WaterSubject

Australia’s CSIRO has a major research project on urban water systems called the Urban Water Program (UWP), which involves collaboration between its divisions of Molecular Science, Building Construction and Engineering, and Land and Water. It is the aim of this project to identify opportunities for more sustainable urban water systems. The project involves characterisation of water systems by costs, water use and demand, contaminant flows, treatment technologies, public acceptance and the costing of urban water system impacts on environments external to the system (ie. externalities). This knowledge will enable identification of water systems that have lower environmental impact and lower costs.

This data is to be used in scenario analysis. Each scenario is described by its water, wastewater and stormwater systems, and is compared to other scenarios according to their costs, contaminant loads discharged to the environment and level of public acceptance. It is an attempt to characterise the triple bottom line outcomes (cost, environment, social) of each scenario. The advantages of each system can then be established and better systems identified along with any trade offs that may need to be made. For example, the outcomes of supplying both potable and non-potable reuse water can be compared to the provision of potable water alone (conventional system), and the scenarios compared by quantifying the amount of imported potable water required, the cost, the contaminant loads discharge throughout the system and an indication of the public’s likely response.

Part of the UWP involved mapping the flow of water and contaminants through the urban water system, and a water and contaminant balance model was developed for this task. This involved mapping contaminants to water pathways and the gathering of contaminant data to describe these loads. By describing the contaminant loads according to their sources, the contaminant balance is able to estimate the effect of water system configurations on contaminant flows. This paper reports the results of the initial outcomes of the contaminant balance for a hypothetical residential area.A contaminant balance for urban residential water systems has been performed for 12 pollutants. The characteristics of the residential site were based on Ellenbrook, a suburb of Perth, Australia. The sources of contaminants were identified and characterised using published literature values. A water balance was used to estimated flow data, and these results were used in conjunction with the contaminant source characteristics to calculate contaminant loads. The contaminants examined were total nitrogen, ammonia, total phosphorus, copper, zinc, lead, cadmium, suspended solids, dissolved solids, chemical oxygen demand, polycyclic aromatic hydrocarbons and oil and grease. Diagrams of contaminant flows through the water, wastewater and stormwater systems are presented. By identifying the sources of contaminants, the diagrams are a useful reference when considering the fate of contaminants in alternative urban water system configurations or how to better handle or reduce these contaminants.Flow of contaminants through a hypothetical urban residential development was estimated using characteristics of the Perth area. Diagrams showing the loads for each contaminant through the water and wastewater system and through the urban residential development were constructed and show indicative loads derived from each residential source. This data may be used to examine the effect of variations in urban water systems on contaminant flows.

For instance, separate treatment of blackwater and greywater is one possible change to system configuration that the diagrams indicate might prove effective. The diagrams highlight the greater contaminant loads associated with blackwater in comparison to greywater, suggesting that treatment of a concentrated blackwater stream might be more efficient than treatment after dilution with greywater. Urine separation technologies are being explored in Europe, and could significantly reduce the flow of N and P to WWTP’s.

The results from this work may help in identifying the major sources of pollutants in the urban water cycle. End of pipe solutions are the current approach to minimising pollution, but future sustainable urban water systems might be best developed by elimination or control of pollution sources.