Feasible monitoring of the inhibitory effects of free NH3 on NO2− oxidation

ABSTRACTThis study investigated nitrite (NO2−) accumulation due to FA (Free Ammonia: NH3) inhibition in an anaerobic-aerobic-anoxic (AOA) process reactor to mainly treat wastewater containing 302−610 mg/L of NH3/NH4+–N. Based on an experimental operation focusing on the nitrification, it was observed that NO2− was accumulated in the aerobic nitrification zone as pH increased, due to inhibition of NO2− conversion to NO3− by FA. This result implied FA inhibition to NOB (NO2−−Oxidizing Bacteria) for converting NO2− to NO3−. The objective of this study is to develop a feasible monitoring procedure for early detection of the FA inhibition toward NO2− accumulation and poor nitrification. Thus, in order to rapidly assess FA concentrations, an NH3 probe was utilized to measure NH3 concentrations together with applying a simple model prediction using the measured NH4+ concentrations, the Henry’s law constant of NH3 and measured pH. The predictive model NH3 levels were verified by a good correlation (89%) with the ...