From nutritional standpoint, artemia is non — selective filter feeder, and eats algae, bacteria, protozoa and yeasts, as long as feed particles diameter is not over 50-70 pm. Artemia feed can be alive or dead in artificial culture system. Artemia can uses bacteria and protozoa as feed sources, which grow in artemia culture medium. This protozoa (such as; Candida, Rhodotorula) can also be directly swallowed by artemia. The best algae’s for artemia nutrition includes: Dunaliella salina, Spirulina and Scenedesmus. For artemia culture, agricultural products can be utilized such as; rice, corn, wheat, barley flours and their bran.

4. Reproduction

All bisexual species holds 42 chromosomes (2n = 42). A. persimilis holds 44 chromosomes (2n = 44) and Artemia partenogenic is diploid, triploid, tetraploid and even pantaploid. As a general rule, artemia populations are defined on the basis of the number of their chromosomes. However, contrary to mammalian, female artemia is heterogametic [3]. Artemia is produced by two ways: sexual and parthenogenesis (development of a new individual from an unfertilized egg). The mature female ovulates each 140 hours.

According to strain of artemia or method of living, it selects one of the following conditions; oviparous or ovoviviparous. In suitable situation of rising, reproduction trend is as larvae production (ovoviviparous) and in unsuitable situation of growth (salinity >50gm/lit and oxygen <5mg/lit) oviparous will occur. In the latter condition, growth of embryo will stop and enters diapauses. In suitable saline and nutritional conditions, females can produce 75 naplius each day and over its lift cycle (50 days), it reproduces 10-11 times.

In extreme hypoxia, due to increasing hemoglobin production, the color of artemia will change from light brown to yellow and then red.

Artemia cysts are spread by wind and birds. Earth pond or region of high salty water is suitable for culture and reproduction of artemia.

Crop profitability is the indicator for a farmer to decide what to grow and what and how much should be the energy inputs for growing that specific crop. Total cost of production in two farming systems and five varieties were showed that highest total cost of production in traditional system than semi-mechanized system and local varieties than breed varieties "Figure 11". The amount of higher consumption of human labor, chemical fertilizer, chemical poison and seed in traditional system lead to increasing total cost of production in this system in compared with semi-mechanized system. Also, because of suitable genetic specifications have higher operation in compared with local varieties. The suitable genetic specifications in breed varieties lead to reducing total cost of production in these varieties in compared with local varieties.

breed varieties than local varieties "Figure 12". Highest gross value of production with average of 11717 $/ha (semi-mechanized system) and 10311 $/ha (traditional system) observed in Gohar rice.

Net return in two farming systems and five varieties were showed that highest net return of semi-mechanized system than traditional system and breed varieties than local varieties "Figure 13". Highest net return with average of 9391 $/ha (semi-mechanized system) and 11239 $/ha (traditional system) observed in Gohar rice.

Productivity in two farming systems and five varieties were showed that highest productivity of semi-mechanized system than traditional system and breed varieties than local varieties "Figure 14". Highest productivity with average of 19.87 kg/$ (semi-mechanized system) and 9.09 kg/$ (traditional system) observed in Gohar rice.

Benefit to cost ratio in two farming systems and five varieties were showed that highest benefit to cost ratio of semi-mechanized system than traditional system and breed varieties than local varieties "Figure 15". Highest benefit to cost ratio with average of 11.21 (semi — mechanized system) and 24.51 (traditional system) observed in Gohar rice.

□ non-mechanized system I mechanized system

0

Figure 13. Net return in varieties rice production under traditional and semi-mechanized system condition

□ non-mechanized system ■ mechanized system

Khan et al. [17] with study energy requirements and economic analysis of wheat, rice and barley production in Australia showed that Cost of production on wheat crop was 323, rice 896 and barley was A$ 246 ha-1. Rice grower obtained the highest return of A$ 2088, as compared to wheat and barley growers, who obtained A$ 589 and 370 ha-1. Therefore, the benefit-cost ratio was the highest on rice farms (3.33) as compared to wheat (2.82) and Barley (2.50). It was concluded that increase in energy consumption at farm level increased yield of rice, hence the farmers with higher cost of production could get better return of their crop [16].

□ non-mechanized system I mechanized system

Figure 15. Benefit to cost ratio in varieties rice production under traditional and semi-mechanized system condition

4. Conclusion

Consider that breed varieties rice and semi-mechanized farming system are suitable case for increasing production of rice according to the limitation of rice fields of Guilan province (Iran). Identifying the way of developing and exploitation, energy indicators in agricultural section of Iran either in the light of having weak economical fundamentals or in the light of strict competition in global scene for obtaining better economical condition, helps that we lead our resources and facilities of our production in a direction that can obtain our suitable place in international occasions faster. According to the results of this research and studying the energy and economic analysis, we can say that the condition of the management of energy consumption in producing breed varieties (Khazar, Hybrid (GRH1) and Gohar (SA13)) are more suitable and according to the need of country about producing rice and limitation of energy sources which are mainly nonrenewable energy, producing breed varieties is a step towards sustainable agriculture.

4.1. Xylose fermenting yeast in natural environments of Ecuador

Lignocellulosic biomass is composed by mainly three different fractions of molecules: cellulose, hemicellulose and lignin. We have already talked about some applications for cellulose and lignin, mainly as ethanol and fuel biomass. Nevertheless, hemicellulose which is mainly composed of xylose, a five carbon sugar, is a very important and abundant source that accounts for 23% to 32% of the dry lignocellulosic biomass weight. This sugar can also be used for the production of ethanol as well as other valuable products.

As part of a survey in biodiversity in Ecuador, the CLQCA or Catholic University Yeast Collection has collected some isolates of yeast that exhibit fermentation skills when xylose and a Nitrogen base are mixed up in culture broths.

Xylose fermenting yeasts have been collected from different provinces of Ecuador, including the Galapagos Islands and the Amazonia. Nevertheless, none of these yeast isolates present high ethanol tolerance nor quick fermentation rates, which make these organisms not suitable for industrial processes. It can probably discourage someone to study natural occurring xylose fermenting yeasts, nonetheless, the genes involved in this physiological processes are still useful for metabolic engineering approaches.

As seen on table 4, only two strains of Schffersomyces (Pichia) stipitis are positive to ferment xylose. This yeast species has been reported to ferment xylose as will be seen further in this chapter.

In terms of ethanol production, there have been a lot of different approaches; in the last times the metabolic engineering of Saccharomyces cerevisiae was regarded as a suitable solution to ferment xylose, arabinose and other non-conventional sugars.

One example of this line of research is to be shown in the following scheme, where there are three different genes in charge of the transport, isomerization and phosphorylation in the process to ferment xylose. This construct has been designed at the Neotropical Center for the Biomass Research as part of the RESETA project. This genetic tool is very versatile and has been thought to be used as a genetic platform where to assay a wide variety of genes. The design of this construct was made by Carvajal et al. in 2011.

This genetic construction is being tested in laboratory conditions, integrated in industrial Saccharomyces cerevisiae. This first step forward to the metabolic engineering is expected to give new perspectives to the residual biomass transformation into valuable products in the context of biorefineries in Ecuador and worldwide.

K. L. Chin and P. S. H’ng

Additional information is available at the end of the chapter http://dx. doi. org/10.5772/51 198

1. Introduction

Rising fossil fuel prices associated with growing demand for energy, and environment concerns are the key factors driving strong interest in renewable energy sources, particular in biofuel. Biofuel refers to any type of fuel whose energy is derived from plant materials. Biofuel which includes solid biomass, liquid fuels and various biogases is among the most rapidly growing renewable energy technologies in recently. Biofuels are commonly divided into two groups based on the technology maturity which using the terms "conventional" and "advanced" for classification. Conventional biofuel technologies include well-established processes that are already producing biofuels on a commercial scale. These biofuels, commonly referred to as first-generation, include sugar — and starch-based ethanol, oil-crop based biodiesel and straight vegetable oil, as well as biogas derived through anaerobic digestion. First generation biofuel processes are useful but limited in most cases: there is a threshold above which they cannot produce enough biofuel without threatening food supplies and biodiversity. Whereas, advanced biofuel technologies are extensions from conventional technologies which some are still in the research and development (R&D), pilot or demonstration phase and they are commonly referred to as second — or third-generation. This category includes hydrotreated vegetable oil (HVO), which is based on animal fat and plant oil, as well as bioethanol based on lignocellulosic biomass, such as cellulosic-ethanol. Although there are wide varieties of advanced biofuels conversion technologies exists today, but they are not commercially available yet. Nevertheless, the most commercializable technology and most used biofuel on the global market is bioethanol.

The organosolv process is a unique and promising LCF fractionation. Using organosolv, lignocellulosic biomass can be converted into cellulosic fibres, hemicellulose sugars and low molecular weight lignin fractions in one-step fractionation [111-113]. Organosolv fractionation is the process to using organic solvents or their aqueous solutions to remove or decompose the network of lignin from lignocellulosic feedstocks with varying simultaneous hemicellulose solubilisation [114]. In this process, an organic or aqueous organic solvent mixture with or without an acid or alkali catalysts is used to dissolve the lignin and part of the hemicellulose, leaving reactive cellulose in the solid phase [106, 115-117]. Usually, the presence of catalyst can increase the solubilisation of hemicellulose and the digestibility of substrate is also further enhanced [118]. Comparing to other chemical pre-treatments the main advantage of organosolv process is that relatively pure, low molecular weight lignin is recovered as a by-product [119]. Organic solvents are always easy to recover by distillation and recycled for fractionation; the chemical recovery in organosolv fractionation processes can separate lignin as a solid material and carbohydrates as syrup, both of which can be used as chemical feedstocks [112, 120, 121]. A variety of organic solvents have been used in the organosolv process such as ethanol, methanol, acetone, ethylene glycol, triethylene glycol, tetrahydrofurfuryl alcohol, glycerol, aqueous phenol, aqueous n-butanol, esters, ketones, organic acids, etc [117, 119, 122]. For economic reasons, among all possible solvents, the use of low-molecular-weight alcohols with lower boiling points such as ethanol and methanol has been favoured [123].

the residual solvents may be inhibitors to enzymatic hydrolysis and fermentation [106], and they should be recycled to reduce operational costs. Otherwise organic solvents are always expensive, so it should be recovered as much as possible, but this causes increase of energy consumption.

The organosolv fractionation seems more feasible for biorefinery of lignocellulosic biomass, as it considers the utilization of all the biomass components. However, there are inherent drawbacks to the organosolv fractionation. In order to avoid the re-precipitation of dissolved lignin, the fractionated solids have to be washed with organic solvent previous water washing, the cumbersome washing processes means more cost. In addition, organosolv fractionation must be performed under extremely tight and efficient control due to the volatility of organic solvents. No digester leaks can be tolerated because of inherent fire and explosion hazard [121]. Its successful commercialization will depend on the development of high-value co-products from lignin and hemicelluloses [124].

Werther Guidi, Frederic E. Pitre and Michel Labrecque

Additional information is available at the end of the chapter http://dx. doi. org/10.5772/51 11 1

1. Introduction

The production of energy by burning biomass (i. e. bioenergy), either directly or through transformation, is one of the most promising alternative sources of sustainable energy. Contrary to fossil fuels, bioenergy does not necessarily result in a net long-term increase in atmospheric greenhouse gases, particularly when production methods take this concern into account. Converting forests, peatlands, or grasslands to production of food-crop based biofuels may release up to 400 times more CO2 than the annual greenhouse gas (GHG) reductions that these biofuels would provide by displacing fossil fuels. On the other hand, biofuels from biomass grown on degraded and abandoned agricultural lands planted with perennials do not have a negative effect on carbon emissions [1]. In addition, when properly managed, bioenergy can enhance both agricultural and rural development by increasing agricultural productivity, creating new opportunities for revenue and employment, and improving access to modern energy services in rural areas, both in developed and developing countries [2].

Biofuels constitute a very broad category of materials that can be derived from sources including municipal by-products, food crops (e. g. maize, sugar cane etc.), agricultural and forestry by-products (straws, stalks, sawdust, etc.) or from specifically-conceived fuel crops. Our analysis focuses on agricultural biofuel crops that can be grown in temperate regions. These crops can be divided into four main categories (Table 1).

Oilseed crops have long been grown in rotation with wheat and barley to produce oil for human, animal or industrial use. Today, these crops primarily provide feedstock for biodiesel. Biodiesel is produced by chemically reacting a vegetable oil with an alcohol such as methanol or ethanol, a process called transesterification. Cereals and starch crops, whose main economical use is for food and fodder, can also be transformed to produce biofuels. For example, the starch in the grains of maize (Zea mays L.), wheat (Triticum aestivum L.) and

Category Common Botanical name Habit Crop life Main

name cycle destination

sorghum (Sorghum bicolor (L.) Moench) can be converted to sugars and then to ethanol by traditional fermentation methods for use in transportation and other fuels (e. g. bioethanol). These crops may also be used to produce biogas, composed principally of methane and carbon dioxide produced by anaerobic digestion of biomass. These energy crops have the advantage of being relatively easy to grow. Most are traditional agricultural crops and are easy to introduce at the farm level since they do not require particularly cutting-edge technological equipment. However, using food crops as a source of bioenergy raises serious issues related to food supply and costs, and consequently has been under increasing criticism from the scientific community and society. In particular, the use of these crops for bioenergy competes directly with their use as food. In addition, since many of these crops are annuals, they require large energy inputs and fertilizer for establishment, growth and management, and thus in the end result in minimal energy gains. For such reasons, these crops may not be efficient either for achieving energy balances or for reducing greenhouse gas emissions.

The category of dedicated energy crops notably includes all lignocellulosic (mostly perennial) crops grown specifically for their biomass and used to produce energy. Such crops include herbaceous (e. g. miscanthus, switchgrass, reed canary grass, etc.) and woody (willow, poplar, eucalyptus) species that have been selected over the past decades for their high biomass yield, high soil and climate adaptability, and high biomass quality. In addition, especially if grown on marginal arable lands, they do not compete directly for use for food [3], do not require large amounts of inputs in terms of annual cultivation and fertilizer applications [4], nor involve the destruction of native forests with severe negative effects on carbon sequestration [5] and biodiversity [6-7].

We shall limit our description to woody species, because they constitute the focus of our research.

Woody crops for energy production include several silvicultural species notably sharing the following characteristics: fast growth and high biomass yield, potential to be managed as a coppice and high management intensity (highly specific needs with regard to fertilization, irrigation, etc).

A recent review of the literature revealed that about ten different terms are used to refer to the silvicultural practice of cultivating woody crops for energy production: short-rotation woody crops, short-rotation intensive culture, short-rotation forestry, short-rotation coppice, intensive culture of forest crops, intensive plantation culture, biomass and/or bioenergy plantation culture, biofuels feedstock production system, energy forestry, short-rotation fiber production system, mini-rotation forestry, silage sycamore, wood grass [8]. The same author suggested adoption of standard terminology based on an earlier work [9] that had defined this cropping system as "a silvicultural system based upon short clear-felling cycles, generally between one and 15 years, employing intensive cultural techniques such as fertilization, irrigation and weed control, and utilizing genetically superior planting material", to which he proposed to add "and often relying on coppice regeneration", since most species used are able to sprout following harvest. The term coppice refers to a silvicultural practice in which the stem of a tree is cut back at ground level, allowing new shoots to regenerate from the stump.

The early growth rate of coppice sprouts is much greater than that of seedlings or cuttings and in this way trees managed as coppice are characterized by remarkably fast growth and high biomass yield [10-11]. The main species under this cultivation regime in temperate climates are poplar (Populus spp) [12], willow (Salix spp) [13] and eucalyptus (Eucalyptus spp.) [14], and to a lesser extent, black locust (Robinia pseudoacacia L.) [15] and alder (Alnus spp.) [16]. All of these species, which are cultivated for biomass production in a specific region, are fast-growing under local conditions, cultivated in dense stands (to take maximum advantage of available nutrients and light, resulting in maximum growth), harvested after short rotation periods (usually between 2-8 years), and coppicable (thus reducing establishment costs). In addition, willows and poplars demonstrate ease of vegetative propagation from dormant hardwood cuttings, a broad genetic base and ease of breeding. These characteristics make them ideal for growing in biomass systems and facilitate clonal selection and ensure great environmental adaptability [17].

Biosorption is a rapid phenomenon of passive metal sequestration by the non-growing biomass. To carry out the studies of metal biosorption in a continuous system is conditioned first a reactor column, which has side ports for sampling. The reactor is packed with carrier material of biomass with a particle size between 1 and 6 mm, to avoid clogging. Both mineral medium such as air are fed through the bottom of the reactor to promote the growth of bacteria and the pH is controlled if the metal to be studied could precipitate at neutral pH. The mineral medium is inoculated with 10% biomass that develop in this medium for the time given the growth kinetics and the reactor is kept in recirculation until the development of biomass (1 g/L) and that adheres to support material. Biomass concentration was estimated by measuring the percent of transmittance to an optical density at 600 nm (Spectronic 20D+) and for the amount of biomass produced in cells/mL was determined using the Table 2 of McFarland nephelometer, described above.

When produced in the reactor is 1 g/L of biomass and this is immobilized in the zeolite, are set constant conditions of operation of the reactor as: air flow 10 times the feed flow of the contaminated medium, hydraulic retention time (HRT) of a day and ambient temperature of 30 °C. The tests are performed to set conditions of initial concentrations of metals and pH set, and takes days to the input samples at different heights of the reactor and output to meet the metal concentration, biomass is recycled to make more time contact between the bacteria and the metal being studied. It can be perform a second and third experimental run at different initial concentrations of feeding and at the same pH, maintaining the feed stream and recirculation same. Other studies may be changing the pH, keeping other conditions constant.

In the experimental runs carried out is analyzed for pH, metal concentration by atomic absorption and to determine the concentration of cells/mL of biomass, measures the percentage of transmittance in the spectronic 20D+ and compared by the technique of Nephelometer of Mc Farland. The support used is analyzed by the technique of sludge digestion, are performed analyzes of biomass produced per day and chemical oxygen demand (COD). At the end of the experiments are performed technical analyses of the medium used X-ray Diffraction (XRD), scanning electron microscopy (SEM) and Energy Dispersive Spectroscopy X-ray (EDS) at different column heights to see if deposited on the support certain amount of heavy metals or all was absorbed by the biomass.

The FAO (1995, 2005) is involved in the task of recording the world statistics of food production and often publishes assessments accounting for the status of world fisheries (FAO 1995, 2005; Froese and Pauly 2012). The catch records are grouped by statistical regions subdivided in 17 sub regions and in the following paragraphs, some highlights on the current status of the fisheries of these regions and sub regions is given, as well as some rough estimations of the biomass on which the exploitation of fish resources is based.

2.1.1. The Atlantic

decrease in biomass of 6 million mt in the last three years (Table 1). In Fig. 2B, the maximum catch of the Atlantic Eastern Central is displayed, and corresponds to 3.7 M mt, attained in the year 2000; this figure corresponds to a biomass of 7.4 M mt, but at the end of the period displays an increase of 100,000 mt. In the Atlantic South eastern, the maximum yield was obtained in the early eighties, with 2.7 M mt (Fig. 2C); the corresponding biomass is 5.4 M mt, with a significant decrease in biomass during the last three years to only 2.6 M mt. The catch trend of the Atlantic North western (Fig. 2D) is declining, with a maximum of 3.5 M mt attained in the early seventies; to this figure corresponds a biomass of 7 M mt (Table 1). The low biomass estimated for the years 2008-2010, with somewhat more than 4.8 M mt, is something to be concerned. The catch trend of the Atlantic South western (Fig. 2E) is not very clear, because it seems to attain a maximum followed by a decline, but the projection of the regression line suggests that the maximum yield will be reached until the year 2030 with

Figure 2. Trend of total catches extracted from several regions of the Atlantic in the period 1950 — 2010. A. Atlantic north eastern; in this region the maximum catches were obtained in the late eighties. B. Atlantic eastern central; the maximum yields were obtained around the year 2000. C. Atlantic south eastern; the maximum yield was obtained in the early eighties. D. Atlantic north western; the maximum yield was obtained by the year 1970, with a declining trend afterwards. E. Atlantic south western. It is not clear whether the maximum yield was attained by the early 2000 s, or it still may grow to a maximum near the year 2030. In the Gulf of Mexico, whose data are included in those of Fig. 2.E, more than 60 species caught and recorded in the statistics, are included in this analysis; here, the MSY was attained in the middle 80s.

2.65 M mt. The corresponding biomass will be 5.3 M mt (Table 1); the stock current biomass is 3.68 M mt. It was possible to examine with some detail the catch trend of the Gulf of Mexico (Fig. 2F), whose values are part of those for the Atlantic South western; in this case, the maximum yield was obtained in the late eighties with 800,000 mt, with a corresponding biomass of 1.6 Million mt; the current biomass is only 1.1 M mt. The global MSY for the Atlantic Ocean is 24.15 M mt, corresponding to a biomass of 48.3 M mt but these values do not correspond to the same year; unfortunately in all cases but one, current yields were left behind and the current biomass is considerably lower than the figures provided. The current biomass estimated for the Atlantic Ocean amounts to 35.78 M mt (Table 1).

Non-sterilized medium (NSM) was fed to S1 and S2 continuous cultures and the aeration rate was gradually increased from 0 to 0.02 vvm. For these experiments, pH was controlled at 4 for S2 strain and not controlled for S1 strain. Ethanol production increased significantly (P < 0.05) as the aeration rate increased during S1 fermentations fed with SM or NSM. In contrast, aeration did not have any effect on ethanol or biomass production during the S2 fermentation fed with NSM (Figure 10-B). For S1 continuous fermentation, medium type (SM or NSM) did not show a significant difference in the production of ethanol (P > 0.05), but it had a significant difference in the production of biomass (P < 0.05). Multiple range tests divided S1 fermentations in aerated (0.01 and 0.02 vvm) and non-aerated systems, indicating higher biomass and ethanol productions in aerated cultures. Nevertheless, no significant difference was found in the productions of biomass or ethanol (P > 0.05) between experiments aerated at 0.01 and those aerated at 0.02 vvm. These results could be attributed to the lower pH (2.3) observed at 0.02 vvm, which could have reduced cell viability. Interestingly, S1 strain flocculation was not observed for 0.02 vvm and biomass retention time was lowered, decreasing the cell population (Figure 10-B).

For all the fermentation conditions, the consumption of reducing sugars was significantly augmented (P < 0.05) as aeration rate increased, reaching 4 ± 2 g L-1 of residual reducing sugars at 0.02 vvm for both medium types. It has been reported that more than 12% of total sugars contained in agave juice are non-fermentable, since fructans hydrolysis is not complete during the cooking step. In this study, oligosaccharides might be taken into account as residual reducing sugars, because they are difficult to degrade by S. cerevisiae.

S2 continuous fermentations were divided by the multiple range test, according to the aeration rates (0, 0.01 and 0.02 vvm), showing an increase in the fermentative capability of the S2 strain as aeration increased. The type of medium led to a significant difference (P < 0.05) in ethanol and biomass production. Nevertheless, no significant differences (P > 0.05) were found in the consumption of reducing sugars between both types of medium. Higher biomass and ethanol production was observed during SM fermentations. Differences between cultures with different types of medium (NSM and SM) could not be attributed to changes in medium composition during sterilization (121 .C, 15 min), since the cooking of agave heads is a more aggressive treatment (100 .C, 36 h). Furthermore, Maillard reactions during the heating are not favored since agave juice nitrogen source content is low (Table 3). Work is ongoing to answer this phenomenon; however, those changes could be attributed to a possible contamination of wild yeast carried by the non-sterilized agave juice. Nevertheless, microscopy did not show any bacterial contamination for fermentation of either strain. Moreover, the pH during S2 continuous fermentation was controlled at 4 for all the experimental conditions in comparison to S1 fermentation, which was not controlled

and reached lowered pH values, which could have limited the microbial contamination. In addition, compared to S2, the capacity of S1 to flocculate could be an advantage for this strain to be retained longer inside the bioreactor. Several studies have proved the capability of inoculated S. cerevisiae strains in continuous fermentations to resist contamination by wild yeast. Cocolin et al. showed by molecular methods that the starters strain was able to drive the fermentation until the end of the process (12 days). On the other hand, de Souza Liberal et al. identified Dekkera bruxellensis as the major contaminant yeast, even though its growth rate is lower than that of S. cerevisiae in batch fermentations. They indicated the possibility that D. bruxellensis grows faster than S. cerevisiae in a continuous culture under certain conditions.

5. Conclusion

Agave plants could be a viable alternative as an accessible raw material for bioethanol production, since high concentration of fermentable sugar is released when agave plant fructans is cooked and/or hydrolyzed. This mixture of sugars, mainly fructose, could be converted into ethanol by microorganism action.

The present study examined the use of batch and continuous fermentation processes for investigating bioethanol production from Agave tequilana Weber var. azul. juice.

The fermentable sugars of agave juice fermentation in batch culture were depleted between 18-24 hours by indigenous tequila S. cerevisiae strains. The ethanol productivity obtained in batch fermentation was 2.36, 2.42 and 1.66 g/Lh for S1, S2 and S3 yeast strains respectively. Agave juice continuous fermentation was examined for increasing ethanol productivity in the fermentation process. For this, a chemostat system was used for investigating the impact of the dilution rate, pH value, nitrogen and phosphorus source addition, micro-aeration and non-sterilized medium on growth, sugar consumption and ethanol production of two S. cerevisiae strains. The dilution rate and nutrient addition have a significant impact on the physiology of the S. cerevisiae yeast strains. When S1 and S2 yeast strains are used in continuous cultures, they show low sugar consumption at D>0.08h-1. The study revealed a nutritional limitation on the agave juice, which was corrected by adding of nitrogen sources and oxygen, achieving S. cerevisiae S1 strain complete sugar consumption with high ethanol conversion at 0.08h-1. The pH did not have a significant effect on the fermentative capability of S. cerevisiae S1 strain at the levels studied. Uncontrolled pH fermentations naturally reached acid values (pH «2.5 ± 0.3), which is advisable, since bacteria or yeasts contamination could be limited. The type of agave juice tested (SM and NSM) did not have a significant effect on ethanol production in S1 cultures, but did have an effect on ethanol production in S2 cultures. These results could be attributed to the higher pH fermentation during S2 continuous cultures, which could have favored the proliferation of contaminant wild yeasts. The ethanol productivity obtained in S1 strain agave juice continuous fermentation process was 3.6 g/Lh. Thus, the ethanol productivity in continuous fermentation is higher, 34.4% more than in S1 strain batch fermentation.

These results showed the possibility of performing agave juice fermentations in continuous

culture feeding non-sterilized medium and taking advantage of the possible improvements

that continuous fermentations and agave plant could offer to the bioethanol industry, such

as high productivity with full sugar consumption.

Brown coal or lignite is a low rank with high moisture content of around 60 %, low heat value and high oxygen content. Therefore, it is hard to use for converted to useful energy. However, it is concluding many outstanding features such as less ash and sulfur content, and especially, including abundant of oxygen-containing functional groups such as carboxyl and phenol groups which are available for ion-exchange with metals. The structural unit of coal models is shown in Figure 4d.