Development of integrated bioprocess for ethanol production from sugar beet

 Dr. sc. Božidar Šantek, Full Professor Department of Biochemical Engineering, Faculty of Food

Technology and Biotechnology, University of Zagreb,Pierotijeva 6/IV, HR-10000, Zagreb, Croatia

bsantek@pbf.hr 

Introduction

- biofuels are viable and realistic alternative in the energy market due to rising environmental concerns and oil prices - biodiesel from plant oils and from animal waste fats - bioethanol from grains, sugar cane and sugar beet - bioethanol production from lignocellulose raw materials at the beginning of the large- scale commercial production (e.g. new plants in the USA)- the production costs of biofuels are higher than production costs of gasoline from fossil oil (e.g. gasoline is 2 times cheaper than bioethanol)

Figure 1. General unit operations in bioethanol production from sugar beet.

LCA -bioethanol prodution from sugar beet

Table 1. Unit operations incorporated in different ethanol production plants used for determination of total and specific area for embedding processes.

Unit operations Process assignation

1 1a 2 3 4 5 6 7 8

Washing /slicing + + + + + + + + +

Diffusion + + + + + - - A A

Evaporation + + + - - - - - -

Sterilization - - - + + - - - -

Juice fermentation + + + + + - - - -

Beet pulp fermentation - - - - - + + A A

Centrifugal separation + + + + + - - - -

Distillation + + + + + + + A A

Ethanol dehydration + + + + + + + + +

Stillage evaporation + + + + - + - - -

Pulp pressing - - - - - + - + -

Pellets forming/drying + + + + - - - + -

Biogas production - - - - + - + - +

Heat recuperation - +* + - - - - + -

(+) incorporated in the process; (-) not incorporated in the process; (*) the calculation with the 50 % of heat recuperation; (A) simultaneous sugar extraction, fermentation and product recovery.

Table 2. Total energy consumption for different processes of bioethanol production from sugar beet

Process No.

Specific energy consumption(kWh/kg)

1 14.875

1a 7.538

2 3.148

3 7.121

4 4.467 (1)

5 3.281

6 0.619 (1)

7 3.068

8 0.411 (1)

(1) Energy obtained from biogas counted in as goodness

0

300

600

900

1200

1500

1 1a 2 3 4 5 6 7 8

Process No.

ato

t (m

2 a/k

g)

Figure 2. The ecological footprint (specific area; atot)

of examined processes for ethanol production.

Experimental set-up of stirred tank bioreactorSugar beet juice- addition of NH4H2PO4 as N and P suorce (1 g/L) - medium sterilization at 121 oC for 20 min prior to inoculation with yeast Saccharomyces cerevisiae - ethanol production in STB (5 L) at 28 oC with 10 % v/v yeast suspension - batch and fed batch cultivation techniques were used - pH value was maintained in the range of 4.5 - 5.0 by the addition of 0.1 M NaOH and 0.1 M H2SO4 - feeding in the fed batch process started when carbon source was almost completely depleted by the addition of a few portions of concentrated sugar beet juice (200 mL; approx. 800 g/L of sugar)

Figure 3. Alteration of substrate (S,●), ethanol (P1,▲) and glycerol (P2,∆) concentration during batch fermentation of raw sugar beet juicein stirred tank bioreactor

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t /h

S, P

1/(g/

L)

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12

P2/(

g/L

)

Figure 4. Alteration of substrate (S,■), ethanol (P1,▲), glycerol (P2, □) and biomass (X, ●) concentration, pH (○) and broth absorbance (A600nm,∆) during fed batch fermentation of raw sugar beet juice in stirred tank bioreactor. Arrows represent the addition of concentrated fresh medium during the fed batch process.

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t /h

S, X

, P

1/(g/

L)

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A60

0nm

, pH

, P2/(

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)

Experimental set-up of HRTB

Sugar beet cossettes- ethanol production at room temperature after bioreactor sterilization at 121 oC for 30 min. - 5 kg of non-sterile raw sugar beet cassettes (23 % dry matter) - addition of NH4H2PO4 (1 g/kg raw sugar beet cossettes) - inoculum Saccharomyces cerevisiae - different quantities of inoculum (9.1-23.7 % V/m of raw sugar beet cossettes) in order to define the broth minimal liquid content - different operational conditions of HRTB [rotation, the working volume of bioreactor (range 20 – 70 %)]

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t /h

P2,P

3/(g/

L);

DM

/%

0

5

10

15

20

25S

, P1/(

g/L

)

Figure 6. Alteration of substrate (S,●), ethanol (P1,▲), glycerol (P2,∆), acetate (P3,□) concentration and dry mass of sugar beet cossettes (DM,○) inside raw sugar beet cossettes during fermentation in HRTB with the inoculum of 16.7 % V/m by periodical rotation

Figure 7. Alteration of substrate (S,●), ethanol (P1,▲), glycerol (P2,∆), acetate (P3,□) concentration in the liquid part of the fermentation broth in the HRTB with inoculum of 16.7 % V/m by periodical rotation

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t /h

S, P

1/(g/

L)

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14

P2,P

3/(g/

L)

Table 3. Comparison among different systems for ethanol production from intermediates of sugar beet processing

Production system t / h Y P/S / g/g E /% Pr / g/(L·h)

RSBJ+STB+BP 98.5 0.424 78.8 0.608

RSBJ+STB+FBP 234 0.502 93.4 0.503

RSBC+HRTB (9.1 % V/m of INM) 93 0.386 71.7 0.497

RSBC+HRTB(13 % V/m of INM) 99 0.369 68.6 0.464

RSBC+HRTB(16.7 % V/m of INM) 102 0.428 79.5 0.476

RSBC+HRTB (20 % v/m of INM) 90 0.281 52.3 0.357

RSBC+HRTB (23.1 % V/m of INM) 68 0.308 57.3 0.467

RSBJ - raw sugar beet juice, RSBC - raw sugar beet cossettes, STB - stirred tank bioreactor, BP - batch process, FBP - fed batch process, INM - inoculum

Rotational set-up of HRTB during ethanol production from raw sugar beet cossettes

Table 4. Investigation of the manner of HRTB rotation

Table 5. Investigation of optimal rotation interval and speed of HRTB

Interval of HRTB rotation (min/h)

3 6 9 12 15

HRTB rotation speed (min-1)

5 + + + + +

10 + + + + +

15 + + + + +

Manner of HRTB rotation Periodical(3-4 rotation/ day)

Constant rotation

HRTB rotation speed (min-1)

5 + +

10 + +

15 + +

Figure 8. Alteration of substrate (S,●), ethanol (P1,▲), glycerol (P2,∆), acetate (P3,□) concentration and dry mass of sugar beet cossettes (DM,○) inside raw sugar

beet cossettes the fermentation broth in HRTB with the inoculum of 16.7 % V/mby 3 min/h rotation and the rotation speed of 15 min-1

020406080

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t(h)

S(gL

-1),

P1 (g

L-1)

0

5

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15

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25

P2 (g

L-1),

P3 (g

L-1),

DW

(%)

Figure 9. Alteration of substrate (S,●), ethanol (P1,▲), glycerol (P2,∆), acetate (P3,□) concentration in the liquid part of the fermentation broth in HRTB with the inoculum of 16.7 % V/m by 3 min/h rotation and the rotation speed of 15 min-1

020406080

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t(h)

S(gL

-1),

P1 (g

L-1)

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25

P2 (g

L-1),

P3 (g

L-1),

DW

(%)

Conclusions

- sugar beet juice and cossettes can be successfully used for ethanol production. - the use of raw sugar beet cossettes in ethanol production eliminates extraction process of sugar beet cossettes by hot water, which considerably reduces energy demand for bioethanol production and final ethanol price. - further research of ethanol production from the raw sugar beet cossettes is required combined with improvement of sampling techniques due to the system heterogeneity

Thank you for your attention !!!