Nitrogen degradation performance and microbial dynamic analysis for the efficient combination of partial denitrification and anammox (PD/A) process

Abstract

The coupling partial denitrification and anammox (PD/A) is a promising technology for deep-level nitrogen removal, and the quickly effective startup remains a huge challenge in real application. In this study, the stability of nitrite (NO2--N) accumulation was investigated in the PD sequential batch reactor (PSBR), and the nitrogen removal performance in response to nitrogen loading rate (NLR) was compared in another independent anammox SBR (ASBR), where the combined PD/A operation was subsequently carried out based on the optimal operating conditions. In the PSBR, nitrate removal efficiency (NRE) maintained around 89–90% with a mean nitrate-to-nitrite transformation ratio (NTR) of 84.43%, and the total proportion of functional bacteria (e.g., Terrimonas, norank_f_A4b, Ellin6067, Defluviicoccus, etc) accounted for 40.98% after long-term acclimation. In the ASBR, increased NLR (0.22 → 0.70 kgN/(m3·d)) depressed the anammox activity owing to the sludge disintegration and adverse nitrogen contribution, however, the dominant Candidatus_Brocadia enriched from 0.50% to 2.05% and realized the efficient retention of functional bacteria, which also laid a good foundation for the rapid startup of PD/A process. As NLR controlled around 0.18 - 0.25 kgN/(m3·d), the total nitrogen removal (ReTN) climbed from 33.88% to 98% with anammox contribution soaring up to 65%, since the higher tight-bound extracellular polymeric substances (T-EPS) production and protein/polysaccharide (PN/PS) ratio accelerated the re-formation of anammox granular sludge. In the end, the potential significances and challenges of PD/A process were further summarized for the mainstream wastewater treatment.