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Platform Chemical Biorefinery and Agroindustrial Waste Management
C H A P T E R
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Platform Chemical Biorefinery and Agroindustrial Waste Management K.P. Gopinath, A.R. Sankaranarayanan, L. Nivedhitha SSN College of Engineering, Chennai, India O U T L I N E 20.1 Introduction
380
20.3.2.4 Consolidated Biomass Processing 386
20.3.3 Adsorbents From Agricultural Waste 386 20.3.4 Bagasse and Sugarcane Cogeneration386 20.3.5 Kraft Paper Process and Biorefinery386
20.2 Agroindustrial Waste Types and Their Global Annual Production 381 20.2.1 Current Scenario of Agroindustrial Waste Production381 20.2.2 Factors Affecting Biomass Yield382
20.4 Advantages and Challenges of Using Agroindustrial Wastes as the Feedstock for Biorefinery 387 20.4.1 Advantages 387
20.3 Present Agroindustrial Waste Management Approaches 383 20.3.1 Current Practices: Traditional Uses383 20.3.2 Bioethanol 384
20.3.2.1 Separate Hydrolysis and Fermentation 385 20.3.2.2 Simultaneous Saccharification and Fermentation385 20.3.2.3 Simultaneous Saccharification and Cofermentation 386
Platform Chemical Biorefinery http://dx.doi.org/10.1016/B978-0-12-802980-0.00020-1
379
20.4.1.1 Availability 387 20.4.1.2 Environmental Sustainability387 20.4.1.3 Renewable Nature 387 20.4.1.4 Economic Viability 388 20.4.1.5 Energy and Economic Security388
20.4.2 Challenges
388
© 2016 Elsevier Inc. All rights reserved.
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20. PLATFORM CHEMICAL BIOREFINERY AND AGROINDUSTRIAL WASTE MANAGEMENT
20.4.2.1 Nonuniformity in Agroindustrial Wastes388 20.4.2.2 Collection, Storage, and Segregation 388 20.4.2.3 Social Perspectives 389 20.4.2.4 Technology 389
20.5 Agroindustrial Waste Biorefinery: Engineering Breakthroughs 389
20.5.1 Continuous Countercurrent Extruder Reactor 389 20.5.2 Rapid Integrated Continuous Countercurrent Hydrolysis 390 20.5.3 Microalgae-Based Biorefinery Processes390
20.6 Conclusions
390
References390
20.1 INTRODUCTION The concept of biorefinery, analogous to a petrochemical refinery, is fast gaining interest (Preisig et al., 2012). The commercialization of this concept requires in-depth studies and the development of industry standards. The challenges include the high specificity of biochemical reactions and enzymatic reactions, which are the requirements of expensive pretreatment steps involved while using biomass as precursors (Menon and Rao, 2012). Studies have shown that localized systems that take into account local conditions while devising waste management strategies coupled with small-scale bioprocesses have succeeded better than compared to a “one size fits all” approach wherein the policy and management are devised to encompass large geographies and a wide spectrum of industrial paradigms (Clark et al., 2008). The challenge is to develop methodologies to exploit local resources using niche technologies to produce commercially viable products like specialty molecules, materials, and fuels (Octave and Thomas, 2009). Though the challenges discussed above have impeded the development of biorefineries, advances in the field of bioreactor design and cost-effective pretreatment processes accompanied by an increased need for developing environmentally sustainable processes in the chemical industry have the potential to take forward the concept of biorefineries. The utilization of agroindustrial wastes for the production of value-added chemicals has a great potential to revolutionize the chemical industry (Chandra et al., 2012). The production of bioethanol has fast gained traction in many parts of the world (Octave and Thomas, 2009). The next frontier is to develop systems and technologies to extract valuable chemical products from agroindustrial waste materials. The idea of using agroindustrial wastes as feedstocks in biorefinery processes is very interesting from the perspective of environmental sustainability. The conceptualization of biorefineries using agroindustrial wastes is analogous to petroleum refineries that use crude oil as a feedstock. Lignocellulosic biomass is the primary constituent of agroindustrial waste, and it has to be considered as an analogue of crude oil in the realm of biorefinery conceptualizations. This chapter aims to provide an outline on agricultural waste generation across major countries and regions and also in terms of the lignocellulosic composition of different types of agricultural wastes. The latter part of the chapter deals with established practices for managing agricultural waste and
20.2 Agroindustrial Waste Types and Their Global Annual Production
381
advantages of biorefinery processes. A brief commentary on breakthroughs in the field of biorefinery processing has also been included.
20.2 AGROINDUSTRIAL WASTE TYPES AND THEIR GLOBAL ANNUAL PRODUCTION 20.2.1 Current Scenario of Agroindustrial Waste Production The primary source of agroindustrial waste is residue from agricultural crops. The cultivation of wheat, maize, rice, soybean, barley, rapeseed, sugarcane, and sugar beet results in the production of 3.3 Gt of agricultural waste per year. China, the United States, and India account for 60% of the crop residues produced (Bentsen and Felby, 2010). The level of agricultural waste production shows considerable differences over crop species, region of cultivation, and social, technical, and local factors (Lobell et al., 2009). It is observed from Fig. 20.1 that developing countries such as India and China contribute significantly to the production of agricultural waste. This combined with their growing demand for resources can be expected to intensify efforts toward realizing the concept of biorefineries using agroindustrial waste as feedstocks. The abundance and perennial source of agricultural waste has a great potential to revolutionize agriculture and allied industries. The effective utilization of agricultural waste as a feedstock to produce valuable platform chemicals can result in higher value additions to the agriculture and allied industries. Fig. 20.2 illustrates the type of crop that produces more waste, which clearly reveals that maize tops the list with approximately more than 900 million tons of waste generated per year. The United States is the largest producer of maize, followed by Brazil and China. Corncobs and corn leaves are
FIGURE 20.1 Potential of agricultural waste in select countries/regions (Bentsen and Felbyl, 2010).
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FIGURE 20.2 Potential for agricultural waste from a variety of crops.
major residues, which are not valuable agro products. The residues produced by wheat and rice agriculture are also abundant, since these crops are considered to be important feedstocks of most of the population-rich growing countries. Wheat straw, wheat husk, rice straw, and rice husk are important agrowastes produced in huge amounts in China and India, as they are the major producers of wheat and rice in the world. Sugarcane is a major commercial crop grown in many developing countries, with Brazil as its major producer. Other countries like India and China are the next largest producers. Only the sugar juice from sugarcane is considered to be a valuable agro product and the rest of the dry matter (bagasse) is considered to be a residue (Bentsen and Felby, 2010).
20.2.2 Factors Affecting Biomass Yield The biomass yield from agricultural residues is not uniform across various regions of the world and is subject to almost the same conditions that determine harvest yields. The biomass yield depends on a multitude of conditions like crop species, nutrient supply, prevailing local climatic conditions, susceptibility to pests, weed pressure, etc. (David et al., 2009; Lobell et al., 2009). The uptake of water and the ability of the soil to hold moisture and facilitate effective water transport in plants can significantly affect the production of crop residues. Apart from technical factors crop residue yields also have a social dimension. A lack of knowledge and a risk-adverse nature prevents the implementation of various strategies that aim to increase the production of crop residues. Another factor that has to be considered is the collection and storage of agriculture waste. Currently, a vast majority of agriculture waste is not collected and stored (IEA, 2010). The logistics related to agricultural biomass collection and storage are complicated by the seasonal nature of agriculture and various streams of agricultural waste (Rentizelas et al., 2009).
20.3 Present Agroindustrial Waste Management Approaches
383
FIGURE 20.3 Potential for agricultural waste in terms of cellulose, hemicelluloses, and lignin in select countries/ regions (Menon and Rao, 2012).
The availability of agricultural waste can be interpreted in terms of the potential for the production of lignocellulosic materials in the form of cellulose, hemicellulose, and lignin. The interpretation of agricultural waste data in terms of composition of lignocellulosic material, viz., lignin, cellulose, and hemicelluloses, would be of greater value, as they provide an accurate picture of the useful feedstocks available for biorefinery processes. Fig. 20.3 shows the potential of lignocellulosic materials for select countries and regions. It can be observed that the largest component of agricultural waste is cellulose, followed by hemicellulose and lignin. To increase the quantity and quality of retrievable biomass from agricultural waste it is necessary to provide conducive conditions and nutrient supply to the crops. There is also a need to sensitize stakeholders in agriculture to devote resources and time for the collection, segregation, and storage of agricultural residues (Bentsen and Felby, 2010). The lignocellulosic composition varies greatly across crop varieties (Table 20.1); whereas rice husks and sorghum contain up to 20–21% lignin, cotton wastes do not contain lignin at all. It would thus be beneficial to thoroughly understand the lignocellulosic composition of different types of agricultural residues to enable their effective utilization as biorefinery feedstock.
20.3 PRESENT AGROINDUSTRIAL WASTE MANAGEMENT APPROACHES 20.3.1 Current Practices: Traditional Uses A large component of agricultural waste goes unutilized and is left on the field. According to previous studies, an optimistic figure for the collection and use of agricultural waste is only about 25%; in countries such as India and South Africa the figure is as low as 10% (Menon
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TABLE 20.1 Average Composition of Agricultural Wastes (Menon and Rao, 2012; Bentsen and Felbyl, 2010) Lignocellulosic Composition (% dry wt) Agrowaste
Cellulose
Hemicellulose
Lignin
Barley hull
34
36
19
Barley straw
40
28
8
Corncob
39
40
10
Corn stover
37
22
15
Cotton
90
10
0
Cotton stalk
31
11
30
Coffee pulp
35
45
17
Rice straw
32
24
18
Rice husk
32
20
17
Wheat straw
37
26
16
Wheat bran
12
37
10
Sugarcane bagasse
35
30
20
Jute fibers
49
20
24
Winter rye
30
24
16
Oilseed rape
27
21
14
Oat straw
33
23
13
Nutshells
28
25
35
Sorghum straw
32
27
18
and Rao, 2012). Traditional agricultural waste management practices include provisions for animal fodder, manure, and direct combustion. Current practices for the management of agricultural wastes are largely geared toward the production of bioethanol, cogeneration, biofuels, and adsorbents (Isah et al., 2015; Kim and Dale, 2005). Fig. 20.4 shows the trends in traditional and modern uses of various agroindustrial wastes. Based on the modern use of all type of wastes, bioethanol production is suggested. Though the conversion of cellulosic biomass into fermentable sugars is a tedious process, various novel techniques have been suggested by many researchers. These techniques enable the conversion to be easier and economical, so that it can be commercially viable.
20.3.2 Bioethanol The general methodology for producing bioethanol is to pretreat biomass in the form of agricultural residue and subject it to a variety of processes such as separate hydrolysis and
20.3 Present Agroindustrial Waste Management Approaches
385
FIGURE 20.4 Traditional and modern uses of agroindustrial wastes (Isah et al., 2015).
fermentation, simultaneous saccharification and cofermentation, simultaneous saccharification and fermentation (SSF), and consolidated biomass processing (Dias et al., 2011; Gray et al., 2006). This is then followed by fermentation using yeast such as Saccharomyces, Kluveryomeces, Debaryomeces, Pichia, and Zymomonas (Menon and Rao, 2012). 20.3.2.1 Separate Hydrolysis and Fermentation This is a two-step process in which the hydrolysis of the pretreated biomass is followed by the fermentation process, both taking place separately. The hydrolysis process uses acid or an enzymatic treatment, which converts the cellulose and hemicellulose to fermentable sugars. In the fermentation stage, the sugars are transformed to yield ethanol by the action of microorganisms. 20.3.2.2 Simultaneous Saccharification and Fermentation This is a one-step process in which the biomass is converted into alcohols. As the cellulosic biomass breaks down into fermentable sugars by the action of enzymes, the microbes present ferment the sugars to yield ethanol. This process has the advantage of lowering the cost of biomass processing and improving the fermentation process. However, it has a disadvantage
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20. PLATFORM CHEMICAL BIOREFINERY AND AGROINDUSTRIAL WASTE MANAGEMENT
of maintaining the temperature so as not to hinder the activity of the enzyme as well as the growth of the microbes. 20.3.2.3 Simultaneous Saccharification and Cofermentation In this process, the pretreated biomass is neutralized and is exposed directly to the enzymes and genetically modified microorganisms that could hydrolyze the biomass and also ferment sugars, respectively. Compared to the SSF process this has the advantage of having better yields and short processing times. However, this process has limitations in terms of the higher costs incurred by genetically engineering the microbes. 20.3.2.4 Consolidated Biomass Processing This process has the benefits of housing the production of enzymes, hydrolysis, and the fermentation of hexose and pentose sugars in a single reactor in the presence of a microbial consortium. This process is quite interesting, as it employs a single microbial consortium for both the hydrolysis and fermentation processes, thereby gaining the advantage of lowering the production costs of ethanol.
20.3.3 Adsorbents From Agricultural Waste Agricultural wastes such as coconut shells, barley husk, rice husk, etc. have been used as adsorbent materials for treating pollutants such as synthetic dyes, organic chemicals, and heavy metals (Isah et al., 2015; Robinson et al., 2002; Vadivelan and Vasanth Kumar, 2005). The agricultural waste materials used for the adsorption processes require various levels of pretreatment and follow a wide variety of action mechanisms. One of the most important adsorbents produced from agricultural wastes is activated carbon.
20.3.4 Bagasse and Sugarcane Cogeneration Sugarcane cogeneration plants utilize waste bagasse for heat requirements and the production of electricity. The electricity thus generated can be used as a captive source of energy for powering operations in sugar mills, or it can be sold commercially to external users (Khatiwada et al., 2012). The bagasse produced from refining cane sugar is also used to make paper, particle boards, and bioethanol. This has achieved the twin benefits of waste management and cheap energy. It is also interesting to note that the CO2 emissions from the burning of bagasse are more than compensated for by the cultivation of sugarcane crops and thus can be considered as zero emissions (Purohit and Michaelowa, 2007). Wong and Sanggari (2014) reported on ethanol production from sugarcane bagasse; the ethanol content in water was estimated using HPLC analysis and was found to be 14.8%.
20.3.5 Kraft Paper Process and Biorefinery Studies have been conducted on using Kraft paper mills in a biorefinery configuration. The wood material was alkali treated and the cellulose-rich stream obtained can be processed into bioethanol, while the lignin stream can be gassified and refined to get dimethyl ether (Fornell et al., 2013). Further, a system of forest biorefinery integrating a Kraft mill to extract
20.4 Advantages and Challenges
387
hemicelluloses using steam explosion and steam treatment techniques has been studied (Sampedro et al., 2014). Black liquor gasification (BLG) is also fast gaining attention. BLG can be processed to recover chemicals used in the pulping process and also for syngas production (Pettersson and Harvey, 2010).
20.4 ADVANTAGES AND CHALLENGES OF USING AGROINDUSTRIAL WASTES AS THE FEEDSTOCK FOR BIOREFINERY 20.4.1 Advantages There are several advantages of utilizing agroindustrial wastes as the feedstock for biorefinery operations, such as easy availability, environmental sustainability, low cost, etc. There are also serious challenges that have to be overcome to make the use of agroindustrial wastes as feedstock for biorefineries viable. A serious impediment faced is the collection, storage, and segregation of agricultural waste. Besides this, certain socioeconomic reasons also have to be taken into account; the risk-adverse nature of stakeholders in the field of agriculture and the attitude of investors and policymakers also have a strong bearing on the utilization of agroindustrial wastes for biorefinery applications. 20.4.1.1 Availability Agricultural waste is an abundant source of raw material and is also renewable. Globally, 140 billion metric tons of biomass (agricultural wastes, manure, forest residues, and municipal wastes) are generated every year from agriculture. When this quantity is converted into energy, it is approximately equivalent to 50 billion tons of oil (UNEP, 2009). Thus the supply side problems faced by many process industries in the realm of raw material procurement can be largely negated. Nevertheless, the seasonal nature of agriculture may pose a challenge to the availability of specific raw materials derived from agroindustrial waste. Biomass liquefaction and further derivation of chemicals would help the industrial community to face this problem (Sampedro et al., 2014). The generalization of the refining process and the types of chemicals derived enable the use of raw materials of any kind in the process, and thus the seasonal availability of specific raw materials will not be an issue in the future. 20.4.1.2 Environmental Sustainability The use of agroindustrial waste promotes environmental sustainability, as the use of waste materials for the production of new products considerably lowers the environmental footprint of the production process. The use of waste materials and green technologies can enable the building of sustainable systems in the long run. Besides offering environmentally sustainable modes for production, the use of agroindustrial feedstock also offers an effective means of waste management. 20.4.1.3 Renewable Nature Agriculture waste is a renewable resource. Unlike crude oil, which is a source for many platform chemicals, agroindustrial wastes are renewable and are constantly regenerated.
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Thus with the increasing demand for specialty chemicals and the threat of peak oil, the utilization of agroindustrial waste in bioprocesses offers a promising alternative to nonrenewable sources of raw material such as crude oil. Biomass could displace fossil fuels and help reduce GHG emissions while closing the carbon cycle loop. As the debate on food versus fuel intensifies, biomass can provide added income to farmers without compromising the production of main food and even nonfood crops (UNEP, 2009). 20.4.1.4 Economic Viability Conventional processes utilize raw materials, which contribute significantly to the overall cost of the finished product. The use of agroindustrial waste as raw materials can significantly reduce the cost of the end product, as the raw material in this case comes with virtually no cost. The use of agroindustrial waste as s feedstock can also add to the income of farmers and can aid in economic development, particularly in the developing countries. Also, the concept of biorefinery can rejuvenate the agricultural economy in developing countries and can act as an additional source of income to distressed farmers. Many developing countries, like India, that suffer from farmer suicides and consequent socioeconomic problems can overcome hurdles by developing the biorefinery sector. This way, economic distress in developing countries can be assuaged. 20.4.1.5 Energy and Economic Security The concept of biorefineries combined with localized production centers can ensure greater economic and energy security. Uncertainties with regard to the supply of energy resources and commodities to consumption centers from far-flung supply locations due to geopolitical uncertainties can be greatly reduced. This scenario assumes a situation wherein a large component of the biorefinery feedstock is in the form of agricultural waste, and biorefineries are developed in consonance with local needs and availabilities of feedstock, a “one size does not fit all” approach.
20.4.2 Challenges 20.4.2.1 Nonuniformity in Agroindustrial Wastes Agroindustrial wastes are a varied set of materials without a uniform composition. Agricultural wastes do not have a standardized means of quality control. The composition of crops can vary from country to country or even from one farm to another. The composition and quality of agroindustrial waste depend upon the nutrition offered to the crop during its lifetime, local climatic conditions, soil, physiology, etc. In the case of waste materials such as bagasse and rice husk/bran, the quality also depends on the industrial process used to process sugarcane and paddy. Thus uniform standards cannot be evolved for agroindustrial wastes to be used as feedstock in biorefineries. 20.4.2.2 Collection, Storage, and Segregation Collection, storage, and segregation of agricultural wastes are required if they are to be used as feedstock in biorefineries. This may entail significant investment in the form of logistics, transportation, storage yards, and labor requirements. For effective utilization the mixture
389
20.5 Agroindustrial Waste Biorefinery: Engineering Breakthroughs
of agricultural wastes has to be segregated based on their lignocellulosic composition. For example, in the case of cotton, waste cotton and cotton stalks have different lignocellulosic composition, whereas cotton contains little or no lignin but cotton stalks are rich in lignin. 20.4.2.3 Social Perspectives Another factor to be considered is the readiness of farmers to invest in collection, storage, and segregation facilities and to try out new modes of waste management apart from existing methods. Whether or not investors are ready to design and operate plants that use new technologies and methods will also play an important role in the future prospects of agroindustrial wastes as biorefinery feedstock. 20.4.2.4 Technology In order to enable agroindustrial waste-based biorefineries in the process industry, new technologies have to be developed, and existing technologies and methods have to be redesigned and reoriented. This will require a large amount of capital investment and research. The challenge is to bring together industry academia and policymakers to develop synergies that will enable technological development to assist in the development of biorefinery processes for the transformation of agroindustrial waste into useful products.
20.5 AGROINDUSTRIAL WASTE BIOREFINERY: ENGINEERING BREAKTHROUGHS Engineering breakthroughs have made the likelihood of the industrial realization of the biorefinery concept possible. Table 20.2 outlines some of the breakthroughs in this field.
20.5.1 Continuous Countercurrent Extruder Reactor PureVision Technology Inc. has developed a continuous countercurrent extruder reactor that can be used to fractionate agricultural waste into its various components such as xylose, TABLE 20.2 Engineering Breakthroughs in the Biorefinery Sector
Organization
Investment (Million Dollars)
Products
Processing Capacity (Million Tons)
Year of Starting
References
M & G Chemicals and Anhui Guozhen Fuyang City, China
325
Cellulosic ethanol and lignin
1
2014
M&G Chemicals (2015)
M & G Chemicals and Novozymes Eastern Province, China
325
Glycols
1
2015
Novozymes (2015)
Iogen Corporation, Canada and Raizen, Brazil
100
Cellulosic ethanol
–
2014
Iogen (2015)
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lignin, and cellulose. The resulting cellulose can then be digested to obtain glucose (PureVision Technology, Inc., 2015). The glucose obtained can then be used to synthesize important industrial chemicals. This breakthrough will enable the simplification of the most complicated steps in the processing of agricultural waste, ie, the separation of various components of biomass, viz. lignin, xylose, and cellulose.
20.5.2 Rapid Integrated Continuous Countercurrent Hydrolysis Rapid Integrated Continuous Countercurrent Hydrolysis is another technology developed by Pure Vision Technology Inc. (2015). This process has been said to be capable of converting raw biomass into a mixed stream of C5 and C6 sugars in the absence of a concentrated acid catalyst or enzymes within 1 h. This technology is said to purge the process of the enzymatic hydrolysis of cellulose.
20.5.3 Microalgae-Based Biorefinery Processes Microalgae could prove to be a promising candidate in the biorefinery process because of its valuable compounds viz. lipids, proteins, and carbohydrates. This process transforms algal biomass into beneficial products such as biofuels. Lee Ju-han, Lee Hyun-wook, and the Korea Institute of Energy Research team led by Yo Yoo-kwan have developed a method for the large-scale production of organic nanoclay– titanium dioxide complexes. Organic nanoclay–titanium complexes are an important constituent in the microalgae biorefinery process (Business Korea, 2015).
20.6 CONCLUSIONS The demand for fuels across the world is ever increasing. This demand can be allayed by using second- and third-generation biofuels. The microalgae biorefinery concept is promising. The advantage of using algal systems over lignocellulosic biomass is coupled with wastewater treatment. Several organizations around the world have taken initiatives to implement the biorefinery process for fuel production. These processes provide us with an opportunity to satisfy the needs of the present generation without having to compromise the future generation, thus paving the way for sustainable development.
References Bentsen, N.S., Felby, C., 2010. Technical potentials of biomass for energy services from current agriculture and forestry in selected countries in Europe, the Americas and Asia. Forest & Landscape Working 54, 31. Business Korea. Green Fuel Breakthrough in Microalgae Bio-refinery Process. http://www.businesskorea.co.kr/ article/3957/green-fuel-breakthrough-microalgae-bio-refinery-process (accessed on 10.03.15.). Chandra, R., Takeuchi, H., Hasegawa, T., 2012. Methane production from lignocellulosic agricultural crop wastes: a review in context to second generation of biofuel production. Renewable and Sustainable Energy Reviews 16 (3), 1462–1476. Clark, J.H., Deswarte, F.E.I., 2008. The Biorefinery Concept – An Integrated Approach. John Wiley & Sons, Ltd, p. 18.
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David, B.L., Kenneth, G.C., Christopher, B.F., 2009. Crop yield gaps: their importance, magnitudes, and causes. Annual Review of Environment and Resources 34, 179–204. Dias, M.O.S., Modesto, M., Ensinas, A.V., Nebra, S.A., Filho, R.M., Rossell, C.E.V., 2011. improving bioethanol production from sugarcane: evaluation of distillation, thermal integration and cogeneration systems. Energy 36 (6), 3691–3703. Fornell, R., Berntsson, T., Åsblad, A., 2013. Techno-economic analysis of a kraft pulp-mill-based biorefinery producing both ethanol and dimethyl ether. Energy 50 (1), 83–92. Gray, K.A., Zhao, L., Emptage, M., 2006. Bioethanol. Current Opinion in Chemical Biology 10 (2), 141–146. IEA (International Energy Agency), 2010. Sustainable Production of Second-Generation Biofuels Potential and Perspectives in Major Economies and Developing Countries. Iogen Corporation. http://www.iogen.ca/cellulosic_ethanol/index.html (accessed on 15.03.15.). Isah, U.,A., Abdulraheem, G., Bala, S., Muhammad, S., Abdullahi, M., 2015. Kinetics, equilibrium and thermodynamics studies of C.I. Reactive blue 19 dye adsorption on coconut shell based activated carbon. International Biodeterioration & Biodegradation 102, 265–273. Khatiwada, D., Seabra, J., Silveira, S., Walter, A., 2012. Power generation from sugarcane biomass – a complementary option to hydroelectricity in Nepal and Brazil. Energy 48 (1), 241–254. Kim, S., Dale, B.E., 2005. Life cycle assessment of various cropping systems utilized for producing biofuels: bioethanol and biodiesel. Biomass and Bioenergy 29 (6), 426–439. Lobell, David B., Cassman, Kenneth G., and Field, Christopher B., 2009. Crop Yield Gaps: Their Importance, Magnitudes, and Causes. NCESR Publications and Research. Paper 3. http://digitalcommons.unl.edu/ncesrpub/3. Menon, V., Rao, M., 2012. Trends in bioconversion of lignocellulose: biofuels, platform chemicals biorefinery concept. Progress in Energy and Combustion Science 38 (4), 522–550. M&G Chemicals. http://www.mg-chemicals.com/en/media/press-releases?news=14 (accessed on 12.03.15.). Novozymes. http://www.novozymes.com/en/investor/news-and-announcements/Pages/Novozymes-and-Mand-G-Chemicals-to-collaborate-on-biomass-based-plastics-in-China.aspx (accessed on 15.03.15.). Octave, S., Thomas, D., 2009. Biorefinery: toward an industrial metabolism. Biochimie 91 (6), 659–664. Pettersson, K., Harvey, S., 2010. CO2 emission balances for different black liquor gasification biorefinery concepts for production of electricity or second-generation liquid biofuels. Energy 35 (2), 1101–1106. Preisig, H.A., Wittgens, B., 2012. Thinking towards synergistic green refineries. Energy Procedia 20, 59–67. PureVision Technology Inc. Biorefinery Breakthrough. http://www.purevisiontechnology.com/Bioenergy_Insight_ December_2011.pdf (accessed on 12.03.15.). Purohit, P., Michaelowa, A., 2007. CDM potential of bagasse cogeneration in India. Energy Policy 35 (10), 4779–4798. Rentizelas, A.A., Tolis, A.J., Ilias, P., 2009. Tatsiopoulos, logistics issues of biomass: the storage problem and the multibiomass supply chain. Renewable and Sustainable Energy Reviews 13 (4), 887–894. Robinson, T., Chandran, B., Nigam, P., 2002. Removal of dyes from an artificial textile dye effluent by two agricultural waste residues, corncob and barley husk. Environment International 28 (1–2), 29–33. Sampedro, R.M., Eugenio, M.E., Moreno, J.A., Revilla, E., Villar, J.C., 2014. Integration of a kraft pulping mill into a forest biorefinery: pre-extraction of hemicellulose by steam explosion versus steam treatment. Bioresource Technology 153, 236–244. United Nations Environmental Programme (UNEP), 2009. Converting Waste Agricultural Biomass Into a Resource Compendium of Technologies. Vadivelan, V., Vasanth Kumar, K., 2005. Equilibrium, kinetics, mechanism, and process design for the sorption of methylene blue onto rice husk. Journal of Colloid and Interface Science 286 (1), 90–100. Wong, Y.C., Sanggari, V., 2014. Bioethanol production from sugarcane bagasse using fermentation process. Oriental Journal of Chemistry 30 (2), 507–513.
20
Platform Chemical Biorefinery and Agroindustrial Waste Management K.P. Gopinath, A.R. Sankaranarayanan, L. Nivedhitha SSN College of Engineering, Chennai, India O U T L I N E 20.1 Introduction
380
20.3.2.4 Consolidated Biomass Processing 386
20.3.3 Adsorbents From Agricultural Waste 386 20.3.4 Bagasse and Sugarcane Cogeneration386 20.3.5 Kraft Paper Process and Biorefinery386
20.2 Agroindustrial Waste Types and Their Global Annual Production 381 20.2.1 Current Scenario of Agroindustrial Waste Production381 20.2.2 Factors Affecting Biomass Yield382
20.4 Advantages and Challenges of Using Agroindustrial Wastes as the Feedstock for Biorefinery 387 20.4.1 Advantages 387
20.3 Present Agroindustrial Waste Management Approaches 383 20.3.1 Current Practices: Traditional Uses383 20.3.2 Bioethanol 384
20.3.2.1 Separate Hydrolysis and Fermentation 385 20.3.2.2 Simultaneous Saccharification and Fermentation385 20.3.2.3 Simultaneous Saccharification and Cofermentation 386
Platform Chemical Biorefinery http://dx.doi.org/10.1016/B978-0-12-802980-0.00020-1
379
20.4.1.1 Availability 387 20.4.1.2 Environmental Sustainability387 20.4.1.3 Renewable Nature 387 20.4.1.4 Economic Viability 388 20.4.1.5 Energy and Economic Security388
20.4.2 Challenges
388
© 2016 Elsevier Inc. All rights reserved.
380
20. PLATFORM CHEMICAL BIOREFINERY AND AGROINDUSTRIAL WASTE MANAGEMENT
20.4.2.1 Nonuniformity in Agroindustrial Wastes388 20.4.2.2 Collection, Storage, and Segregation 388 20.4.2.3 Social Perspectives 389 20.4.2.4 Technology 389
20.5 Agroindustrial Waste Biorefinery: Engineering Breakthroughs 389
20.5.1 Continuous Countercurrent Extruder Reactor 389 20.5.2 Rapid Integrated Continuous Countercurrent Hydrolysis 390 20.5.3 Microalgae-Based Biorefinery Processes390
20.6 Conclusions
390
References390
20.1 INTRODUCTION The concept of biorefinery, analogous to a petrochemical refinery, is fast gaining interest (Preisig et al., 2012). The commercialization of this concept requires in-depth studies and the development of industry standards. The challenges include the high specificity of biochemical reactions and enzymatic reactions, which are the requirements of expensive pretreatment steps involved while using biomass as precursors (Menon and Rao, 2012). Studies have shown that localized systems that take into account local conditions while devising waste management strategies coupled with small-scale bioprocesses have succeeded better than compared to a “one size fits all” approach wherein the policy and management are devised to encompass large geographies and a wide spectrum of industrial paradigms (Clark et al., 2008). The challenge is to develop methodologies to exploit local resources using niche technologies to produce commercially viable products like specialty molecules, materials, and fuels (Octave and Thomas, 2009). Though the challenges discussed above have impeded the development of biorefineries, advances in the field of bioreactor design and cost-effective pretreatment processes accompanied by an increased need for developing environmentally sustainable processes in the chemical industry have the potential to take forward the concept of biorefineries. The utilization of agroindustrial wastes for the production of value-added chemicals has a great potential to revolutionize the chemical industry (Chandra et al., 2012). The production of bioethanol has fast gained traction in many parts of the world (Octave and Thomas, 2009). The next frontier is to develop systems and technologies to extract valuable chemical products from agroindustrial waste materials. The idea of using agroindustrial wastes as feedstocks in biorefinery processes is very interesting from the perspective of environmental sustainability. The conceptualization of biorefineries using agroindustrial wastes is analogous to petroleum refineries that use crude oil as a feedstock. Lignocellulosic biomass is the primary constituent of agroindustrial waste, and it has to be considered as an analogue of crude oil in the realm of biorefinery conceptualizations. This chapter aims to provide an outline on agricultural waste generation across major countries and regions and also in terms of the lignocellulosic composition of different types of agricultural wastes. The latter part of the chapter deals with established practices for managing agricultural waste and
20.2 Agroindustrial Waste Types and Their Global Annual Production
381
advantages of biorefinery processes. A brief commentary on breakthroughs in the field of biorefinery processing has also been included.
20.2 AGROINDUSTRIAL WASTE TYPES AND THEIR GLOBAL ANNUAL PRODUCTION 20.2.1 Current Scenario of Agroindustrial Waste Production The primary source of agroindustrial waste is residue from agricultural crops. The cultivation of wheat, maize, rice, soybean, barley, rapeseed, sugarcane, and sugar beet results in the production of 3.3 Gt of agricultural waste per year. China, the United States, and India account for 60% of the crop residues produced (Bentsen and Felby, 2010). The level of agricultural waste production shows considerable differences over crop species, region of cultivation, and social, technical, and local factors (Lobell et al., 2009). It is observed from Fig. 20.1 that developing countries such as India and China contribute significantly to the production of agricultural waste. This combined with their growing demand for resources can be expected to intensify efforts toward realizing the concept of biorefineries using agroindustrial waste as feedstocks. The abundance and perennial source of agricultural waste has a great potential to revolutionize agriculture and allied industries. The effective utilization of agricultural waste as a feedstock to produce valuable platform chemicals can result in higher value additions to the agriculture and allied industries. Fig. 20.2 illustrates the type of crop that produces more waste, which clearly reveals that maize tops the list with approximately more than 900 million tons of waste generated per year. The United States is the largest producer of maize, followed by Brazil and China. Corncobs and corn leaves are
FIGURE 20.1 Potential of agricultural waste in select countries/regions (Bentsen and Felbyl, 2010).
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FIGURE 20.2 Potential for agricultural waste from a variety of crops.
major residues, which are not valuable agro products. The residues produced by wheat and rice agriculture are also abundant, since these crops are considered to be important feedstocks of most of the population-rich growing countries. Wheat straw, wheat husk, rice straw, and rice husk are important agrowastes produced in huge amounts in China and India, as they are the major producers of wheat and rice in the world. Sugarcane is a major commercial crop grown in many developing countries, with Brazil as its major producer. Other countries like India and China are the next largest producers. Only the sugar juice from sugarcane is considered to be a valuable agro product and the rest of the dry matter (bagasse) is considered to be a residue (Bentsen and Felby, 2010).
20.2.2 Factors Affecting Biomass Yield The biomass yield from agricultural residues is not uniform across various regions of the world and is subject to almost the same conditions that determine harvest yields. The biomass yield depends on a multitude of conditions like crop species, nutrient supply, prevailing local climatic conditions, susceptibility to pests, weed pressure, etc. (David et al., 2009; Lobell et al., 2009). The uptake of water and the ability of the soil to hold moisture and facilitate effective water transport in plants can significantly affect the production of crop residues. Apart from technical factors crop residue yields also have a social dimension. A lack of knowledge and a risk-adverse nature prevents the implementation of various strategies that aim to increase the production of crop residues. Another factor that has to be considered is the collection and storage of agriculture waste. Currently, a vast majority of agriculture waste is not collected and stored (IEA, 2010). The logistics related to agricultural biomass collection and storage are complicated by the seasonal nature of agriculture and various streams of agricultural waste (Rentizelas et al., 2009).
20.3 Present Agroindustrial Waste Management Approaches
383
FIGURE 20.3 Potential for agricultural waste in terms of cellulose, hemicelluloses, and lignin in select countries/ regions (Menon and Rao, 2012).
The availability of agricultural waste can be interpreted in terms of the potential for the production of lignocellulosic materials in the form of cellulose, hemicellulose, and lignin. The interpretation of agricultural waste data in terms of composition of lignocellulosic material, viz., lignin, cellulose, and hemicelluloses, would be of greater value, as they provide an accurate picture of the useful feedstocks available for biorefinery processes. Fig. 20.3 shows the potential of lignocellulosic materials for select countries and regions. It can be observed that the largest component of agricultural waste is cellulose, followed by hemicellulose and lignin. To increase the quantity and quality of retrievable biomass from agricultural waste it is necessary to provide conducive conditions and nutrient supply to the crops. There is also a need to sensitize stakeholders in agriculture to devote resources and time for the collection, segregation, and storage of agricultural residues (Bentsen and Felby, 2010). The lignocellulosic composition varies greatly across crop varieties (Table 20.1); whereas rice husks and sorghum contain up to 20–21% lignin, cotton wastes do not contain lignin at all. It would thus be beneficial to thoroughly understand the lignocellulosic composition of different types of agricultural residues to enable their effective utilization as biorefinery feedstock.
20.3 PRESENT AGROINDUSTRIAL WASTE MANAGEMENT APPROACHES 20.3.1 Current Practices: Traditional Uses A large component of agricultural waste goes unutilized and is left on the field. According to previous studies, an optimistic figure for the collection and use of agricultural waste is only about 25%; in countries such as India and South Africa the figure is as low as 10% (Menon
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TABLE 20.1 Average Composition of Agricultural Wastes (Menon and Rao, 2012; Bentsen and Felbyl, 2010) Lignocellulosic Composition (% dry wt) Agrowaste
Cellulose
Hemicellulose
Lignin
Barley hull
34
36
19
Barley straw
40
28
8
Corncob
39
40
10
Corn stover
37
22
15
Cotton
90
10
0
Cotton stalk
31
11
30
Coffee pulp
35
45
17
Rice straw
32
24
18
Rice husk
32
20
17
Wheat straw
37
26
16
Wheat bran
12
37
10
Sugarcane bagasse
35
30
20
Jute fibers
49
20
24
Winter rye
30
24
16
Oilseed rape
27
21
14
Oat straw
33
23
13
Nutshells
28
25
35
Sorghum straw
32
27
18
and Rao, 2012). Traditional agricultural waste management practices include provisions for animal fodder, manure, and direct combustion. Current practices for the management of agricultural wastes are largely geared toward the production of bioethanol, cogeneration, biofuels, and adsorbents (Isah et al., 2015; Kim and Dale, 2005). Fig. 20.4 shows the trends in traditional and modern uses of various agroindustrial wastes. Based on the modern use of all type of wastes, bioethanol production is suggested. Though the conversion of cellulosic biomass into fermentable sugars is a tedious process, various novel techniques have been suggested by many researchers. These techniques enable the conversion to be easier and economical, so that it can be commercially viable.
20.3.2 Bioethanol The general methodology for producing bioethanol is to pretreat biomass in the form of agricultural residue and subject it to a variety of processes such as separate hydrolysis and
20.3 Present Agroindustrial Waste Management Approaches
385
FIGURE 20.4 Traditional and modern uses of agroindustrial wastes (Isah et al., 2015).
fermentation, simultaneous saccharification and cofermentation, simultaneous saccharification and fermentation (SSF), and consolidated biomass processing (Dias et al., 2011; Gray et al., 2006). This is then followed by fermentation using yeast such as Saccharomyces, Kluveryomeces, Debaryomeces, Pichia, and Zymomonas (Menon and Rao, 2012). 20.3.2.1 Separate Hydrolysis and Fermentation This is a two-step process in which the hydrolysis of the pretreated biomass is followed by the fermentation process, both taking place separately. The hydrolysis process uses acid or an enzymatic treatment, which converts the cellulose and hemicellulose to fermentable sugars. In the fermentation stage, the sugars are transformed to yield ethanol by the action of microorganisms. 20.3.2.2 Simultaneous Saccharification and Fermentation This is a one-step process in which the biomass is converted into alcohols. As the cellulosic biomass breaks down into fermentable sugars by the action of enzymes, the microbes present ferment the sugars to yield ethanol. This process has the advantage of lowering the cost of biomass processing and improving the fermentation process. However, it has a disadvantage
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of maintaining the temperature so as not to hinder the activity of the enzyme as well as the growth of the microbes. 20.3.2.3 Simultaneous Saccharification and Cofermentation In this process, the pretreated biomass is neutralized and is exposed directly to the enzymes and genetically modified microorganisms that could hydrolyze the biomass and also ferment sugars, respectively. Compared to the SSF process this has the advantage of having better yields and short processing times. However, this process has limitations in terms of the higher costs incurred by genetically engineering the microbes. 20.3.2.4 Consolidated Biomass Processing This process has the benefits of housing the production of enzymes, hydrolysis, and the fermentation of hexose and pentose sugars in a single reactor in the presence of a microbial consortium. This process is quite interesting, as it employs a single microbial consortium for both the hydrolysis and fermentation processes, thereby gaining the advantage of lowering the production costs of ethanol.
20.3.3 Adsorbents From Agricultural Waste Agricultural wastes such as coconut shells, barley husk, rice husk, etc. have been used as adsorbent materials for treating pollutants such as synthetic dyes, organic chemicals, and heavy metals (Isah et al., 2015; Robinson et al., 2002; Vadivelan and Vasanth Kumar, 2005). The agricultural waste materials used for the adsorption processes require various levels of pretreatment and follow a wide variety of action mechanisms. One of the most important adsorbents produced from agricultural wastes is activated carbon.
20.3.4 Bagasse and Sugarcane Cogeneration Sugarcane cogeneration plants utilize waste bagasse for heat requirements and the production of electricity. The electricity thus generated can be used as a captive source of energy for powering operations in sugar mills, or it can be sold commercially to external users (Khatiwada et al., 2012). The bagasse produced from refining cane sugar is also used to make paper, particle boards, and bioethanol. This has achieved the twin benefits of waste management and cheap energy. It is also interesting to note that the CO2 emissions from the burning of bagasse are more than compensated for by the cultivation of sugarcane crops and thus can be considered as zero emissions (Purohit and Michaelowa, 2007). Wong and Sanggari (2014) reported on ethanol production from sugarcane bagasse; the ethanol content in water was estimated using HPLC analysis and was found to be 14.8%.
20.3.5 Kraft Paper Process and Biorefinery Studies have been conducted on using Kraft paper mills in a biorefinery configuration. The wood material was alkali treated and the cellulose-rich stream obtained can be processed into bioethanol, while the lignin stream can be gassified and refined to get dimethyl ether (Fornell et al., 2013). Further, a system of forest biorefinery integrating a Kraft mill to extract
20.4 Advantages and Challenges
387
hemicelluloses using steam explosion and steam treatment techniques has been studied (Sampedro et al., 2014). Black liquor gasification (BLG) is also fast gaining attention. BLG can be processed to recover chemicals used in the pulping process and also for syngas production (Pettersson and Harvey, 2010).
20.4 ADVANTAGES AND CHALLENGES OF USING AGROINDUSTRIAL WASTES AS THE FEEDSTOCK FOR BIOREFINERY 20.4.1 Advantages There are several advantages of utilizing agroindustrial wastes as the feedstock for biorefinery operations, such as easy availability, environmental sustainability, low cost, etc. There are also serious challenges that have to be overcome to make the use of agroindustrial wastes as feedstock for biorefineries viable. A serious impediment faced is the collection, storage, and segregation of agricultural waste. Besides this, certain socioeconomic reasons also have to be taken into account; the risk-adverse nature of stakeholders in the field of agriculture and the attitude of investors and policymakers also have a strong bearing on the utilization of agroindustrial wastes for biorefinery applications. 20.4.1.1 Availability Agricultural waste is an abundant source of raw material and is also renewable. Globally, 140 billion metric tons of biomass (agricultural wastes, manure, forest residues, and municipal wastes) are generated every year from agriculture. When this quantity is converted into energy, it is approximately equivalent to 50 billion tons of oil (UNEP, 2009). Thus the supply side problems faced by many process industries in the realm of raw material procurement can be largely negated. Nevertheless, the seasonal nature of agriculture may pose a challenge to the availability of specific raw materials derived from agroindustrial waste. Biomass liquefaction and further derivation of chemicals would help the industrial community to face this problem (Sampedro et al., 2014). The generalization of the refining process and the types of chemicals derived enable the use of raw materials of any kind in the process, and thus the seasonal availability of specific raw materials will not be an issue in the future. 20.4.1.2 Environmental Sustainability The use of agroindustrial waste promotes environmental sustainability, as the use of waste materials for the production of new products considerably lowers the environmental footprint of the production process. The use of waste materials and green technologies can enable the building of sustainable systems in the long run. Besides offering environmentally sustainable modes for production, the use of agroindustrial feedstock also offers an effective means of waste management. 20.4.1.3 Renewable Nature Agriculture waste is a renewable resource. Unlike crude oil, which is a source for many platform chemicals, agroindustrial wastes are renewable and are constantly regenerated.
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20. PLATFORM CHEMICAL BIOREFINERY AND AGROINDUSTRIAL WASTE MANAGEMENT
Thus with the increasing demand for specialty chemicals and the threat of peak oil, the utilization of agroindustrial waste in bioprocesses offers a promising alternative to nonrenewable sources of raw material such as crude oil. Biomass could displace fossil fuels and help reduce GHG emissions while closing the carbon cycle loop. As the debate on food versus fuel intensifies, biomass can provide added income to farmers without compromising the production of main food and even nonfood crops (UNEP, 2009). 20.4.1.4 Economic Viability Conventional processes utilize raw materials, which contribute significantly to the overall cost of the finished product. The use of agroindustrial waste as raw materials can significantly reduce the cost of the end product, as the raw material in this case comes with virtually no cost. The use of agroindustrial waste as s feedstock can also add to the income of farmers and can aid in economic development, particularly in the developing countries. Also, the concept of biorefinery can rejuvenate the agricultural economy in developing countries and can act as an additional source of income to distressed farmers. Many developing countries, like India, that suffer from farmer suicides and consequent socioeconomic problems can overcome hurdles by developing the biorefinery sector. This way, economic distress in developing countries can be assuaged. 20.4.1.5 Energy and Economic Security The concept of biorefineries combined with localized production centers can ensure greater economic and energy security. Uncertainties with regard to the supply of energy resources and commodities to consumption centers from far-flung supply locations due to geopolitical uncertainties can be greatly reduced. This scenario assumes a situation wherein a large component of the biorefinery feedstock is in the form of agricultural waste, and biorefineries are developed in consonance with local needs and availabilities of feedstock, a “one size does not fit all” approach.
20.4.2 Challenges 20.4.2.1 Nonuniformity in Agroindustrial Wastes Agroindustrial wastes are a varied set of materials without a uniform composition. Agricultural wastes do not have a standardized means of quality control. The composition of crops can vary from country to country or even from one farm to another. The composition and quality of agroindustrial waste depend upon the nutrition offered to the crop during its lifetime, local climatic conditions, soil, physiology, etc. In the case of waste materials such as bagasse and rice husk/bran, the quality also depends on the industrial process used to process sugarcane and paddy. Thus uniform standards cannot be evolved for agroindustrial wastes to be used as feedstock in biorefineries. 20.4.2.2 Collection, Storage, and Segregation Collection, storage, and segregation of agricultural wastes are required if they are to be used as feedstock in biorefineries. This may entail significant investment in the form of logistics, transportation, storage yards, and labor requirements. For effective utilization the mixture
389
20.5 Agroindustrial Waste Biorefinery: Engineering Breakthroughs
of agricultural wastes has to be segregated based on their lignocellulosic composition. For example, in the case of cotton, waste cotton and cotton stalks have different lignocellulosic composition, whereas cotton contains little or no lignin but cotton stalks are rich in lignin. 20.4.2.3 Social Perspectives Another factor to be considered is the readiness of farmers to invest in collection, storage, and segregation facilities and to try out new modes of waste management apart from existing methods. Whether or not investors are ready to design and operate plants that use new technologies and methods will also play an important role in the future prospects of agroindustrial wastes as biorefinery feedstock. 20.4.2.4 Technology In order to enable agroindustrial waste-based biorefineries in the process industry, new technologies have to be developed, and existing technologies and methods have to be redesigned and reoriented. This will require a large amount of capital investment and research. The challenge is to bring together industry academia and policymakers to develop synergies that will enable technological development to assist in the development of biorefinery processes for the transformation of agroindustrial waste into useful products.
20.5 AGROINDUSTRIAL WASTE BIOREFINERY: ENGINEERING BREAKTHROUGHS Engineering breakthroughs have made the likelihood of the industrial realization of the biorefinery concept possible. Table 20.2 outlines some of the breakthroughs in this field.
20.5.1 Continuous Countercurrent Extruder Reactor PureVision Technology Inc. has developed a continuous countercurrent extruder reactor that can be used to fractionate agricultural waste into its various components such as xylose, TABLE 20.2 Engineering Breakthroughs in the Biorefinery Sector
Organization
Investment (Million Dollars)
Products
Processing Capacity (Million Tons)
Year of Starting
References
M & G Chemicals and Anhui Guozhen Fuyang City, China
325
Cellulosic ethanol and lignin
1
2014
M&G Chemicals (2015)
M & G Chemicals and Novozymes Eastern Province, China
325
Glycols
1
2015
Novozymes (2015)
Iogen Corporation, Canada and Raizen, Brazil
100
Cellulosic ethanol
–
2014
Iogen (2015)
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20. PLATFORM CHEMICAL BIOREFINERY AND AGROINDUSTRIAL WASTE MANAGEMENT
lignin, and cellulose. The resulting cellulose can then be digested to obtain glucose (PureVision Technology, Inc., 2015). The glucose obtained can then be used to synthesize important industrial chemicals. This breakthrough will enable the simplification of the most complicated steps in the processing of agricultural waste, ie, the separation of various components of biomass, viz. lignin, xylose, and cellulose.
20.5.2 Rapid Integrated Continuous Countercurrent Hydrolysis Rapid Integrated Continuous Countercurrent Hydrolysis is another technology developed by Pure Vision Technology Inc. (2015). This process has been said to be capable of converting raw biomass into a mixed stream of C5 and C6 sugars in the absence of a concentrated acid catalyst or enzymes within 1 h. This technology is said to purge the process of the enzymatic hydrolysis of cellulose.
20.5.3 Microalgae-Based Biorefinery Processes Microalgae could prove to be a promising candidate in the biorefinery process because of its valuable compounds viz. lipids, proteins, and carbohydrates. This process transforms algal biomass into beneficial products such as biofuels. Lee Ju-han, Lee Hyun-wook, and the Korea Institute of Energy Research team led by Yo Yoo-kwan have developed a method for the large-scale production of organic nanoclay– titanium dioxide complexes. Organic nanoclay–titanium complexes are an important constituent in the microalgae biorefinery process (Business Korea, 2015).
20.6 CONCLUSIONS The demand for fuels across the world is ever increasing. This demand can be allayed by using second- and third-generation biofuels. The microalgae biorefinery concept is promising. The advantage of using algal systems over lignocellulosic biomass is coupled with wastewater treatment. Several organizations around the world have taken initiatives to implement the biorefinery process for fuel production. These processes provide us with an opportunity to satisfy the needs of the present generation without having to compromise the future generation, thus paving the way for sustainable development.
References Bentsen, N.S., Felby, C., 2010. Technical potentials of biomass for energy services from current agriculture and forestry in selected countries in Europe, the Americas and Asia. Forest & Landscape Working 54, 31. Business Korea. Green Fuel Breakthrough in Microalgae Bio-refinery Process. http://www.businesskorea.co.kr/ article/3957/green-fuel-breakthrough-microalgae-bio-refinery-process (accessed on 10.03.15.). Chandra, R., Takeuchi, H., Hasegawa, T., 2012. Methane production from lignocellulosic agricultural crop wastes: a review in context to second generation of biofuel production. Renewable and Sustainable Energy Reviews 16 (3), 1462–1476. Clark, J.H., Deswarte, F.E.I., 2008. The Biorefinery Concept – An Integrated Approach. John Wiley & Sons, Ltd, p. 18.
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