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

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, μ_max and K_s were determined to be 0.14 (±0.01) h^-1 and 1.88 (±1.80) mg/L, respectively. At 37°C, μ_max 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, μ_max and K_s were 0.04 (±0.002) h^-1 and 3.72 (±1.05) mg/L, respectively, whereas at 37°C and 125 rpm, μ_max and K_s were 0.07 (±0.008) h^-1 and 1.65 (±2.06) mg/L. In the SSTR the kinetic parameters μ_max and K_s at room temperature were determined to be 0.12 (±0.009) h^-1 and 2.18 (±0.47) mg/L, respectively. Although the μ_max values for both types of reactors were similar, the shaker flask experiments resulted in considerable error. Error analysis on calculated values of K_s 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.