Effect of humic acid on the single-stage nitrogen removal using anammox and partial nitritation (SNAP) process: performance and bacterial communities

Abstract

The present research investigated the effect of humic acid on nitrogen removal performance and microbial community structure in a single-stage nitrogen removal using anammox and partial nitrification (SNAP) reactor. The results showed that 576 mg·L−1 humic acid enhanced nitrogen removal efficiency maximally to 96% and nitrogen removal rate to 1.61 kgN·m−3·d−1. COD concentration (provided by humic acid) of 120–233 mg·L−1, the nitrogen removal rate (NRR) was 1.27 kgN·m−3·d−1. COD concentration (provided by humic acid) of 259–658 mg·L−1 enhanced the NRR above 1.5 kgN·m−3·d−1, and COD concentration increased to 691–1637 mg·L−1, the average NRR decreased to 1.45 kgN·m−3·d−1. The results indicated COD concentration of 691–1637 mg·L−1 has the strongest positive effect on the anammox reaction. The analysis of high throughput sequencing presented COD concentration of 500 mg·L−1 promoted the growth of Candidatus_brocadia, and 1500 mg·L−1 COD concentration improved Candidatus kuenenia growth. Functional genes from KEGG and COG database showed that the expressions of nitrate reductase and nitrite reductase were highly promoted with the increase of humic acid concentration, which proved the nitrification enhanced by humic acid. All findings in this study were inferred that humic acid enhanced nitrogen removal in SNAP reactor. This result will improve the practical and effective use of the SNAP process to treat landfill leachate in engineering application.