Fluid dynamic study of anaerobic digester: optimization of mixing and geometric configuration by using response surface methodology and factorial design

Abstract

Mixing is an important parameter in order to have an efficient anaerobic digestion. Computational fluid dynamics can provide a detailed modeling about the hydrodynamics and mixing of anaerobic digestion. In this research, a study about the fluid dynamic of anaerobic digester is carried out with the aim to find the best configuration that optimizes mixing. External recirculating pumps are used as mixing system. Respect to other works reported in literature, results obtained by simulations in COMSOL Multiphysics™ are used for factorial and response surface design. The effect of nozzles number for plane, the inlet angle of fluid, recirculation velocity, phase displacement between plans on average velocity are studied. Results show that the best configuration has four nozzles for plane, the inlet angle of fluid at 45°, recirculation velocity of 2 m/s with nozzles alignment. Response surface methodology is carried out finding a mathematical model of second order for average velocity: its optimal value is 0.25 m/s. The future construction of anaerobic digester will verify the obtained results.