Water Journal : Water Journal December 2012
sustainability refereed paper technical features 86 DECEMBER 2012 water areas that do not have a sewerage outlet nearby, requiring a localised or decentralised solution. Traditionally, the solution would have been to build a local sewage treatment plant and install a gravity sewer. At a forecast cost of $315m, this is a large expenditure making searching for cost savings an important imperative. Translated across the state of Victoria, which is estimated to have in the order of 250,000 septic systems, and assuming they had a similar failure rate as Yarra Valley Water, it is estimated that there could be about 100,000 septic systems in a similar predicament. Hence, the challenge is magnified. Collectively, we have a strong need to find a cheaper solution. In addition to finding a cheaper solution, Yarra Valley Water was also interested in exploring whether a more environmentally sustainable solution could be found. To help with this, CSIRO and RMIT Centre for Design were engaged to undertake a study of the Kinglake West region of 74 households. The area was selected as it could be isolated and studied as a unique separate system, and because it abutted the environmentally sensitive Kinglake National Park. Kinglake is located approximately 50km north of the Melbourne CBD. A range of possible options was identified, includind on-property options, conveyance options and treatment plant options. The on-property options consisted of urine separation toilets, a greywater system and septic tank. Urine is a source of phosphorus, a key ingredient in fertiliser. The urine, or ‘yellow water, once it is diluted with water’, was used in a nearby turf farm, exploring the potential use as a resource. The greywater systems take shower and laundry wastewater and treat it onsite, allowing residents to re-use it for non-potable purposes such as toilet flushing, clothes washing and garden watering. This assists them to reduce water consumption and conserve rainwater (their primary source of water) for drinking. Conveyance systems consisted of a gravity sewer, septic tank effluent pump (STEP) and septic tank effluent gravity (STEG) system. A STEP and STEG system provides the first stage of sewage treatment at the property, settling out sludge like a typical septic tank. The liquid effluent is then conveyed to a pressurised sewage system at a local treatment plant. A range of alternative treatment plants was also investigated, includind a natural system, living machines, and package plants. The CSIRO and RMIT study by Sharma et al. (2006) and Grant and Opray (2006) using life cycle assessment, identified that an alternative servicing configuration could deliver better environmental outcomes than a traditional servicing configuration consisting of a gravity sewer and local treatment plant. A multi-criteria analysis incorporating social and economic parameters was then used to determine the optimal solution. Finally, a community cost assessment was completed to select the best community cost solution. The option finally adopted for construction consisted of an onsite greywater treatment system to recycle water for use in toilet flushing and garden irrigation at each house, a rainwater tank for all other uses, and a urine separation toilet in each household to collect and store urine in an onsite tank. Urine is collected by truck from each household for reuse on a turf farm (Figure 3). Collection of blackwater is via a pressure sewer system utilising septic tank effluent pumps (STEP). A packaged recirculating media filter plant with ultraviolet disinfection was selected for end-of-line treatment with the final effluent reused for agricultural irrigation. Project deliverables transferrable to benefits outside the study area, such as greenhouse gas reduction and nutrient discharge reduction, were converted into monetary external benefits and included in the community cost analysis. In this instance, external funding was obtained from the Victorian Water Trust to fund these benefits to ensure a viable business case. The Kinglake West project is designed to demonstrate how a backlog area can be serviced to increase reliability in water supply from 90% to 100%, decrease the urban runoff of nutrients into the local stream by 80%, decrease greenhouse gas emissions by 30%, and deliver the solution at a 20% lower community cost. Assessment of this project has also included a social perspectives analysis (ISF, 2011) and an agronomic trial (Wriggley and Bannan, 2012). CSIRO has also been engaged to evaluate the effectiveness of the project against the original theoretical forecasts. This is planned for completion by the end of 2012. Existing development: Blackburn Yarra Valley Water has an existing reticulated network of over 9,000km of both water pipes and sewers. The average age of these assets is about 50 years old, while the design life is about 70 years. Renewal, therefore, offers another potential opportunity to re-evaluate the possibility of delivering a more sustainable system. Looking at it from another perspective, if we do not incorporate our existing infrastructure when seeking a more sustainable future, and end up just replacing like with like when we renew our system, we will arrive in the future with a system predominantly no more sustainable than it is today. Kinglake West – Sustainable Servicing Project interceptor tank wastewater from kitchen and ‘blackwater’ from toilet (excluding urine) garden irrigation sewer pipe pump urine tank toilet flushing water from laundry and shower urine separating toilet greywater system urine collection truck 1. Greywater System This unit is installed next to the house and treats greywater (from shower and laundry) to a high standard for recycling. The water can then be reused for garden irrigation, toilet flushing and clothes washing. 2. Urine Separating Toilet Allows urine to be diverted to a secure storage tank onsite, while solids and toilet paper are flushed to sewer via the interceptor tank. 3. Urine Storage Tank This is installed under the house or underground where possible. It stores urine from the urine separating toilet until it is collected by truck. The tank itself and the pipework from the toilet have an air tight seal. 4. Interceptor tank Consists of a small pump and storage tank which are all installed underground. This collects wastewater from the toilet and kitchen prior to it being discharged to the reticulated sewer in the street. Sustainable servicing option urine tank 1 2 3 4 Figure 3. Kinglake West is an example of how a backlog site can be serviced increasing reliability from 90% to 100%, discharge 80% less nutrients, and discharge 30% less greenhouse gas at a 20% lower community cost.
Water Journal February 2013
Water Journal November 2012-1