Sustainability trade-offs in the planning and design of cluster scale greywater reuse systems

It is becoming increasingly accepted that the conventional approach to urban water resources management (WRM) is unsustainable and that securing urban water supplies for both anthropogenic and environmental uses requires a different approach. Water sensitive urban design (WSUD) is a holistic approach that seeks to integrate the management of the potable water, stormwater and wastewater cycles that provides such an alternative. WSUD has been well recognised in Australia, particularly in the area of stormwater management. However, there is less guidance in the area of wastewater management. The management of wastewater in a WSUD context involves initiatives such as minimising the volume of wastewater generated and reusing wastewater where appropriate. Despite a number of examples of large-scale and individual household wastewater reuse schemes throughout Australia, there has been little experience with reuse schemes at the intermediate, cluster scale. Furthermore, the sustainability of these reuse schemes is often not considered. This paper discusses the design of a cluster scale greywater reuse scheme for a proposed development in Streaky Bay, South Australia, using two components of sustainability, economic and environmental with the corresponding assessment criteria of net present value and total energy. Several different sized cluster scale reuse schemes are considered, and the trade-offs between the two sustainability criteria are obtained. The results of the analysis over a 50-year time period indicate that cluster scale greywater reuse is significantly more sustainable than individual reuse schemes. The results also suggest that, for this case study, reuse schemes that service a larger number of houses are more sustainable than smaller schemes. The trade-offs between the pipe materials selected are investigated and it is found that trade-offs between cost and energy only exist for certain materials. The sensitivity of the design to the population density is also investigated and the results compared to the initial analysis. It is found that increasing population density reduces the total cost and total energy of the reuse scheme. These results are important, as they illustrate the types of trade-offs that should be taken into consideration in the planning and design of greywater reuse schemes at the cluster scale.