Sustainability Report 2006/07Eastern Treatment Plant
The Eastern Treatment Plant typically treats about 40% of Melbourne’s sewage and services about 1.5 million people in Melbourne’s south-eastern and eastern suburbs.
The vast majority of inflows – which have fallen significantly during the drought – come from households and commercial businesses.An increasing amount of fully treated effluent is recycled and the rest flows via the 56-kilometre South Eastern Outfall pipeline to the Mornington Peninsula where it is discharged into Bass Strait at Boags Rocks under an EPA Victoria licence.
New opportunities for reuse
A new phase in the evolution of the Eastern Treatment Plant has begun with the construction of a facility to trial tertiary treatment technologies.
In February, Melbourne Water began the 12-month trials, which are the first stage and a vital part of the plant’s major upgrade to tertiary treatment.
The trials are determining the best possible treatment method, and will help to design the works and refine the cost of the upgrade, which is due to be commissioned in late 2012.
The trials will enable Melbourne Water to test technologies for filtration, advanced treatment and disinfection of recycled water, and will enable intensive monitoring and analysis of results using online instruments and an onsite laboratory. More than 10 treatment trains or sequences are being tested with detailed sampling plans and operational conditions.
Under our Works Approval with EPA Victoria, Melbourne Water is due to decide the preferred technology in early 2009. We will also make a recommendation to implement additional advanced treatment as part of the tertiary upgrade in the context of decisions around extension of the South Eastern Outfall.
The upgrade, which was announced by the Victorian Government in October 2006, means that the plant will produce Class A (rather than the current Class C) recycled water.
Environmental improvements
Reducing ammonia in the effluent
Melbourne Water completed works during the year to upgrade the six existing aeration tanks. Construction of additional tanks will be completed by 2010.
The upgrade is the first stage of a significant and complex project to reduce the level of ammonia in the treated effluent being discharged into the marine environment at Boags Rocks. The plant is now reducing ammonia in the effluent by 75%.
Previous studies examining the effect of treated effluent on the marine environment have found that ammonia levels were having a detrimental impact on the marine environment. Reducing the level of ammonia is reducing the impact of effluent at the outfall and ensuring that Melbourne Water meets our EPA Victoria licence requirements for the plant.
Environmental monitoring
Monitoring around the ocean outfall at Boags Rocks commissioned by Melbourne Water assesses the environmental impacts of the discharge from the plant and likely impacts of upgraded treatment and other effluent management options.
The long-term monitoring program, requested by EPA Victoria, began in 1999. Outcomes of the monitoring, together with the tertiary treatment trials, are helping to guide future management options.
This year, Melbourne Water gained a deeper understanding of the ecology of the rock platform and flora and fauna at the discharge point. Studies show that loss of the alga H Banksia on the Boags Rocks platform may be due to ammonia toxicity near the outfall but the effects further away may be due to competition by other species favoured by elevated nutrients.
In a report to EPA Victoria, Melbourne Water proposed future monitoring to detect changes arising from improvements in effluent quality arising from ammonia removal, reduced nutrients, reduced solids following filtration, and reduced discharge flow caused by increased water recycling.
Improving the plant’s performance
Construction began during the year on a biofilter to treat the air from the inlet works, which is currently vented direct to the atmosphere. This work is in addition to recent modifications to the existing return activated sludge channel biofilter.
Together these initiatives will significantly reduce odour emissions from the site to help meet EPA Victoria licence requirements.
Three stages of works are associated with the plant’s odour reduction strategy, which was based on odour sampling and analysis, modelling, odour complaints history, design standards and a cost-effective works program to meet these standards.
The next stage of works includes covering the primary sedimentation tanks and settled sewage channels and treating the air from under the covers. The final stage is an odour control plant on a ventilation stack associated with the South Eastern trunk sewer.
Further works to upgrade the sludge drying precinct were completed. These works have improved environmental compliance, drying and harvesting efficiency, the quality of biosolids harvested and the safety of drying operations while reducing operational risks.
The sludge drying pans were refurbished, which involved removing unsuitable clay material, restoring the clay liner and placing recycled crushed concrete over the pans as a wear layer to enable the movement of heavy machinery.
The supernatant collection system was improved, and temporary pipework replaced by buried pipes in the sludge delivery system. Both these measures have reduced the risk of contaminated run-off to local waterways and improved operational efficiency.
Extended power outage
A fire on an electricity pole owned by our distributor cut power to the plant for 16 hours in July. The duty shift team started generators and equipment in order of priority to prevent a spill from the sewerage system and then restore as much of the treatment process as possible.
The available power from the generators enabled the plant’s immediate essential operation to be restored. All possible flows were diverted to the Western Treatment Plant.
Subsequent analysis showed that the treated effluent complied with the requirements of the EPA Victoria discharge licence and Class C recycled water.
The fire was started by a build-up of dust on the pole and rain, which caused tracking (arcing) between the conductors.