Design of zero liquid discharge desalination (ZLDD) systems consisting of freeze desalination, membrane distillation, and crystallization powered by green energies

Zero liquid discharge desalination (ZLDD) is a sustainable solution to the global water scarcity problem. It provides high water recovery, zero waste generation and valuable salt production. In this work, a mathematical model of a novel ZLDD system that consists of freeze desalination (FD) and membrane distillation-crystallization (MD-C) has been developed based on the theories of heat and mass transfer as well as experimental results. To improve the energy efficiency of the system, effects of important parameters, such as (1) the feed temperature, concentration, and distillate temperature of MD and (2) the recovery ratio of FD on system operating curves and energy consumptions have been systematically investigated with the aid of mathematical modelling. In addition, the potential of using green energies to power this hybrid system has been explored. For a lab-scale hybrid ZLDD system operating at optimized conditions with a daily seawater processing capacity of 72 kg, 50% of its heating energy can be supported by a 50.5 m(2) solar panel and its cooling energy can be 100% provided by re-gasification of 207-kg liquefied natural gas (LNG). This work may provide useful guidance in designing a low-cost FD-MD-C hybrid system for ZLDD.