A review of alginate-like extracellular polymers from excess sludge: Extraction, characterization, and potential application

Long-term operation of wastewater treatment plants results in the production of a large amount of sewage sludge whose disposal is a critical problem. The excess sludge from both conventional activated sludge and aerobic granular sludge contains a high concentration of extracellular polymeric substances, which contributes to the granular sludge formation and dehydration process. ALEs, characterized by their exceptional gel-forming attributes, are classified as a form of structural extracellular polymeric substances, and gained more attention, then the other extractions, such as sulfated polysaccharides, hyaluronic acid-like polymers, sulfated glycosaminoglycans-like polymers, and amyloid-like proteins. Furthermore, ALEs hold potential for recycling as versatile biomaterials, finding utility across various domains, including coating materials, adsorbents, flame retardants, slow-release materials, and seed coatings. This study discusses the extraction method, primary structure, and potential application scenarios of ALE that is a high value-added biomaterial in EPSs. Efficient extraction and application of ALEs are expected to lead to a marked change in wastewater treatment plants, thereby contributing to the development of a sustainable and circular economy.