poultry waste is produced in a large amount, about 97.5 Â 10
6 cubic meter of biogas
can be produced by utilizing all poultry waste in an AD process (Arshad et al. 2018).
2.3.2 Agriculture Residues
Agricultural crop residues are one of the essential sources of biofuel energy. It
contains woody substances, crops remain, and fruits and vegetable residues. Crop
residues can be gathered from two sites: first in the agricultural field where crops are
grown and harvested, and second from the factories or industries where crops are
processed. The residues collected from the field include leaves, twigs, seeds, and
straw, whereas those obtained from processing sites include bagasse, roots, and
husk, etc. Crops like wheat, rice, corn, sugarcane, and cotton produce large
quantities of residues beneficial for biogas generation. Other than croplands,
processing factories produce fruits and vegetable wastes and their derivatives,
which are equally important. Asia accounts for 61% of the vegetable production
worldwide, i.e. largest source. About 30% of the global fruit supply comes from
India, Brazil, and China. Industries, from all over the world, produce large quantities
of these wastes including 81 million tonnes of potatoes, 37 million tonnes of
tomatoes, 29 million tonnes of citrus, 25 million tonnes of bananas, 17 million
tonnes of apples and grapes (Paudel et al. 2017). Grassland is also getting attention
because of its beneficiary use in biogas production. Grass silage has a high number
of volatile solids which is directly proportional to biogas yield. About 300 m
3 of
methane can be generated by using one ton of volatile solid (Nizami et al. 2009).
Typically, agricultural straw has a low nitrogen content and they are lignocellulosic, which make them difficult to digest in the process of biogas generation. Their
complex structure is the main limitation of ineffective processing. To prevent this
problem, several researches have suggested pre-treatment methods (Onthong and
Juntarachat 2017). De-lignification treatment is a suggested method to break down
the complicated polymer structures of agricultural and forest wastes. It can be carried
out through several chemicals, mechanical, biological, thermal, and combined
approaches as well (Yu et al. 2019).
2.3.3 Municipal Solid Waste
Municipal solid waste (MSW) is continuously increasing with a rapidly growing
population globally. It is estimated that the annual production of MSW will grow to
nearly 27 billion tons per year until the year 2050 (Ali et al. 2019). The organic
portion of MSW is approximately 46%, comprising food waste, kitchen waste, and
garden waste. Other than an organic fraction, paper waste makes up about 17%,
plastic waste 10%, glass and metals 9%, and others 18%. One ton of organic portion
of MSW can produce around 200 m
3 of biogas which can generate 400 kWh of
electricity (Tyagi et al. 2018). Food waste is a major portion of this organic waste. It
has a high carbon-nitrogen ratio as well as volatile solids and total solids ratio.
2 Microbial and Biotechnological Advancement in Biogas Production
43
6 cubic meter of biogas
can be produced by utilizing all poultry waste in an AD process (Arshad et al. 2018).
2.3.2 Agriculture Residues
Agricultural crop residues are one of the essential sources of biofuel energy. It
contains woody substances, crops remain, and fruits and vegetable residues. Crop
residues can be gathered from two sites: first in the agricultural field where crops are
grown and harvested, and second from the factories or industries where crops are
processed. The residues collected from the field include leaves, twigs, seeds, and
straw, whereas those obtained from processing sites include bagasse, roots, and
husk, etc. Crops like wheat, rice, corn, sugarcane, and cotton produce large
quantities of residues beneficial for biogas generation. Other than croplands,
processing factories produce fruits and vegetable wastes and their derivatives,
which are equally important. Asia accounts for 61% of the vegetable production
worldwide, i.e. largest source. About 30% of the global fruit supply comes from
India, Brazil, and China. Industries, from all over the world, produce large quantities
of these wastes including 81 million tonnes of potatoes, 37 million tonnes of
tomatoes, 29 million tonnes of citrus, 25 million tonnes of bananas, 17 million
tonnes of apples and grapes (Paudel et al. 2017). Grassland is also getting attention
because of its beneficiary use in biogas production. Grass silage has a high number
of volatile solids which is directly proportional to biogas yield. About 300 m
3 of
methane can be generated by using one ton of volatile solid (Nizami et al. 2009).
Typically, agricultural straw has a low nitrogen content and they are lignocellulosic, which make them difficult to digest in the process of biogas generation. Their
complex structure is the main limitation of ineffective processing. To prevent this
problem, several researches have suggested pre-treatment methods (Onthong and
Juntarachat 2017). De-lignification treatment is a suggested method to break down
the complicated polymer structures of agricultural and forest wastes. It can be carried
out through several chemicals, mechanical, biological, thermal, and combined
approaches as well (Yu et al. 2019).
2.3.3 Municipal Solid Waste
Municipal solid waste (MSW) is continuously increasing with a rapidly growing
population globally. It is estimated that the annual production of MSW will grow to
nearly 27 billion tons per year until the year 2050 (Ali et al. 2019). The organic
portion of MSW is approximately 46%, comprising food waste, kitchen waste, and
garden waste. Other than an organic fraction, paper waste makes up about 17%,
plastic waste 10%, glass and metals 9%, and others 18%. One ton of organic portion
of MSW can produce around 200 m
3 of biogas which can generate 400 kWh of
electricity (Tyagi et al. 2018). Food waste is a major portion of this organic waste. It
has a high carbon-nitrogen ratio as well as volatile solids and total solids ratio.
2 Microbial and Biotechnological Advancement in Biogas Production
43