Sustainability Report 2006/07Eastern Treatment Plant
The Eastern Treatment Plant typically treats about 370 million litres of sewage a day from about 1.5 million people in Melbourne’s south-eastern and eastern suburbs. Inflows have reduced significantly as a result of the drought.
The vast majority of sewage that flows into the plant is from residential and commercial sources. An increasing amount of fully treated effluent is recycled and the rest flows through a 56-kilometre pipeline to the Mornington Peninsula where it is discharged into Bass Strait at Boags Rocks under an EPA Victoria licence.
A new era
A $300 million upgrade to tertiary treatment announced by the Victorian Government in October 2006 will lead to expanded recycling at the Eastern Treatment Plant.
Technological advances will enable the plant to turn treated effluent into a valuable and reusable water resource and, together with ammonia reduction initiatives, further protect the marine environment at the discharge point in Bass Strait.
Once the upgrade is complete in 2012, the plant will be able to upgrade the current Class C recycled water to Class A, enabling wider use in industry, agriculture, new housing estates and other uses.
Producing Class A water requires tertiary treatment processes that are based on filtering water and disinfecting it using ultraviolet light and chlorine.
The processes and technology to be used will be determined by the requirements of the end users of the recycled water and through extensive technology trials in 2008 using effluent from the plant.
The trials were designed during the year and expressions of interest sought from technology providers. A decision on the preferred process technology will be made in 2008/09.
Works continued on an $84 million project to reduce ammonia in treated effluent discharged from the plant.
Modifications to the existing aeration tanks will be completed in early 2008. Detailed design and construction of new aeration tanks began during the year.
The project, which aims to reduce ammonia levels in treated effluent by 75%, follows a 1999 CSIRO study that found ammonia was impacting on the marine environment at Boags Rocks, where the effluent is discharged.
Impact studies
In the past year, Melbourne Water commissioned detailed scientific studies to examine possible impacts at the ocean outfall at Boags Rocks in future scenarios.
The studies included the likely impact of upgraded treatment and outfall location, effluent flows taking into account various levels of water recycling, aesthetic impacts (such as colour, odour and litter), ecotoxicity (toxic effects on the ecosystem), and health risk assessment for recreational users.
The studies enabled ‘safe’ dilutions to be determined for protection of rock platform algal species under the various effluent discharge scenarios, and indicated that tertiary treatment would achieve significant reductions in turbidity, foam and possibly odour, but not colour.
Recreational water quality is typically rated good to very good but health risks will be higher during extreme wet weather. However, tertiary filtration and UV disinfection will reduce these risks, as could an extended outfall.
Further studies will be undertaken into advanced treatment to manage residual aesthetic impacts, as an alternative to extending the outfall.
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Improving the plant’s performance
The $46 million Eastern Green Energy Project that was completed during the year has improved the efficiency of the plant. Seven new generators that can run solely on biogas and/or natural gas have replaced five older generators that required diesel and biogas in the plant’s power station, and three new electric motors have replaced old inefficient engines that used biogas and diesel in the outfall pumping station.
This new equipment enables the plant to fully utilise renewable biogas developed in the treatment process while providing greater reliability and reduced maintenance costs (see Eastern Green Energy Project).
A $28 million facility that will significantly improve pre-treatment is planned for the plant as a result of a detailed triple bottom line analysis completed during the year. Pre-treatment involves capturing and treating grit and screenings.
The pre-treatment facility, to be completed in 2011/12, will reduce waste sent to landfill, enable organics to be retained in sewage and so help produce biogas to power the plant, reduce odour and greenhouse gas emissions, protect downstream equipment, and help maximise treatment performance and peak flow handling.
A key odour-reduction project to optimise the return activated sludge channel biofilter was completed in February 2007. The two-year project, which included increasing the height of the stack to improve dispersion, is the first to be completed as part of an odour reduction strategy for the plant. The strategy and associated works were based on a community survey, odour sampling and modelling.
Detailed design was completed on a second project, a $12 million biofilter to treat air from the inlet works. This project received EPA Victoria works approval, and construction is expected to begin in 2007/08.
The sludge drying precinct was upgraded to improve environmental compliance, drying efficiency, the quality of biosolids produced and the safety of drying operations while reducing operational risks.
A key element of the project was augmenting the supernatant collection system to increase capacity and prevent the discharge of contaminated run-off to local waterways. (Supernatant is a by-product of the sludge drying process.)
Works included the construction of a rising main and gravity pipes, an upgrade of culverts and modifications to a pump station. Pit levels were raised and monitoring installed to reduce the risk of spills. This project will be completed by the end of August 2007.
WorkSafe Victoria renewed Melbourne Water’s licence to operate the Eastern Treatment Plant as a major hazard facility after receiving our safety case submission during the year. In granting the five-year licence, WorkSafe Victoria acknowledged the efforts made by Melbourne Water employees in producing the safety case, which it said clearly demonstrated an improvement in documentation and management of engineering and procedural control measures at the plant.
Recycled water cross-connection incident
In March 2007, an independent investigation was launched when recycled water was supplied inadvertently through a drinking water tap to a new administration building at the Eastern Treatment Plant.
The investigation found that the recycled water, which is only suitable for use onsite in the treatment process, was supplied to the building for 19 days in March 2007 when a recycled water pipe was inadvertently cross-connected with a drinking water supply to the kitchen in the building. Twenty-two employees and contractors experienced gastro-type symptoms including upset stomachs, nausea and headaches. All recovered relatively quickly, with one employee and two contractors requiring time off from work.
We acted immediately to isolate the source and provided assistance to all affected employees, working closely with Department of Human Services and WorkSafe Victoria. Employees and contractors were verbally notified of the incident immediately with written notification following.
A full list of potentially affected visitors to the plant was compiled and all those affected notified of the incident. Counselling services were made available to all employees and contractors at the plant and medical personnel were available both onsite and via telephone, with any medical expenses fully reimbursed by Melbourne Water.
Ongoing care of, and communication with, employees and contractors impacted by the incident continues.
We completed a thorough investigation, and a debrief in consultation with the Department of Human Services and WorkSafe. As a result of the investigation, Melbourne Water has implemented a number of actions to ensure this type of incident does not occur again. These actions include:
- Improved labeling of recycled water pipes
- Increasing contractor awareness of the use of recycled water onsite
- Improved procedures for making connections to drinking water systems at the plant.