Substrates for Anaerobic Digestion

The digestion process takes place at psicofilic (5-20 C), mesophilic (30-45 °C), or thermophilic (45-60 C) tanperature conditions. It is important to keep a constant temperature during the digestion process, as tanperature changes or fluctuations will effect the biogas production negatively. 

The necessary concentration for the micronutrients is very low and in the range between 0.05 und 0.06 mg/L. Only iron is necessary in higher concentration between 1 and 10 mg/L [79], 

All types of biomass can be used as substrates for biogas production as long as they contain carbohydrates, proteins, fats, cellulose, and hemiceUuloses as main components. The composition of biogas and the methane yield depends on the feedstock type, the digestion system, and the retention time [82]. The theoretical gas yield varies with the content of carbohydrates, proteins, and fats (Table 1.1). 

The real methane content in practice is generally higher than the theoretical values shown in Table 1.1 because a part of CO2 is solubilized in the digestate. 

Carbohydrates and proteins show much faster conversion rates but lower gas yields. All substrates should be free of pathogens and other organisms otherwise, pasteurization at 70 °C or sterilization at 130 °C is necessary prior fermentation. 

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The conversion of water hyacinth to methane gas by anaerobic digestion has been studied by a number of researchers (, 61-62). The basic findings are that water hyacinth is a good substrate for anaerobic digestion, with gas production rates and yields similar to those of primary sewage sludge. Both the nutrient content (>2-3% N, 0.3-0.6% P of dry weight) and solids content of the freshly harvested plants (95% water, 5% solids) are very suitable for this conversion process. 

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