Anaerobic digestion, is microbial decomposition of organic materials in absence of oxygen, which results in production of methane and stable compounds. Anaerobic digestion technology has three phases: pre-treatment, digestion and post-treatment. Fermentation bacteria, hydrogen producer bacteria and methanogene bacteria, are the main three groups of metabolic micro-organisms for methanogenic fermentation. Anaerobic digestion in comparison with aerobic composting, is a net energy-producer. 500-1000 kwh energy per ton of wet waste is generated in anaerobic digestion process, while in aerobic composting, 500-750 kwh energy is consumed for treatment of each ton of wet waste. Methane yield is 0.2-.0.5 Nm3 per kg volatile solids added in anaerobic digestion process. During this study, a 22 litre reactor was used for anaerobic digestion of putrescible solid wastes with high total solids (TS) content and 15-20 days retention time. The reactor was heated by a hot-water coil inside it, therefore, internal temperature was kept in the range of 33-37°C. Results show 2500 to 9400 litre biogas generation per 1 m3 of reactor volume per day and more than 50% reduction in organic substances (as TS).
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