Determining design and scale-up parameters for degradation of atrazine with suspended Pseudomonas sp. ADP in aqueous bioreactors

Abstract

This work investigated the kinetic parameters of atrazine mineralization by suspended cells of Pseudomonas sp. ADP in both shake flasks and spherical stirred tank batch reactors (SSTR). The degradation of atrazine and growth of Pseudomonas sp. ADP were studied. Experiments were performed at different temperatures and stirring speeds in both reactors at varying initial concentrations of atrazine. Cell growth and atrazine concentration were monitored over time, and a Monod model with one limiting substrate was used to characterize the kinetic behavior. Temperature, stirring speed, and reactor type were all found to significantly affect the regressed Monod parameters. At 27°C and 200 rpm, for the shaker flask experiments, μmax and Ks were determined to be 0.14 (±0.01) h-1 and 1.88 (±1.80) mg/L, respectively. At 37°C, μmax and K s increased to 0.25 (±0.05) h-1 and 9.59 (±6.55) mg/L, respectively. As expected, stirrer speed was also found to significantly alter the kinetic parameters. At 27°C and 125 rpm, μmax and Ks were 0.04 (±0.002) h-1 and 3.72 (±1.05) mg/L, respectively, whereas at 37°C and 125 rpm, μmax and Ks were 0.07 (±0.008) h-1 and 1.65 (±2.06) mg/L. In the SSTR the kinetic parameters μmax and Ks at room temperature were determined to be 0.12 (±0.009) h-1 and 2.18 (±0.47) mg/L, respectively. Although the μmax values for both types of reactors were similar, the shaker flask experiments resulted in considerable error. Error analysis on calculated values of Ks were found to impact estimates in atrazine concentration by as much as two orders of magnitude, depending on the reactor design, illustrating the importance of these factors in reactor scale-up. © 2008 American Chemical Society and American Institute of Chemical Engineers.