Feasibility of double nitrite supply through partial nitrification and partial denitrification driven by sludge fermentation.

Challenges in obtaining stable nitrite have impeded the use of anammox in municipal wastewater treatment. This study explored the feasibility of using sludge fermentation products as carbon source and selective nitrification inhibitor to supply nitrite via partial nitrification (PN) and partial denitrification (PD). PD was initiated within 15 days, achieving nitrite transformation rate of over 90 % with a carbon/nitrogen ratio of 3 and a reaction time of 0.75 h. The dominant genus, Romboutsia, increased in relative abundance from 4.1 to 35 %. Organic acids in sludge fermentation products, like acetate (200 mg/L) and propionate (400 mg/L), selectively suppressed nitrite-oxidizing bacteria (NOB) more than ammonia-oxidizing bacteria (AOB), leading to PN. Combining anaerobic exposure with sludge fermentation products addition achieved PN with over 80.0 % nitrite accumulation. AOB increased tenfold in the long term, significantly outpacing NOB growth. This strategy simplifies difficulty of anammox application and shows broad application potential in municipal wastewater treatment.