Chapter 17Biotechnological Potential of Cereal(Wheat and Rice) Straw and Bran Residues

Hongzhang Chen, Ye Yang and Jianxing Zhang

Contents

17.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32817.2 The Utilization of Cereal Straw and Bran Residues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329

17.2.1 Firewood Fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32917.2.2 Paper Making . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32917.2.3 Animal Feed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33017.2.4 Returning Straw to Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33017.2.5 Lignocellulose Chemical Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330

17.3 Fractionated Conversion of Cereal Straw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33117.3.1 Bringing Out the Concept of Fractionated Conversion Process . . . . . . . . . . . . . 33117.3.2 Flow Diagram of Ecological Industry Chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33217.3.3 Fractionated Conversion for Various Products . . . . . . . . . . . . . . . . . . . . . . . . . . . 333

17.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339

Abstract Cereal straw, one of the most abundant renewable lignocellulose re-sources which possess valuable components, has gradually become the research hotspot as a promising substitute for both the fossil fuel resource and petroleum-basedindustry with the increasing calling for bio-fuel and green chemistry. However, ex-isting technologies of straw utilization unilaterally emphasize the primary utiliza-tion of the whole plant or some certain components, which not only result in lowtechnical content of corresponding products but also fail to make full use of thelignocellulose resources. Based on the decades of research work, we find out thatthe bio-structural inhomogeneities of straw, both in the chemical composition andmolecular structure between each part of straw, are the ultimate reasons why strawcan not be utilized in a whole.Thus, the concept of fractionated conversion of strawemerges as the time requires. In this chapter, this innovative concept is explained

H. Chen (B)State Key Laboratory of Biochemical Engineering, Institute of Process Engineering,Chinese Academy of Sciences, Beijing 100190, PR Chinae-mail: hzchen@home.ipe.ac.cn

P. Singh nee’ Nigam, A. Pandey (eds.), Biotechnology for Agro-Industrial ResiduesUtilisation, DOI 10.1007/978-1-4020-9942-7 17,C© Springer Science+Business Media B.V. 2009

327

328 H. Chen et al.

in detail by taking the fractionated conversion of the corn straw, rice straw and ricehusk as examples. Only through utilizing different parts of straw in the guidance ofits structures and characteristics we can make full use of the straw resources.

Keywords Fractionated conversion · Biomass total utilization · Cereal straw ·Steam explosion · Inhomogeneity · Biorefinery

17.1 Introduction

Along with the fast growing of world’s population and great development of socialeconomy, though the petroleum-based agriculture and industry have greatly boostedthe development of both the society and people’s living standard, in less than 400years, we human beings have almost used up the fossil fuels such as coal, oil, andnatural gas formed and accumulated through 2.5 billion years and caused a series ofproblems such as energy crisis, resource exhaustion and environment deteriorationwhich not only threaten the living of ourselves but also confront the chemical indus-try with new challenge of human beings’ sustainable development. Meanwhile, thetraditional starch–based fermentation industry, however, cost as many as several bil-lion tons of foodstuff per year, hence the limitation of both arable land and foodstuffset huge barrier to its development (Wyman 2007).

Energy shortage, food shortage and the call for developing biomass resource aschemical raw material in Green Chemistry starting from 1990s stimulate the coun-tries worldwide to notice that the utilization of natural cellulose material like strawholds the strategic significance to their development. European Union has broughtforward a short-term goal of alleviating the fossil energy dependence on each mem-ber country by cutting down 20–30% cost of bio-fuel production and actualizing27–48% motor vehicle using bio-fuel (Council 2006).

The United States has invested several billion US dollars in the research work ofsubstitutable energy and clean energy since the announcement of “Advanced EnergyInitiative” (Milliken et al. 2007) in 2006, including non-grain crop based ethanolproduction, and reducing the technical costs of renewable energy such as windenergy, solar energy, geothermal energy and biomass energy. They have alreadyinvested 354 million US dollars, to reach the final goal of replacing 75% petroleumimported from Middle East by 2025 (President Bush 2006; Schell et al. 2008). Chi-nese government has pointed out clearly to strengthen the utilization of biomassresource and exploit the technology of biomass-based clean liquid fuel productionin the “China’s Agenda 21 —White Paper on China’s Population, Environment, andDevelopment in the 21st Century”.

Cereal straw is one of the most abundant, annually renewable resources in theworld. According to a valid data, there are as many as 2.9 billion tons of cerealstraw produced per year all over the world, and only in China there is 0.7 billion tonscereal straw produced per year. However, such abundant resource has not attractedenough attentions and thus has not been utilized reasonably. In fact, cereal straw isthe production of plants’ photosynthesis, which is constituted by high percentage

17 Biotechnological Potential of Cereal (Wheat and Rice) Straw and Bran Residues 329

of macromolecule compounds such as cellulose, hemi-cellulose and lignin. Bothcellulose and hemi-cellulose are polymers made up of fermentable sugar which canbe fermented into chemical materials and liquid fuel such as ethanol, acetone, aceticacid, as well as be used as the fermenting materials of antibiotics, organic acid andenzyme after hydrolysis. Lignin, comprised of phenylpropane derivatives, can befurther transformed to other chemicals used as the raw material in organic chemistryindustry (Chen 2005).

17.2 The Utilization of Cereal Straw and Bran Residues

Cereal straw is one of the most abundant renewable resources in the world, longbefore human have been utilizing it in various different forms.

17.2.1 Firewood Fuel

As a traditional energy transforming mode, direct combustion is economic, low costand easy to promote. However, according to the research, using natural straw asthe fuel to combust directly has pretty low combustive efficiency because it is verydifficult to be combusted completely. As a result, the heat loss usually varies from30% to 90%, which not only wastes the resource but also causes serious pollutionproblem to the environment. Presently, relative research of straw as one kind offuel is concentrated on the improvement of the low caloric value, and researchessuch as central gas supply of straw gasification, technology of methane or ethanolproduction from straw fermentation are on the way.

17.2.2 Paper Making

The utilization history of lignocellulose and fiber material has much to do withpaper making industry which can date back to 3rd Century BC (Kamm et al. 2005;Kamm et al. 2007). Plant fiber is the raw material in the pulp and paper industry.Nowadays, wood fiber accounts for more than 90% of the world paper, nevertheless,to those countries which lack in wood fiber, fiber material such as straw is a goodsubstitute. China is the largest straw pulp -producing country in the world, provid-ing more than 75% of the world’s non-wood pulp (Chen 2008). Pulp and paperindustry all focus on the utilization of the cellulose component in the fiber materialand removal of both the hemi-cellulose and lignin components which accounts forthe formation of black liquor. This process not only wastes the hemi-cellulose andlignin components, but the removal step dramatically generates the increment ofthe cost, and the black liquor pollutes the nearby environment especially the waterresources. Obviously, it is urgent to develop new technology for straw utilizationin solving the problems mentioned above. Fortunately, there are researchers whobring out biotechnologies such as bio-pulping (Chen et al. 2002), bio-bleaching andenzymatic deinking (Chen 2005) to tackle the pollution problem.

330 H. Chen et al.

17.2.3 Animal Feed

The development of animal husbandry depends on the sufficient supply of feedstuff.Countries like New Zealand, Australia have abundant meadow which can affordforage-based animal husbandry while other developed countries like America canafford grain-based animal husbandry. China is a country which has a large popula-tion and relatively less cultivatable land, in other words, neither forage nor grain issustainable for the country’s fast growing animal husbandry. The abundant straw re-source is undoubtedly the most suitable choice considering the national conditions.In fact, the crop straw occupies about 30% of the livestock feedstuff. However,limited by the straw structure itself, natural straw has high percentage of lignin andash components while only low percentage of raw protein, and poor palatability,which together lead to the low digestion and insufficient amount of nourishment.Ruminant such as cattle and sheep can digest about 40–50% of the straw on averagewhile pig can only digest 3–25% and chicken are the worst, almost can’t digest it atall (Liu 2006). Therefore, it is necessary to develop straw processing technology inorder to decrease or even eliminate its limitation of digestion and nourishment. Now,the feed industry has made great progress due to the straw processing technologieslike silage and straw ammoniation.

17.2.4 Returning Straw to Soil

It is a tradition in the agriculture history to use organic fertilizer, and the easiestand most traditional method is returning straw which mainly contains both strawmulching and straw incorporation to the soil. According to straw returning appli-cation, the soil can gain more organism and nutrient which can bring soil fertilitybetterment as well as adjustment of the physical properties, and finally optimize theenvironment of farmland. However, the problem is that returning natural straw tosoil directly needs multiple kinds of microorganisms in the soil to function togetherto decompose which may take as long as several years. Obviously this kind of return-ing is so slow to the extent that the undecomposed straw can not function as fertilizerbut also set some barriers to the new shoots. As a result, nowadays returning themanure of ruminant to soil and other compost are more commonly used.

17.2.5 Lignocellulose Chemical Industry

Up to now, it has been more than 200 years since the lignocellulose and cellulosefiber chemical industry was founded (Kamm et al. 2005). Utilizing the complexbiorefinery technologies, through corresponding chemical processing, the lignocel-lulose can be decomposed into different fractions such as cellulose, hemi-cellulose,lignin, extraction and ash, from which the product line is based (Kamm et al. 2007).For example, to produce vanillin from lignin, gain carbohydrates from cellulose, andprepare furfural from hemi-cellulose. Wood has gained wide research and industryutilization because of its high content of homogeneous component of cellulose. As

17 Biotechnological Potential of Cereal (Wheat and Rice) Straw and Bran Residues 331

the substitute material of wood, straw catches more and more attention from world-wide researchers and becomes the research hotspot.

In general, state of the art of straw utilizing mainly focuses on the primary utiliza-tion of straw which are weak in foundation, integrity and system. The reports uni-laterally emphasize on the utilization of the whole plant or some certain componentand fail to reach the goal of making full use of the three main components (cellulose,hemi-cellulose and lignin) of the lignocellulose resources which accounts for theproblems of the low technical content on the using of biomass resource and the poorquality of the corresponding products. In order to solve problems mentioned abovefundamentally, the most crucial point is to realize that the bio-structural inhomo-geneity of straw, that is to say, the differences, both in the chemical compositionand structure between each part of straw, are the ultimate reason that straw can notbe used in a whole.

The three main components—cellulose, hemi-cellulose and lignin crosslinktightly in the unpretreated straw, and due to their totally different chemical structuresand properties, none of them can be utilized efficiently. Therefore, it is necessary toseparate each component apart while maintaining the macromolecule’s integralityas much as possible. Only through this processing, the different fractions can beutilized in an optimized way and fulfill their greatest value. Meanwhile, we shouldcultivate a clear sense that not only the cellulose component is a valuable resource,the other components are also potential resources rather than wastes which awaitthe future industrial utilization. Secondly, the breakthrough of straw transformationtechnology calls for new development of corresponding process engineering theoryon the solid phase complex materials.

Finally, it is more important to investigate the characteristics of straw utilizationand technical bottle-neck, and build up systematic theory on the straw transfor-mation. As for the utilization of biomass resource, applying mechanically existingknowledge is far from enough to solve the technical problems and it is necessary tobuild up more updating, comprehensive and systematic theory to guide the develop-ment of cellulose science.

In this chapter we will discuss about corn straw, rice straw and rice husk as exam-ples to introduce the progress of research work done for the fractionated conversionof cereal straw in our laboratory.

17.3 Fractionated Conversion of Cereal Straw

17.3.1 Bringing Out the Concept of FractionatedConversion Process

Since the 1970s, the transformation and utilization technology of biomass havemade great progress, however, from the aspect of current utilization and develop-ment of biomass resource, there are still large amount of barriers and problems, oneof which is the unilateral emphasis on the biological or thermal chemical technologywithout the sense of total utilization of natural solid phase organic material through

332 H. Chen et al.

fractionating and recycling. The single utilization technology not only wastes muchof the biomass resource but also causes pollutions to the environment, therefore,looking for new effective technology of biomass utilization becomes the inevitabletrend. Under such circumstances, the concept of fractionated conversion emerges asthe time requires.

Based on the summarization of our many years research experience, we bringout the concept of fractionated conversion of cereal straw. Now the question ariseswhat is this so-called fractionated conversion of cereal straw? In fact it is a processin which preparation of biomass products depends on the compositions and char-acteristics of the raw materials. The main route is biotransformation and thermalchemical transformation, biotechnology and other physical or chemical methodswill be used as well if necessary in this conversion.

17.3.2 Flow Diagram of Ecological Industry Chain

Technical process scheme (shown in Fig. 17.1) is as follows:

(1) Cutting up straw into 5 cm or so pieces, and adding water to adjust the moistureto about 35% (Chen and Liu 2007).

Straw

Fiberboardmodified materials

Paper makingCellulose acetate

Carboxymethyl celluloseCellulose derivatives

Short fiber

Water washedliquid

Water washing

Straw explosion

Long fiber

Xylo-oligosaccharide

Purification

Solid fiber

Fermentedresidue

AshPyrolysisSimultaneous

saccharification& fermentation

Solid statefermentation

Utilization oflignin

Nano-silicadioxide

Bio-oil fuelEthanol, hydrogenacetone, butanol

Cellulase

Fig. 17.1 Brief introduction of flow diagram of ecological industry chain

17 Biotechnological Potential of Cereal (Wheat and Rice) Straw and Bran Residues 333

(2) Using steam explosion pre-treatment to activate the raw straw, and the conditionof steam explosion is 1.5 MPa, maintaining for 3.5 min (Chen and Liu 2007).

(3) Fibers separated from the steam exploded (SE) production can produce mediumand high density strawboard directly. SE production can also be washed withwater. The water washed liquor can be used as stuff to produce xylo-oligosaccharide, and the solid fiber can be separated into two main parts: thelong fiber part and the short fiber part through the carding equipment.

(4) Long fiber part can be used in ethanol autocatalytic pulping, preparation ofcellulose acetate (Zhang and Chen 2007) and carboxymethyl cellulose.

(5) The separated short fiber part can be the appropriate substrate to produce cellu-lase in solid state fermentation (Xu et al. 2002) which can be used in the laterfermentation of ethanol (Chen et al. 2007), hydrogen (Li and Chen 2007) andacetone butanol (Qureshi et al. 2007).

(6) Simultaneous saccharification and fermentation (SSF) (Han and Chen 2008) forfuel ethanol: use the short fiber as the substrate, adding cellulase obtained fromthe solid state fermentation and activated yeast (Chen and Jin 2006; Rudolfet al. 2005) to conduct SSF.

(7) Utilization of fermentation residues: they can be used in generating electricityor preparing bio-fuel (Luo et al. 2004).

(8) Utilization of straw ash: reclaim the valuable nano-silicon dioxide from ash.

17.3.3 Fractionated Conversion for Various Products

17.3.3.1 Fractionated Utilization of SE Corn Straw

Cut up the corn straw into 5 cm or so pieces and then add 30% (wt. %) water tothe material and mix them up. Put them into a 0.5 m3 steam explosion reactor, keepthe steam pressure at 1.5 MP in the reactor and maintain for 3, 4, 5 min respectively,and then release the pressure in a quick shot. Then the steam exploded straw isextracted with 5 times water (wt. %) and both the water washed liquor and the solidmaterial are collected. The sugar content of water washed liquor can be determinedby HPLC. The solid material then is separated into long fiber part and short fiberpart through the carding equipment. The utilization of each fraction are as follows:xylo-oligosaccharide can be distilled from the water washed liquor and then preparelevulinic acid; long fiber part can be used as paper pulping and the short fiber partcan ferment ethanol and acetone butanol.

Content of the long fiber part of the SE products decreases along with the in-tensity of steam explosion. In the same steam pressure of 1.5 MPa, maintaining aslong as 3 min, 4 min and 5 min, the contents of long fiber are 69.71% , 46.53% ,45.39%, respectively. And the weight proportion of long fiber and short fiber are1:0.45, 1:1.15, 1:1.17, consequently.

Compared with the natural corn straw, the cellulose content of SE product canreach 40% or so which is higher than that of natural corn straw; the content ofhemi-cellulose decreases from 30% to 20%. Under the same SE condition, the

334 H. Chen et al.

Fig. 17.2 The ethanol yieldof fractionated corn straw

1.5 MP ax3m in

Eth

anol

yie

ld r

ate

/%

0

2

4

6

8

10

12

14

16

1.5 MP ax4m in 1.5 MP ax5m in

Long fiber fractionShort fiber fraction

content of neutral washing component in long fiber part and short fiber part is differ-ent and the former one has a lower percentage; the contents of ash and lignin haveless discrepancy.

The ethanol fermentation test using fractionated SE corn straw as substrate wasconducted. In general, all ethanol yields (shown in Fig. 17.2) were above 10% andthe short fiber part had the highest yield of above 14%.

17.3.3.2 Fractionated Conversion at Morphological OrganicLevel of Rice Straw

a. Inhomogeneity of rice straw structureIn the angle of configuration, rice straw can be divided into four main differentorgans: root (seed root, adventitious root, branch root), stalk (node and intern-ode), leaf (leaf blade and leaf sheath) and panicle (threshing panicle), and thestraw roots (Jin and Chen 2006) are usually kept in the soil after harvest. InFig. 17.3, it is clearly shown that the differences in chemical compositions resultin the different transforming capacity of straw’s morphological fractions; there-fore the utilization of rice straw in a fractionated way is not only important butalso necessary.

b. Inhomogeneity of capacity of ethanol fermentation of rice straw’s morphologicalfractions

Using abundant agricultural cereal straw to prepare fuel ethanol in order to partlyreplace fossil fuel is a significant developmental trend. However, the structural in-homogeneity and large amount of non-fiber cells of straw directly lead to poorethanol yield and high cost. Under such circumstances, investigation on the capacityof ethanol fermentation of rice straw’s morphological fractions will turn out to bethe pertinent basic guidance of appropriate transformation of fractionated rice straw.Under the same SSF condition, the different ethanol yields of leaf sheath, leaf blade,node, internode and panicle respectively are shown in the Fig. 17.4 (Jin 2007).

17 Biotechnological Potential of Cereal (Wheat and Rice) Straw and Bran Residues 335

Fig. 17.3 Chemical composition of each morphological fraction of rice straw lower than 40 mesh

Cellulose component of the straw will firstly be hydrolyzed into glucose whichthen transformed to ethanol via microorganism fermentation, the biochemical reac-tion is as formula (17.1):

(C6H10O5)n → n C6H12O6 → 2n C2H5OH + 2n CO2 (17.1)

Fig. 17.4 Ethanol yield of each morphological fraction of rice straw (Jin 2007)

336 H. Chen et al.

According to the formula, the theoretical yield of ethanol from glucose is 0.51g-ethanol/g-glucose.

In Fig. 17.4, the vertical coordinate is the ethanol yield (wt.%) which denotesthe ethanol yield per gram of substrate in the SSF test. Obviously each fraction hasdistinguished transforming capacity. Under the same SSF condition, the sequenceof capacity of ethanol fermentation is: internode > node >leaf sheath > leaf blade> panicle, and when the fermenting time reaches as much as 48 hours, the ethanolyield can reach 11.5%, 9.0%, 6.9%, 6.9% and 6.3%, respectively. Internode has thehighest ethanol yield which towers above that of leaf sheath and leaf blade 66.7%.This law has positive correlativity with the enzymatic capacity of each morphologi-cal fraction of rice straw basically. Via the investigation of different transformationcapacity of each morphological fraction of rice straw, it is more testified that toutilize rice straw in a fractionated way is very necessary.

17.3.3.3 Fractionated Conversion of Cereal Husk

Due to the abundant published papers on the research using bran and chaff, we willmainly introduce the total utilization of rice husk based on our research work.

Rice husk is characteristic of small cumulus density, hard husk and poor degra-dation capacity which directly lead to the ignorance of its utilization. The maincomponents of rice husk are cellulose, lignin and silicon derivatives which mayvary with the different breeds and producing areas. The average contents are: rawfiber 35.5% ∼ 45% (polycondensed pentose 16% ∼ 22%), lignin 21% ∼ 26%, ash11.4% ∼ 22%, and silicon dioxide 10% ∼ 21%.

Based on the characteristics of each component of rice husk and our researchwork, we bring forward the new technical process of multilevel utilization of ricehusk which includes classifying rice husk into rich in silicon part, hemi-cellulosepart and short fiber part and then adopting corresponding feasible means to utilizeeach part. The detailed processing is as follows: the rich in silicon part can preparenano-silicon dioxide directly, and the hemi-cellulose part can prepare furfural whilethe short fiber part can be hydrolyzed to ferment fuel ethanol, together these canrealize the effective total utilization of rice husk.

1. Project scheme

Technical process scheme (shown in Fig. 17.5) is as follows:

(1) SE pre-treatment of rice husk.(2) Mechanical carding of rice husk: using mechanical carding equipment to sep-

arate SE rice husk into 3 parts, hemicellulose, component rich in silicon andshort fiber.

(3) Preparation of fuel ethanol in SSF: using cellulose enzymatic hydrolysis-fermentation coupling method to prepare fuel ethanol.

(4) Preparation of furfural: to prepare furfural either by catalyzed with solid su-peracid or in acid free autocatalysis.

(5) Preparation of nano-silicon dioxide with component rich in silicon.

17 Biotechnological Potential of Cereal (Wheat and Rice) Straw and Bran Residues 337

Rice Husk

Componentrich in silicon

Steam Explosion

Extraction

MechanicalCarding

Short fiber

Fluidizedpyrolysis Simultaneous

Saccharifiction andFermentation

Distillation

FermentationResidue

Ball milling &crushing

Nano-SiliconDioxide

Heat recovery

Acid freeautocatalysis

Catalyzed bysolid superacid

Furfural

Fuel Ethanol

Dilute Acid Extraction

Fig. 17.5 Flow diagram of rice husk’s utilization

2. Preparation of nano-silicon dioxide from SE rice husk’s rich in silicon part

Compared with other biomass resources like wood, straw has much higher ashcontent, above 60% of which is silicon dioxide. Among all the straws, rice strawhas the highest content of both the ash content and the percentage of silicon dioxidein the ash. In the plant, silicon dioxide usually appears as amorphous global nano-conglomeration (10 nm or so) which is comprised of SiOn(OH)4–2n. For a long time,the effect of ash on the cellulose enzymatic hydrolysis has always been ignored,however, according to the research into the correlation between the physicochemicalcharacteristic of silicon and cellulose hydrolysis in the cell wall of rice straw, anew discovery emerges that the content of lignin and insoluble silicon has distinctsynergistic relation which uncovers their synergistic effect on blocking the cellulosefrom hydrolysis.

Using steam explosion to pretreat straw, then to separate fiber tissue fromparenchyma cell in carding to obtain most of the ash part, in this way the decreaseof ash amount can reduce its inhibiting effect on hydrolysis as well as collect thesilicon for better utilization. Research result shows that silicon dioxide still existsin the residues after enzymatic hydrolysis and fermentation, and SE pre-treatmentcauses no effect on the configuration of silicon dioxide which is still at amorphousstate. Besides, the extremely low impure heavy metal ion content in the straw fa-cilitates the preparation of high purity amorphous nano-silicon dioxide which notonly cuts down the production cost but also enhances the added value of straw.Such obtained nano-silicon dioxide is white powder which has an average granulardiameter of 50 nm, and the total impure ion content is below 5.5 mg/kg (< 10 ppm)which reaches the high purity level.

338 H. Chen et al.

X-ray Diffraction (XRD) study on the structure of silicon dioxide in the rice huskunder different SE pretreating conditions, comparing with crystalloid SiO2 map,indicates some important discoveries. From the comparison map, except the positionand intensity coincidence of several apices, the positions and intensities of otherapices are distinct, in other words, the produced SiO2 still existed in amorphous statewhich testifies that the SE pre-treatment and carding process have no effect on theSiO2 structure. SiO2 obtained after the acid bath and combustion is not nano-levelSiO2 yet, and it needs further disposal with Ball Mill.

3. Fermentation of SE rice husk’s short fiber part to ethanol in SSF

Using plant cellulose as the raw material to ferment ethanol is an effective ap-proach to solve the current ethanol fermentation problems, such as the high costand limitations of raw material resources. The fermentation results of the SE ricehusk are shown in the Table 17.1 clearly in which the steam explosion and latercarding cause similar effects on the fermentation yield as enzymatic hydrolysis,and the short fiber parts obtained from the mechanical carding are more suitable toferment ethanol and also gain much higher yield because of the increase of materialaccessibility to enzyme.

Table 17.1 Effects of steam explosion and carding on the ethanol fermentation yield

Carded SE material Ethanol yield(%)

1.5 MPa 6 min∗ Rich in silicon part 7.08Short fiber part 11.46

1.6 MPa 5 min∗ Rich in silicon part 7.85Short fiber part 12.48

∗ the SE condition of raw material.

4. Preparation of fufural from SE rice husk hemi-cellulose part

Presently, the main industrial raw materials for industrial furfural production arecorncob and bagasse. And the industrial process is to add sulfuric acid as cata-lyst, and then after two reactions the hemi-cellulose can be hydrolyzed to pentosewhich can be finally hydrolyzed into furfural. Steam explosion pre-treatment candecompose most of the hemi-cellulose into xylose and part of them can be furtherhydrolyzed into furfural, meanwhile there is some acid produced in the steam ex-plosion process which can act as catalyst in the later furfural preparation.

A series of tests were conducted on the preparation of furfural from SE ricehusk’s hemi-cellulose especially on the preparation process from SE extractionliquor and optimize the reaction conditions. The results show great prospect in de-veloping innovative process for the industrial furfural production and perfect thetotal utilization of rice husk.

17 Biotechnological Potential of Cereal (Wheat and Rice) Straw and Bran Residues 339

17.4 Conclusion

Agricultural straws may vary in component contents with the breeds and environ-mental conditions, and even the same breed of straws can have distinct differenceson the chemical compositions and structures on each morphological fraction. There-fore, unless utilize the straw resource by combining multiple subjects of knowledge,technology and industrial information, none of one single technology can realize thedevelopment and utilization of straw resource.

To optimize cellulose processing by refining biomass pre-treatment and utiliz-ing the residues is an advisable method to reduce cost and enhance comprehensiveutilization of straw. According to genetic engineering technology, we can designor cultivate specific microorganism which can ferment both C-5 and C-6 sugarsand bear some inhibitions to promote current fermentation technology. And withthe increasing knowledge of the relation between straw’s cell wall structure andinner mechanism of enzymatic hydrolysis, the gene modified straw can be designedto meet the wanted needs(Energy 2006; Sedlak et al. 2003). The natural macro-molecule and high polymer, and those high polymers obtained from microorganismfermentation, can also be the ideal raw material for the production of bio-basedmaterial and chemicals.

In a word, to establish the biomass transforming and utilizing technology net-work with the fractionated conversion of lignocellulose in the core can not only setnew ecological balanced system but also can form new biorefining product chain,thereby initiate an innovative way to realize the farthest utilization of lignocelluloseand ultimately substitute the petroleum product chain.

Acknowledgments This work was financially supported by National Basic Research Program ofChina (973 Program, 2004CB719700), National key technology R&D program (2007BAD39B01)and Knowledge Innovation Program of Chinese Academy of Sciences (KSCX1-YW-11A1).

Abbreviations

SE: Steam ExplodedSSF : Simultaneous saccharification and fermentationHPLC: High Pressure Liquid Chromatography

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