Transcript Biocnversion of CO2 and Biomass processes

Bioconversion of CO2 and
Biomass processes
朱信
Hsin Chu
Professor
Dept. of Environmental Engineering
National Cheng Kung University
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Bacterial methanogens
Nonphotosynthetic pathways for
carbon dioxide fixation
Algae photosynthesis
Plants photosynthesis
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1. Methanogenic and Acetogenic
Bacteria
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Methanogenic archaebacteria
Obligate anaerobes: grow in freshwater and
marine sediments, peats, swamps and wetlands,
rice paddies, landfills, sewage sludge, manure
piles, and the gut of animals
Major cause of the natural methane release
More than half: 0.4 × 109 tons/yr
Optimal condition
20~95℃
Use either CO+H2 or CO2+H2 as their only
sources of carbon and energy (carbon monoxide
dehydrogenase/acetyl-CoA synthase)
CO  H 2O
CO2  2H   2e
CH3  CFeSP  CO  CoA
acetyl  CoA  CFeSP
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1.1 Thermophilic Methanogens
 Waste gases from blast furnaces: CO + H2 + CO2
Low caloric value: 755 kcal/m3
A column bioreactor: 55℃ and pH 7.4
 A mixture of cultures of three bacteria
Among them, the photosynthetic bacterium Rhodospirillum
rubrum carries out the water gas-shift reaction:
CO + H2O → H2 + CO2
 A mixture of two methanogens
Methanobacterium formicicum provides a high rate of
hydrogen uptake but is inhibited by CO
Methanosarcina barkeri has a smaller rate of hydrogen
uptake but is more tolerant of CO
4H2 + CO2 → CH4 + 2H2O
High caloric value → 6420 kcal/m3
 The methane yield was about 83%, compared to the
nonbiological catalytic methods: 300~700℃ and 3~20 atm
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1.2 Extremely Thermophilic Methanogens
80~110℃
Using CO2 as their sole carbon source and
molecular hydrogen or reduced sulfur compounds
as electron donors
May be the earliest and most primitive forms of
life that still exist
Methanothermas fervidus
Found at shallow depth from a volcanic spring in
Iceland
Methanococcus jannaschij
Found from a deep-sea hydrothermal vent
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1.3 Bio Conversion of Methane to
Methanol (Car Fuel)
Methylosinus trichosporium
Has methane monooxygenase
Methylobacterium organophylum
Has methane oxygenaye
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1.4 Thermophilic Homoacetogens
 Homoacetogenic bacteria
strictly anaerobic
 Thermoanaerobacter kivui
4 H2 + 2 CO 2 → CH3COOH + 2H2O
 The carboxy group is derived from CO, which is formed
from CO2 by the nickle enzyme carbon monoxide
dehydrogenase.
 The methyl group is formed by the reduction of CO2 in
sequence first by formate dehydrogenase, followed by
a series of enzymatic reactions on reduced C1
intermediates bound to tetrahydrofolate.
 Acetyl-CoA is then produced from the methyl group
and CO in a reaction catalyzed by carbon monoxide
dehydrogenase.
 Acetogenesis was suggested to be involved in recycling
of 10 to 20% of the carbon on earth.
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2. Algae Photosynthesis
 Natural photosynthesis in plants and microorganisms
About 1011 tons CO2/yr
However, the efficiency of solar energy conversion in
plant production under optimal growth conditions is
only 5 to 6%.
Under field conditions, only 1~2% for sugarcane, 0.15%
for forests
 Photosynthesis is much more efficient in microalgae
than in terrestrial C3 and C4 plants.
Algae can utilize the high concentrations of nitrate and
phosphate nutrients contained in municipal and
agricultural effluents for the fixation of CO2 emitted
from power stations or steel plants.
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Ribulose-1, 5-biphosphate
carboxylase/oxygenase (RuBisCO)
The most abundant protein on earth
(1) Acting as monooxygenase when O2 is the
substrate
(2) Acting as carboxylase when CO2 is the
substrate
Aquatic cyanobacteria and microalgae
In the form of HCO3-
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2.1 Microalgae
 Marine green alga Tetraselmis suecica
The photosynthetic efficiency is 9~10% (optimal) or
4.6~5.1% (field).
The CO2 utilization efficiency is close to 100%.
Good for ambient air (0.035% CO2), pure CO2, and stack
gases (15% CO2).
Max. growth rate ≒ 0.61 d-1.33
Maximal growth rate with 20% CO2 in a mineral nutrient
medium at an NaCl conc. of 1.5%
Growth rate is still 50% of the maximal even at 9% NaCl.
 Hot spring alga chlorella sp. UK 001
Optimal growth temp. in the ranges 35 to 40℃
Max. growth rate >> 0.32 h-1.39
2.2 Macroalgae
Marie macroalgae Gracilaria sp. and Gracilaria chilensis also
work
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3. Biomass Process
 Plants: carbohydrate, cellulose
Microorganisms: algae, bacteria
 Next slide (Tale 6.1)
The composition of plants is remarkably constant.
Stoichiometric composition of wood: CH1.44O0.66
Photosynthesis reaction:
CO2 + 0.72H2O → CH1.44O0.66 + 1.03O2
 Second slide (Table 6.2)
Biomass can be burned as fuel
 Third slide (Table 6.3)
Rapid rotational crops: energy farms
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