ammonia which is toxic to other groups of microorganisms (Weiland et al.
2009). Martinez-Sosa et al. (2011) and Smith et al. (2013) have also observed
lower methane production under psychrophilic conditions. Fouling smell was
also increased when the temperature of the digester was lowered (Gao et al.
2014). Microbial growth depends on the temperature being maintained at various stages of the process in the digester. Ennouri et al. (2016) treated urban and
industrial sludge samples and found that treatment at temperature of about
120
C leads to higher biogas formation. Bowen et al. (2014) reported those
temperatures less than the optimal required led to lower substrate utilization
which indirectly affects the digestion process. Kundu et al. (2014) confirmed that
increase in process temperatures is associated with lower negative effects compared to lower temperatures. Similarly, Westerholm et al. (2017) have also
reported that increased temperatures are beneficial for the bioprocess to take
place while studying thermophilic-to-mesophilic temperature adaptation. During
the process of scale up, it would be difficult to control the temperature at the
required level as the ratio between surface area and volume of the digester will be
decreased. Heat exchangers like cooling coil, cooling baffles, vessel wall, and
external loop are generally used for controlling excess heat so as to control the
temperature. Stanton number describes the ratio between “heat transfer capacity
through coils and convection capacity in cooling water.” This is very useful for
designing a heat exchanger. The various devices which are used for temperature
monitoring are bimetal thermometers, liquid thermometers, thermistors, crystal
window tape, infrared detectors, etc. Clemens (2006) suggested that for
maintaining temperature in biogas digesters, temperature control devices have
to be used. Matsakas et al. (2020) evaluated a novel pretreatment method for
enhancing methane production using hybrid system of organosolv-steam explosion fractionation. The approach was used for obtaining pretreated solid which is
highly digestible from birch and spruce woodchips.
(c) Feedstock.
The non-lignocellulosic liquid feedstock which is generally used for anaerobic digestion process is palm oil mill effluent (Sri Rahayu et al. 2015). GuardiaPuebla et al. (2014) treated coffee wastewater and reported methane gas production of about 61%. They have also studied the influence of OLR and HRT in
the treatment of coffee wet wastewater in a UASB reactor. Chicken feather was
pretreated and was found to be effective as 75% of the feather was transformed
into protein after 8 days (Patinvoh et al. 2016b). Janke et al. (2015) used vinasse
as a feedstock, but lower yields of biogas were found. They suggested a reactor
design with higher OLR and lower HRT. Pig and cattle manure were used as
feedstock for the production of biogas (Matulaitis et al. 2015). The process
showed that pig liquid manure gave more biogas yields compared to pig solid
manure and cattle manure. The solid feedstock for anaerobic treatment includes
food residues (Yong et al. 2015). Zhang et al. (2007) has suggested that
lignocellulosic wastes are abundant renewable organic resources with 200 billion
236
R. Kumar et al.
2009). Martinez-Sosa et al. (2011) and Smith et al. (2013) have also observed
lower methane production under psychrophilic conditions. Fouling smell was
also increased when the temperature of the digester was lowered (Gao et al.
2014). Microbial growth depends on the temperature being maintained at various stages of the process in the digester. Ennouri et al. (2016) treated urban and
industrial sludge samples and found that treatment at temperature of about
120
C leads to higher biogas formation. Bowen et al. (2014) reported those
temperatures less than the optimal required led to lower substrate utilization
which indirectly affects the digestion process. Kundu et al. (2014) confirmed that
increase in process temperatures is associated with lower negative effects compared to lower temperatures. Similarly, Westerholm et al. (2017) have also
reported that increased temperatures are beneficial for the bioprocess to take
place while studying thermophilic-to-mesophilic temperature adaptation. During
the process of scale up, it would be difficult to control the temperature at the
required level as the ratio between surface area and volume of the digester will be
decreased. Heat exchangers like cooling coil, cooling baffles, vessel wall, and
external loop are generally used for controlling excess heat so as to control the
temperature. Stanton number describes the ratio between “heat transfer capacity
through coils and convection capacity in cooling water.” This is very useful for
designing a heat exchanger. The various devices which are used for temperature
monitoring are bimetal thermometers, liquid thermometers, thermistors, crystal
window tape, infrared detectors, etc. Clemens (2006) suggested that for
maintaining temperature in biogas digesters, temperature control devices have
to be used. Matsakas et al. (2020) evaluated a novel pretreatment method for
enhancing methane production using hybrid system of organosolv-steam explosion fractionation. The approach was used for obtaining pretreated solid which is
highly digestible from birch and spruce woodchips.
(c) Feedstock.
The non-lignocellulosic liquid feedstock which is generally used for anaerobic digestion process is palm oil mill effluent (Sri Rahayu et al. 2015). GuardiaPuebla et al. (2014) treated coffee wastewater and reported methane gas production of about 61%. They have also studied the influence of OLR and HRT in
the treatment of coffee wet wastewater in a UASB reactor. Chicken feather was
pretreated and was found to be effective as 75% of the feather was transformed
into protein after 8 days (Patinvoh et al. 2016b). Janke et al. (2015) used vinasse
as a feedstock, but lower yields of biogas were found. They suggested a reactor
design with higher OLR and lower HRT. Pig and cattle manure were used as
feedstock for the production of biogas (Matulaitis et al. 2015). The process
showed that pig liquid manure gave more biogas yields compared to pig solid
manure and cattle manure. The solid feedstock for anaerobic treatment includes
food residues (Yong et al. 2015). Zhang et al. (2007) has suggested that
lignocellulosic wastes are abundant renewable organic resources with 200 billion
236
R. Kumar et al.