Hybrid pressure retarded osmosis–membrane distillation (PRO–MD) process for osmotic power and clean water generation

Abstract

A novel pressure retarded osmosis–membrane distillation (PRO–MD) hybrid process has been experimentally conceived for sustainable production of renewable osmotic power and clean water from various waters. The proposed PRO–MD system may possess unique advantages of high water recovery rate, huge osmotic power generation, well-controlled membrane fouling, and minimal environmental impacts. Experimental results show that the PRO–MD hybrid process is promising such that not only it can harvest osmotic energy from freshwater but also from wastewater. When employing a 2 M NaCl MD concentrate as the draw solution, ultrahigh power densities of 31.0 W m⁻² and 9.3 W m⁻² have been demonstrated by the PRO subsystem using deionized water and real wastewater brine as feeds, respectively. Simultaneously, high-purity potable water with a flux of 32.5–63.1 L (m⁻² h⁻¹) can be produced by the MD subsystem at 40–60 °C without any detrimental effects of fouling. The energy consumption in the MD subsystem might be further reduced by applying a heat exchanger in the hybrid system and using low-grade heat or solar energy to heat up the feed solution. The newly developed PRO–MD hybrid process would provide insightful guidelines for the exploration of alternative green technologies for renewable osmotic power and clean water production.