Sustainability Report 2006/07Waste assessment
Waste is produced by our sewage treatment plants and our water treatment facilities, and collected in stormwater litter and sediment traps.
Sewage treatment plant waste
Waste from our treatment plants includes:
- Treated effluent – sewage that has been treated to a high standard at our sewage treatment plants and discharged into Port Phillip Bay or Bass Strait or further treated for water recycling
- Biosolids – a by-product of the sewage treatment process
- Grit and screenings – litter, gravel, sand and other non-biodegradable material collected by screens and grit-removal tanks in a pre-treatment facility.
A total of 112,990 million litres of treated effluent was discharged into Bass Strait from the Eastern Treatment Plant compared with 108,128 million litres last year, while 80,868 million litres was discharged from the Western Treatment Plant into Port Phillip Bay compared with 122,816 million litres last year.
Some 44,400 cubic metres of biosolids were generated at the Eastern Treatment Plant, contributing to the 1.19 million cubic metres stored onsite, and 5840 tonnes of grit and screenings were collected and sent to landfill for disposal, at a total cost of $494,210.
The Western Treatment Plant generated 17,000 dry tonnes of biosolids (the same as last year), bringing total biosolids stockpiled at the plant to 1.37 million dry tonnes. We continued to explore options for using biosolids as a resource.
Water treatment plant waste
Waste from our water treatment plants are called water treatment residuals, or sludges, and are a by-product of the water treatment process. They generally consist of clay minerals, organic matter, nutrients, hydroxides of aluminium and polyelectrolytes.
In 2007/08, Melbourne Water produced 237 million litres of water treatment residuals, mostly from Winneke water treatment plant, with about 1% produced from small local water treatment plants. This compares with 156.4 million litres last year.
The increase in water treatment residuals this year is due to a return to full operations at Winneke following temporary reductions in treatment levels in 2006/07to accommodate a power supply upgrade, cleaning of the Winneke-Preston pipeline and commissioning of a new clarifier and two new filters.
The Yan Yean water treatment plant also produces water treatment residuals, which are stored in drying pans onsite.
Water treatment residuals from the Winneke water treatment plant are discharged to sewer under a trade waste agreement with Yarra Valley Water. Melbourne Water is reviewing options for reusing the sludge with the aim of ending disposal to sewer.
Stormwater litter and sediment trap wasteLitter and sediment are collected in traps located in the drainage, waterways and wetlands systems.
In addition to constructed litter and sediment traps, we regularly collect debris from about 5000 sites including road culverts, drainage grilles and grates, and other known litter ‘hotspots’. Debris comprises 75% to 80% organic litter, with the rest rubbish and litter (usually plastics).
All debris/litter is taken to standard landfill facilities. Silt is tested for contaminants to determine whether it can be reused as clean fill or taken to a contaminated landfill facility. About one-quarter of silt material is contaminated.
This year, we collected 7000 cubic metres of litter from 130 litter traps, and a further 4000 cubic metres of silt from 346 silt traps in wetlands, with a total disposal cost of $1.96 million. Last year, total disposal costs were $2 million for 13,500 cubic metres of silt and 2500 cubic metres of litter.
Managing e-wasteMelbourne Water recognises the environmental problems and loss of valuable resources associated with the global increase in e-waste – unwanted, metal-rich electrical consumer goods, including mobile phones, screens and computers.
We donate useful end-of-life computers to not-for-profit charities. This year we engaged a recycling and asset disposal business to dispose of computing equipment unsuitable for reuse. No equipment was disposed to landfill.