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Environmental Accounting for the Urban Water System: Past, Present and Future - Oregon
Arden, S. AND Cissy Ma. Environmental Accounting for the Urban Water System: Past, Present and Future - Oregon. 2017 AWRA annual conference, Portland, Oregon, November 05 - 09, 2017.
To understand water system behavior from a historic perspective.
The modern urban water system (UWS), or the provision of supply, sanitation and drainage services in an urban context, represents the ever-evolving physical manifestation of society’s propensity to solve pressing water problems. While solutions generally entail immediate benefits – more reliable water supply, cleaner water, reduced environmental impacts – costs are often displaced in time or space. This is due not only to the complexity of the systems and solutions, but also to the tendency to ignore non-economic costs. Thus, solutions to past problems might often be the cause of problems at a later time. During the 19th century, centralized water distribution systems increased hygiene and easy access to water supply in cities, which inadvertently overwhelmed the existing ‘water closets’, or prototypical sewage systems; improved sewage collection infrastructure removed the sewage from urban houses and streets, but these concentrated, untreated effluents were discharged and destroyed the environments; building of centralized wastewater treatment plants began to remedy the widespread environmental impacts, but required huge energy expenditures driven by concomitant fossil fuel use and greenhouse gas emissions and air pollutions; etc. Each new solution, although imparting benefit, entailed additional cost. By becoming more aware of the cost implications and holistic thinking of past solutions, we stand a better chance of making more informed decisions with respect to present problems. This work provides the full resource costs associated with the historical evolution of a representative US UWS from mid-19th century to present time, as well as cost implications of proposed solutions to present problems. Uniquely providing a “common currency” to compare different units and scales in UWS, Emergy accounting is used as a thermodynamic-based measure of resource cost, allowing the quantification of the work done by the environment in the provisioning of different degrees of supply, sanitation and drainage services. Therefore, the behavior of a system as a whole and the interactions between subcomponents can be observed and optimized and its sustainability can be assessed. Using non-potable reuse systems as an example of a present-day solution to the problems of water scarcity and energy consumption, we showcase not only how the system tools like full resource costs can be applied in assessing holistically the global system efficiency, but also whether the solution implementation aligns with the beneficial systems which increase intake energy (first priority) and its efficient use (second priority) on all scales (not just maximizing levels with more energy, and not maximizing some levels at the expense of others) in a historical context.