Weak magnetic field stimulated nitrite oxidizing bacteria and destroyed the SNAD process

Abstract Simultaneous partial nitrification, anammox and denitrification (SNAD) process was successfully constructed in a fixed bed reactor. The ammonium and TN removal efficiencies exceeded 90% under the collaboration of ammonium oxidizing bacteria (AOB), anammox and denitrifying bacteria (DNB). However, the well cooperation was interrupted after introducing the weak MF of 3.5 mT, which was reflected directly by the increased nitrite oxidizing bacteria (NOB) activity and decreased AOB, anammox and DNB activities calculated via mass balance. Moreover, drastic microbial community structure changes induced by weak MF were observed. The dominant phylum changed from Proteobacteria (25.6%) to Deferribacteres (35.2%). The weak MF suppressed the growth of AOB (genus Nitrosomanas), anammox (genus Candidatus Brocadia and clone Anammox) and DNB (genus Denitratisoma) while promoted the enrichment of NOB (genus Nitrospira). Moreover, the weakened NH3-NH2OH, NO-N2O and N2O-N2 pathways might explain the deterioration of SNAD process caused by weak MF.