Deciphering the short-term deactivation mechanism of the anammox performance under calcium stress

[Display omitted] •The effect of high-concentration calcium on anammox performance was investigated.•The relative abundance of the microbe was not the key reason for nitrogen removal.•Calcite was the main form of calcium precipitates in the granules.•The short-term inhibition of the bioactivity could be regained at 2000 mgCa2+/L. High-concentration calcium was contained in some wastewater, e.g., leachate. In this study, the response of the anammox performance to calcium (∼2000 mg/L) and the potential mechanisms were investigated in the serum bottles. 5 runs were conducted and 12 bottles were operated in each run, i.e., B1-3 (control), B4-6 (100 mg/L Ca2+), B7-9 (500 mg/L Ca2+) and B10-12 (2000 mg/L Ca2+). The dominant genus Ca. Kuenenia decreased from 19.3% to 3.8% with the increase of the calcium concentration in the bulk according to the taxonomy analysis. However, the specific anammox activity (SAA) only decreased from 5.8 ± 0.1 to 0.9 ± 0.02 mgN/(gVSS·h) in Run 1 when the calcium dosage was 2000 mg/L. Specifically, the SAA was only 16.1% that of the control in Run 1, however, the inhibition was reversible and the SAA regained to 73.2% that of the control in Run 5. Meanwhile, the porosity decreased from 82.4% to 69.9% at 2000 mg/L Ca2+. Calcium content in the granules with 2000 mg/L Ca2+was 7.8 times that of the control after Run 5. Therefore, the calcium precipitates blocking the granular pores was deduced to be responsible for the decline of the SAA.