In addition, the culture in the reactor needs to be sterilized frequently
(every 1–3 months as has been concluded by studies reported by Duangmanee
et al. [80], Chen et al. [81], and Goud and Mohan [82]); otherwise, methanogens
establish themselves again in the reactor.
Pure cultures are suitable for a pure substrate such as glucose, xylose, etc. to
produce H 2 . However, there is still no proof that such a process would be technically
feasible at large scale, i.e., heating digesters of the same volumes as found in
wastewater treatment plants to 100 or 120
C to sterilize the culture. Moreover,
such a process will be economically unprofitable. The full-scale application of heat
treatment is technically complicated and questionable, as has been discussed by
Hawkes et al. [83] and Valdez-Vazquez and Poggi-Varaldo [84].
Pure culture (where sterilization is used to maintain the culture’s integrity for
usually a single strain) is used in the production of special commodities such as
flavors, antibiotics and other drugs, etc. The demand for special commodities is not
as high as that for fuel such as H 2 , and at the same time, the price of these products is
high compared to the targeted prices of biofuels. Therefore, the use of sterilization in
the case of special commodity production is still economically profitable. The
reactor volume used in the production of the special commodities is not as large as
the targeted reactors for H 2 production, the substrate is not waste, and the substrate
flow rate is not as high as that targeted for H 2 production.
Pure cultures are expensive and require sterilized conditions (substrate, reactor,
nutrients, etc.), while mixed cultures use non-sterile substrates such as waste
streams. Mixed cultures can be obtained from wastewater treatment facilities, livestock manure, agriculture soil, swamps and marshland, compost, and other natural
sources. Hydrogen yields from mixed cultures utilizing carbohydrate, palm oil, and
rice production facilities have been shown to reach maximum values of about
2.52 mol/mol glucose [85]. For the reasons mentioned earlier, pure or single culture
studies are out of the scope of this chapter which focuses on waste streams to make
the anaerobic treatment of industrial waste sustainable.
2 Metabolic Pathways of Dark Hydrogen Fermentation
The interaction of the various microorganisms in mixed culture anaerobic fermentation (MCF) results in a metabolic network that incorporates the bioreactions
through which the substrate is converted to intermediate metabolites and finally
into CH 4 . Figure 8.3 shows a typical and generally accepted metabolic network for
glucose fermentation in MCF for biohydrogen production [86]. During the fermentation of glucose, pyruvate is the central branching metabolite and the redox couple
(nicotinamide adenine dinucleotide (NAD)/NADH) serves as the electron carrier.
The oxidation of excess NADH (reaction 2) produces H 2 . Briefly, H 2 is produced
in two catabolic steps: (1) cleavage (decarboxylation) of pyruvate to acetyl-CoA,
CO 2 and H 2 (reaction 2) [86, 87], and hydrogenase [87] and (2) cleavage of formate
(reaction 7), which is catalyzed by formate hydrogenlyase [86].
8 Biohydrogen of Industrial Waste
333
(every 1–3 months as has been concluded by studies reported by Duangmanee
et al. [80], Chen et al. [81], and Goud and Mohan [82]); otherwise, methanogens
establish themselves again in the reactor.
Pure cultures are suitable for a pure substrate such as glucose, xylose, etc. to
produce H 2 . However, there is still no proof that such a process would be technically
feasible at large scale, i.e., heating digesters of the same volumes as found in
wastewater treatment plants to 100 or 120
C to sterilize the culture. Moreover,
such a process will be economically unprofitable. The full-scale application of heat
treatment is technically complicated and questionable, as has been discussed by
Hawkes et al. [83] and Valdez-Vazquez and Poggi-Varaldo [84].
Pure culture (where sterilization is used to maintain the culture’s integrity for
usually a single strain) is used in the production of special commodities such as
flavors, antibiotics and other drugs, etc. The demand for special commodities is not
as high as that for fuel such as H 2 , and at the same time, the price of these products is
high compared to the targeted prices of biofuels. Therefore, the use of sterilization in
the case of special commodity production is still economically profitable. The
reactor volume used in the production of the special commodities is not as large as
the targeted reactors for H 2 production, the substrate is not waste, and the substrate
flow rate is not as high as that targeted for H 2 production.
Pure cultures are expensive and require sterilized conditions (substrate, reactor,
nutrients, etc.), while mixed cultures use non-sterile substrates such as waste
streams. Mixed cultures can be obtained from wastewater treatment facilities, livestock manure, agriculture soil, swamps and marshland, compost, and other natural
sources. Hydrogen yields from mixed cultures utilizing carbohydrate, palm oil, and
rice production facilities have been shown to reach maximum values of about
2.52 mol/mol glucose [85]. For the reasons mentioned earlier, pure or single culture
studies are out of the scope of this chapter which focuses on waste streams to make
the anaerobic treatment of industrial waste sustainable.
2 Metabolic Pathways of Dark Hydrogen Fermentation
The interaction of the various microorganisms in mixed culture anaerobic fermentation (MCF) results in a metabolic network that incorporates the bioreactions
through which the substrate is converted to intermediate metabolites and finally
into CH 4 . Figure 8.3 shows a typical and generally accepted metabolic network for
glucose fermentation in MCF for biohydrogen production [86]. During the fermentation of glucose, pyruvate is the central branching metabolite and the redox couple
(nicotinamide adenine dinucleotide (NAD)/NADH) serves as the electron carrier.
The oxidation of excess NADH (reaction 2) produces H 2 . Briefly, H 2 is produced
in two catabolic steps: (1) cleavage (decarboxylation) of pyruvate to acetyl-CoA,
CO 2 and H 2 (reaction 2) [86, 87], and hydrogenase [87] and (2) cleavage of formate
(reaction 7), which is catalyzed by formate hydrogenlyase [86].
8 Biohydrogen of Industrial Waste
333