Although heat treatment application in lab studies is simple, its practical application at the industrial scale is technically complicated. Moreover, heating a digester
with volume of several thousand cubic meter to the temperatures usually used to
induce spore-forming and maintain it for a specific duration is an energy drain which
decreases the net energy yield of the waste treatment. Detailed and comprehensive
energy analysis for various wastes is required to establish the net energy yield for
various reactor designs at different operation conditions during H 2 production via
dark fermentation. The absence of a standard protocol for heat treatment application
to mixed cultures and lack of data on energy consumption and energy analysis
during studies involving heat treatment limit the applicability of the results to largescale applications.
4.2.2 Acid/Base Treatment
Treating the culture with acid (pH 3) or alkaline (pH 9 to 11.5) enriches
H 2 -producing bacteria in anaerobic mixed cultures [226–228]. Acid/base treatment
of cultures in industrial-scale bioreactors by maintaining pH 3 or pH 9 to 11.5 would
consume large quantities of acid and alkaline and requires equipment for feeding,
mixing, pH control, and then neutralizing or adjusting the pH to the desired initial pH
(usually 5.0–5.5). The acid and base consumption adds cost and lowers the economic profit of the process. For example, 48.3% of the overall cost of H 2 production
during dark-photo fermentation was the cost of the acid required to adjust the pH
[229]. Therefore, using an acidic or alkaline waste to pretreat the culture would offset
the cost of acid/base and enhance the sustainability of waste treatment.
4.2.3 Methanogen Inhibitors
Inhibitors used to inhibit methanogens can be classified into two types: natural and
synthetic. Long-chain fatty acids (LCFAs) at a concentration greater than some
threshold levels inhibit methanogens. LCFAs can be obtained from food processing
wastewater, such as from the vegetable oil industry. Obviously, such waste could be
used as a co-substrate with carbohydrate-rich waste to produce H 2 . Pendyala et al.
[230] reported H 2 yield of 17 mL/g COD fed from fermenting a food and paper
cardboard waste blend using linoleic acid (C18:2)-treated (2 g/L) anaerobic mixed
culture. The efficacy of LCFAs in dark fermentation hydrogen production studies for
pure substrates has been reported in several studies [53, 210, 218, 219]. More studies
are required to assess the effectiveness of LCFAs with different industrial wastes.
Replacing BESA and chloroform with LCFAs increases the sustainability of H 2
production from industrial wastewater treatment. Linoleic acid increased the H 2
yield to the same level in three different mixed cultures from different sources
compared to their controls [210].
Inhibitors such as 2-bromoethanesulfonic acid sodium salt (BESA) and chloroform can inhibit methanogens and block CH 4 formation. They have been used
8 Biohydrogen of Industrial Waste
351
with volume of several thousand cubic meter to the temperatures usually used to
induce spore-forming and maintain it for a specific duration is an energy drain which
decreases the net energy yield of the waste treatment. Detailed and comprehensive
energy analysis for various wastes is required to establish the net energy yield for
various reactor designs at different operation conditions during H 2 production via
dark fermentation. The absence of a standard protocol for heat treatment application
to mixed cultures and lack of data on energy consumption and energy analysis
during studies involving heat treatment limit the applicability of the results to largescale applications.
4.2.2 Acid/Base Treatment
Treating the culture with acid (pH 3) or alkaline (pH 9 to 11.5) enriches
H 2 -producing bacteria in anaerobic mixed cultures [226–228]. Acid/base treatment
of cultures in industrial-scale bioreactors by maintaining pH 3 or pH 9 to 11.5 would
consume large quantities of acid and alkaline and requires equipment for feeding,
mixing, pH control, and then neutralizing or adjusting the pH to the desired initial pH
(usually 5.0–5.5). The acid and base consumption adds cost and lowers the economic profit of the process. For example, 48.3% of the overall cost of H 2 production
during dark-photo fermentation was the cost of the acid required to adjust the pH
[229]. Therefore, using an acidic or alkaline waste to pretreat the culture would offset
the cost of acid/base and enhance the sustainability of waste treatment.
4.2.3 Methanogen Inhibitors
Inhibitors used to inhibit methanogens can be classified into two types: natural and
synthetic. Long-chain fatty acids (LCFAs) at a concentration greater than some
threshold levels inhibit methanogens. LCFAs can be obtained from food processing
wastewater, such as from the vegetable oil industry. Obviously, such waste could be
used as a co-substrate with carbohydrate-rich waste to produce H 2 . Pendyala et al.
[230] reported H 2 yield of 17 mL/g COD fed from fermenting a food and paper
cardboard waste blend using linoleic acid (C18:2)-treated (2 g/L) anaerobic mixed
culture. The efficacy of LCFAs in dark fermentation hydrogen production studies for
pure substrates has been reported in several studies [53, 210, 218, 219]. More studies
are required to assess the effectiveness of LCFAs with different industrial wastes.
Replacing BESA and chloroform with LCFAs increases the sustainability of H 2
production from industrial wastewater treatment. Linoleic acid increased the H 2
yield to the same level in three different mixed cultures from different sources
compared to their controls [210].
Inhibitors such as 2-bromoethanesulfonic acid sodium salt (BESA) and chloroform can inhibit methanogens and block CH 4 formation. They have been used
8 Biohydrogen of Industrial Waste
351