Fundamental kinetic parameters of suspended and biofilm atrazine degrading cells

In vast areas of the United States the widely used herbicide atrazine has been found in groundwater at concentrations surpassing the allowed EPA limit of three parts-per-billion for this pollutant. Preliminary studies suggest that bacterial bioremediation offers a viable, safe and highly effective alternative to eliminate atrazine from the water table and the environment. It has been shown that the bacterium Pseudomonas sp. ADP (P. ADP) is capable of degrading atrazine to carbon dioxide, water, and ammonia. In order to improve the performance of bioremediation techniques a better understanding of bacterial degradation is needed. This study summarizes efforts to characterize the kinetic rates of atrazine degradation by P. ADP. Unique to this work is the focus on extraction of the kinetic rate parameters when P. ADP is both in suspension and in a neighboring biofilm culture.; In performing this work, first, the degradation of atrazine by P. ADP was studied in bacterial cells kept in suspension. The Monod kinetic parameters for this process were found to be mumax = 0.12 (+/-0.0093) h-1 and Ks = 2.18 (+/-0.47) mg/L, (n=5, regression error). In the process of performing this work, it was discovered that traditional methods of determining kinetics in shake flasks resulted in parameters with large variation; this large error range was shown to have a dramatic effect on reactor scale-up and prediction of parameter estimates for in-situ remediation conditions.; Second, the kinetics of atrazine degradation were analyzed in the context of a P. ADP biofilm. Here, a novel spherical stirred tank reactor (SSTR) was designed which allowed for P.ADP biofilm formation during continuous operation. Although substantial variation resulted in the quantification of the biofilm mass under specific fixed conditions, it was concluded that the suspended P. ADP cells have a mugrowth that is two orders-of-magnitude greater than the comparable biofilm under the same temperature and feed conditions. Also, the value for mumax in the biofilm was determined to be two orders-of-magnitude smaller than the suspended cells. These results are important for developing a more complete understanding of biofilm-mediated degradation.