Multifaceted role of Mg in mitigating cold stress during digestate treatment via anammox-induced magnesium phosphate mineralization.

Anaerobic ammonium oxidation (anammox)-induced magnesium phosphate (MP) mineralization offers a sustainable strategy for simultaneous nitrogen removal and phosphorus recovery from wastewater. This study demonstrates that Mg's introduction not only supplied substrate for MP bio-mineralization, but also mitigated cold stress on nitrogen removal by improving energy metabolism and electron transfer efficiency. At about 13.4 °C, Mg addition significantly enhanced nitrogen removal efficiency of reactor by 23 % versus Mg-free operation. Mg further promoted extracellular protein secretion (15-21 %) and hydrophobic domain exposure in extracellular polymeric substances, synergizing with MP crystals to enhance granular aggregation. In anammox consortia, 73 % interactions exhibit positive synergistic relationships, forming an efficient nitrogen removal system primarily driven by direct anammox bacteria-denitrifiers cooperation, while heterotrophic bacteria amplified efficacy through indirect metabolic facilitation. Moreover, the bio-induced MP process showed reliable low-temperature adaptability. This work clarifies Mg's multifunctional role underpinning low-temperature resilience, and provides theoretical foundations for all-weather operation of anammox-MP system.