Selective separation membranes for fractionating organics and salts for industrial wastewater treatment: Design strategies and process assessment

Inorganic salts are generated in nearly all chemical and allied industrial manufacturing processes; however, most existing wastewater treatment technologies and environmental discharge policies place limited attention on salt management. Although the concept of "complete treatment" has been applied in industry for decades, the presence of salts (especially at high salinity) in wastewater strongly affects the efficiency of conventional approaches, such as advanced oxidation processes, electrochemical/biological treatments, and advanced treatments. Thus, the minimal and zero liquid discharge requirements are challenging to satisfy. Membrane technology may potentially solve this issue owing to its controllable separation precision; however, the development of a unique membrane that can fractionate multiple components (i.e., chemical oxygen demand and salts) in wastewater is still in its infancy. This perspective article aimed to identify a particular membrane type that may potentially simplify the complexity of industrial wastewaters. On the basis of an enhanced understanding of membrane selectivity, the main parameters of a selective separation membrane (SSM) that allows effective differentiation of various solute transport behaviors are discussed herein. Furthermore, a rational membrane integration method based on the recent advances pertaining to new membrane materials is suggested to elucidate the mechanism of membrane processes and determine the separation efficiency limit. Notably, an optimal cleaning strategy is proposed for alleviating the membrane fouling propensity while maximizing its performance regeneration capacity. Overall, we present the main principles and guidelines for designing next-generation SSMs and describe an integrated process for the resource reclamation of industrial wastewaters.