Theoretical and experimental investigation of a solar-driven air gap membrane distillation system for the treatment of hypersaline brine

The treatment of highly concentrated saline brine using reverse osmosis is energy-intensive and poses significant operational challenges due to high osmotic pressure and scaling potential. Solar-powered membrane distillation offers a promising solution for treating concentrated brine in decentralized applications. This study theoretically and experimentally investigates the performance of a parabolic trough collector-powered air gap membrane distillation system for the treatment of highly concentrated saline brine. A theoretical sub-model for the parabolic trough collector and a transport model for the air gap membrane distillation module were developed independently and subsequently coupled to simulate the system performance. Experimental tests were conducted using deionized water to optimize the operating parameters. Based on the optimized parameters, the system performance was further evaluated using real concentrated brine samples with salinity ranging from 10,000 to 50,000 mg/L. The results revealed that at a solar intensity of 950 W/m 2 , the freshwater yield and gain output ratio reached 1.202 kg/h and 0.32, respectively. Freshwater yield and gain output ratio increased with increasing solar intensity and cooling liquid flow rate, while they decreased with increasing feedwater flow rate and air gap thickness. Within the tested operating ranges, the highest system performance was obtained at feedwater flow rate, cooling liquid flow rate, and an air gap thickness of 0.5 kg/min, 4 kg/min, and 10 mm, respectively. Moreover, increasing the feed salinity from 10,000 to 50,000 mg/L reduced the freshwater production and gain output ratio by 47.12% and 27.84%, respectively, at a solar intensity of 900 W/m 2 .