**3. Sources of biogas**

There are a variety of wastes that can be used as sources, or feedstocks, that are fed into the digester to produce biogas. Most of biodegradable organic compounds could be transformed into biogas by anaerobic digestion, and biodegradability is the characteristic indicating to what extent this is possible. Raw materials for producing biogas by anaerobic digestion are biomass feedstocks which include; municipal solid waste (MSW), industrial solid wastes and industrial wastewaters, food waste, livestock manure, sewage sludge, agricultural manures, catch crops, energy crops, and microalgae [12, 52–57]. The largest resource is represented by animal manure and slurries from cattle and pig production units as well as from poultry, fish, fur, etc. [58–61]. Manure of animal is considered as a main carbon source for biogas and involves pig manure, cattle, and poultry. The total solids present in animal manures consist of 90% moisture content and volatile solids. It performs as perfect substrate because of its great buffering capacity [62–64]. In most countries, sewage sludge and agricultural manures have been the principal sources for some time, complemented by slaughterhouse, dairy, and restaurant waste. More recently, biogas plants are increasingly using municipal solid waste (MSW), industrial solid wastes, and industrial wastewaters as feedstocks [12].

Nowadays, sludge from municipal wastewater treatment plants is considered as major source of organic matter for biogas generation in Sweden. Other familiar

### *Recent Advances of Biogas Production and Future Perspective DOI: http://dx.doi.org/10.5772/intechopen.93231*

substrates for biogas generation in co-digestion plants involve source-sorted food waste and manure, slaughterhouse waste, and waste from the feed and food industries [65]. Sewage sludge is usually used as a feedstock to provide energy to power sewage treatment works. For many years, sewage sludge and agricultural manures was the principal inputs, making up over 80% of the total.

However, more lately, the manufacturers have been testing with biogas particular agricultural crops, involving maize and rapeseed. Both the crop itself and the generated fodder (silage) are utilized. Animal waste is increasingly used as a feedstock throughout the world. In the EU, there are now over 750 biogas plants processing animal waste, many of them on a large scale. Organic waste from households and municipal authorities is also an important source of biogas [12].

The urban solid waste production, or municipal waste, increases with population growth, high economic activity, and goods production. Biogas has the potential to be produced from widely available, abundant raw materials, including agricultural residues (e.g., animal manure), landfill and food waste, and aquatic biomass and lignocellulosic raw materials [66, 67]. Wood, agricultural residues, and dung of animal are the sources of energy for biogas technique [24, 68]. The use of wastewater from inorganic sources, such as chromium, has also been studied as an alternative for energy production, a more environmentally sustainable approach that avoids landfill disposal of these wastes [69, 70]. Industrial waste and wastewater have potential uses in biogas production due to their characteristics, such as high organic load [66, 71]. Algae are considered as a potential biomass feedstock for decreasing our dependence on nonrenewable energy sources for electric power, transportation, and heat production [53].

Livestock manure, i.e., dung of cow is an efficient feedstock for biogas production getting high cumulative biogas yield with steady performance, with a continuous process. Therefore, cow dung is more favorable in the biogas process [72, 73]. In general, there are different kinds of biomass resources to produce biogas, including animal manures, municipal solid wastes, food wastes, industrial wastes, agricultural residues, poultry wastes, forestry wastes, microalgae, and some dedicated energy crops [54–57].
