Exergy-based sustainability assessment of continuous photobiological hydrogen production using anaerobic bacterium Rhodospirillum rubrum

The present research work was aimed at analyzing a continuous photobioreactor for hydrogen production from syngas via Rhodospirillum rubrum from exergetic point of view. Exergy balance equation was developed for the investigated photobioreactor based on both conventional exergy and eco-exergy concepts in order to determine its exergetic performance parameters. Two new exergetic criteria called the process exergetic efficiency and normalized exergy destruction were also introduced in order to maximize biohydrogen production and minimize resources destruction. The results obtained showed that the process exergy efficiency, a decision making parameter, varied between 14.71-22.90% and 14.71-22.84% using the conventional exergy and eco-exergy approaches, respectively. The minimum normalized exergy destruction was found to be 0.97 using both approaches. In general, no noticeable changes were observed in the conventional exergetic and eco-exergetic performance parameters of the bioreactor over 540 h of continuous operation. Nevertheless, eco-exergetic analysis owing to the inclusion of the work of information embedded in the genomes of living organisms is still recommended for improving the design features of photobioreactors for hydrogen production. The outcomes of the present study could provide practical insights to engineers and researchers dealing with analysis, design, development, optimization, and improvement of large-scale photobioreactors for hydrogen production.