Sustainability Report 2006/07Western Treatment Plant
The Western Treatment Plant provides an essential public service to greater Melbourne, treating about 500 million litres of sewage a day. However, this year inflows were reduced significantly due to the drought.
Detailed conservation plans are in place for the site’s wetlands, which are protected by five international treaties. The entire 11,000-hectare site is listed under the Ramsar Convention on wetlands of international importance.
Improving the environment
An Environment Improvement Plan that defines objectives and targets to ensure a high level of environmental performance at the Western Treatment Plant was completed and approved by EPA Victoria during the year.
The five-year plan, which was produced with the plant’s Community Liaison Committee, Biodiversity Conservation Advisory Committee and EPA Victoria, describes how Melbourne Water intends to protect and improve the environment and meet its regulatory obligations.
It is the third environment improvement plan produced by Melbourne Water for the Western Treatment Plant as part of its accredited licence.
In recent years, Melbourne Water completed environmental upgrades that complement the natural processes in the plant’s lagoon systems with new technology. We have reduced nitrogen discharges to Port Phillip Bay by almost 60% since 2000/01, achieving targets established in the Port Phillip Bay Environment Study. These targets provide capacity for population growth and ensure enough nitrogen remains to enrich the foreshore areas and grow worms, which provides necessary habitat for migratory wader birds. We removed 1560 tonnes of nitrogen this year.
We have also introduced a range of initiatives to reduce odour as residential and recreational assets are developed next to the Western Treatment Plant.
A biological odour control facility commissioned early in the year treats foul air extracted from the incoming Western Trunk Sewer. The $10 million facility, believed to be the largest of its type in Australia, treats 35 cubic metres per second of air through biologically active media in fibreglass towers. The treated air is then discharged to the atmosphere via a vent stack.
A 12-month odour risk assessment study was completed in June 2007. This study included seasonal monitoring such as fieldwork and community surveys to verify odour modelling. The study has recommended a staged program of odour reduction works, including a chemical dosing facility, to be constructed at the Hoppers Crossing pumping station by June 2008.
Lagoon cover repairs were completed at the 55 East lagoon early in the year. The cover, like others on the plant’s lagoons, reduces odour and captures biogas to power the plant. The cover, installed in 1998, had deteriorated in places due to extreme heat and the presence of hydrogen sulphide.
Creating new solutions under lagoon covers
Accumulated sludge in the lagoons has the potential to affect the efficiency of the anaerobic reactors to process sewage and create biogas that helps to power the plant.
Melbourne Water worked with two technology providers to develop techniques to desludge the covered lagoons. Because of odour and safety concerns, a traditional solution such as removing the covers to dredge the lagoons could not be considered. Two system prototypes were trialled and proven during the year. The preferred provider will be selected by the end of 2007 with a working solution in place by mid-2008.
Sludge will be dried and harvested more efficiently, creating further opportunities for beneficial use of biosolids, in new drying pans being constructed at the Western Treatment Plant. Work on the 24 drying pans began during the year and is expected to be completed by the end of 2007.
Chlorine spill
A rupture in a pipeline caused chlorinated water to spill in the Class A recycled water chlorine disinfection plant located at the Western Treatment Plant in August 2006.
Chlorine leak alarms were automatically activated and the plant shut down as soon as possible. There was no leak to the outside environment, and a section of the PVC pipeline was replaced after Melbourne Water and the Country Fire Authority instigated clean-up measures to ensure the area was safe.
Following the debrief, 16 actions were identified to improve emergency response including enhancements to the control system and securing personal protective equipment to minimise operator health and safety risks.
Case study
Diversifying land use
The Western Treatment Plant consists of a sewage treatment area and a buffer zone used for primary production, interspersed with areas of high conservation value.
Under a land use strategy, Melbourne Water is diversifying primary production activities and supporting areas with important conservation values.
Diversification around the current livestock production activities has included trials with crops that could reduce greenhouse gas emissions. This year trials were carried out on maize, barley, wheat, canola, triticale and oats, and rotational trials used barley and canola with lucerne.
Studies were completed to verify the minimum amount of recycled water needed to supply conservation lagoons and wetlands. Recycled water was used to flush soil at the plant on a routine application as part of a salinity management plan, and trials were undertaken using gypsum to manage salinity in the soil profile.
The baseline condition of the 700-hectare northern grassland area of the site was assessed to enable the benefits from planned improvements to be monitored. Weed and vermin control measures are being carried out in the area, which has important habitat and conservation value.
Parks Victoria published a draft management plan for the Werribee Regional Park, a 240-hectare section of land on the eastern fringe of the plant that was transferred to Parks Victoria in 2005. The first stage of the park is expected to open in December 2008. A further 30 hectares was transferred for expansion of the Werribee Open Range Zoo.
Western Treatment Plant Farm Manager, Peter Nilon with lucerne crop watered with recycled water.