Biomass as a Source of Energy
light |
||
CO2+H2O | (CH2O)n+O2 | |
chlorophyll |
During photosynthesis, solar energy is trapped into light harvesting molecules in the chloroplasts by reduction of CO2 into carbohydrates, fats and proteins. Radiant energy stored in plant is known as primary production which later on creates plant biomass or biomaterial. The rate of storage of photosynthetic products is known as 'primary productivity'. The energy remaining as organic matter (after respiration) is called as net primary productivity (NPP). N.P.P. is expressed as KCal or g/m2/yr. NPP accumulates over time as plant biomass. It is expressed as dry weight of organic matter per unit area (g/m2). Biomass differs from production, which is the rate of organic matter production by photosynthesis. N.P.P. and biomass of some world ecosystems are given in Table 19.2. The biomass is all forms of matter derived from biological activities and present on the surface of soil or at different depth of vast body of water, lakes, rivers, sea and ocean.
Ecosystems (in order of productivity) |
Mean net primary production per unit area (g/m2/yr) |
Mean biomass per unit area (kg/m2) |
Tropical forests | ||
Rain | 2,000.0 |
44.00 |
Seasonal | 1,500.0 |
36.00 |
Temperate forests | ||
Evergreen | 1,300.0 |
36.00 |
Deciduous | 1,200.0 |
20.00 |
Boreal forest | 800.0 |
20.00 |
Savanna | 700.0 |
4.00 |
Wood land and shrub land | 600.0 |
4.00 |
Tundra and alpine meadows | 144.0 |
0.67 |
Desert shrub | 71.0 |
0.67 |
Moreover, photosynthetic efficiency affects the accumulation of biomass as it depends on plant efficiency and light intensity. We are fortunate enough to have abundant sun-shine in our country. Total energy received in India is about 60 x l013 MWH, with 250-300 days of useful sun shine per year in most part of the country (Anonymous, 1981).
Table 19.3. Biomass as the source of energy.
Sources of biomass | Forms of biomass | Conversion process | Forms of energy |
A. Plantations : | |||
Silviculture | Fire wood | Combustion | Heat (fire) |
(Energy plantations) | Fuel wood | Destructive distillation | Charcoal |
Agriculture | Carbohydrate | Fermentation | Ethanol |
(Energy crops) | Hydrocarbon | Fermentation | Fuel oil |
Aquatic biomass | Aquaculture | Fermentation | Methanol |
Weeds | Whole plant body | Fermentation | Methane |
B. Residues/wastes/weeds : | |||
Rural/urban/industrial wastes |
Wastes | Combustion | Fire/fuel |
Pyrolysis | Fuel oil | ||
Fermentation | Methan and ethanol | ||
Forestry wastes | Wastes | Combustion | Fire/fuel |
Pyrolysis | Oil gas | ||
Gasification | ,Gas | ||
Fermentation | Methane, ethanol | ||
Agricultural wastes | Wastes | Fermentation | Methane |
Weeds and aquatic biomass | Fermentation | Methane | |
Cattle | dung | Combustion | Fire/fuel |
Fermentation | Methane (Biogas) |
Photo-respiration differs from the normal respiration. The later takes place in dark and is associated with oxidation of compounds produced during photosynthesis, which occurs in peroxisomes. Photo-respiratory CO2 arises from glycolate pathway, not from glycolysis. In this pathway, 4 molecules of glycolates are converted into one molecule of glucose and 2 molecules of CO2; CO2 is released when glycine is converted into serine. Glycolate is oxidized to glycolate by enzyme glycolate oxidase.