Sludge enrichment and intermittent gradient aeration: Modulating microbial communities for start-up of partial nitrification in a sequencing batch reactor (SBR).

A novel approach has been proposed integrating sludge enrichment with intermittent gradient aeration to achieve partial nitrification (PN). Results indicated that this method suppressed nitrite-oxidizing bacteria (NOB) activity while maintained ammonia-oxidizing bacteria (AOB) activity, achieving an 82.87 % nitrite accumulation rate (NAR) during startup. During stable operation, specific ammonia oxidation rate and specific nitrite oxidation rate reached 18.44 and 2.67 mg N/g MLVSS/h, respectively. Shortening anoxic time from 30 to 20 min enhanced ammonia removal efficiency by 12.5 %, increasing NAR to 89.55 %. Further reduction to 5 min yielded 38.46 % and 91.88 %, respectively. AOB abundance enriched from 0.62 % to 22.28 %, with the AOB-to-NOB ratio jumping from 0.22 to 59.58. This research presented a rapid and effective strategy for achieving PN.