| The phenol biodegradation and microbial growth kinetics of suspended cultures of the psychrotrophic microorganism P. putida Q5 were modeled as a function of temperature in the range of 10 to 25°C. The Haldane parameter, K1, decreased with decreasing temperature, indicating the inhibition effect was stronger. The Luong model was found to better fit the kinetics of unacclimated cultures.; The response of an immobilized-cell fluidized-bed reactor (ICFBR) to step changes in phenol loading (ranging from 40 to 500% through step changes in either feed concentration or dilution rate) was investigated for a pure culture of Pseudomonas putida Q5. Two external-loop airlift ICFBRs containing biofilm-covered sand particles were operated at steady-state feed concentrations of 180 to 590 mg/L phenol and dilution rates from 0.025 to 0.069 h–1 at 10°C. Steady-state biofilm thicknesses ranged from 3 to 35 μm, depending upon the organic loading and the sand concentration (11–23 g/L). Two types of responses were noted. Low-level responses were characterized by a lack of response in the bulk phenol concentration. High-level responses were characterized by a rapid increase in the bulk phenol concentration and washout of the suspended biomass; the bioparticles were retained in the system.; A unique unsteady-state process model which simulated the response of all four process variables: the bulk phenol concentration, the suspended biomass concentration, the concentration profile of the substrate in the biofilm and the biofilm thickness, was implemented. Unique features included a balance on suspended cells, the consideration of an inactive fraction in the biofilm, and liquid-biofilm diffusional resistance and detachment. The model represented the wide range of conditions (described above) and the responses observed in four verification experiments, Accurate simulation of the experiments depended upon the use of kinetics determined using unacclimated suspended cells, as they were found to be more sensitive to phenol inhibition than the acclimated cultures. Also, growth rate hysteresis was included by adding a simple function that decreased the growth rate in proportion to the level of phenol present in the bulk fluid during a transient. The solution was simple enough to be used for future work with estimation and nonlinear control. |
