Performance evaluation of a control strategy for photosynthetic biogas upgrading in a semi-industrial scale photobioreactor

Abstract

The validation of a control strategy for biogas upgrading via light-driven CO₂ consumption by microalgae and H₂S oxidation by oxidizing bacteria using the oxygen photosynthetically generated was performed in a semi-industrial scale (9.6 m³) photobioreactor. The control system was able to support CO₂ concentrations lower than 2% with O₂ contents ≤ 1% regardless of the pH in the cultivation broth (ranging from 9.05 to 9.50). Moreover, the control system was efficient to cope with variations in biogas flowrate from 143 to 420 L h^-1, resulting in a biomethane composition of CO₂ < 2.4%, CH₄ > 95.5%, O₂ < 1% and no H₂S. Despite the poor robustness of this technology against failures in biogas and liquid supply (CH₄ concentration of 67.5 and 70.9% after 2 h of biogas or liquid stoppage, respectively), the control system was capable of restoring biomethane quality in less than 2 h when biogas or liquid supply was resumed.