Advancing Zero Waste Discharge with an Integrated Solar Enabled Membrane Desalination System

Abstract

Management of concentrate streams in inland applications has an uncertain long-term sustainable outlook. This study investigates an intensified solar-energy capture desalination system that integrates membrane distillation (MD) with a hybrid concentrated solar power (CSP)/photovoltaic (PV) collector to realize self-sustained zero-waste discharge system for effective management of concentrate streams in inland and off-grid applications. The demonstration-scale CSP/PV system is capable of producing up to 125 kWh of thermal energy and 45 kWh of electrical energy that is directly supplied to the air gap MD (AGMD) pilot system. Experiments were done on the hybrid CSP/PV-MD system to evaluate the performance under various combinations of operating conditions including MD and CSP flow rates, pre-heating, operating temperature, and vacuum pressure. Experimental results indicate that doubling the MD flowrate results in approximately 116% and 40% more thermal and electric energy utilization, respectively, and nearly double the distillate production. Compared to the winter months, operating the system in summer months when direct normal irradiance (DNI) is highest results in a sixfold increase in average distillate production (30 L in winter and 180 L in summer) and a 45% decrease in specific electrical energy consumption (2.44 kWh/m3 winter and 1.35 kWh/m3 summer). Furthermore, the relative specific thermal energy consumption decreases by 30% when allowing the thermal storage reservoir to preheat in the winter. Overall, experimental results highlight the tradeoff between distillate production and thermal and electrical energy production and consumption under various environmental conditions, and allow for a direct cost comparison to be made against various other concentrate management technologies.