Biofilm ecology in wastewater treatment systems: From microscale ecological insights to macroscale process optimization

Biofilm-based processes are promising for advanced biological wastewater treatment, yet their optimization remains largely empirical due to the critical gap between ecological insights and reliable practical applications. This review addresses the critical gap by systematically exploring biofilm ecology and establishing a causal framework from microscale ecological principles to macroscale process optimization in biofilm-based processes. First, the fundamental ecological principles governing biofilm function and stability are elucidated to lay the theoretical basis for understanding biofilm ecology, emphasizing the roles of biodiversity, microbial interactions and community assembly in shaping functionality and stability of biofilm ecosystems. Second, the ecological causes of core engineering bottlenecks (e.g., long startup period, unstable long-term operation and performance deterioration under environment stress) are uncovered based on spatiotemporal heterogeneity and stress adaptation mechanism, which establishes the causal framework linking microscale ecological principles to macroscale reactor performance. Based on ecological principles and potential ecological causes, some mechanism-driven regulation strategies and advanced technologies supporting these regulation strategies are discussed. Finally, we discuss the challenges lie in translating ecological insights into practical applications, and propose the development of “biofilm digital twins” to simulate, predict and optimize the real bioreactor performance. This innovative framework facilitates the future shift from one-size-fits-all design protocols to adaptive ecology-inspired regulation strategies, paving the way for next-generation biofilm engineering.