(644d) Reverse Osmosis Specific Energy (ROSE) Analysis Tool

Water scarcity and groundwater contamination in many regions around the globe has sparked major efforts to preserve and diversify regional water portfolios through desalination and water reuse. Reverse osmosis (RO) is now a well-established membrane-based  technology for seawater and brackish water desalination in small- (i.e., residential, boating) to municipal-scale applications, as well as advanced water treatment in water re-use applications. Given that electrical energy can be a major portion of RO operational costs, optimization of RO energy consumption is imperative in RO process design and operations. At present, however, effective tools for both system design and training are lacking for rapid analysis of RO energy consumption. Accordingly, in the present study, a web-based application for RO specific energy (ROSE) analysis was developed, implementing and expanding on a theoretical RO process analysis framework developed at UCLA [1]. ROSE is an interactive analysis tool that is built on a cloud computing platform, remotely accessible via a standard web browser interface. ROSE enables rapid evaluation, optimization, and comparison of RO energy consumption with respect to RO process design, operational constraints, thermodynamic cross-flow restriction, and utilization of energy recovery devices (ERD). For example, ROSE allows visual interactive exploration of RO specific energy consumption (SEC=Energy Consumption/Water Production) as impacted by various factors, including water salinity, temperature, membrane properties, pump curves, energy recovery devices, and flow rates. In addition to incorporating user-specified system constraints (e.g., due to equipment mechanical limits), ROSE SEC analysis ensures the appropriate constraints to within the thermodynamically feasible region of RO operation, as governed by system parameters (e.g., product recovery, pump and ERD efficiencies, membrane salt rejection). The model prediction has been verified using sea water desalination field data from a UCLA pilot plant deployed in Naval Base Ventura County, Port Hueneme, California. In addition, in demonstrating the utility of ROSE, a comparative evaluation was conducted on a number of small-scale RO desalination systems that are commercially considered as low energy (i.e., equipped with ERDs). ROSE analysis, implementing a fundamental basis for system comparison, revealed that most of the commercial systems evaluated were not energy optimal and have relatively low energy recovery efficiencies (<50%). Using ROSE, potential strategies for improving energy efficiency of small RO systems were identified and quantified with respect to thermodynamic constraints.

 [1] A. Zhu, P. D. Christofides, and Y. Cohen, "Effect of Thermodynamic Restriction on Energy Cost Optimization of RO Membrane Water Desalination", Ind. Eng. Chem. Res. 2009, 48, 6010–6021