Variations of N concentrations and microbial community in the start-up of anammox using anaerobic heterotrophic sludge: Influence of a long reaction-phase time and comparison of the efficiencies of attached-versus suspended-growth cultures

Anaerobic sludge was capable of producing anaerobic ammonium oxidation (anammox) cultures. However, the low activity of anammox bacteria in the seed sludge often led to a long time for stable anammox to initiate. The objective of this study was to investigate the influence of an extended reaction-phase time in the sequencing batch reactor (SBR) on the rapid startup of anaerobic ammonium oxidation (anammox) using anaerobic heterotrophic bacteria as the seed sludge. After the startup, suspended and attached bacteria in anammox were separately analyzed for comparison. The variations of nitrogen concentrations and shifts of the microbial community structures were studied. The results showed that anammox occurred after a long reaction-phase time in the SBR with the efficient removals of NH4+ (96.4%) and NO2- (99.8%). The effective NO2- treatment before anammox startup was attributable to inevitable denitrification or dissimilatory nitrate reduction (e.g., Denitratisoma). The occurrence of anammox was supported by the anammox stoichiometry, bacteria diversity variation, and principal component analysis. The overall nitrogen removal rate (NRR) and nitrogen removal efficiency (NRE) was 0.07 kg/m(3)-d and 92.8%, respectively. The relative molar quantities of NH4+ and NO2- removed as well as N-2 and NO3- formed were 1(1):1.29(1.32):1.45(1.02):0.15(0.26), as the numbers in the parentheses represent the theoretical values. Denitratisoma and Desulfatiglans dominated in the seed sludge, whereas Candidatus_Jettenia abundances were significantly higher in anammox attached-(26.0%) and suspended growth cultures (14.5%). Fifty-three genera were simultaneously identified in all samples, suggesting their importance in the startup of anammox from anaerobic sludge. Candidatus_Jettenia was observed to be more associated with the growth of anammox biofilm (the abundances were 26.0% and 14.5% in attached- and suspended-growth cultures, respectively) and supported the fine nitrogen removal performance in the attached growth cultures.

Automated summary

This study successfully initiated the process of anaerobic ammonium oxidation (anammox) by extending the reaction-phase time in a sequencing batch reactor. High removal efficiencies of NH4+ and NO2- were achieved, and the presence of anammox was supported by stoichiometry, bacterial diversity variation, and principal component analysis.