Valorization of seafood waste into chitosan for sustainable wastewater treatment: Extraction, functionalization, and process applications.

Wastewater generated from industrial and marine activities is considered one of the most pressing global environmental challenges due to the presence of hazardous contaminants, including heavy metals, organic pollutants (such as dyes, phenolic compounds, and pharmaceuticals), and oil-in-water emulsions. At the same time, marine industries generate substantial amounts of crustacean waste that can harm the environment when improperly disposed of. From this valuable marine waste, chitosan, the second most abundant biopolymer after cellulose, can be chemically extracted from crustacean shells such as shrimp, fish, lobster, crab, krill, and squid. The term "extracted, environmentally friendly chitosan" refers to chitosan obtained from marine waste via chemical extraction, which is the primary focus of this review. The biomass-derived chitosan can become a source of several applications, including wastewater treatment, specifically oil-in-water separation, heavy-metal removal, organic contaminant adsorption, and desalination. This review covers marine sources of chitosan, chemical extraction methods, and the application of marine-derived chitosan-based materials in wastewater treatment. Focusing on research published from 2020 to 2025, this review examines marine-derived chitosan-based materials, adsorbents, membranes, and hydrogels, and highlights their application in water treatment. This review not only promotes cleaner water technologies but also fosters the transition towards sustainable valorization of marine waste through chitosan. Overall, this review highlights the significant potential of marine-derived chitosan-based materials as sustainable and efficient solutions for advanced wastewater treatment and marine waste valorization.