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CHAPTER I

Introduction

1.1 Rationale and background

Currently, the worldwide awareness of global climate change, it was being caused by the
extensive use of fossil fuel wherewith carbon dioxide (CO 2) emissions from fossil fuels
containing carbon combustion. To reduce the emission of CO 2 from fossil fuels to the
atmosphere, researchers are looking at alternative fuels that combat the mentioned problem.
Among the alternative fuels, biogas including biohydrogen and biomethane is a promising one to
in place of fossil fuels due to biohydrogen is clean energy with no CO x, SO x and NO x emissions,
high energy content which greater than other hydrocarbon fuel about 2.75 times, rapid burning
speed and high-octane number (Hawkes et al., 2002). Additionally, gas mixture consisting of
biohydrogen (10-60%) and biomethane were referred to the enhance performance (Kongjan,
2010). There are several biological ways to produce biogas from organic wastes and residues,
among that anaerobic dark fermentation is more popular because environmentally friendly,
renewable, sustainable, cheap energy and capable to utilize the organic wastes and residues to
eliminate the pollution.
Biogas production by microbial fermentation pass through anaerobic digestion using
organic wastes and residues is one of the oldest technologies for bioenergy formation as well as
wastewater treatment. The process is a multi-step involving large groups of microbial
populations, which are linked process steps, in which complex organic compound such as
carbohydrates, proteins and lipids are degraded into single molecules, including mono sugar,
amino acid and long chain fatty acid by hydrolytic bacteria. Acidogenesis, fermentative products
of hydrolysis are further broken down into acetic acid (51%), hydrogen (19%) and the remaining
are alcohols, lactic acid and higher VFA by fermentative and acidogenic bacteria. Acetogenesis,
fermentation products with longer than two carbon atoms for volatile fatty acids (VFAs), longer
than one carbon atom for alcohols are oxidized to acetate and hydrogen by obligate proton
reducing bacteria in syntrophic relationship with methanogenic archaea (Boe, 2006).
Methanogenesis, the intermediate products of the preceding stage are utilized by methanogenic
archaea to further convert these products to methane and carbon dioxide. Mostly of methane
formation of 70% is originated pass through acetate pathway by aceticlastic methanogens and the
rest of 30% is generated from conversion of hydrogen and carbon dioxide by hydrogenotrophic
methanogens.