Study of the dynamics and material transformation characteristics of nitrite denitrification in UASB

Nitrite is known to accumulate in wastewater treatment plants and play an important role during the biological denitrogenation process. In this study, wastewater with high nitrite concentration was effectively treated, and the possible material transformation of nitrite and carbon by microorganisms is discussed herein. While inoculating pre-acclimatized floccular sludge, nitrite-denitrifying granular sludge was obtained after approximately 15 days of cultivation in a denitrifying upflow anaerobic sludge blanket (UASB) reactor. The nitrite removal efficiency (R-NO2-N (%)) was always greater than 98%. At the same time, the nitrite removal rate (R-NO2-N (%)) reached 0.46 g N g VSS-1 d(-1). The granular sludge taken from the reactor was characterized. The fluorescence in situ hybridization (FISH) result showed that the microbial community structure was also changed during the granular sludge formation process and that the nitrite denitrifying bacteria increased in population size. Based on the carbon balance, the stoichiometric equation of nitrite denitrification was obtained and a biomass yield value was calculated. The practical ratio of chemical oxygen demand (COD) and nitrite was 2:1, which was higher than the theoretical value. The measured effluent pH was negligibly different from the stoichiometric value.