Molecular Based Characterization of the Microbial Ecology and Activity of Anammox Bioreactors

Anaerobic ammonium oxidation (anammox) is the biological oxidation of ammonia using nitrite as an electron acceptor to produce dinitrogen gas. Anammox requires 60% less oxygen and no external organic carbon compared to conventional biological nitrogen removal (BNR). Despite these significant advantages, full-scale installations of anammox are uncommon primarily owing to the lack of well established process monitoring and control strategies that result in stable anammox reactor performance. The primary aim of this study was to determine the impact of long term operation with actual anaerobic digestion centrate from a full-scale operational wastewater treatment facility on the community diversity of an anammox bioreactor. A secondary aim was to develop and apply molecular biomarkers based on structural and functional genes to permit inference of anammox population activity. Over long-term operation, bacteria related to C. Brocadia sp. 40 were consistently the dominant anammox bacteria present in the anammox reactor. There was also a marked shift in biomass morphology from discrete cells to granular clusters. This morphological shift was paralleled by a shift also to more stable nitrogen removal performance in general and the succession and establishment of bacteria related to the Chlorobi-Bacteroidetes superfamily. There was good correspondence between anammox reactor nitrogen removal performance and anammox bacterial concentrations. Biomarkers for anammox activity based on structural (16S-23S rRNA intergenic spacer region, ISR) and functional (hydrazine oxygenasehzo) genes were developed and compared. Based on responses to exposure to oxygen and nitrite mediated inhibition and correlation with nitrogen removal performancehzo expression was a more sensitive indicator of anammox activity than ISR.