Nowadays, recycled water has provided sufficient flexibility to satisfy short-term freshwater needs and increase the reliability of long-term water supplies in many water scarce areas. It becomes an essential component of integrated water resources management. However, the current applications of recycled water are still quite limited with non-potable purposes such as irrigation, industrial uses, toilet flushing, car washing and environmental flows. There is a potential to exploit and develop new end uses of recycled water in both urban and rural areas. This can contribute largely to freshwater savings, wastewater reduction and water sustainability.
This thesis put forwards a conceptual decision making framework for the systematic feasibility assessment of sustainable water management strategies in related to new end uses of recycled water’s planning, establishment and implementation. Due to the transparency, objectivity and comprehensiveness, the analytic framework can facilitate the optional management strategy selection process within a larger context of the community, processes, and models in recycled water decision-making. Based on that, a simplified quantitative Multi-criteria Analysis (MCA) was conducted in Rouse Hill Development Area (RHDA), Sydney, Australia, using the Multi-attribute Utility Theory (MAUT) technique. The results indicated that recycled water for a household laundry was the optimum solution which best satisfied the overall evaluation criteria. Another two management options can be excluded from further consideration in initial stages, namely the implementation of Level 1 water restriction on the use of recycled water and recycled water for swimming pools.
With the identified strengths of recycled water use in washing machines, five relevant management alternatives were proposed according to different recycled water treatment technologies such as microfiltration (MF), granular activated carbon (GAC) or reverse osmosis (RO), and types of washing machines (WMs). Accordingly, a comprehensive quantitative assessment on the trade-off among a variety of issues (e.g., technical, risk, social, environmental and economic aspects) was performed over the alternatives. Overall, the MF treated recycled water coupled with new washing machines and the MF-GAC treated recycled water coupled with existing washing machines were shown to be preferred options. The results could provide a powerful guidance for sustainable water reuse in the long term. However, more detailed field trials and investigations are still needed to understand, predict and manage the impact of selected recycled water new end use alternatives effectively.
Notably, public acceptability becomes important to ensure the successful development of recycled water new application in household laundries. This thesis addresses social issues by extensive social attitude surveys conducted in three locations of Australia, namely Port Macquarie, Melbourne and Sydney. Based on responses from Port Macquarie and Melbourne, the regression models provide conclusions about which characteristics are more likely to lead to the acceptance of recycled water from society. Three attitudinal variables (i.e., recycled water is an alternative to drinking water, attitude and cost) and three psychological variables (i.e., odour, reading and a small treatment unit) were found to be the key driving forces behind domestic water reuse behaviour. Comparatively, survey results in Sydney indicated slightly different aspects of concern. Due to experience in current use on dual pipe systems, Sydney residents interviewed have established good cognitions on the appearance and cost of recycled water. They were more concerned about the colour of clothes and potential damage to washing machines. The overall findings could drive future research to achieve a better public perception of the new end uses of recycled water.
Moreover, the thesis also demonstrates the feasibility and cost-effectiveness of applying a zeolite filtration column as an effective ion-exchange resin for recycled water softening prior to use in washing machines. At the laboratory scale, the column service life for a typical washing machine was approximately one month without material regeneration on the basis of an optimal contact time (i.e., 5 minutes) and the calculated breakthrough capacity (i.e., 14 milligram hardness ions per gram of zeolites). It is believed that with a full application at households, this unit is likely to play a positive role in guaranteeing the recycled water quality as well as changing the public perception on the safe use of recycled water.