Strategy for Rapid and Stable Operation of Nitritation Using Formic Acid As a Selective Inhibitor

The effectiveness of formic acid on partial nitrification in sequence batch reactor (SBR) is studied. In addition, the mechanism for achieving and maintaining stable partial nitrification by formic acid is also analyzed. The results of the long-term effect of formic acid on partial nitrification showed that when formic acid was not added, the effluent was primarily nitrate. After adding formic acid for 1 week, the partial nitrification operated stably, and the average ammonia conversion rate and nitrite accumulation rates were 99.25% and 89.41%, respectively, while the yield of nitrite was only 46.22%. After stopping formic acid dosing, the partial nitrification was maintained for ∼20 days, and during this period, the nitrite yield increased to 85.89%. The high-throughput analysis of the activated sludge samples showed that the ammonia oxidizing bacteria (AOB) Nitrosomonas and Sphingomonas only presented in the formic acid system. The denitrifiers Acidovorax, Bacillus, Comamonas, Flavobacterium, Lactococcus, Paracoccus, Terrimonas, and Thauera enriched when the formic acid was added. The long-term effect of formic acid on partial nitrification was consistent with the results of the molecular operating environment simulation analysis and the high-throughput sequencing analysis. Therefore, formic acid was considered to be responsible for the partial nitrification process in this study. By measuring the oxygen uptake rate, the activities of AOB and nitrite oxidizing bacteria (NOB) were analyzed, and the results indicated that formic acid dosing promoted AOB activity more than inhibiting NOB.