Making waves: Towards sustainability in wastewater management through the biological-ecological coupling system

The increasing complexity of municipal wastewater, driven by emerging contaminants, together with rising energy demand and growing water scarcity, is challenging the sustainability of conventional wastewater treatment systems. Traditional biological processes often exhibit limited removal efficiency for complex pollutants, high energy consumption, and insufficient recovery of carbon and nutrients, constraining their role in a circular water economy. And although ecological purification processes can effectively enhance pollutant attenuation through the synergistic action of plants, microorganisms, and functional substrates, their standalone application remains limited under high pollutant loads. In this context, biological-ecological coupling systems, which integrate engineered biological treatment with ecological purification processes, have emerged as a promising pathway toward the "One Water" vision and sustainable water cycle management. By redistributing treatment functions along the ecological gradient, these systems can enhance pollutant removal robustness, improve nutrient transformation stability, reduce energy and carbon footprints, and enable resource recovery through biomass utilization. Despite these advantages, their wider implementation remains limited by key challenges, including large land requirements and environmental sensitivity of ecological units, incomplete mechanistic understanding of coupled processes, inefficient biomass valorization pathways, and insufficient quantification of ecosystem service benefits. Addressing these issues requires clarifying material and energy flows, developing compact and resilient system designs, advancing resource recovery strategies, and integrating ecological service assessment into performance evaluation frameworks. This work provides a systematic perspective on the development, challenges, and future directions of biological-ecological coupling systems, aiming to support their transition from demonstration projects to scalable solutions for sustainable wastewater management.