Chapter 15 Microbiological Processes

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Chapter 15Microbiological Processes

• CH350/EV350
• Spring 2008

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Chemistry versus Biology

• Abiotic processes occur through purely chemical
  or physical processes
• Biotic processes involve biological organisms
• Plants photosynthesis
• Microorganisms
• Bacteria
• Fungi
• Algae
• Protozoa
• Degradation, synthesis, and other chemical
  transformations

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Classification by carbon source

• Autotrophes grow on inorganic carbon sources
  such as CO2, HCO3-, or CO32-
• Photoautotrophes use light energy
• Plants and algae
• Chemoautotrophes use chemical energy
• Most bacteria are chemoautotrophes
• Heterotrophs use presynthesized organic
  compounds as a carbon source degraders/consumers
  of organic waste materials
• Some bacteria can use pollutants as a carbon
  source

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Classification by source of electron acceptor

• Microorganisms that facilitate redox reactions
• Degradation of organic matter
• Aerobes use molecular oxygen (O2) in air or
  water to oxidize organic matter
• O2 4H3O 4e- ? 6H2O
• Anaerobes use electron poor species such as
  sulfate (SO42-) as electron acceptor
• SO42- 9H3O 8e- ? HS- 13H2O

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Carbon Cycle
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Forms of organic carbon in the ocean
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Key reactions involving carbon and microorganisms

• Photosynthesis
• CO2 H2O sunlight ? CH2O O2
• Respiration
• CH2O O2 ? CO2 H2O

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Biomass degradation

• CH2O 5H2O ? CO2(g) 4H3O 4e-
• pEo(w) pE at pH 7 8.20
• Need an electron acceptor to oxidize organic
  matter
• Oxygen as electron acceptor
• O2 4H3O 4e- ? 6H2O
• pEo(w) 13.80
• Combined reaction
• CH2O O2 ? CO2 H2O
• pEo(w) 13.8 8.2 22.00
• DG -500 kJ
• Abiotic reaction is slow, but rapid when
  microorganisms facilitate the process

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Biomass degradation in low oxygen environments

• Nitrate as an oxidizing agent
• 2NO3- 12H3O 10e- ? N2 18H2O
• pEo(w) 12.65
• 4NO3- 5CH2O ? 2N2 5CO2 11H2O
• pEo(w) 12.65 8.2 20.85
• DG -481 kJ/mol CH2O
• Abiotic reaction is slow, but rapid when
  microorganisms facilitate the process

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Biomass degradation in low oxygen environments

• Sulfate as an oxidizing agent
• SO42- 9H3O 8e- ? HS- 13H2O
• pEo(w) -3.75
• SO42- 2CH2O H3O ? HS- 2CO2 3H2O
• pEo(w) -3.75 8.2 4.45
• DG -102 kJ/mol CH2O

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Biomass degradation in low oxygen environments

• Self oxidation of biomass
• CO2 8H3O 8e- ? CH4 10H2O
• pEo(w) -4.13
• 2CH2O ? CH4 CO2
• pEo(w) -34.13 8.2 4.07
• DG -93 kJ/mol CH2O
• Other products can be formed other than methane,
  namely carboxylic acids

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Reaction progression
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Alage photosynthesis and respiration can
dramatically affect O2 concentrations in water
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Oxygen demand of water samples

• Biological Oxygen Demand (BOD)
• How much O2 will be used up decaying OM in water
• Incubate bacteria in water sample, measure O2
  consumed
• Good water quality Low BOD lt 1 mg/L O2
• Poor water quality High BOD gt5 mg/L O2
• Chemical Oxygen Demand (COD)
• Oxidize organic material with dichromate to
  estimate BOD
• 3CH2O 16H3O 2Cr2O72- ? 4Cr3 3CO2 27H2O