A biofilm model for fixed-bed anaerobic reactors: Performance analysis considering diffusional resistances and axial dispersion

A biofilm model has been developed to describe the performance of a fixed-bed anaerobic bioreactor taking into consideration the diffusional resistance of the biofilm. The acidogenic reaction has been considered to follow first-order kinetics whereas the methanogenic reaction is considered to have zero-order kinetics. The effects of diffusional resistances inside the biofilm and the backmixing of the bulk liquid have been incorporated to obtain general analytical solutions for first-order and sere-order kinetics. The effects of various process variables of physical importance are investigated parametrically. It is found that the reaction rates for (soluble organics --> volatile fatty acid --> methane + CO2) increase with an increase in the peclet number, hydraulic residence time and biofilm thickness. However, soluble organics conversion is not affected by the biofilm thickness when it is greater than 0.06 cm.