Modeling the influence of nonionic surfactants on biodegradation of phenanthrene

Surfactant 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 five coupled differential equations. The model accounts for the concurrent utilization of surfactants for cell growth. The system of differential equations has been solved by numerical integration to calculate the oxygen utilization, cell mass production and substrate concentration as a function of time. Sensitivity analysis of the model indicates that the maximum specific growth rate, the oxygen consumption coefficient, cell yield coefficient and dissolution coefficient are the most significant parameters that control the process. Four commercial nonionic surfactants at a concentration of 25 mg/L were tested to evaluate their effect 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 surfactants enhanced the biodegradation rate for phenanthrene. The results also indicated that the most significant effect of surfactant addition was the increase in the dissolution rate of phenanthrene to the aqueous phase.