1. BIOGAS
1.1. Biogas is a mixture of methane and carbon dioxide
1.2. Biogas properties similar to natural gas
1.3. Biogas is the common name for the mixture of gases released from anaerobic digestion
1.4. Typically biogas is composed of methane (60 to 70 %), carbon dioxide, hydrogen, nitrogen, hydrogen sulphide.
2. ANAEROBIC DIGESTION
2.1. Definition
2.1.1. A biochemical process consisting of several groups of microorganisms that degrade the organic matter into a gaseous mixture consisting of methane and carbon dioxide (biogas) in the absence of oxygen.
2.2. Process
2.2.1. Disintegration => Hydrolysis => Acidogenesis => Acetogenesis => Methanogenesis
2.3. Factors affecting
2.3.1. pH
2.3.2. Temperature
2.3.3. The nature of the feedstock
2.3.4. The presence of toxic or inhibitory substances
2.3.5. The organic loading rate
2.4. Advantages and disadvantages
2.4.1. Advantages
2.4.2. Disadvantages
2.5. Main parameters
2.5.1. Temperature of operation
2.5.1.1. Mesophilic anaerobic digestion (35–40°C)
2.5.1.2. Thermophilic anaerobic digestion (50–60°C)
2.5.1.3. Psychrophilic anaerobic digestion (<20°C)
2.5.2. Solid content of digesting mixture
2.5.2.1. Wet anaerobic systems: are in a slurry form and can still be mixed through agitation
2.5.2.2. Dry anaerobic systems: the plug-flow type digesters are most suitable
2.5.3. Number of bioreactors
2.5.3.1. A single bioreactor or a combination of bioreactors of different or the same design
2.5.4. Continuous or batch mode of operation
2.5.5. Small or large scale systems
2.5.5.1. Applied in agriculture in the form of on-farm digesters
2.5.5.2. The produced biogas is utilised for heat as well as electricity production.