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Biohydrogen production by fermentative processes

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					 Biohydrogen production by
   fermentative processes
                 Freda R Hawkes


        Wastewater Treatment Research Unit
School of Technology and School of Applied Sciences
              University of Glamorgan

         http://www.glam.ac.uk/wastewater
Biologically, hydrogen may be
produced:
     • Photosynthetically
     • Fermentatively
Photosynthesis in green plants
and green and blue-green algae

              light
6H2O + 6CO2       C6H12O6 + 6O2
                  + cellular
                   energy
Bacterial photosynthesis

          light
Reduced           cell material +
organic           cellular energy
compounds
Photosynthetic H2 production in
 green and blue-green algae -
        biophotolysis

          light
    H2O           0.5O2 + H2
H2 production in green algae

              hydrogenase
 2H+ + 2 electrons    H2
  Biophotolysis in green algae


H2O                               2H+
                   2e
0.5O2                             H2
      photosynthesis    hydrogenase
   Hydrogenase in green algae
• is induced in low amounts by dark
  anaerobic pre-incubation
• its role - managing dark/light transition
• is O2 sensitive, so H2 production
  decreases in light
• hence two-stage processes suggested
                Biophotolysis
“There is a need to increase the yield of H2
  production by a factor of ten or more and
  to develop a protocol that works with
  minimum media before the process can be
  viable in commercial applications.”

      Ghirardi et al. Trends in Biotechnology Dec 2000
           Biophotolysis

“biophotolysis processes must achieve
 close to a 10% solar energy conversion
 efficiently to be competitive with
 alternative sources of renewable
 hydrogen…Another challenge is to scale
 up with economically viable bioreactors”

              Benneman J Appl Phycol Dec 2000
    Challenges for biophotolysis
Photobioreactor design
    • construction
    • economics
Operating protocol
    • inducing hydrogenase
    • maintaining low O2 concentration
    • avoiding culture contamination
Photosynthetic H2 production in
 blue-green algae and bacteria

                   nitrogenase
N2 + 8H+ + 8e- + energy      2NH3 + H2
Nitrogenase in blue-green algae and
              bacteria
•   produces more H2 if N2 is absent
•   is inhibited by NH3, O2
•   is energy requiring
•   turnover rate 1000x slower than
    hydrogenase
  H2 production by photosynthetic
              bacteria

• uses nitrogenase
• requires organic compounds
• does not produce O2
 H2 production by blue green algae

“…nitrogen-fixing Cyanobacteria can be
 dismissed as potential candidates for
 future development as they could not,
 even with additional research and
 development, achieve the necessary
 efficiency goals mandated by the
 economic analysis”.
              Benneman J. Appl. Phycol. Dec 2000
Biologically, hydrogen may be
produced:
     • Photosynthetically
     • Fermentatively
     Fermentative H2 production
• property of many species of bacteria,
  particularly Clostridia
• dark, anaerobic process
• carbohydrates are favoured substrate
• involves hydrogenase
• produces CO2
• maximum H2 yield with acetate as
  fermentation product
    Fermentative H2 production -
              H2 yield

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

yield: 0.5 m3 H2 / kg carbohydrate
thermodynamically unfavourable as H2 conc rises
    Fermentative H2 production
           technology
Process similarities with
• classical acetone/butanol process
       conditions favouring solvents depress
       acetate/H2 production
• anaerobic digestion
            methanogens consume H2
Optimisation, design and operating parameters
  not established
 Fermentative H2 Production R & D

Research has used:   Commercialisation
                     requires:
pure microbial        stable mixed microflora
cultures,
sterile feedstock,   non-sterile feed-stocks
batch operation      continuous processes
Effect of lowering dissolved H2 conc
                   Non-Sparging    Sparging
H2 yield
( mol/mol gluc)      0.85       1.43

Acetic mgl-1          773        785
n-butyric mgl-1       1742       1929
Acetone mgl-1         0          1
Butanol mgl-1         4          6
        Mizuno et al. Bioresource Technol. (2000)
       Sustainable biohydrogen
   production: process optimisation
EPSRC grant 2001-2004, Hawkes DL, Dinsdale R, Hawkes FR


Objectives:
• to determine optimal operating parameters
  giving stable long-term generation of H2 on
  high strength complex biomass substrates
• to develop strategies to increase H2 yield
   Sustainable biohydrogen production:
           process optimisation
EPSRC grant 2001-2004, Hawkes DL, Dinsdale R, Hawkes FR

  H2 yield optimisation by:
  • sparging with anaerobic digester biogas
  • sparging with fuel cell exhaust
  • operation at thermophilic temperature
  • on-line H2 measurement in off-gas with
    PEM fuel cell.
  Economics of fermentative H2
          production
• Unit cost of fermentative H2 from
  sugar cane 0.26 DM/kWh (Tanisho,
  1996).
• Unit cost for wind-powered
  electrolysis plants 0.5-0.2 DM/kWh
  (Dutton et al., 2000)
      Challenges for fermentative H2
               production
• what organic material can be used as
  substrate?
• how may yield and rate of H2 production be
  optimised?
• what use may be made of fermentation end
  products?
• what are the overall process economics?
                 References
Beneman J R. (2000) Hydrogen production by
 microalgae. J. Applied Phycology 12, 291-300.
Ghirardi ML, Zhang L, Lee JW, Flynn T, Seibert
 M, Greenbaum E and Melis A. (2000)
 Microalgae: a green source of renewable energy.
 Trends in Biotechnology 18, 506-511.
Mizuno O, Dinsdale R, Hawkes FR, Hawkes DL,
 Noike T. (2000) Enhancement of hydrogen
 production from glucose by nitrogen gas
 sparging. Bioresource Technology 73 (1) 59-65.

				
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Description: Biohydrogen production by fermentative processes