Methane fermentation normally comprises three reaction phases: hydrolytic - acidogenic, acetogenic, and methan ogenic ( Ahring 2003; Thauer at al. 2008). Complex organic wastes ( carbohydrates, proteins, and lipids) are first extracellularly degraded into monomers and oligomers by hydrolytic- acidogenic bacteria and then these are taken up py the bacteria degraded into volatile fatty acids (VFAS) such as acetate, propionate, and butyrate; hydrogen; carbon dioxide; and alcohols..VFAS such as propionate and butyrate, and alcohols are converted into acetate, carbon dioxide, and hydrogen by acetogenic bacteria. In the methanogenic phase, methane in produced from acetate by aceticlastic methanogen and from hydrogen / carbon dioxide (CO2) by hydrogen it topic methanogen.
Methane fermentation is carried out at various temperature ranges: generally under mesophilic ( around 35° C) and thermophilic ( around 55°C) conditions and additionally under a paychrophilic (4-20 C°) or an extreme thermophilic (70 C°) condition for the hydrolyytic process (Sekiguchi et al. 2001; Liu et al.2008 ). In methanogenic bioreactorsca neutral Ph (6.6-7.6) is usually maintained because this is the preferred Ph range of methanogenic archaea.