08.08.2015   Switchgrass

Processing Routes for Cellulosic Ethanol Fermentation

Biofuel production (such as ethanol) is a complex process using lignocellulosic feedstock (such as switchgrass, sweet sorghum bagasse, pine wood chips, etc.) compared to sugarcane syrup or corn. The carbohydrates in lignocellulosic feedstock are much more problematic in terms of both solubility and utilizing their different component sugars (mainly glucose, xylose and arabinose) compared to starch in corn or sucrose in sugarcane syrup. The complexity of lignocellulosic feedstock provides different routes for fermentation including direct microbial conversion (DMC), separate hydrolysis and fermentation (SHF) and simultaneous saccharification and co-fermentation (SSCF).

Strain

Xylose [g T1]

Ethanol

bl-‘l

Yield [g g_1]

Productivity

Ійі-‘И

References

Bacteria: naturally occurring

Bacillus macerans DMS 1574

20

3.30

0.16

0.03

Schepers et al. 1987

Bacteroides polypragmatus NRCC 2288

44

6.50

0.15

0.09

Patel 1984

Clostridium saccharolyticum ATCC 35040

25

5.20

0.21

0.05

Asther et al. 1985

C. thermohydrosulfuricum 39E

5

2.00

0.39

Ng et al. 1981

Envinia chrysanthemi B374

5

0.23“

Tolan and Firm 1987

Thermoanaerobacter ethanolicus ATCC 31938

4

1.50

0.36

Lacis and Lawford 1988

Bacteria: recomb inantb

Envinia chrysanthemi B374 (pdc)

5

0.44“

Tolan and Finn 1987

Escherichia coli B, pL01297 (pdc, adhB)

80

39.20

0.49

0.70c

Ohta et al. 1990

E. coli В KOll (pdc, adhB, frd")

80

41.60

0.52

0.87

Ohta et al. 1991a

Klebsiella oxytoca M5A1 (pdc, adhB)

100

46.00

0.46

0.96

Ohta et al. 1991b

Klebsiella planticola SDF20 (pdc, pfh)

17

7.70

0.44

0.18

Feldmann et al. 1989

Zymomonas mobilis CP4 (pZB5)

25

11.00

0.44

0.57

Zhang et al. 1995

Yeasts: naturally occurring

Candida blankii ATCC 18735

50

5.10

0.10

0.07

Gong et al. 1983

Ccutdidci fennel tci

20

3.90

0.20

0.07

Nigam et al. 1985

Candida fructus JCM-1513

20

4.70

0.24

0.02

Baraniak et al. 1988

336 Compendium of Bioenergy Plants: Swii

Candida guilliermondii ATCC 22017

40

4.50

0.11

0.04

Maleszka et al. 1982

Candida shehatae CBS 4705

50

24.00

0.48

0.19

Slininger et al. 1985

Candida shehatae CSIR-Y492

90

26.20

0.29

0.66

du Preez et al. 1983

Candida sp. CSIR-62 A/2

50

20.10

0.40

0.42

du Preez et al. 1985

Candida tenius CBS 4435 (ll)d

20

6.40

0.32

0.03

Toivola et al. 1984

Candida tropicalis KY 5014 (2)

20

2.80

0.14

0.06

Morikawa et al. 1985

Clavispora sp. UWO(PS) 83-877-1 (ll)d

20

5.90

0.30

0.11

Nigam, Margararitis et al. 1985

Kluyveromyces cellobiovorus KV 5199 (3)

20

4.40

0.22

0.09

Morikawa et al. 1985

Kluyveromyces marxianus

20

5.60

0.28

0.10

Margaritis et al. 1982

Pachysolen tannophilus NRRL Y-2460

20

6.20

0.31

0.06

Delgenes et al. 1986

Pachysolen tannophilus RL171

50

13.80

0.28

0.28

Woods and Millis 1985

Pichia segobiensis CBS 6857

20

5.00

0.25

0.02

Toivola et al. 1984

Pichia stipitis CBS 5773(5)

20

5.90

0.30

0.02

Toivola et al. 1984

Pichia stipitis CBS 5776

50

22.30

0.45

0.34

Tran and Chambers 1986

Schizosaccharomyces pombe ATCC 2478 (8)

50

5.00

0.10

0.07

Gong et al. 1983

Yeasts: recombinant’

Saccharomyces cerevisiae (XYL 1, XYL 2)

21.7

1.60

0.07

0.07

Kotter and Ciriacy 1993

Saccharomyces cerevisiae TJ1 (XYL 1, XYL 2)

50

2.70

0.05

0.02

Tantirungkij et al. 1993

Saccharomyces cerevisiae H550 (XYL 1, XYL 2)

49.2

0.30

0.01

0.01

Meinander et al. 1994

Schizosaccharomyces pombe (xyl A)

50

21.00

0.42

0.19

Chan et al. 1989

Table 4. contd….

Biological and Biosystems Engineering 337

Note:

ag ethanol gA xylose consumed

bThe relevant genotype is given in parantheses. pdc, pyruvate decarboxylase; pfl, pyruvate formate lyase; adhB, alcohol dehydrogenase II;/rd, fumarate reductase, pZB5 carries the genes for xylose isomerase, xylulokinase, transketolase and transalolase cMaximum volumetric productivity

dFigures in parentheses denote number of strains investigated (if more than one)

eThe relevant genotype is given in parenthese. XYL 1, xylose reductase; XYL 2, xylitol dehydrogenase; xyl A, xylose isomerase

Note:

SSF, Simultaneous saccharification and fermentation SSCF, Simultaneous saccharification and co-fermentation SHCF, Separate hydrolysis and co-fermentation

Direct Microbial Conversion (DMC) or Consolidated Bio-Processing (CBP)

Direct Microbial Conversion (DMC) is a consolidated process of production of cellulolytic enzymes (cellulase and xylanase mixture), hydrolysis of lignocellulosic biomass and fermentation into bioproducts such as ethanol in a single vessel. Clostridium phytofermentans would be an ideal microorganism for DMC ethanol production. However, C. phytofermentans has been reported to produce low ethanol yields (less than 0.2% (w/v)) with several by-products such as hydrogen, acetic acid, and formic acid that ultimately lowers ethanol productivity (Warnick et al. 2002).