Water Journal : Water Journal December 2012
small water & wastewater systems refereed paper technical features 66 DECEMBER 2012 water • Source water quality: with better quality source water and, therefore, reduced treatment requirements prioritised; • Proximity to known tri-generation water demands: water sources close to tri- generation plants were prioritised; • Synergies with existing infrastructure: including sewer mining options that could be located with an existing sewer pump station were preferred; • Synergies with energy and waste systems: systems that had potential for co-location with tri-generation plants and major sewer pumping stations were prioritised; and • Treatment scale for sewer mining: sewer mining treatment becomes more cost effective at a certain scale, therefore, smaller schemes were consolidated to improve economies of scale. By applying these criteria the 34 ‘refined’ opportunities were identified. Figure 7 locates these opportunities and illustrates the relative (potential) supply contribution of each opportunity category (in GL/year). The figure also defines recycled water precincts, according to the pink boundaries shown. The following key opportunities were identified: • Sewer Mining: Nine main localities were identified that captured both local wastewater and other wastewater that passes through the LGA from upstream catchments. • Thermal Desalination: Opportunities close to Sydney Harbour and proximate to proposed tri-generation plants. • Stormwater: Approximately 20 stormwater harvesting opportunities were included within the refined opportunities category. They represented locations where large stormwater mains converged with medium to large open space areas such that reasonable storages could be located there. WSUD and stormwater opportunities Stormwater pollution reduction opportunities were assessed according to the categories of Redevelopment, Renewals, Retrofitting and Reuse, for stormwater volumes supplied to the decentralised network. MUSIC modelling was undertaken for each category in the context of the land use within their sub-catchment to determine the pollutant benefit associated with each. Unit costs were applied to the application of WSUD initiatives, including rain-gardens, wetlands and stormwater storages and treatment, to get a cost per unit weight of key pollutants including nitrogen and phosphorus. One output of this analysis was ‘rainfall diagrams’ illustrating the contribution to pollution reduction of each WSUD category. Figure 8 illustrates that existing WSUD and trapped gully pits, as well as projected infill development, will contribute significantly to reducing total suspended solids loads against the assessed baseline. Opportunity Assessment In preparing the Decentralised Water Master Plan, there was not an intention to ‘pick winners’, as there are a number of factors that could influence the priority and cost effectiveness of opportunities Table 1. WSUD opportunity category summary. Category Description Information source Redevelopment Incorporating WSUD initiatives into major and infill redevelopments Known major redevelopments within the City and infill development areas based on residential and commercial growth estimates Renewal Installing WSUD infrastructure with programmed road, footpath and drainage works City of Sydney capital infrastructure renewal programs Retrofit Incorporating WSUD and stormwater harvesting initiatives into existing major and minor public open spaces and private residential and non- residential properties Major and minor open space areas across the city (with minor public spaces being less than 400m2) Lot scale retrofits of residential and non-residential properties Reuse Treated stormwater transferred to a decentralised water network for non-potable uses beyond open space irrigation Large stormwater harvesting schemes proximate to network demand centres. Figure 7. Recycled water demand opportunity by supply type. Figure 8. Total suspended solids rainfall chart.
Water Journal February 2013
Water Journal November 2012-1