Stability of Nitritation Combined with Limited Filamentous Bulking Under Intermittent Aeration

Abstract

Limited filamentous bulking (LFB) combined with nitritation under low dissolved oxygen (DO) is a new technology for enhancing nitrogen removal and reducing aeration requirements. In order to investigate the feasibility and sustainability of this technology, two sequence batch reactors (SBRs) were operated under different regimes to stimulate different aeration modes under low DO (0.3-0.8 mg·L-1). Sludge settleability, nitrite accumulation ratio (NAR), total nitrogen (TN) removal rate, dynamic variation of dominant filaments, and nitrifying bacterial communities were investigated. The results indicated that short-cut nitrification combined with LFB could be achieved under intermittent aeration, and the ratio of anoxic/aerobic was 15 min/30 min, the value of sludge volume index (SVI) was maintained from 170 mL·g-1 to 200 mL·g-1. An NAR above 95% was achieved under real-time continuous aeration. Meanwhile, LFB was induced when nitrite started to accumulate, and the dominant filament was Type 0092. However, the limited bulking was not maintained for the long term. After a transfer from continuous aeration to intermittent aeration, LFB reappeared in 60 days and the value of SVI remained between 170 mL·g-1 and 200 mL·g-1. The process of nitritation combined with LFB was maintained stably for the next two months, and the TN removal rate was above 66%. FISH analysis indicated that the identical dominant filaments were M. parvicella and Type 0092 for maintaining limited bulking in the two reactors. qPCR results showed that proportion of AOB in the total bacteria increased from the previous 0.53% to 2.19% in the end, whereas that of NOB decreased from 17.5% to 3.2% in SBR A. Moreover, the proportion of AOB increased from 0.51% to 1.53%, whereas that of NOB decreased from 18.05% to 11.01% in SBR B.