Biodiesel is produced primarily through the transesterification reaction of triglycerides and alcohol usually in the presence of a metal catalyst and can be visualized by the chemical re­action equation found in Scheme 1. where "R" groups are functional carbon chains varying in length and level of saturation and "M" is a metal, usually referring to sodium or potassi­um. The resultant glycerol that is produced is generally treated as a by-product and either sold for commodities use or burned to provide heating if necessary. This process is depend­ent on water content and pH, which dictates pre-processing demands in order to minimize the formation of soaps and maximize the production of wanted fatty acid ester compounds.

During this reaction the fatty acids tails are removed from the glycerol backbone leaving a glycerol molecule and one to three fatty acid esters (almost always either ethyl or methyl al­cohol yielding a methyl or ethyl ester). These fatty acid methyl esters (FAME) or ethyl esters (FAEE) will vary in characteristics as a fuel based on carbon chain length as well as degree of unsaturation and location of unsaturated bonds. Some of the characteristics of biodiesel that are affected by fatty acid chemistry are viscosity, cloud point, and freezing point, among other factors important to engine performance. In general, there are several trade­offs that must be made with regards to saturation of fatty acids, branching of the fatty acid chain, and the carbon chain length, as each will have positive and negative attributes affect­ing fuel performance.

As the length of the molecule increases, the cetane number, and thus the heat of combustion, increases, this in turn decreases NOx emissions. However, as the length of the fatty acid chain increases, the resultant biodiesel has increased viscosity leading to a pre-heating re­quirement. Also, as fatty acids become more branched there is a benefit of the gel point (the temperature at which the fuel becomes gel-like and has complications flowing through fuel lines) decreasing. The negative to higher branching is that the cetane number will decrease due to a more difficult combustion. As saturation of the fatty acid chain increases, there is a decrease in NOx emissions and an improvement in fuel stability. As saturation increases, there is an increase in melting point and viscosity, both undesirable traits in a fuel.

Since there are so many trade-offs in the production of biodiesel, it is very difficult, if not impossible, to pick one ideal source of fatty acid for conversion to fuel. The multitude of cli­mates across the globe will necessitate various traits in fuel such as the gel point, melting/ freezing point, and oxidative stability. This leads to the argument of localized production of specific biomass sources that can be tailored to produce the types of lipids most suited to fuel that specific region, which will keep transportation costs down, as well as provide for the local economy. In following this method, there will be ample biomass produced to meet the specific needs of each climate, reducing environmental stresses that can occur due to overproduction for large scale purposes.

Although acetogens are able of utilizing CO and CO2/H2 as carbon and energy source, other constituents such as vitamins, trace metal elements, minerals and reducing agents are also required for maintenance of high metabolic activity [16, 113]. Studies indicated that forma­tion of ethanol in solventogenic Clostridiais non-growth associated and limitation of growth by reducing availability of carbon-, nitrogen — and phosphate — nutrients shift the balance from acidogenesis to solventogenesis [113, 200, 201]. Optimization of medium formulation for C. Ijungdahlii through reduction of B-vitamin concentrations and elimination of yeast ex­tract significantly enhanced the final ethanol yield to 48 g/l in a CSTR with cell recycling (23 g/l without cell recycling) [113]. Another study by Klasson et al. showed thatthe replacement of yeast extract with cellobiose not only increased maximum cell concentration, but also en­hanced ethanol yield by 4-fold [14]. Media formulation for C. autoethanogenum was investi­gated using Plackett-Burman and central composite designs, but only low ethanol yield was recorded overall [202]. In an attempt to reduce the cost of fermentation medium and im­prove process economics, 0.5 g/l of cotton seed extract without other nutrient supplementa­tion was shown to be a superior medium for C. carboxidivorans strain P7 in producing ethanol from syngas fermentation [203]. A recent study showed that increasing concentra­tions of trace metal ions such as Ni2+, Zn2+, SeO4-, WO4-, Fe2+ and elimination of Cu2+ from medium improved enzymatic activities (FDH, CODH, and hydrogenase), growth and etha­nol production in "C. ragsdalei" under autotrophic conditions [107].

A low redox potential is necessary for strict anaerobes to grow, hence reducing agents such as sodium thioglycolate, ascorbic acid, methyl viologen, benzyl viologen, titanium (III)—cit — rate, potassium ferricyanide, cysteine-HCl and sodium sulfide are commonly added to fer­mentation medium [14, 16, 204]. Furthermore, the addition of reducing agent directs the electron and carbon flow towards solventogenesis by enhancing the availability of reducing equivalents to form NADH for alcohol production [16, 205]. Excessive addition of reducing agents can cause slower microbial growth due to reduced ATP formation from acetogenesis so it is important to determine the optimum concentration of reducing agents [14, 16]. The sulfur containing gases (e. g. H2S) present in syngas are toxic to chemical catalysts but can be beneficial for microbial catalysts by reducing medium redox potential, stimulate redox sen­sitive enzymes such as CODH, and promote alcohol formation [206, 207].

Tomota and Fujiki [123] observed that the presence of a small amount of activated carbon promotes BuOH fermentation of corn. Oda [124] compared various activated carbons for the removal of BuOH in order to avoid its toxicity. The commercial supernorite proved to be the most effective with intermittent additions. Oda [125] studied the effect of pre-treatment of carbons on BuOH removing capacity, but similar beneficial results were obtained by adding commercial active C to the mash and the acid or alkali treated activated carbons. Yamazaki et al. [126—128] packed activated carbon into a column, and after saturation with ABE solvents it was heated at 150 °C, and steamed to recover solvents, when 98% of the BuOH and 99% of the Me2CO could be recovered. Activated carbon could be used repeatedly without refreshing. The efficiency of carbon was a little reduced by repeated sorption with soft carbon but hardly reduced with hard carbon. Freundlich’s adsorption isotherm by some commercial carbons was, respectively, for Me2CO and BuOH at 37°, x/m=0.151C052 and x/m=0.275C057, where x was the amount of solvent (millimole L-1) adsorbed by a mg of adsorbent, and C the concentration, (millimole L-1) of solvent remaining after equilibrium was reached. The amount of BuOH absorbed by carbon was >4 times as large as that of Me2CO, and this selective sorption was more marked with increasing concentration of solvents. The sorption of BuOH was slower than that of Me2CO, and >48 h was necessary for reaching equilibrium. Smaller granules of carbon were more effective, and carbon packed in a bag suspended in fermenting mash was convenient. Fermentation experiments with 12-18 g sugar and 5-6 g C/100 ml proved to be the optimal. Carbon granules of the size 2-4 mm3 were most adequate. Addition of carbon after the growth phase or the maximal acidity phase gave best results. A sugar mash (12 g/100 ml) was fermented with 6 g/100 ml. active C in 3 days by C. acetobutylicum to give a solvent yield of 36% (based on added sugar). The ratio of produced Me2CO and BuOH was 1:2.

Urbas [129] developed a method for adsorption of ABE components from ferment mash produced by C. acetobutylicum on activated carbons with elution by a volatile solvent. Elution was carried out by feeding the solvent vapor to the carbon bed that is maintained at, or slightly less than, the solvent condensation temperature at a rate of ~1/2 bed vol h-1 until the volatile solvent is detected in the eluate and continuing until ~1/2 additional bed volume of eluate is collected. The 1st fraction was mainly water (up to ~96% of the initial amount) and the 2nd a concentrated aqueous solution of the organic compound in the volatile solvent. The solvent is distilled off. The concentration of the final aq. solution is ~30%. The volatile solvents were Me2CO, 2-butanone, EtOAc, i-PrOH, MeOH, and Et2O.

A series of adsorbents such as bone charcoal, activated charcoal, silicalite, polymeric resins (XAD series), bonopore, and polyvinylpyridine were tested in the separation of butanol from aqueous solutions and/or fermentation broth by adsorption. Usage of silicalite appeared to be the more attractive as it could be used to concentrate butanol from dilute solutions (5 to 790-810 g L-1) and resulted in complete desorption of ABE solvents. In addition, silicalite could be regen­erated by heat treatment. The energy requirement for butanol recovery by adsorption-desorp­tion processes was 1,948 kcal kg-1 butanol as compared to 5,789 kcal kg-1 butanol during steam stripping distillation. Other techniques such as gas stripping and pervaporation required 5,220 and 3,295 kcal kg-1 butanol, respectively [130]. Milestone and Bibby [131] studied the usability of silicalite, which provided a possible economic route for the separation of alcohols from dilute solutions. Thus, EtOH was concentrated from a 2% (wt/vol) solution to 35% and BuOH from 0.5 to 98% (wt/vol) by adsorption on silicalite and subsequent thermal desorption. Maddox [132] found that 85 mg BuOH/g silicalite can be adsorbed from ferment liquors.

Polymeric resins with high n-butanol adsorption affinities were identified from a candidate pool of commercially available materials representing a wide array of physical and chemical properties. Resin hydrophobicity, which was dictated by the chemical structure of its constit­uent monomer units, most greatly influenced the resin-aqueous equilibrium partitioning of n — butanol, whereas ionic functionalization appeared to have no effect. In general, those materials derived from poly(styrene-co-divinylbenzene) possessed the greatest n-butanol affinity, while the adsorption potential of these resins was limited by their specific surface area. Resins were tested for their ability to serve as effective in situ product recovery devices in the n-butanol fermentation by C. acetobutylicum ATCC 824 [133]. In small-scale batch fermentation, addition of 0.05 kg L-1 Dowex Optipore SD-2 facilitated achievement of effective n-butanol titers as high as 2.22% (w/v), well above the inhibitory threshold of C. acetobutylicum ATCC 824, and nearly twice that of traditional, single-phase fermentation. Retrieval of n-butanol from resins via thermal treatment was demonstrated with high efficiency and predicted to be economically favorable [133]. Testing performed on four different polymeric resins in the fermentation by C. acetobutylicum showed that the pH increasing could prevent adsorption of intermediates such as acetic and butyric acids. Bonopore, the polymer giving the best adsorption pattern for butanol with no undesirable effects. The adsorption characteristic of butanol from aqueous fermentation broth were also determined on RA, GDX-105, and PVP resins. The adsorption order is GDX-105>RA>PVP and the isotherms could be represented by the Langmuir equation. The adsorption increases with increasing temperature excepting very low concentrations of butanol. The AG0, AH0 and AS0 values for the butanol adsorption processes from aqueous solutions on GDX-105 showed that the enthalpy decreased and the entropy increased [134].

In butanol/isopropanol batch fermentation, adsorption of alcohols can increase the substrate conversion. The fouling of adsorbents by cell and medium components is severe, but this has no measurable effect on the adsorption capacity of butanol in at least three successive fermen­tations. With the addition of some adsorbents it was found that the fermentation was drawn towards production of butyric and acetic acids [135].

Catalytic hydrotreating of liquid biomass is continuously gaining ground as the most effec­tive technology for liquid biomass conversion to both ground — and air-transportation fuels. The UOP company of Honeywell, via the technology it has developed for catalytic hydro­treating of liquid biomass (Figure 11), has announced imminent collaboration with oil and airline companies such as Petrochina, Air China and Boeing for the demonstration of the sustainable air-transport in China. This initiative will lead a strategic collaboration between the National Energy Agency of china with the Commerce and Development Agency of USA leading to the development of the new biofuels market in China.

Selective Product

Deoxygenation hydrogenation separation

H2

Light

biofuels

“Green”

kerosene

Liquid

recycle

Figure 11. Vegetable oil and animal fats conversion technology to renewable fuels of UOP [61]

In the EU airline companies collaborate with universities, research centers and biofuels com­panies in order to confront their extensive contribution to CO2 emissions. Since 2008 most airline companies promote the use of biofuels in selected flights as shown in Table 7 [62]. As it is obvious most pilot flights have taken place with Hydrotreated Renewable Jet (HRJ), which is kerosene/jet produced via catalytic hydrotreatment of liquid biomass. Moreover, Lufthansa has also completed a 6-month exploration program of employing HRJ in a 50/50 mixture with fossil kerosene in one of the 4 cylinders of a plane employed for the flight be­tween Hamburg-Frankfurt-Hamburg with excellent results [63].

Besides the future applications for air-transportation, the automotive industry is also exhib­iting increased interest for the broad use of biofuels resulting from catalytic hydrotreatment of liquid biomass. In fact these paraffinic biofuels can be employed in higher than 7%v/v blending ratio (which is the maximum limit for FAME) as they exhibit high cetane number and have significant oxidation stability [64]

The highest interest is exhibited by oil companies around the catalytic hydrotreatment of liq­uid biomass technology for the production of biofuels and particularly to its application to oil from micro-algae. ExxonMobil has invested 600M$ in the Synthetic Genomics company of the pioneer scientist Craig Ventner aiming to research of converting micro-algae to bio­fuels with minimal cost. BP has also invested 10M$ for collaboration with Martek for the production of biofuels from micro-algae for air-, train-, ground — and marine transportation applications.

4. Conclusion

Catalytic hydrotreatment of liquid biomass is the only proven technology that can overcome its limitations as a feedstock for fuel production (low H/C ratio, high oxygen and water con­tent). Even though it has recently started to be investigated as an alternative technology for biofuels production, it fastly gains ground due to the encouraging experimental results and successful pilot/demo and industrial applications. Catalytic hydrotreatment of liquid bio­mass leads to a wide range of new alterative fuels including bio-naphtha, bio-jet and bio­diesel, are paraffinic in nature and as a result exhibiting high heating values, increased oxidation stability and negligible acidity and corrosivity. As a result it is not over-optimistic to claim that this technology will broaden the biofuels market into scales capable to actually mitigate the climate change problems.

Acknowledgements

The author would like to thank Ms Iva Simcic and InTech Europe for enabling her to publish this book chapter, while she is grateful to Mr Athanasios Dimitriadis who provided support, offered comments, proofreading and design. Finally she would like to express her apprecia­tion for the financial support provided by the EU project BIOFUELS-2G which is co-fi­nanced by the European Program LIFE+.

Author details

Stella Bezergianni*

Address all correspondence to: sbezerg@cperi. certh. gr

Chemical Processes & Energy Resources Institute (CPERI), Centre for Research & Technolo­gy Hellas (CERTH), Thermi-Thessaloniki, Greece

Microwave apparatus (Microwave Accelerated Reaction System (MARS 5), CEM Corpora­tion) shown in Figure 9 was used to study the effect of carrying out experiments in a sealed reactor under high pressure and high temperature. The microwave apparatus operates at
2.45 GHz frequency, while the microwave output can be manipulated up to maximum pow­er of 1,200 Watts. This apparatus also consists of a fluoropolymer-coated microwave cavity, a cavity exhaust fan and tubing to vent fumes and a digital computer programmable for 100 programs consisting of up to five stages each. Inside the cavity is an alternating turntable system which can hold up to 13 reactor vessels, thus performing simultaneous experiments on 13 samples is possible.

The sealed Teflon-reactor vessel can handle pressures up to 5MPa and temperatures up to 250 oC. The reactor can be connected to the pressure and temperature control mechanisms of the MARS 5, for online monitoring and for operational safety. Some of the experiments were also carried out in a similar apparatus (Ethos) manufactured by Milestone General Co, Ltd.

Inside Cavity

Microwave Apparatus

Tmax = ~240 °С Pmax = ~5MPa

Sealed Reactor

Figure 9. Microwave apparatus for pressurized synthesis of ETBE in a sealed reactor vessel (MARS5, CEM Corporation, Japan)

In a typical experiment, about 0.25 mol each of the reactants (TBA and ETOH) were placed inside the vessel, and mixed with 20g of Amberlyst 15 catalysts. The reactor was sealed and connected to temperature and pressure sensors, then microwave was irradiated until the set irradiation time has elapsed. After cooling the vessel to reach a temperature below 50 oC, the reactor was opened and an aliquot part of the products was taken for analysis.

Figure 10 shows the yields of ETBE using MW at various power at irradiation time of 1 min. A maximum yield of about 87% was obtained at MW power of 350W. At this condition, the attained temperature was around 87oC as shown in Figure 11, higher than the boiling points of the two alcohols. The yield was also found to be dependent on the amount of catalysts, reaction time and microwave power.

It comes from agricultural waste which is concentrated into charcoal-like biomass by heat­ing it. Very little processing required, low-tech, naturally holds CO2 rather than releasing it into the air. Primarily, biochar has been used as a means to enrich soil by keeping CO2 in it, and not into the air. As fuel, the off-gasses have been used in home heating. There is contro­versy surrounding the amount of acreage it would take to make fuel production based on biochar viable on a meaningful scale. Furthermore, use of agriculture wastes which rich with inorganic elements (NPK—) as compost (fertilizer) in agriculture.

1.1. Microbes

Clostridium is a group of obligate, Gram positive, endospore-forming anaerobes. There are lots of strains used for ABE fermentation in different culture collections, such as ATCC (American Type Culture Collection), DSM (German Collection of Microorganisms, or Deut­sche Sammlung Von Mikroorganismen), NCIMB (National Collections of Industrial & Ma­rine Bactria Ltd), and NRRL (Midwest Area National Center for Agriculture Utilization Research, US Department of Agriculture). The different strains share similar phonotype such as main metabolic pathway and end products. Molecular biology technology offers ef­ficient method for classification. The butanol-producing clostridium can be assigned to four groups according to their genetic background, named C. acetobutylicum, C. beijerinckii, C. sac­charoperbutyl acetonicum, and C. saccharobutylicum, respectively. C. acetobutylicum is phyloge — netically distinct from the other three groups.

The common substrate for the solvent production by these strains is soluble starch. The orig­inal starch-fermenting strains belong to C. acetobutylicum. A recently isolated butanol-pro­ducing strain C. saccharobutylicum showed high hemicellulotic activity (Berezina et al., 2009). All of the four group strains can ferment glucose-containing medium to produce solvent. In 4% glucose TYA medium, C. beijerinckii gave the lowest solvent yield (28%), while the sol­vent yield was upper than 30% compared to the other three groups (Shaheen et al., 2000). In standard supplement maize medium (SMM), C. acetobutylicum is the best strain for maize fermentation, and the total solvent concentration can reach 19g/L. The solvent yield was 16, 14, and 11 for that of C. beijerinckii, C. saccharoperbutyl acetonicum, and C. saccharobutylicum respectively. However, C. acetobutylicum can’t ferment molasses well and it produces bright yellow riboflavin in milk, which is different from other groups and easy identified. The best molasses-fermenting strains belong to C. saccharobutylicum and C. beijerinckii (Shaheen et al., 2000). C. saccharoperbutyl acetonicum can utilize sugar, molasses and maize. Comparing to C. acetobutylicum, C. beijerinckii was more tolerant to acetic acid and formic acid (Cho et al., 2012), which suggests the advantage when using lignocellulosic hydrolysate treated with acetic and formic acid as substrate.

There are also some C. beijerinckii strains produce isopropanol instead of acetone (George et al., 1983). Some microorganisms can produce biobutanol from carbon monoxide (CO) and molecular hydrogen (H2), including acetogens, Butyribacterium methylotrophicum, C. autoetha — nogenum, C. ljungdahlii and C. carboxidiworans. The C. carboxidivorans strain P7(T) genome possessed a complete Wood-Ljungdahl pathway gene cluster which is responsible for CO, hydrogen fixation and conversion to acetyl-CoA(Fig.2) (Bruant et al., 2010).

While hydrocarbon-based biofuel production relies on the biosynthetic pathways discussed in the previous section, the source of feedstock plays an important role in the overall produc­tion process. As discussed in the Introduction to this chapter, there are two main feedstocks for biofuel production: lignocellulosic biomass and gaseous CO2 supporting the production of second and third generation biofuels, respectively (Figure 1). Both processes ultimately rely on CO2 and sunlight as the carbon and energy source, but the microbial conversion processes are distinctly different between the two feedstocks. Lignocellulosic biomass deconstruction produces organic carbon, mostly in the form of hexoses and pentoses (C5 and C6 sugars); this feedstock requires heterotrophic microorganisms to convert the organic carbon into biofuel. Alternatively, the fixation of inorganic carbon feedstock (CO2/HCO3-) into biofuel is reliant upon autotrophic microbes. The heterotroph vs. autotroph requirement of the respective feedstocks is an important distinction from both the metabolic engineering and biofuel production perspectives. Only a few model microorganisms are capable of both heterotrophy and autotrophy, resulting in different host candidates for second and third generation biofuel production. The feedstock will also influence the metabolic engineering targets, as hetero- trophs utilize glycolysis and oxidative phosphorylation pathways for carbon consumption and energy production while oxygen-generating autotrophs utilize the Calvin-Benson-Bassham cycle and photosynthesis under light conditions (Figure 4). This section will discuss the host

Dasari et al. [46] observed the formation of acetol (hydroxyacetone) together with 1,2-PDO using copper-chromite catalyst at 473 K and 15 bar hydrogen pressure. Moreover, glycerol hydrogenolysis to 1,2-PDO occurred even in the absence of water. Since the copper-chromite catalyst was reduced in a stream of hydrogen prior to the reaction, no surface hydroxyl spe­cies were present to take part in the reaction. Therefore, the mechanism suggested by Mon — tassier et al. (Figure 9) was not able to explain these results. Dasari et al. proposed a new mechanism in which glycerol is first dehydrated to acetol, which is further hydrogenated to 1,2-PDO (Figure 10). Based on their findings, a two step process was developed [47]. In the first step, acetol is generated from glycerol dehydration by a reactive distillation process, op­erating at 513 K, slight vacuum and using copper-chromite catalyst. The acetol obtained is then hydrogenated at 15 bar H2 pressure using the same catalyst. The process was patented in the USA in 2005 [48].

V"0H "Г""он

о 0H

Acetol 1,2-PDO

According to Schlaf, acid-catalyzed hydrogenolytic cleavage of — OH group occurs through an initial protonation of the hydroxyl group that leads to the formation of a carbocation and water [49]. Thermodynamically, the formation of a secondary carbocation is more favored than the formation of a primary carbocation. Therefore, operating under acid conditions should bring about higher selectivity to 1,3-PDO. The fact that product distribution is usual­ly shifted towards 1,2-PDO seems to be a complex function of operating conditions, catalyst and starting materials. Ethylene glycol, ethanol, methanol and methane are usually reported as degradation products. Ethylene glycol and methanol are formed from the C-C bond cleavage reaction of glycerol, while ethanol stems from the further hydrogenolysis of ethyl­ene glycol.

Two treatments showed the highest production of biohydrogen, the treatment 2 in the repetition 1 and the treatment 3 in the repetition 3, the maximum value was obtained with the treatment 2 in the repetition 1 in which were used wastes from lettuce and cabbage leaves, tomato, onion, garlic, pimento, orange, lemon, mango, guava and papaya. The acid conditions were implemented 8 days with value of pH near to 4, the operation of bioreactor was between 5 and 5,5. In the treatment 3 in the repetition 3 were used the same wastes, the acid condition was applied during 7 days with value of pH near to 4,5; the pH of bioreactor operation was between 5 and 5,5. Although was generated more quantity of hydrogen in the treatment 2 during the repetition 1, was in the treatment 3 in the repetition 3 where was obtained the greater hydrogen contentinthegas (18,04%) andgreaterrateofgeneration ofhydrogen.

The maximum production of hydrogen was obtained at the second stage when the pretreat­ment of acidification was applied during 8 days with a value for the pH of 4, a pH of reactor operation between 5 and 5,5; and a value of chemical oxygen demand (COD) near to 20.000 mg/liter of O2. At the first stage when was used a quantity of wastes from tropical fruits greater than wastes of lettuce and cabbage leaves, the chemical oxygen demand (COD) initial was 54.000 mg/liter of O2, however the hydrogen production was significantly less respect to second stage. This indicates that a high value of chemical oxygen demand could inhibit the hydrogen generation; this result is according to reports of different authors [13, 23—29]. When were used vegetal wastes (without wastes of tropical fruits) as lettuce and cabbage leaves, tomato, onion, garlic and husk of cape gooseberry, there were no acid conditions at beginning the process and was necessary to add acid, however there was no response in the biosystems and the pH always was upper than 4,5. Under these conditions there was no production of hydrogen. In addition the chemical oxygen demand was low (12.000 mg/liter of O2).

The results shows that is feasible to produce biohydrogen (hydrogen) when are employed organic wastes from the Central Wholesaler of Antioquia. The wastes should be submitted to a pretreatment acid with a pH between 3,5 y 4,0; during 7 days (or less), then the operation pH should be increased until a value between 5 and 5,5. The chemical oxygen demand (COD) should be between 20.000 and 54.000 mg/liter of O2 this is possible to reach when in the bioprocess is employed a proportion similar of tropical fruit waste and vegetal waste.

2. Conclusions

• It was possible to generate hydrogen from organic wastes of Central Wholesaler of Antio — quia and to improve the bioprocess.

• The chemical oxygen demand (COD) promoted the biohydrogen production, the best results were obtained to values between 20.000 and 54.000 mg/liter of O2. These values were achieved with a heterogeneous mix of fruits and vegetal wastes.

• There was not generation of biohydrogen when the bioprocess started with a pH upper than 4. This ratifies that to generate biohydrogen by anaerobic fermentation is necessary to apply a pretreatment, in this research, a pretreatment under acid conditions (pH between 3,5 and 4,0) was successful.

• Colombia has a high potential to generate hydrogen by anaerobic fermentation due to organic wastes available, these wastes could generate until 28’825.609 m3 of biohydrogen and supply an energetic potential of 144 GW, value upper than the installed potential (13,5 GW).

• The results show that is possible to produce biohydrogen by anaerobic fermentation of organic wastes and providing new sources energetic.

Acknowledgements

The authors acknowledge to National University of Colombia in Medellm and the Central Wholesaler of Antioquia by the financial support to research.

Author details

Edilson Leon Moreno Cardenas*, Deisy Juliana Cano Quintero and Cortes Marin Elkin Alonso

*Address all correspondence to: elmorenoc@unal. edu. co

Engineering Agricultural Department, National University of Colombia, Medellm, Colombia