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The Yan Yean Water Filtration Plant
Yan Yean water treatment plant 30km north of Melbourne, was the first Build Own Operate Transfer (BOOT) project in the Australian water industry. The plant was provided at a cost of $25 million by joint venture partners Transfield and United Utilities Australia, to enable continued use of Yan Yean reservoir particularly during summer months when demand is high.
Construction was undertaken by Transfield, while United Utilities Australia remains responsible for operations.
Water from the reservoir, which is the oldest in Victoria, has noticeable colour, high iron concentration and turbidity due to its shallowness, plus the nature of the soils and vegetation in the area. Extensive testing using a pilot plant was conducted to find the best treatment process. This proved to be filtration through coal and sand media.
How the treatment works
Screened water from the reservoir flows by gravity to the treatment plant where coagulant chemicals are mixed with the water to cause the colour and turbidity particles to stick together. The water is then filtered to trap and remove the particles. Lime is added to make the water less corrosive, fluoride is added for dental health and the water is disinfected with chlorine prior to distribution.
Screening
Intake screens on the reservoir outlet tower prevent the entry of fish, weeds and other debris into the pipeline to the plant.
Coagulation
Chemicals (coagulant, lime and polymer) are added to the water before its enters the filters. Rapid mixing distributes the chemicals, enabling them to react with the fine suspended particles and causing them to cluster together
Filtration
Yan Yean water treatment plant has ten filter tanks, each containing layers of sand and coal. Water enters the filter from a central channel and flows under gravity through the layers of filter media and fine nozzles in the floor of the filter, leaving behind the coagulated impurities.
Lime, fluoride and disinfection
The clean water flows out of the filter into the pump station where lime is added to make it less corrosive. The water is then pumped to a treated water storage tank. Immediately prior to the tank, chlorine is added to disinfect the water as is fluoride for dental health.
The treated water storage
The 40 million litre capacity treated water storage tank balances fluctuations in Melbourne's water demand, provides storage for emergencies such as fire fighting and provides a delay period for the disinfection process to be completed.
Cleaning the filters
The impurities trapped by the filter media are removed by backwashing with air and water. The backwash process starts automatically with the process occurring at least once a day or more frequently as required. During the backwash operation the inlet gate to the filter closes and the water level is drawn down to just above the media. An air and water wash system systematically forces air only, then air and water and finally water only through the filter nozzles and media, releasing the trapped impurities. The dirty washwater is collected in the central channel and when the process is complete, the filter automatically comes back into operation.
Disposing of washwater
The dirty washwater is collected and pumped initially to a holding tank and from there to dewatering basins where the water and impurities separate. The clear water runs back into the reservoir and the sludge settles in the basins. The sludge is allowed to dry before being disposed of to landfill.
Operating the treatment plant
Operation is to world's best practice with advanced IT systems monitoring every aspect of the plant operations around the clock, enabling full control from remote locations if necessary. An on-site laboratory allows constant water sampling and testing to be undertaken, ensuring that only water treated to the highest quality standards passes on to consumers.