Kuan-Yeow Show1, Duu-Jong Lee2

xDepartment of Environmental Science and Engineering, Fudan University,

Shanghai, China

^Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan

9.1 INTRODUCTION

Extensive effort is being made globally to exploring renewable energy sources that could replace fossil fuels in mitigating global warming and other environmental issues. Hydrogen is a promising fuel alternative to conventional fossil fuels because it releases energy ex­plosively without air pollutants in combustion. Most of the hydrogen in use currently is produced through thermochemical processes via electricity generation from fossil fuels. Because the current hydrogen fuel is based on the use of nonrenewable fossil-fuel resources, a major issue related to conventional hydrogen production is sustainability.

Biohydrogen production is deemed a key development in creating a sustainable energy supply and a promising alternative to fossil fuels. Hydrogen production via biological pro­cesses is carried out largely at ambient temperatures and pressures and hence is less energy intensive than chemical or electrochemical ones. As a desired green energy product of natural bioconversion, biohydrogen metabolism is primarily the domain of bacteria and microalgae. Within these groups, it involves many taxonomically diverse species, a variety of enzymes, and metabolic pathways and processes (Schulz, 1996; Vignais et al., 2001; Weaver et al., 1980). Biological processes use the enzyme hydrogenase or nitrogenase as a hydrogen-producing protein. This enzyme regulates the hydrogen metabolism of prokaryotes and some eukaryotic organisms, including green algae. The function of nitrogenase as well as hydrogenase is linked with the utilization of metabolic products of photosynthetic reactions that generate reductants from water.

Current development of algal hydrogen production is focusing on biophotolysis and photosynthesis-hydrogen production using various microbial species. Sunlight is necessary for hydrogen production by photosynthetic microorganisms. Photoautotrophic green microalgae and cyanobacteria use carbon dioxide and sunlight as the respective sole carbon and energy sources. The reducing power for cellular photosynthesis and/or biophotolysis comes from water oxidation under light irradiation (Ghirardi et al., 2000; Schutz et al.,

2004) . This chapter examines the perspectives and state-of-the-art of algal hydrogen research in the context of pathways of hydrogen production, bioreactor design and operation, and eco­nomic evaluation. Prospects and challenges in algal hydrogen production are also outlined.