Design and control of a mechatronic system for the homogenization of compost in anaerobic digesters

This paper presents important aspects that are considered in the design and construction of a low-cost low-maintenance mixer for anaerobic digesters. An acceptable and uniform temperature should be maintained throughout the digester to prevent localized pockets of depressed temperature and undesired bacterial activity. Variations in temperature of even a few degrees affect almost all biological activity including the inhibition of some anaerobic bacteria, particularly methane-forming bacteria. Because of this, an adequate mixing of the digester content is needed to prevent the development of localized pockets of temperature variation. The mixer consists of a mechatronic system formed basically of a metallic structure, a three-phase digital inverter and a three-phase electric motor. The mechatronic system completes the indispensable mixing in the anaerobic digestion without the need of using the high-cost high-maintenance systems used in conventional digesters such as turbines, immersion and recirculation pump. When applying the proposed design, the results will show savings in energy and resources.