Differentiation of performance and functional bacteria of anammox processes with different anammox sludge impaired by low temperature

In order to study the differentiation of performance and functional bacteria of anaerobic ammonium oxidation (anammox) processes inoculated with different anammox sludge impaired by low temperature, two upflow anaerobic sludge bed reactors were constructed to treat synthetic nitrogen-contained wastewater. Experimental results showed that anammox sludge exposed to lower room temperature of 0-15 C for nearly 1 month recovered anammox activity on Day 1 without sludge lysis, and the total nitrogen removal rate (TNRR) gradually increased from 3.23 to 13.41 kg m(-3) d(-1). Stover-Kincannon model predicted a maximum nitrogen removal potential (U-max) of 177.62 kg m(-3) d(-1). However, anammox sludge exposed to - 20 C environment for nearly 30 days experienced three stages of sludge lysis (Days 1-2), sludge lag (Days 3-7) and propagation stage (Days 8-77). Due to the activity loss and FA inhibition, the maximum TNRR of 4.04 kg m(-3) d(-1) and a predicted U-max of 8.51 kg m(-3) d(-1) were observed after 77 days' operation. After long-term operation (291 d), the dominant functional bacteria and genes were changed; even two reactors had similar operation performance. Anammox genus Candidatus Jettenia had the maximum RA values of 16.01% with higher nitrogen removal-related genes nirB/K/S, hdh and hzo in reactor feeding sludge exposed to 0-15 C, but Candidatus Brocadia was dominant with higher hzs gene in reactor inoculating sludge suffering from - 20 C environment. This work would be helpful to restart the anammox reactor with seeding sludge after long-term storage of anammox sludge under lower temperature conditions. Graphic abstract