Automatic Accretion Facilitated by Current Produced by Microbial Growth in Ocean Sediment

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Automatic Accretion Facilitated by Current
Produced by Microbial Growth in Ocean Sediment

• Christopher M. OMalley
• 30 March 2004

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Presentation Outline

• Fundamental Question Goals
• Electrochemistry of Accretion
• Biochemistry of Modified Microbial Fuel Cell
• Experimentation Field Tests
• Preliminary Data Analysis
• Potential Applications
• Conclusions Recommendations
• Questions Comments

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Fundamental Thesis Question
In what manner are the significant design
variables for both the modified microbial fuel
cell and the accretion process controlled as to
produce the best material while minimizing damage
to the environment?
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Goals of Project

• Maximize rate of Accretion
• Maximize current through the system
• Minimize environmental damage
• Conduct field test analyze data
• Perform a comprehensive energy balance
• Apply system to a real life situations

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Accretion

• Natural galvanized reactions in seawater
• Enhanced by passing a constant electrical current
• Aqueous ions combine to form solid precipitate
• Main components are calcium carbonate and
  magnesium hydroxide

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Electrochemistry

• pH reduction
• Maximum solubility of ions
• Ions attracted to oppositely charged electrodes
• Constant current required
• Anode degradation

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Reaction Location
Throughout
Anode Surface
Inter-Media Space
Inter-Media Space
Cathode Surface
Cathode Surface
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Microbial Fuel Cell

• Similar to a conventional fuel cell
• Utilizes microbes as source of electricity
• Mediators shuttle electrons to a carbon fiber
  electrode
• Takes in glucose and releases carbon dioxide
• Proton flux across a polymer electrolyte membrane

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Modified Microbial Fuel Cell

• Simpler design
• Use of carbon fiber electrode in sediment
• Potential difference with water level
• No use of mediators or electron acceptors
• Microbes grow in sediment and pass electrons to
  the electrode
• Electrons flow along the electrode to the water
  level above creating current

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Biochemistry

• Redox reactions
• Electron Transport System (ETS)
• Biochemical Oxygen Demand (BOD)
• Activated sludge
• Sediment

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Rate of Accretion

• Amount of matter precipitated on the cathode per
  unit time
• Main design variable for real life applications
• Depends upon current, voltage, resistance, and pH
• Current dependent upon microbial population and
  metabolism

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Current Production

• Current production dependent on biomass
  conversion
• Initial lag while microorganisms adjust
• Current becomes constant in flow system
• Current drops as resistance increases
• Current directly proportional to rate of accretion

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Environmental Implications

• pH decreases in closed system
• Anode degradation
• Free ions released into immediate area
• Reduction of microorganisms

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Preliminary Data

• Results from previous years works
• Laboratory testing
• Activated sludge and sediment
• Alumninum, Copper, Zinc, Lead, Galvanized steel,
  and Carbon fiber electrodes tested
• Result trends reproduced recently

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Data Analysis

• Water recycled every 8 hours to simulate a flow
  system
• Values measured and compared with Voltage
  Current x Resistance
• Results scaled up to simulate real life
  application
• Time is the greatest factor
• Economics

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Boston Harbor Field Test

• To be conducted in late April/early May
• Scaled up model to be tested
• Goal is to develop a geometric product
• Measure environmental impact
• Determine viability of real life applications

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Energy Balance

• Estimate number of electrons produced
• Degree of Reduction g The number of equivalents
  of available electrons per gram of Carbon atoms.
  Equal to the valence electron number of any
  element.
• Movement of electrons through system is neglected
  Number of electrons produced in sediment and
  number of electrons participating in accretion
  reactions compared.
• Number of electrons participating in accertion
  reactions is based on stoichiometric coefficients

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Energy Balance

• Elemental Balance
• Aerobic Growth
• Energy Content

Shuler, Michael L. and Fikret Kargi. Bioprocess
Engineering Basic Concepts. Upper Saddle
River, NJ Prentice Hall, 2nd ed., (2002).
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Potential Applications

• Dock and pylon repair
• Barrier construction
• Canal wall preservation
• Ocean floor contouring
• Beach front property protection

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Future Work

• Analyze field test results
• Comprehensive energy balance
• Determine exact relationships between key
  variables
• Design system for practical use

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Conclusions

• Proof of concept analysis successful and it is
  beneficial to utilize microbes as a renewable
  source of energy for an accretion process
• Rate of accretion proportional to current
• Time and money remain the biggest issues with
  real life applications
• Geometry of system can be altered as to adapt to
  practical applications
• Much work is needed to fully comprehend the
  intricacies of auto-accretion

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Acknowledgements

• Professors DiBiasio, Miller, and Carrera
• Professor Dan Gibson
• Debbie Lavern Upper Blackstone Wastewater
  Remediation Facility
• Anne Giblin Woods Hole Oceanographic Institute
• Bruce Jacobson National Parks Service (Boston
  Harbor)
• Graphite Engineering Sales
• Joe Kaupu and Sandy Natale
• Jack Ferraro and Doug White
• Faculty, Staff, and Students of the Chemical
  Engineering Department

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Questions Comments