Kinetics modeling of two phase biodegradation in a hollow fiber membrane bioreactor

A hollow fiber membrane bioreactor (HFMB) was used for two-phase biodegradation of phenol directly from wastewater. In a non-dispersive approach, phenol was extracted from the wastewater to 2-undecanone, and concomitantly back-extracted into the cell culture medium for biodegradation by suspended cells of Pseudomonas putida ATCC 11172. Cell growth in the HFMB was characterized by the absence of lag phase, high cell growth and biodegradation rates. For example, 1000 mg/L phenol was metabolized within 28 h, with specific growth rates and average biodegradation rates of 0.51 h−1 and 59 mg/L-h, respectively. A kinetics model based on steady state mass transfer and Haldane growth kinetics was formulated to examine the mass transfer and biodegradation of phenol in the HFMB. The model described the experimental data with reasonable accuracy and the overall mass transfer coefficient on the shell and the tube sides were estimated using empirical correlations as 3.83 × 10−8 and 1.26 × 10−6 m/s, respectively. Phenol diffusion through the shell side boundary layer was the rate-limiting step. The model indicated that about 18% of the biomass in the HFMB was present on the surfaces as biofilms and the biodegradation kinetics of the biofilms was same as that of the suspended cells. Model simulations were carried out to examine the effects of various operating conditions on bioreactor performance, and HFMB performance improved significantly by increasing shell side flow rate.