Optimal sizing and dispatch for a community-scale potable water recycling facility

This study explores economic and environmental impacts of a community-scale potable water recycling facility (WRF) by developing an optimal capacity and dispatch model, formulated as a mixed-integer linear program (MILP) that minimizes utility service costs, operating costs, and annualized capital costs where water recycling is augmented by service from central utilities. Model constraints govern operations of a sequencing batch reactor, reverse osmosis unit, and equalization equipment by enforcing flow balances. A solution method is also presented for a special case where water demand is constant, allowing WRF configurations to be screened for feasibility with minimal computational requirements. The generalized model is parameterized for a new residential community in Austin, TX to explore sensitivity to key parameters. Case study results indicate the WRF increases annualized costs by 15% relative to a business-as-usual (BAU) scenario without water recycling. Utility service demands for water (−50%) and sewer (−74%) decrease in the case study, accompanied by significant increases to electricity consumption (+167%) and indirect carbon emissions (+163%). Parameter exploration identifies regions where the WRF could be cost-effective based on utility rates, water demand, and capital costs. In systems facing supply constraints, the WRF modeled herein is a feasible alternative for incrementally expanding water supplies.