Investigation of a Plant Blade Shaped Reverse Solar Interfacial Membrane Still for Near-Zero Liquid Discharge

Abstract

With the rapid development of solar-driven interfacial desalination technology, the ability to tolerate high salinity and achieve stable evaporation has become a vital research focus. This paper presents a leaf-shaped multi-stage interfacial membrane distiller with reverse arrangement. By utilizing the dripping effect induced by gravitational water potential, a flowing liquid film is formed within the interfacial evaporator to prevent the salt crystallization on the evaporator surface. Through the circulation of concentrated seawater, freshwater recovery and near-zero liquid discharge are simultaneously achieved. A thermodynamic theoretical model was established to investigate the proportion of various heat losses. Through indoor steady-state experiments, the relationships between evaporation temperature and water production rate with respect to petiole thickness, leaf inclination angle, and feed salinity were obtained. Moreover, a four-stage blade-shaped distiller could achieve a water production rate of 2.08 kg/m²/h with a seawater salinity of 3.5 wt%. After five cycles of desalination of the concentrated brine, a cumulative recovery ratio of 84.7% was achieved. Due to the increase in concentrated brine salinity, the gained output ratio decreased from 1.35 to 0.7 with increasing number of desalination cycles. In actual weather conditions, the water production rate obtained by the 4-stage blade distiller under an average irradiation of 831.6W/m2 was 6.06 kg/m2/h. The proposed bionic still provides a novel strategy for achieving multi-scale and massive solar interface desalination applications.

Keywords: Solar desalination, Solar interfacial still, membrane distillation, Zero liquid discharge