solids (Mayer et al. 2014). Three reported anaerobic digestion technologies
according to the total solid content of feedstocks are wet, semi-dry, and dry methods
for roughly 10% – !20% TS content. It is reported that during the batch anaerobic
digestion of cardboard or food waste, the biogas production decreases in the
presence of high TS contents (Forster-Carneiro et al. 2008; Guendouz et al. 2012),
whereas the gas yield increases with higher VS (Gao et al. 2012).
Chemical and Biological Oxygen Demand Both COD and biological oxygen
demand (BOD) are used to quantify the organic matter in feedstocks and to predict
its applicability in anaerobic digestion process (De Mes et al. 2003; Angelidaki and
Sanders 2004). BOD is the measure of the oxygen needed by biodegrading microbes.
Carbon/Nitrogen Ratio It represents the association between the amount of carbon
and nitrogen in a feedstock, and 25:1 ratio is reported to be better for optimal process
(Gerardi 2003). Kwietniewska and Tys (2014) reported that 20–35:1 is an optimum
C/N ratio range for anaerobic digestion. Anaerobic digestion of high protein
containing substrate leads to higher ammonia content causing alkaline pH, leading
to methanogens inhibition (Khalid et al. 2011). Wang et al. (2014) reported that
temperature and C/N ratio directly affect anaerobic digestion performance.
Inhibitory Constituents Feedstocks may contain constituents that can inhibit
anaerobic digestion, such as NH 3 , H 2 S, and heavy metals, where free NH 3 directly
affects the process (Gerardi 2003). Among all the microbes in anaerobic digesters,
methanogens are highly susceptible to NH 3 inhibition (Chen et al. 2008).
Agronomic Practices Various endeavours to improve the gas (methane) production from agro-based feedstocks are always preferred. However, the content and
yield of such agro-based substrates are greatly affected by environmental and
geographical conditions, land characteristics, type of plants, and overall farming
practices. It was reported that Agrogas has showed better methane yield (367 NL
kg/VS), mainly due to high carbohydrates and low lignin in the substrate.
3.5
Organic Waste: Types, Sources, and Uses
Depending on the feedstock source, biogas generally contains methane (!50%),
CO 2 ( 50%), and traces of hydrogen, water vapour, CO, N 2 , and different
compounds of S, H(OSiH 2 ) n OH, (OSiH 2 ) n , halogens, and heavy metals. The ease
of availability for different feedstock for anaerobic digestion is one of the main
selection criteria. Feedstock’s energy production potential differs based on the type,
concentration, and pretreatment of the biodegradable matter. Some of the reported
common sources of organic feedstock are:
• Agro-based feedstock
• Community-based feedstock
• Industrial feedstock
70
S. Elangovan et al.
according to the total solid content of feedstocks are wet, semi-dry, and dry methods
for roughly 10% – !20% TS content. It is reported that during the batch anaerobic
digestion of cardboard or food waste, the biogas production decreases in the
presence of high TS contents (Forster-Carneiro et al. 2008; Guendouz et al. 2012),
whereas the gas yield increases with higher VS (Gao et al. 2012).
Chemical and Biological Oxygen Demand Both COD and biological oxygen
demand (BOD) are used to quantify the organic matter in feedstocks and to predict
its applicability in anaerobic digestion process (De Mes et al. 2003; Angelidaki and
Sanders 2004). BOD is the measure of the oxygen needed by biodegrading microbes.
Carbon/Nitrogen Ratio It represents the association between the amount of carbon
and nitrogen in a feedstock, and 25:1 ratio is reported to be better for optimal process
(Gerardi 2003). Kwietniewska and Tys (2014) reported that 20–35:1 is an optimum
C/N ratio range for anaerobic digestion. Anaerobic digestion of high protein
containing substrate leads to higher ammonia content causing alkaline pH, leading
to methanogens inhibition (Khalid et al. 2011). Wang et al. (2014) reported that
temperature and C/N ratio directly affect anaerobic digestion performance.
Inhibitory Constituents Feedstocks may contain constituents that can inhibit
anaerobic digestion, such as NH 3 , H 2 S, and heavy metals, where free NH 3 directly
affects the process (Gerardi 2003). Among all the microbes in anaerobic digesters,
methanogens are highly susceptible to NH 3 inhibition (Chen et al. 2008).
Agronomic Practices Various endeavours to improve the gas (methane) production from agro-based feedstocks are always preferred. However, the content and
yield of such agro-based substrates are greatly affected by environmental and
geographical conditions, land characteristics, type of plants, and overall farming
practices. It was reported that Agrogas has showed better methane yield (367 NL
kg/VS), mainly due to high carbohydrates and low lignin in the substrate.
3.5
Organic Waste: Types, Sources, and Uses
Depending on the feedstock source, biogas generally contains methane (!50%),
CO 2 ( 50%), and traces of hydrogen, water vapour, CO, N 2 , and different
compounds of S, H(OSiH 2 ) n OH, (OSiH 2 ) n , halogens, and heavy metals. The ease
of availability for different feedstock for anaerobic digestion is one of the main
selection criteria. Feedstock’s energy production potential differs based on the type,
concentration, and pretreatment of the biodegradable matter. Some of the reported
common sources of organic feedstock are:
• Agro-based feedstock
• Community-based feedstock
• Industrial feedstock
70
S. Elangovan et al.