Agricultural residues and energy crops as potentially ... - PubAg - USDA

10117 CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources 2010 5, No. 059

Review

Agricultural residues and energy crops as potentially economical and novel substrates for microbial production of butanol (a biofuel) N. Qureshi* Address: United States Department of Agriculture, National Center for Agricultural Utilization Research, Bioenergy Research Unit, 1815 N University Street, Pecoria, IL 61604, USA. *Correspondence: Fax: (309) 681-6427. Email: [email protected] 25 May 2010 5 October 2010

Received: Accepted:

doi: 10.1079/PAVSNNR20105059 The electronic version of this article is the definitive one. It is located here: http://www.cabi.org/cabreviews g

CAB International 2010 (Online ISSN 1749-8848)

Abstract This review describes the production of acetone butanol ethanol (ABE) from a variety of agricultural residues and energy crops employing biochemical or fermentation processes. A number of organisms are available for this bioconversion including Clostridium beijerinckii P260, C. beijerinckii BA101, Clostridium acetobutylicum and Clostridium saccharobutylicum P262. Some of these strains (P260 and P262) were used in an industrial setting in South Africa. One of the major limitations of these cultures is that none of them produce greater than 30 g/l total ABE unless integrated with simultaneous product recovery to reduce the toxicity of accumulated products. These cultures can utilize both hexose and pentose sugars derived from lignocellulosic hydrolysates such as maize (corn) fibre, wheat straw (one of the novel substrates), barley straw, maize stover and switchgrass. Substrates such as Jerusalem artichoke, maize, rye, millet, molasses, potato, soya molasses and agricultural wastes can also be used by the cultures listed. Additional carbohydrates that can be used include dextrins, fructose, sucrose and lactose. It is recommended that cultures that can produce greater amounts of ABE per litre of culture broth be developed. In order to economize the process of butanol production by fermentation, process technologies have been developed that integrate lignocellulosic biomass hydrolysis, fermentation and simultaneous product recovery. It should be noted that in continuous process where a product was recovered simultaneously, 461.3 g/l ABE was produced from 1125 g sugar in a 1 litre culture volume. Keywords: Butanol, Acetone butanol ethanol (ABE), Agricultural residues, Wheat straw, Corn stover, Clostridium beijerinckii P260, Simultaneous saccharification fermentation and recovery (SSFR), Butanol/ABE yield, ABE productivity Review Methodology: We searched the literature using ScienceDirect with the following keywords: Butanol production from agricultural residues; Butanol from wheat straw, corn stover and barley straw; economic analysis of butanol fermentation. We also searched the literature using Google with the above phrases and keywords.

Introduction Butanol fermentation was first discovered by Pasteur in 1861 [1], and this work was followed by studies on the

Mention of trade names of commercial products in this review is solely for the purpose of providing scientific information and does not imply recommendation or endorsement by the United States Department of Agriculture.

production of this chemical and feedstock by various investigators in the latter part of the nineteenth century. In the early part of the twentieth century, Chaim Weizman (Manchester University, 1912) isolated a bacterial strain capable of producing significant amounts of acetone and butanol that was named Clostridium acetobutylicum. He operated the first acetone production plant from starch. At that time (during the First and Second World Wars), acetone was used strategically to make cordite, a smokeless gun powder and large plants were erected in USA and

http://www.cabi.org/cabreviews

2

Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources

Canada. During the war periods, there was little use of butanol. However, after the war, demand increased and the fermentation substrate was changed to molasses [2]. Following the expiration of the Weizman patent in the 1930s, large plants were erected in Japan, the USA and South Africa (NCP: National Chemical Products in Germiston). During the 1950s and 1960s, the production of butanol suffered because of consistent bacteriophage infections, decreased molasses quality (through improved sugar processing), increased molasses prices (because of increased use for animal feed) and reduced butanol prices as a result of improved petrochemical technology (chemicals and fuels were produced at cheaper prices because of developed petroleum processes and technologies). Since acetone butanol ethanol (ABE) fermentation could not compete with petroleum-derived butanol, numerous plants were closed. However, a number of plants in South Africa, China and former Soviet Union continued to be in operation until the early 1980s. Some butanol plants continued operation in China and former Soviet Union even until after the 1980s, but, little was known about these plants. In a report presented in the Clostridium 10 scientific meeting (Wageningen, The Netherlands), it was disclosed that some ABE plants were still operational in China [3]. In this meeting, at least one new plant was reported to be in operation in Brazil. In anticipation of the depletion of fossil fuels, increasing prices of transportation oils and climatic/environmental changes, research interest on the production of butanol from renewable resources has returned. Research has intensified and the use of agricultural residues and waste materials along with new process technology is being sought. A number of reports have emphasized that the cost of the substrate is one of the most influential factors for the production of butanol [4–6]. For this reason, maize or molasses cannot be used as substrates because their value as food and feed increase their cost, making them uneconomical. Hence, substrates such as agricultural residues, including wheat straw, barley straw, maize stover and switchgrass offer potential alternatives. Their prices ranged from $26.5 to $66.1 per tonne as opposed to $256.3 per tonne for maize about one-and-a-half years ago [7]. This suggests that maize price is several times higher than the residue price. In addition to feedstock price, process technology such as the development of high-productivity reactors, recovery of final product using alternative product removal techniques and process integration such as combining hydrolysis (biomass), fermentation and product recovery is expected to make a significant contribution in reducing production costs for butanol. It should be noted that butanol is a superior fuel to ethanol as it contains 30% more energy and its low vapour pressure facilitates its use in existing gasoline supply and distribution channels [8]. Compared to ethanol, butanol is less volatile, not sensitive to water, less hazardous to handle, less flammable, has a slightly higher octane number

and can be mixed with gasoline in any proportion. For these reasons, production of butanol from agricultural residues is gaining momentum. In a report on the production of butanol from corn cobs, Marchal et al. [9] scaled up the production of butanol from a 4 litre bioreactor to 48 000 litres successfully. This report and a report on a Russian plant [2] suggest that the use of agricultural residues and energy crops along with newly developed process technologies will make the production of butanol economically viable. However, it should be noted that these agricultural residues require pretreatment to soften the cellulosic structure to make enzymes accessible to the fibrous structure. Chemical pretreatment may result in the generation of cell growth and fermentation inhibitors. This is one of the basic challenges that should be overcome when processing lignocellulosic biomass. The objective of this review is to present to the reader information on the production of butanol from various cellulosic biomass substrates and the process technologies that make it possible. In recent months, the use of several lignocellulosic materials including wheat straw, barley straw, maize stover, switchgrass, dried distillers’ grains and solubles, has been explored for such fermentation. It is also emphasized that detoxification of some of the biomass hydrolysates can be achieved by overliming [10, 11]. Additionally, a number of microbial cultures (Escherichia coli, Clostridium acetobutylicum, Lactococcus lactis, and Lactobacillus buchneri) are under development with the aim of producing butanol in higher concentrations from agricultural biomass hydrolysates [12, 13].

Microbial Cultures and their Capability of using Various Sugars A number of microbial strains exist that can produce butanol including C. acetobutylicum P262 (also known as Clostridium saccharobutylicum), C. beijerinckii P260, C. acetobutylicum NRRL B643, C. acetobutylicum ATCC 824, C. acetobutylicum B18, C. beijerinckii 8052, C. beijerinckii BA101 C. beijerinckii LMD 27.6. C. beijerinckii P260 and C. saccharobutylicum P262 are industrial strains and have been used in a butanol-producing commercial plant in South Africa. Other strains that have been used for this fermentation include Clostridium butylicum, Clostridium aurantibutyricum and Clostridium tetanomorphum. Details of some of these strains are provided in previous reports [1, 14]. A major characteristic of these strains is that they rarely produce greater than 30 g/l total ABE. The typical ratio of ABE in the fermentation broth is 3 : 6 : 1 of which butanol is the highest. An interesting advantage of butanol-producing cultures is that they can use both hexose and pentose sugars. In cellulosic biomass, the concentration of pentose sugars ranges from 20 to 30%. It should be noted that hexose- and pentose-containing substrates such as woody biomass, agricultural residues and energy


N. Qureshi

crops require hydrolysis to simple sugars prior to their use for fermentation. Substrates for Butanol Production Butanol-producing cultures can utilize a wide variety of carbohydrates including lactose, sucrose (molasses), glucose, fructose, mannose, dextrin, starch, xylose, arabinose and inulin derived from feed materials such as whey permeate, maize, millet, rye, sugar beet, wheat, oats, Jerusalem artichoke and sulfite waste liquor (a by-product of paper industry that contains glucose, xylose and arabinose). Xylose and arabinose are pentose sugars and are present in cellulosic substrates. The ability to use all these carbohydrates makes it possible to ferment nearly all the agricultural substrates such as woody biomass, agricultural residues, waste materials and energy crops including switchgrass and miscanthus. Cane molasses, whey permeate, potatoes, maize starch and soya molasses As a feedstock, cane molasses has numerous advantages compared to maize including easy handling and the fact that it contains sucrose that is easily hydrolysed by solventogenic (ABE) clostridia followed by the conversion of sugars to butanol. Additional advantages of molasses have been described elsewhere [14]. Whey permeate, a by-product of the dairy industry, is another valuable substrate which contains approximately 44–50 g/l lactose. Butanol-producing cultures can hydrolyse lactose to its component sugars followed by their use for producing butanol [15]. The culture does not require any additional exogenous enzyme for this hydrolysis. Whey permeate with this concentration of lactose is an ideal substrate for butanol fermentation as the culture cannot use more than 50 g/l sugar for producing ABE in a batch process. This limitation is because of the butanol toxicity to the culture. Since Clostridia are capable of hydrolysing starch, potatoes and potato wastes have been evaluated as potential substrates for fermentation [16]. Starch concentration in the medium was limited to 45–48 g/l. To investigate if the hydrolytic step is required before fermentation, both hydrolysed and unhydrolysed potatoes were used for this fermentation. Unhydrolysed potato starch resulted in the production of 12 g/l ABE, whereas after hydrolysis it resulted in the production of 10.4–11.4 g/l ABE suggesting that hydrolysis is not a requirement for using this substrate for ABE fermentation. Similarly, maize starch can be readily fermented to ABE. Soya molasses is another substrate that can be used for butanol fermentation. Spray-dried soya molasses contains approximately 746 g carbohydrates per kg of which 434 g/kg (58%) are fermentable sugars including glucose, sucrose, fructose and galactose [17]. The sugars that cannot be fermented by Clostridia include pinitol, raffinose,

3

verbascose, melibiose and stachyose. However, their use should be possible after hydrolysis either using enzymes or dilute acid. Alternately, a solventogenic strain can be developed that can hydrolyse these sugars to monomeric carbohydrates and convert them to butanol. In addition to the above-mentioned substrates, substrates such as contaminated maize and fruit industry wastes have been demonstrated to be useful for this fermentation [18].

Novel substrates for butanol production Maize fibre Maize fibre is a by-product of the maize wet milling process. In USA, 4.7106 dry tonnes of maize fibre are produced annually. This substrate has been used to produce butanol after hydrolysis using dilute sulfuric acid pretreatment and enzymatic saccharification [19]. It was discovered that hydrolysed maize fibre could not be fermented directly to butanol as it contained inhibitors that arrested cell growth and fermentation. In order to ferment this substrate, the hydrolysate was treated with lime [Ca(OH)2; overliming] followed by passing through a column packed with adsorbent resin XAD-4 (trade name). The inhibitors were removed and the resultant hydrolysate was fermented successfully. In the fermentation, 9.3 g/l ABE was produced using the treated hydrolysate. Since, maize fibre contains 60–70% carbohydrates, 4.7106 dry tonnes of maize fibre would result in the production of 1.22106 tonnes of ABE (0.733106 tonnes of butanol). In another report, maize fibre xylan was used to produce ABE [20] in an integrated process from which toxic butanol was removed simultaneously.

Distillers dry grains and soluble (DDGS) Because of low capital costs, the maize to ethanol conversion industry produces ethanol largely from dry-milled maize. Unlike the wet-milling process, in this process solids are not removed prior to fermentation to ethanol. After fermentation, solids that contain maize fibre, cell mass and other insoluble components are removed and dried. Currently, this cellulosic fibre and biomass is used as cattle feed. However, it is also viewed as a potential substrate for butanol fermentation. In the USA, 5.1109 kg of DDGS is produced annually. This amount of DDGS can be converted to 720106 kg of butanol (1.20109 kg ABE). In a recent study, Ezeji and Blaschek [21] used hydrolysed DDGS for the production of butanol using C. beijerinckii BA101, C. beijerinckii P260, C. acetobutylicum 824, Clostridium sacchrobutylicum P262 and C. butylicum 592. Prior to fermentation, DDGS was hydrolysed to monomeric sugars using various pretreatments (hot water, ammonia fibre expansion (AFEX) and dilute sulfuric acid) and enzymatic hydrolysis. Dilute sulfuric acid


4


(A) Biomass (wheat straw)

Product (butanol or ABE)

Hydrolysis of Biomass (step I)

Fermentation (step II)

Recovery (step III)

(B)

Biomass (wheat straw)

Hydrolysis + Fermentation + Recovery

Condenser

Reactor

Step I + II + III (combined)

Butanol or ABE

Figure 1 A schematic diagram of butanol/ABE production from biomass (wheat straw) in a separate hydrolysis, fermentation and recovery process, and in an integrated system. (a) Separate process. (b) Integrated process

pretreatment was found to be toxic to the cultures. In order to detoxify the hydrolysate, it was treated with Ca(OH)2. The detoxified hydrolysate resulted in the production of 4.9 to 12.1 g/l ABE. It should be noted that hot-water- and AFEX-pretreated DDGS did not require inhibitor removal from these hydrolysates. Hot-waterpretreated and enzymatically hydrolysed DDGS resulted in the production of 10.5–12.8 g/l ABE. AFEX-pretreated and enzymatically hydrolysed DDGS resulted in the production of 7.9–11.6 g/l ABE.

Wheat straw Wheat straw is another potential substrate that can be used for the production of ABE. In a recent study, wheat straw was pretreated using dilute (1%, v/v) sulfuric acid followed by enzymatic hydrolysis [22]. The hydrolysate so obtained was subjected to butanol fermentation using C. beijerinckii P260. Fermentation was vigorous and up to 25.0 g/l ABE was produced with a productivity of 0.60 g/l.h. This productivity is greater than 210% of that achieved in a control experiment where glucose was used as a substrate, suggesting that no inhibitors were present in the hydrolysate. Rather it was speculated that some unknown fermentation-stimulating chemicals were present that resulted in the enhanced production of ABE.

These studies suggested that wheat straw is an excellent substrate for butanol production by C. beijerinckii P260 and during pretreatment with dilute sulfuric acid no inhibitors were generated. Both increase in total ABE (25 g/l) and productivity will result in better economics of this biofuel production as compared to DDGS and maize fibre. Furthermore, the hydrolysate obtained in the above studies was supplemented with additional sugar (60 g/l), thus resulting in a total sugar concentration of 128.3 g/l [22]. Then the medium was used for ABE production in an integrated system from which ABE was recovered simultaneously. In this medium, cell growth was good and the culture produced 47.6 g/l ABE from 128.3 g/l sugar. As stated above, producing more than 30 g/l ABE is not possible because of butanol’s toxicity to the culture, unless butanol is simultaneously removed.

Simultaneous saccharification, fermentation and product recovery In the above process, wheat straw was hydrolysed prior to fermentation. This suggested that the process of butanol production from pretreated wheat straw would involve three separate steps known as saccharification or hydrolysis, fermentation and product recovery (Figure 1a). These three steps are sequential and must be


N. Qureshi

exercised in the order in which they are shown in this Figure. The use of these three steps would require comparatively more capital for bioconversion of wheat straw to butanol. In order to reduce the number of steps required for this biofuel production from wheat straw the above three steps were combined into one step and hence saccharification, fermentation and product recovery were performed simultaneously (Figure 1b). Wheat straw was hydrolysed using enzymes at fermentation conditions (35 C and pH 5.0). During biomass hydrolysis, the rate of generation of sugars was equal or higher than sugar consumption by the culture to produce butanol. The product (ABE) was recovered by gas stripping using gases (CO2 and H2) produced in the fermentation system [23, 24]. The gases were circulated through the bioreactor contents (wheat straw and cell mass) which picked butanol from the broth. In order to separate butanol vapours from the gases, the gases were cooled in a condenser and liquid butanol/ABE was collected in a receiver. The system was operated until all the sugars present in wheat straw were released and utilized by the culture for cell growth and butanol production. For such integrated processes, two different fermentation systems were used: batch and fed-batch. Schematic diagrams of the separate (hydrolysis, fermentation and recovery) process and the integrated process are presented in Figure 1a, b. It is interesting to note that even the reaction intermediates (acetic and butyric acids) could not leave the system until they were converted to butanol. Also, concentration of butanol/ABE in the recovered stream was much higher than present in the reactor which would also reduce the amount of energy required for further separation of butanol. By simultaneously removing butanol from the reactor, the concentration and thus the toxicity due to butanol was kept low which kept the culture growing and producing butanol continuously.

Barley straw Studies on the use of other substrates such as barley straw hydrolysate were performed [25]. The barley straw was hydrolysed in a similar manner as wheat straw and subjected to fermentation. The culture did not accumulate more than 7.1 g/l total ABE, suggesting that variability of substrate is an important factor when converting agricultural residues to butanol. In case of wheat straw hydrolysate, the culture was able to produce 25.0 g/l ABE with an enhanced productivity. The results obtained from barley straw hydrolysate fermentation (ABE 7.1 g/l and productivity 0.1 g/l.h) suggested that this substrate is toxic to the culture. To reduce this potential toxicity effect, the barley straw hydrolysate was subjected to a number of treatments including dilution with water, mixing with wheat straw hydrolysate (1 : 1 ratio) and treating with lime (overliming). The results obtained from all three treatment methods were encouraging. Treatment of the

5

hydrolysate with lime produced superior results (production of 26.6 g/l ABE with a productivity of 0.39 g/l.h) and demonstrated that this detoxification method is effective in removing fermentation inhibitors from the culture medium. Further studies on the use of this substrate and process integration for butanol production are being investigated.

Maize stover Maize stover is another potential substrate and is available in abundance in the mid-western region of USA. Approximately 2.201011 dry kg of stover could be available for the production of biofuels. For the current investigations on conversion of maize stover to butanol, the stover was hydrolysed using dilute sulfuric acid and the enzymatic method. The resultant maize stover hydrolysate was subjected to ABE fermentation using C. beijerinckii P260. The hydrolysate did not support any cell growth or fermentation, suggesting that it contained fermentation inhibitors. In order to circumvent this inhibitor problem, the maize stover hydrolysate was treated with lime as in case of barley straw hydrolysate and fermented using C. beijerinckii P260. Additionally, the dilution approaches were also applied. All three techniques were successful in reducing toxicity or removing inhibitors. The overlimed hydrolysate resulted in the production of 26.3 g/l ABE with a productivity of 0.31 g/l.h [7]. These and other studies suggest that the development of cultures capable of tolerating inhibitors would be of great benefit. In another report on the production of ABE from maize stover hydrolysate (65% total sugars), 25.6–25.8 g/l ABE was produced from this substrate [26]. No inhibition from inhibitors was reported. However, the maize stover was pretreated with SO2, followed by enzymatic treatment. It appears that pretreatment with SO2 does not result in the generation of inhibitors at toxic levels. It should also be noted that their hydrolysate contained 81.0–83.0 g/l total sugars as compared to 52.9–60.3 g/l that we achieved in our maize stover hydrolysate [7, 25].

Switchgrass Switchgrass is an energy crop and can be used for producing fuels including ABE. For this study, switchgrass hydrolysates were prepared as described for wheat straw and barley straw hydrolysates. The resultant hydrolysate was subjected to fermentation without any additional treatment and it resulted in the production of 1.5 g/l ABE. As this ABE concentration is low, it was speculated that fermentation inhibitors were present in the hydrolysate. In order to produce ABE, the above three detoxification techniques were applied to the hydrolysate. Upon dilution with water, the culture was able to produce 14.6 g/l ABE [7]. It should be noted that treatment with lime remained


6


Table 1 A comparison of butanol/ABE production from agricultural residues and energy crops

Culture

Substrate

ABE Max ABE concentration yield (7) (g/l)

C. C. C. C. C. C. C. C. C. C. C. C.

Potato starch Mixed Ag Res. Corn fibre DDGS Wheat straw Barley straw Corn stover Corn stover Switchgrass HW, CC, SS Corncobs Inulin

12.1 14.8 9.3+0.5 12.1 47.6 26.6 26.3 25.7 14.6 – 20.5 23–24

actobutylicum DSM1731 beijerinckii BA101 beijerinckii BA101 saccharobutylicum P262 beijerinckii P260 beijerinckii P260 beijerinckii P260 acetobutylicum P262 beijerinckii P260 acetobutylicum2 acetobutylicum IFP913 acetobutylicum IFP9042

0.241 – 0.39 0.31 0.37 0.43 0.44 0.34 0.39 0.36 0.31 –

ABE production (g/l.h) Comments

References

0.24 0.22 0.10 – 0.36 0.39 0.31 – 0.17 – 0.96 0.671

[16] [18] [19] [21] [22] [25] [7] [26] [7] [2] [9] [27]

Unhydrolysed potato starch Actual agric waste Lime and XAD-4 treated Lime-treated DDGS Simultaneous product removal Lime-treated hydrolysate Lime-treated hydrolysate Corn stover treated with SO2 Dilution with water Large plant in Soviet Union 48 m3 size reactor Inulinase was used

Mixed Ag. Res.: mixed agricultural residues and wastes; DDGS: Dried Distillers’ Grains and Solubles; HW, CC, SS: hemp waste, corncobs, and sunflower shells. 1 Calculated value. 2 Independently isolated strain. – Not reported.

unsuccessful and no ABE was produced from switchgrass hydrolysate treated in this manner.

Hemp waste, corn cobs and sunflower shells In an effort to reduce the use of food or feed-grade substrates including molasses and rye flour, an attempt was made to utilize agricultural waste materials such as hemp waste, corn cobs and sunflower shells [2]. These substrates are high in pentose sugars and low in hexoses such as glucose and galactose. These agricultural residues were hydrolysed using dilute sulfuric acid treatment at temperatures ranging from 115 to 125 C. The hydrolysates so obtained were mixed with rye flour or molasses before fermentation, possibly because of an inability of the culture to grow in undiluted or untreated hydrolysates. The authors indicated that the hydrolysate contained some inhibitors such as acetic and formic acids, and furfural. Depending upon concentrations, these chemicals can be toxic to C. acetobutylicum cultures. It should be noted that the concentrations of these inhibitors varied with the substrate used and the method of hydrolysis. With mild hydrolysis of corn cobs, the concentration of toxic chemicals was 2.7 g/l formic acid and 1 g/l furfural. The maximum level of formic acid that was tolerated by the culture was 0.2 g/l, whereas for furfural it was 2.5 g/l. At these hydrolysis temperatures, the Maillard reaction occurred, which formed melanoids (amino acids reacted with sugars). Melanoids affected the culture negatively. Production of ABE from hemp waste, corn cobs and sunflower shells was performed on a commercial scale in the 1960s in USSR. During fermentation, half of the sugars were converted to ABE and half to gases (CO2 and H2). ABE yields ranged from 0.33 to 0.39. The hydrolytic studies were performed from April 1959 to January 1961

at the Doshukino plant research facility in Russia (then USSR). At this plant, about 925 tonnes/month of corn cobs (dry weight) were hydrolysed (in 1962), from which 312 tonnes/month pentose sugars were produced. In addition to ABE, CO2 and H2 gases were also produced, separated and used in the plant. Separated CO2 was sold as dry ice and liquid CO2. H2 gas may have been used as an energy source in the plant. Besides these gases, 30 000 m3 of biogas were produced per day from the fermentation sludge in a thermophilic methanogenic fermentation. Methane gas produced was used to provide process heat for distillation and sterilization. Additional by-product included production and separation of 400– 600 mg/l fermentation broth cobalamin. ABE production and generation of by-products made this fermentation profitable. In another extensive report on the conversion of corn cobs to ABE, Marchal et al. [9] demonstrated successful corn cob hydrolysis and the production of butanol using C. acetobutylicum. Corn cobs were pretreated using steam explosion followed by hydrolysis using enzymes. Fermentation studies were performed in a 4-litre bioreactor and scaled up to 50 m3 system. In a 48-m3 bioreactor, 20.5 g/l total ABE was produced with an ABE yield and productivity of 0.31 and 0.45 g/l.h, respectively. These results are superior to the results obtained in a 4-litre bioreactor in which 17.7 g/l total ABE was produced with an ABE yield and productivity of 0.27 and 0.41 g/l.h, respectively (Table 1). In this report, a number of growth and fermentation inhibitors were identified and these included: acetovanillin, p-coumaric acid, ferulic acid, furfural, p-hydroxybenzoic aldehyde, 5-(hydroxymethyl)-2furfural, pyrocatechol, syringic acid, syringic aldehyde, vanillic acid and vanillin. It should be noted that these inhibitors were present in steam-exploded corn cob hydrolysate. If the agricultural residues are pretreated with


N. Qureshi

dilute sulfuric acid, the concentrations of inhibitors might increase significantly.

7

References 1. Jones DT, Woods DR. Acetone-butanol fermentation revisited. Microbiological Reviews 1986;50:484–524.

Jerusalem artichoke The Jerusalem artichoke is an agricultural crop with considerable potential as a carbohydrate substrate for butanol production by fermentation [1]. The carbohydrate in the tuber is mainly a short oligomeric fructans that has an inulinic structure. The inulin must first be hydrolysed with a chemical (preferably acid) or enzyme (inulinase) before butanol fermentation. Marchal et al. [27] investigated the use of Jerusalem artichoke juice for acetone butanol production and isolated a microbial strain that possessed inulinase activity. However, supplementation with additional inulinase enzyme for complete hydrolysis was necessary prior to butanol fermentation. With an optimized process, these investigators were able to produce 23–24 g/l acetone butanol. This process was tested at the pilot plant scale. Table 1 summarizes the production of butanol/ABE from various agricultural residues and energy crops using different microbial cultures.

2. Zverlov VV, Berezina O, Velikodvorskaya GA, Schwarz WH. Bacterial acetone and butanol production by industrial fermentation in the Soviet union: use of hydrolyzed agricultural waste for biorefinery. Applied Microbiology and Biotechnology 2006;71:587–97. 3. Hu S. Characterization of an isolate of high-ratio butanol producing C. acetobutylicum (Shanghai Institute of Biological Sciences, China). Paper presented in Clostridium 10 (The 10th workshop on the genetics and physiology and acid and solvent producing Clostridia), Wageningen, The Netherlands, 29 September 2008. 4. Marlatt JA, Datta R. Acetone–butanol fermentation process development and economic evaluation. Biotechnology Progress 1986;2:23–8. 5. Qureshi N, Maddox IS. Application of novel technology to the ABE fermentation process: an economic analysis. Applied Biochemistry and Biotechnology 1992;34:441–8. 6. Qureshi N, Blaschek HP. Economics of butanol fermentation using hyper-butanol producing Clostridium beijerinckii BA101. Transactions of the Institution of Chemical Engineers (Trans IChemE): (Chemical Engineering Research and Design). 2000;78:139–44. 7. Qureshi N, Saha BC, Hector RE, Dien B, Hughes SR, Liu S, et al. Production of butanol (a biofuel) from agricultural residues: II – use of corn stover and switchgrass hydrolysates. Biomass and Bioenergy 2010;34:566–71.

Conclusion In conclusion, butanol can be produced from various simple sugars, starch (starchy crops) and lignocellulosic biomass. The cellulosic biomass that has been used for this fermentation includes maize fibre, agricultural waste, soya molasses, maize fibre, dried distillers’ grains and soluble (DDGS), wheat straw, barley straw, maize stover and switchgrass. Among all the agricultural residues, wheat straw has been found to be superior to all as the culture (C. beijerinckii P260) was not inhibited by wheat straw hydrolysate. The use of barley straw and maize stover required overliming prior to fermentation. In addition to microbial cultures and agricultural residues, process technology plays a major role in economizing the process of butanol production by fermentation. In a continuous process, 461.3 g/l ABE was produced in 1 litre culture volume from 1125 g sugar when integrated with simultaneous product removal [28]. We were able to integrate wheat straw hydrolysis, fermentation and product recovery in a single reactor for economizing the process of butanol production from this substrate.

Acknowledgements I would like to thank Michael A. Cotta (United States Department of Agriculture, National Center for Agricultural Utilization Research, Bioenergy Research Unit, Peoria, IL, USA) for reading this article and providing constructive comments.

8. Anon. Biobutanol on the horizon. Chemical Engineering Progress 2007; March Issue:10. 9. Marchal R, Ropars M, Pourquie J, Fayolle F, Vandecasteele JP. Large-scale enzymatic hydrolysis of agricultural lignocellulosic biomass. Part 2: Conversion into acetonebutanol. Bioresource Technology 1992;42:205–17. 10. Maddox IS, Murray AE. Production of n-butanol by fermentation of wood hydrolysate. Biotechnology Letters 1983;5:175–8. 11. Clark TA, Mackie KL. Fermentation inhibitors in wood hydrolysates derived from the softwood Pinus radiata. Journal of Chemical Technology and Biotechnology 1984;34B:101–10. 12. Qureshi N, Ezeji TC. Butanol ‘a superior biofuel’ production from agricultural residues (renewable biomass): recent progress in technology. Biofuels, Bioproducts and Biorefining (Biofpr) 2008;2:319–30. 13. Liu S, Bischoff KM, Hughes SR, Qureshi N, Rich JO. Functional expression of the thiolase gene thl from Clostridium beijerinckii P260 in Lactococcus lactis and Lactobacillus buchneri. New Biotechnology 2010;27:283–8. 14. Qureshi N, Blaschek HP. Butanol production from agricultural biomass. In: Shetty K, Pometto A, Paliyath G, editors. Food Biotechnology. Taylor and Francis Group plc, Boca Raton, FL; 2005. p. 525–51. 15. Maddox IS, Qureshi N, Gutierrez NA. Utilization of whey and process technology by Clostridia. In: Woods DR, editor. The Clostridia and Biotechnology. Butterworth Heinemann, MA; 1993. p. 343–69. 16. Gutierrez NA, Maddox IS, Schuster KC, Swoboda H, Gapes JR. Strain comparison and medium preparation for the


8

Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources acetone–butanol–ethanol (ABE) fermentation process using a substrate of potato. Bioresource Technology 1998;66:263–5.

17. Qureshi N, Lolas A, Blaschek HP. Soy molasses as fermentation substrate for production of butanol using Clostridium beijerinckii BA101. Journal of Industrial Microbiology and Biotechnology 2001;26:290–5. 18. Jesse T, Ezeji TC, Qureshi N, Blaschek HP. Production of butanol from starch-based waste packing peanuts and agricultural waste. Journal of Industrial Microbiology and Biotechnology 2002;29:117–23. 19. Qureshi N, Ebener J, Ezeji TC, Dien B, Cotta MA, Blaschek HP. Butanol production by Clostridium beijerinckii BA101. Part I: Use of acid and enzyme hydrolysed corn fiber. Bioresource Technology 2008;99:5915–22. 20. Qureshi N, Li X, Hughes SR, Saha BC, Cotta MA. Production of acetone butanol ethanol from corn fiber xylan using Clostridium acetobutylicum. Biotechnology Progress 2006;22:673–80. 21. Ezeji TC, Blaschek HP. Fermentation of dried distillers’ grains and soluble (DDGS) hydrolysates to solvents and value-added products by solventogenic clostridia. Bioresource Technology 2008;99:5232–42. 22. Qureshi N, Saha BC, Cotta MA. Butanol production from wheat straw hydrolysate using Clostridium beijerinckii. Bioprocess and Biosystems Engineering 2007;30:419–27.

23. Qureshi N, Saha BC, Hector RE, Hughes SR, Cotta MA. Butanol production from wheat straw by simultaneous saccharification and fermentation using Clostridium beijerinckii: Part I – Batch fermentation. Biomass and Bioenergy 2008;32:168–75. 24. Qureshi N, Saha BC, Cotta MA. Butanol production from wheat straw by simultaneous saccharification and fermentation using Clostridium beijerinckii: Part II – Fed-batch fermentation. Biomass and Bioenergy 2008;32:176–83. 25. Qureshi N, Saha BC, Dien B, Hector R, Cotta MA. Production of butanol (a biofuel) from agricultural residues: I - Use of barley straw hydrolysate. Biomass and Bioenergy 2010;34:559–65. 26. Parekh SR, Parekh RS, Wayman M. Ethanol and butanol production by fermentation of enzymatically saccharified SO2-prehydrolysed lignocellulosics. Enzyme and Microbial Technology 1988;10:660–8. 27. Marchal R, Blanchet D, Vandecasteele JP. Industrial optimization of acetone-butanol fermentation: A study of the optimization of Jerusalem artichokes. Applied Microbiology and Biotechnology 1985;23:92–8. 28. Ezeji TC, Qureshi N, Blaschek HP. A novel process for continuous butanol production employing Clostridium beijerinckii and simultaneous product removal using gas stripping. Biomass and Bioenergy 2010; Submitted.

Supplied by the U.S. Department of Agriculture, National Center for Agricultural Utilization Research, Peoria, Illinois
