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Bacterial Growth and
Energetics
CEE 6650
SPRING 2017 – DR. RR DUPONT
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Bacterial Growth and
Energetics
Microorganisms Consume Substrate & Carry Out OxidationReduction Reactions (Energy Reaction)
Growth Occurs by Production of Additional Cells (Synthesis
Reaction)
In Biological Treatment
◦ Biomass Produced Continuously
◦ From Consumption of Substrate In The Wastewater
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Bacterial Reproduction
Bacteria Generally Reproduce by Binary Fission
◦ Original Cell Becomes Two New Organisms
Time Required for Each Division
◦ Generation Time (20 Minutes To Several Days)
If Generation Time were 30 Minutes
◦ In 12 Hours,
◦ 1 Bacterium Would Yield 224 (Or 16,777,216) Cells
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Bacterial Reproduction
In Biological Treatment or
Real World, Bacteria Do Not
Continue To Divide
Indefinitely Because of
Environmental Limitations,
Such as Substrate & Nutrient
Availability
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Bacterial Growth in Batch Reactor
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Log Growth Phase
Rapid Growth/High Energy System
Corresponds to Area of Highest Cell
Growth
Corresponds to Area of Fastest
Substrate Utilization, BUT
◦ High Levels of Substrate Remain
◦ Lots of Dispersed Bacteria
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Log Growth Phase Rate
Expressions
Michaelis-Menton Equation
◦when S »» Ks
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Declining Growth Phase
Substrate Becomes Limiting
Rate of Substrate Uptake Reduced
Rate of Cell Growth Reduced
Energy of System Reduced
Bacteria Begin to Floc - Form “Activated
Sludge”
Beginning of Optimal Operating Point
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Declining Growth Phase Rate
Expressions
Michaelis-Menton Equation
◦when S «« Ks
r
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Endogendous Respiration Phase
External Substrate Unavailable to Most
Organisms
Cell Mass Decline as Internal Cellular
Material Used for Maintenance Energy in
Absence of External Substrate
Cells Eventually Die, Lyse, and Release
Internal Cell Material
Residual Mass Always Exists as Cell Wall
Material, Cytoplasm, etc., Not Completely
Biodegradable
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Endogenous Respiration Phase Rate
Expressions
No Longer Substrate Mediated Reaction
Cell Decay Proportional to Remaining, Live
Cell Mass
Reaction First Order w/Respect to Cell
Mass
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Manipulation of Cell Dynamics
BOD
Endogenous Respiration
Declining
Growth
Mass of Organisms
Control Efficiency of Plant Operation In Terms
of Effluent Quality & Settling Efficiency by
Operating Plant in Area Where Cells Are in
Region of Declining Growth/Endogenous
Respiration
Residual Nonbiodegradable Cell Mass
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Manipulation of Cell Dynamics
Aeration Tank Used to Provide Intimate
Contact between Bugs, Waste & 02 So Bugs Can
Grow on Organics & Remove them From WW
Sedimentation Tank Used After Aeration Tank
to Settle Out Floc Formed in Aeration Tank
Some Cell Material is Recycled Back Into
Aeration Tank to Ensure Growth is Always in
Declining/Endogenous Region of Growth
Curve
Some Cell Material is Wasted
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Manipulation of Cell Dynamics
Endogenous Respiration
Sludge Wasting
Declining
Growth
Mass of Organisms
BOD
Residual Nonbiodegradable
Cell Mass
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Manipulation of Cell Dynamics
Amount to Recycle Determined Based on
F/M Ratio
Food to Microorganism Ratio
Amount of Food/Unit Amount of Bugs in
Aeration Tank
We Will Talk More About this Parameter a
Bit Later
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Bacterial Growth and Biomass Yield
Cell Growth Occurs Concurrently With
Oxidation of Organic or Inorganic
Compounds
The Ratio of Amount of Biomass Product to
Amount of Substrate Consumed Is Defined
As Biomass Yield, Y
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Bacterial Growth and Biomass Yield
Substrate Can be Organic Matter
or Inorganic Compounds
(e.g., ammonia – in the case of nitrification).
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Measuring Biomass Growth
Because Biomass Mostly Organic Material,
Increase In Biomass Measured by Volatile
Suspend Solids (VSS) or Particulate COD
(Total COD Minus Soluble COD)
VSS Is Parameter Most Commonly Used
Should be Noted that VSS Measures Other
Particulate Organic Matter In Addition to
Biomass – McKinney Discussion Later
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Estimating Biomass Yield and Oxygen
Requirements from Stoichiometry
Stoichiometric Relationship Exists
Between Substrate Removed, Amount of
Oxygen Consumed & Observed Biomass
Yield
Most Common Approach Used to Define
Fate of Substrate Is to Prepare COD Mass
Balance
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Estimating Biomass Yield from Stoichiometry
Following Equation Illustrates Aerobic
Oxidation of Glucose w/Production of Cell
Material & Oxidized End Products
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Estimating Biomass Yield from Stoichiometry
Biomass Yield Based on Glucose Consumed
Obtained as Follows:
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Estimating Biomass Yield from
Stoichiometry
In Practice, COD & VSS Used to
Represent Organic Matter & New
Cells, Respectively
To Express Biomass Yield On COD
Basis, COD of Glucose Must Be
Determined
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Estimating Biomass Yield from Stoichiometry
COD of Glucose
Estimated as Follows:
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Estimating Biomass Yield from
Stoichiometry
Theoretical Yield Expressed in Terms of
COD, Accounting for Portion of Substrate
Converted to New Cells, Is Following:
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Estimating Biomass Yield from
Stoichiometry
Actual Observed Yield In
Biological Treatment Process Will
be Less Than Value Estimated
Because Portion of Substrate
Incorporated Into Cell Mass Will
be Oxidized Over Time (For
Maintenance Energy)
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Estimating Biomass Yield from
Stoichiometry
Quantity of Oxygen Utilized by
Oxidization of Cell Mass May be
Estimated as Follows:
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Estimating Biomass Yield from
Stoichiometry
COD of Cell Tissue is as Follows:
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Estimating Biomass Yield from
Stoichiometry
Oxygen Consumed per Unit of
COD Utilized can be
Determined as:
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Estimating Biomass Yield from
Stoichiometry
Should be Noted that COD of Oxidized
Substrate = Oxygen Consumed:
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Estimating Biomass Yield from
Stoichiometry
Oxygen Consumed per unit of COD
Used is:
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EXAMPLE 7-1
The aerobic completely mixed
biological treatment process
without recycle, as shown, receives
wastewater with a biodegradable
soluble COD concentration of 500
g/m3. The flow rate is 1000 m3/d
and reactor effluent biodegradable
soluble COD and VSS concentration
are 10 and 200 g/m3, respectively.
Based on these data:
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EXAMPLE 7-1
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EXAMPLE 7-1
What is the observed yield in
g VSS/g COD removed?
What is the amount of oxygen
used in g O2/g COD removed
and in g/d?
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Solution
Determine the observed yield. Assume the
following generation reaction is applicable:
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Solution
The g VSS/d produced is:
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Solution
The g COD/day removed is:
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Solution
The observed yield is:
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Solution
Determine the amount of oxygen
used per g COD removed by
applying mass balance.
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Solution
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Solution
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Solution
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Solution
The oxygen used is estimated as
follows:
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Solution
Amount of oxygen used per unit
COD removed.
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