Yarra Valley Water’s $20 million investment in Melbourne’s north

Yarra Valley Water is investing $20 million to replace the Wallan Sewage Treatment Plant, which provides source water for the Wallan Recycled Water Treatment Plant. 

This recycled water will be supplied to new residential developments in and around Wallan. The Wallan Sewage Treatment Plant is located in Melbourne’s northern growth corridor, and collects sewage from the townships of Wallan, Wallan East, Beveridge, Wandong and Heathcote Junction. Pat McCafferty, Managing Director, Yarra Valley Water, says the production of recycled water will provide a new drought-proof water source that can be used in homes for flushing toilets and washing laundry, as well as outdoors for irrigating gardens and sports fields.

‘In response to the establishment of the new development corridor extending from Craigieburn through to Wallan, Yarra Valley Water prepared a new sewerage strategy for servicing the corridor, and the Wallan Sewage Treatment Plant will play a crucial part to allow for the growing communities. Growth in the Wallan area, notably in the Wallara Waters and Mandalay developments, has generated additional demand on the existing sewage treatment plant, placing stress on the current two-million-litres-per-day capacity of the plant.’

An activated sludge-treated plant is being constructed with a four-million-litres-per-day capacity (dry weather). Tertiary filtration and ultraviolet (UV) disinfection also form part of the treatment process. The new sewage-treatment plant will feed water into the recycling process, allowing Class A water to be supplied to residential development in the area.

The township of Wallan was originally serviced by Goulburn Valley Water; however, in 2004, the government determined that Yarra Valley Water would take over servicing responsibility for the area. In 2006, Yarra Valley Water assumed responsibility for the Wallan Sewage Treatment Plant, which included the Wallan 100 per cent Class C re-use scheme. This meant that recycled water was provided to re-use customers in the area for farming use. The implementation of the scheme involved the construction of a winter storage lagoon on the site.

The new recycled water treatment plant uses a combination of dual-media filters, ultrafiltration, UV disinfection and chlorination to treat Class C effluent to Class A recycled water standard. The existing sewage treatment plant is located adjacent to land that was originally the Wallan Airport, but is now being developed as a residential estate. The old lagoon-based treatment plant was originally constructed in 1988 with a nominal capacity of above two million litres per day. The existing treatment plant currently utilises a series of lagoons to achieve the biological treatment of sewage, as opposed to many other Yarra Valley Water plants, which utilise activated sludge systems. During this process, sewage is treated by utilising microorganisms, contained within the sewage, that help to break down the organic matter.

The first treatment lagoon is aerated by surface aerators to provide aeration and mixing of the sewage. Sewage then flows by gravity through the other treatment lagoons in a predefined sequence, which allows treatment and maturation to occur. In the lagoon, natural biological and chemical processes aid to treat the sewage, while the use of aerators increases the efficiency of the process.

Over the course of treatment, removal of soluble organic matter, phosphorus, nitrogen and suspended solids will occur. Sludge accumulates at the bottom of the lagoons. Lagoon sludge depths are periodically tested and are desludged once the level of sludge is near capacity. Sewage then flows into the winter storage lagoons, and excess flows are pumped in, as well. During the colder months of the year, winter storage lagoons are steadily filled. During the warmer irrigation season, treated Class C effluent is used by several re-use customers for pasture irrigation.

Read the full article in Future Water Yearbook 2016

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