Biofiltration technology has received much attention because of its effectiveness, economy and environmentally friendly property, which can filter the odors caused chiefly by H2S via the biological treatments. In this study, the lattice Boltzmann method is adopted to numerically investigate the heterogeneous flow in three porous biofilter models. The numerical results indicate that the property of porous media and the inlet flow condition have significant influence on the value of critical Rayleigh number. With the increase of Darcy number and porosity, the critical Rayleigh number will gradually decrease; however, it will steadily increase with the augment of inlet Reynolds number. The present study is helpful to provide a rational theoretical guidance for the optimized design of biofilters.