A simplified generic chemical equation for the overall processes outlined above is
as follows:
C 6 H 12 O 6 ! 3CO 2 þ 3CH 4
5.6.1 Anaerobic Digestion [AD]
Biogas can be produced in four simple steps as shown in Figs. 5.2 and 5.3 flowchart.
There are four key biological and chemical stages of anaerobic digestion:
1. Hydrolysis
2. Acidogenesis
3. Acetogenesis
4. Methanogenesis
Table 5.2 Lignocellulosic biomass fraction of some feedstocks (Isikgor and Becer 2015)
Lignocellulosic feedstocks
Cellulose (%)
Hemicellulose (%)
Lignin (%)
Sugar cane bagasse
42
25
20
Softwood
45–50
25–35
25–35
Hardwood
40–55
24–40
18–25
Corn stover
38
26
19
Corn cobs
45
35
15
Nut shells
25–30
25–30
30–40
Rice Straw
32
24
18
Grasses
25–40
25–50
10–30
Newspaper
40–55
25–40
18–30
Banana waste
13.2
14.8
14
Wheat straw
29–35
26–32
16–21
Bagasse
54.87
16.52
23.33
Sponge gourd fibers
66.59
17.44
15.46
Agricultural residues
5–15
37–50
25–50
Hardwood
20–25
45–47
25–40
Softwood
30–60
40–45
25–29
Grasses
0
25–40
35–50
Waste papers from chemical pulps
6–10
50–70
12–20
Newspaper
12
40–55
25–40
Sorted refuse
60
20
20
Leaves
15–20
80–85
0
Cotton seed hairs
80–95
5–20
0
Paper
85–99
0
0–15
Switch grass
45
31.4
12
Sweet sorghum
45
27
21
128
S. M. Bhatt and S. Bhat