In this paper study results of selected production methods for agricultural biogas are shown and technical and technological aspects of these methods are described for monosubstrate bioreactors. Based on the available literature, modelling of mixing in bioreactors using computational fluid dynamics (CFD) was is demonstrated. As part of the research, the numerical simulation method was used with a tool that contains CFD codes. The model k-ε is used to simulate the mean flow characteristics under turbulent flow conditions. This is a two-equation model that gives a general description of turbulence. The work presents the results of numerical studies that make it possible to understand the characteristics of fluid flow in the adhesive bed used for the production of agricultural biogas. The tests showed that in the core of the adhesive bed there is a flow of 0.19 m∙s ^–1, while in the outer part of the bed there is a flow in the range 0.01–0.02 m∙s ^–1. Taking into account the substrate inflow of 0.17 m∙s ^–1 (in the upper part of the fermentor), it was observed that the Klinkenberg effect for autocyclic movement (from bottom to top) takes place. The novelty in the article is the observation of the dominant flow in the core of the bed and the autocyclic flow in the opposite direction in the peripheral areas of the adhesive bed.