The effect of magnetite on the start-up and N2O emission reduction of the anammox process
In order to observe the effect of magnetite during anammox start-up and stabilization stages, a novel up-flow anaerobic sludge blanket reactor using magnetite as a functional bio-carrier was designed and operated. Continuous experiments indicated that magnetite could shorten the endogenous denitrification stage and improve the nitrogen removal rate. The nitrogen removal performance increased from −0.06 to 1.17 kg N per m3 per d of R1 and from −0.08 to 1.18 kg N per m3 per d of R0 (as control reactor) on day 150. Analysis of variance (ANOVA) results of NRR during days 90–150 showed that R1 was statistically different from R0 (p = 0.045 < 0.05). The corresponding quantitative polymerase chain reaction results of nirS and nirK, fluorescence in situ hybridization results and Illumina MiSeq sequencing showed that proliferation of the anammox bacteria was promoted by magnetite with an increase of the nitrogen loading rate. The reduced N2O emission (25.06 ± 15.27 μmol L−1) combined with the reduced nosZ qPCR results (2.26 ± 0.029 × 106 copies per ng) revealed that this magnetite–anammox reactor also can serve as an ideal alternative for N2O emission reduction in ammonium-rich wastewater treatment.