Journal of Scientific & Industrial Research Vol. 63, September 2004, pp. 729-738

Biohydrogen production as a potential energy resource – Present state-of-art

Kaushik Nath and Debabrata Das* Department of Biotechnology, Indian Institute of Technology, Kharagpur 721 302

Biological production is one of the most challenging areas of technology development for sustainable gaseous energy generation. The future of biological depends not only on research advances, i.e. improvement in efficiency through genetically engineered microorganisms and/or the development of , but also on economic considerations, as compared to fossil fuels, social acceptance, and the development of hydrogen energy systems. The present study critically updates various biohydrogenation processes with special references to their merits and demerits. Different approaches towards improvement of the bioprocesses are also outlined. Keywords: Hydrogen , Biophotolysis, Photofermentation, Light energy, Dark , Energy conversion efficiency IPC Code: Int. Cl. 7: C 12 P 1/02

1 Introduction Hydrogen holds much promise as a dream fuel of the future against the projection of the global energy crisis. In the past few years the concept of the has been put forth as a clean and efficient replacement for the petroleum based economy we now live under. It is a versatile energy carrier with the potential for extensive use in power generation and in many other applications. About half of all hydrogen produced is used in the manufacture of ammonia, which is itself mostly used in making fertilizers; a further 37 per cent is used in oil refineries for removal of impurities or for upgrading heavier oil fractions into lighter and more valuable products; 8 per cent in methanol production and 4 per cent in a wide variety of chemical, metallurgical and other uses. 1 per cent of hydrogen production is used in the world’s space programmes 1 (Fig. 1). The future widespread use of hydrogen is likely to be in the transportation sector where it will help reduce pollution. Vehicles can be powered with hydrogen fuel cells, which are three-times more efficient than a gasoline powered engine. As on today, in all these areas hydrogen utilization is equivalent to 3 per cent of the energy consumption, but it is expected to grow significantly in future 2. More than 500 b cu m of hydrogen are produced each year, for use in a wide variety of processes. This amount of hydrogen could produce 6.5 EJ of energy, equivalent to about 1.5 per cent of world energy consumption 3. 99 per cent of this hydrogen is produced from fossil fuels, primarily natural gas, with chemical production and sources accounting for the rest. At present, all of the CO 2 generated is released to atmosphere. Catalytic steam reforming of naphtha or natural gas, gasification of coal, and electrolysis of water are some of the classical methods of hydrogen manufacturing currently in vogue. But all these methods are highly energy intensive, thereby incurring higher cost and not always environmentally benign. On the contrary, biological processes are particularly useful for this application because they are catalyzed by microorganisms in an aqueous environment at ambient temperature and pressure. Furthermore, these techniques are well suited for decentralized energy production in small-scale installations in locations where biomass or wastes are available, thus avoiding energy expenditure 1 and costs for transport . From thermodynamic perspective, as the organic substrates dissolved and Fig.1—Different uses of hydrogen 730 J SCI IND RES VOL 63 SEPTEMBER 2004

diluted in wastewater are in a high entropy state, it is somewhat difficult to obtain their combustion enthalpy by mechanical means 4. Here comes the importance of biological hydrogen production process where microorganisms can recover and concentrate the energy from high water content organic resources such as, industrial wastewater and sludges in a usable form. Thus, biohydrogenation, in a sense, an entropy reducing process, which could not be realized by mechanical or chemical systems 4. Interest in started getting prominence in early 90s, when it became apparent that atmospheric pollution by fossil fuels is not only unhealthy locally, but might also cause significant climate changes globally. As a result, biological hydrogen production became a focus of Governmental support, particularly in Germany, the US and Japan, with least efforts in the other countries. The present paper briefly describes state-of-the-art of various biological hydrogen production processes. Attempts have also been made to highlight both the advantages and bottlenecks of each process towards improvement of production and process efficiency.

2 Biohydrogenation – State-of-the-Art Hydrogen metabolism is primarily the domain of and micro-. Within these groups, it involves many microbial species, including significantly different taxonomic and physiological types, various enzymes and metabolic pathways. Table 1 summarizes various biological hydrogen production processes with general overall reactions involved therein, broad classification of microorganisms used and their relative advantages.

Table 1 — Different biological hydrogen production processes with their advantages

Process General reactions and broad classification of Advantages microorganisms used

1 Direct biophotolysis 2 H 2O + light = 2 H 2 + O 2 (i) Can produce H 2 directly from water and sunlight Micro-algae (ii) Solar conversion energy increased by 10- folds as compared to trees, crops

2 Indirect biophotolysis 6 H 2O + 6 CO 2 + light = C 6H12 O6 + 6 O 2 (i) Can produce H 2 from water

C6H12 O6 + 2 H 2O = 4 H 2 + 2 CH 3COOH + 2 CO 2 (ii) Has the ability to fix N 2 from atmosphere

2 CH 3COOH + 4 H 2O + light = 8 H 2 + 4 CO 2

Overall reaction: 12 H 2O + light = 12 H 2 + 6 O 2

Microalgae,

3 (i) It can produce H 2 all day long without light (ii) A variety of carbon sources can be used as C6H12 O6 + 6 H 2O = 12 H 2 + 6 CO 2 substrates (iii) It produces valuable metabolites such as Fermentative bacteria butyric, lactic, and acetic acids as by products (iv) It is anaerobic process, so there is no O 2 limitation problem 4 Photo -fermentation (i) A wide spectral light energy can be used by CH 3COOH + 2 H 2O + light = 4 H 2 + 2 CO 2 these bacteria (ii) Can use different waste materials like distillery Purple bacteria, effluents, waste, etc. Microalgae

5 Hybrid reactor system Stage I (combined dark and C6H12 O6 + 2 H 2O = 4 H 2 + 2 CH 3COOH + 2 CO 2 Two stage fermentation can improve the overall photo- fermentation) yield of hydrogen Stage II CH 3COOH + 2 H 2O + light = 4 H 2 + 2 CO 2

Fermentative bacteria followed by anoxygenic phototrophic bacteria (PNS)

NATH & DAS: BIOHYDROGEN PRODUCTION AS A POTENTIAL ENERGY RESOURCE 731

2.1 Direct Biophotolysis Direct biophotolysis employs the dissociation of water molecules under sunlight in the presence of microalgae. It uses the same process found in plants and algal , but adapts them for the generation of hydrogen gas, instead of carbon containing biomass 5 (Fig. 2). Green microalgae Fig. 2—Direct biophotolysis possess the genetic, enzymatic, metabolic, and electron transport machinery to photoproduce hydrogen gas. Several researchers have reported algal photolysis using various species like Scenedesmus obliquus , Chlamydomonas reinhardii , C. moewusii (ref.5). Biophotolysis is an inherently attractive process since solar energy is used to convert a readily available substrate, water to oxygen, and hydrogen. This approach, if successful, would allow virtually unlimited production of hydrogen from the earth’s most plentiful available resources −water and light 6. Hydrogen production by green algae requires several minutes to a few hours of anaerobic incubation in the dark to induce the synthesis and/or activation of enzymes involved in hydrogen metabolism, including a reversible hydrogenase enzyme. Since hydrogenase activity is extremely oxygen sensitive the concurrent production of O 2 poses a serious limitation. This is the major bottleneck of the process. Sweeping out the oxygen, as it is produced, could mitigate this inhibition to a great extent 7. Although this would not be practical for large-scale operation. Some other attempts to overcome this problem include the use of O 2 absorbers, both reversible and irreversible, and the use of O 2 tolerant hydrogenase enzymes. But these attempts have met with 8 limited success . One promising solution is to develop microalgae with an O 2 insensitive hydrogenase reaction. Apart from these there are tremendous biological and engineering challenges to be overcome in realizing this goal. Direct biophotolysis requires entire production area to be enclosed in photobioreactor, which is able to both produce and capture H 2 and O 2. But this approach seems to be economically not viable as handling of H 2/O 2 mixtures in large volumes and over large areas would likely be impractical 6. The reducing power generated by photosynthesis must be produced as close as possible to the maximal possible solar conversion efficiency of about 10 per cent and then efficiently transferred to hydrogenase. Currently, photosynthetic organisms like higher plants capture only 3-4 per cent of sunlight’s available energy 7. Thus, direct biophotolysis, although theoretically attractive as a hydrogen production process, suffers from the major limitations of oxygen sensitivity, low light conversion efficiency and gas separation (Table 2). Future studies will pursue the possibility of "sweeping" oxygen from the system or development of a hydrogenase engineered to be insensitive to oxygen inactivation. In addition, this method requires enclosure of the solar capture area within a photo-, which creates great engineering challenges.

2.2 Indirect Biophotolysis Cyanobacteria (also known as blue-green algae, cyanophyceae, or cyanophytes) are a large and diverse group of photoautotrophic microorganisms, which can evolve hydrogen by indirect biophotolysis of water (Fig. 3). Photosystem II utilizes the energy of sunlight in photosynthesis to extract electrons from water molecules. Electrons released upon the oxidation of water are transported to the Fe-S protein ferredoxin on the reducing side of photosystem I. The hydrogenase in the stroma of the algal chloroplast accepts electrons from reduced 5 ferredoxin and donates them to two protons to generate one H 2 molecule . For photobiological hydrogen production, cyanobacteria have been adjudged as one of the ideal candidates since they have simple nutritional requirements as they can grow in air (N 2 and CO 2), water and mineral salts, with light as the only energy sources 9. Hydrogen production by cyanobacteria has been studied for over three decades and has revealed that efficient photoconversion of H 2O to H 2 is influenced by many factors. Hydrogen production has been assessed in various species and strains, within at least 14 genera, under a vast range of culture conditions 10 . The need of light for hydrogen evolution, nitrogenase, oxygen sensitivity, and lower hydrogen evolution vs acetylene reduction are some 732 J SCI IND RES VOL 63 SEPTEMBER 2004

Table 2—Major bottlenecks of the processes and various approaches to overcome

Processes Major limitations Approaches to overcome References

1 Direct (a) O 2 sensitivity of hydrogenase (a) biophotolysis enzyme (i) Use of O 2 absorbers, both irreversible (glucose- 6 oxidase, dithionite) and reversible (hemoglobin)

(ii) Use of O 2 tolerant uptake hydrogenase 13 (b)Low light conversion efficiency (b) (i) Genetic manipulation of light gathering antenna 14 (ii) Optimization of light input into photobioreactor 15

2 Indirect (a) Enzyme inhibition by O 2 (a) To achieve O 2 tolerant hydrogenase activity by 13 biophotolysis classical mutagenesis

(b) H 2 consumption by an uptake (b) Genetic modification of strains to eliminate uptake 16 hydrogenase hydrogenase (c) Overall low production rate (c) Genetic modification to increase levels of 17 bidirectional hydrogenase activity

3 Dark fermentation (a) Relatively lower achievable (a) Metabolic shift of biochemical pathways to arrest the 18 yields of H 2 formation of alcohol and acids (b) As yields increase, H 2 (b) Maintaining low partial pressure of H 2 19 fermentation becomes thermodynamically unfavorable (c) Product gas mixture contains (c) Efficient removal of gases 20 CO 2 which has to be separated

4 Photofermentation (a) Light conversion efficiency is (a) very low, only 1-5 per cent (i) Elimination of competing microorganisms (e.g. 21 micro- algae) using light filters (b) Inhomogeneity of light (ii) Co-cultures of photo heterotrophic bacteria with 22 distribution different light utilization characteristics

(c) O 2 is a strong inhibitor of (iii) Control of photosynthetic protein expression to 6 hydrogenase allow efficient absorption of light energy (b) Improvement in photoreactor design with light 6 diffuser

5 Hybrid reactor Relatively newer approach, − 23 system techno-economic feasibility is yet to be studied

Fig. 3—Indirect biophotolysis of the important factors of biophotolysis 10 . The cultivation of cyanobacteria in nitrate-free media under air and CO 2, followed by incubation in light under argon and CO 2 atmosphere, has rapidly become standard, since it results in immediate hydrogen production. Localization of nitrogenase in heterocysts provides an oxygen-free environment and the ability of heterocystous cyanobacteria to fix nitrogen in air 11 . Hydrogenase and nitrogenase inhibitors are used in an attempt to screen for aerobic hydrogen evolution potential. It has been observed that these inhibitors allow for hydrogen to be released from aerobic cultures in amounts similar to those in argon 11 . Photobiological technology holds great promise but because oxygen is produced along with the hydrogen the technology must overcome the limitation of oxygen sensitivity of the hydrogen-evolving enzyme systems. NATH & DAS: BIOHYDROGEN PRODUCTION AS A POTENTIAL ENERGY RESOURCE 733

Researchers are addressing this issue by screening for naturally occurring organisms that are more tolerant of oxygen, and by creating new genetic forms of the organisms that can sustain hydrogen production in the presence of oxygen 12 . A new system is also being developed that uses a metabolic switch (sulphur deprivation) to cycle algal cells between a photosynthetic growth phase and a hydrogen production phase 12 .

2.3 Photofermentation The efficiency of light energy used for the production Fig. 4—Schematic of hydrogen production by photosynthetic bacteria of hydrogen by photosynthetic bacteria is theoretically much higher compared with cyanobacteria. The advantages of phototrophic bacteria can be attributed to the following facts:

(i) High theoretical conversion yields, (ii) Lack of O 2 evolving activity, which otherwise causes O 2 inactivation problems in different biological systems, (iii) Ability to use wide spectral light energy, and (iv) Ability to consume organic substrates derived from wastes in association with wastewater treatment.

These organisms have an important role in the anaerobic cycling of organic matter – as producers (photoautrophs, utilizing CO 2 as their carbon source and H 2 as their electron donor), and as consumers (photoheterotrophs, using organic molecules as their carbon source and electron donor) 24 . Production of hydrogen by photosynthetic bacteria takes place under illumination and in the presence of an inert anaerobic atmosphere (such as argon or helium), from the break down of organic subtracts like, malate and lactate (Fig. 4). These anions of organic acids are preferred substrates. Apart from different organic acids and , several wastewaters have also been attempted to explore their suitability to be used as substrates for PNS bacteria to produce hydrogen. The efficiency of phototrophic bacteria for biological production of hydrogen is closely associated with several important variables. Photochemical efficiency is one of those. A generalized expression for photochemical efficiency has been put forward by Akkerman et al .12

Efficiency (per cent) = Hydrogen energy content H2 production rate × Absorbed light energy

For the photoautotrophic hydrogen production, photochemical efficiencies are only 3-10 per cent when the oxygen is totally and immediately removed. Such low efficiencies of photoautotrophic process pose a major limitation towards its commercial acceptance. On the other hand, photochemical efficiency of photoheterotrophic bacteria is comparatively higher than that of photoautotrophs. However, this is essentially based on artificial light, the efficiency of which can reach 10 per cent or even more by only at low light intensities with low hydrogen production rates 12 . The energy conversion efficiency of light energy into hydrogen in the presence of phototosynthetic bacteria varies under different light sources. It is believed that the hydrogen production by photosynthetic bacteria may depend on the spectral distribution, since the bacteria utilize the specific light wavelengths for photosynthesis. An approach for the improvement of hydrogen production by photosynthetic bacteria is the control of photosynthetic protein expression to allow efficient absorption of light energy. A method for the enhancement of the bacterial light-dependent hydrogen production is proposed by Miyake et al .4 by rearrangement of light harvesting systems. Genetic manipulation of photosynthetic pigment content of bacteria by ‘promoter competition method’ can be controlled for making the light penetration easy 4. 734 J SCI IND RES VOL 63 SEPTEMBER 2004

Inhomogeneity of the light distribution in the reactor also contributes to lower the overall light conversion efficiency. To enhance the total efficiency of light to hydrogen conversion in a photobioreactor, light energy should be equally distributed throughout the reactor. The spectrum of light in the reactor also affects hydrogen evolution. An important point of the application of solar energy is the efficiency of the conversion. It is said that the plant photosynthesis is done with energy conversion efficiency as low as 1 per cent 4. Another limitation of photofermentation is lower achievable yield of hydrogen. Koku et al .25 have proposed several conditions for maximum hydrogen production. Among these maintaining a maximal activity of nitrogenase and minimal activity of hydrogenase, a favorable molar ratio of carbon source to nitrogen source and availability of uniform distribution of light through the culture are important. Efforts to improve hydrogen production by photosynthetic bacteria also include elimination of competing microorganisms, such as micro algae, using light filters, as proposed by Ko and Noike 21 . The use of co-cultures of photoheterotrophic bacteria with different light utilization characteristics 22 , novel photobiorector designs 26 and use of specific waste streams as substrates for photo-fermentation 27 have also been explored as alternative options for improving the efficiency of photosynthetic processes. The main bottleneck for practical application of photobiological hydrogen production is the required scaling- up of the system. A large surface area is needed to collect light. Construction of a photobioreactor with a large surface/volume ratio for direct absorption of sunlight is expensive. A possible alternative is the utilization of solar collectors. Again, a drawback of these collector systems is the high production cost with the currently available technology.

2.4 Dark Fermentation Carbohydrates, mainly glucose, are the preferred carbon sources for fermentation process, which predominantly give rise to acetic and butyric acids together with hydrogen. Here, pyruvate the product of glucose catabolism is oxidized to acetyl-CoA, which can be converted to acetyl phosphate and results in generation of ATP and excretion of acetate. Pyruvate oxidation to acetyl-CoA requires ferredoxin (Fd) reduction. Reduced Fd is oxidized by hydrogenase, which generates Fd and releases electrons as molecular hydrogen.

Pyruvate + CoA + 2 Fd(ox) → Acetyl-CoA + 2Fd(red) + CO 2 2 Fd(red) → 2 Fd(ox) + H 2

Despite having higher evolution rate of hydrogen the yield of hydrogen from fermentation process is lower than that of other chemical/electrochemical processes, and thus the process is not economically viable in its present form. The pathways and experimental evidences cited in literature reveal that a maximum of four mole of hydrogen could be obtained from one mol of glucose . The relatively low yield of hydrogen during fermentation is a natural consequence of the fact that have been optimized by evolution to produce cell biomass and not hydrogen. Thus, a portion of the substrate (pyruvate) is used to produce ATP giving a product (acetate), which is excreted. Moreover, in many organisms the actual yields of hydrogen are reduced by hydrogen recycling owing to the presence of one or more uptake hydrogenase, which consume a part of hydrogen produced 6. The generation of hydrogen by fermentative bacteria also accompanies the formation of organic acids as metabolic products, but these anaerobes are incapable of further breaking down the acids. Accumulation of these acids causes a sharp drop of culture pH and subsequent inhibition of bacterial hydrogen production 28,29 . Bacteria cannot sustain at pH smaller than 5.0 and this necessitates to evolve a way to reduce acid production or to carry out certain biochemical reactions which reduces the proton concentration on the outside of the cell in proportion to the culture pH (ref. 30). The use of an aciduric facultative anaerobe of which the lower limit of pH for H 2 production is as low as possible to reduce alkali consumption might be an option. Another approach to improve the hydrogen yield is to block the formation of these acids through redirection of metabolic pathways 18,31 . The hydrogen yield is reportedly increased to 3.8 mol/(mol glucose) by blocking the pathways of organic acid 18 formation by proton-suicide technique using NaBr and NaBrO 3. NATH & DAS: BIOHYDROGEN PRODUCTION AS A POTENTIAL ENERGY RESOURCE 735

Gas sparging has been found to be a useful technique to reduce hydrogen partial pressure in the liquid phase for enhancement of its yield. Mizuno et al .19 have observed that specific hydrogen production rate has increased from 1.446 mL hydrogen/min/g biomass to 3.131 mL hydrogen/min/g biomass under nitrogen sparging conditions. With N 2 sparging at a flow rate approx 15-times the hydrogen production rate the hydrogen yield was 1.43 mol H 2/(mol glucose). This shows about 50 per cent increase in hydrogen yield with nitrogen sparging.

2.5 Hybrid Reactor System The idea of combined dark and photofermentation system takes into consideration the very fact of relatively lower achievable yield of hydrogen in dark fermentation and also the non-utilization of the acids produced therein. The combination of photosynthetic bacteria with that of anaerobic could provide an integrated system for maximization of hydrogen yield 32 . In such a system, anaerobic fermentation of (or organic wastes) produces intermediates such as, low molecular weight organic acids, which are then converted to hydrogen by photosynthetic bacteria in the second step in a photobioreactor. Lee et al .23 have studied the combination of purple nonsulphur photosynthetic bacteria and anaerobic bacteria for efficient conversion of wastewater into hydrogen. In this study, effluents from three carbohydrate-fed reactors (CSTR, ASBR, and UASB) have been used for hydrogen production. In another study, Kim et al. 33 have combined dark fermentation with photofermentation to improve hydrogen productivity from food processing wastewater and sewage sludge. The conversion efficiency of light energy to hydrogen, with the supply of an appropriate carbon source, is one of the key factors for hydrogen production by biological systems. Anaerobic bacteria decompose carbohydrates to obtain both energy and electron. Because reaction with only negative free energy could be possible, organic acids formed by the could not be decomposed to hydrogen any more. Complete degradation of glucose to hydrogen and carbon dioxide is virtually impossible by anaerobic digestion. But photosynthetic bacteria could use light energy to overcome the positive free energy of reaction (bacteria can utilize organic acids for hydrogen production) 5. The conversion of malate and lactate to hydrogen by photosynthetic bacteria (mainly purple non-sulphur) is well documented 22, 25 . The main products of anaerobic fermentation are acetic and butyric acids. Thus, further conversion of these acids into hydrogen by photofermentation underlines the synergy of the integrated process. This combination of both kinds of bacteria not only reduces the light energy demand of the photosynthetic bacteria but also enhances the hydrogen yield as well 5,34 . Dark hydrogen fermentation is an incomplete oxidation, yielding not only hydrogen and CO 2, but also organic acids like, acetic acid. Therefore, for an economically sound process the remaining carbonaceous compounds are to be converted, either in a photo-bioreactor to H 2 and CO 2 or in a methane reactor to CH 4 and CO 2. If the dark hydrogen fermentation is not followed by further conversion the H 2 yield will not warrant economic feasibility.

3 Energy Potentials of Biohydrogen and other Bioenergy Resources Biohydrogen, bioethanol, and biomethane have many comparable points of resemblance, both in terms of renewablity of their raw materials for production and their end-uses as fuels. However, bioethanol is a liquid fuel, which unlike any gaseous fuel requires the process of distillation and dehydration during production. Considering yields of ethanol from glucose as 1.6 mol/mol glucose, lower heating value of ethanol and glucose as 296 and 712 kcal/mol, the distillation energy of ethanol as 50 per cent of the energy of the produced ethanol produced 35 , therefore,

Energy recovered as ethanol from glucose 0.50 = ()296× 1.6 × × 100 per cent 712 = 33.25 per cent

A simplified stoichiometric equation for producing hydrogen by utilization of glucose as substrate can be written as:

C6H12 O6 + 6H 2O = 12H 2 + 6CO 2 ... (1) 736 J SCI IND RES VOL 63 SEPTEMBER 2004

The stoichiometric coefficients of the two gasses on the right hand side indicate that the volumetric ratio of hydrogen to carbon dioxide should be 2 to 1. It is interesting to note that half the produced hydrogen comes from glucose and half from water, which is split in this reaction. The gross heating value of hydrogen is 68.6 kcal/mol, so that the energy yield per mol of glucose reacted can be calculated as follows:

Hydrogen energy yield = 68.6 kcal/mol ×12 mol = 823.2 kcal

This can be compared to the energy yield of methane from anaerobic digestion, with reaction:

C6H12 O6 = 3CH 4 + 3CO 2 ... (2)

In Eq. (2), 180 g of glucose produces 48 g of methane and 132 g of CO 2. The gross heating value of methane is 212.27 kcal/mol.

Methane energy yield = 212.27 kcal/mol × 3 mol = 636.81 kcal

Therefore, theoretically it is evident that the energetic of hydrogen production compares favourably with methane production. Anaerobic conversion of carbohydrates into methane gas is well known. In the biomethanation process the appropriate residues produce volatile acids in such a manner that it allows methanogens to build up, resulting in the formation of CH 4 and CO 2. Several studies with energy crops producing methane are found in literature with algae, kelp and water hyacinth 36, 37 . It has been observed that conversion efficiencies of various crops grown for methane production are generally under 50 per cent, depending on degree of mixing and the content of celluloses/hemicelluloses. Energy recovery in biomethanation of distillery waste, both with and without recycling of spent slurry varies within 56-65 per cent 38 . In another study, using live stock waste 32 GJ of methane was obtained from an overall energy input of 82.5 GJ 39 . This shows that overall energy conversion of this process of biomethanation is only 38.78 per cent. A comparison of production costs, conversion efficiency, and net CO 2 emissions for different hydrogen production processes are given in Table 3. In the biological hydrogen production from biomass, CO 2 is one of the products. Besides CO 2 and H 2, no other gaseous products are expected from the dark fermentation. NATH & DAS: BIOHYDROGEN PRODUCTION AS A POTENTIAL ENERGY RESOURCE 737

Table 3 — Comparison of hydrogen production costs, conversion efficiency and net CO 2 emissions

Production processes Conversion efficiency Production costs CO 2 emissions References 3 3 (per cent) (US$/Nm H 2) (kg/Nm H 2)

Natural gas reforming 75 0.45 0.8 40 Electrolysis of water with conventional electricity N A 0.32 1.8 40 Electrolysis with electricity from wind turbines ~75 0.35 0 40 Steam-reforming of bio-methane ~20 0.45 0 40 Photobiological hydrogen ~ 10 ~10** 0 10 Electrolysis with electricity from photovoltaic cells N A 4.13 0 40 2-stage bioprocess for hydrogen from biomass 15 0.35 0 40 Indirect micro-algal biophotolysis ~7 10* N A 41,42 Cyanobacterial biophotolysis N A 15* N A 43 Fermentative hydrogen ~22 ~ 40** N A 5 Hydrogen from coal/biomass N A 4** N A 44 * US$/GJ ** US$/MBTU N A − Not available

Hydrogen is currently more expensive than other fuel options, so it is likely to play a major role in the economy in the long run, if technology improvements succeed in bringing down costs. Biological hydrogen production, employing renewable biomass may be a potential answer to overcome some of the economic constraints to fulfill many of our energy needs. There is scope to use sugarcane juice; molasses or distillery effluent as substrates, because they contain sugar in significant quantities. Therefore, production as well as unit energy cost of biohydrogen would be reduced drastically. However, a rigorous techno-economic analysis is necessary to draw a cost-effective comparison between biologically produced hydrogen and the various other conventional fossil fuels. But economic survey, based on fuel cost estimation, turns out to somewhat complicated when applied in practical terms. This is because of the intervening several other techno-economic parameters. The socially relevant cost of bringing any fuel to market must also include such factors as pollution and other short and long-term environmental cost, as well as direct and indirect health cost. When these factors are taken into consideration, together with its initial cost competitiveness, hydrogen is surely the most logical choice for a worldwide energy medium.

4 Concluding Remarks It is widely acknowledged that hydrogen can offer tremendous potentials as a clean and renewable energy currency. As a consequence, biological hydrogen production has been the subject of basic and applied research for several decades. Many research works are available on the , enzymology, and process technology of biohydrogen production processes. Each process has its pros and cons in terms of technology and productivity. Most of these works focus on the enhancement of hydrogen yield and also energy efficiencies of the respective processes. But unfortunately, all these processes have yet to be evaluated rigorously in terms of the cost for commercialization. Therefore, it is particularly imperative to address several techno-economic challenges for cost-effective production as well as commercial application of biohydrogen. Acknowledgement Financial assistance obtained from the Department of Biotechnology, Government of India, is acknowledged.

References 1 Elam C C, Gregoire Padro C E, Sandrock G, Luzzi A, Lindblad P & Hagen E-F, Realizing the hydrogen future: the International Energy Agency’s efforts to advance hydrogen energy technologies, Int J Hydrogen Ener, 28 (2003) 601-607. 2 Boyles D, Bio-energy technology – Thermodynamics and costs (John Wiley & Sons, New York) 1984, pp 8-13. 3 Nath K & Das D, Hydrogen from biomass, Cur Sci, 85 (2003) 265-271. 4 Miyake J, Miyake M & Asada Y, Biotechnological hydrogen production: research for efficient light energy conversion, J Biotechnol, 70 (1999) 89-101. 5 Das D & Veziroglu T N, Hydrogen production by biological processes: A survey of literature, Int J Hydrogen Ener, 26 (2001) 13- 28. 738 J SCI IND RES VOL 63 SEPTEMBER 2004

6 Hallenbeck P C & Benemann J R, Biological hydrogen production; fundamentals and limiting processes, Int J Hydrogen Ener, 27 (2002) 1185-1193. 7 Benemann J, Hydrogen biotechnology: progress and prospects, Nature Biotech , 14 (1996) 1101-1103. 8 Ghirardi M L, Togasaki R K & Seibert M, Oxygen sensitivity of algal hydrogen production, Appl Biochem Biotechnol, 63 (1997) 141-149. 9 Hansel A & Lindblad P, Mini-review: towards optimization of cyanobacteria as biotechnologically relevant producers of molecular hydrogen, a clean and renewable energy source, Appl Environ Microbiol , 50 (1998) 153-160. 10 Benemann J R, Feasibility analysis of photobiological hydrogen production. Int J Hydrogen Ener, 22 (1997) 979-987. 11 Pinto F A L, Troshina O & Lindblad P, A brief look at three decades of research on cyanobacterial hydrogen evolution, Int J Hydrogen Ener, 27 (2002) 1209-1215. 12 Akkerman I, Janssen M, Rocha J & Wijffels R H, Photobiological hydrogen production: photochemical efficiency and bioreactor design, Int J Hydrogen Ener, 27 (2002) 1195-1208. 13 McTavish H, Sayavedra-Soto L A & Arp D J, Substitution of Azotobacter vinelandii hydrogenase small subunit cysteines by serines can create insensitivity to inhibition by O 2 and preferentially damages H 2 oxidation over H 2 evolution, J Bacteriol, 177 (1995) 3960– 3964. 14 Polle J E W, Kanakagiri S, Jin E, Masuda T & Melis A, Truncated chlorophyll antenna size of the photosystems––a practical method to improve microalgal productivity and hydrogen production in mass culture, Int J Hydrogen Ener, 27 (2002) 1257-1264. 15 Gordon J, Tailoring optical systems to optimized photobioreactors. Int J Hydrogen Ener, 27 (2002) 1175-1184. 16 Levin D B, Pitt L & Love M, Biohydrogen production: prospects and limitations to practical application. Int J Hydrogen Ener, 29 (2004) 173-185. 17 Carrasco C D, Buettner J A & Golden J W, Programmed DNA rearrangement of a cyanobacterial hupL gene in heterocysts, Proc Natl Acad Sci USA , 92 (1995) 791-795. 18 Kumar N, Ghosh A & Das D, Redirection of biochemical pathways for the enhancement of H 2 production by Enterobacter cloacae, Biotechnol Lett, 23 (2001) 537-541. 19 Mizuno O, Dinsdale R, Hawkes F R, Hawkes D L & Noike T, Enhancement of hydrogen production from glucose by nitrogen gas sparging, Bioresource Technol , 73 (2000) 59-65. 20 Tanisho S, Kuromoto M & Kadokura N, Effect of CO2 removal on hydrogen production by fermentatio n, Int J Hydrogen Ener, 23 (1998) 559-563. 21 Ko I-B & Noike T, Use of blue optical filters for suppression of growth of algae in hydrogen producing non-axenic cultures of RV, Int J Hydrogen Ener, 27 (2002) 1297-1302. 22 Kondo T, Arakawa M, Wakayama T & Miyake J, Hydrogen production by combining two types of photosynthetic bacteria with different characteristics, Int J Hydrogen Ener, 27 (2002) 1303-1308. 23 Lee C-M, Chen P-C, Wang C-C & Tung Y-C, production using purple non-sulphur bacteria with hydrogen fermentation reactor effluent, Int J Hydrogen Ener, 27 (2002) 1308-1314. 24 Zehnder P & Alexander J B. Biology of anaerobic microorganisms (John Wiley and Sons, New York) 1988, pp 39-79. 25 Koku H, Eroglu I, Gunduz U, Yucel M & Turker L. Aspects of metabolism of hydrogen production by Rhodobacter sphaeroides , Int J Hydrogen Ener, 27 (2002) 1315-1329. 26 Hoekema S, Bijmans M, Janssen M, Tramper J & Wijffels R H, A pneumatically agitated flat-panel photobiorector with gas recirculation: anaerobic photoheterotrophic cultivation of a purple non-sulphur bacterium, Int J Hydrogen Ener, 27 (2002) 1331- 1338. 27 Zhu H, Ueda S, Asada Y & Miyaki J, Hydrogen production as a novel process of wastewater treatment – studies on tofu wastewater with entrapped R. sphaeroides and mutagenesis, Int J Hydrogen Ener, 27 (2002) 1349-1358. 28 Oh Y-K, Seol E-H, Kim J R & Park S, Fermentative biohydrogen production by a new chemoheterotrophic bacterium Citrobacte r sp. Y19, Int J Hydrogen Ener, 28 (2003) 1353-1359. 29 Oh Y-K, Seol E-H, Yeol Lee E & Park S, Fermentative hydrogen production by a new chemolithotrophic bacterium Rhodopseudomonas palustris P4. Int J Hydrogen Ener, 27 (2002) 1373-1379. 30 Fabiano B & Perego P, Thermodynamic study and optimization of hydrogen production by Enterobacter aerogenes , Int J Hydrogen Ener, 27 (2002) 149-156. 31 Mahyudin A R, Furutani Y, Nakashimada Y, Kakizono T & Nishio N, Enhanced hydrogen production in altered mixed acid fermentation of glucose by Enterobacter aerogenes, J Ferment Bioeng , 83 (1997) 358-363. 32 Yokoi H, Mori S, Hirose J, Hayashi S & Takasaki Y, H 2 production from starch by a mixed culture of Clostridium butyricum and Rhodobacter sp M-19, Biotechol Lett, 20 (1998) 895-899. 33 Kim M S, Moon K W & Lee S K, Hydrogen production from food processing wastewater and sewage sludge by anaerobic dark fermentation combined with photofermentation ,. Biohydrogen II , edited by J Miyake et al (Elsevier, Amsterdam) 2001, pp 263-272. 34 Fascetti E, D`addario E, Todini O & Robertiello A, Photosynthtic hydrogen evolution with volatile organic acids derived from the fermentation of source selected municipal solid wastes, Int J Hydrogen Ener, 23 (1998) 753 -760. 35 Tanisho S, Feasibility study of biological hydrogen production from sugar cane by fermentation, edited by T N Veziroglu, C-J Winter, J P Basselt, and G Kreysa, Hydrogen energy progress XI, Proc Eleventh WHEC, Stuttgart , 3 (1996) 2601-2606. 36 Chin K K & Goh T N, Bioconversion of solar energy: methane production through water hyacinth, Proc Second Symp Ener Biomass Wastes , Institute of Gas Technology, Chicago, (1978) 215-228. NATH & DAS: BIOHYDROGEN PRODUCTION AS A POTENTIAL ENERGY RESOURCE 739

37 Roychowdhury S, Cox D, Nag M & Cipico P E, Continuous generation of hydrogen from sewage sludge, edited by J C Bolcich and T N Veziroglu, Hydro Ener Prog Twelve, Proc Twelfth WHEC , Argentina (1998) 533-541. 38 Das D, Ghose T K, Joshi A P & Gopalkrishnan K S, Treatment of distillery wastes by a two phase biomethanation process, Proc Ener Biomass Wastes , Chicago, Ilinois , (Pergamon Press, New York) 7 (1983) 601-626. 39 Lewis C W, Fuels from biomass –Energy outlay versus energy returns: A critical appraisal, Energy, 2 (1977) 241-248. 40 Reith J H, Wijffels R H & Barten H, Biomethane and biohydrogen- status and perspective of biological methane and hydrogen production, Dutch Biol Hydr Foundat , The Netherlands, (2003) 118-125. 41 Benemann J R, Process analysis and economics of biophotolysis of water, a preliminary assessment, Rep Int Ener Agency Hydrog Program , Photoproduction Hydr Annex 10 , (1998) IEA/H2/10/TR-2-98. 42 Benemann J R, Hydrogen production by microalgea, J Appl Phycol, 12 (2000) 291-300. 43 Tredici M R, Chini Zittelli G & Benemann J R, A tubular integral gas exchange photobioreactor for biological hydrogen production, edited by O R Zaborsky, Biohydrogen (Plenum Press, London) 1998, 391-401. 44 Bockris J O’M, The economics of hydrogen as a fuel, Int J Hydrogen Ener, 6 (1981) 223-241.

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