Optimization of Membrane Processes at the Water-Energy Nexus

Abstract

Abstract Water and energy are two of the most pressing problems faced by the world today. Osmotic membrane processes such as Reverse Osmosis (RO) and Pressure Retarded Osmosis (PRO) can help alleviate both of these challenges. This work focuses on systematic optimization of a two-stage RO-PRO process for energy-efficient seawater desalination which integrates RO for desalination and PRO for power generation into a single process. RO-PRO is of great significance at the water-energy nexus given that water production, pump energy consumption, and hydraulic/osmotic energy recovery are essentially intertwined. The optimization problem is formulated to minimize the Specific Energy Consumption (SEC) subject to specified total membrane area and total water recovery. By solving the optimization model, the best design (e.g., allocation of membrane area among different units) and operating conditions (e.g. applied pressure in each membrane unit) are simultaneously determined. It is shown that the proposed twostage RO-PRO is energy-efficient than single- and two-stage ROs as well as one-stage RO-PRO.