Experimental investigation of a solar-heated direct contact membrane distillation system using evacuated tube collectors

Solar-powered membrane distillation (SP-MD) is examined as a promising renewable solution in the desalination and water treatment industry. In this study, an innovative direct contact membrane distillation (DCMD) module to directly utilize solar thermal energy is proposed. While previous studies focused more on utilizing solar energy indirectly (i.e. to heat the feed water outside the MD module), the proposed system integrates hollow fiber membranes inside evacuated tube solar collectors in order to achieve a more compact system. The performance of the direct SP-MD module is measured first indoors in a bench-scale experiment, and then tested outdoors under sunlight. Results show that applying radiation directly can enhance the efficiency and permeate flux up to 17% compared to the same process when radiation is not applied under the same operating conditions. The daily operation of a stand-alone, directly heated SP-MD unit equipped with 0.035 m2 membrane area achieved a permeate flux of 2.2 to 6.5 kg·m−2·h−1 depending on solar intensity.