The development of facile strategies and techniques to fabricate nanofiltration (NF) membranes with ideal molecular sieving ability has received growing attention in both academia and industry. Chitosan (CS) is deemed to be a promising renewable membrane material. However, the scalable and low-cost fabrication of pure CS membranes is severely limited by their poor solubility in organic solvents. Herein, a simple and effective film casting strategy is presented to prepare a positively charged CS-based NF membrane for effective rejection of dye and salt in textile wastewater. The penetration performance of CS membranes can be elaborately tuned by regulating the casting parameters during the fabrication process. The as-synthesized CS membranes with suitable thickness and tensile strength exhibit considerable water permeance and high rejection rates of up to 94.8% for CaCl 2 and 87.8% for MgSO 4 . Especially, the CS membrane with a molecular size cutoff of 5.015 Å (hydrated radius) shows an ultrahigh rejection rate of >99% to six kinds of conventional dyes in textile wastewater. The long-time evaluation of dye and salt separation demonstrates the superior stability of the CS membrane. This work aims to develop a facile and cost-effective solution to construct CS NF membranes with superhigh filtration capacity for dye and salt removal from actual textile wastewater.
In recent years, membrane technologies have been developed to address water shortage and energy crisis. Forward osmosis (FO), as an emerging membrane-based water treatment technology, employs an extremely concentrated draw solution (DS) to draw water pass through the semi-permeable membrane from a feed solution. DS as a critical material in FO process plays a key role in determining separation performance and energy cost. Most of existing DSs after FO still require a regeneration step making its return to initial state. Therefore, selecting suitable DS with low reverse solute, high flux, and easy regeneration is critical for improving FO energy efficiency. Numerous novel DSs with improved performance and lower regeneration cost have been developed. However, none reviews reported the categories of DS based on the energy used for recovery up to now, leading to the lack of enough awareness of energy consumption in DS regeneration. This review will give a comprehensive overview on the existing DSs based on the types of energy utilized for DS regeneration. DS categories based on different types of energy used for DS recovery, mainly including direct use based, chemical energy based, waste heat based, electric energy based, magnetic field energy based, and solar energy based are proposed. The respective benefits and detriments of the majority of DS are addressed respectively according to the current reported literatures. Finally, future directions of energy applied to DS recovery are also discussed.
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