3. Potential bio-hydrogen and methane production from lignocellulosic biomass

Alternative fuels are recently in high demand owing to concerns about depletion of fossil fuels and harmful gases emission problem which results in climate change and environmental deterioration [37]. Biofuels (fuel alcohol, biodiesel/bio-jet, and biogas) can be a suitable alternative to fossil fuels as they are derived from renewable feedstocks, biodegradable, and combusted based on carbon dioxide cycle [38]. Biofuels can be used for the energy generation by combustion or other technologies. They have been used in transportation and power generation sectors, in which the share of biofuel in transport fuel demand has been increasing and reached 3% in 2017 [39]. Biogas (hydrogen and methane) is a highly promising biofuel because it can be produced from a variety of organic feedstocks, including waste biomass which can attribute to the waste reduction simultaneously with energy production [40].

#### 3.1 Hydrogen

Hydrogen is a noncarbonaceous fuel and energy carrier possessing higher net calorific value compared to other fuels [41]. It can be directly converted into energy in fuel cell or mixed with natural gas for use in internal combustion and jet engines, as well as the gas power turbines. Combustion of hydrogen yields only water; thus it is considered as a clean energy source. The limitation in using hydrogen is its explosivity when mixed with oxygen, leading to difficulty in its storage and distribution [42]. Production of hydrogen from lignocellulosic biomass can be achieved by gasification and microbial fermentation technologies. Gasification is very energy-intensive and releases large amount of carbon, sulfur, and nitrogen oxides to the atmosphere [43]. Therefore, attention had been paid to the microbial fermentation process as it is more environmentally friendly. Bio-hydrogen is a term used to call hydrogen produced via microbial fermentation. Dark- and photo-fermentation are typically applied for bio-hydrogen production. Dark fermentation of organic carbon substrates is carried out by obligate or facultative anaerobic bacteria yielding bio-hydrogen and other side products, such as volatile fatty acids (VFAs) and alcohols. Photo-fermentation requires energy from light to aid the decomposition of organic substrates by photosynthetic bacteria, mostly purple non-sulfur bacteria (PNSB) [44]. The dark fermentative bacteria are capable of utilizing various substrates with high rate of hydrogen production. A drawback of dark fermentation is

Bio-hydrogen and Methane Production from Lignocellulosic Materials DOI: http://dx.doi.org/10.5772/intechopen.85138

through the action of peroxidase and laccase. Biological pretreatment is environmentally friendly as no chemicals and lower energy are used compared with other

Currently, the combined physical, chemical, and biological pretreatment process is investigated for enhancing the degradation efficiency [21]. The combined process is more effective as compared to a single process. Yu et al. [35] combined physical,

3. Potential bio-hydrogen and methane production from lignocellulosic

it can be produced from a variety of organic feedstocks, including waste biomass which can attribute to the waste reduction simultaneously with energy

Hydrogen is a noncarbonaceous fuel and energy carrier possessing higher net calorific value compared to other fuels [41]. It can be directly converted into energy in fuel cell or mixed with natural gas for use in internal combustion and jet engines, as well as the gas power turbines. Combustion of hydrogen yields only water; thus it is considered as a clean energy source. The limitation in using hydrogen is its explosivity when mixed with oxygen, leading to difficulty in its storage and distribution [42]. Production of hydrogen from lignocellulosic biomass can be achieved by gasification and microbial fermentation technologies. Gasification is very energy-intensive and releases large amount of carbon, sulfur, and nitrogen oxides to the atmosphere [43]. Therefore, attention had been paid to the microbial fermentation process as it is more environmentally friendly. Bio-hydrogen is a term used to call hydrogen produced via microbial fermentation. Dark- and photo-fermentation are typically applied for bio-hydrogen production. Dark fermentation of organic carbon substrates is carried out by obligate or facultative anaerobic bacteria yielding bio-hydrogen and other side products, such as volatile fatty acids (VFAs) and alcohols. Photo-fermentation requires energy from light to aid the decomposition of organic substrates by photosynthetic bacteria, mostly purple non-sulfur bacteria (PNSB) [44]. The dark fermentative bacteria are capable of utilizing various substrates with high rate of hydrogen production. A drawback of dark fermentation is

Alternative fuels are recently in high demand owing to concerns about depletion of fossil fuels and harmful gases emission problem which results in climate change and environmental deterioration [37]. Biofuels (fuel alcohol, biodiesel/bio-jet, and biogas) can be a suitable alternative to fossil fuels as they are derived from renewable feedstocks, biodegradable, and combusted based on carbon dioxide cycle [38]. Biofuels can be used for the energy generation by combustion or other technologies. They have been used in transportation and power generation sectors, in which the share of biofuel in transport fuel demand has been increasing and reached 3% in 2017 [39]. Biogas (hydrogen and methane) is a highly promising biofuel because

pretreatment methods. The advantages and disadvantages of biological

chemical, and biological pretreatment process to pretreat rice husk. Results indicate that the combination of chemical (2% H2SO4) and biological (P. ostreatus) pretreatments leads to a higher lignin degradation than single-step pretreatments. The combined pretreatment of napier grass carried out using 2% NaOH along with cellulase enzyme was found to be more effective as compared with single alkaline pretreatment, in which a 3.97 time higher methane production (MP) was

pretreatment methods are given in Table 1.

Biomass for Bioenergy - Recent Trends and Future Challenges

obtained [36].

biomass

production [40].

3.1 Hydrogen

110

its low yield due to the large quantity of side products formed. The substrates for photo-fermentative bacteria are limited to simple sugars and organic acids, and the hydrogen production rate by photo-fermentation is usually lower than dark fermentation [44]. However, with the high substrate conversion efficiency and high hydrogen yield (HY), the photo-fermentation is also considered a promising technology for bio-hydrogen production [45]. In addition, recent research reported the sequential dark-photo-fermentation as an efficient bio-hydrogen production process. The VFAs from dark fermentation are further utilized for hydrogen production in photo-fermentation, thus the HY and substrate conversion efficiency can be improved via sequential dark-photo-fermentation [45–47]. Typical reactions for dark fermentation with acetic acid formation and photo-fermentation can be stated as follows:

$$\text{Dark formulation}: \text{C}\_6\text{H}\_{12}\text{O}\_6 \rightarrow 2\text{CH}\_3\text{COOH} + 2\text{CO}\_2 + 4\text{H}\_2 \tag{1}$$

$$\text{Photo-fermion} : 2\text{CH}\_3\text{COOH} + 4\text{H}\_2\text{O} + \text{Light} \rightarrow 4\text{CO}\_2 + 8\text{H}\_2 \tag{2}$$

Despite the continuing research at the laboratory scale, the biological hydrogen production from lignocellulosic biomass at pilot and industrial scales is still limited. Various kinds of lignocellulosic feedstock have been investigated for bio-hydrogen production by different microorganisms. Typically, the feedstocks are pretreated prior to fermentation in order to enhance hydrogen production efficiency. Pretreatment of the biomass can be conducted by physical (such as size reduction), physicochemical (such as steam, ammonia fiber, and carbon dioxide explosion, hot water, and microwave pretreatment), chemical (such as alkaline, diluted acid, and hydrogen peroxide pretreatment), and biological (such as enzymatic pretreatment) methods. The yield of hydrogen from lignocellulosic feedstocks is diverse depending on the types of substrates, pretreatment methods and microorganisms used. Under mesophilic condition, dark fermentation of untreated water hyacinth by mixed culture of Enterobacter sp. and Clostridium sp. resulted in 119.6 mL-H2/g-VS [48]. Enzymatic hydrolysates of agave bagasse yielded 1.53–3.40 mol-H2/mol-substrate by anaerobic mixed cultures [49, 50]. Higher hydrogen production from acid hydrolysate of sugarcane bagasse (6980 mL-H2/Lsubstrate) was observed with mixed cultures compared to the pure culture of Enterobacter aerogenes (1000 mL-H2/L-substrate) [51, 52].

The pretreated lignocellulosic biomass (in solid form) can also be directly fermented to hydrogen. Alkaline-pretreated sugarcane bagasse fermentation by C. beijerinckii yielded 0.733 mmol-H2/g-substrate [53]. The HY of 51.9 mL-H2/L-substrate was obtained by fermenting corn stover obtained after steam explosion using mixed cultures of C. celluloblyticum and Citrobacter amalonaticus [54]. The pretreated solid biomass could also be used as feedstocks for hydrogen production via simultaneous saccharification and fermentation (SSF) process. The cellulolytic enzymes mostly perform well under thermophilic condition (50–60°C). However, hydrogen production by SSF under mesophilic condition had been investigated by some researchers based on the optimal temperature for growth and activity of hydrogen producers. Hydrogen yield of 72 mL-H2/g-substrate was obtained from acetic acid steam-exploded corn straw by SSF with Ethanoligenens harbinense at 37°C [55]. A lower yield of 68 mL-H2/g-substrate was obtained from steam-exploded corn straw by SSF with C. bytyricum AS1 at 35°C [56].

Fermentation under thermophilic condition (50–65°C) was reported to improve dark fermentative hydrogen production via enhancing substrate degradation rate. Various thermophilic hydrogen producers, such as Thermoanaerobacterium thermosaccharolyticum [57, 58], C. thermosaccharolyticum, and C. thermocellum [59, 60], as well as thermophilic mixed cultures [61], were applied for hydrogen

production from lignocellulosic feedstocks and their hydrolysates. HY of 1947 mL-H2/L-substrate from microwave-assisted acid hydrolysate of oil palm trunk (OPT) was achieved using T. thermosaccharolyticum KKU19 [62], while the enzymatic hydrolysate of lime-pretreated OPT yielded 2179 mL-H2/L-substrate using the same strain [58]. Corn stover hydrolysate obtained by diluted sulfuric acid pretreatment was fermented by T. thermosaccharolyticum W16 with a yield of 2.24 mol-H2/mol-sugar [63]. When the enzymatic hydrolysate of NaOH-pretreated corn stover was used, the strain W16 produced 108.5 mmol-H2/L-substrate [64]. Solid residues of sweet sorghum stalk after hydrogen fermentation was subjected to diluted sulfuric acid hydrolysis. The resulting acid-treated slurry was further fermented by C. thermosaccharolyticum DSM572 and yielded 2.5 mmol-H2/gsubstrate [65]. Activated sludge and anaerobic granular sludge produced 627 and 822 mL-H2/L-substrate from diluted sulfuric acid hydrolysate of corn stover under thermophilic condition, which were 2.3 and 3.7 times higher than those obtained under mesophilic condition [61]. Sweet sorghum stalks were used as substrate for hydrogen production by mixed cultures of C. thermocellum DSM7072 and C. thermosaccharolyticum DSM572. The HY of 5.1 mmol-H2/g-substrate was observed [59]. Fermentation of hydrogen by thermophilic microorganisms could overcome the technical challenge of SSF regarding difference between optimal temperatures for enzymatic saccharification and fermentation. SSF of lime-pretreated OPT by T. thermosaccharolyticum KKU19 achieved a maximum yield of 60.22 mL-H2/gpretreated OPT [66]. Fungal-pretreated cornstalk yielded 89.3 mL-H2/g-substrate by SSF process with T. thermosaccharolyticum W16 [67].

oligosaccharides in corncob hydrolysate contributed to the hydrogen produced by dark fermentation, while acetic acid, butyric acid, and alcohols in the dark fermentation effluent contributed to the hydrogen produced by photo-fermentation [75]. A pilot scale test of sequential dark-photo-fermentation from corn stover was investigated. Sewage sludge and photo-hydrogen-producing consortia HAU-M1 were used as inoculum for dark and photo-fermentation, respectively. The overall

Methane is a fuel gas mainly produced from anaerobic digestion process. Organic substrates are decomposed by diverse microbial communities through a series of metabolic stages during anaerobic digestion, resulting in gaseous products called biogas and inorganic molecules remaining in digestate. Biogas mainly comprises methane (50–75%), carbon dioxide (25–40%), nitrogen (<5%), hydrogen (<1%), oxygen (<1%), and hydrogen sulfide (50–5000 ppm) [76]. Biogas is suitable for use in internal combustion engines and gas turbine generators. Methane has higher octane rating than gasoline, and its combustion produces less CO2 as

Methane production by anaerobic digestion process involved multiple steps performed by several groups of microorganisms. Typically, anaerobic digestion is divided into four steps that are hydrolysis, acidogenesis, acetogenesis, and

methanogenesis. In hydrolysis step, complex organic matters (such as cellulose and protein) are converted into simpler and soluble molecules (such as sugars and amino acids) by hydrolase enzymes excreted by facultative and strictly anaerobic microorganisms called fermentative bacteria. The soluble molecules produced by the hydrolysis steps are then utilized by acidogenic bacteria to produce short-chain organic acids (such as acetic, butyric, and propionic acids) along with hydrogen, carbon dioxide, and alcohols in the acidogenesis step. These products are further consumed in the acetogenesis step to produce acetic acid by acetogenic bacteria. In the last step, acetic acid, hydrogen with carbon dioxide, formic acids, and alcohols were utilized by methanogenic bacteria to produce methane under obligate anaerobic condition [76]. The optimal condition for methanogenic bacteria and other groups of bacteria are different. Some researchers, therefore, introduced two-stage hydrogen and methane production carried out by separating the fermentation into two phases of acidogenesis and methanogenesis, which can promote the methane

fermentation rate and increase energy yield from feedstocks [27, 58].

[79–82]. Alkaline pretreatment and combination of alkaline with other

yield compared to un-pretreated feedstocks [83].

113

pretreatment methods are usually employed, while the thermal pretreatment is reported as the suitable method resulting in greater than 50% increased methane

Theoretically, the yield of methane, at standard temperature and pressure, from cellulose and hemicellulose are 415 and 424 mL-CH4/g with 50% methane content in the biogas [76]. Since the compositions of lignocellulosic biomass are diverse, the yield of methane varies depending on the type lignocellulosic feedstocks used.

Methane production from various lignocellulosic biomasses has been investigated by different research groups. Due to their complex structures which limit the bioavailability, hydrolysis was reported as the rate-limiting step for methane production from lignocellulosic feedstocks [78]. In order to increase methane production rate (MPR) and improve methane production efficiency, different pretreatment methods such as size reduction, thermal, hydrothermal, alkaline, dilute acid, thermal alkaline/dilute acid, and fungal pretreatments were applied

/ m<sup>3</sup>

d from dark and

volumetric hydrogen production rate (HPR) was 7.8 and 4.7 m<sup>3</sup>

Bio-hydrogen and Methane Production from Lignocellulosic Materials

photo-fermentation, respectively [47].

DOI: http://dx.doi.org/10.5772/intechopen.85138

compared to fossil fuels [77].

3.2 Methane

Co-digestion with nitrogen-rich organic biomass was reported to enhance hydrogen production from lignocellulosic feedstocks. The OPT hydrolysate codigested with slaughterhouse wastewater by T. thermosaccharolyticum KKU19 gave 2604 mL-H2/L-substrate [68]. Co-digestion of napier grass and its silage with cow dung with the bioaugmentation of C. butyricum TISTR 1032 yielded 6.98 and 27.71 mL-H2/g-volatile solid (VS) [69]. Wheat straw and cheese whey were codigested by anaerobic granular sludge, and the hydrogen production of 4554, 3685, and 4132 mL-H2/L-substrate were observed in 0.11-L serological bottle, 1-L bioreactor, and 4-L bioreactor, respectively [70].

Photo-fermentative hydrogen production mostly uses simple sugars (such as glucose) or organic acids (such as acetic and butyric acids) as substrates. Lignocellulosic hydrolysates with sugar monomers were investigated for hydrogen production. Photo-fermentation of enzymatic hydrolysate of ammonia pretreated wheat straw by Rhodobacter capsulatus-PK gave 712 mL-H2/L-substrate [71]. Corn stalk pith was hydrolyzed by cellulase enzyme. The resulting hydrolysate was fermented by photosynthetic consortium comprising R. capsulatus, R. sphaeroides, Rhodopseudomonas capsulata, Rhodopseudomonas palustris, and Rhodospirillum rubrum, in which a HY of 2.6 mol-H2/mol-sugar consumed was achieved [72].

Sequential dark-photo-fermentation was applied to increase HY from lignocellulosic biomass. The organic acids obtained from dark fermentation of lignocellulosic biomass are used as substrate for photo-fermentation. The yield of hydrogen from water hyacinth was enhanced from 76.7 to 596.1 mL-H2/g-total volatile solid (TVS) by combining dark fermentation (using mixed hydrogen-producing bacteria) with photo-fermentation (using R. palustris) [73]. Dark fermentation of pretreated corn stalk by mixed culture from cow dung yield 192.9 mL-H2/g-TVS. The yield was increased to 401.5 m mL-H2/g-TVS by combining with photofermentation using R. sphaeroides HY01 [74]. Yang et al. [75] reported a HY from pretreated corncob by dark fermentation with mixed cultures from dairy manure of 120.2 mL-H2/g-corncob. Photo-fermentation of the effluent from this process gave 713.6 mL-H2/g-COD. The authors also stated that reducing sugars and

Bio-hydrogen and Methane Production from Lignocellulosic Materials DOI: http://dx.doi.org/10.5772/intechopen.85138

oligosaccharides in corncob hydrolysate contributed to the hydrogen produced by dark fermentation, while acetic acid, butyric acid, and alcohols in the dark fermentation effluent contributed to the hydrogen produced by photo-fermentation [75]. A pilot scale test of sequential dark-photo-fermentation from corn stover was investigated. Sewage sludge and photo-hydrogen-producing consortia HAU-M1 were used as inoculum for dark and photo-fermentation, respectively. The overall volumetric hydrogen production rate (HPR) was 7.8 and 4.7 m<sup>3</sup> / m<sup>3</sup> d from dark and photo-fermentation, respectively [47].

### 3.2 Methane

production from lignocellulosic feedstocks and their hydrolysates. HY of 1947 mL-H2/L-substrate from microwave-assisted acid hydrolysate of oil palm trunk (OPT) was achieved using T. thermosaccharolyticum KKU19 [62], while the enzymatic hydrolysate of lime-pretreated OPT yielded 2179 mL-H2/L-substrate using the same strain [58]. Corn stover hydrolysate obtained by diluted sulfuric acid pretreatment was fermented by T. thermosaccharolyticum W16 with a yield of 2.24 mol-H2/mol-sugar [63]. When the enzymatic hydrolysate of NaOH-pretreated corn stover was used, the strain W16 produced 108.5 mmol-H2/L-substrate [64]. Solid residues of sweet sorghum stalk after hydrogen fermentation was subjected to diluted sulfuric acid hydrolysis. The resulting acid-treated slurry was further fermented by C. thermosaccharolyticum DSM572 and yielded 2.5 mmol-H2/gsubstrate [65]. Activated sludge and anaerobic granular sludge produced 627 and 822 mL-H2/L-substrate from diluted sulfuric acid hydrolysate of corn stover under thermophilic condition, which were 2.3 and 3.7 times higher than those obtained under mesophilic condition [61]. Sweet sorghum stalks were used as substrate for hydrogen production by mixed cultures of C. thermocellum DSM7072 and C. thermosaccharolyticum DSM572. The HY of 5.1 mmol-H2/g-substrate was observed [59]. Fermentation of hydrogen by thermophilic microorganisms could overcome the technical challenge of SSF regarding difference between optimal temperatures for enzymatic saccharification and fermentation. SSF of lime-pretreated OPT by T. thermosaccharolyticum KKU19 achieved a maximum yield of 60.22 mL-H2/gpretreated OPT [66]. Fungal-pretreated cornstalk yielded 89.3 mL-H2/g-substrate

Biomass for Bioenergy - Recent Trends and Future Challenges

by SSF process with T. thermosaccharolyticum W16 [67].

actor, and 4-L bioreactor, respectively [70].

112

Co-digestion with nitrogen-rich organic biomass was reported to enhance hydrogen production from lignocellulosic feedstocks. The OPT hydrolysate codigested with slaughterhouse wastewater by T. thermosaccharolyticum KKU19 gave 2604 mL-H2/L-substrate [68]. Co-digestion of napier grass and its silage with cow dung with the bioaugmentation of C. butyricum TISTR 1032 yielded 6.98 and 27.71 mL-H2/g-volatile solid (VS) [69]. Wheat straw and cheese whey were codigested by anaerobic granular sludge, and the hydrogen production of 4554, 3685, and 4132 mL-H2/L-substrate were observed in 0.11-L serological bottle, 1-L biore-

Photo-fermentative hydrogen production mostly uses simple sugars (such as glucose) or organic acids (such as acetic and butyric acids) as substrates. Lignocellulosic hydrolysates with sugar monomers were investigated for hydrogen production. Photo-fermentation of enzymatic hydrolysate of ammonia pretreated wheat straw by Rhodobacter capsulatus-PK gave 712 mL-H2/L-substrate [71]. Corn stalk pith was hydrolyzed by cellulase enzyme. The resulting hydrolysate was fermented

by photosynthetic consortium comprising R. capsulatus, R. sphaeroides, Rhodopseudomonas capsulata, Rhodopseudomonas palustris, and Rhodospirillum rubrum, in which a HY of 2.6 mol-H2/mol-sugar consumed was achieved [72]. Sequential dark-photo-fermentation was applied to increase HY from lignocellulosic biomass. The organic acids obtained from dark fermentation of lignocellulosic biomass are used as substrate for photo-fermentation. The yield of hydrogen from water hyacinth was enhanced from 76.7 to 596.1 mL-H2/g-total volatile solid (TVS) by combining dark fermentation (using mixed hydrogen-producing bacteria) with photo-fermentation (using R. palustris) [73]. Dark fermentation of pretreated corn stalk by mixed culture from cow dung yield 192.9 mL-H2/g-TVS. The yield was increased to 401.5 m mL-H2/g-TVS by combining with photofermentation using R. sphaeroides HY01 [74]. Yang et al. [75] reported a HY from pretreated corncob by dark fermentation with mixed cultures from dairy manure of 120.2 mL-H2/g-corncob. Photo-fermentation of the effluent from this process gave

713.6 mL-H2/g-COD. The authors also stated that reducing sugars and

Methane is a fuel gas mainly produced from anaerobic digestion process. Organic substrates are decomposed by diverse microbial communities through a series of metabolic stages during anaerobic digestion, resulting in gaseous products called biogas and inorganic molecules remaining in digestate. Biogas mainly comprises methane (50–75%), carbon dioxide (25–40%), nitrogen (<5%), hydrogen (<1%), oxygen (<1%), and hydrogen sulfide (50–5000 ppm) [76]. Biogas is suitable for use in internal combustion engines and gas turbine generators. Methane has higher octane rating than gasoline, and its combustion produces less CO2 as compared to fossil fuels [77].

Methane production by anaerobic digestion process involved multiple steps performed by several groups of microorganisms. Typically, anaerobic digestion is divided into four steps that are hydrolysis, acidogenesis, acetogenesis, and methanogenesis. In hydrolysis step, complex organic matters (such as cellulose and protein) are converted into simpler and soluble molecules (such as sugars and amino acids) by hydrolase enzymes excreted by facultative and strictly anaerobic microorganisms called fermentative bacteria. The soluble molecules produced by the hydrolysis steps are then utilized by acidogenic bacteria to produce short-chain organic acids (such as acetic, butyric, and propionic acids) along with hydrogen, carbon dioxide, and alcohols in the acidogenesis step. These products are further consumed in the acetogenesis step to produce acetic acid by acetogenic bacteria. In the last step, acetic acid, hydrogen with carbon dioxide, formic acids, and alcohols were utilized by methanogenic bacteria to produce methane under obligate anaerobic condition [76]. The optimal condition for methanogenic bacteria and other groups of bacteria are different. Some researchers, therefore, introduced two-stage hydrogen and methane production carried out by separating the fermentation into two phases of acidogenesis and methanogenesis, which can promote the methane fermentation rate and increase energy yield from feedstocks [27, 58].

Methane production from various lignocellulosic biomasses has been investigated by different research groups. Due to their complex structures which limit the bioavailability, hydrolysis was reported as the rate-limiting step for methane production from lignocellulosic feedstocks [78]. In order to increase methane production rate (MPR) and improve methane production efficiency, different pretreatment methods such as size reduction, thermal, hydrothermal, alkaline, dilute acid, thermal alkaline/dilute acid, and fungal pretreatments were applied [79–82]. Alkaline pretreatment and combination of alkaline with other pretreatment methods are usually employed, while the thermal pretreatment is reported as the suitable method resulting in greater than 50% increased methane yield compared to un-pretreated feedstocks [83].

Theoretically, the yield of methane, at standard temperature and pressure, from cellulose and hemicellulose are 415 and 424 mL-CH4/g with 50% methane content in the biogas [76]. Since the compositions of lignocellulosic biomass are diverse, the yield of methane varies depending on the type lignocellulosic feedstocks used.

Herbaceous biomasses are common lignocellulosic feedstocks for methane production. Corn stover yielded 320–335 mL-CH4/g-VS [79, 84]. Co-digestion of corn stover with goose manure increased the methane yield (MY) to 393 mL-CH4/g-VS [85]. The straws of wheat, rice, and corn gave 240–329 mL-CH4/g-VS [86–91]. Relatively low values HY were observed from biomass of grasses (142– 301 mL-CH4/g-VS) [36, 83, 92, 93] and woody biomass (136–205 mL-CH4/g-TS) [79, 94], while bagasse feedstocks yielded relatively high values of 330– 420 mL-CH4/g-VS [95, 96].

easily digested by fermentative microorganisms. However, there is the concern on food competition and arable land when food crops are used to produce biofuels [105]. Thus, lignocellulosic biomass is developed as the second-generation feedstocks. Due to its compositions, lignocellulosic biomass is difficult to be digested by microorganisms. Therefore, the pretreatment and hydrolysis of the lignocellulosic biomass are needed in order to obtain its underlying monosugars prior the fermentation. Recently, the third-generation feedstock, i.e., microalgae has received high attention to produce hydrogen. Microalgae have rapid growth rate with a high capturing ability for CO2 and other greenhouse gases. They can be cultivated without soil and have a very short harvesting cycle (1–10 days) [106, 107]. Microalgae biomass consists of high carbohydrates (cellulose and starch) and lipid contents that can be converted to hydrogen by hydrogen producers. HY, HPR, and the overall economy of the process [102] are affected by the differences in carbohydrate content, bioavailability, and biodegradation rate of the first-, second-, and thirdgeneration feedstocks. In addition, the concentrations of feedstocks must be considered because a feedstock or product inhibition can occur in the fermentation

Bio-hydrogen and Methane Production from Lignocellulosic Materials

DOI: http://dx.doi.org/10.5772/intechopen.85138

Nitrogen is required for growth of hydrogen-producing bacteria. Nitrogen source for fermentative hydrogen production is classified into inorganic and organic. Examples of inorganic nitrogen are ammonia nitrogen [109], ammonium bicarbonate [110], and ammonium chloride [111, 112]. Ammonia nitrogen is the most widely used inorganic nitrogen with its optimal concentration in the range 0.1 to 7.0 g/L [113, 114]. Peptone, yeast extract, and corn steep liquor are the examples of organic nitrogen. Ferchichi et al. [115] and Ueno et al. [116] reported that a higher HY was obtained when organic nitrogen is supplied to the fermentation medium. In fermentative hydrogen production, phosphate is needed due to its nutritious value as well as buffering capacity. An increase in phosphate concentration results in increase of the capability of the bacteria to produce hydrogen. However, too high concentrations of phosphate could cause the substrate inhibition [113, 117]. The optimum C/N and C/P ratios are 74:200 and 599:1000, respectively [118, 119].

Temperature affects the maximum specific growth rate, substrate utilization rate, hydrolysis of the substrate, mass transfer rate, hydrogen partial pressure, hydrogenase activity, and the metabolic pathway of the bacteria resulting in a shift of byproduct compositions [101, 120, 121]. Fermentative hydrogen production can be operated under a wide range of temperature, i.e., mesophilic (25–40°C), thermophilic (40–65°C), or hyperthermophilic (>80°C) ranges [122]. Thermophilic condition gave a higher hydrogen production than the mesophilic condition. Sotelo-Navarro et al. [123] reported that the bio-hydrogen production from disposable diapers at 55°C was greater at 35°C. This could be due to the increased pace of microbial metabolism in the thermophilic condition. The optimal temperature for fermentative hydrogen

pH affects the activity of hydrogenase as well as the metabolism pathway of the microorganisms [109]. Low pH inhibited hydrogenase activity [124, 125] resulting in longer lag time [126] and the inhibition of dark fermentation process. This can be

production varies depending on the inoculum and substrate types.

process [108].

4.4 Temperature

4.5 pH

115

4.3 Nitrogen and phosphate

Two-stage hydrogen and methane production was reported as a successful process to produce hydrogen together with methane and enhance energy recovery from lignocellulosic biomass. Energy yield from OPT hydrolysate increased from 0.8 to 10.6 kJ/g-COD by applying two-stage thermophilic hydrogen and mesophilic methane production in comparison to one-stage thermophilic hydrogen production [57]. The HY of 53.8 mL-H2/g-VS together with HY of 133.9 mL-CH4/g-VS was achieved by two-stage fermentation of maize silage [97]. Sequential hydrogen and methane fermentation of sugarcane bagasse hydrolysate obtained by steam explosion yielded a total energy of 304.11 kJ/L-substrate [78]. The gaseous (hydrogen and methane) recovery from mixed sugarcane bagasse hydrolysate and water hyacinth was maximized by continuous two-stage hydrogen and methane production at a hydraulic retention time of 8 h and 10 days, respectively, providing energy yield of 8.97 KJ/g-COD [98]. Continuous two-stage hydrogen and methane production from agave bagasse enzymatic hydrolysate was optimized at an organic loading rate of 44 g-COD/L-d (for hydrogen) and 20 g-COD/L-d (for methane), in which 9.22 kJ/g-bagasse was recovered [99].
