Desorption Strategies and Reusability of Biopolymeric Adsorbents and Semisynthetic Derivatives in Hydrogel and Hydrogel Composites Used in Adsorption Processes

Adsorption is a promising technique for the removal of persistent contaminants, since it is a relatively cheap process with low energy requirements and does not produce secondary contamination. However, the large-scale implementation of an adsorption process usually involves a dual column process for either pressure swing or temperature swing operations. Therefore, the reusability of adsorbents is a key characteristic to consider and evaluate but is often overlooked during the development of new materials. To be reused, the adsorbent should successfully release the contaminant by a desorption or regeneration step without compromising the chemical and physical stability of the matrix. The efficiency of desorption/regeneration methods depends greatly on the chemical characteristics of the contaminants, the nature of the adsorbents, and the adsorption mechanisms responsible for the adsorbent–adsorbate interactions. This review focuses on the desorption strategies that have been used for the regeneration of biobased hydrogels and hydrogel composites, materials that have been successfully applied in the adsorption of wastewater contaminants. The strategies can be divided into chemical and physical methods. The chemical methods include the use of desorption agents, photocatalytic oxidation, and CO₂ bubbling; and the physical methods include thermal and ultrasonic treatments. These regeneration strategies have shown different efficiencies as well as specific advantages and drawbacks that need to be considered to select the most suitable method for a specific application.