Unravelling the importance of Ca 2+ and Mg 2+ as essential in anammox culture medium.

The mechanism and nitrogen removal performance of anammox process under different concentrations of Ca ²⁺ and Mg ²⁺ 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 Ca ²⁺ and 30 mg/L Mg ²⁺ achieved a higher anammox performance with an average total nitrogen (TN) removal efficiency of 85.8%. Under the Mg ²⁺ concentration of 30 mg/L, a higher Ca ²⁺ could accelerate anammox process by promoting the amplification of Candidatus Brocadia (0.62%) and production of Diguanylate cyclase (DGC-s: 6.54 × 10 ⁸ copies/μL DNA) which function was to synthesize c-di-GMP. While under the Ca ²⁺ concentration of 49 mg/L, Mg ²⁺ concentration at appropriate rang could promote the degradation process of c-di-GMP. Since Ca ²⁺ had positive linear relationship with TN removal (R ²  = 0.96), a higher Ca ²⁺ concentration is recommended in the culture medium. This study provided a potential method for optimization of anammox process.
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