potential risks associated with the range of end uses for recycled water in the future.
We continued working with the National Health and Medical Research Council to develop the Australian Guidelines for Water Recycling. We are represented on the working group for two of the three new guideline modules.
Werribee Irrigation District
Southern Rural Water continues to receive large volumes of recycled water from the Western Treatment Plant for growers in the Werribee Irrigation District.
More flexible supply arrangements were established to meet the increased demand of growers, who faced low river water allocations and groundwater bans due to the drought.
For the second season in a row, Melbourne Water supplied higher recycled water volumes than are contractually required by Southern Rural Water, to provide Werribee farmers with drought relief. A total of 12,519 million litres was supplied to Southern Rural Water for existing and new customers compared with 10,964 million litres in 2006/07.
Standpipes relocated
Since December 2006, Class A recycled water has been supplied to businesses and organisations from two temporary standpipes at the Western Treatment Plant, primarily as a drought relief measure. Under a process managed by City West Water, recycled water is transported by tankers and used for open space watering, and dust suppression in road construction.
This year, Melbourne Water undertook earthworks and roadworks to establish a new?filling area with two permanent standpipes at the Western Treatment Plant. The project will be commissioned early in 2008/09.
The move was in response to safety risks associated with traffic along the old filling site on Farm Road, deterioration of the adjacent roadway, and the opportunity to establish more permanent and advanced access to recycled water at the site. Tankers supplied 158 million litres of recycled water from the standpipes (compared with 88 million litres in 2006/07), with up to 60 tankers a day using the site at peak summer times.