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Bioethanol Production From Jatropha Curcas Seed Cake

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In these recent years, a rapid depletion of fossil fuels has becoming a major issue in world as a demand towards fuel consumption per number of population is explodes either in air, land or water transportation sector and it is responsible for 60% of total world oil consumption. This situation has led to an unstable world oil price and depleting of crude oil reserves, and a major concern now is about the environmental effects mainly on global warming that become worst because of the highly consumption of fossil fuels as the sources of energy. The transportation sector accounts for more than 70% of global carbon monoxide (CO) and 19% of global carbon dioxide (CO2) emissions (Balat, 2011) and according to World Energy Council petroleum, natural gas and coal (non-renewable energy sources), which are the good source of energy, collectively contribute nearly 82% of global energy needs and one fifth of the CO2 emission is due to 60% of petroleum based fuels (Shaheen et al., 2013). Moreover, based on the statistic from United Nation Environment Programme (UNEP) in a report of UNEP Yearbook 2014 emerging issue update on Air Pollution: Worlds’ Worst Environmental Health Risk stated that over 3.5 million people die each year from air pollution and according to World Health Organization (WHO), outdoor air pollution caused 3.7 million premature deaths in 2012 and indoor air pollution is responsible for about 4.3 million premature deaths every year.

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Owing to this impending crisis, the attention towards biofuel or known as biomass-based fuels and methods to treat wastes into fuel as an alternative to replace and reduce our reliance on fossil fuel as energy sources has been increasing tremendously within governments and private sectors due to various benefits such as the potential of biofuel to reduce the emission of greenhouse gases (GHG), innovative potential to create a cost competitive and its practicality.

Biomass based-fuels offer many other advantages over petroleum based-fuels: (1) biofuels are easily available from common biomass sources, (2) they are representing a CO2 cycle in combustion, (3) biofuels have a considerable environmentally friendly potential and (4) they are biodegradable and contribute to sustainability (Balat, 2011). Biofuels includes solid, liquid and gas and the major biofuel encompass bio-ethanol, biodiesel, biogas, bio-methanol, bio-syngas (CO + H2), bio-oil, bio-char, bio-hydrogen, Fischer – Tropsch liquids petroleum, and vegetable oil (Gupta and Verma, 2014).

Bioethanol has been receiving widespread interest at the international, national and regional levels. The global market for bioethanol has entered a phase of rapid, transitional growth (Sarkar et al., 2012). Moreover, the world bioethanol production has grown from 66.77 billion liters in 2008 to 88.69 billion liters in 2013 and is expected to reach 90.38 billion in 2014 (Baker, 2014). Ethanol is produced from different constituents of the raw materials (Blazek and Gilbert, 2011). The feedstock can be conveniently classified into three categories: (i) sucrose-based (e.g. sugar cane, sugar beet, sweet sorghum and fruits), (ii) starch-based (e.g. corn (maize) grain, milo, wheat, rice, potatoes, cassava, sweet potatoes and barley), and (iii) lignocellulosic biomass (e.g. wood, straw and grasses) (Pejin et al., 2012).

Biomass like cellulosic agricultural waste is the most abundant biomass on the earth and ethanol can be produced from lignocellulosic materials such as agricultural residues, wood, paper and yard waste in municipal solid waste, and dedicated energy crops, which constitute the most abundant renewable organic component in biosphere. Using biomass like cellulosic agricultural waste is the potential promising natural renewable, inexpensive, cost effective and sustainable sources used for considerable and commercial production of bio-energy as bioethanol (Gupta and Verma, 2014).

Since Asian countries like Malaysia are not self sufficient in edible oil production and in order to avoid a crisis among food and biofuel, non-edible seed oils like Jatropha curcas has attracted extensive attraction due to its several unique characteristics (Liang et al., 2010) such as high oil content (43-61% in the seed kernel) and endurance to grow in wasteland and marginal land even polluted soils without using arable land (Zhang et al., 2013). The Jatropha oil has the potential to be an excellent biodiesel feedstock and the seed cakes from biodiesel production are valuable as a source for bioethanol production since the seed cakes encompasses fiber (14%) and carbohydrates (50%) or lignin (19%) or carbohydrates (27%) (Liang et al., 2010).

Considering the average amount of oil extracted from Jatropha curcas seeds is 30 % by weight, each ton of oil extracted generates about 2.3 tons of seed cake (dos Santos et al., 2014). Regarded as a crop to complement the production of biodiesel, the use of Jatropha curcas will produce thousands of tons of seed cake. In this scenario, a major challenge is to decrease the value of these residues, making the biodiesel industry more consistent and competitive. One possible strategy is to leverage the significant percentage of carbohydrates present in this residual biomass, 30 to 38 % (dos Santos et al., 2014), for the production of bioethanol through hydrolytic and fermentative processes, as has been suggested for other residues from the biodiesel industry (Macedo et al., 2011).

The conversion of bioethanol from Jatropha curcas seed cake usually includes three basic steps which are pretreatment, hydrolysis and fermentation. Pre-treatment is the initial steps in lignocellulosic fermentation and it is the most important step for separation of free cellulose from the residue (Gupta and Verma, 2014). For Jatropha curcas seed cake used in this study, since the sample is the waste from biodiesel production, the pretreatment is believed has been done in one of the method to produce biodiesel which is ultrasonic-assisted reactive reaction. The next process is hydrolysis. The most commonly applied method can be classified into two groups: chemical hydrolysis and also enzymatic hydrolysis (Balat, 2010). Hydrolysis method is responsible to convert carbohydrate polymer mainly cellulose, into simple sugar before fermentation (Balat, 2010).

Since this study will be focusing on enzymatic hydrolysis, the process will be conducted with the help of cellulose enzyme from efficient microbes that have ability to secrete cellulose enzyme (Gupta and Verma, 2014) which is Trichoderma reesei. After enzymatic hydrolysis of cellulose by adding numerous cellulolytic microorganisms and their mutual enzymatic activity, it releases a surplus amount of glucose (Gupta and Verma, 2015). Hence, to stop the formation and accumulation of glucose, fermentative microorganisms such as Saccharomyces cerevisae, Escherichia coli, Zyomonas mobilis and Pichia stipitis can be added to produce ethanol from glucose (Gupta and Verma, 2015). Along the hydrolysis and fermentation process, the crystallinity of cellulose and degradation products from lignin and hemicellulose might be one of the inhibitory factors that affect the process efficiency. The application of additives, such as polymers and non-ionic surfactant is an efficient way to reduce the non-productive adsorption of enzymes onto lignin during the hydrolysis of biomass. The discovered principle has explained that the additives could prevent unspecific binding of exposed lignin onto cellulose, thereby producing better adsorption and recycle of enzymes and also higher hydrolysis yields [19, 20]. Park et al. examined the effect of several surfactants on enzymatic hydrolysis of newspaper, and found Tweens to be among the best performers, with two time’s higher conversion at 80 h than that without surfactant.

In spite of all the advantages of utilizing jatropha curcas as a potential feedstock for biofuel production, there are some problem arises when jatropha biodiesel still cannot compete with fossil fuels on domestic market presently and as to become a viable biofuel in those markets, its value chains need to be more profitable and this may be achieved by finding higher-value uses for by-products (especially seedcake) (van Eijick et al., 2014). Besides that, as Jatropha curcas is one of the lignocellulosic biomass, it has a rigid structures of a carbohydrate polymer matrix (mainly cellulose and hemicelluloses) that are cross linked and strongly bounded to lignin (Toquero and Bolado, 2014). This structural complexity is defined as biomass recalcitrance, and will severely restrict enzymatic and microbial accessibility (Pu et al., 2013). Efficient pretreatments are thus required to overcome this problem and disrupt the heterogenous matrix, increase the surface area and also unlock the carbohydrates from their lignin association, thereby enhancing enzymatic digestibility (Toquero and Bolado, 2014).

Even the pretreatment is an essential step to ensure the efficiency of the whole bioethanol production, the cost is the most expensive and substantial research and development at identifying lower cost alternatives is needed in order to reduce the whole cost production (Karimi et al., 2014). As this study is taking Jatropha curcas seed cake after ultrasonic assisted reactive biodiesel extraction, we believed that delignification process occurred during the ultrasonication extraction process hence showing that further pretreatment is unnecessary for bioethanol conversion process. Thus by using the seed cake as a feedstock, it has the ability to cut almost half of the total cost of conventional bioethanol production process. High enzyme cost is also one of the obstacle in producing bioethanol (Lee et al., 2011) hence it is essential to use enzyme that can degrade different cellulases and hemicellulases, thermo-tolerence and is well adapted to fermenter cultivations (Kahar, 2013) such as Trichoderma reesei.

The aim of this study is to determine the potential of Jatropha curcas seed cake after biodiesel extraction to be utilized as a bioethanol product through separate hydrolysis and fermentation method with the help of cellulase enzyme (Trichoderma reesei) and fermentive microorganism (Saccharomyces cerevisiae). This study is also aiming to generate criteria needed in both hydrolysis and fermentation process by using Response Surface Methodological (RSM) model in order to achieve the optimum conditions for enhancing bioethanol production from Jatropha curcas seed cake. Lastly, this study will be demonstrating a Continuous Stirred Tank Reactor (CSTR) for bioethanol production system considering optimum result obtained from RSM model.

Considering the aim and problems stated, hence this study will be carried out to achieve the following outlined objectives:

  1. To determine the potential of Jatropha curcas seed cake as a lignocellulosic feedstock for bioethanol production.
  2. To study the bioethanol production from Jatropha curcas seed cake via Simultaneous Saccharification and Fermentation (SSF) by Saccharomyces cerevisiae, Candida glabrata and Escherichia coli.
  3. To investigate the effect of surfactant (Tween 20) in increasing hydrolysis rate and ethanol production of Jatropha seed cake’s fermentation.
  4. To prove lignin concentration effect in glucose consumption rate and ethanol production by Saccharomyces cerevisiae, Candida glabrata and Escherichia coli.

This study will be focusing on bioconversion of lignocellulosic materials which is Jatropha curcas seed cake that being produced as a waste from biodiesel production. The fresh stalk of Jatropha curcas sample is supplied by BIONAS Company in Sarawak. For the pre-treatment process, as the sample is already being treated in biodiesel production by ultrasonication method, this study is determining and comparing the amount of lignocellulosic composition: lignin, cellulose and hemicelluloses between seed cake and the fresh Jatropha curcas seed stalk by using Van Soest Fiber Analysis method in order to ensure the availability of lignocellulosic compound (mainly cellulose) in the seed cake to be utilized in the next bioconversion process.

In hydrolysis method to produce glucose, this study will be focusing on enzymatic hydrolysis by using an enzyme from efficient microbe which is cellulose from Trichoderma reesei (Sigma Aldrich) to produce cellulase enzyme. High liquid performance chromatography (HPLC) will be used in order to determine the amount of glucose production in hydrolysis method. In fermentation process to produce ethanol from glucose, this study will be focusing on microorganisms that have ability to convert hexose and pentose sugars into ethanol, which are yeast Saccharomyces cerevisiae and bacteria Escherichia coli. As the biomass still contains a significant amount of lignin, addition of surfactant is considered as one of the best possibility to enhance the enzymatic reaction and increase the overall ethanol production.

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