Comparative evaluation of adsorptive and repulsive separation using cellulose nanofiber/calcium alginate composite hydrogel filtration membranes with improved degradability

Among several approaches to address hard-to-manage dye wastewater, adsorption is one of the widely used methods, but the usage of these adsorbents can be constrained by their high material and process costs depending on the adsorbent materials as well as handling a large amount of adsorbents in a bulk solution. To overcome the problems, hydrogel membranes have recently attracted much attention because they can provide several strengths such as adsorption removal, confined adsorption sites, and filtration separation. However, to the best of our knowledge, it is still quite rare to find an in-depth comparative evaluation of adsorptive removal and repulsive separation in hydrogel membrane filtration. Herein, this study aims to bridge the gap between existing knowledge and undisclosed phenomena. Through a thorough comparative evaluation of adsorptive removal and repulsive separation in hydrogel membrane filtration, we found that repulsive separation was more suitable and sustainable than adsorptive removal because it was free from internal membrane fouling, adsorption sites’ saturation, and the cake layer formation on the surface. As a result, the hydrogel membranes could maintain excellent real-time separation performance while mitigating severe flux and rejection decline. Furthermore, we significantly improved the degradability of the spent hydrogel membrane under high saline conditions by 6.3 times compared to the control membrane by fine-tuning the structural properties via dual crosslinking, while maintaining the mechanical properties during filtration. It was possible due to the extended distance between polymer chains by dual crosslinking, reducing the burden imposed by plastic waste generated from the spent membrane.