i.Feedstock

Any biodegradable waste that has fats, proteins, carbohydrates, cellulose, and hemicelluloses is suitable as feedstock in anaerobic digestion. However, the various feedstocks have different theoretical chemical oxygen demand (COD) and the potential biogas. They have different or varied biochemical structure and rate of its biodegradability leading to differences in productivity. The factors in feedstock that influence biogas productivity are BOD, volatile solids, carbon/nitrogen (C:N) ratio, COD, volatile solids (VS) content, and presence of inhibitory substances [78, 101].

#### ii.Temperature

The bio-digestive process can be accelerated within tolerable limits by heating process. The same holds true for the processes involved in making biogas. The microorganisms engaged in anaerobic digestion perform both thermophilic and mesophilic digestion. Temperatures between 45 and 80°C are ideal for thermophiles, while those between 25 and 40°C are ideal for mesophiles, yet the Psychrophilic bacteria operate below 25°C [67]. A decrease in methane concentration and a rise in CO2 might impair the heating value of the gas produced if global warming is not controlled. The best number to use for reliable and productive biogas production depends on the organism being used [94, 101].
