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The bioremediation potential of Pseudomonas fluorescens was studied in an internal draft tube (inverse fluidized bed) biofilm reactor (IDTBR) under batch recirculation conditions using synthetic phenol of various concentrations (400, 600, 800, 1000, and 1200 mg/L). The performance of IDTBR was investigated and the characteristics of biomass and biofilm were determined by evaluating biofilm dry density and thickness, bioparticle density, suspended and attached biomass concentration, chemical oxygen demand, and phenol removal efficiency. Biodegradation kinetics had been studied for the suspended biomass culture and biofilm systems. Suspended biomass followed substrate inhibition kinetics, and the experimental data fitted well with the Haldane model. The correlation coefficient, R 2 , and root-mean-square error (RMSE) obtained for the Haldane model with respect to specific growth rate were .9389 and .00729, respectively, and with respect to specific phenol consumption rate were .9259 and .00972, respectively. It was also observed experimentally that biofilm overcame substrate inhibition effect and fitted the same to the Monod model (R 2 = .9831, RMSE = .00884 for specific growth rate and R 2 = .9686, RMSE = .00912 for specific phenol consumption rate).

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Gas-liquid mass transfer studies were carried out in inverse fluidized bed biofilm reactor (IFBBR) for the biodegradation of phenol. Studies were done to analyze the effect of superficial air velocity (U g ), gas holdup (E g ), and biofilm characteristics such as biofilm thickness, biofilm dry density, suspended and attached biomass concentration, and bioparticle density on oxygen transfer rate (OTR) and gas-liquid volumetric mass transfer coefficient (k L a) for different superficial air velocities and various particle sizes (2.9, 3.5, and 3.8 mm). Average OTR and k L a was found to be high [(OTR) avg. 5 0.0159 min 21 ; (k L a) avg. 5 1.8823 g/(L min)] for the particle size of 3.5 mm at the optimum superficial air velocity (U gm ) of 0.220 m/s which created high turbulence with smaller bubble size. Higher volumetric mass transfer coefficient and OTR resulted in higher percentage of Chemical Oxygen Demand (COD) removal (98%) and phenol degradation (100%) in IFBBR. The gas holdup dominated over the smaller size bubbles resulting in higher mass (oxygen) transfer rate. Thin, dense, and stable biofilm was produced at U gm . Above U gm , thickness of the biofilm was increased where the detachment force did not control the outgrowth of biofilm anymore and thus the k L a was found to be decreasing. V C 2015 American Institute of Chemical Engineers Environ Prog, 35: 433-438, 2016