| Abstract: | The concentration of dissolved oxygen (DO) strongly influences the performance of aerobic biofilm reactors because organic oxidation is limited by the availability of oxygen. However, it is not necessary to maintain a high DO level in the reactors in order to overcome this limitation. Excessive aeration wastes energy. Therefore, the determination of the onset of DO limitation against organic substrate removal in aerobic biofilm reactors is important for their effective operation. This study is aimed at developing an expression to determine the onset of DO limitation and hence to control the aeration system. The expression developed is as follows:
, where Sb and Cb are the bulk concentrations of organic substrate and DO, respectively; Dws and Dwc are the diffusion coefficients of organic substrate and oxygen in the reactors respectively; and Rb is an overall ratio of oxygen consumption to organic substrate removal in the reactors. The latter is the key parameter in the equation, and is determined by the characteristics of the substrate, biofilm, and reactor. In order to measure the value of Rb, the authors have developed a micro-biofilm reactor. The value of Rb was determined to be 0.13 (mg O2 mg−1 CODcr) for glucose removal with this reactor. The equation has, subsequently, been verified with data from batch and continuous experiments. |
