Biohydrogen Production from Anaerobic Fermentation - Biotechnology in China: Biofuels and Bioenergy - page 158

with the dark fermentation alone. The total hydrogen production rate was 0.24 m 3
H 2 /m 3 /day, and the overall energy recovery efficiency was 23% (based on cellu-
lose removed). No external electrical energy input was need for the MEC.
Although the combined process of dark fermentation and photofermentation or
coupling of dark fermentation and an MEC could significantly enhance the
hydrogen yield, how to achieve the optimal design and match the different func-
tional processes is a key barrier that we have to overcome.
5 Perspectives
Biohydrogen is a renewable and clean energy source, making it an alternative for
sustainable production, particularly when it is produced from organic wastes.
However, although significant progress has been achieved in recent years in China
and worldwide, developing a cost-effective system for biohydrogen production is
still very challengeable, and the following bottlenecks should be addressed:
- Limitation of dark hydrogen fermentation. Although 4 mol H 2 /mol glucose can
be produced theoretically by clostridia, the yield achieved in reality is much
lower since significant reducing equivalents are diverted toward by-products
during the fermentation. Therefore, reducing by-product accumulation can
significantly improve the hydrogen yield, which can be realized by engineering
hydrogen-producing bacteria, taking advantage of understanding biological
fundamentals and advances in modern biotechnology.
- Coupling system for hydrogen production. Hydrogen production can be
enhanced when dark fermentation, an MFC, and an MEC are integrated toge-
ther, but optimization is needed for these units. For example, the pH of the
effluent discharged from dark fermentation should be adjusted for photosyn-
thetic bacteria and exoelectrogens in the MFC and MEC units, and more
intricate aspects underlying the reliable operation of the coupling system need to
be identified, which may generate significant costs.
- Policies. Like other bioenergy technologies, laws and regulations play an
important role in the production of biohydrogen. More investment is needed for
fundamental studies and technology innovations targeting low-cost and high
hydrogen recovery. Meanwhile, more preferable policies and/or strategies are
needed to balance the fraction of renewable energy in the Chinese market to
foster the industrialization of biohydrogen in the near future.
Acknowledgements The authors would like to thank the National Natural Science Foundation
of China (grant no. 51078100), the National Creative Research Groups (grant no. 50821002), the
National High-Tech R&D Program of China (grant no. 2009AA062906), and the State Key
Laboratory of Urban Water Resource and Environment (grant no. 2010DX11 and grant no.
2011TS09) for financial support.