Environmental Engineering Reference
In-Depth Information
they need to survive by exploiting solar energy through the process of photosyn-
thesis. Heterotrophic organisms, though, of which zoo mass primarily consists of,
need to consume organic substances to produce energy.
Biomass can be divided into primary and secondary products. The former are
produced by direct use of solar energy through photosynthesis. In terms of energy
supply, these are farm and forestry products from energy crop cultivation (i.e.
fast-growing trees, energy grasses) or plant by-products, residues, and waste from
farming and forestry including the corresponding downstream industry and pri-
vate households (i.e. straw, residual and demolition wood, organic components in
household and industrial waste). Secondary products are generated by the decom-
position or conversion of organic substances in higher organisms (e.g. the diges-
tion system of animals); these are for example liquid manure and sewage sludge.
2.5.1 Principles
Structure and composition of plants. Plants consist of the stem, leaves and
roots. The latter anchors the plant in the ground and enables it to withdraw water
and nutrients from the soil. The stem carries the leaves, supplies the plant with
water and nutrients from the root, and carries the organic substances generated in
the leaves to the root. The leaves absorb the sunlight required for photosynthesis.
They enable the gas exchange of carbon dioxide (CO 2 ), oxygen (O 2 ) and steam
(H 2 O) for photosynthesis, breathing and transpiration (Fig. 2.47). For the purpose
of multiplication, plants generate blossoms from which the reproductive seeds are
growing.
Sun
Plant
Sun light
Composition
Heating value
of the dry
of organic
plant matter
in %
compounds
in MJ/kg
C
H
O
N
P
K
S
Ca
Si
40 - 47
6
40 - 44
1 - 5
0.05 - 0.8
0.3 - 5
0.05 - 8
0.3 - 5
0.05 - 3
Sugar
Starch
Celluloses
Fat
Oil
Proteins
15.6
17.9
17.8
36 - 40
36 - 40
23.8
CO 2
CO 2
Air
O 2
Lignin
24.0
O H O
2
,
2
Mg
0.05 - 1
0.005 - 0.01
0.02 - 1
B
Cl
H 2
Cu
0.0002 - 0.002
Fe
Mn
0.005 - 0.1
0.002 - 0.03
Nutrients
Soil
Zn
0.001 - 0.01
Fig. 2.47 Formation and composition of plant matter (see /2-7/)
Photosynthesis. The most important process for biomass generation is photosyn-
thesis. Using light energy carbon dioxide (CO 2 ) is absorbed by the process of
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