Bioconversion of CO 2 and Biomass processes

1. Bioconversion of CO2 and Biomass processes 朱信 Hsin Chu Professor Dept. of Environmental Engineering National Cheng Kung University

2. Bacterial methanogens Nonphotosynthetic pathways for carbon dioxide fixation • Algae photosynthesis • Plants photosynthesis

3. Methanogenic and Acetogenic Bacteria • 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)

4. 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 COMethanosarcina 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

5. 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

6. 1.3 Bio Conversion of Methane to Methanol (Car Fuel) • Methylosinus trichosporium Has methane monooxygenase • Methylobacterium organophylum Has methane oxygenaye

7. 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.

8. 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.

9. 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-

10. 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

11. 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