Floc management enables integrated anammox and enhanced biological phosphorus removal for sustainable ultra-efficient nutrient removal

Nutrient removal from wastewater is crucial for global wastewater recycling and sustainable reuse. However, traditional methods for nitrogen and phosphorus removal face limitations in terms of energy consumption, operational complexity and environmental impact. Here we develop a floc management strategy to integrate anammox and enhanced biological phosphorus removal (EBPR) processes in a single-stage hybrid system (biofilms and flocs). This integrated approach resolves the conflicts between anammox and EBPR processes concerning ecological niche and solid retention time, enabling ultraefficient nitrogen and phosphorus removal efficiencies of 97.7 ± 1.3% and 97.4 ± 0.7%, respectively, in low-carbon municipal wastewater treatment. Notably, anammox benefitted from substrate competition with endogenous denitrification (both nitrite and nitrate) with floc loss, resulting in a significant enrichment of anammox bacteria in biofilms (12.5%) under mainstream conditions. Meanwhile, controlling floc concentrations at around 1,000 mg l−1 could maintain low polyphosphate levels in flocs, effectively addressing the additional phosphorus removal burden imposed by the enrichment of phosphorus-accumulating organisms in biofilms. This work offers a transformative solution to the long-standing challenge of integrating anammox and EBPR, paving the way for more sustainable and energy-efficient nutrient removal in wastewater treatment. The enhanced removal of nitrogen and phosphorus is realized by floc management in an integrated system of anammox and enhanced biological phosphorus removal.