On the Cover

Two-step bubble column-photobioreactor photosynthetic biogas upgrading for biomethane production by utilizing alkaline microalgal medium is a novel biogas upgrading technology to reduce both the cost and energy requirements of conventional physicochemical upgrading technologies. Studies attempting to optimize this technology by simultaneous investigation of the bubble column-photobioreactor setup have experienced considerable variability in results and conclusions. To identify the sources of such variation, in the June 2021 Issue of Biofuel Research Journal, a team of Irish researchers reported the comparative influence of design factors on the performance of CO­₂ removal and O₂ stripping from the bubble column (DOI: 10.18331/BRJ2021.8.2.2). Seven design factors were analysed using the L16 Taguchi orthogonal array as a screening design of experiment, including superficial gas velocity, liquid to gas flow rate (L/G) ratio, empty bed residence time, liquid inlet pH, liquid inlet alkalinity, temperature, and algal concentration. In particular, the results showed that pH and L/G ratio are the most critical design factors for CO₂ removal efficiency with a significant interactive effect. The impact of L/G ratio, algal concentration, and pH (in that order of impact) caused up to a 90% variation in O₂ content in biomethane; algal concentration had a diminishing role as the L/G ratio increased, though. This study is the first to use a screening design of experiment to critically analyze the main effects of, and interactions between, different design factors on the bubble column performance for biogas upgrading. The study indicates the possibility of using state-of-the-art bubble column designs and operational strategies for photosynthetic biogas upgrading. Cover art by BiofuelResJ. ©2021.