Fundamentals in the design and scaling of biodigesters with mixing by hydraulic recirculation of wastewater for biogas production using dimensional analysis

In the present work were established fundamentals relations and criteria for characterization and scaling on the biogas production of a biodigester operated with mixing by hydraulic recirculation of the wastewater. An ovoid geometry for the biodigester was chosen, and with the scale factor and geometric relationships were developed equations to scaling geometrically the biodigester, building the biodigester.slx program for the calculates in Simulink (Matlab® software). Seventeen process variables were identified and by means of the dimensional analysis accord to the p theorem of Vaschy-Buckingham were correlated to generate the dimensionless numbers of Geometry, Reynolds, Power, Recirculation, and Damköhler I. The dimensionless functions and dimensionless numbers allowed developing expressions for power consumption and the biogas production volumetric rate from the recirculation velocity and hydraulic recirculation rate, respectively. The above was done considering the next three aspects, the behavior of the wastewater as non-Newtonian fluid, the sludge and manure concentration, and the mixing effect by hydraulic recirculation of the wastewater. Further, from the similitude principles of geometry, kinematic, dynamic, and chemical were established criteria and equations for scaling of recirculation velocity, the power consumption, and the biogas production volumetric rate. The work is a platform to study biogas production by anaerobic digestion in biodigesters operated by batch with mixing by hydraulic recirculation of the wastewater.

Keywords: Biogas production, anaerobic digestion, biodigester, hydraulic recirculation, scaling.