Inorganic salts in sub-/supercritical water—Part A: Behavior characteristics and mechanisms

Conventional physical, biochemical, and incineration treatments of hypersaline organic wastewater have some major drawbacks, such as the incomplete removal of organic matter, severe secondary pollution, increased salinity, or massive salt-out problems. Supercritical water oxidation (SCWO) is an advanced oxidation technology for treating organic wastewater, which has been in development for decades; however, a new technology that combines SCWO with supercritical water desalination (SCWD) has been proposed, which is uniquely advantageous for treating hypersaline and refractory organic wastewater because it causes no secondary pollution and exhibits a high removal rate, fast reaction speed, and effective desalination. To further improve this new combination method, the behavior characteristics and mechanisms of inorganic salts in sub-/supercritical water require significant attention. In this review, the authors evaluate the conventional technologies for treating wastewater, introduce the research and development of SCWO and SCWD processes, and then emphatically analyze the behavior and mechanisms of inorganic salts in sub-/supercritical water, such as their phase equilibrium, dissolution, crystallization, and deposition. Finally, the contents, methods, conclusions, and shortcomings of previous studies are systematically and objectively summarized, and a preliminary theory of salt behavior and future research topics are proposed.