Result of "Table 16" (balance energy indices) showed that between paddy yield, straw yield, husk yield and biomass yield with production energy and production energy to consumption energy ratio have a positive and very significant correlation, also between paddy yield, straw yield, husk yield and biomass yield with consumption energy to production energy ratio energy intensity a negative and significant correlation in probability level of 1% were recorded.

Result of "Table 17" (energy indices) showed that between paddy yield, straw yield, husk yield and biomass yield with input energy, output energy, energy ratio, energy productivity, net energy gain and water and energy productivity have a positive and very significant correlation, also between paddy yield, straw yield, husk yield and biomass yield with energy intensity a negative and significant correlation in probability level of 1% were recorded.

Cellulose is the most abundant carbohydrate polymer in the planet. This remarkable molecule is composed by monomers of glucose linked up by glycosidic (p 1—4) boundaries that provides this molecule with the capacity of forming linear, fibrous shapes of straight chains. These simple chains are joined by hydrogen bonds, provoking the formation of resistant and strong fibers which are the main components of plant cell walls.

abundant in nature has developed certain enzymes groups that allow them to decompose the glycosidic links and use the released glucose contained in cellulose. Thus, cellulose is recycled very efficiently in nature, sustaining the carbon equilibrium in biosphere, which relies fundamentally in anabolic and catabolic cycles of cellulose, where microbes play a main role.

Cellulose is formed during photosynthesis, where CO2 and the energy from the sun are taken by plant cells, where this transformation takes place. Cellulose naturally is a structural molecule synthesized by plants to allow them to grow. Glucose is also a fuel molecule in as much as the bonds are in the a configuration, thus forming fuel reserve molecules such as amylose and amylopectin, both molecules components of starch.

Cellulose recycling in nature is in the order of 1015 kg per year [1]. This number is so high that we could make enough fuel ethanol to supply 100 times the energy requirements of the entire world in a rampant development scenario projection for 2035 [2]. In other words, we may probably need "only" 1 per cent of the cellulose synthesized by plants in one year, so we can have enough liquid fuel to run our vehicles and industries. In this calculation, it is not taken into account the biogas (to run power plants) and biofertilizers (to return minerals to soil) production if all the ethanol from cellulose were produced within biorefineries. If humankind had the technology, cultural and economic conditions to efficiently pick this cellulose up, we may probably reach the sustainable and clean environmental goals for future. Nevertheless, this utopia is not yet possible in current historical conditions, so we need to focus on much less ambitious objectives, such as the recovery and technological transformation of agricultural feedstocks and industrial leftovers. Figure 1 shows the crude oil we’ll need in 2035. The amount is very impressive, that is 110 million barrels crude per day to keep running our industrial and mobilization needs.

Before the worldwide petroleum reserves are depleted, humankind must change the energetic matrix based on oil and look for sustainable and clean sources to produce fuels. An analysis made by Bruce Dale from the Department of Chemical Engineering and Materials Science at Michigan State University (USA), show a clear disadvantage in terms of energy input of gasoline production compared to first and second generation ethanol (Table 1). In this scenario, the issues are not necessarily lying on the economic or technical feasibility of the conversion processes, but in political and ethical issues.

The energy input to produce gasoline is 0.19 times higher than the energy harvested; the GHG emission are the highest (94 kg/MJ). The cellulosic ethanol case exhibits a much higher energy output than the energy required to produce it. Moreover, GHG emissions are much lower than gasoline case (11 kg/MJ). In the case of corn ethanol the energy balance is still positive even though the margin remains narrow.

Lignocellulose is an element of the plant cell wall, and it majorly composes of hemicellulose, cellulose and lignin.

Lignin is a natural complex polymer and the chief noncarbohydrate constituent of wood binds to cellulose fibers providing mechanical strength and structural support of plants where it can be found extensively in the cell walls of all woody plants. Lignin is the most abundant natural source after cellulose, and between 40 and 50 million tons of lignin per annum are produced worldwide [30], constituting one-fourth to one-third of the total dry weight of trees. As the chemical composition of lignin has a certain variation, it is not possible to define the precise structure of lignin.

Due to the mechanical strength of lignocellulose supported by lignin, lignocellulose is known to be recalcitrant carbon pools. Lignocellulose is very slowly bioconvertible in anaerobic environments due to its rigid structure, as lignin is non-degradable [31] and the lignin suppresses degradation of lignocellulosic fibers such as hemicellulose and celluloses [10]. For this reason, it is often pointed out as the main cause of low BM in plant biomass. Many studies reported that lignin content and the efficiency of enzymatic hydrolysis have an inverse relationship. [23,29,32] In this text, pretreatment of substrate to increase biogas productivity usually focuses on improving hydrolysis by releasing lignocellulosic bindings, occasionally degrading lignin polymers. To the contrast of the critical role of lignin for anaerobic digestion, a larger amount of lignin is preferable to obtain energy from combustion, as higher heating values of biomass positively correlate with lignin content [33,34]. The higher heating value is the absolute value of the specific energy combustion, when solid biofuel burns in oxygen in a calorimetric bomb under specific conditions.

Lignocellulose is namely most abundant for plant biomass, likewise it’s often called lignocellulosic biomass. High concentration of lignocellulose can also be found in animal slurry, since animals are fed plants i. e. grass, straw, etc. Bruni et al.[35] reported that the concentration of lignocellulose in DM ranged 40-50%. Lignocellulose in animal slurries has different characteristics compared to plants, whose structure is broken down during animal digestion. The concentrations of each lignocellulosic fibrous fraction are shown in Figure 7.

Lignocellulose fraction in VS in animal slurry ranged 30 — 80%. Relatively lower lignocellulose was found in pig and mink slurry, whereas it was higher for cow slurry, which seems to be due to a different animal diet. The concentration of lignin in VS for most animal slurries was larger than 10% except for pig fattening slurry. Within the pig slurry, the lignin was highest for sow slurry. In detail, lignin was 8.6(±6.0)% for piglet, 4.8(±5.5)% for fattening pig, 12.5(±1.2)% for sow and 10.6(±1.1) for mixture of sow and piglet slurry, respectively. In case of cow manure, dairy cow had most abundant lignin at 18.0 (±2.1)%, whereas cattle and calf contains 13.1(±2.1)% and 10.1(±2.2)%, respectively. The concentration of lignin in mink slurry was 10.8%. The concentration of hemicellulose was similar to the lignin concentration, ranging 8.1% to 26.3%. However, the larger amounts were found in the slurry of young animals and in pig slurry, whereas high concentration of lignin was found cow in manure. The highest concentration of lignocellulose in VS with larger amount of cellulose and lignocellulose of calf slurry seems to be due to straw used for the bedding materials. In case of mink slurry, as can be seen in figure 6, the concentration of lignocellulose in VS and distribution of each fibrous fraction is similar to piglet slurry. The results of lignocellulose charaterisation and BMP clearly demonstrate that pattern of inverse relationship between lignin and BMP, which is in accordance to literatures [10,23,29,32].

In case of plant biomass, Triolo et al. [36] reported lignocellulose concentration in VS to be in the range of 49.0 — 82.8%, and lignin concentration in VS was 3.6 — 10.5% for grass and crop residues, whereas the concentration of lignin was larger for woody biomass, that is, 13.9 — 24.0%. In comparison with lignocellulosic characteristics of plant biomass from Triolo et al. [36], the concentrations of lignocellulose seem to be at approximately the same level, except pig fattening slurry. It is interesting that lignin of grass and pig slurries are relatively similar while the concentration of lignin in cow manure seems to be close to woody biomass to some extent. These results seem to be because lignin in straw and grass, which is cow diet, is up-concentrated up to the level of woody biomass, while relatively easily degradable organic pools are degraded. This result highlights that cow manure has critically high concentration of lignin that is the same level with woody biomass which is known as critical digestibility. Likewise, the difference between lignin and lignocellulose concentrations between pig and cow slurry seems to be more dependent on animal diet than management method, except calf manure.

Acetic acid, at present, most demand of the commercial acetic acid is met synthetically. The production involves fermentation by a species of Acetobacter, which converts ethanol to acetic acid with a small final concentrations percentage (4-6%), using almost exclusively for vinegar production. In commercial practice, the actual yield roughly 75-80% of the theoretical yield [5].

Ferulic acid, as a precursor for numerous aromatic chemicals used in the chemistry industry, can be produced from lignocellulosic feedstock [88].

Levulinic Acid, Formic Acid and Furfural, their biorefinery process usually involves the use of dilute acid as a catalyst but it differs from other dilute-acid lignocellulosic — fractionating processes in that free monomer sugars are not the product. Instead, these monosaccharides are converted into the platform chemicals levulinic acid and furfural as the final products by multiple acid-catalysed reactions [103].

Based on the above single distillation experiments, a multiple molecular distillation experiment was carried out to further evaluate the separation characteristics of bio-oil (Guo et al., 2010b). The feed bio-oil, which was pre-treated by centrifugation, filtration, and vacuum distillation, was firstly distilled at 80 °C and 1600 Pa to obtain the distilled fraction 1 (DF-1) and the residual fraction 1 (RF-1). A part of RF-1 was then further distilled at 340 Pa to obtain DF-2 and RF-2 fractions. In the multiple distillation process, the distilled fraction yield of each distillation process was about 26 wt%. The amounts of water in RF-1 and RF-2 were greatly reduced. The RFs from the two processes had higher heating values than the feed bio-oil or DFs. The acid content was 11.37 wt% in the feed bio-oil, while it was 17.36 wt% for DF-1, nearly four times higher than that in RF-1 (4.56 wt%). In the second process, the acid content of RF-2 was further reduced to 1.38 wt%. The content of monophenols in RF-1 was 36.24 wt%, about twice that in DF-1 (18.02 wt%). Sugars showed non-distillable character in the two distillation processes, and no amounts could be detected in the DF.

In order to gain a deeper insight into the bio-oil distillation properties, Guo (Guo et al., 2010b) proposed a separation factor to evaluate the separation characteristics. The separation factors of acetic acid and 1-hydroxy-2-propanone were approximately 0.9, implying that they could be mostly distilled off. 2-Methoxyphenol, phenol, 2(5H)-furanone, and 2-methoxy-4-methylphenol, the separation factors of which ranged from 0.61 to 0.74, proved to be difficult to separate effectively. Higher molecular weight compounds, such as 3-methoxy-1,2-benzenediol, 4-methoxy-1,2-benzenediol, and 1,2-benzenediol, were very difficult to distil, having separation factors close to zero.

The construction of bioreactors is based on a simple principle: make the pollutants are converted into the substrate (food) of microorganisms, and that these, while feeding and increases its population, decontaminated water. For the construction of a bioreactor is necessary to know the type of microorganisms with which they are going to work and as well as the growth curve characteristic of them [5].

The key factor of a bioreactor is to maintain microorganisms in the growth stage most of the time as possible, i. e. keep the microbial population to its maximum level, to optimize the efficiency of the degradation processes. This is achieved by controlling the environmental conditions (temperature, pH, aeration and nutrient availability) and the flows in and out, so never lack food and do not reach the death phase or endogenous [2, 5].

The teams that are made homogeneous reactions can be of three general types: discontinuous (batch), continuous flow steady and unsteady flow semicontinuous.

Batch reactors are simple to operate and industrially used when small amounts are to treat substance. Continuous reactors are ideal for industrial purposes be treated when large quantities of substance and can achieve good control of product quality. Semicontinuous reactors are more flexible systems, but more difficult to analyze and operate than previous; in them the reaction rate can be controlled with a good strategy at the dosage of the reactants [48].

In a perfect batch reactor there is no entry or exit of reactant. It is further assumed that the reactor is well stirred, i. e. that the composition is the same at all points of the reactor for a given time instant. Since the input and output are zero the material balance is:

All points have the same composition; the volume control to perform the balance is the entire reactor. Evaluating the terms:

dt

And given that: Na = Nao(1 — Xa) results:

dXA

rAV = NA0

dt

Integrating gives the equation for the design for the batch reactor:

If the reaction volume remains constant may be expressed in function of the concentration of reagent Ca = Na / V

This intermittent or batch reactor is characterized by the variation in the reaction’s degree and the properties of the reaction mixture with the lapse of time [49]

A batch reactor has no inflow or outflow reagents of the reaction products while being performed. In almost every batch reactors, the longer that a reactant in the reactor, most of it becomes product to reach equilibrium is exhausted or the reagent [50].

The reactor of the continuous flow type, in which the degree of reaction can vary with respect to the position in the reactor, but not a function of time. Therefore, one of the classifications of the reactors is based on the operation method [49].

Normally, the conversion increases with time that the reagents remain in the reactor. In the case of continuous flow systems, this time usually increases with increasing reactor volume; therefore, the conversion X is a function of reactor volume V [50].

The tubular reactor plug flow (RTFP) is characterized in that the flow is directed, without any element of the exceeding or being mixed with any other element located before or after that, i. e. no mixing in the flow direction (axial direction). As a result, all fluid elements have the same residence time within the reactor [48].

As fluid composition varies along the reactor, material balance must be performed in a differential volume element transverse to the direction of flow.

The recirculation ratio is defined:

r = flow which is recycled
flow out

Raising the design equation for the reactor (within the recycle loop) without expansion

If its considers that there is no expansion or contraction in the reactor, raising the junction of the inlet and the recirculation Vt = (R + 1) Vo and furthermore Ca1 = (Cao + CAf) / (R + 1),

therefore the equation of reactor design is:

Another classification relates to the shape. If a laboratory vessel is equipped with a stirrer efficient, composition and temperature of the reaction mass will tend to be equal in all areas of the reactor. A container in which there is uniformity of properties is called a stirred tank reactor (or well mixed) or STR [48].

Nearly 0.3% of solar energy incident on the sea surface is fixed by phytoplankton the tiny plant organisms suspended in natural waters, over the 40-60 meters of the upper water column, accounts to 75% of primary productivity of an area of the word oceans near to 3.51014 square meters; the remaining 25% is produced by macro algae. The amount of biomass of all the consumers is based upon primary production by phytoplankton, which range between 0.05 — 0.5 gCm-2d-1, but in some very productive upwelling zones or in some grass beds, it can be as high as 5 gCm-2d-1 (Russell-Hunter 1970; Margalef 1974; Cushing and Walsh 1976). As a result of this photosynthetic process, the carbon gross production of the sea amounts to 15.5 x 1010 mt of Carbon per year, equivalent to a net production of 1.5 x 1010 mt, most of it in shore waters. By having in mind the energetic efficiency, these figures amount to 8 per cent of global aquatic primary production (Pauly and Christensen 1995; Friedland et al. 2012), meaning that there is a maximum limit to fisheries production.

Biological production through the fixation of light is a process interacting with the degradation or dissipation of energy by all organisms; in other words, the persistence of life as we know it, depends on a permanent input of energy, which after being fixed and transformed in chemical energy by the plants, is dissipated constantly by all organisms on Earth. Human beings have been able to simplify the food webs channelizing the production

of a few species which are exploited by man; agriculture systems are a typical example of this process. However, this implies a limit to the maximum potential production of biomass by organisms (Pauly and Christensen 1995; Friedland et al. 2012; Botsford 2012).

Agave juice bioethanol production from involves multiple steps: at harvest, fermentable sugars are obtained from heads of the agave plant by steaming, milling and pressing. During the steaming process, the polysaccharides (fructans) are hydrolyzed into a mixture of sugars consisting of fructose mainly. After fermentation, the alcohol from the must is purified by distillation and dehydration for obtaining anhydrous ethanol.

Alcoholic Fermentation is one of the most important stages in the bioethanol process, as sugars (mainly fructose) are transformed into ethanol and CO2. Agave juice can be fermented by inoculation (with selected microorganisms) or spontaneously (without inoculums). Significant differences were observed between fermentation conducted with controlled microorganism or inoculated media and spontaneous or no inoculated media. The introduction of selected strains allows fermentation to be regulated and accelerated. Inoculation of culture media with starter cultures allows a high population of selected strain, thereby assuring it dominance. The results are quicker ethanol synthesis, shorter fermentation time, and higher productivity.

Knowledge of physiological behavior of indigenous tequila yeast used in the agave juice alcoholic fermentation process for obtaining bioethanol is still limited. The raw material and physiochemical and biological conditions have significant impact on the productivity fermentation process. For these reasons, a better knowledge of the physiological and metabolic features of these yeasts in agave juice fermentation is required. A study of bioethanol production from Agave tequilana Weber var. azul juice fermentations is presented below. For this, the alcoholic fermentation of Agave tequilana Weber var. azul juice was carried out in batch and continuous modes of fermentation process.

a. Agave tequilana Weber var. azul juice characterization

The Agave tequilana Weber juice used in the experimentation was supplied by a distillery. The sugar concentration of the agave juice was 20 °Bx and pH was 4.0. In the distillery, the agave plants are cooked in an autoclave at 95 to 100°C for 4 hours.

Amino acid analyses were determined by HPLC [17]. The acid hydrolysis of agave juice was performed as reported by Umagath et al. [18].

Table 3. Amino acid composition of grape and agave juices.

Due to the advantages of converting tar into useful gases and adjusting the compositions of product gases, catalyst cracking has been of interest since the middle 1980s. The simplified mechanism for catalyst tar reforming can be described as follows [7-9]. First, methane or other hydrocarbons are dissociatively adsorbed onto a metal site where metal catalyzed dehydrogenation occurs. Water is also dissociatively adsorbed onto the ceramic support, hydroxylating the surface. At the appropriate temperature, the OH radicals migrate to the metal sites, leading to oxidation of the intermediate hydrocarbon fragments and surface carbon to CO + H2. David [9,10] summarized the criteria for catalyst as follows:

1. the catalysts must be effective in removing tar;

2. if the desired product was syngas, the catalysts must be capable of reforming methane;

3. The catalysts should provide a suitable syngas ratio for the intended process;

4. the catalysts should be resistant to deactivation as a result of carbon fouling and sintering;

5. the catalysts should be easily regenerated.

6. The catalysts should be strong; and

7. the catalysts should be inexpensive.

Moulijn J. A. [11] has classified main causes of the deactivation into five reasons that are poisoning, fouling, thermal degradation (sintering, evaporation) initiated by the often high temperature, mechanical damage and corrosion/leaching by the reaction mixture. The deactivation phenomenon inside a catalyst particle is described on Figure 2 [11]. Among them, thermal degradation reason often occurs during catalyst reforming tar at relative high temperature (Figure 3).

Once the celluloses disconnect from the lignin, acid or enzymes will be used to hydrolyze the newly freed celluloses into simple monosaccharides (mainly glucose). There are three principle methods of extracting sugars from sugars. These are concentrated acid hydrolysis, dilute acid hydrolysis and enzymatic hydrolysis.

1.1.1.1. Concentrated acid hydrolysis process

The primary advantage of the concentrated acid process is the potential for high sugar recovery efficiency [18]. It has been reported that a glucose yield of 72-82% can be achieved from mixed wood chips using such a concentrated acid hydrolysis process [26]. In general, concentrated acid hydrolysis is much more effective than dilute acid hydrolysis [27]. Furthermore, the concentrated-acid processes can operate at low temperature (e. g. 40°C), which is a clear advantage compared to dilute acid processes. However, the concentration of acid used is very high in this method (e. g. 30-70%), and dilution and heating of the concentrated acid during the hydrolysis process make it extremely corrosive. Therefore, the process requires either expensive alloys or specialized non-metallic constructions, such as ceramic or carbon-brick lining. The acid recovery is an energy-demanding process.

Despite the disadvantages, the concentrated acid process is still of interest. The concentrated acid process offers more potential for cost reductions than the dilute sulfuric acid process [28]. The concentrated acid hydrolysis process works by adding 70-77% sulfuric acid to the pre-treated lignocellulosic biomass. The acid is added in the ratio of 1.25 to 1.5 acid to 1 lignocellulosic biomass and the temperature is controlled at 40-60oC. Water is then added to dilute the acid to 20-30% and the mixture is again heated to 100oC for 1 hour. The gel produced from this mixture is then pressed to release an acid sugar mixture. The acid is then recovered partly by anion membranes and partly in the form of H2S from anaerobic waste water treatment. The process was claimed to have a low overall cost for the ethanol produced [29].

1.1.1.2. Dilute acid hydrolysis

Dilute acid hydrolysis process is similar to the concentrated acid hydrolysis except using very low concentration of sulfuric acid at higher cooking temperature. Biomass is treated with dilute acid at relatively mild conditions which the hemicelluose fraction is hydrolyzed and normally higher temperature is carried out for depolymerisation of cellulose into glucose. The highest yield of hemicellulose derived sugars were found at a temperature of 190°C, and a reaction time of 5 — 10 min, whereas in second stage hydrolysis considerably higher temperature (230 °C) was found for hydrolysis of cellulose [30].