Unravelling the importance of Ca2+ and Mg2+ as essential in anammox culture medium.

Abstract The mechanism and nitrogen removal performance of anammox process under different concentrations of Ca2+ and Mg2+ were explored from the perspective of molecular biology analysis based on the metabolic changes of the second messenger cyclic diguanylate (c-di-GMP). After 100-day operation, reactor with 98 mg/L Ca2+ and 30 mg/L Mg2+ achieved a higher anammox performance with an average total nitrogen (TN) removal efficiency of 85.8%. Under the Mg2+concentration of 30 mg/L, a higher Ca2+ could accelerate anammox process by promoting the amplification of Candidatus Brocadia (0.62%) and production of Diguanylate cyclase (DGC-s: 6.54 × 108 copies/μL DNA) which function was to synthesize c-di-GMP. While under the Ca2+concentration of 49 mg/L, Mg2+ concentration at appropriate rang could promote the degradation process of c-di-GMP. Since Ca2+ had positive linear relationship with TN removal (R2 = 0.96), a higher Ca2+ concentration is recommended in the culture medium. This study provided a potential method for optimization of anammox process.