A comprehensive review on algae removal and control by coagulation-based processes: mechanism, material, and application

The increasing occurrence of harmful algae blooms globally poses significant challenges to water management. In water treatment utilities, coagulation is the first treatment process of the multi-barrier strategy designed to address algae-laden source water. Since the coagulation efficiency directly impacts all downstream treatment processes, it is critical to optimize coagulation conditions to remove algal cells to the extent possible without causing cell damage. Moreover, the importance of coagulation extends to source water management. Coagulation-based processes have demonstrated great potential as in-lake measures to mitigate eutrophication and control algal blooms. This review aims to serve as a holistic resource of coagulation-based techniques for algae removal. Studies focusing on the coagulation removal of algae in source management and treatment mitigation are critically reviewed with emphasis on the following aspects. Introductory sections present the common algae of interest to water management and outline the theoretical background of interfacial phenomena in the coagulation system. Commonly used experimental methods and emerging techniques in coagulation studies are summarized with representative results. In addition, inorganic and organic coagulant materials of synthetic or natural origins and their applications in algae removal are discussed in depth. The latest developments in enhanced algae removal, propelled by electrochemical processes and sonication, are presented with fundamental technical concepts. Furthermore, practical considerations for using coagulation to remove algae in both water treatment facilities and natural waterbodies are discussed in detail with results from pilot- and full-scale studies. Finally, the article concludes by identifying limitations and challenges associated with the current body of literature and proposing directions for future research.