Intensified Modular Solar Desalination toward Zero Liquid Discharge

Abstract:

Solar-driven evaporator based on porous black carbon has attracted research attention due to its high solar energy conversion and feasibility for industrial adaptation without significant capital and operation costs. It has been considered a promising technique for efficient high salinity brine treatment because it uses sunlight as the thermal energy source. In this work, we introduce a novel solar carbon tubular device to produce fresh water toward zero liquid discharge desalination. The innovative operational principles of this device include: (i) the use of ‘black’ graphite foam (GF) as an effective photothermal energy absorber and heat conductor, which directly heats up saltwater to produce freshwater vapor, and (ii) application of superhydrophobic (SP) coating on the internal surface of GF channels, which helps to contain liquid water and allows only vapor to pass through. The solar desalination element demonstrated excellent vapor production (~6.6 kgm²h) with >99.5% salt rejection of 3.5 wt. % NaCl under simulated concentrated solar-thermal irradiation, i.e., 3-sun with heat radiation. Unlike state-of-the-art 2D solar evaporator, the light absorbing surface is separated from the saltwater in a flowing channel; therefore, it was operated at a high salt concentration of >10 wt.% NaCl without noticeable water evaporation rate decay. Also, the SP membrane keeps salt crystal precipitation from depositing onto the surface. Using thermal energy from concentrated solar power, the new Intensified Modular Solar Desalination (IMSD) process is thus proposed to produce freshwater and further concentrate the brine before it goes through crystallization. IMSD is thus a zero-liquid-discharge facilitating process that minimizes wastewater discharge, maximizes freshwater production, and allows the recovery of valuable materials from the brine.