Microbial Fuel Cells - PDF by oaw14128

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									 USC                Geobiology

Biofuels for energy production and
          Waste disposal

 Provost’s Energy Retreat FEEI

     February 24 & 25, 2006

          Ken Nealson
 Wrigley Professor of Geobiology
     USC                        Geobiology

             Energy Flow on Earth
               PS Bacteria                  Animals
               Cyanobacteria                Fungi
               Algae & Plants               Bacteria
   Energy                          Biomass
(178,000 TW)                       Organic C
               CO2                       Lithotrophs

Geothermal                         Reduced
  Energy                          Inorganics
 (30 TW)                          (organic C)
   USC                    Geobiology

Biomass                    CH3OH        3/1
                           CH3CH2OH    2.5/1

                         Biofuels – methanol
   USC                 Geobiology
          Don’t always have to “win”
           breaking even might be enough!

                      Biofuel          Pollution removal
                       Cells             water purification
                                         industrial water
                                         industrial waste

Waste      Biofuel Cell Interruption of the process!
           (Imagine many other fuels being used
               by these Microbial Fuel Cells)
    USC                 Geobiology

What is a microbial fuel cell?

Advantages of MFCs

Disadvantages of MFCs

State of the Art
                    Demonstrate these with
Challenges           examples of our work
                     when appropriate.
          USC                    Geobiology
What is a Microbial Fuel Cell?
Fuel cell with microbe as a catalyst

Known since early 1900’s
     First report of a microbial fuel cell in 1911 (Potter)

Take advantage of way life works:
      Take up fuel, extract electrons
      electron flow to an acceptor is used to charge a
               “biological capacitor”
      charged capacitor used to make biological energy
Fuel cell just short circuits this process

MFCs come in two types: mediated and mediator-less
        Two Types of Microbial Fuel Cells
           Mediated Fuel Cell                                           Mediator-less Fuel Cell
                          Load                                                          Load

Oxidized Fuel                            Oxidant           Oxidized Fuel                               Oxidant




    Fuel                                 Reduced Oxidant         Fuel                                  Reduced Oxidant

                = Oxidized Mediator                                      = Oxidized carrier molecule
                = Reduced Mediator                                       = Reduced carrier molecule
                = Ion Exchange Membrane                                  = Ion Exchange Membrane
                                                                         = Outer membrane electron carriers (i.e.
 • Almost any microbe can produce electricity
   with an electron shuttle (innefficient !)                   • No additional electron shuttle is
 • Mediators are mostly phenolic compounds,                      needed
   which are expensive & sometimes toxic                       • Few known microbes have this
 • A mediator-less microbial fuel cell is                        ability
   possible if the microbes can give electrons                 • Shewanella & iron reducers do !
   directly to the electrode
            USC                    Geobiology

Mediator-less fuel cells take advantage of special bacteria

Isolated ~ 15 years ago -- Shewanella, Geobacter, others
       Iron/manganese reducing bacteria

      Famous for reducing solid substrates (Fe & Mn oxides)

      Subsequently found to have enzymes on outside of the cell

      Unusual for bacteria, but necessary for this reaction

Example shown in next slide
Enrichment Culture                         Five Days Incubation

                       Solid Substrate
Pure Culture on MnO2                     Breathing Mn oxide!

                Microbial Fuel Cell
                                        N2 inlet      10 ohm      Air inlet

                               N2 outlet                                 Air outlet
                                                       Pt leads

                                   Anode                             Cathode
                            port for
                                       Graphite felt           Pt coated graphite
                                        electrode                 felt electrode
         Scale in inches
                                                 Clamp holding ion
                                                exchange membrane

Used to evaluate strains in the laboratory
Anode – graphite with bacterial catalyst
Glass – autoclavable, re-usable
Extra ports for electrochemical measurements
Cathode platinized graphite (Surya Prakash’s help!)
        USC                Geobiology
Potential advantages of MFCs

1. Catalysts are inexpensive – essentially “free”

2. Catalysts are diverse and robust
    extreme conditions of pH, Eh, T, salinity, etc.

3.Catalysts are versatile – single type can use
   wide variety of substrates

4.Catalysts can self repair (proteins, DNA,
   membranes, etc.)
        USC                  Geobiology

More than 50 different Shewanella species known
 So far, all produce current

From ~ 4 oC to 55 oC; wide salinity range
  65 different carbon sources

Very tough and robust organisms

Just the tip of the iceberg of biological diversity

(other Fe-reducers are known that grow to 110oC!)
                                      Response to different fuels
                                           (Shewanella) Formate
• MR-1 can grow by converting lactate to
                                                                                        0.3                                   MFC OD of 0.8

                                                                        Current (mA)
                        lactate → pyruvate → acetate → CO2
• MR-1 can also use these products to                                                  0.15
  maintain and produce current                                                                                        Lactate
                                                                                        0.1              Lactate          (1mM)           Form ate
                                                                                                           (1mM)                                 (1mM)
•Can also switch from one to another with ease:                                        0.05
                                                                                              0            5         10            15         20         25
                             Acetate                                                                                 Tim e (Hours)
                 0.05                                                                   0.05
                0.045                                                                  0.045
                 0.04                                MFC OD of 0.3                      0.04                                       MFC OD of 0.3
                0.035                                                                  0.035
                                                                        Current (mA)
 Current (mA)

                 0.03                                                                   0.03
                0.025                                                                  0.025
                                                            Acetate                                                                     Succinate
                 0.02                      Lactate              (1mM)                   0.02
                                               (1mM)                                                                Lactate                 (1mM)
                0.015                                                                  0.015                          (1mM)
                 0.01       Lactate                                                     0.01            Lactate
                              (1mM)                                                                         (1mM)
                0.005                                                                  0.005
                    0                                                                      0
                        0             10             20         30      40                        0            10             20            30           40

                                            Tim e (hours)                                                            Tim e (hours)
            USC                    Geobiology

Potential disadvantages of MFCs
1. Current density is low

2. Difficult to run and maintain

3. Sensitive to breakdown and decay

Almost certainly all these “disadvantages”
 are built on misconceptions
 These arise from use of mediated MFCs
         USC               Geobiology

State of the art:

1. Many bacteria now known that produce current in
     mediator-less MFCs
2. Mechanism of current production not understood
3. Current densities are getting into the range of
    interest – mA/cm2 (wide range of abilities)
4. Interesting development has to do with microbial
    consortia – current density is always higher
          USC              Geobiology

Chang et al., 2006, Electrochemically
 active bacteria (EAB) and mediator-less
 microbial fuel cells. J. Microbiol. Biotechnol.

Power densities range from: 16 to 4,300 mW/m2

I have a PDF of this I will send to anyone who
  wants – reviews much of what I have said today.
      USC                Geobiology

Challenges to be addressed:

1. How do they work? Mechanisms?
    genetic and genomic approaches

2. Physiology of the cells – interface with FC
    biofilms, etc.

3. Microbial communities and consortia
   enrichment cultures
       USC                 Geobiology

9 mutants that knock out ability to produce current
     4 are involved with iron reduction
     5 are not –

3 mutants that increase current production
     all of these are cytochromes leading to
       other termini

Several regulatory mutants that increase or
 decrease the level of current production
Table 1. Electrochemical activities of Shewanella oneidensis MR-1 and its mutants

                       Growth1 on       Max. current   Coulomb3
Strain   Gene                                                        CV4 test
                     Lactate/Fumarate      (μA)          (C)

  1      ΔluxSrif         +++            65.0±6.1      2.53±0.25       ++

  2      ΔmtrA            +++             7.3±0.5      0.42±0.09        +

  3      ΔomcA            +++             4.6±0.2      0.32±0.01       +/-

  4      ΔhydB            +++           61.0±15.4      2.63±0.37        +

         ΔhydB and
  5                       +++           66.3±17.9      2.94±0.48        +

  6      ΔhydA            +++           54.0±10.0      2.53±0.72        +

  7      ΔtatC              +            15.3±2.9      0.97±0.16       ++

  8      Δmpw             +++            48.0±7.2      2.15±0.09        +

  9      Δfur              ++            26.0±2.0      1.30±0.25        +

 10      Δcrp               +            19.0±6.6      1.11±0.36        +

 11      Wild type        +++            68.0±7.8      2.56±0.18        +

 12      E.coli           +++2            5.0±0.1          -            -
        USC              Geobiology

How do the catalysts work?

Mutant screening
 genome of Shewanella has been sequenced
  use this information to make directed mutants

 mutant analysis identifies those genes
  coding for proteins involved with current prod.

 so far great success using this approach
     USC                 Geobiology

Understanding the catalyst:

Role of attachment, biofilms, connections

  No doubt of catalytic ability
  Question of how to control and direct it

This is issue of physiology of cells:
                         Shewanella oneidensis MR-1 biofilm current
                                        production                                                  1.2

                         MR-1 Biofilm on Anode (4 day growth)                                                 Injection of planktonic cells (OD 0.8)
                1                                                                                    1
                                  Erroneous data point
               0.8                                                                                  0.8
                                       Maximum current value ≈ 0.8 mA
Current (mA)

                                                                                     Current (mA)
               0.6                                                                                  0.6

                                                                                                                          Maximum current value ≈ 0.3 mA
               0.4                                                                                  0.4

               0.2                                                                                  0.2

                0                                                                                    0
                     0        5          10        15        20     25          30                        0      1    2        3        4         5   6    7      8
                                                Time (hrs)                                                                         Time (Hours)
                                                                         Courtesy of PNNL and KIST

               Graphite felt electrode with MR-1                  Graphite felt electrode without                                  Graphite felt electrode with
                             biofilm                                           MR-1                                                planktonic MR-1 (OD 0.4)
MR-1 biofilm/electrode images (PNNL)
      USC             Geobiology
Many questions to answer and
 things to optimize
However, these approaches, coupled
 with modeling should lead to an optimum
 catalyst that can be combined with
 optimum design to yield high power
To this end: we were just awarded a MURI
From DOD for this work (5 from USC).
(Prakash,Ronney,Wang,Mansfeld, Nealson)
       USC                Geobiology

Prospects & Approach:

Understand the system
Optimize to produce adequate current
Scale up or down for specific applications:
     waste disposal
     remote power supplies
     water treatment
        USC                     Geobiology

                                     Scale up
                    Production     Waste
   Research tool                  Disposal
Same scale
     Teaching        MFC            Treatment

        Devices      Remote
                   Scale down
  USC               Geobiology

Waste Disposal:

 7 billion tons of sewage sludge generated
      in the US

     We estimate that 90% of this could be
       metabolized by efficient MFC approach
     If properly designed, we could get paid
       for this process by current production

   USC                Geobiology

  Biofuels for energy production and
            Waste disposal


             Ken Nealson
   Wrigley Professor of Geobiology
USC   Geobiology
  Microbial Fuel Cell Operation
Fuels            Ion Exchange                                                         Oxidant                          Catalyst
  Organic or       Membranes                                                                       Atmospheric           Microbe at
  inorganic        Solid polymer or single                                                         oxygen                anode
  matter           compartment reactor                                                                                   Pt at cathode
                                                                                                                         (soon to be
                                         -         e- e-                      e-
                                      e                                              e-
                                    e-                                               e-
                                   e-                                                e- -
                                                   Proton Exchange Membrane
                                  Anode Catalyst

                                                                               Cathode Catalyst
          Fuel                                                                                                     Oxidant
                                 e-                                                               e-


        Oxidized                                                                 H+                    Reaction    Reduced
          Fuel         H+                                                         H+                               Oxidant
                      H+ +     +                                            +        +
                        H H+ H                                           H+H H+ H+ H
         USC                                                            Geobiology

                                        e-   e- e-                          e-
                              e                                                   e-
                             e-                                                   e-

                                             Proton Exchange Membrane
                       e                                                           e-

                                                                             Cathode Catalyst
                           Anode Catalyst
  Fuel                                                                                                           Oxidant
                       e-                                                                       e-


Oxidized                                                                                        H+               Reduced
  Fuel          H+                                                                              H+               Oxidant
            H+             +                                            +                               +
                   H+ H+ H                                      H+H         H+ H+ H

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