Microalgae biofilm barrier to assist the simultaneous nitrogen and phosphorus removal in anammox: Molecular mechanism on sludge granulation and microbial metabolism

Nitrate leaching, inefficient phosphorus removal and poor resistance ability to low temperature are main technical bottlenecks in anammox process. In this work, a microalgae biofilm-anammox integrated system was developed to simultaneously remove nitrate and phosphorus at 12 °C. In integrated system, the total nitrogen and phosphorus removal efficiency reached 89.9 % and 94.2 % at 25 °C, increased by 15.7 % and 59.5 % than single anammox system, respectively. Particularly, the integrated system has a higher tolerance to low temperature (12 °C), with total nitrogen and phosphorus removal efficiency (75.8 % and 82.0 %). Furthermore, molecular spectroscopy and rheological tool revealed that microalgae increased the extracellular protein density and sludge mechanical strength, improved the resistance ability of integrated system to low temperature stress. Importantly, microalgae regulated the dominant species of anammox bacteria in anammox at varying temperature. At 25 °C, Candidatus Brocadia (22.97 %) dominated the nitrogen removal, while Candidatus Kuenenia (14.38 %) was dominative at 12 °C. Besides, the gene associated with nitrogen cycle and metabolic hierarchy were also modulated. This work would shed the light on the strategy development of integrating microalgae with anammox system for simultaneously nitrogen and phosphorus removal at low temperature.