Enrichment of DNRA bacteria: Shift of microbial community and its combination with anammox to promote TN removal

Abstract

Both anammox and dissimilatory nitrate reduction to ammonium (DNRA) are important processes of nitrogen metabolism, coexisting in a variety of natural ecosystems. However, the combined nitrogen removal of DNRA bacteria and anammox bacteria has not been achieved under laboratory conditions. Here, an anammox coupled DNRA system was constructed, in which DNRA bacteria convert nitrate generated from anammox process to ammonia for anammox metabolism again. DNRA bacteria were enriched form 2.11 * 105 to 3.02 * 107 copies/ng DNA in a non-woven fabric membrane bioreactor under a high C/N ratio environment. After 137 days’ operation, ammonia production efficiency from nitrate reached 60.65%. By nrfA gene sequencing analysis, Geobacter, some strains of Desulfovibrio and Desulfobulbus and a strain of traditional denitrifying bacteria Thauera sp. MZIT exhibiting DNRA function accounted for 20% of all bacteria. Small amount of anammox bacteria were detected from the system through qPCR tests, indicating that this system can mimic the natural habitats where anammox and DNRA together contributed to enhancement of total nitrogen removal rates. This study illustrated that DNRA bacteria could be enriched at high C/N ratio and natural processes are reproducible through engineering precise control.