75
sugars. Pretreatment includes physical, chemical, biological, and their combinations (Alvira et al. 2010).
The anaerobic fermentation process can be enhanced if the digestate is recycled
and mixed with substrate feed. The solids content of feeding materials should be
adjusted to 5–10%.
5.1.3.11 Feedstock Size
Feeding material size is one of the factors affecting biogas production. Materials
should not be too large because it will lead to digester blockage and will also make
it difficult for bacteria to decompose. Small-sized materials will have larger surface
areas and increased microbial activity, resulting in faster decomposition. According
to Sharma et al. (1988),when substrates having five different particle sizes (0.088,
0.4, 1.0, 6.0, and 30.0 mm) were digested and their biogas output were compared, it
was shown that the optimal size for producing biogas was 0.088 and 0.4 mm. Some
other studies also suggested that a physical pretreatment method, such as grinding
and chopping, can significantly reduce digester size design as compared with digesters using untreated substrates,without reducing the biogas production (Moorhead
and Nordstedt 1993; Gollakota and Meher 1988).
5.2 AD Systems
5.2.1 Small-Scale Biogas Digesters
Small-scale biogas plants have mostly been popularized in developing countries. In
many of those countries, massive government-led (China, India) or governmentNGO biogas programs were initiated with the aim of popularizing this technology.
Based on the construction methodology, there are two main types of plants
including:
• Constructed on-site plants: these plants are often made of brick, mortar and
concrete.
• Prefabricated plants (PBD): these plants are produced off-site and installed at the
farms. They are made of fiber-reinforced plastic (FRP), tubular (known as bag
plants or soft plastic plants), and hard plastics, such as hard polyvinyl chloride
(PVC), acrylonitrile butadiene styrene (ABS), high-density polyethylene
(HDPE), linear low-density polyethylene (LLDPE), and modified plastics.
5 Anaerobic Digestion of Rice Straw for Biogas Production
sugars. Pretreatment includes physical, chemical, biological, and their combinations (Alvira et al. 2010).
The anaerobic fermentation process can be enhanced if the digestate is recycled
and mixed with substrate feed. The solids content of feeding materials should be
adjusted to 5–10%.
5.1.3.11 Feedstock Size
Feeding material size is one of the factors affecting biogas production. Materials
should not be too large because it will lead to digester blockage and will also make
it difficult for bacteria to decompose. Small-sized materials will have larger surface
areas and increased microbial activity, resulting in faster decomposition. According
to Sharma et al. (1988),when substrates having five different particle sizes (0.088,
0.4, 1.0, 6.0, and 30.0 mm) were digested and their biogas output were compared, it
was shown that the optimal size for producing biogas was 0.088 and 0.4 mm. Some
other studies also suggested that a physical pretreatment method, such as grinding
and chopping, can significantly reduce digester size design as compared with digesters using untreated substrates,without reducing the biogas production (Moorhead
and Nordstedt 1993; Gollakota and Meher 1988).
5.2 AD Systems
5.2.1 Small-Scale Biogas Digesters
Small-scale biogas plants have mostly been popularized in developing countries. In
many of those countries, massive government-led (China, India) or governmentNGO biogas programs were initiated with the aim of popularizing this technology.
Based on the construction methodology, there are two main types of plants
including:
• Constructed on-site plants: these plants are often made of brick, mortar and
concrete.
• Prefabricated plants (PBD): these plants are produced off-site and installed at the
farms. They are made of fiber-reinforced plastic (FRP), tubular (known as bag
plants or soft plastic plants), and hard plastics, such as hard polyvinyl chloride
(PVC), acrylonitrile butadiene styrene (ABS), high-density polyethylene
(HDPE), linear low-density polyethylene (LLDPE), and modified plastics.
5 Anaerobic Digestion of Rice Straw for Biogas Production