Ni and Co are essential
co-factors of enzymes involved in the anaerobic digestion process
[9,8e11]. Ni is a well-known cofactor of F430, which is required for
catalyzing the methane formation from methyl S-CoM in the conversion
of acetic acid, hydrogen, and carbon dioxide to methane by
acetoclastic and hydrogenotrophic methanogens (Fig. 1) [10]. In
addition, Ni helps to maintain cell wall stability in some methanogens
[11]. Therefore, an appropriate Ni concentration in the
fermentation medium is required for maximizing the methane
production process. Co is a key component of corrinoid, which is
known to bind to coenzyme M [CoM] methylase