1955 due to the excessive availability of oil. In the 1990s, profitability and prevention of waste production, pollution prevention, were reasons for the stimulation of
biogas technology (Deublein and Steinhauser 2011). In the twentieth century,
Germans invented “Imhoff digesters” for sewage sludge treatment. Using the same
technology, larger anaerobic digesters were used for the treatment of sewage sludge
for public national gas grid in 1920 (Bond and Templeton 2011).
2.2.3 Types of Digesters
2.2.3.1 Fixed Dome Digesters
Fixed dome digesters are being operated in China since the early twentieth century
and commonly used in developing countries: Ghana, Kenya, and India (Akinbami
et al. 2001; Chen et al. 2008; Bond and Templeton 2011; Nzila et al. 2012). They are
also called “Hydraulic” or “Chinese” digesters (Santerre and Smith 1982). Clay,
concrete, and cement are used for the inner walls of the digester to make it
impermeable (Chen et al. 2008). An inlet pipe is used to fill the digester chamber
and biogas is collected in the storage section. Due to the height difference between
the expansion chamber and slurry in the digester, gas pressure is produced. Some
substrate is introduced into the expansion chamber as the produced gas requires
space and presses it. A digester is immediately filled again with slurry as the gas
releases (Sasse et al. 1991). They are built underground (Santerre and Smith 1982)
and thus, require skilled labor incurring higher costs (Veen et al. 2009). Another cost
factor is the transportation of construction materials in case biogas plants are
constructed in remote areas (Pérez et al. 2014). The main advantage of this model
lies in its low maintenance costs as it is immovable, and the absence of metallic parts
makes it immune to rusting. This model does not produce gas at constant volume and
the pressure of the gas is not maintained, thus less inefficient to run a gas generator,
and gas heater. The construction material is prone to crack, which leads to digester
failures. The lifespan is over three years for these types of digesters (Cheng et al.
2014).
2.2.3.2 Floating Drum Digesters
This digester was built in 1962 and its original name was Khadi and Village
Industries Commission (KVIC). This model is widely used in India (Rajendran
et al. 2012). Like fixed dome reactors, these digesters are also constructed underground using steel and concrete. The digester is cylindrical and there is a moveable
inverted drum for the collection of gas, which is made of PVC or steel. The drum
moves upward as the gas is produced and falls back as the gas is drawn off. (Singh
and Sooch 2004; Rajendran et al. 2012). There are no mechanisms for heating or
mixing in these digesters (Cheng et al. 2014; Surendra et al. 2014). This model has
an advantage of the production of the gas at constant volumes, as the drum maintains
it. Moreover, stored gas volume can be determined easily, and the overall digester’s
operations are simple. However, the downsides affiliated with this type of digester
are its high construction costs due to expensive raw materials (steel). Since steel is
2 Microbial and Biotechnological Advancement in Biogas Production
39
biogas technology (Deublein and Steinhauser 2011). In the twentieth century,
Germans invented “Imhoff digesters” for sewage sludge treatment. Using the same
technology, larger anaerobic digesters were used for the treatment of sewage sludge
for public national gas grid in 1920 (Bond and Templeton 2011).
2.2.3 Types of Digesters
2.2.3.1 Fixed Dome Digesters
Fixed dome digesters are being operated in China since the early twentieth century
and commonly used in developing countries: Ghana, Kenya, and India (Akinbami
et al. 2001; Chen et al. 2008; Bond and Templeton 2011; Nzila et al. 2012). They are
also called “Hydraulic” or “Chinese” digesters (Santerre and Smith 1982). Clay,
concrete, and cement are used for the inner walls of the digester to make it
impermeable (Chen et al. 2008). An inlet pipe is used to fill the digester chamber
and biogas is collected in the storage section. Due to the height difference between
the expansion chamber and slurry in the digester, gas pressure is produced. Some
substrate is introduced into the expansion chamber as the produced gas requires
space and presses it. A digester is immediately filled again with slurry as the gas
releases (Sasse et al. 1991). They are built underground (Santerre and Smith 1982)
and thus, require skilled labor incurring higher costs (Veen et al. 2009). Another cost
factor is the transportation of construction materials in case biogas plants are
constructed in remote areas (Pérez et al. 2014). The main advantage of this model
lies in its low maintenance costs as it is immovable, and the absence of metallic parts
makes it immune to rusting. This model does not produce gas at constant volume and
the pressure of the gas is not maintained, thus less inefficient to run a gas generator,
and gas heater. The construction material is prone to crack, which leads to digester
failures. The lifespan is over three years for these types of digesters (Cheng et al.
2014).
2.2.3.2 Floating Drum Digesters
This digester was built in 1962 and its original name was Khadi and Village
Industries Commission (KVIC). This model is widely used in India (Rajendran
et al. 2012). Like fixed dome reactors, these digesters are also constructed underground using steel and concrete. The digester is cylindrical and there is a moveable
inverted drum for the collection of gas, which is made of PVC or steel. The drum
moves upward as the gas is produced and falls back as the gas is drawn off. (Singh
and Sooch 2004; Rajendran et al. 2012). There are no mechanisms for heating or
mixing in these digesters (Cheng et al. 2014; Surendra et al. 2014). This model has
an advantage of the production of the gas at constant volumes, as the drum maintains
it. Moreover, stored gas volume can be determined easily, and the overall digester’s
operations are simple. However, the downsides affiliated with this type of digester
are its high construction costs due to expensive raw materials (steel). Since steel is
2 Microbial and Biotechnological Advancement in Biogas Production
39