Can solar energy help ZLD technologies to reduce their environmental footprint?-A Review

Water is the primary factor for life on earth, and its demand is continuously increasing significantly. Therefore, freshwater scarcity is one of the world's critical challenges due to the depletion and contamination of its res-ervoirs. Climate change, irrational exploitation, and waste disposal from various sources to the natural water reserves are the major causes of the contamination. Moreover, the increased utility of desalination systems has also magnified the production of rejected brine, whose disposal in water bodies and land will also result in a hazardous situation for future generations. Therefore, it is necessary to adopt sustainable approaches in the present for the welfare of future generations. Given the same, the concept of zero liquid discharge (ZLD) has emerged as a strong alternative for freshwater production in the most sustainable manner. It is a dual-purpose technology of fresh water production with dry salts from the brine by preventing the brine discharge into the environment. The sustainability of ZLD desalination systems can be further increased by using solar energy to fulfill their energy requirement. Hence, various technical and economic aspects of ZLD desalination technologies are presented in this review, along with the discussion on the feasibility of solar energy to achieve ZLD. An analysis is carried out on the impact of solar energy on the energy, economic and environmental potential of ZLD desalination technologies, whose outcome shows wind-aided intensified evaporation, reverse osmosis, and electrodialysis metathesis have higher potential compared to rest technologies.