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

A novel strategy integrating sludge enrichment with intermittent gradient aeration has been introduced to achieve partial nitrification (PN) without supplemental organic carbon. Over a 115-day experimental period, the effects of this combined strategy on ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were examined, with the aerobic-to-anoxic ratio optimized to achieve higher ammonia nitrogen removal efficiency. The results indicate that intermittent gradient aeration at various rates (2.0, 1.5, 1.0, and 0.5 Lair/min) during the process reduced NOB activity by 80.29% while maintaining high AOB activity, leading to a nitrite accumulation rate (NAR) of 82.87% within 11 days. During the stabilization phase, the anoxic duration in the intermittent aeration cycle was decreased from 30 to 20 minutes, maintaining a high average NAR of 89.55%. Further shortening the anoxic phase to 5 minutes resulted in a 38.46% increase in ammonia nitrogen removal efficiency while the PN process remained stable. The initial presence of AOB at 0.62% significantly led to Nitrosomonas' relative abundance surged to 22.28% and concurrently, the relative abundance ratio of AOB to NOB escalated from 0.22 to 59.58 by the 112th day. This study presents a novel approach to rapidly and efficiently achieving PN.