<p>Conversion of ammonia to nitrate is sensitive to a number of inhibitors. There is limited information on the nitrification inhibition coefficient and kinetic model in the current literature. Octyl Phenol Ethoxylate (OPE) and Bisphenol A (BPA) inhibition constants were found in nitrogen removal using an activated sludge system. Firstly, OPE and BPA free wastewater was used to determine the optimum operating conditions. The effect of OPE and BPA concentration on system performance was investigated. The ammonium removal rate was less affected by lower OPE and BPA concentrations. When the BPA and OPE concentrations were increased from 0 mg/L to 30 mg/L, the outlet ammonium nitrogen concentrations were increased respectively from 2.8 mg/L to 49.8 mg/L and from 2.6 mg/L to 20.40 mg/L. Due to the inhibition created by these compounds on Nitrobacter, nitrite nitrogen increased in the medium. As the OPE and BPA concentrations increased, the conversion rate of the ammonium nitrogen into nitrate decreased. Based on the experimental results, a kinetic model was developed, and the OPE and BPA inhibition constants (KOPE and KBPA) were found to be 40.7 mg/L and 11.76 mg/L, respectively. In nitrogen removal, BPA created a higher inhibition effect in comparison to OPE.</p>