Water Journal : Water Journal April 2015
WATER APRIL 2015 42 Feature Article WATER TREATMENT INNOVATIONS One of the unique design features is that the plant can use water of variable quality from three different sources – surface water from Mundaring Weir and the Lower Helena Dam, and water from the Integrated Water Supply Scheme (IWSS), which includes groundwater and desalinated water. By being able to process raw water from different sources, the plant can reliably deliver water of required quality and volume to regional communities. The flexibility and robustness afforded by this approach sets the facility apart from other large water treatment plants around Australia and globally. The Mundaring Water Treatment Plant employs dissolved air floatation/filtration, biological activated carbon filtration andchloramination (normal mode) with an alternative process stream using ultraviolet disinfection (contingency mode). The integration of Dissolved Air Flotation/Filtration (DAFF) and Biological Activated Carbon (BAC) provides a robust and cost-effective treatment solution, enabling reduced levels of natural organic matter in the water with minimal disinfection by-products. DAFF removes most of the suspended organic solids and BAC mainly removes the dissolved organic matter. DAFF is the integration of a traditional Dissolved Air Flotation (DAF) with a filtration system, resulting in a smaller footprint. In addition, the common backwashing facilities for DAFF and BAC reduced the required civil, mechanical and electrical works, which resulted in significant cost and construction schedule savings. BAC in a plant of this scale is an Australian first and provides a more cost-effective and less operator-intensive option when compared to Powder Activated Carbon. In addition, instead of lime, the plant uses sodium hydroxide and carbon dioxide for re-carbonating water, removing the necessity for a costly lime plant and sludge waste disposal. A novel system of commercial incentives has been established for the plant to achieve water quality and quantity objectives over its 35-year operating period. Deviances in water quality result in financial penalties (abatements) to the private sector partners. As a result, the instrumentation and control systems deployed on the project provide early warning of water quality tolerance infringements in order to minimise, and ideally eliminate, abatements. Water quality is monitored at five different stages of the treatment process. These measurements are also regularly verified by independent off-site laboratory analysis. BUSHFIRE PROTECTION INNOVATIONS The treatment plant is located high in the Mundaring Hills, in a heavily wooded area that is highly susceptible to bushfires. During bushfires, the facility has to remain operational to deliver water supplies for firefighting in local and regional communities. In the absence of any state or Australian standards, the engineering team conceived, developed and implemented a bushfire protection network from first principles, applying technology developed for the oil and gas industry. The integrated bushfire protection scheme consists of a buffer zone around the plant, a high-pressure water “oil-safe” spray curtain to protect key areas from radiant heat, and an External Water Spray System (EWSS) to protect critical buildings against ember attack. The bushfire deluge system and the EWSS use the plant’s raw water and treated water pump station residual pipework pressures to deliver high-pressure water for fire protection, without additional pressure-boosting equipment. SUCCESSFUL OUTCOMES The plant was completed in December 2013 and officially opened by the Western Australian Premier and Water Minister in March 2014. Since the plant’s commissioning, the Perth Hills and the Goldfields and Agricultural region of WA have benefited from a secure 24/7 supply of significantly improved freshwater quality, being fully compliant with the Australian Drinking Water Guidelines for the first time in history. As part of the project, the Water Corporation created the Mundaring Weir precinct close to the new water treatment plant. The public site includes signs, historic sites, gardens, walks and trails that collectively tell the story of the Goldfields and Agricultural Water Supply Scheme, one of the world’s great engineering feats. WJ Aerial shot of Pump Station C. Because the plant is located in a bushfire-prone area, its design incorporates an integrated bushfire protection network.
Water Journal February 2015
Water and CSG