1 Bioconversion of CO 2 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 1.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 × 10 9 tons/yr  Optimal condition 20~95 ℃  Use either CO+H 2 or CO2+H 2 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 + H 2 + CO 2 Low caloric value: 755 kcal/m 3 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 + H 2 O → H 2 + CO 2  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 4H 2 + CO 2 → CH 4 + 2H 2 O High caloric value → 6420 kcal/m 3  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 CO 2 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 1.3Bio 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 H CO 2 → CH 3 COOH + 2H 2 O  The carboxy group is derived from CO, which is formed from CO 2 by the nickle enzyme carbon monoxide dehydrogenase.  The methyl group is formed by the reduction of CO 2 in sequence first by formate dehydrogenase, followed by a series of enzymatic reactions on reduced C 1 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 tons CO 2 /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 C 3 and C 4 plants. Algae can utilize the high concentrations of nitrate and phosphate nutrients contained in municipal and agricultural effluents for the fixation of CO 2 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 O 2 is the substrate (2)Acting as carboxylase when CO 2 is the substrate  Aquatic cyanobacteria and microalgae In the form of HCO 3 -

Microalgae  Marine green alga Tetraselmis suecica The photosynthetic efficiency is 9~10% (optimal) or 4.6~5.1% (field). The CO 2 utilization efficiency is close to 100%. Good for ambient air (0.035% CO 2 ), pure CO 2, and stack gases (15% CO 2 ). Max. growth rate ≒ 0.61 d Maximal growth rate with 20% CO 2 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 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) Next slide (Tale 6.1) The composition of plants is remarkably constant. Stoichiometric composition of wood: CH 1.44 O 0.66 Photosynthesis reaction: CO H 2 O → CH 1.44 O O 2  Second slide (Table 6.2) Second slide (Table 6.2) Biomass can be burned as fuel  Third slide (Table 6.3) Third slide (Table 6.3) Rapid rotational crops: energy farms