SciELO - Scientific Electronic Library Online

 
vol.52 issue7Sucrosesucrose and citric acid in preservative solutions with nano silver particles in the vase life of rosaPhenology of ‘Méndez’ avocado in southern Jalisco, México author indexsubject indexsearch form
Home Pagealphabetic serial listing  

Services on Demand

Journal

Article

Indicators

Related links

  • Have no similar articlesSimilars in SciELO

Share


Agrociencia

On-line version ISSN 2521-9766Print version ISSN 1405-3195

Agrociencia vol.52 n.7 México Oct./Nov. 2018

 

Food Science

Four generations of raw materials used for ethanol production: challenges and opportunities

L. Alexis Alonso-Gómez1 

L. Arturo Bello-Pérez1  * 

1 Instituto Politécnico Nacional- CEPROBI, Carretera Yautepec-Jojutla Km 6, Calle Ceprobi 8, Colonia San Isidro, 62731 Yautepec, Morelos, México. labellop@ipn.mx


Abstract

The problem of depletion of fossil fuel reserves and the generation of pollutants from their combustion has sparked a search for alternative fuels such as ethanol. In several countries, ethanol produced from sugarcane and maize is mixed with gasoline and used as fuel for transport vehicles. This has decreased generation of pollutants and dependence on international oil prices, especially in countries that do not produce oil. To produce ethanol, low-cost raw material, such as lignocellulosic residues, agricultural crops with a high starch content, algae and others have been tested. In this essay, we analyze four generations of raw material for ethanol production. We mention current research interest in transformation processes and alternatives to improve production processes to yield ethanol fuel at a lower cost.

Key words: ethanol; starch; fuel; energy

Resumen

El problema de disminución de las reservas de combustibles fósiles y la generación de contaminantes debido a su combustión, han provocado la búsqueda de combustibles alternativos como el etanol. En varios países se usa el etanol producido desde caña de azúcar y maíz, mezclado con la gasolina, como combustible para los vehículos de transporte. Esto ha disminuido la generación de contaminantes y la dependencia de los precios internacionales del petróleo, sobre todo en países que no lo producen. Para producir etanol se buscan materias primas de bajo costo como los residuos lignocelulósicos, cultivos agrícolas con alto contenido de almidón, algas y otras fuentes. En este ensayo se hace un análisis de las cuatro generaciones de materias primas para producir etanol, se mencionan los intereses actuales de investigación en los procesos de transformación, así como las alternativas para mejorar procesos de producción, con la finalidad de tener etanol carburante a menor costo.

Palabras clave: etanol; almidón; combustible; energía

Introduction

The world faces the fact that population increases vertiginously and industrialization, as well as consumption of unrenewable resources such as oil and its derivatives, grows in the same measure. To make economic growth independent of the use of fossil fuels and environmental pollution from combustion, interest has increased in using renewable resources to obtain energy, known as alternative energy sources (Plaza Castillo et al., 2015). A renewable resource is biomass generated by photosynthetic organisms (autotrophs) that store energy in the form of sugars, which can be transformed into ethanol for use as biofuel through the process of fermentation. To reduce the competition for crop land that may exist between renewable resources and food production, non-conventional (low-cost) byproducts and raw material not used for human food or animal feed with a high content of fermentable starch or sugars are sought (Hernández-Uribe et al., 2014; Hoyos-Leyva et al., 2017).

On a commercial scale, Brazil and the US have successfully and massively implemented ethanol as an alternative fuel and have shown that it can be competitive with gasoline in terms of price and energy (Chandel et al., 2014). In the US 96 % of the gasoline market is E10 (10 % v/v ethanol with 90 % V/V gasoline) and ethanol produced from corn starch comprises nearly three fourths of the biofuel produced in the country. Its disadvantage is that it comes from a raw material used for food (Schwab et al., 2016). For Flex Fuel Vehicles (FFV), there is an E85 mixture that contains 51 to 85 % ethanol, depending on the season and the geographic location. As of March 2016, there were 310l service stations that sold E85, and 16.8 x106 FFV registered throughout the USA (US Department of Energy, 2016). Brazil obtains most of its ethanol from sugarcane, and in 2014 there were 448 functional first generation (1G) ethanol production units. In Brazil, 80 % of the light vehicles are FFV and the production of ethanol in 2014 satisfied all the E25 mixture (25 % ethanol v/v with 75 % gasoline v/v), thus reducing import of 550 x106 barrels of oil (ANP, 2014).

Regional policies and international treaties aimed to mitigate climate change reflect the effort of governments to promote ethanol production and use. As a result, production of this biofuel increased due partly to its positive energy balance and its neutrality in terms of generating CO2, proven advantages of first-generation technologies. Between 2007 and 2010, ethanol production almost doubled (Table 1). Since the 1970s, Brazil has been the leader with sugarcane, but was surpassed by the US where maize is processed by dry milling as well as other cereals such as sorghum in a lower proportion (Linton et al., 2011).

Table 1 Annual production of bioethanol be country or region (m3 x 106). 

País 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016
EUA 24.7 35.2 41.4 50.3 52.7 50.3 50.3 54.1 56.0 59.6
Brasil 18.9 24.5 24.9 26.2 21.1 21.1 23.7 23.4 26.8 28.2
Europa 2.1 2.7 3.9 4.5 4.4 4.4 5.2 5.5 5.2 5.3
China 1.8 1.9 2.0 2.0 2.1 2.1 2.6 2.4 3.1 3.2
Canadá 0.8 0.8 1.1 1.3 1.7 1.7 1.9 1.9 1.6 1.7
Resto del mundo 1.2 1.5 3.5 3.7 2.6 2.8 2.7 5.6 4.3 5.0
MUNDO 49.6 66.7 76.8 88.2 84.8 82.5 86.6 93.0 97.0 103.1

Adapted from: U.S. Energy Information Administration (2017).

In 2012, average world production of fuel ethanol was 232,000 m3 d-1, of which 138,408 m3 d-1 (59.5 %) was produced in the USA and 63,374 m3 d-1 (27.4 %) in Brazil (ANP, 2014). Production of ethanol in the USA in 2013 was 134,588 m3 d-1, 145,818 m3 d-1 in 2014 and 151,649 m3d-1in 2015. In 2015, US ethanol consumption was 143,780 m3 d-1, and for 2016 and 2017 a consumption of 156,240 m3 d-1 was predicted; this amount is estimated assuming a mixture of 10.0 % during those years (U.S. Energy Information Administration, 2016b), based on the trend reported by Petroleum Supply Monthly that the mixture of ethanol increased 9.8 % in 2013 to 9.9 % in 2015 (U.S. Energy Information Administration, 2016a).

Another reason for using ethanol as a fuel for cars mixed with gasolines it that this mixture does not need addition of Methyl Tertbutyl Ether (MTBE) whose function is to act as an oxygenator (Solomon et al., 2007). MTBE is associated with health problems; combustion of gasoline with MTBE causes irritation to eyes and damage to the respiratory tract. This has led to the study of ethanol production in the different stages of its production, which includes different raw material and microorganisms. Of 9659 documents found in Scopus from 2007 to 2017 with the key words ethanol and biomass, 1063, 1071, 970, 979 and 1014 correspond to 2013, 2014, 2015, 2016 and 2017, respectively. Moreover, the US, China, Brazil and India are the countries that have published the most, with 2737, 1236, 791, 605 documents, respectively, in this period. Nearly 740 results on patents contain the words ethanol, anhydrous, biomass and fermentation from 2010 to 2017.

The raw material used for fuel ethanol can vary depending on the plant structure and the way it stores energy. Sugarcane stems store it in the form of sucrose, and for this use in 2013 almost 8.6 million ha were cultivated in Brazil with an average yield of 70 t ha-1 and an annual total of 596 million t of sugarcane for ethanol production (Alves et al., 2018). Maize grains store energy in the form of starch; in 2017 fuel ethanol from maize used in the US was 57 billion L year-1 (Liu et al. 2017). Crop residues, such as wheat straw or maize stover store energy in the form of complex carbohydrates such as cellulose and hemicellulose. Thus, the characteristics of the raw materials determine the pretreatments and treatments necessary to obtained fermentable sugars, which are converted to ethanol by microorganisms.

Most of the documents reviewed report studies and advances in ethanol yield from lignocellulosic raw material (2nd generation, 2G), or with organisms that rapidly produce biomass (3rd generation, 3G), or with genetically modified microorganisms (4th generation, 4G). There is uncertainty on the likelihood that the processes used to produce 2G, 3G and 4G biofuels meet expected yields. To date, there are technical and economic barriers that have not been overcome, especially for 2G and later biofuels since they will be competitive with fossil fuels when they can be produced on a large scale and when costs per unit of energy are lower. According to Cheng and Timilsina (2011), the main obstacle to developing 2G biofuels are high production costs in the pre-treatment stage, the high cost of enzymes used to hydrolyze lignocellulosic material, and the difficulty of converting 5-carbon sugars to ethanol. For 3G ethanol, the difficulty for its commercialization lies in the cost of harvesting the algae and the problems that contaminating algae cause (Cheng and Timilsina 2011). For 4G ethanol, there are gaps in knowledge for predicting the behavior of genetically modified microorganisms, to potentiate their desirable characteristics and maintain them unchanged over time (Peralta-Yahya et al., 2012).

The objective of this essay is to show, analyze and discuss information on ethanol production, specifically on the diverse generations of raw material used in its production. Particularly, the advantages and disadvantages are highlighted, as well as the evolutionary trends of this biotechnological process.

Raw material

First generation

Alcohol is obtained by the process of fermentation of the sugars present in the different raw materials, which can be metabolized by microorganisms of the genera Saccharomyces, Zymomonas, Kluyveromyces, and Zygosaccharomyces (Table 2).

Table 2 Microorganisms used in ethanol production. 

Microorganismo empleado Sustrato Referencia
Saccharomyces cerevisiae and Schizosaccharomyces pombae Melazas, jugo de caña,
remolacha azucarera, naranja
y arroz
(Jayaraman et al., 2017)
Zymomonas mobilis mutant Jugo de caña (Rofiqah et al., 2017)
Saccharomyces Diasticus Jugo de anacardo (Karuppaiya et al., 2012)
Pichia stipitis NRRL-Y-7124 Saccharomyces cerevisiae RL-11 Kluyveromyces fragilis Kf1 Residuos de la industria del
café
(Mussatto et al., 2012)
Aspergillus awamori Rhizopus japonicus Zymomonas mobilis Almidón de papa (Liu y Lien, 2016)
Zygosaccharomyces rouxii Kluyveromyces marxianus Ogataea (Hansenula) polymorpha Dekkera bruxellensis Pichia kudriavzevii Zygosaccharomyces bailii N/A (Radecka et al., 2015)

Raw materials with available fermentable sugars

These sugars are present in sugarcane, sugar beets and sweet sorghum. Use of these raw materials requires only milling, fermentation, distillation and denaturalization (so that it is not apt for human consumption). Moreover, for its use in mixtures with gasoline, it must be dehydrated (Solomon et al., 2007), which is necessary to displace its azeotropic point. Methods of dehydration include adsorption with molecular meshes, pervaporation, vacuum distillation, extractive distillation with solvents or with salts or with both at the same time. Ethanol is also dehydrated with hybrid processes that combine two or more of the above processes (Uyazán et al., 2004).

In Brazil, they are researching how to reduce ethanol production costs through integration in the use of energy and systems of co-generation in production plants (Cortes-Rodriguez et al., 2018) and decreasing expenditures of vapor and water (Pina et al., 2017), or the use of sugarcane bagasse in the integration of first generation (1G) and second generation (2G) ethanol production processes; 2G processes involve the use of lignocellulosic substrates (as will be discussed below) and the use of sweet sorghum as complementary raw material, grown in areas neighboring the sugarcane and harvested between cycles of the main crop (Jonker et al., 2015). Also studied is the sustainable development and updating of the technologies of biorefineries for producing bioelectricity (Khatiwada et al., 2016). After more than 50 years of experience with 1G ethanol, progress was oriented more toward optimization of the integral use of raw materials and the byproducts of the processes, integration of first generation processes with second generation processes, analysis of the effects of the varieties of the same raw material, crop conditions, harvest seasons and methods, and storage time of the raw material on ethanol yields (Gumienna et al., 2016; Dos Passos Bernardes et al., 2016). One important aspect is mechanized harvest of sugarcane, which increases the presence of inorganic compounds such as potassium, calcium, silica, iron and copper, relative to the traditional process of burning and manual cutting. Thai et al. (2012) report increases of 13 % calcium, 32 % magnesium and 7.6 % silica in the sugarcane juice after mechanical harvesting, relative to traditional burning and cutting. These minerals affect fermentation because magnesium increases ethanol yield, but an excess of copper reduces yields to 0.35 g g-1 (Costa et al., 2015).

Interest in sweet sorghum and other sorghum types for ethanol production has increased. This crop can be grown with little water (compared with other cereals) and is highly efficient photosynthetically for conversion of CO2 to biomass. Moreover, total sugar content of the juice of the sweet sorghum stem is comparable with that of sugarcane juice (Chuck-Hernandez et al., 2012). Sugarcane processing machinery has been adapted to harvest and mill sweet sorghum. Peralta-Contreras et al. (2013) proposed designing machinery specifically for sorghum stems to improve juice extraction indexes. Sorghum has many qualities, but its high moisture content (70%) and the low bulk density limit the distances within which transporting it after harvest is profitable (Chuck-Hernandez et al., 2012; Zegada-Lizarazu and Monti 2012). Also, conservation of the sugars in the stems is difficult because the native bacteria of the crop, such as Leuconostoc, degrade a large proportion of sugars during transport and storage. Inhibitors of Leuconostoc growth during transport, such as SO2 gas, have been tested. However, storing the gas in hermetic tanks at the sorghum collection sites, as well as its elimination when it arrives at the processing plant, make it an expensive system (Lingle et al., 2012).

Extracted sweet juices lose 20 % of their fermentable sugar content in three days at ambient temperature and 40 % to 50 % in seven days (De Oliveira Filho et al., 2016). Other affected aspects are decreased pH, increase in total acidity and quantity of reducing sugars. Furthermore, the presence of ethyl acetate, acetaldehyde and ethyl carbamate in sweet juices have a negative effect on fermentation, causing low yields (De Oliveira Filho et al., 2016). Juices from milled material must be filtered, clarified and pasteurized. Filtering removes lignocellulosic fractions, leaves, dirt and other contaminants from the collection stage. Clarifying is done to eliminate inorganic compounds, and pasteurization eliminates the microorganisms present. For clarification, the processes of sedimentation, sulfation, and carbonatation generate byproducts known as sludge. To generate less contaminating sludge from clarification, natural products are used, such as extracts from leaves and seeds of Moringa oleifera Lam., which remove more iron and calcium than synthetic polymers (Costa et al., 2015). High-pressure treatment (600 MPa 6 min-1) is an alternative to high temperatures for elimination of microorganisms and inactivating enzymes from sweet juices (Huang et al., 2015). Also, ohmic heating for 1 min and 32 V cm-1 has been tested to inactivate polyphenol oxidase and reduce microorganisms (Saxena et al., 2016). High-pressure methods and ohmic heating maintain juice quality stable and inhibit enzymatic activity, thus increasing its useful life in storage. Therefore, the search for methods of conserving raw materials and sweet juices for long periods without loss of fermentable sugars requires further study.

First generation technology has been applied industrially for 40 years. For this reason, besides the studies mentioned, there are many studies related to analysis of environmental problems this technology generates. Among these problems is the biomass produced, separated in the process of distillation and known as vinasse, which is produced at a ratio of 12 L vinasse L-1 ethanol (Silva et al. 2007). Vinasse is a liquid with suspended particles, acid pH and high chemical oxygen demand (COD) because of the organic matter present. Forty years ago, vinasse was a highly contaminating liquid residue that caused serious environmental problems in the aquifers where it was discharged. Its final disposal was a problem because there was little technology to treat it and costs were high. This situation changed because of new technologies with better results that decreased operation costs. To treat residues of alcoholic fermentation, physicochemical, chemical and biological methods were tested. The biological methods are the most appropriate due to the large quantity of organic biodegradable compounds present in their composition (Sheehan and Greenfield, 1980). Several alternatives were proposed for the treatment or reuse of vinasses, among which is feeding chickens (Hidalgo et al. 2009), production of biogas (Cruz-Salomón et al., 2017), and fertigation (Mijangos et al., 2014). In addition, standardized methods were created to analyze life cycles to determine entrance and exits of energy, evaluate generation of byproducts and residues in the entire supply chain, and minimize impacts from crop establishment to consumption of fuel ethanol (Cavalett et al., 2012; Gallejones et al., 2015; Miret et al., 2016).

From the above, it can be inferred that the main interests concerning raw materials with high fermentable sugar content are increasing yields, improving energy balances, diversifying raw materials, and diminishing environmental impact.

Raw materials with high starch content

Other first-generation sources used to obtain ethanol are raw materials that have a high starch content, such as cereals, tubers and rhizomes. For these raw materials, the following steps are used for ethanol production: milling, liquification, saccharification, fermentation, distillation and dehydration. The country with more published studies on ethanol from starch between 2012 and 2015 was China, the US and India with 187, 181 and 74 published documents, respectively. The main research topics center in three fundamental areas: understanding agronomic aspects and their effect on ethanol yields, new operations in industrial processes, and new laboratory techniques to predict starch contents and ethanol yields.

In agronomy, the study of maize and sorghum with several focuses is highlighted, especially on final ethanol yield, for example effects of deficient irrigation (Liu et al., 2013), content of moisture at harvest (Huang et al., 2012), fungus infections and harvest maturity (Dien et al., 2012). In other cereals, transgenic rice with high carbohydrate content was analyzed to evaluate its ethanol yields (Kim et al., 2015).

In industry, the method most used to fragment the cereals is dry milling (Orts and McMahan 2016), in which whole cereal grains are converted into flour, which is processed without separating the grain components. The flour is mixed with water to form a paste and α-amylase, pullulanase and amyl glycosidase are added to convert the starch into glucose. Ammonia is added to the process as a nitrogen source for the yeast and to control system pH. This high-glucose mixture is converted to ethanol by action of the yeast, while the solid residue, which has high fiber, lipid and protein contents, is toasted and converted into a byproduct known as distillers degraded grain soluble (DDGS). DDGS are mixed with syrup from the process and sold as a supplement for livestock. Wet milling is less used because of its high cost and water consumption, but starch from the grains is isolated and ethanol yield is higher (Kandil et al., 2011). Dry milling begins the process with starch, which is mixed with lipids and proteins, and in the processes of liquefication and saccharification these macromolecules decrease enzyme activity because they act as inhibitors of the process (Srichuwong et al., 2010). For this reason, we recommend investigating the interactions of the non-starch components (lipids and proteins) with starch and their effects during hydrolysis. To understand whether pigments are also inhibitors of the process Wang et al. (2016) validated the use of pigmented sorghum and determined that the high content of anthocyanins had no effect on ethanol yield.

In the industrial stage there are innovative methods for extracting fermentable sugars and non-structured carbohydrates with a diffusion process that uses biomass from chopped sweet sorghum stems and grains (Appiah-Nkansah et al., 2016). The process of milling and elimination of physical barriers that limit interaction of enzymes with the starch was studied and, according to Chuck et al. (2012), ethanol yield improves when the sorghum grains are decorticated. In the studies mentioned, cereal treatment technologies and ethanol yield are compared; energy expenditures decrease and ethanol yields increase. However, quantitative analysis of expenditures and comparison of different process proposals should be studied. It is also necessary to evaluate water balances and economic analyses of the process before initiating industrial scaling.

In the laboratory, development of a practical method of detecting approximate starch and ethanol contents using spectroscopy FT-NIR is highlighted (Li et al., 2015). This could speed up industrial scale analysis to control the ethanol production process systematically.

Fruits, rhizomes, roots and tubers are non-conventional sources of starch used particularly in tropical countries. Graefe et al. (2011) analyzed ethanol production from bananas in Costa Rica and Ecuador. Bananas have an advantage over tubers because of their ripening and, because they are climacteric, they naturally hydrolyze starch and thus no enzyme treatment is required to reach the fermentable sugars (Asiedu, 1987; Bugaud et al., 2009). Production of ethanol from bananas at different stages of ripeness showed that the highest ethanol yield was from green bananas, immediately after harvesting. Ethanol yield from overripe bananas was 23 % less than with immature bananas. This result is attributed to a decrease in dry-base matter because of the metabolic activity during ripening (Hammond et al., 1996). Due the higher yields, it is recommended to used green bananas to produce ethanol. However, technical problems exist, such as peeling the fruit because the shape of the bananas makes automatizing the process difficult, and the peel is strongly attached to the pulp at that physiological stage of the fruit.

One problem of biotechnological processes is inhibition by the end-product. In the measure that alcoholic fermentation occurs, ethanol is produced, which inhibits the metabolic pathway and the process of bioconversion is detained until it causes cell death. A method used to decrease this inhibition is to ferment the sugars immediately after their release. This is achieved by simultaneous saccharification and fermentation (SSF). Fermentable sugars are produced by starch hydrolysis, and fermentation is carried out in the same reactor. Several raw materials were processed in this way, and the results are better than separate saccharification and fermentation. With green bananas, theoretic ethanol efficiencies above 95 % were obtained in an enzyme SSF system and the use of glucoamylases, pectinolytic enzymes and yeast (Bello et al., 2012). Feasibility of a non-domesticated variety of mandioca (Manihot glaziovii), as a non-food raw material with a high starch content, was evaluated for production of ethanol by SSF. Ethanol concentrations of 190 g L-1 were obtained. Another technological development in inhibitors is Zimomonas mobilis bacteria isolated from the African palm and Mexican pulque. They are osmotolerant and resistant to high concentrations of ethanol and permit fermentation at high concentrations, or very high gravity (VHG). The advantage is that at high sugar concentrations (up to 360 g L-1) there is no contamination by other bacteria. In these conditions, ethanol concentration from sweet sorghum was 17.6% v/v (Deesuth et al., 2016). Process integration can produce better yields than individual processes. Chu-ky et al. (2016) tested simultaneous very high gravity liquefication, saccharification and fermentation (SLSF-VHG) in rice by-products (broken rice grain) and obtained a theoretical 83.2% ethanol.

In Brazil and Colombia new sources and methods for ethanol production are being sought. Soccol (1997) achieved degradation of raw mandioca starch granules during fermentation in solid state with amyloglucosidase from Rhizopus oryzae.Cinelli et al. (2015) described the method of cold hydrolysis of starches in which the process’ energy demand decreases because of starch hydrolysis at temperatures below its gelling temperature, that is, with starch in its granular form. This technology generates another perspective of the process as an alternative method that can be carried out without the liquefication stage, which is achieved through amylolytic enzyme complexes composed of endo-amylases, exo-amylases and debranching enzymes. In Indonesia, Jusuf and Ginting (2014) and Kusmiyati (2015) studied sweet potato (Ipomoea batatas L.) and the tuber Iles Iles (Amorphophalus campanulatus), respectively, as sources for ethanol production. These tubers have high potential for transformation because of their high yield per unit of cultivated area. Sweet potatoes yield more than 30 t ha-1 of tubers, which are 22.5 % starch, wet base, while Iles Iles has the advantage of being cheap and not used for human food. As an alternative source, ethanol yield of starch extracted from Taro corm (Colocasia esculenta), a perennial plant of the Araceae family was evaluated. Taro is cultivated in the tropics and subtropics of South America, Asia, Oceania and Africa (Wu et al., 2016). With this raw material, theoretic yields of 94.2% ethanol were achieved, an attractive yield for ethanol production.

Second generation

In the last decade, most of the research in liquid fuels evaluated the commercialization of ethanol produced with farm residues (cereal straw, leaves and dry branches of forest crops) or industrial residues (sugarcane bagasse and DDGS), composed mainly of cellulose, hemicellulose and lignin; these biofuels are 2G.

The amount of residue generated by an industry and that can be used to produce 2G ethanol is illustrated by Brazilian ethanol production units, which processed more than 602 x106 t of sugarcane and produced 24 x 109 L of ethanol from 2013 to 2014. Each ton of sugarcane processed generates 270 to 280 kg of bagasse (Canilha et al., 2012), demonstrating the high potential of residual biomass for 2G ethanol production with these lignocellulosic residues.

These residues are the source for cogeneration of heat and electricity in distilleries through thermochemical processes, such as direct combustion, pyrolysis or gasification (Henrique et al., 2014), but their biochemical transformation has certain technical limitations due to the chemical nature of the lignocellulosic residues, which is heterogeneous and different pretreatments, or modifications to the raw material, must be applied. It is necessary to conduct laboratory studies that show the technical feasibility of bioconversion of lignocellulosic residues to ethanol.

Enzyme hydrolysis of cellulose is a limiting step in 2G ethanol production because it needs complex enzymatic cocktails to de-polymerize the residues, in addition to the complexity of the structural arrangement of the components of the lignocellulosic residues that make hydrolysis difficult. Lignin is a main component of these residues, forming a structural arrangement together with the cellulose and the hemicellulose that makes it difficult for cellulases to access the cellulose hydrolyze it to glucose. Moreover, some cellulolytic enzymes are often adsorbed by the hydrophobic surface of lignin that, therefore, prevents them from acting on cellulose (Huron et al., 2016). Phenolic compounds (tannins) of lignin, when de-polymerized, also become inhibitors of fermentation, so that the effects and interactions of the inhibitors of the processes of fermentation should be analyzed and understood to enable improvement of production yields.

As mentioned in the section about the first generation, green or immature banana pulp can be used to produce ethanol, but one of the limiting steps is the peeling process. Eliminating the banana peel can be avoided because both the banana peel and the pulp have high carbohydrate content (Gebregergs et al., 2016), and both parts have been studied for ethanol production (Parthiban et al., 2011). Therefore, ethanol can be obtained from unpeeled green bananas. However, it should be taken into account that some carbohydrates in the pulp and peel of green bananas are complex polysaccharides and cannot be metabolized by yeasts. For this reason, it is necessary to hydrolyze the lignin, the cellulose and pectin to convert them into simple sugars. This is an example of a raw material for ethanol production found in 1G and 2G groups.

Milling bananas with their peel has technical problems derived from the high viscosity and presence of fibers during and after milling (Afanador, 2005). Oberoi et al. (2011) report the use of dryers such as electric ovens to obtain a dry brittle material that can be ground in laboratory mills, but in industrial processing this would increase energy costs. Here, there is a knowledge gap regarding decreasing viscosity in this step of the process without drying and milling or the use of alternative energy (solar energy, for example) for the drying process.

Second generation technology has given way to the concept of biorefineries because through 2G processes ethanol is obtained as well as methanol, synthesis gas, 2.5-dimethylfurane and tannins, a determining factor for obtaining diverse products from lignocellulosic raw materials. In this sense, one of the goals is to integrate 1G and 2G technologies. Flório and Junior (2013) performed a heat analysis of production of electricity and 2G ethanol from sugarcane bagasse and obtained better heat effectivity since, besides fermenting sugarcane sucrose and the glucoses that constitute cellulose, the process was optimized, and they sought to ferment pentoses (mainly xylose) that form a structural part of the hemicellulose. The process of bioethanol production was simulated with the mixture glucose/xylose, and the effect of temperature, pH and sugar concentrations was evaluated. The variables of the process were reproduced using different conditions of operation and it was demonstrated that simulation is a useful tool for generating an optimal profile of alcoholic fermentation with the glucose/xylose mixture (Reyes et al., 2016).

With the concept of biorefinery, Xu et al. (2018) propose obtaining diverse products from lignocellulosic raw material using a modified method of simultaneous saccharification and fermentation (MSSF), which involves ecological technologies like hydrothermal pre-treatments and organic solvents for production of a high cellulose content solid to be transformed into ethanol. In addition, solvents are recycled to produce adhesives based on plant proteins, and the xylose present in the aqueous phase is used to obtain furfural. This type of integrated proposals may be attractive for promoting commercial ethanol production from lignocellulosic biomass.

Saccharomyces cereviciae and Zymomonas mobilis, used to ferment hexoses, cannot use pentoses as a substrate because the metabolic route for pentose conversion is unlike that of hexoses. For this reason, other yeasts and bacteria are being studied. Candida shehatae (Guan et al., 2013) and Pichia stipitis (Travaini et al., 2016) have a high potential for fermenting pentoses; their disadvantage is their low tolerance to ethanol, and in the processes with these microorganisms inhibition by the end-product occurs. As a solution to this technical problem, Kluveromyces marxianus yeast has been proposed; it tolerates ethanol and can ferment hexoses and pentoses (Lin et al., 2013). To increase use of pentoses, process integration through use of fungi that metabolize wood without pre-treating the lignin is being investigated. Mattila et al. (2017) used a single step and a single microorganism for production of bioethanol with phlebioid fungus species, achieving an ethanol yield of 5.9 g L-1.

Third generation

The search for raw materials for ethanol production has increased interest in rapid generation of biomass with high energy density (energy crops). Among these crops are found perennial grasses, micro- and macro-algae, and cyanobacteria, all grouped in the denomination of third generation (3G) biofuels. Algae are not seen as raw material for ethanol production, but as producers of hydrogen as the substrate for thermochemical conversion and as lipids for biodiesel (Brennan and Owende 2010). Starches can be obtained by converting biomass from macroalgae. The starches are then hydrolyzed and fermented to produce bioethanol (Adams et al., 2009; Khambhaty et al., 2013; Scholz et al., 2013; Sudhakar et al., 2016) and biobutanol, which has a higher energy density and greater compatibility with gasoline than bioethanol (Dürre, 2008). One study on the economic feasibility of microalgae as raw material for biorefineries was reported by Konda et al. (2015). They highlight the potential advantages of producing a broad portfolio of chemical products from microalgae to give economic viability to industrial clusters denominated biorefineries. In the laboratory, isolated alga strains are handled, but in natural conditions water sources have a problem called eutrophication, which is the proliferation of algae because of excess nutrients in the water. To solve this problem, using these algae was proposed for ethanol production and water quality improvement. Chen et al. (2017) patented a pre-treatment technique using electro-coagulation and acid saccharification of algae in lakes. They obtained up to 156 mg glucose g-1 of algae, which is available for transformation to ethanol. The type of macroalgae most used industrially are seaweeds, which are pluricellular organisms that efficiently convert nutrients in the water and CO2 into biomass. There are around 9,200 species of seaweed, but only 221 are economically important (Mohammed, 2013). Macroalgae are raw material for bioethanol production because they do not have a high content of lipids, as do microalgae, but they do have a high content of sugars and other carbohydrates that can be fermented. The alga growth variables studied are those that affect production of carbohydrates, such as light, temperature, nutrients, salinity and pH. With respect to the effect of light, according to George et al. (2014), a photosynthetic light intensity of 60 μmol m-1s-1 and 12:12 h (light:dark) cycles achieved a biomass production of 7.9 mg L-1 d-1 with Ankistrodesmus falcatus. It is important to consider that the pretreatments, liquefication and saccharification of the macroalgae have difficulties similar to those of the second-generation raw materials since they also contained polysaccharides that must be hydrolyzed to fermentable sugars, an aspect that requires more research. Microalgae have a high content of lipids, but also of carbohydrates. For this reason, Scenedesmus sp. has been proposed as raw material for integrated production of ethanol and biodiesel (Sivaramakrishnan and Incharoensakdi, 2018).

Another high-density crop in lakes and lagoons is water hyacinth (Eichhornia crassipe), which is an environmental problem because of its high growth rate; it prevents light and oxygen from penetrating these bodies of water and cause the death of other species in these ecosystems. Water hyacinth is composed mainly of cellulose, which can be converted to glucose, the fermentable substrate for ethanol production (Zhang et al., 2018). Different pre-treatments were tested for water hyacinth, and the most effective was the combination of diluted acid and microorganisms (Phanerochaete chrysosporium), which resulted in highly purified cellulose (39.4 %) and high content of reducing sugars (430.66 mg g−1).

Fourth generation

Advances in bioengineering have led to the concept of fourth generation biofuels (4G), which use genetically modified organisms (GMO) that capture more CO2, such as genetically modified sugarcane that has high content of lipids for simultaneous production of ethanol and biodiesel (Huang et al., 2016). Also, fermentation with genetically modified E. coli produces triglycerides from sugarcane sweet juices that are later transformed to biodiesel. Amyris (USA), LS9 (USA) Sapphire Energy (USA), Solazyme (USA) and Terrebonne (Canada) study the way to scale the process to industrial levels (Steen et al., 2010; Westfall and Gardner, 2011). The use of GMO has had positive results in yield and efficiency. According to Tanimura et al. (2015), the genetically modified yeast Scheffersomyces shehatae JCM 18690, can simultaneously hydrolyze and ferment starch with a productivity of up to 0.92 g L-1 d-1 after ten days, comparable to the highest yield reported in ethanol production from maize with S. cerevisiae. Huerta et al. (2005) increased the theoretical yield of converting glucose or xylose into ethanol up to 27 % by genetically improving ethanologenic strains of E. coli KO11. One of the main objectives was to optimize the expression of the gene PdcZm, which codes for pyruvate decarboxylase enzymes, and to find or generate more active versions of the same gene.

Future trends

The largest proportion of the costs of producing biofuels is associated with raw materials (Neto et al., 2016). Thus, proposals for the industrial sector and systems of technological innovation in biofuels is focused on reducing production costs and on finding new raw materials that meet economic and environmental requirements and do not affect human food security.

One viable alternative for bioethanol production is process integration, which helps to improve productivity and use of energy resources and has an impact in reducing operation costs. One example is the production of 1G and 2G ethanol from sugarcane and its bagasse, which can reduce the final cost of ethanol enough to make it competitive with fossil fuels (Neto et al., 2016). Technical analyses and economic studies should be conducted on integrated processes. From sugarcane, a raw material of high productivity, applicable results are obtained from integrated processes at an industrial scale, but other less productive raw materials, such as those with high starch content, should be analyzed in technological integration processes. Moreover, using carbon dioxide from the ethanol production plant (fermentation stage) in algae production offers a new perspective for integration of technologies 1G/3G.

The concept of biorefineries is a way of integrating processes; it broadens the spectrum of products of a production plant and, therefore, market possibilities. But its level of complexity is advanced, posing challenges in the integral use of raw materials and calling for further study because of the number variables involved.

A recent proposal concerns synthetic ethanol production from organic wastes such as paper, wood and cow manure. The residues are dried in the same plant where ethanol is produced. They are stored for a short period and introduced into the gasifier together with carbon to produce carbon monoxide and hydrogen (“syngas”) as well as pure carbon. “Syngas” is refined and subjected to a catalytic process before being compressed for transfer to the reactor for ethanol synthesis. In this process, collection of the raw material has a major impact on the cost of the end product, and the carbon used to improve economic efficiency increases costs. The cost of ethanol, with an internal return rate of 10 %, was 0.433 USD L-1 with paper wastes, 0.51 USD L-1 with wood waste and 1.45 USD L-1 with cow manure. Economic feasibility of producing ethanol was greater with the mixture of wood waste and carbon. Using carbon in the mixture may be an option for obtaining energy with household generated organic waste (Gwank et al., 2018).

Petrochemical installations for producing and refining oil contribute CO2 emissions as does combustion of the energy compounds (gasoline, diesel, butane and natural gas). Combustion of oil derivatives produces only emissions and no fixation which occurs with other gases (for example, nitrogen), and there is no stage at which these emissions can be decreased; thus, it causes environmental pollution. In contrast, CO2 generated by ethanol combustion is less than that generated by fossil fuels and can be fixed through photosynthesis and thus its release into the atmosphere is lower, contributing less to the greenhouse effect (Quintella et al., 2011).

Life cycle analysis (LCA) of biofuels helps to understand the impact of the generated CO2 on the environment. An evaluation conducted by the Centro de Tecnología Copersucar (CTC) showed that for each ton of sugarcane, the net effect is fixation of 694.7 kg CO2, considering the entire cycle, from sugarcane cultivation up to its final use as ethanol. These results showed that emission of 206.8 kg CO2 per t of sugarcane is avoided when ethanol is used instead of gasoline (Paula et al., 2010).

Diverse factors should be considered during the life cycle analysis of ethanol. Sugarcane under given conditions can generate negative CO2 balances, but because of the variety of raw materials with which ethanol can be obtained, each of them should be analyzed specifically. For example, application of chemical fertilizers and irrigation water for the crop that can be used to produce ethanol inevitably involves CO2 emissions in the processes of production (Gelfand et al., 2011). Clearing and converting land to crop fields damage the soil carbon store; this is denominated carbon debt (the amount of CO2 released by land use change). Production of precise reliable tools for determining and quantifying each relevant contribution, anthropogenic or not, in the life cycle of ethanol is a challenge.

Conclusions

Diversification of raw materials for ethanol production led to the classification of first and second generation. First generation ethanol is the use of materials rich in simple sugars (sucrose from sugarcane) and starch (from maize). In the production of second-generation ethanol, the aim is to take advantage of low-cost agricultural byproducts (maize stover, wheat straw, etc.) that are rich in lignocellulosic compounds. Third generation biofuels involve raw materials such as perennial grasses, micro and macro algae, and cyanobacteria. In the case of macro algae, their simple sugars and starch can be used to produce ethanol. In the production of fourth generation ethanol, genetically modified crops (such as sugarcane that is more efficient in capturing CO2) and genetically modified microorganisms with greater efficiency in converting substrate into product. Today, the search is for high-starch raw materials, preferably non-food crops that are high-yielding and low-cost, as promising alternatives for ethanol production at lower cost than production from sugarcane and maize (food in Mexico and whose use is prohibited in energy laws.

Literatura Citada

Adams, J. M., J. A. Gallagher, and I. S. Donnison. 2009. Fermentation study on Saccharina latissima for bioethanol production considering variable pre-treatments. J. Appl. Phycol. 21: 569-574. [ Links ]

Afanador, A. M. 2005. El banano verde de rechazo en la produccion de alcohol carburante. Rev. Escuela Ing. Antioquia 3: 51-68. [ Links ]

Alves, L., H. Jarbas, and R. Cooke. 2018. Water management for sugarcane and corn under future climate scenarios in Brazil. Agric. Water Manag. http://doi.org/10.1016/j.agwat.2018.01.019 [ Links ]

ANP. 2014. Brazilian Statistical Yearbook of Oil, gas and Biofuels (in portuguese). 236 p. [ Links ]

Appiah-Nkansah, N. B., K. Zhang, W. Rooney, and D. Wang. 2016. Model study on extraction of fermentable sugars and nonstructural carbohydrate from sweet sorghum using diffusion process. Industr. Crops Products 83: 654-662. [ Links ]

Asiedu, J. J. 1987. Physicochemical changes in plantain (Musa paradisiaca) during ripening and the effect of degree of ripeness on drying. Trop. Sci. 27: 249-260. [ Links ]

Bello, R. H., O. Souza, N. Sellin, S. H. W. Medeiros, and C. Marangoni. 2012. Effect of the microfiltration phase on pervaporation of ethanol produced from banana residues. Computer Aided Chem. Eng. 31: 820-824. [ Links ]

Brennan, L., and P. Owende. 2010. Biofuels from microalgae -A review of technologies for production, processing, and extractions of biofuels and co-products. Renew. Sustainable Energy Rev. 14: 557-577. [ Links ]

Bugaud, C., P. Alter, M. O. Daribo, and J. M. Brillouet. 2009. Comparison of the physico-chemical characteristics of a new triploid banana hybrid, FLHORBAN 920, and the Cavendish variety. J. Sci. Food Agric. 89: 407-413. [ Links ]

Canilha, L., A. K. Chandel, T. Suzane Dos Santos Milessi, F. A. F. Antunes, W. Luiz Da Costa Freitas, F. M. Das Graças Almeida, and S. S. Da Silva. 2012. Bioconversion of sugarcane biomass into ethanol: An overview about composition, pretreatment methods, detoxification of hydrolysates, enzymatic saccharification, and ethanol fermentation. J. Biomed. Biotechnol. 2012: 1-16. [ Links ]

Cavalett, O., T. L. Junqueira, M. O. S. Dias, C. D. F. Jesus, P. E. Mantelatto, M. P.Cunha, H. C. J. Franco, T. F. Cardoso, R. Maciel Filho, C. E. V. Rossell, and A. Bonomi. 2012. Environmental and economic assessment of sugarcane first generation biorefineries in Brazil. Clean Technol. Environ. Policy. Springer-Verlag 14: 399-410. [ Links ]

Chandel, A. K., T. L. Junqueira, E. R. Morais, V. L. R. Gouveia, O. Cavalett, E. C. Rivera, V. C. Geraldo, A. Bonomi, and S. S. Da Silva. 2014. Techno-economic analysis of second-generation ethanol in Brazil: Competitive, complementary aspects with first-generation ethanol. Biofuels in Brazil. Springer Int. Pub. pp: 1-29. [ Links ]

Chen, S. T., Y. P. Tsai, J. H. Ciou, Z. Y. Huang, W. C. Lin, and H. Shiu. 2017 Study on saccharification techniques of alga waste harvested from a eutrophic water body for the transformation of ethanol. Renew. Energy 101: 311-315 [ Links ]

Cheng, J. J. and G. R.Timilsina. 2011 Status and barriers of advanced biofuel technologies: A review. Renew. Energy 36: 3541-3549. [ Links ]

Chuck-Hernandez, C., M. Peralta-Contreras, G. Bando-Carranza, M. Vera-Garcia, N. Gaxiola-Cuevas, R. Tamayo-Limon, F. Cardenas-Torres, E. Perez-Carrillo, and S. O. Serna-Saldivar. 2012. Bioconversion into ethanol of decorticated red sorghum (Sorghum bicolor L. Moench) supplemented with its phenolic extract or spent bran. Biotechnol. Lett. 34: 97-102. [ Links ]

Chu-Ky, S., T.-H. Pham, K. L. T.Bui, T. T. Nguyen, K. D. Pham, H. D. T. Nguyen, H. N. Luong, V-P. Tu, T. -H. Nguyen, P. H. Ho, and T. M. Le. 2016. Simultaneous liquefaction, saccharification and fermentation at very high gravity of rice at pilot scale for potable ethanol production and distillers dried grains composition. Food Bioprod. Proces. 98: 79-85. [ Links ]

Cinelli, B. A., L. R. Castilho, D. M. G. Freire, and A. M. Castro. 2015. A brief review on the emerging technology of ethanol production by cold hydrolysis of raw starch. Fuel 150: 721-729. [ Links ]

Cortes-Rodríguez, E. F., N. A. Fukushima, R. Palacios-Bereche, A. V. Ensinas, and S. A. Nebra. 2018. Vinasse concentration and juice evaporation system integrated to the conventional ethanol production process from sugarcane and heat integration and impacts in cogeneration system. Renew. Energy 115: 474-88. [ Links ]

Costa, G. H. G., I. S. Masson, L. A. De Freita, J. P. Roviero, and M. J. R. Mutton. 2015. Reflects of clarification of sugarcane juice with moringa on inorganic compounds of sugar VHP | Reflexos da clarificação do caldo de cana com moringa sobre compostos inorgânicos do açúcar VHP. Rev. Bras. Eng. Agric. Amb. 19: 154-159. [ Links ]

Cruz-Salomón, A., R. Meza-Gordillo, A. Rosales-Quintero, C. Ventura-Canseco, S. Lagunas-Rivera, and J. Carrasco-Cervantes. 2017. Biogas production from a native beverage vinasse using a modified UASB bioreactor. Fuel 198: 170-174. [ Links ]

Deesuth, O., P. Laopaiboon, and L. Laopaiboon. 2016. High ethanol production under optimal aeration conditions and yeast composition in a very high gravity fermentation from sweet sorghum juice by Saccharomyces cerevisiae. Ind. Crops Products 92: 263-270. [ Links ]

De Oliveira Filho, J. H., A. M. Bortoletto, and A. R. Alcarde. 2016. Post-harvest quality of stored sugarcane stalks and their reflection on the production of cane spirit | Qualidade pós-colheita de colmos de cana armazenados e seus reflexos na produção de cachaça. Braz. J. Food Tech. 19. doi: 10.1590/1981-6723.6915. [ Links ]

Dien, B. S., D. T. Wicklow, V. Singh, R. A.Moreau, J. K. Winkler-Moser, and M. A. Cotta. 2012. Influence of Stenocarpella maydis infected corn on the composition of corn kernel and its conversion into ethanol. Cer. Chem. 89: 15-23. [ Links ]

Dos Passos Bernardes, A., G. F. Tremblay, G. Bélanger, P. Seguin, A. Brégard, and A. Vanasse. 2016. Bagasse silage from sweet pearl millet and sweet sorghum as influenced by harvest dates and delays between biomass chopping and pressing. BioEnergy Res. Springer US 9: 88-97. [ Links ]

Dürre, P. 2008. Fermentative butanol production: bulk chemical and biofuel. Ann. New York Ac. Sci. 1125: 353-62. [ Links ]

Flório, D. N., and S. D. O. Junior. 2013. Thermoeconomic analysis of combined production of electricity and second generation ethanol based on the dilute acid hydrolisis of sugarcane bagasse. Proceedings of the 26th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, ECOS 2013. [ Links ]

Gallejones, P., G. Pardo, A. Aizpurua, and A. del Prado. 2015. Life cycle assessment of first-generation biofuels using a nitrogen crop model. Sci. The Tot. Env. 505: 1191-1201. [ Links ]

Gebregergs, A., M. Gebresemati, and O. Sahu. 2016. Industrial ethanol from banana peels for developing countries: Response surface methodology. Pacific Science Review. Nat. Sci. and Eng. 18: 22-29. [ Links ]

Gelfand I., T. Zenone, P. Jasrotia, J. Chen J, S. K. Hamilton, and G. P. Robertson. 2011. Carbon debt of Conservation Reserve Program (CRP) grasslands converted to bioenergy production, Proc. of the Nat. Ac. of Sci. of the U. S. A. 108: 13864-13869. [ Links ]

George, B., I. Pancha, C. Desai, K. Chokshi, C. Paliwal, T. Ghosh, and S. Mishra. 2014. Effects of different media composition, light intensity and photoperiod on morphology and physiology of freshwater microalgae Ankistrodesmus falcatus - A potential strain for bio-fuel production. Biores. Tech. 171: 367-374. [ Links ]

Graefe, S., D. Dufour, A. Giraldo, L. A. Muñoz, P. Mora, H. Solís, H. Garcés, and A. Gonzalez. 2011. Energy and carbon footprints of ethanol production using banana and cooking banana discard: A case study from Costa Rica and Ecuador. Biomass and Bioenergy, 35: 2640-2649. [ Links ]

Guan, D., Y. Li, R. Shiroma, M. Ike, and K. Tokuyasu. 2013. Sequential incubation of Candida shehatae and ethanol-tolerant yeast cells for efficient ethanol production from a mixture of glucose, xylose and cellobiose. Biores. Tech. 132: 419-422. [ Links ]

Gumienna, M., A. Szwengiel, A. Szczepańska-Alvarez, K. Szambelan, M. Lasik-Kurdyś, Z. Czarnecki, and A. Sitarski. 2016. The impact of sugar beet varieties and cultivation conditions on ethanol productivity. Biomass and Bioenergy 85: 228-234. [ Links ]

Gwak, Y. R., Y. B. Kim, I. S. Gwak, and S. H. Lee. 2018. Economic evaluation of synthetic ethanol production by using domestic biowaste and coal mixture. Fuel 213: 115-122. [ Links ]

Hammond, J. B., R. Egg, D. Diggins, and C. G. Coble. 1996. Alcohol from bananas. Biores. Tech. 56: 125-130. [ Links ]

Henrique, M., L. Silveira, M. Siika-aho, and K. Kruus. 2014. Biofuels in Brazil. (October 2015), pp. 151-172. doi: 10.1007/978-3-319-05020-1. [ Links ]

Hernandez-Uribe, J. P., F. J. Garcia-Suarez, F. Gutierrz-Meraz, S. L. Rodriguez-Ambriz, and L. A. Bello-Perez. 2014. By-Products derived of the starch isolation from tubers: Physicochemical and functional properties. J. Food Agr. Env. 12: 43-46. [ Links ]

Hidalgo, K, B. Rodriguez, M. Valdivié, M. Febles 2009. Utilización de la vinaza de destilería como aditivo para pollos en ceba. Rev. Cub. C. Agr. 43: 281-284. [ Links ]

Hoyos-Leyva, J. D., L. A. Bello-Perez, H. Yee-Madeira, M. E. Rodriguez-Garcia, and A. Aguirre-Cruz. 2017. Characterization of the flour and starch of aroid cultivars grown in Mexico. Starch/Starke 69: 1-8. [ Links ]

Huang, H., W. Liu, V. Singh, M. G. C. Danao, and S. R. Eckhoff. 2012. Effect of harvest moisture content on selected yellow dent corn: Dry-grind fermentation characteristics and DDGS composition. Cer. Chem. 89: 217-221. [ Links ]

Huang, H., S. Long, and V. Singh. 2016. Techno-economic analysis of biodiesel and ethanol co-production from lipid-producing sugarcane. Biof., Biop. Bioref. John Wiley & Sons, Ltd. 10: 299-315. [ Links ]

Huang, H. W., Y. H. Chang, and C. Y. Wang. 2015. High ressure pasteurization of sugarcane juice: Evaluation of microbiological shelf life and quality evolution during refrigerated storage. Food Bioproc. Tech. 8: 2483-2494. [ Links ]

Huerta, G., J. Utrilla, G. Hernandez, F. Bolivar, G. Gosset, and A. Martinez. 2005. Metabolic engineering to increase the ethanol flux and yield in ethanologenic Escherichia coli. Rev. Mex. Ing. Quím. 4: 25-36. [ Links ]

Huron, M., D. Hudebine, N. L. Ferreira, and D. Lachenal. 2016. Impact of delignification on the morphology and the reactivity of steam exploded wheat straw. Ind. Crops and Prod. 79: 104-109. [ Links ]

Jayaraman, P., A. Livingstone, S. Harikrishnan, S. Vinoth, and R. Logamba. 2017. Evaluation of ethanol production using various carbon substrates by Sacharomyces cerevisiae and Schizosacharomyces pombae. J. Pure App. Microb. 11: 1469-1478. [ Links ]

Jonker, J. G. G., F. van der Hilst, H. M. Junginger, O. Cavalett, M. F. Chagas, and A. P. C. Faaij. 2015. Outlook for ethanol production costs in Brazil up to 2030, for different biomass crops and industrial technologies. App. Energy 147: 593-610. [ Links ]

Jusuf, M. and E. Ginting. 2014. The prospects and challenges of sweet potato as bio-ethanol source in Indonesia. Energy Procedia 47: 173-179. [ Links ]

Kandil, A., J. Li, T. Vasanthan, D. C. Bressler, and R. T. Tyler. 2011. Compositional changes in whole grain flours as a result of solvent washing and their effect on starch amylolysis. Food Res. Int. Elsevier Ltd. 44: 167-173. [ Links ]

Karuppaiya, M., T. Viruthagiri, and K. Manikandan. 2012. Statistical screening of medium components on ethanol production from cashew apple juice using Saccharomyces diasticus. Int. J. Biotech. Bioeng. 6: 400-403. [ Links ]

Khambhaty, Y., D. Upadhyay, Y. Kriplani, N. Joshi, K. Mody, and M. R. Gandhi. 2013. Bioethanol from macroalgal biomass: Utilization of marine yeast for production of the Same. BioEnergy Res. Springer-Verlag 6: 188-195. [ Links ]

Khatiwada, D., S. Leduc, S. Silveira, and I. McCallum. 2016. Optimizing ethanol and bioelectricity production in sugarcane biorefineries in Brazil. Renew. Energy 85: 371-386. [ Links ]

Kim, S. M., E. Khullar, W. Liu, M. Lanahan, P. Lessard, S. Dohle, J. Emery, R. M. Raab, and V. Singh. 2015. Rice straw with altered carbohydrate content: Feedstock for ethanol production. ASABE 58: 523-528. [ Links ]

Konda, N. V. S. N. M., S. Singh, B. A. Simmons, and D. Klein-Marcuschamer. 2015. An investigation on the economic feasibility of macroalgae as a Ppotential feedstock for biorefineries. BioEnergy Res. Springer US. 8: 1046-1056. [ Links ]

Kusmiyati, K., H. Susanto. 2015. Fuel grade bioethanol broduction from Iles-iles (Amorphophalus campanulatus) Tuber. Int J. Renew. Energy Dev. 23: 199-206. [ Links ]

Li, J., M. G. C. Danao, S. F. Chen, S. Li, V. Singh, and P. J. Brown. 2015. Prediction of starch content and ethanol yields of sorghum grain using near infrared spectroscopy. IM Publications LLP, 23: 85-92. [ Links ]

Lin, Y. S., W. C. Lee, K. J. Duan, and Y. H. Lin. 2013. Ethanol production by simultaneous saccharification and fermentation in rotary drum reactor using thermotolerant Kluveromyces marxianus. App. Energy 105: 389-394. [ Links ]

Lingle, S. E., T. L. Tew, H. Rukavina, and D. L. Boykin. 2012. Post-harvest changes in sweet sorghum I: Brix and sugars. Bioenergy Res. 5: 158-167. [ Links ]

Linton, J. A., J. C. Miller, R. D. Little, D. R. Petrolia, and K. H. Coble. 2011. Economic feasibility of producing sweet sorghum as an ethanol feedstock in the southeastern United States. Biomass and Bioenergy 35: 3050-3057. [ Links ]

Liu, L., N. Klocke, S. Yan, D. Rogers, A. Schlegel, F. Lamm, S. I. Chang, and D. Wang. 2013. Impact of deficit irrigation on maize physical and chemical properties and ethanol yield. Cereal Chem. 90: 453-462. [ Links ]

Liu, X. V., S K. Hoekman, and A. Broch. 2017. Potential water requirements of increased ethanol fuel in the USA. Energy Sustainab. Soc. 7: 1-13. [ Links ]

Liu, Y. K., and P.M. Lien. 2016. Bioethanol production from potato starch by a novel vertical mass-flow type bioreactor with a co-cultured-cell strategy. J. Taiwan Inst. Chem. Eng. 62: 162-168. [ Links ]

Mattila, H., J. Kuuskeri, and T. Lundell. 2017. Single-step, single-organism bioethanol production and bioconversion of lignocellulose waste materials by phlebioid fungal species. Biores. Tech. 225: 254-261. [ Links ]

Miret, C., P. Chazara, L. Montastruc, S. Negny, and S. Domenech. 2016. Design of bioethanol green supply chain: Comparison between first and second generation biomass concerning economic, environmental and social criteria. Comp. Chem. Eng. 85: 16-35. [ Links ]

Mijangos-Cortes, J., M. Gonzalez-Muñoz, E. España-Gamboa, J. Dominguez-Maldonado, and L. Alzate-Gaviria. 2014. Fertigation of sweet sorghum (Sorghum bicolor L. Moench.) in laboratory and nursery assays with treated vinasses of hidrated ethanol of UASB reactor. Rev. Mex. de Ing. Quím. 13: 713-722. [ Links ]

Mohammed, G. .2013. Seaweed farming. Calicut Research Centre of CMFRI. Calicut Kerala, India. Customized training Book. 259-262. http://eprints.cmfri.org.in/9734/1/Gulshad.pdfLinks ]

Mussatto, S. I., E. M. S. Machado, L. M. Carneiro, and J. A. Teixeira. 2012. Sugars metabolism and ethanol production by different yeast strains from coffee industry wastes hydrolysates. App. Energy 92: 763-768. [ Links ]

Neto, C. J. D., E. B. Sydney, L. P. de Souza Vandenberghe, and C. R. Soccol. 2016. Green fuels technology. Green Energy Tech. 387-406. doi: 10.1007/978-3-319-30205-8. [ Links ]

Oberoi, H. S., P. V. Vadlani, L. Saida, S. Bansal, and J. D. Hughes. 2011. Ethanol production from banana peels using statistically optimized simultaneous saccharification and fermentation process. Waste Manage. 31: 1576-1584. [ Links ]

Orts, W. J. and C. M. McMahan. 2016. Biorefinery developments for advanced biofuels from a sustainable array of biomass feedstocks: Survey of recent biomass conversion research from Agricultural Research Service. BioEnergy Res. Springer NY LLC. 9: 430-446 [ Links ]

Parthiban, R., M. Sivarajan, and M. Sukumar. 2011. Ethanol production from banana peel waste using Saccharomyces cerevisiae. Second International Conference on Sustainable Energy and Intelligent System (SEISCON 2011) .University, Maduravoyal, Chennai, Tamil Nadu, India. July. 20-22, 2011. http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=6143305Links ]

Paula, M., F. A. R. Pereira, E. R. A. Arias, B. R. Scheeren, C. C. Souza, and D. S. Mata. 2010. Fixação de carbono e a emissão dos gases de efeito estufa na exploração da cana de açúcar. Ciência Agrotec., Lavras. 34: 633-640. [ Links ]

Peralta-Contreras, M., C. Chuck-Hernandez, E. Perez-Carrillo , G. Bando-Carranza, M. Vera-Garcia, N. Gaxiola-Cuevas , R. Tamayo-Limon , F. Cardenas-Torres , and S. O. Serna-Saldivar. 2013. Fate of free amino nitrogen during liquefaction and yeast fermentation of maize and sorghums differing in endosperm texture. Food Biop. Proc. 91: 46-53. [ Links ]

Peralta-Yahya, P. P., F. Zhang, S. B. del Cardayre, and J. D. Keasling. 2012. Microbial engineering for the production of advanced biofuels. Nature. England, 488: 320-328. [ Links ]

Pina, E. A., R. Palacios-Bereche, M. F. Chavez-Rodriguez, A. V. Ensinas, M. Modesto, and S. A. Nebra. 2017. Reduction of process steam demand and water-usage through heat integration in sugar and ethanol production from sugarcane and evaluation of different plant configurations. Energy 138: 1263-80. [ Links ]

Plaza Castillo, J., C. Daza Mafiolis, E. Coral Escobar, A. Garcia Barrientos, and R. Villafuerte Segura. 2015. Design, construction and implementation of a low cost solar-wind hybrid energy system. IEEE Latin Am. Trans. 13: 3304-3309. [ Links ]

Quintella, C. M., M. M. Meira, S. Freire, N. da Costa, P. Ramos, G.G. de Souza, H. Bezerra, A. Sueli, M. Santana, and A. de Araujo Moreira. 2011. Brazilian potential for CCS for negative balance emission of CO2 from biomass energy. Energy Proc. 4: 2926-2932. [ Links ]

Radecka, D., V. Mukherjee, R. Q. Mateo, M. Stojiljkovic, M. R. Foulquié-Moreno, J.M. Thevelein. 2015. Looking beyond Saccharomyces: the potential of non-conventional yeast species for desirable traits in bioethanol fermentation. Nielsen, J. (ed). FEMS Yeast Res. 15(6): fov053. [ Links ]

Reyes, J., P. Quintana, C. Coronado, and A. Castro. 2016. Simulacion del proceso de produccion de bioetanol a partir de la mezcla glucosa/xilosa incluyendo los efectos de temperatura, pH y concentracion de azúcares. Rev. Mex. Ing. Quím. 15: 1-9 [ Links ]

Rofiqah, U., T. Widjaja, A. Altway, A. Bramantyo. 2017. Extractive fermentation of sugarcane juice to produce high yield and productivity of bioethanol. J. Physics Conf. Series 824: 12063. [ Links ]

Saxena, J., H. A. Makroo, and B. Srivastava. 2016. Optimization of time-electric field combination for PPO inactivation in sugarcane juice by ohmic heating and its shelf life assessment. LWT - Food Sci. Tech. 71: 329-338. [ Links ]

Scholz, M. J., M. R. Riley, and J. L. Cuello. 2013. Acid hydrolysis and fermentation of microalgal starches to ethanol by the yeast Saccharomyces cerevisiae. Biomass and Bioenergy 48: 59-65. [ Links ]

Schwab, A., K. Moriarty, A. Milbrandt, J. Geiger, and J. L. Nrel. 2016. 2013 Bioenergy Market Report (March). [ Links ]

Sheehan, G. J., and P. Greenfield. 1980. Utilisation, treatment and disposal of distillery wastewater. Water Res. Pergamon 14: 257-277. [ Links ]

Silva, M. A., N. P. Griebeler, and L. C. Borges. 2007. Uso de vinhaça e impactos nas propriedades do solo e lençol freático. Rev. Bras. Engen. Agríc. Ambiental. Dep. Eng. Agr. - UFCG / Cnpq, 11: 108-114. [ Links ]

Sivaramakrishnan, R., and A. Incharoensakdi. 2018. Utilization of microalgae feedstock for concomitant production of bioethanol and biodiesel. Fuel 217: 458-466. [ Links ]

Soccol, C. R. 1997. Biodegradation of cassava crude starch granules during solid state fermentation by Rhizopus glucoamylase. Arq. Biol. Tech. 40: 771-785. [ Links ]

Solomon, B. D., J. R. Barnes, and K. E. Halvorsen. 2007. Grain and cellulosic ethanol: History, economics, and energy policy. Biomass and Bioenergy 31: 416-425. [ Links ]

Srichuwong, S., J. Gutesa, M. Blanco, S. A. Duvick, C. Gardner, and J. L. Jane. 2010. characterization of corn grains for dry-grind ethanol production. J. ASTM Int. 7: 1-10. [ Links ]

Steen, E. J., Y. Kang, G. Bokinsky, Z. Hu, A. Schirmer, A. McClure, S. B. del Cardayre, and J. D. Keasling. 2010. Microbial production of fatty-acid-derived fuels and chemicals from plant biomass. Nature. Macmillan Publishers Limited. All rights reserved. 463: 559-562. [ Links ]

Sudhakar, M. P., R. Merlyn, K. Arunkumar, and K. Perumal. 2016. Characterization, pretreatment and saccharification of spent seaweed biomass for bioethanol production using baker’s yeast. Biomass and Bioenergy 90: 148-154. [ Links ]

Tanimura, A., M. Kikukawa, S. Yamaguchi, S. Kishino, J. Ogawa, and J. Shima. 2015. Direct ethanol production from starch using a natural isolate, Scheffersomyces shehatae: Toward consolidated bioprocessing. Sci. Reports 5: 95-93 . [ Links ]

Thai, C. C. D., H. Bakir, and W. O. S. Doherty .2012. Insights to the Clarification of Sugar Cane Juice Expressed from Sugar Cane Stalk and Trash. J. Agr. Food Chem. 60: 2916-2923. [ Links ]

Travaini, R., E. Barrado, and S. Bolado-Rodríguez. 2016. Effect of ozonolysis parameters on the inhibitory compound generation and on the production of ethanol by Pichia stipitis and acetone-butanol-ethanol by Clostridium from ozonated and water washed sugarcane bagasse. Biores. Tech. 218: 850-858. [ Links ]

U.S Energy Information Administration. 2016. Petroleum Supply Monthly. http://www.eia.gov/petroleum/supply/monthly/ (Accessed: September 2016). [ Links ]

U.S Energy Information Administration. 2017. Short-term Energy Outlook. (September 2017). [ Links ]

US Department of Energy. 2016. Alternative Fuels Data Center: Alternative Fueling Station Counts by State. http://www.afdc.energy.gov/fuels/stations_counts.html (Accessed: September 2016). [ Links ]

Uyazán, A. M., I. D. Gil, J. L. Aguilar, G. Rodríguez, and L. A. Caicedo. 2004. Deshidratación del etanol. Ing. Inv. 56: 49-59. [ Links ]

Wang, Z., H. Huang, E. G. De Mejia, Q. Li, and V. Singh. 2016. Use of pigmented maize in both conventional dry-grind and modified processes using granular starch hydrolyzing enzyme. AACC 93: 344-351 [ Links ]

Westfall, P. J. and T. S. Gardner. 2011. Industrial fermentation of renewable diesel fuels. Curr. Op. Biotech. 22: 344-350. [ Links ]

Wu, W. H., W. C. Hung, K. Y. Lo, Y. H. Chen, H. P. Wan, and K. C. Cheng. 2016. Bioethanol production from taro waste using thermo-tolerant yeast Kluyveromyces marxianus K21. Biores. Tech. 201: 27-32. [ Links ]

Xu, Y., J. Li, M. Zhang, and D. Wang. 2018. Modified simultaneous saccharification and fermentation to enhance bioethanol titers and yields. Fuel 215: 647-54. [ Links ]

Zegada-Lizarazu, W., and A. Monti. 2012. Are we ready to cultivate sweet sorghum as a bioenergy feedstock? A review on field management practices. Biomass and Bioenergy 40: 1-12. [ Links ]

Zhang, Q., Yan W., Hui H., and Chen W. 2018. Enhancing bioethanol production from water hyacinth by new combined pretreatment methods. Biores. Tech. 251: 358-363. [ Links ]

Received: May 2017; Accepted: March 2018

* Author for correspondence: labellop@ipn.mx

Creative Commons License Este es un artículo publicado en acceso abierto bajo una licencia Creative Commons