Desalination, minimal and zero liquid discharge powered by renewable energy sources: Current status and future perspectives

In recent decades, freshwater reserves have been under high threats, generated mainly by anthropogenic causes such as rapid population growth and climate change. Currently, one of the technologies that has been used to meet the freshwater global demand is seawater desalination. However, this solution has two major drawbacks. First, the discharge of reject brines with a high concentration of pollutants and nitrates, causing environmental problems such as eutrophication processes. Second, desalination systems, both membrane and thermal technologies, have a high energy consumption that is supplied with fossil fuels, contributing to the emission of greenhouse gas. Recently, to solve both problems, the zero -or minimal- liquid discharge strategy has emerged. This alternative for brine management is based on recovery of more than 90% of the freshwater fraction and salts, which can be revalued. Currently, there are some zero liquid discharge desalination plants that incorporate renewables to supply the necessary energy, making desalination a totally sustainable and environmentally-friendly process. Zero liquid discharge desalination plants powered by renewables already exist, although in an immature stage. This paper analyzes and discusses the potential of combining different renewables with the most developed and efficient desalination technologies. In addition, the most important plants and solutions currently installed on a real scale, mostly the result of different research projects, are described and compared.