The recovery of alginate-like extracellular polymer (ALE) from municipal sludge is a highly anticipated approach for addressing resource and climate crises, achieving sustainable development, and transforming water-resource factories. This review begins with the recovery of ALE from sludge and analyzes the current status of ALE-recovery research. The goal of ALE recovery is product-centered, and the approach considers the entire recovery chain. For the first time, this study presents a timeline of ALE research and clarifies the sequence of events in this research. Two aspects of a series of critical issues in ALE recycling are discussed: the value-added benefit of ALE recycling and its external influence. Different types of sludge and extraction methods are among the many key factors in a sewage-treatment plant that affect the recovery rate of ALE. We believe that introducing ALE recovery into the sludge-treatment process will have a series of external effects (such as changes in the properties of the treated sludge) that will affect further treatment. In addition, the environmental and economic sustainability of ALE recovery still requires further analysis, and the environmental risks due to the presence of pollutants in products that utilize ALE need to be investigated further. Herein, we summarize the current status of research regarding ALE recovery, which is expected to provide useful reference information for the large-scale recovery of ALE anticipated in the future.
