A low-cost, open-source gas flow meter for laboratory-scale bioreactors

Biogas production measurement is a fundamental aspect of anaerobic digestion research. Lab-scale experiments usually require devices capable of measuring low flowrates and low relative pressures. Despite the existence of multiple commercially available alternatives for such demands, each with particular advantages and limitations, researchers have often resorted to in-house developed systems. This inclination is motivated by cost savings and the potential for of customization to suit specific research needs. Those systems, however, are seldom reproduced beyond laboratory walls due to overly complex designs, limited component availability or unpublished software. In this work, we developed a fully open-source lab-scale biogas flow meter equipped with datalogging capabilities. Our approach relied on inexpensive, widely available electronic modules. The flow meter was calibrated, tested and validated in batch biogas production experiments, alongside a comparative assessment with a proprietary device widely used in the field. The semi-continuous gas meter presented a resolution of 7.45 +/- 0.13 mL and maintained a stable pulse volume (under 2 % relative standard deviation) for flowrates ranging from 60 mL h-1 to 1120 mL h-1. The device was not sensitive to the evaporative loss of up to 7 mL of packing liquid, demonstrating its applicability to long-term experiments. The developed system was shown to be robust and reliable and can be easily reproduced, revised and enhanced in laboratories everywhere.