In Situ Measurement Of Biofilm Kinetic Parameters By Using Oxygen Microelectrode

The methods to obtain the kinetic parameters of biofilm accurately are very important when the biofilm models are used in research, and the forecasting ability of the biofilm models depends on the accuracy of the kinetic parameters. As the complexity of the inner structure and the reaction processes of biofilm, it is very difficult to obtain the kinetic parameters of biofilm exactly. In this study, two kinds of in situ methods to detect the biofilm kinetic parameters were established: the"diffusion-reaction model mothod"and the"oxygen uptake rate method". After optimizing the configuration of separated oxygen microelectrode and establishing the in-situ detecting system, the two in-situ methods were used to detect the biofilm kinetic parameters.The"diffusion-reaction model method"could be used to estimate the biofilm kinetic parameters by detecting the oxygen distribution profiles in the biofilm in the endogenous phase and growing phase with an oxygen microelectrode. After obtaining the oxygen distribution profiles, the biofilm kinetic parameters could be calculated based on the diffusion-reaction equations under the stabilized conditions. The average values of the OURin (endogenous respiratory rate), Kd (endogenous decay rate) and the Ko (Monod half saturation coefficient to the oxygen) in the biofilm which were estimated by this in-situ method were 8.52 mg O2/ (gVSS·h), 0.0035h-1 and 1.0mg/L respectively. Compared with the activated sludge system, the endogenous respiratory rate and the endogenous decay rate were smaller; the Monod half saturation coefficient was higher.The"oxygen uptake rate method"could be used to estimate the biofilm kinetic parameters by combining the Monod equation and the respiration rate profiles which were detected with an oxygen microelectrode after injecting minim of substrate solution to some depth of the biofilm. After acquiring the kinetic parameters of the microcosmic detected points in the different depths of the biofilm, the apparent values of the biofilm kinetic parameters could be attained by averaging the microcosmic parameters. The apparent values of the Y (yield coefficient),μmax(maximum growing rate)and the Ks (Monod half saturation coefficient to the glucose) were 0.44, 4.00d-1, 41.06mg/L respectively by the in situ method of"oxygen uptake rate". Compared with the values after destroying the biofilm structure, the Y,μmaxand the Ks which were detected using the in situ method were approximate, smaller and higher respectively. Further more, the in situ method of"oxygen uptake rate"could study the kinetic parameters of the microorganisms in the different depths of the biofilm. The results showed that the Y in the different depths of the biofilm which varied from 0.40 to 0.45 didn't have much diversification; theμmaxdecreased gradually with the depth increasing, which changed from 5.74 d-1 on the surface of biofilm to 2.45 d-1 at the bottom of biofilm; the Ks increased gradually with the depth increasing, which changed from 36.63mg/L on the surface of biofilm to 48.04mg/L at the bottom of biofilm.