A hydro-topological strategy enables self-regulating biofilms for sustainable wastewater treatment

The moving bed biofilm reactor (MBBR) is a cornerstone technology in modern wastewater treatment, yet its performance is often hindered by carrier clogging, which significantly reduces overall treatment efficiency and undermines the technology's environmental benefits. Here, we introduce a V-carrier hydro-topological design strategy that enables biofilm self-regulation, allowing simultaneous control of biofilm thickness and continuous hydraulic shear-induced self-cleaning. In a pure biofilm system treating real municipal wastewater for over 500 days, the V-carrier achieves stable and efficient nutrient removal even under low-temperature (9.1 °C) and high-loading conditions. Crucially, it achieves a 3.2-fold higher unit biomass nitrification rate with a biofilm biomass 44% lower than a conventional K3 carrier, demonstrating that treatment efficiency is decoupled from biomass quantity through optimal ecological niche design. This work establishes a paradigm for biofilm reactor design, transforming carriers from passive substrates into active regulators of microbial ecosystems, with profound implications for sustainable water infrastructure.