Mixing of substrate in anaerobic digesters plays a crucial role in maintaining process stability, improving mass transfer, and preventing stratification. This study presents a simple and low-cost automation approach for pneumatic (barbotage) mixing in a biogas reactor using internally produced biogas as the working medium. The proposed system is based on cyclic gas injection controlled by a time relay and a solenoid valve operating in an open-loop configuration. Unlike manual operation, where mixing cycles depend on operator actions, the proposed system enables repeatable intermittent mixing defined by two parameters: valve opening time (T_on) and pause duration (T_off). The system was implemented on a laboratory-scale biogas plant (BEM-100) and evaluated under manual and automated operating modes. Experimental results indicate an increase in average biogas yield from 99.35 m³/t (manual mode) to 125.63 m³/t (automatic mode), corresponding to an approximate increase of 21%. However, this improvement should be interpreted cautiously due to the absence of detailed statistical validation and controlled environmental parameter monitoring. The proposed solution demonstrates that simple timer-based automation can improve operational repeatability and potentially enhance biogas production in small-scale installations without the need for complex control systems.
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