Designing for sustainable water and nutrient outcomes in urban developments in Melbourne
Melbourne does not have enough water to meet anticipated population growth of about 1 million people by 2030. The Victorian Government White Paper (2004) estimates by 2030 the potable demand will be 659,000 ML/yr (based on projected population and average demand in the 1990’s) however the reliable yield is currently only 566,000 ML/yr. This is without considering climate change which is estimated to drop available yield by 8 - 35%.
The natural capacity of Port Phillip Bay to process nitrogen has also been reached. A 1996 CSIRO study recommended nitrogen discharges to the bay be reduced by 1000 tonnes per year. Future development must therefore be designed to not increase nitrogen loading.
Given water and nitrogen limitations exist for Melbourne, Yarra Valley Water commissioned a life cycle assessment of two representative development options to determine how to service these in the environmentally best way. A greenfield site at Kalkallo and a principal activity centre at Box Hill were selected. This paper presents findings of the water and contaminant balance from this study.
Kalkallo is located approximately 35 kilometres north of Melbourne and growth forecasts project it will be developed within ten to twenty years. The area earmarked for development covers 3062 hectares comprising residential, commercial, industrial and community land uses with a projected population of 86,000 people.
Box Hill is already a densely populated hub in Melbourne’s eastern suburbs. The projected development comprises twenty ten-storey buildings, of which two floors are commercial and eight floors are residential, with 128 residents per building.
Four water and sewerage servicing options for the developments were selected by Yarra Valley Water, namely:
1. Conventional centralised reticulated supply and wastewater;
2. Third pipe system with recycled water;
3. Third pipe system using stormwater; and
4. Self contained servicing configuration drawing upon on-site greywater reuse, rainwater tanks and on-site wastewater systems.
Varying levels of end-use management were considered. The water balance was undertaken using the model Aquacycle and the contaminant balance was calculated using typical water quality values and the water balance results.
Analysis of the Kalkallo results demonstrates:
1. Recycled water supplied by third pipe requires significantly less storage space than stormwater. To supply garden and toilet with 95% reliability and adopting end-use management measures based on the White Paper, a 22 ML recycled water storage is required compared to a 1100 ML stormwater storage. This equates to 0.9 hectares compared to 44 hectares (assuming a uniform 2.5 metre storage depth).
2. A self sufficient residential water supply (i.e. without connection to water mains) must sacrifice reliability. Greywater (without storage or treatment) for toilet and garden use, an 8.5 kilolitre rainwater tank for all other uses, and end-use management beyond White Paper levels was not capable of meeting demand. (A 30 kL rainwater tank and 13 kL greywater storage is required for 100% reliability).
3. Significant reductions of imported water, wastewater discharge, stormwater discharge and contaminant loads beyond those of a conventional urban development can be achieved. Adopting end-use management recommendations of the White Paper and using a third pipe for toilet and garden use can reduce imported water consumption by 43%, wastewater discharge by 50% (if recycled water is used for third pipe) and stormwater by 37% (if stormwater is used for third pipe). Contaminant loads (e.g. Nitrogen, Phosphorous, BOD) from the wastewater treatment plant can also be reduced by 50% if recycled water is used for third pipe or 34% from the stormwater system if stormwater is used for third pipe. If end-use demand management beyond the White Paper is adopted, residential areas use greywater for garden and toilet, and rainwater tanks supply all other indoor uses, imported water consumption can be reduced by 70%, wastewater discharge by 53% and stormwater discharge by 25%. This would reduce contaminant loads discharging from the wastewater treatment plant by 53% and into the stormwater system by 25%.
Analysis of the Box Hill results demonstrates:
1. On-site treatment systems do not require large storage volumes when used in apartment towers. If all blackwater and greywater is directed to an on-site treatment unit and the most water efficient appliances are used, a storage volume of only 4.5 kL is required for 100% reliable supply of clothes washers, toilets, fire sprinklers and gardens.
2. Imported water consumption and wastewater discharge can be significantly reduced beyond White Paper’s end-use management measures. Recycled water via a third pipe for clothes washers, toilets, fire sprinklers and gardens can further reduce imported water consumption and wastewater discharge by 38%. This can be increased to 53% and 54% respectively if the highest rated water efficient appliances are installed.
3. Contaminant loads can be reduced by 38% beyond the White Paper if wastewater is recycled for clothes washers, toilets, fire sprinklers and gardens. This increases to 54% if the most efficient water appliances are used.