Advancements in the Remediation of Black-Odorous Urban Waters in China: Mechanisms, Technologies, and a Representative Case Analysis

Black-odorous urban waters are a major obstacle to improving China’s urban aquatic ecology and living environment. This review of domestic research and practices summarizes the spatial distribution, pollution characteristics, and governance status of these waters. Blackening mainly arises from metal sulfides (FeS, MnS) and colored dissolved organic matter (CDOM), while odors come from algal metabolites (2-MIB, mercaptans), sulfur compounds (H2S, VOSCs), and nitrogen compounds (ammonia, amines). At the molecular level, a “substance–pathway–effect” chain shows that metal sulfide precipitation under anaerobic conditions (DO < 0.2 mg/L, ORP < −200 mV) dominates in sewage-dominated urban waters, whereas CDOM-driven optical darkening is more prominent in eutrophic urban lakes. The review also compares physical, chemical, and biological–ecological restoration methods in pollutant removal, cost, and long-term stability. Although remediation coverage and phased progress are increasing, source control and interception remain incomplete, technical adaptability is insufficient, and operation and maintenance systems are inadequate. Future efforts should focus on precise source tracing, ecological priority, intelligent control, and regular maintenance, shifting from eliminating black-odorous waters to restoring ecology.