A Study on Biohydrogen Production based on Biophotolysis from Cyanobacteria

Abstract

Hydrogen (H₂) has long been promoted as an ideal fuel, as it permits a completely clean combustion and has great potential to provide clean power needed for transport and electricity generation. The unicellular, nitrogen-fixing cyanobacterium Cyanothece sp. ATCC 51142 is a promising strain with a remarkable capability of producing large quantities of H₂. Under anaerobic condition, the cyanobacterium carries out the biological fixation of atmospheric nitrogen (N₂) into ammonia (NH₃), concurrently producing H₂ as by-product. The aim of this thesis was to improve our understanding of the growth and H₂ production of Cyanothece sp. ATCC 51142 in order to develop a continuous and practical cyanobacterial H₂ production process. In order to effectively handle incompatible requirements between the cyanobacterial growth and its sequential H₂ production, a novel two-stage chemostat photobioreactor (PBR) system was designed and developed, with an aim to improve H₂ production yield as well as extend its production duration. The system has been operated non-stop for consecutive 30 days without any losses in its performance and subsequently demonstrated a remarkable improvement in H₂ production, with more than 6.4 times higher yield than that of a single-stage batch system. With the continuous mode of operation, a continuous collection of produced biomass from the PBR is also permitted (more than 7.3 times improvement in biomass yield than that of a single-stage batch system). At an industrial scale, this biomass could undergo further downstream processing to generate a multistreamline of high valued by-products such as e.g. vitamins, pharmaceuticals and human nutrition, which can subsequently contribute to a significant improvement in an economic viability of biohydrogen process.