Ultra-rapid achievement of denitrifying nitrite accumulation using anoxic starvation treatment

Partial denitrification (PD) can stably supply nitrite (NO2–) for Anammox, and their combined processes have sprung up in recent decades. However, behind this prosperity, the existing starting methods still restrict the establishment of PD systems to months. This study proposed a novel PD start-up method, "anoxic starvation treatment", and explored its feasibility and effectiveness. Results showed that denitrifying nitrite accumulation immediately occurred after 5-day starvation, and the nitrate-to-nitrite transformation ratio at 20th min was kept at ∼72 % within the 9-day normal operation. During starvation, it was essential to regularly evaluate the NO2– accumulation potential via assaying denitrifying activity, which helped set the duration of starving treatment. Besides, additional starvation treatment during normal operations could also improve the NO2– accumulation performance by relieving further NO2– reduction. After three operation rounds, the high-throughput sequencing analysis showed that Exiguobacterium became the dominant genus (∼40 %). However, Thauera, the widely recognized candidate for PD, merely shared 3.57 % in relative abundance, raising speculation about whether Thauera is a promoter or beneficiary.