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 m(3) per d of R1 and from -0.08 to 1.18 kg N per m(3) 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 mu mol L-1) combined with the reduced nosZ qPCR results (2.26 +/- 0.029 x 10(6) copies per ng) revealed that this magnetitea-nammox reactor also can serve as an ideal alternative for N2O emission reduction in ammonium-rich wastewater treatment.