Dried Distillers ’ Grains and Solubles (DDGS)

Dry and wet mill ethanol production from corn starch is regarded as an essentially mature technology for producing bioethanol. Currently, dry-grind ethanol plants produce the majority of ethanol fuel (ca. 60%) in the United States. With concerns regarding net energy balance and food compared to fuel debate, ethanol production from corn is expected to stabilize (von Braun 2007). Some incremental increases in energy efficiency of this process, however, can be expected as coproduct (DDGS) utilization is incorporated into next — generation plants. Currently, DDGS from corn ethanol production is used as animal feed. Seven million metric tons of DDGS were estimated to have been produced from corn ethanol processing in the United States at the end of 2008 (Blaschek et al. 2010). DDGS conversion into liquid fuels and incorporation of DDGS into the ethanol biorefinery industry will increase the efficiency and profitability of corn ethanol plants (Blaschek et al. 2010).

Ezeji and Blaschek (2008a) conducted a comprehensive study evaluating fermentation capability of dilute acid, LHW, or AFEX pretreated DDGS hydrolysates by solventogenic Clostridium species. The ABE production profiles over the course of a 120-hour fermentation of detoxified dilute acid pretreated DDGS hydrolysates elucidated that C. beijerinckii 260, Clostridium acetobutylicum 824, Clostridium saccharobutylicum 262, C. beijerinckii 592, and C. beijerinckii BA101 produced maximum ABE concentrations of 8.1, 4.9, 12.1, 7.5, and 6.8 g/L, respectively, and total residual acids of 4.7, 4.2, 5.2, 4.0, and 4.1 g/L, respectively (Table 3.2). During the 72-hour fermentation of LHW and AFEX pretreated DDGS and con­tained 48.8 and 41.4 g/L total sugars, C. beijerinckii 260, C. acetobutylicum 824, C. saccharo- butylicum 262, C. beijerinckii 592, and C. beijerinckii BA101 produced maximum ABE concentrations of 12.8, 11.4, 10.5, 12.9, and 11.5 g/L, respectively, and total residual acids of 4.0, 5.3, 4.9, 7.4, and 4.4 g/L, respectively. For AFEX pretreated DDGS medium, C. beijer — inckii 260, C. acetobutylicum 824, C. saccharobutylicum 262, C. beijerinckii 592, and C. bei- jerinckii BA101 produced maximum ABE concentrations of 10.2, 9.0, 7.9, 11.6, and 10.4 g/L, respectively, and total residual acids of 5.4, 4.0, 5.2, 4.3, and 5.1 g/L. Importantly, LHW

Table 3.2. Production of butanol from lignocellulosic biomass. Table shows type of pretreatment and biomass detoxification processes employed prior to ABE fermentation.

Substrate

Hydrolysis Method

Treatment to Remove Inhibitors

Culture

Butanol Produced (g/L)

ABE

Produced (g/L)

Yield

(g ABE/g sugar)

References

Bagasse

Alkali pretreated + enzyme hydrolyzed

Ammonium sulfate + activated carbon

Clostridium

saccharoperbutylacetonicum ATCC 27022

11.0

14.0

0.30

Soni et al. (1982)

Rice straw

Above

Above

Above

10.0

13.0

0.28

Soni et al. (1982)

Wheat straw

Alkali pretreated + enzyme hydrolyzed

None

Clostridium acetobutylicum IFP 921

10.3

17.7

0.22

Marchal et al. (1984)

Corn stover

Steam explosion

Ca(OH)2

C. acetobutylicum NCIB644

8.0

12.8

0.27

Marchal et al. (1986)

Corn fiber

Dilute sulfuric acid

XAD-4 resin

Clostridium beijerinckii BA101

6.4

9.3

0.39

Qureshi et al. (2008a)

DDGS

AFEX

None

C. beijerinckii 260

7.7

10.2

0.32

Ezeji & Blaschek (2008a)

Above

Hot water

None

C. acetobutylicum 824

8.5

11.4

0.31

Ezeji & Blaschek (2008a)

Above

Dilute sulfuric acid

Over-liming

Clostridium saccharobutylicum 262

C. beijerinckii 260 C. beijerinckii 592 C. acetobutylicum 824

7.2

5.6

5.2 3.8

12.1

8.1

7.5

4.9

0.35

0.31

0.30

0.31

Above

Above

Above

Above

ABE, acetone butanol ethanol; DDGS, dried distillers’ grains and solubles; AFEX, ammonia fiber expansion.

and AFEX pretreated DDGS hydrolysates were not subjected to any detoxification process prior to fermentation and there was no significant difference between total ABE produced from DDGS and that of the control (mixed glucose-mannose-arabinose-xylose [GMAX]) with cor­responding amounts of GMAX. Wang et al. (2009a), in addition, investigated the effect of total solids loading on pretreatment of DDGS by electrolyzed water and ABE fermentation. DDGS samples pretreated at 30% solids loading with alkaline electrolyzed water (ALEW) produced 16.9 g/L total ABE in 72 hours upon fermentation by C. beijerinckii P260.

To improve C. beijerinckii BA 101 tolerance to toxic compound generated during pretreat­ment and hydrolysis of lignocellulosic biomass and enhance fermentation capability of AEW — pretreated DDGS, Wang et al. (2009b) conducted microorganism adaptation studies where C. beijerinckii BA 101 was treated with increasing amounts of acid-pretreated DDGS hydro­lysates containing lignocellulosic degradation compounds that are inhibitory to solventogenic Clostridium species. Hydrolysates — adapted C. beijerinckii BA101 strains were able to adjust to the inhibitory environment in less than 20 hours and produce approximately the same amount of ABE at a comparable time to that of the control fermentation.

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