Biohydrogen Production through Fermentative Technology

The human race since its inception has been faced with the dilemma of fulfilling its energy requirements. It has led to economic competition and in extreme case scenarios, even wars. Hydrogen gas has always remained a promising option for fulfilling the energy requirements. However, currently hydrogen production suffers from many hurdles such as high economic costs, technical limitations and difficulty in storage. Hydrogen is present abundantly in nature but not in its natural form and is found as compounds such as water, methane and biomolecules.

The use of hydrogen as a future energy fuel holds great promise because it is a clean fuel (generates only water vapour and energy). Another advantage is that it has the highest energy content per unit weight- 122 kJ/g and is environmentally safe(Das & Veziroglu, 2008).

Photosynthesis and fermentation are the chief biological methods of hydrogen production with fermentation process clearly holding an advantage over the latter in having better rates of hydrogen production and the option of utilising different wastes.

Mark D. Redwood et al. 2009 have reviewed and suggested using a combination of micro-organisms for maximising H2 production(Redwood, Paterson-Beedle, & Macaskie, 2008).

However, present processes are neither economically viable nor the yield is sufficient for large scale economic applications. Another potential disadvantage pointed out sometimes is that hydrogen is a dangerous fuel but so is gasoline if not handled properly and hydrogen can serve as a safer fuel if treated with care (Pudukudy, Yaakob, Mohammad, Narayanan, & Sopian, 2014).

Hydrogen can be produced by the following processes-

Non-renewable (fossil fuel) technologies include SMR (Steam Methane Reforming). SMR is currently the commercially viable method suitable for hydrogen production(Lam & Lee, 2011).

The SMR reaction can be depicted by the following equations(Lam & Lee, 2011)-

CH4+H2O⇔CO+3H2 ΔH=+206kJ/mol.

CO+H2O⇔CO2+H2 ΔH=−102kJ/mol.

From renewable sources, hydrogen can be produced via two major pathways- light dependent and light independent. Light dependent pathways include direct and indirect photolysis and photo-fermentation while indirect pathway includes dark fermentation. These processes are briefly presented in Table 1

Table 1

Type of pathway	Rate of H2 production (mol H2/l/h)	Organisms	By products	Advantages/Disadvantages
Direct biophotolysis	2.5- 12	Algae	O2	No extra energy required, sunlight provides energy.
Indirect biophotolysis		Algae	O2	Can fix N2 too.
Photo-fermentation		Algae and purple bacteria	CO2	Wide spectrum of light is utilised
Dark fermentation	12- 83	Fermentative bacteria	CO2, CH4, H2S, CO, Acetate etc.	No light input needed. Oxygen limitation is not an issue here.VFA accumulates in the effluent.
Hybrid Systems (Both dark and photo fermentation)	10- 15 X 103	Fermentative bacteria and phototrophs	CO2	Can contribute towards maximising overall yield and take advantage of both processes.

Table ref- Hallenbeck, Abo-Hashesh, & Ghosh, 2012,Kothari, Singh, Tyagi, & Tyagi, 2012, Argun & Kargi, 2011, Dasgupta et al., 2010 and S. Srikanth, S.V. Mohan, M.P. Devi, D. Peri, P.N. Sarma, 2009.

Direct Biophotolysis-

Sunlight is converted into chemical energy here and green algae have this ability. Direct biophotolysis can be represented by the following equation-

2H₂O         →         2H₂ + O₂ (Energy Source- sunlight) +1498 kJ

The reaction is rather slow because of the large amount of energy that needs to be overcome first (Perera, Ketheesan, Gadhamshetty, & Nirmalakhandan, 2010). Other disadvantages are the high bioreactor cost and costs involved in the separation of hydrogen and oxygen. The process can become feasible in future if photon conversion can significantly improved upon (Show, Lee, & Chang, 2011). In theory, two moles of H₂ should be produced from two moles of water but in actual the yield is much lower partly because of enzyme inhibition by oxygen (Dasgupta et al., 2010).

O₂ produced acts as an inhibitory agent of all hydrogen productivity and affects gene expression, leads to unstable mRNA and also affects catalytic enzyme activity (Eroglu & Melis, 2011).

Biophotolysis process has not received much attention largely due to the fact that uniform distribution of light and effective penetration is not easy to maintain, effective light collection would require a very large surface area(Show et al., 2011) and unless direct sunlight is utilised, the process will not be economically feasible(Kothari et al., 2012).

Indirect Biophotolysis-

Indirect biophotolysis can also result in hydrogen production from water. The reaction can be represented by the following reactions depending on the substrate being employed-

12H₂O            →             12H₂ + 6O₂ (Energy Source- sunlight)

Dark Fermentation-

Dark fermentation employs anaerobic bacteria without using sunlight. Dark fermentation products are typically hydrogen (H₂), carbon dioxide (CO₂), methane (CH₄), carbon monoxide (CO) and dihydrogen sulfide (H₂S) (Muhamad, Johan, Isa, & Kutty, 2011). The maximum yield from dark fermentation equals 4 moles of hydrogen whenever acetate is produced but in practice butyrate and propionate are also formed that brings down the yield. Advantages of dark fermentation include no sunlight requirement, multi-varied substrate utilisation and simple reactor design but overcoming low H₂ yield remains an issue. Reactions can be represented as follows-

Acetate C₆H₁₂O₆ + 2H₂O           →                2CH₃COOH + 4H₂ + 2CO₂

Butyrate C₆H₁₂O₆ + 2H₂O         →               2C₃H₇COOH + 2H₂ + 2CO₂

Propionate C₆H₁₂O₆ + 2H₂        →                2C₂H₅COOH + 2H₂O

Photo fermentation is the process wherein hydrogen and carbon dioxide production occurs with energy being provided by sunlight to breakdown organic compounds (Argun & Kargi, 2011). It may be represented by the following equation-

2CH₃COOH + 4H₂O                   →                (Energy source- Sunlight) 8H₂ + 4CO₂

Photo fermentation has the advantages of high hydrogen yield (theoretically a maximum of 12 moles), no oxygen production, and the ability to employ varied spectra of light.

Shortcomings include limited efficiency in the conversion of light, nitrogenise is energy intensive enzyme and the higher costs of bioreactors (Muhamad et al., 2011). Future strategies aim towards combining both fermentation technologies in order to maximise hydrogen production.

References-

Argun, H., & Kargi, F. (2011). Bio-hydrogen production by different operational modes of dark and photo-fermentation: An overview. International Journal of Hydrogen Energy, 36(13), 7443–7459. doi:10.1016/j.ijhydene.2011.03.116

Das, D., & Veziroglu, T. (2008). Advances in biological hydrogen production processes. International Journal of Hydrogen Energy, 33(21), 6046–6057. doi:10.1016/j.ijhydene.2008.07.098

Dasgupta, C. N., Jose Gilbert, J., Lindblad, P., Heidorn, T., Borgvang, S. a., Skjanes, K., & Das, D. (2010). Recent trends on the development of photobiological processes and photobioreactors for the improvement of hydrogen production. International Journal of Hydrogen Energy, 35(19), 10218–10238. doi:10.1016/j.ijhydene.2010.06.029

Eroglu, E., & Melis, A. (2011). Photobiological hydrogen production: Recent advances and state of the art. Bioresource Technology, 102(18), 8403–13. doi:10.1016/j.biortech.2011.03.026

Hallenbeck, P. C., Abo-Hashesh, M., & Ghosh, D. (2012). Strategies for improving biological hydrogen production. Bioresource Technology, 110, 1–9. doi:10.1016/j.biortech.2012.01.103

Kothari, R., Singh, D. P., Tyagi, V. V., & Tyagi, S. K. (2012). Fermentative hydrogen production – An alternative clean energy source. Renewable and Sustainable Energy Reviews, 16(4), 2337–2346. doi:10.1016/j.rser.2012.01.002

Lam, M. K., & Lee, K. T. (2011). Renewable and sustainable bioenergies production from palm oil mill effluent (POME): win-win strategies toward better environmental protection. Biotechnology Advances, 29(1), 124–41. doi:10.1016/j.biotechadv.2010.10.001

Muhamad, N. S., Johan, N. A., Isa, M. H., & Kutty, S. R. M. (2011). Biohydrogen production using dark and photo fermentation: A mini review. 2011 National Postgraduate Conference, 1–9. doi:10.1109/NatPC.2011.6136349

Perera, K. R. J., Ketheesan, B., Gadhamshetty, V., & Nirmalakhandan, N. (2010). Fermentative biohydrogen production: Evaluation of net energy gain. International Journal of Hydrogen Energy, 35(22), 12224–12233. doi:10.1016/j.ijhydene.2010.08.037

Pudukudy, M., Yaakob, Z., Mohammad, M., Narayanan, B., & Sopian, K. (2014). Renewable hydrogen economy in Asia – Opportunities and challenges: An overview. Renewable and Sustainable Energy Reviews, 30, 743–757. doi:10.1016/j.rser.2013.11.015

Redwood, M. D., Paterson-Beedle, M., & Macaskie, L. E. (2008). Integrating dark and light bio-hydrogen production strategies: towards the hydrogen economy. Reviews in Environmental Science and Bio/Technology, 8(2), 149–185. doi:10.1007/s11157-008-9144-9

Show, K.-Y., Lee, D.-J., & Chang, J.-S. (2011). Bioreactor and process design for biohydrogen production. Bioresource Technology, 102(18), 8524–33. doi:10.1016/j.biortech.2011.04.055

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