The concept of biomass is largely extended among the bioenergy, agricultural, biotechnology and other specialists. When a farmer talks about biomass, he or she is referring to the foliage, fruits, grains, stems or waste materials produced in crops.

In the animal husbandry activities, biomass is referred to the manure and purines excreted by farm animals. On the other hand, talking about cell’s biotechnology, biomass is referred to the cell production in a culture: biomass of yeast produced during fermentative processes.

In other terms, biomass constitutes a broad range of biological matter including the vegetal coverage of the planet, the micro and macro organisms living on the planet, including humankind.

Displaying in this manner the concept of biomass, allows the broadening of its quantitative and qualitative applications and uses. This way of thinking on biomass plays with the absolute and relative values of the concept and may certainly boost the current scheme of exploitation of biomass sources.

BMP is the maximum methane yield through anaerobic digestion, thereby BMP is identified with the cumulative methane yield at the end of a fermentation test. However, termination of fermentation is not clearly defined. Hence, the fermentation duration may vary from 7 to 365 days [26]. VDI 4630 [18] mentions that digestion should be terminated when daily biogas production per batch is less than 1% of the cumulative gas production, which is applied for our study. As BMP is the maximum methane yield, it is the most important parameter to evaluate the quality of feedstock for biogas production, and is used to design real scale biogas reactors. BMP is most frequently presented as being the unit of methane volume in terms of kg VS, hence, the BMP level varies depending on organic compositions in VS. Cumulative methane productions of the animal manures tested as a function of time are presented in Figure 4. As can be seen in Figure 4, the great majority of methane was produced in the first 2 weeks and thereafter only small amounts of gas were released. The cumulative methane curves generally follow first order kinetics, since the hydrolysis process is the rate limiting process [27,28].

Whereas DM and VS are quantitative parameters for methane production potentials, BMP is the quality parameter that is reflected of bioconversion of organic compositions, which have dependency of methane potentials of each organic composition and its BD. Hence, the BMP value can be used as an index of the BD of substrates to biogas reactors [29].

Figure 5 gives the comparison of BMP results in terms of kg VS and of kg slurry of the animal slurry tested for this study. As can be seen in Figure 4, BMP of various animal slurries ranges between 170 — 400 CH4 NL kg-1 VS. Most of the cow slurry is shown at the lowest level within the tested slurries, whereas high methane potential of pig slurries is found. This result has a good agreement with previous studies [10,23]. Mink slurry had the second highest BMP within the samples tested. BMP in terms of kg slurry had much larger variation in the range of 1.8 — 70 CH4 NL kg-1 slurry of which two different terms of BMP were somewhat opposite, due to such a large variation of the DM concentration. Since the variation of the DM concentration in animal slurry is larger than methane potential per unit of VS, the results indicate that the water content of the animal slurry is the most significant parameter for methane productivity in reactors compared to BMP.

Figure 5 indicates that control of the DM concentration is more crucial than control of BD of substrate with respect to increasing methane yield within the range that pumping is appropriate. Figure 6 shows a good linear correlation between DM concentration and biomethane potentials per kg slurry (R2 =0.896). The results highlight the importance of a qualified control of water content in animal slurry. Controlling of DM could be achieved by co-digesting solid organic substrate such as energy crops, for this reason, energy crop has been widely used as co-substrate to enhance biogas productivity [16]. Sufficient water content is inevitable for the wet fermentation procedure, as too low concentrations of water decrease the biomethane production rate. However the 94.1% water content of effluent from the tested reactor indicates that there is need of optimizing it by codigesting solid organic residues. The high content of water was probably caused by spillage of cleaning water, which contributed to the lowest potential biomethane yield per unit of biogas reactor, in spite of high BMP results among the animal slurries included, as BMP is the methane potential in term of VS concentration.

As one of main polysaccharides in lignocellulosic biomass, xylan has a variety of applications in our everyday life and affects our well-being. For example, (1) xylans are important functional ingredients in baked products [98]; (2) xylans can be potentially used for producing hydrogels as biodegradable coatings and also encapsulation matrices in many industrial applications; (3) xyl, the main constituent from xylans, can be converted to xylitol which is used as a natural food sweetener and a sugar substitute [99]; (4) xylans can be used for clarification of juices and improvement in the consistency of beer [100]; (5) xylans are also important for livestock industry as they are critical factors for silage digestibility; (6) xylans are major constituents in non-nutritional animal feed [101]; (7) xylans can be converted to sugars and then further to fuels and chemicals; (8) enzymes that degrade xylan can facilitate paper pulping and biobleaching of pulp [100].

Xylans, the main component in hemicellulose, are heteropolysaccharides with homopolymeric backbone chains of 1,4 linked р-d-xylopyranose units. In addition to xylose, xylans may also contain arabinose, glucuronic acid or its 4-0- methyl ether, acetic, ferulic, and p-coumaric acids. Xylans can be categorized as linear homoxylan, arabinoxylan, glucuronoxylan, and glucuronoarabinoxylan. Depends on the different sources of xylan (i. e. soft — and hard — wood, grasses, and cereals), the composition of xylans differs [100].

Hemicellulose can be derived via chemical treatment or enzymatic hydrolysis. As discussed in Section 2.1.1, several pre-treatments listed in Table 1 are available to fractionate, solubilize and hydrolyze and separate hemicellulose from cellulose and lignin components. Generally, hemicelluloses are solublized by either high temperature and short residence time (270°C, 1 min) or lower temperature and longer residence time (190 °C, 10 min) [102]. However, some of chemical treatment result in hemicellulose degradation by-products such as furfural and 5-hydroxymethyl furfural (HMF) which are inhibitors for microorganisms involved in downstream fermentation if applicable.

Biodegradation of xylan requires enzymes including endo-p-1,4-xylanase, p-xylosidase, and several accessory enzymes, such as a-L-arabinofuranosidase, a-glucuronidase, acetylxylan esterase, ferulic acid esterase, and p-coumaric acid esterase, which are necessary for hydrolyzing various substituted xylans. The endo-xylanase attacks the main chains of xylans while p-xylosidase breaks xylooligosaccharides to monomeric sugar xylose. The a — arabinofuranosidase and a-glucuronidase remove the arabinose and 4-O-methyl glucuronic acid substituents from the xylan backbone [100]. The esterases hydrolyze the ester linkages between xylose units of the xylan and acetic acid (acetylxylan esterase) or between arabinose side chain residues and phenolic acids, for example ferulic acid (ferulic acid esterase) and p — coumaric acid (p-coumaric acid esterase) [100].

Hemicellulose hydrolysates from lignocellulosic biomass either obtained by chemical treatment or enzymatic hydrolysis are attractive feedstock for producing bioethanol, 2,3- butanediol or xylitol. Other value added products from hemicellulose hydrolysate include (1) ferulic acid, and (2) lactic acid which can be used in the food, pharmaceutical, and cosmetic industries [100].

As the composition of the bio-oil and the effects of the operating conditions on the distribution of each fraction are both complicated, Wang et al. (2009) put forward a statistical method to directly evaluate the separation level of bio-oil by molecular distillation. The separation coefficients of four groups, "Complete Isolation", "Nonvaporization", "Enrichment", and "Even Distribution", were calculated from the ratios of relative peak of a single component with respect to total components. The results showed that "Complete Isolation" had the largest percentage, followed by "Even Distribution", "Non-vaporization", and "Enrichment" which contained only small parts. Meanwhile, the temperature had a significant effect on the distributions of the compounds.

The McFarland nephelometer was described in 1907 by J. McFarland as an instrument for estimating the number of bacteria in suspensions used for calculating the bacterial opsonic index and for vaccine preparation.

Another important factor is known that cells per milliliter are taken at a given time, and a

known way is through the % of transmittance and that can be determined by the technique

of McFarland nephelometer, which is described below.

McFarland Nephelometer Standards

a. Set up 10 test tubes or vials of equal size and quality: Use new hoses washed and completely dry.

b. Prepare H2SO4 1% chemically pure.

c. Prepare an aqueous solution of barium chloride, 1% chemically pure.

d. Add to the tubes the designated amounts of the two solutions as shown in Table 2 for a total of 10 mL/tube.

e. Close the tubes or vials. The suspension of barium sulphate corresponding to an approximately homogeneous precipitate of density of the cells per milliliter in the standard variable, as shown in the Table 2.

f. In the Figure 3(a) shows the % of transmittance against the number. From the tube which can be removed if there is not a spectrophotometer to read the transmittance, and in Figure 3(b) shows the number of cells that are depending on number.

Population density is monitored by taking readings of % of transmittance, which compared to the McFarland nephelometer; transmittance readings should be less than 10% in order to maintain the population density. This technique is used to know the time and turbidity of most practical way to achieve the desired amount of biomass for biosorption experiments batch system and continuous [39].

(a)

Ernesto A. Chavez and Alejandra Chavez-Hidalgo

Additional information is available at the end of the chapter http://dx. doi. org/10.5772/54520

1. Introduction

In the world oceans there is large amount of biomass suspended in the photic zone of water column. Part of the living part is of plant origin, the phytoplankton and other is the animal component or zooplankton. There is also large proportion of particulate organic matter composed by remains of dead animals and feces. They represent the basis of the food webs with three or four trophic levels where all the consumers are animals in whose top the carnivores or top predators, are found. In all aquatic trophic webs, many species are exploited.

Chiefly Mexican, agaves are also native to the southern and western United States and central and tropical South America. They are succulents with a large rosette of thick, fleshy

leaves, each ending generally in a sharp point and with a spiny margin; the stout stem is usually short, the leaves apparently springing from the root. Agave taxa give particulars for all 197 taxa in the two subgenera, Littaea and Agave. The first of a slender form with high in saponin concentration is intended as ornament mainly, except Dasylirion spp. Species, which is the raw material to produce Sotol (a Mexican distilled alcoholic beverage). Also the Littaea is used as raw material producing medicinal steroids, since contains smilagenin. In the other hand, the species in the subgenus Agave have been exploited since the ancient pre­Columbian civilization mainly for producing: fiber, fodder, food and alcoholic beverage (Table 2) [14].

There are still many questions related to tar and the problems they may cause. Tar is a viscous black liquid derived from pyrolysis of organic matter as well as a complex mixture of hydrocarbons [1]. Various research groups are defining tar differently. In the EU/IEA/US — DOE meeting on tar measurement protocol held in Brussels in the year 1998, it was agreed by a number of experts to define tar as all organic contaminants with a molecular weight larger than benzene [2]

The presence of tar in product gas may cause blockage and corrosion of equipment and be responsible for fouling or reducing overall efficiency of processes. Tar is formed when biomass is heated the molecular bonds of the biomass break; the smallest molecules gaseous, the larger molecules are called primary tars. These primary tars, which are always fragments of the original material, can react to secondary tars by further reactions at the same temperature and to tertiary tars at high temperature [3, 4, 5, 6] Figure 1 show tar is quite complex and hard to decompose. By far, tar removal is the most problematic during biomass gasification. Hence, the successful implementation of gasification technology for gas engine/turbine based power projects depends much on the effective and efficient removal/conversion of tar from the producer gas. Up to now, a great amount of work concerning tar reduction or reforming has been reported with abundant technologies to remove tar from biomass product gas.

J. Han, and H. Kim had divided tar removal methods into five groups: mechanical methods (using cyclone, filters ceramic), granular beds, Electrostatic precipitators and Scrubbers; self­modification, selecting optimal operation parameters for gasifier or using a low tar gasifier; Catalytic cracking; Thermal cracking and Plasma methods [5]. The review shows that the primary use of mechanism methods is to capture the fly ash or particles from product gas; the effect on tar removal is also very good. However, these methods only remove or capture the tar from product gases, while the energy in tar is lost. The self-modification and other methods can not only reduce the tar but also convert the tar into useful gases. The self­modification methods include: selecting better gasifer, and optimizing operation parameters. Tar reduced by modifying operation parameter is at the expense of reducing the heat value of gases. Catalyst cracking and thermal cracking are generally used to decompose or reduce tar though there are still some disadvantages. Plasma technology cannot only

Original biomass chemical structures
(Celluloses, lignin starches, hemicelluloses etc.)

Very fast/ low temperature, 673 К to 973 К
(Acids, Ketoses, phenols, guaiacols, furans…)

Fast/ everage temperature 973 to 1123K (Phenols, Monoaromatic, Hydrocarbons…)

Slow/ high temperature 1123 to 2273 К PAH: 2-ring, 3- ring, 4-ring, 5-ring, 6-ring

Figure 1. Formation of biomass tars and compounds formed

effectively remove fly ash, NOx and SO2, but also sharply decrease the formation of tar during biomass gasification. In order to get highly efficient tar decomposition, the temperature of thermal cracking needs to be very high, which results in operating cost increase. Catalyst cracking can modify the composition of product gases at low temperature with high carbon conversion efficiency. Nevertheless, there still exists a short coming such as: the commercial Ni-based and alkali metal catalysts will be inactive by deposited carbon, and H2S. The newly developed novel catalyst can overcome the disadvantages by use of expensive metals (Co, Pt, Ru, Pd and Rh), and also catalyst supports (AhO3, Al, SiO, TiO2, ZrO2, MgO or WO3) and perform tar removal with high and stable activity even under the presence of high concentration of H2S in some cases. In order to satisfying both high and stable activity and good price, the development of catalyst meets the need to be continuing.

hydrolysis step [24], [25]. Lignocellulosic biomass consists of three major components; Cellulose, hemicellulose and lignin and are in the form of highly complex lignocellulosic matrix. Depending on type of lignocellulosic biomass, the lignin content varies from about 10 — 25%, the hemi celluloses content from about 20 — 35% and the cellulose content from about 35 — 50%. Lignin is a polymer of phenyl propanoid units interlinked through a variety of non-hydrolysable C — C and C-O-C bonds. It therefore is a complex molecule with no clear chemical definition as its structure varies with plant species. Hemicellulose is an amorphous heterogenous group of branched polysaccharides. Its structure is characterised by a long linear backbone of one repeating sugar type with short branched side chains composed of acetate and sugars. Cellulose is a linear molecule consisting of repeating cellobiose units held together by Beta — glycosidic linkages. Cellulose is more homogeneous than hemicellulose but is also highly crystalline and highly resistant to depolymerisation. The three components of lignin, hemicellulose and cellulose are tightly bound to each other in the biomass. In fact hemicellulose acts as a bonding agent between cellulose and lignin. In order to convert this biomass to fuel ethanol, the biomass has to be broken up into the individual components first before the molecular chains within each component can be broken up further into simpler molecules.

treatments can cause hydrolysis of hemicellulose, and partial depolymerization of lignin, the increase of specific surface area, decrease of the degrees of polymerization and crystallinity of cellulose.

Microwave treatment is a physical-chemical process involving both thermal and non­thermal effects. Treatments can be carried out by immersing the biomass in dilute chemical reagents and exposing the slurry to microwave radiation for a period of time [178]. The treatment of ultrasound on lignocellulosic biomass have been used for extracting hemicelluloses, cellulose and lignin [179]. Some researchers have also shown that saccharification of cellulose is enhanced efficiently by ultrasonic pre-treatment [180]. The efficiency of ultrasound in the treatment of vegetal materials has been already proved [181]. The well known benefits from ultrasounds, such as swelling of vegetal cells and fragmentation due to the cavitational effect associated to the ultrasonic treatment. Furthermore, mechanical impacts produced by the collapse of cavitation bubbles, give an important benefit of opening up the solid substrates surface for enzymatic hydrolysis [180].

However, the high energy radiation methods are usually energy-intensive and prohibitively expensive; appear to be strongly substrate-specific. The current estimation of overall cost from high energy radiation techniques looks too high, lack commercial appeal.