MODELING THE INFLUENCE OF NONIONIC SURFACTANTS ON BIODEGRADATION OF PHENANTHRENE KAUSER JAHAN 1 *, TARIQ AHMED 2* M and WALTER J. MAIER 3 1 Department of Civil Engineering, Rowan University, Glassboro, NJ 08028, U.S.A.; 2 School of Environmental Science, Engineering and Policy, Drexel University, Philadelphia, PA 19104, U.S.A. and 3 Department of Civil Engineering, University of Minnesota, Minneapolis, MN 55455, U.S.A. (First received September 1995; accepted in revised form September 1998) AbstractÐSurfactant mediated solubilization and simultaneous microbial degradation of phenanthrene in a completely mixed batch system has been studied. A mathematical model is presented based on the rates of solids dissolution, substrate biodegradation and oxygen uptake in terms of ®ve coupled dier- ential equations. The model accounts for the concurrent utilization of surfactants for cell growth. The system of dierential equations has been solved by numerical integration to calculate the oxygen utiliz- ation, cell mass production and substrate concentration as a function of time. Sensitivity analysis of the model indicates that the maximum speci®c growth rate, the oxygen consumption coecient, cell yield coecient and dissolution coecient are the most signi®cant parameters that control the process. Four commercial nonionic surfactants at a concentration of 25 mg/L were tested to evaluate their eect on biodegradation rates of phenanthrene. The model could adequately predict the oxygen uptake, cell growth and substrate disappearance data observed in the experimental studies. The presence of surfac- tants enhanced the biodegradation rate for phenanthrene. The results also indicated that the most sig- ni®cant eect of surfactant addition was the increase in the dissolution rate of phenanthrene to the aqueous phase. # 1999 Elsevier Science Ltd. All rights reserved Key wordsÐbiodegradation, bioremediation, polycyclic aromatic hydrocarbon, phenanthrene, nonionic surfactants, modeling, solid substrate, kinetic parameters, mass transfer, batch reactor NOMENCLATURE C xs = excess phase substrate concentration (M/ L 3 ) C s = aqueous solubility of the solid substrate (M/L 3 ) C 1 = aqueous concentration of substrate 1 (M/ L 3 ) C 2 = aqueous concentration of substrate 2 (M/ L 3 ) C 1 (t) = aqueous concentration of substrate 1 at time t (M/L 3 ) K = overall mass transfer coecient (L/T) K d = endogenous decay coecient (1/T) K sa = the surface area of the solid substrate (C xs ) in contact with the bulk water phase (L 2 /M) K s,1 = half saturation constants of substrate 1 (M/L 3 ) K s,2 = half saturation constants of substrate 2 (M/L 3 ) K 21 = dimensionless interaction coecient of C 2 on utilization rate of C 1 K 12 = dimensionless interaction coecient of C 1 on utilization rate of C 2 O x = cumulative oxygen consumption in the reactor (M/L 3 ) X = active cell mass concentration (M/L 3 ) Y 1 = dimensionless cell yield coecient for sub- strate 1 (mg VSS/mg of substrate) Y 2 = dimensionless cell yield coecient for sub- strate 2 (mg VSS/mg of substrate) Y ox,1 = dimensionless oxygen consumption coe- cient for substrate 1 (mg oxygen/mg of VSS) Y ox,2 = dimensionless oxygen consumption coe- cient for substrate 2 (mg oxygen/mg of VSS) Y ox,D = dimensionless oxygen consumption coe- cient for endogenous respiration (mg oxy- gen/mg of VSS) m 1 = speci®c growth rate of substrate 1 (1/T) m 2 = speci®c growth rate of substrate 2 (1/T) m max,1 = maximum speci®c growth rate coecients for substrates 1 (1/T) m max,2 = maximum speci®c growth rate coecients for substrates 2 (1/T) INTRODUCTION Surfactant enhanced mobilization and subsequent biodegradation of slightly soluble organic com- pounds is an eective groundwater/soil remediation Wat. Res. Vol. 33, No. 9, pp. 2181±2193, 1999 # 1999 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0043-1354/99/$ - see front matter PII: S0043-1354(98)00423-0 *Author to whom all correspondence should be addressed. 2181