Reject brine management: Denitrification and zero liquid discharge (ZLD)—Current status, challenges and future prospects

Water is at the core of sustainable development. Moreover, it is essential for social, economic, and environmental well-being. However, water resource availability has been significantly threatened in the 21st century. In general, freshwater supplies are being depleted by natural and anthropogenic activities, such as rapid population growth, industrialization, and intensive agriculture. In addition, one of the main causes of water resource shortages is water body contamination. Nitrate pollution is considered one of the most pressing global environmental problems, both in surface and groundwater. The literature reveals that numerous nitrogen removal processes have been developed and proposed. To overcome this problem, desalination is a robust and mature technique for obtaining fresh water from saltwater, and is considered an efficient and reliable process. However, there is growing concern about the adverse environmental impacts generated by brine where concentrated rejection by desalination results in high salinity together with chemical residues. To solve this problem, a zero liquid discharge (ZLD) strategy has been proposed in the specific literature. Furthermore, ZLD can be used to treat and recover valuable resources. This study analyzes and discusses the current status of brine treatment technologies targeting ZLD, highlighting their advantages and disadvantages. Technologies based on membranes and thermal energy were also analyzed, and their performance and operating costs were compared. Finally, the different denitrification processes are listed. This ZLD solution is currently considered an essential and compulsory treatment in reject brine to remove nitrate that, because of high concentrations in the environment, is one of the most widespread global contaminants.