The products obtained from algal biomass include bio-oil, biodiesel, bioethanol, biomethane, biohydrogen, and other value-added products. Table 1.8 lists the different products obtained from algal biomass and the conversion technologies used for their production.

Algal biomass is very rich in oil content. This oil can be extracted from the algal biomass by solvent extraction methods. It can be used as such as fuel, or it can be converted to biodiesel, by the process of transesterification, for use as a

transportation fuel. Biodiesel, used as a transportation fuel, has a distinct advan­tage where it can be used directly in any diesel engine, without modification. Bioalcohol is the most widely used liquid fuel. It can be generated from micro­algae by two methods: (1) the conventional yeast-mediated fermentation of car­bohydrate rich algal biomass such as starch containing green algae, glycogen containing cyanobacteria, and glycerol-rich Dunaliella, and (2) ‘‘self-fermenta­tion’’ of carbohydrates contained in algae by endogenous algal enzymes induced under anaerobic conditions. This has been reported for Chlamydomonas [28]. Both these processes give a product yield that is uneconomical. However, there are many companies which are attempting to devise economically viable methods for ethanol production from algal biomass. One such company Algenol Biofuels Inc. has successfully developed the Direct to Ethanol® algae technology. In this technology, overexpression of the genes responsible for converting carbohydrates to ethanol is achieved by genetic modification techniques, resulting in metaboli — cally hybrid algae which have an increased photosynthetic ability. These hybrid algae use CO2 from the surroundings (collected from industrial emissions), and produce ethanol within the algal cells. This ethanol diffuses through the cell wall into the culture medium and evaporates along with water into the head space provided for it in an enclosed, sealed photobioreactor. The ethanol-water vapor mixture condenses on the inner surface of the photobioreactor and is collected as liquid, which is further concentrated and distilled into fuel ethanol. Optimization of cultivation and productivity of the hybrid algae is being evaluated. This tech­nology is expected to provide an 80% reduction in GHGs compared to gasoline. Biomethane is produced by the usual anaerobic fermentation methods described in ‘‘Anaerobic Digestion’’. The yield of methane is again lower with algal biomass due to the natural tendency of most species of algal biomass to resist biodegra­dation. In addition to this, the ammonia which is released from the algal biomass acts as an inhibitor in the microbiological conversion process. The problem of resistance of the algal biomass toward biodegradation has been addressed by using thermochemical and mechanical pretreatment techniques which solubilize the biomass by breaking down the recalcitrant cell walls. This has been found to increase the methane production rates by about 30% for microalgal biomass harvested from sewage ponds [28].

The second problem posed by the inhibitory effect of ammonia has been cir­cumvented by adding carbon-rich wastes to the microalgal biomass. The additional bacterial biomass added by way of this carbon-rich waste reduces ammonia levels through nitrogen sequestration, thus improving the methane yields. Biotechnol­ogy-based approaches such as developing bacterial cultures that are more resistant to ammonia inhibition are also being explored. Hydrogen can be generated from algal biomass by mainly three ways; (1) Dark fermentation, where anaerobic fermentation of carbohydrate products such as starch, glycogen, and glycerol is carried out by anaerobic bacteria, in absence of light. This process yields hydro­gen, solvents, and mixed acids, (2) Light-driven fermentations, also called photo­fermentations, where the organic acids formed during dark fermentation are converted into hydrogen by nitrogen-fixing photosynthetic bacteria, and (3) Bio­photolysis, which involves the splitting of water into hydrogen and oxygen by microalgae.

The other value-added products obtained from algae include, small molecules such as iodine, algin, mannitol, and lignin-related fractions; polymers such as alginates, carrageenans, agars, and sulfated polysaccharides; high value oils such as long-chain polyunsaturated fatty acids (PUFA) which include substances having a high nutraceutical value, e. g., arachidonic acid, docosahexanoic acid, eicosa — pentanoic acid, etc. Research in algal methods of conversion merits special attention because it provides third-generation biofuels which do not compete with food crops nor with the arable land required for their cultivation and hence remains excluded from the food versus fuel controversy. Algal biorefineries are now being set up which are expected to give multiple products in a cost-effective manner using the different biomass conversion technologies mentioned above (Table 1.8). These are discussed in ‘‘Aquaculture-Based Biorefinery (Algae and Seaweed Based Biorefinery)’’.

By varying the temperature of biomass the briquette density, briquette crushing strength and moisture stability can be varied. In a screw extruder, the temperature does not remain constant in the axial direction of the press but gradually increases. Internal and external friction causes local heating and the material develops self­bonding properties at elevated temperatures. It can also be assumed that the moisture present in the material forms steam under high pressure conditions which then hydrolyses the hemicellulose and lignin portions of biomass into lower molecular carbohydrates, lignin products, sugar polymers and other derivatives. These products, when subjected to heat and pressure in the die, act as adhesive binders and provide a bonding effect ‘‘in situ’’. The addition of heat also relaxes the inherent fibers in biomass and apparently softens its structure, thereby reducing their resistance to briquetting which in turn results in decreased specific power consumption and a corresponding increase in production rate and reduction in wear of the contact parts. However, the temperature should not be increased beyond the decomposition temperature of biomass which is around 300°C.

The complete dissolution of native biomass in ILs using conventional heating (oil bath) may take several hours at high temperatures. In order to reduce the energy costs associated with heating, a commercial microwave oven was used to heat the wood/IL mixture before it was heated using a conventional oil bath. The appli­cation of 100 pulses of 3 s reduced the time necessary to dissolve pine sawdust (particle size 0.125-0.250 mm) completely from 46 to 16 h [36]. Microwave irradiation also accelerated the production of 5-hydroxymethylfurfural and furfural directly from milled corn stalks, rice straws, and pine wood, reducing the reaction time down to a few minutes [35].

Ultrasounds can also accelerate the complete dissolution of cellulose in [BMIM][Cl] and [AMIM][Cl] from several hours to several minutes [56]. The exposure of pine sawdust (particle size 0.125-0.250 mm) to 1 h of ultrasound at 40°C before IL treatment reduced the time necessary to dissolve the sample from 46 to 23 h [36].

HDO or hydrotreating of fatty acids was developed based on hydrodesulfurization (HDS) method which is used in purification of hydrocarbons feedstock in petro­chemical industry. The milestone for this technology was the first patent describing a method of hydrotreating of fatty acids and triglycerides of them made by Craig et al. [10]. Commercially available hydrotreating catalysts, such as bimetallic cobalt-molybdenum (Co-Mo) or nickel-molybdenum (Ni-Mo), were used for hydrotreating fatty acids and their derivatives in a temperature range of 350-450°C and 4.8-15.2 MPa hydrogen pressure. Results showed high conversion of different fatty acid feedstocks (canola oil, palm oil, rapeseed oil, sunflower oil, soybean oil, and tall oil fatty acids fraction) to hydrocarbons.

The general approach of this technique is catalytic deoxygenation of fatty acids, their esters, or triglycerides over a catalyst promoting hydrogenation reaction. The fatty acid transformation should be preferably performed in a hydrogen-rich atmosphere to promote hydrogenation/hydrogenolysis of carboxylic group.

9.2.4.1 Apple Pomace

Apple pomace is the solid phase resulting from pressing apples for juice, con­taining the pulp, peels, and cores. It accounts for 25-35% of the dry weight of processed apple. It has very high moisture content and can be easily decomposed by microorganisms. It is of yellow-to-brown color [7]. It is a rich source of many nutrients including carbohydrates, minerals, fibers except protein [162]. Apple pomace has high contents of carbohydrates with about 9.5-22.0% of fermentable sugar [174] which makes it a good substrate for fermentation while its low protein content indicates its unsuitability as animal feed [67, 86].

The amount of initial sugar content, however, depends upon the variety of apple processed, the processing conditions used, and the amount of filter aids added [66].

Alcohol-soluble compounds (monosaccharides, oligosaccharides, and malic acid) accounted for 32-45 wt% of oven-dry pomace. Glucose and fructose are the major components of this fraction. Apple pomace is an acidic substrate and has con­siderable buffering capacity due to the presence of malic acid in it. Apple pomace has high levels of Biochemical Oxygen Demand/Chemical Oxygen Demand (BOD/COD) and is highly biodegradable. The proximate composition of apple pomace is shown in Table 9.5.

9.2.4.2 Banana Waste

Banana waste mainly comprises the peels and stalks. The physicochemical char­acteristics given in Table 9.6 clearly show that it can be used for ethanol production.

Traditionally, alcohol is produced from liquid or liquid mash via submerged microbial fermentation. In recent years, there has been a considerable interest in the production of alcohol from food processing wastes such as apple pomace because of (i) the rising energy costs of molasses and (ii) the negative cost of values of wastes as substrates. Apple pomace is not readily amenable to sub­merged microbial fermentation due to its nature. The solid-state fermentation of apple pomace offers several advantages for ethanol production such as higher yield but has difficulty of ethanol extraction from the solid materials. Different microorganisms (Table 9.12) have been used for the production of ethanol,

predominantly yeast belonging to S. cerevisiae that has been a microorganism of choice.

Hang [66] developed a solid-state fermentation system of apple pomace with S. cerevisiae at 30°C in 96 h producing 43 g ethanol/kg of apple pomace. Ethanol was separated out by vacuum evaporation with a separation efficiency of 99%. Blending the pomace with molasses lowered the ethanol yield and fermentation efficiency. However, fermentation by immobilized yeast did not increase the yield of ethanol from the apple pomace. Jarosz [77] collected apple pomace from three factories and fermented at 30°C for 72 h with or without addition of inoculum. The natural microflora induced the fermentation but addition of yeast accelerated the fermentation and brought to the 78.9% of the theoretical yield of ethanol.

Sandhu and Joshi [160] reported that natural fermentation of apple pomace was inferior to the yeast inoculated fermentation for ethanol, crude, and soluble pro­teins. The production of ethanol in natural fermentation was almost half that of S. cerevisiae fermentated apple pomace. Joshi et al. [85, 88] provided partial aseptic and anaerobic condition to the solid-state fermentation of apple pomace by addition of SO2 and found that addition of SO2 up to 200 ppm increased the ethanol content by S. cerevisiae while it was 150 ppm for Candida utilis and Torula utilis. The amount of ethanol present in the fermented apple pomace depends upon the initial sugar content in the apple pomace which in turn is influenced by variety of apple processed, the processing conditions, and the amount of the pressing aids employed.

Ethanol recovery by manual squeezing, direct distillation of fermented pulp, percolation of fermented pulp and hydraulic pressing in three stages with interstate water addition from solid-state fermented pulpy material have revealed that hydraulic pressing in three stages with interstate water addition, led to 79.68% ethanol recovery with 60.53% ethanol in the pooled extract of that in the fermented pulp. Ngadi and Correia [130] found that when the apple pomace was fermented at 77 and 85% of moisture level yielded 19.26 and 18.10% of ethanol on dry weight basis. The original pH and the initial moisture content of apple pomace was found to be suitable for ethanol production, decreasing the pH or increasing the moisture content reduced the ethanol content [87]. Fermentation time increased the ethanol production up to 96 h at 30°C and among the different nitrogen sources tried, ammonium sulfate gave the highest ethanol production and S. cerevisiae giving better response to it than Candida utilis and Torula utilis. Addition of 0.4% of ammonium sulfate increased the ethanol yield. The combined effect of AMS and ZnSO4, however, was detrimental to ethanol production but AMS alone gave better ethanol yield.

Gupta [61] found that the addition of nitrogen, phosphate, and trace elements to the SSF of apple pomace with Saccharomyces diasticus enhanced the fermentation efficiency to 67.7, 68.5, and 68.8%, respectively (control having fermentation efficiency of about 43.8%). Distillation of fermented extract with a bucchi evap — orater yielded 0.029, 4.1, 0.0003, 0.01, and 0.011% of methyl, ethyl, n-propyl, isobuty1, and isoamyl alcohols, respectively [66]. Joshi and Sandhu [83] found that all the yeast fermented apple pomace distillates contained methyl and butyl alcohols and aldehyde. S. cerevisiae fermented distillate had more desirable characteristics than those obtained from fermentation with other yeasts and thus, had potential for conversion into potable alcohol. The step-by-step process involved in ethanol production from food processing industry waste is shown in

Fig. 9.16.

Words are compendious in expressing our deep gratitude and profound indebt­edness to Prof. D. S. Chauhan, Vice Chancellor, Uttarakhand Technical Univer­sity, Dehradun for his dexterous guidance, invaluable suggestions and perceptive enthusiasm which enabled us to accomplish this project. His association, inspi­ration, constructive criticism and encouragement throughout the period of our academic and our personal life, especially for the time spent in informal discus­sions have all been a valuable part of our learning experience.

We accord our cordial thanks to Prof. Wook-Jin Chung (Director, Energy and Environment Fusion Technology Center, Myongji University, South Korea) and Prof. Hern Kim (Department of Environmental Engineering and Energy, Myongji University, South Korea) for their timely support and suggestions during our stay at Myongji University.

We owe our sincere thanks to Prof. Seeram Ramakrishna, Vice-President (Research Strategy), National University of Singapore for his motivation. Our heartfelt thanks to Mr. A. L. Shah, Director, THDC Institute of Hydropower Engineering and Technology, Tehri (Constitute Institute of Uttarakhand Technical University) for his encouragement.

We would like to thank the production team at Springer-Verlag Heidelberg, particularly Dr. Marion Hertel, Beate Siek, Elizabeth Hawkins, Birgit Munch and Tobias Wassermann for their patience, help and suggestions.

We extend our sincere gratitude, love, and appreciation to our family members, especially parents, Mr. Chinnappan, Mrs. Mariya, Mr. Pawan Kumar Sambher and Mrs. Sudesh Sambher, brother Doss Chinnappan, and sister Amutha Chinnappan (Department of Environmental Engineering and Energy, Myongji University, South Korea) for their support throughout this book project. We are also indebted to our sons Suvir Baskar and Yavin Baskar, who missed our company in many days, we were working on this project. We hope they will appreciate this effort when they grow up. This book is also dedicated to my late brother, Julian Chinnappan.

As editors we bear responsibility for all interpretations, opinions and errors in this work. We welcome valuable comments and suggestions from our readers.

February 2012 Dr. Chinnappan Baskar

E-mail: baskarc@yahoo. com; Website: www. baskarc. com

Dr. Shikha Baskar

Biomass can be used to generate various forms of energy. Biomass conversion into biofuels (which serve as a source of energy when burnt) has already been dis­cussed in the earlier sections. This section focuses on the use of biomass for electricity generation. The conventional sources of electricity generation include the nonrenewable sources such as coal, natural gas, nuclear energy, hydroelectric power, petroleum and other fossil fuels, and the renewable sources such as bio­mass, wind energy, solar energy, and geothermal source of energy. Currently, the world over, nuclear energy, fossil fuel, and natural gas are the major sources of commercial generation of electricity. The prospective shortage of fossil fuel and

Fig. 1.31 Biorefinery platform

the adverse health and environmental effects of these sources (e. g., emission of GHGs and adverse effects related to the electricity generation from nuclear sources) have made it imperative that a transition be made from these to more safe and environment friendly sources such as renewable sources for the generation of electricity. Presently, a very small proportion of electricity generation is from renewable sources. Biomass is a very significant source of energy which can be tapped for the generation of electricity. The most common types of biomass used for electricity generation are agricultural residues, forest residues, and dedicated energy crops. The use of biomass for electricity generation has been increasing

Fig. 1.32 Petroleum refinery platform gradually by an average of about 13 TWh per year between 2000 and 2008, and constitutes about 2% of the total global generation of electricity over the last 20 years [57]. Figure 1.33 shows the contribution of biomass toward electricity generation at the global level.

The US is the major producer of electricity from biomass (producing 26% of the global electricity production from biomass), followed by Germany (15%), Brazil (7%),and Japan (7%).

Projects are being undertaken where combined heat and power generation (CHP) systems are developed which have the capacity to fulfill the energy and power requirements of large populations using biomass energy. In this context, it is worthwhile to mention an experimental model bioenergy village—Juhunde (Fig. 1.34) which has been developed by the International Centre for Sustainable Development in Gottingen, Germany under the leadership of Professor Hans Ruppert of the University of Gottingen. A large biomass fermenter converts the waste biomass collected from the surroundings into methane. A combined heat and power station burns this gas to either provide heating through a combined village heating grid or provides electricity through a public grid. The energy produced by this plant is sufficient to satisfy all the energy needs of the Juhunde village which has about 770 inhabitants. The post-fermentation residue is used as a fertilizer for growing further biomass. Delegations from Japan and China have since visited this bioenergy village to study the technology involved therein and the possibility of scaling up the project to suit larger requirements [58]. The economics and sca­lability of such projects need to be studied critically so that more such self­sustaining localities can be developed.

Evans et al. [57] have enlisted the cost of power production from biomass cited in the literature. There is a considerable variation in the cost of power which depends mainly on the feedstock factors such as cost of generating/procuring the

MANURE

BIOMASS

WOOD

CHIPS feedstock and energy density of the feedstock, transportation factors such as cost of transportation of the biomass, other factors such as conversion technology used.

Another form of liquid fuel from biomass is ‘‘biodiesel’’, which is derived from the vegetable oils extracted by crushing oilseeds, although waste cooking oil or animal fats (tallow) can also be used. The oil is strained and usually ‘‘esterified’’, by combining the fatty acid molecules in the oil with methanol or ethanol. Vegetable oil esters have been shown to make good-quality clean-burning diesel fuel.

The use of vegetable oils for combustion in diesel engines has occurred for over 100 years. In fact, Rudolf Diesel tested his first prototype on vegetable oils, which can be used, ‘‘raw’’, in an emergency. While it is feasible to run diesel engines on raw vegetable oils, in general the oils must first be chemically transformed to resemble petroleum-based diesel more closely. The raw oil can be obtained from a variety of annual and perennial plant species. Perennials include oil palms, coconut palms, physica nut and Chinese tallow tree. Annuals include sunflower, groundnut, soybean and rapeseed. Many of these plants can produce high yields of oil, with positive energy and carbon balances. Transformation of the raw oil is necessary to avoid problems associated with variations in feedstock. The oil can undergo thermal or catalytic cracking, Kolbe electrolysis, or transesterification processes in order to obtain better characteristics. Untreated oil causes problems through incomplete combustion, resulting in the buildup of sooty residues, waxes, gums, etc.

Biodiesel refers to a vegetable oil — or animal fat-based diesel fuel consisting of long-chain alkyl (methyl, propyl or ethyl) esters. Biodiesel is typically made by chemically reacting lipids (e. g., vegetable oil, animal fat (tallow)) with an alcohol. Biodiesel is meant to be used in standard diesel engines and is thus distinct from the vegetable and waste oils used to fuel converted diesel engines. Biodiesel can be used alone, or blended with petrodiesel.

Blends of biodiesel and conventional hydrocarbon-based diesel products are most commonly distributed for use in the retail diesel fuel marketplace. Much of the world uses a system known as the ‘‘B’’ factor to state the amount of biodiesel in any fuel mix:

• 100% biodiesel is referred to as B100, while

• 20% biodiesel is labeled B20

• 5% biodiesel is labeled B5

• 2% biodiesel is labeled B2.

Obviously, the higher the percentage of biodiesel, the more ecology-friendly the fuel is. Blends of 20% biodiesel with 80% petroleum diesel (B20) can gen­erally be used in unmodified diesel engines. Biodiesel can also be used in its pure form (B100), but may require certain engine modifications to avoid maintenance and performance problems. Blending B100 with petroleum diesel may be accomplished by:

• Mixing in tanks at manufacturing point prior to delivery to tanker truck.

• Splash mixing in the tanker truck (adding specific percentages of biodiesel and petroleum diesel).

• In-line mixing, two components arrive at tanker truck simultaneously.

• Metered pump mixing, petroleum diesel and biodiesel meters are set to X total volume, transfer pump pulls from two points and mix is complete on leaving pump.

There is ongoing research into finding more suitable crops and improving oil yield. Using the current yields, vast amounts of land and fresh water would be needed to produce enough oil to completely replace fossil fuel usage. It would require twice the land area of the US to be devoted to soybean production, or two — thirds to be devoted to rapeseed production, to meet the current US heating and transportation needs. Specially bred mustard varieties can produce reasonably high oil yields and are very useful in crop rotation with cereals, and have the added benefit that the meal leftover after the oil has been pressed out can act as an effective and biodegradable pesticide.

It was experimented with using algae as a biodiesel source and it was found that these oil-rich algae can be processed into biodiesel, with the dried remainder further reprocessed to create ethanol. In addition to its projected high yield, algaculture—unlike crop-based biofuels—does not entail a decrease in food production, since it requires neither farmland nor fresh water. Many companies are pursuing algae bio-reactors for various purposes, including scaling up biodiesel production to commercial levels.

4.4.1 General Toxicity of Ionic Liquids

There is a general scarcity of toxicology data and studies on ILs [109]. Tests were developed to measure the toxicity on unicellular and multicellular organisms. A measure of toxicity is the concentration (EC50) of the IL that induces a 50% decrease of the organism viability. These tests are, however, expensive and time­consuming, severely restricting the number of ILs/organisms that can be tested. Effective screening is necessary to focus resources on a limited number of IL structures. Also, the IL interactions with the organisms or culture medium are not fully understood, which potentially affects the interpretation of the results. The IL may change the chemical composition of the culture medium, its pH, and cause interferences with widely used spectrophotometric methods [110].

The survival rate or microorganisms, invertebrates and human cell lines was assessed as a function of the ionic liquid concentration [60, 111-114]. The toxicity from 1-alkyl-3-methyl-imidazolium ILs was found to increase as the length of the alkyl chain increased [60, 115]. The IL cation mostly determines the toxicity of the IL. Only minimal effect from the anion was observed [60, 113, 115]. The toxicity of ILs was also assessed on Clostridium sp., a bacterium capable to ferment sugars. No growth was observed above concentrations of 58 mM in [EMIM][OAc], 56 mM in [EMIM][DEP], and 54 mM in [MMIM][DMP]. But at low concentra­tion below 15 mM, [EMIM][OAc] stimulated the growth and glucose fermentation by pH modulation in the culture medium [116].

It should be pointed out that IL toxicity can also come from the formation of by-products from the acid hydrolysis of biomass, such as furfurals, which are known to reduce cell viability and inhibits fermentation [117].