Dynamic performance metrics to assess sustainability and cost effectiveness of integrated urban water systems

Abstract A comprehensive set of metrics quantifying sustainability and cost effectiveness of urban water systems is required to rigorously inform policy, design and management decisions, as cities all over the world face the combined pressures of drought and flood, climatic uncertainty, rising population, and an increasingly complex wastewater. These metrics need to be generated using an integrated system approach covering the whole urban water cycle, be capable of assessing a wide range of scenarios including innovations, be able simulate system metric dynamics at a range of time steps including sub-daily, and to create a comprehensive set of technical, economic and environmental variables. A dynamic system engineering modelling framework has been developed to provide a comprehensive set of dynamic performance metrics, integrating all six subsystems of the water cycle viz. (a) water supply; (b) urban water consumers; (c) industrial water consumers (e.g. metallurgical, plastics, construction, recycling industries also as processor or residues); (d) agricultural water consumers; (e) stormwater generation and treatment; and (f) sewerage and wastewater treatment. Dynamic material, component and energy balances, thermodynamics and kinetics, along with life cycle assessment and process economics enable the following variables to be simultaneously throughout the integrated water system viz. water, wastewater, rainfall, stormwater; dissolved constituents (e.g. BOD, TN); embodied energy of system/structures, energy consumed and generated; dynamic environmental impacts and greenhouse gas emissions (arising from water, wastewater, stormwater, dissolved constituents, reagents, infrastructure materials, sludge processing, recycling of materials, direct greenhouse gas emissions, energy); and financial costs (operating and capital). The novel framework has been applied to an innovative urban case study site; a MATLAB/Simulink® simulation model linked to Simapro® data compares infrastructure scales at the site viz. (a) conventional city-scale infrastructure; (b) suburban-scale infrastructure with dual reticulation of potable and recycled water to every house; and (c) household-scale infrastructure, where each house has a grey water recycling unit.