In the present work, the biodegradation of naphthalene (polycyclic aromatic hydrocarbon) has been studied using isolated Bacillus cereus RKS4 (MH681588.1). The process variables such as pH (5.0-9.0), temperature (25-40 degrees C), and naphthalene concentration (10-50 mg/L) have been optimized using central composite design (CCD) of response surface methodology (RSM). Analysis of variance (ANOVA) shows a high value of R-2 (0.98) and confirm that the second-order regression model is in agreement with experimental data. The maximum removal of naphthalene (96.1%) were obtained at pH of 7.0, naphthalene concentration of 10 mg/L, and temperature of 32.0 degrees C. Further, the biodegradation of naphthalene was studied in a pilot-scale integrated aerobic treatment plant (IATP) at various flow rates. GC-MS analysis reveals that catechol and 2-naphthol were the major intermediate metabolites observed during biodegradation. The kinetics of naphthalene biodegradation was examined by Monod and Teissier-Edwards models and kinetic parameters were obtained to be mu max: 0.165 per day, K-s: 7.91 mg/L by Monod and mu max: 0.321 per day, K-s: 11.5 mg/L, K-i: 33.2 mg/L by Teissier-Edwards. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.