Shifting paradigms in phosphorus recovery: A comprehensive review from activated sludge to biofilm

As a primary pathway for mitigating the global phosphorus pollution crisis, widely used conventional activated sludge phosphorus recovery processes in municipal wastewater treatment plants (WWTPs) are facing increasing challenges due to continuously declining influent carbon and phosphorus concentrations. This review systematically compares activated sludge processes with emerging biofilm processes, highlighting a conceptual shift from the biomass growth driven enhanced biological phosphorus removal theory to the novel DAM theory centered on microbial metabolism in biofilms. The DAM theory conceptualizes the biofilm as a reusable, tunable phosphorus reservoir, where periodic accumulation in biofilms promotes liquid phase recovery even under low carbon source conditions. In terms of mechanism, extracellular polymeric substances are examined for their roles in phosphorus transfer, storage, and transformation. Microbial interactions are analyzed, with particular emphasis on the functional roles of glycogen-accumulating organisms in different processes and their implications for system stability. Ultimately, this review proposes a novel phosphorus recovery paradigm based on biofilm processes to circumvent the operational bottlenecks associated with insufficient influent carbon in WWTPs, providing a theoretical framework and technical guidance for sustainable nutrient management.