Nitrogen removal enhancement through competitive inhibition of nitrite oxidizing bacteria in mainstream partial nitritation/anammox: Anammox seeding and influent C/N ratios

Abstract

Mainstream partial nitritation/anaerobic ammonium oxidation (annamox) (PN/A) has received a lot of attention, but stable nitrite oxidizing bacteria (NOB) inhibition remains a key challenge. This study investigated the main parameters affecting the competitive inhibition of NOB. For stable nitrogen removal in single-stage PN/A, the addition of organic matter and anammox seeding ratio were considered as major variables. By increasing the influent C/N ratio to 3.0, the nitrogen removal efficiency (NRE) improved from 63.4 ± 1.5% to 71.4 ± 2.7%. In addition, increasing the anammox seeding ratio to 37.2% further stabilized PN/A-based nitrogen removal, resulting in an increase of NRE to 81.4 ± 4.2%. In batch experiments, the effects of these two variables on the nitrogen conversion pathway were investigated in depth. In mainstream PN/A, the addition of organic matter selectively deteriorated NOB in competition for oxygen with aerobic heterotrophic bacteria. In addition, at a C/N ratio greater than 1.5, the effect was more pronounced. The anammox seeding ratio is a major variable in nitrite competition with NOB. An increase in this ratio exacerbated the role of NOB in the nitrogen conversion pathway. These results indicate that in depth insights into microorganisms competing with NOB in various nitrogen conversion pathways may be key parameters for achieving stable nitrogen removal from mainstream flows.