Methane fermention normally comprises three reaction phases:hydrolyic-acidogenic,acetogenic,and methano-genic(Ahr2003;Thauer et al.2008).Complex organic wastes (carbohydrates,proteins,and lipids)are first extracellularly degraded into monomers and oligomers by hydrolyic-acidogenic bacteria and then these are taken up by the bacteria to be further 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 is produced from acetate by aceticlastic methanogen and from hydrogen/carbon dioxide(Co2) by hydrogenotrophic methanogen.