Acidophilic partial nitrification rapid startup and robustness validation for municipal wastewater treatment:...

Acidophilic partial nitrification (a-PN) is a promising short-flow nitrogen conversion biotechnology, but achieving a rapid startup remains a significant challenge. This study explored strategies for starting up a-PN in real municipal wastewater treatment using sequencing batch reactors (SBRs). The influent alkalinity-to-NH₄⁺ molar ratio was maintained at 0.5-0.6 in the control reactor (SBRa), while other reactors were supplemented with sodium formate (150 mg COD/L, SBRb), hydroxylamine (5 mg/L, SBRc), and sludge alkaline fermentation liquid (NH₄⁺-N=227.97±7.08 mg/L, COD=2463.98±125.17 mg/L, SBRd). Results indicated that the system using the composite strategy with sodium formate addition achieved a 93.7 % nitrite accumulation ratio (NAR) within just 4 days. Furthermore, stable a-PN performance was maintained in the systems without external substrate addition with pH ranging from 5.7 to 7.4. The established a-PN systems demonstrated robust performance, maintained a high NAR of 92.84 %-98.84 %, even under the intense impact of traditional nitrification biomass for 13 consecutive days. Although the relative abundances of Nitrosomonas and Nitrospira temporarily increased, traditional ammonia oxidizing bacteria and nitrite oxidizing bacteria were completely eliminated, falling to undetectable levels after long-term operation. Notably, amo and hao genes exhibited opposite trends: amo decreased significantly from 356 reads to 22-46 reads, while hao substantially increased by 186.6 %-613.1 %, from 626 reads to 1168-2838 reads. This suggests that hao may play a more crucial functional role in the a-PN process, and unidentified nitrifying communities may be driving acidophilic partial nitrification. Overall, our study advances the understanding of rapid startup strategies of a-PN and provides novel perspectives on the microbial structure and functional genes involved in a-PN system.