Bioenergy systems for the future 3 production of bioalcohol and biomethane

Bioenergy systems for the future 3 production of bioalcohol and biomethane Bioenergy systems for the future 3 production of bioalcohol and biomethane Bioenergy systems for the future 3 production of bioalcohol and biomethane Bioenergy systems for the future 3 production of bioalcohol and biomethane

Production of bioalcohol and

biomethane

K Ghasemzadeh*, E Jalilnejad*, A Basile†

*Urmia University of Technology, Urmia, Iran,†Institute on Membrane Technology(ITM-CNR), Rende, Italy

Abbreviations

AD anaerobic digestion

BOD biochemical oxygen demand

COD chemical oxygen demand

COx carbon oxides

DME dimethyl ether

LHW liquid hot water

Bioenergy Systems for the Future http://dx.doi.org/10.1016/B978-0-08-101031-0.00003-X

© 2017 Elsevier Ltd All rights reserved.

biofuels (bioalcohol and biomethane) because it is widely available from inexhaustiblefeedstocks that can effectively reduce its production cost.

Indeed, biofuel can be produced from various kinds of renewable materials such ascorn, sorghum, cellulose, and algae biomass However, among all biofuels, bioalcoholsuch as bioethanol and biomethane is more productable than other types On the basis

of the raw material used for its production, bioethanol and biomethane are divided intovarious types (Aditiya et al., 2016) However, their production involves many pro-cesses such as pretreatment, fermentation, recovery, and refining (Thomson, 2008)

To the best of our knowledge, the largest energy demand in biofuel production isfor the steam and electricity used in the fermentation/distillation process Hence, bio-alcohol and biomethane will not be significant without improvements in this processand reduced energy requirements

Membrane separation technologies have gained more and more attention due totheir reduced energy requirements, lower labor costs, lower floor space requirements,and wide flexibility of operation (Suresh et al., 1999) This technology has beenapplied in many processes of bioalcohol and biomethane production instead of thetraditional process (Stevens et al., 2004; Larson, 2008; Noraini et al., 2014;Bergeron et al., 2012; Galanakis, 2012) Therefore, the main aim of this chapter is

to present a state-of-the-art review on the bioalcohol and biomethane production cesses and also on the applications of membrane technologies for their production

In general, biofuels are referred to liquid, gas, and solid fuels, such as ethanol, anol, biodiesel, Fischer-Tropsch diesel, hydrogen, and methane, which are predomi-nantly produced from biomass Renewable and carbon-neutral biofuels are necessaryfor environmental and economic sustainability Between 1980 and 2005, worldwideproduction of biofuels increased significantly by an order of magnitude from 4.4 to50.1 billion liters, with further dramatic increases in the next years (Koh andGhazoul, 2008; Murray, 2005; Licht, 2008) The economics of each fuel vary withlocation, feedstock, fermentation technology, and several other factors Politicalagendas and environmental concerns also play a crucial role in the production and uti-lization of biofuels The challenging point on use of these fuels is fitting biofuels intothe enormous current fuel distribution and vehicle infrastructure (Nexant, Inc, 2006).Major benefits of biofuels are summarized inTable 3.1

meth-With regard to the presented studies (Nigam and Singh, 2011; Alam et al., 2012),biofuels can broadly be classified as primary and secondary biofuels based on their sourceand type The primary biofuels, also named as natural biofuels, such as vegetables, animalwaste, landfill gas, fuelwood, wood chips, and pellets, are used in an unprocessed form,primarily for heating, cooking, or electricity production The secondary biofuels likeethanol, methane, biodiesel, and DME are produced by processing of biomass and can

be used in vehicles and various industrial processes

The secondary biofuels are modified primary fuels, which are further divided intofirst-, second-, and third-generation biofuels on the basis of raw material and

technology used for their production They are produced in the form of solids (e.g.,charcoal) liquids (e.g., ethanol, biodiesel, pyrolysis oils, and bio-oil), or gases (e.g.,biogas (methane), synthesis gas, and hydrogen) and can be used in transport andhigh-temperature industrial processes (Thomson, 2008; Hoekman, 2009) A tee dia-gram for classification of biofuel is shown inFig 3.1.

The first-generation liquid biofuels are generally produced from sugars, grains, orseeds like wheat, palm, corn, soybean, sugarcane, rapeseed, oil crops, sugar beet,and maize and require a relatively simple process to produce the finished fuel product.Ethanol is the most well-known first-generation biofuel produced by fermenting sugarextracted from crop plants and starch contained in maize kernels or other starchy crops(Nigam and Singh, 2011; Hoekman, 2009; Suresh et al., 1999; Stevens et al., 2004) Due

to the increasing growth in production and consumption of biofuels, first-generationfuels are being produced in significant commercial quantity in a number of countries.However, the first generation is claimed to be not very successful because of the conflictwith food supply and high production cost due to competition with food; thus, it affectsfood security and global food markets These limitations favor the search of nonediblebiomass for the production of biofuels (Larson, 2008; Noraini et al., 2014)

Second-generation liquid biofuels are generally produced by two differentapproaches, that is, biological or thermochemical processing, from agricultural ligno-cellulosic biomass, which are either nonedible residues of food crop production or

Table 3.1 Major benefit of biofuels

Economic consequences

Sustainability

Fuel diversity

Increased number of rural manufacturing jobs

Increased income taxes

Increased investments in plant and equipment

Agriculture development

International competitiveness

Reducing the dependency on imported petroleum

Environmental consequences

Greenhouse gas reduction

Reducing of air pollution

nonedible whole plant biomass (e.g., grasses or trees specifically grown for production

of energy) This generation has more advantages compared with the first generationdue to higher production yield and lower land requirement and also using nonediblefeedstocks that limits the direct food versus fuel competition associated with first-generation biofuels Feedstock involved in the process can be bred specifically forenergy purposes, enabling higher production per unit land area, and a greater amount

of above-ground plant material can be used to produce biofuels It appears evidentfrom the literature (Bergeron et al., 2012; Galanakis, 2012) that production ofsecond-generation biofuel requires most sophisticated processing production equip-ment, more investment per unit of production, and larger-scale facilities to confineand curtail capital cost scale economies, which are discussed in future sections Toachieve the potential energy and economic outcome of second-generation biofuels,further research, development and application are required on feedstock productionand conversion technologies (Prado et al., 2016)

As indicated in Fig 3.1, third-generation biofuels use microbes and macro- andmicroalgae feedstocks as a very promising source for renewable energy productionsince it can fix the greenhouse gas (CO) by photosynthesis and does not compete with

Source: Algae, sea weeds Firewood, wood chips,

pellets, animal waste, and landfill gas – Bioethanol or butanol by

enzymatic hydrolysis

– Biodiesel from algae

– Bioethanol from algae and sea weeds – Hydrogen from green algae and microbes

– Biomethane by anaerobic digestion – Methanol, DME, etc by thermochemical processes

– Bioethanol or butanol by

fermentation of sugars

(sugars cane, sugars

beet, etc) or starch

(wheat, potato, corn, etc)

– Biodiesel by

transesterification of plant

oils (sunflower, palm,

soybean, etc)

Second generation Third generation Natural biofuels

Secondary biofuels Primary biofuels

Biofuels

Fig 3.1 Classification of biofuels

the production of food; hence, it is devoid of the major drawbacks associated with and second-generation biofuels On the basis of current scientific knowledge and tech-nology projections, some microorganisms like yeast, fungi, and microalgae can be used

first-as potential sources for biofuel first-as they can biosynthesize and store large amounts of fattyacids in their biomass (Alam et al., 2012; Noraini et al., 2014) Microalgae can producelipids, proteins, and carbohydrates in large amounts over short periods of time, and theseproducts can be processed into both biofuels and valuable coproducts (Costa et al.,

2012) Fuel production from algae has various advantages such as high growth rate,capability of growing under several conditions including in wastewater, high-efficiency

CO2mitigation, less water demand than land crops, and more cost-effective farming(Noraini et al., 2014)

3.2.1 Bioalcohol production

The alcohols are oxygenated fuels in which the alcohol molecule has one or more gen that decreases the combustion heat The alcohols used for motor fuels are meth-anol (CH3OH), ethanol (C2H5OH), propanol (C3H7OH), and butanol (C4H9OH), butamong them, only methanol and bioethanol fuels are technically and economicallysuitable for internal combustion engines (ICEs) (Demirbas, 2007; Ishola et al.,

oxy-2013) Bioethanol is a liquid biofuel that can be produced from several different mass feedstock and conversion technologies It contains 35% oxygen, which reducesparticulate and NOxemissions from combustion and also reduced hydrocarbons, car-bon monoxide, and particulates in exhaust gases Currently, ethanol is the availablecommercial biofuel and the most modern biomass-based transportation fuels, whichsticks out as the most important liquid biofuel with a global production of 88.7 billionliters in 2011 (Balat, 2011) Bioethanol has been focused as a high potential alternative

bio-to substitute liquid fossil fuels due bio-to its eco-friendly characteristics and relatively lowproduction cost when compared with other biobased fuels Bioethanol has a higheroctane number (108), low cetane number, broader flammability limits, higher flamespeeds, and higher heats of vaporization than gasoline These properties allow for ahigher compression ratio, shorter burn time, and leaner burn engine, which lead to the-oretical efficiency advantages over gasoline in an ICE (Aditiya et al., 2016; Demirbas,

2007) Adding ethanol to gasoline has a positive effect on the air quality in every luted urban areas It has been stated that 10% blend of bioethanolS with gasoline wouldreduce the carbon dioxide emission by 3%–6%, which makes bioethanol a cleaner fuel

pol-in addition to bepol-ing a renewable alternative to petroleum (Demirbas, 2007; Hansen

et al., 2005)

Bioethanol can be used as a 5% blend with petrol under the EU quality standard EN

228 This blend requires no engine modification and is covered by vehicle warranties.With engine modification, it can be used at higher levels, for example, E85 (85% bio-ethanol) (Balat et al., 2008) Bioethanol is widely used in the United States and in Brazil.The United States and Brazil remain the two largest producers of ethanol accountingtogether for 90% of the global bioethanol production In 2010, the United States gen-erated 49 billion liters, or 57% of global output, and Brazil produced 28 billion liters, or33% of the total output Corn is the primary feedstock for US ethanol, and sugarcane is

the dominant source of ethanol in Brazil (Balat, 2011; Balat et al., 2008).Table 3.2shows rate of ethanol production from different agro-waste, at various countries ofthe world during 2010.

3.2.1.1 Production feedstocks

Biological feedstocks that contain appreciable amounts of sugar—or materials thatcan be converted into sugar, such as starch or cellulose—can be fermented to producebioethanol (Demirbas, 2007) Feedstocks of bioethanol can be conveniently classifiedinto three categories of agricultural raw materials: (i) sucrose-containing feedstocks,(ii) starchy materials, and (iii) lignocellulosic materials.Fig 3.2indicates the feed-stock classification for bioethanol production The availability of these materialsfor bioethanol can vary considerably from season to season and depends on geo-graphic locations

For a given production line, the comparison of the feedstocks includes severalissues (Balat, 2011): (1) chemical composition of the biomass, (2) cultivation prac-tices, (3) availability of land and land use practices, (4) use of resources, (5) energybalance, (6) emission of greenhouse gases, acidifying gases and ozone depletiongases, (7) absorption of minerals to water and soil, (8) injection of pesticides, (9) soilerosion, (10) contribution to biodiversity and landscape value losses, (11) farmgate price of the biomass, (12) logistic cost (transport and storage of the biomass),(13) direct economic value of the feedstocks taking into account the coproducts,(14) creation or maintenance of employment, and (15) water requirements and wateravailability Since feedstocks typically account for greater than one-third of theproduction costs, maximizing bioethanol yield is imperative Table 3.3 illustratesthe various feedstocks that can be utilized for bioethanol production and their com-parative production potential (Balat, 2009, 2011)

Sucrose containing feedstocks

Feedstock for bioethanol is essentially composed of sugarcane and sugar beet.Two-thirds of world sugar production is from sugarcane and one-third is fromsugar beet (Prado et al., 2016; Koc¸ar and Civaş, 2013) Sugarcane as a biofuel crophas much expanded in the last decade, yielding anhydrous bioethanol (gasolineadditive) and hydrated bioethanol by fermentation and distillation of sugarcanejuice and molasses (Hartemink, 2008) Sugarcane is grown in tropical and subtrop-ical countries, while sugar beet is only grown in temperate-climate countries.Brazil is the largest single producer of sugarcane with about 31% of global sugar-cane production, average sugarcane yield of about 82.4 tons/ha, and bioethanolyield per hectare of around 6650 L/ha (Koc¸ar and Civaş, 2013; Hartemink,2008; Gauder et al., 2011) In Asia (India, Thailand, and Philippines), sugarcane

is produced on small fields owned by small farmers For example, India has around

7 million small farmers with an average of around 0.25 ha sugarcane fields (LinojKumar et al., 2006)

Sugar beet, a cultivated plant ofBeta vulgaris, is a plant whose tuber contains ahigh concentration of sucrose In 2009, France, the United States, Germany, Russia,

Table 3.2 Rate of bioethanol production from agro-waste at various countries/continents

Rice wastes (Tg)/

total bioethanol(GL)

Barley waste (Tg)/

total bioethanol(GL)

Corn waste (Tg)/total bioethanol(GL)

and Turkey were the world’s five largest sugar beet producers In European countries,beet molasses are the most utilized sucrose-containing feedstock The advantages withsugar beet are a lower cycle of crop production, higher yield, high tolerance of a widerange of climatic variations, and low water and fertilizer requirement Compared withsugarcane, sugar beet requires 35%–40% less water and fertilizer (Demirbas, 2007;Koc¸ar and Civaş, 2013).

Sweet sorghum (Sorghum bicolor L.) is one of the most drought-resistant tural crops as it has the capability to remain dormant during the driest periods andrequires fewer inputs to achieve its maximal production Of the many crops beinginvestigated for energy and industry, sweet sorghum is one of the most promising can-didates, particularly for bioethanol production principally in developing countries(Stevens et al., 2004; Whitfield et al., 2012)

agricul-Bioethanol feedstocks

residues

Energy

Agriculture wastes

Paper wastes

Fig 3.2 Feedstock classification of bioethanol production

Table 3.3 Comparison of various bioethanol feedstocks

or starch(%)

Conversionrate tobioethanol(L/ton)

Bioethanolyield (ton/

ha/year)

Cost($/m3

Starchy materials

Another type of feedstock used for bioethanol production are starch-based materials.Starch is a biopolymer and defined as a homopolymer consisting only one monomer,

D-glucose To produce bioethanol from starch, it is necessary to break down the chains

of this carbohydrate for obtaining glucose syrup through hydrolysis, which can beconverted into bioethanol by yeasts This type of feedstock is the most utilized forbioethanol production in North America and Europe Corn/maize and wheat are mainlyemployed with these purposes The United States is predominantly a producer of bio-ethanol derived from corn, and production is concentrated in Midwestern states withabundant corn supplies (Cardona and Sanchez, 2007; Shapouri et al., 2006) Maize isincreasingly used as a feedstock for the production of ethanol fuel It is widely cultivatedthroughout the world, and a greater weight of maize is produced each year than any othergrain The United States produces 40% of the world’s harvest; other top producing coun-tries include China, Brazil, Mexico, Indonesia, India, France, and Argentina Worldwideproduction was 817 million tons in 2009, more than rice (678 million tons) or wheat (682million tons) (Koc¸ar and Civaş, 2013; Shapouri et al., 2006) The starch-based bioethanolindustry has been commercially viable for about many years; in that time, tremendousimprovements have been made in enzyme efficiency, reducing process costs and timeand increasing bioethanol yields

Lignocellulosic biomass

Globally, many lignocellulosic agro-residues such as rice straw, wheat straw, cane bagasse, sugarcane tops, cotton stalk, soft bamboo, and switchgrass have beenused to produce bioethanol as abundantly available feedstocks (Ravindranath et al.,

sugar-2011) Lignocellulosic materials can be classified in four groups based on the type

of resource: (1) forest residues, (2) municipal solid waste, (3) waste paper, and (4) cropresidue resources These materials could produce up to 442 billion liters per year ofbioethanol (Balat, 2011; Gupta and Verma, 2015)

The production cost of bioethanol from food crops is very high as the raw materials(maize or sugarcane) constitute about 40%–70% of the production cost As a result,promoting the use of second-generation bioethanol from lignocellulosic biomassessuch as nonfood crops, crop residues, and food/crop waste is an alternative way toalleviate the cost and the land use conflict between food needs and fuel needs (Sunand Cheng, 2002)

Chemical composition of lignocellulosic materials is a key factor affecting ciency of biofuel production during conversion processes As the lignocellulosiccomplex is made up of a matrix of cellulose and lignin bound by hemicelluloses,the main challenge in this case is to reduce the degree of crystallinity of thecellulose and increase the fraction of amorphous cellulose by the process of pre-treatment, the most suitable form for the hydrolysis step (Tye et al., 2016) Lignin

effi-is one of the drawbacks of using lignocellulosic biomass materials in fermentation,

as it makes lignocellulose resistant to chemical and biological degradation Sugars

in lignocellulosics are not easily available, due to this tight structure, and require aprevious pretreatment to make the hydrocarbon polymers available to

saccharification and fermentation In general, the difficulties of using losic materials are their poor porosity, high crystallinity, and lignin contents Thecost of bioethanol production from lignocellulosic materials is relatively high whenbased on current technologies, and the main challenges are the low yield and highcost of the hydrolysis process In spite of this matter, by considering these mate-rials as a cheap and abundant feedstocks, they can be a promising renewableresource for bioethanol production at reasonable costs (Balat, 2011; Sun andCheng, 2002; Tye et al., 2016).

lignocellu-Macro/Microalgea

Interest has now been diverted to the third-generation biomass like algae, since thefirst-generation feedstock (edible crops, sugars, and starches) are under serious con-troversy considering the competition between food and fuel and the second-generationbiomass (lignocellulosic biomass) is limited by the high cost for lignin removal as itsincredible resistance to degradation and makes biomass saccharification costly.Microalgae and macroalgae are the two groups of algae investigated as potential fuelsources Algal biofuels, also called advanced biofuels, are seen as one of the mostpromising solutions of global energy crisis and climate change for the years to come(Alam et al., 2012; Noraini et al., 2014) The production of third-generation biofuelshas many advantages over the plants used for producing first- and second-generationbiofuels due to their faster growth; capability of growing under several conditions,including in saline, brackish, and wastewater; reduced need for water and otherresource inputs; the possibility of not occupying arable lands for their cultivation,greenhouse gas fixation ability (net zero emission balance), and high productioncapacity of lipids (Costa et al., 2012)

Cell wall composition of algae differs from those of terrestrial plants The keydifference is low content or the absence of lignin in macro- and microalgal feedstocks,which make them less resistant to conversion into simple sugars The biochemicalcomposition of microalgae grown under normal conditions primarily encompassesproteins (30%–50%), carbohydrates (20%–40%), and lipids (8%–15%) The typesand quantities of basic monosaccharide components such as mannose, galactose,and arabinose are potentially very suitable for conversion into bioethanol(de Farias Silva and Bertucco, 2016)

Ethanol production from microalgae has been reported using the main classes ofmicroalgae, that is, green (Ulva lactuca and U pertusa), red (Kappaphycus alvarezii,Gelidium amansii, G elegans, and Gracilaria salicornia), and brown (Laminariajaponica, L hyperborea, Saccharina latissima, Sargassum fulvellum, Undariapinnatifida, and Alaria crassifolia) According to the results reported in manyresearches, the standard strains ofSaccharomyces cerevisiae with only a few that haveassessed ethanologenic or solventogenic bacterial strains such as Clostridiumpasteurianum and recombinant E coli were utilized for optimal utilization and con-version of such diverse carbohydrates to bioethanol (Costa et al., 2012; de Farias Silvaand Bertucco, 2016; Doan et al., 2012)

3.2.1.2 Production methods

Biofuels are made from biobased materials through different processes like tation and thermochemical processes The type of feedstock chosen for ethanolproduction has a significant impact on the design of fermentation process Ethanol

fermen-is produced from a variety of sugar- or starch-containing crops, with modifications

in the design of the feedstock preparation processes The modifications are required

to accommodate the physical properties of the feedstock and the nature of the hydrate (i.e., sugar vs starch) (Nigam and Singh, 2011) Bioethanol productionprocesses for different resources are discussed in detail in this section

carbo-Bioethanol from sugar-/starch-containing feedstock

Sucrose-containing feedstocks, as the most utilized substrate for bioethanol production,are mostly preferred because of the easier conversion of sucrose into ethanol comparedwith starchy and lignocellulosic biomass No conversion of the feedstock is required forthis substrate, as the disaccharides can be directly broken down by the microorganismsduring bioethanol production In spite of this simple procedure, the processing of thesesubstrates is generally too expensive for bioethanol production, because of the availabil-ity and transport costs of its feedstocks First-generation bioethanol is mostly producedfrom corn and sugarcane using a well-established technology as shown in Fig 3.3.Fermentable sugars are extracted by grinding or crushing, followed by fermentation

to ethanol Further, ethanol is separated from the product stream by distillation, followed

by dehydration (Suresh et al., 1999; Larson, 2008; Balat, 2011)

Starch is a high-yielding feedstock for bioethanol production Grains such as cornand wheat contain starch, which is a polysaccharide of glucose units linked byα (1–4)andα (1–6) glycosidic bonds Starch is not directly fermented by microorganisms likeyeast Production of ethanol from starch is performed by either dry grind or wet mill-ing process, which are different in the extraction method of glucose and coproductsformed As indicated inFig 3.3, the extracted starch is hydrolyzed into glucose byusing the specific enzymes likeα-amylase and glucoamylase, and glucose is then fer-mented to ethanol (Thatoi et al., 2016; Chen and Fu, 2015)

Milling Liquefaction and

Sugar Feedstock

Fig 3.3 Process diagram for bioethanol production from sugar and starch feedstocks

Bioethanol from lignocellulosic materials

Four process steps for ethanol production from lignocellulosic materials are possible,namely, as pretreatment, hydrolysis, fermentation, and product separation/distillation.Schematic flow sheet for the bioconversion of biomass to bioethanol is shown inFig 3.4 The main challenge for this material is to reduce the degree of crystallinity

of the cellulose and increase the fraction of amorphous cellulose by the process of treatment as the most suitable form for the hydrolysis step After pretreatment, thecellulose undergoes enzymatic hydrolysis in order to obtain glucose that is converted

pre-to ethanol by microorganisms (Sun and Cheng, 2002; Tye et al., 2016; Chen and

Fu, 2015)

Pretreatment process

The most important processing challenge in the production of biofuel is pretreatment

of the biomass for further chemical or biological treatment Pretreatment methodschange the native properties of the substrate by solubilization and separation ofone or more of components of biomass and making the remaining solid biomass moreaccessible to further treatment For instance, starchy substrates can be fermented afterbreaking starch molecule into simpler glucose molecules, and this can be done by apretreatment step For lignocellulosic biomass, the pretreatment is done to break thematrix in order to reduce the degree of crystallinity of the cellulose, increase the frac-tion of amorphous cellulose, and convert it to the most suitable form for enzymaticattack (Balat, 2011; Chen and Fu, 2015)

Pretreatment methods can be categorized into physical, chemical, biological, andphysicochemical methods, which are discussed in detail below The goals of an effec-tive pretreatment process are (i) to form sugars directly or subsequently by hydrolysis

Simultaneous saccharification and fermentation (SSF)

Lignin Residue-to-power production

Recirculation of process streams

Waste management

Fermentation (Conversion of sugars to bioethanol)

Enzymatic hydrolysis (Convers enzymatic hydrolysis (Conversion of cellulose to sugar)

Pretreatment (Solubilisation

of hemicellulose)

Fig 3.4 Schematic flow sheet for the bioconversion of bioethanol from biomass

(ii) to avoid loss and/or degradation of sugars formed, (iii) to limit formation of itory products, (iv) to reduce energy demands, and (v) to minimize costs (Balat, 2011;Tye et al., 2016).

inhib-Physical pretreatment The primary steps for ethanol production from residues are combination of methods like mechanical milling, grinding, and chippingthat are used to diminish the particle size, increase the surface area, and improve themass transfer characteristics Also these methods reduce the cellulose crystallinity andimprove the efficiency of downstream processing Besides the mechanical combina-tion, the physical pretreatment technology also includes uncatalyzed steam explosion,liquid hot water pretreatment, and high-energy radiation, of which steam explosionloosen the recalcitrant structure of plant cell wall by increasing surface area andremoves pentose sugar, but the major drawback of steam treatment during enzymatichydrolysis is generation of some cellulose inhibitory compounds that hamper theenzymatic hydrolysis of the cellulose substrates (Tye et al., 2016; Chen and Fu, 2015).Chemical and physicochemical pretreatment Chemical pretreatment methodsinclude ozonolysis, acid hydrolysis, and alkali hydrolysis that involve the usage ofdilute acid, alkali, ammonia, organic solvent, sulfuric and formic acids, SO2, CO2,

agro-or other chemicals The physicochemical pretreatment methods include ammoniafiber explosion and steam pretreatment These methods are easy in operation and havegood conversion yields in short span of time But the major impedance of chemicalpretreatment is that the utilization of such chemicals affects the total economy of bio-conversion of cellulosic biomass Shenoy et al (Balat, 2011) showed that amongchemical treatments, the dilute sulfuric acid-based pretreatment is most popular bymeans of enzymatic hydrolysis using agricultural biomasses

Biological pretreatment The biological pretreatment methods mainly involveutilizing different fungal species like brown rot, white rot, and soft rot fungi fordegradation of the lignocellulosic complex to liberate cellulose Biological pre-treatment renders the degradation of lignin and hemicellulose, and white rot fungiseem to be the most effective microorganism Brown rot attacks cellulose, while whiteand soft rots attack both cellulose and lignin Celluloseless mutant was developed forselective degradation of lignin and to prevent the loss of cellulose, but in most cases ofbiological pretreatment, the rate of hydrolysis is very low The advantages of biolog-ical pretreatment include low energy requirement and mild environmental conditions(Tye et al., 2016; Mosier et al., 2005) The major effects of pretreatment on lignocel-lulosic feedstocks are illustrated inFig 3.5

Hydrolysis process As the pretreatment is finished, the material is prepared forhydrolysis, which means the process of cleavage of a molecule by adding a water mol-ecule as shown below: