FAQs: Anaerobic, Aerobic, Anoxic
BACKGROUND
In wastewater treatment cells grow until the reach maximum size, and then divide into two in a process
called binary fission. This process can happen every 20 to 30 minutes under optimum growth conditions.
During cell growth, there are maintenance needs that the bacteria have. These maintenance needs are
met through energy released from food molecules. All bacteria have enzymes, which enable them to
break down food and pass it through the cell membrane.
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Respiration: The process of obtaining energy from food molecules which is controlled by
enzymes.
Enzymes: Protein molecules that each cell makes. Enzymes are needed for all biochemical
reactions because they help the cell break down the organic materials so they can go through
the cell membrane (outer wall of the cell).
Synthesis: An energy consuming reaction that results in the production of new biomass
Endogenous Respiration: When synthesized biomass and storage products become the energy
source for the reaction. This decreases the amount of biomass present.
AEROBIC RESPIRATION
This is how BOD is removed in activated sludge. Oxygen is
the final electron receptor in these reactions. Sources of
energy (food) include carbohydrates, and proteins. End
products of aerobic respiration include water, energy,
and carbon dioxide.
Aerobic: Free dissolved oxygen is present
Aeration Tank
Aerobic Organisms: These organisms only have enzyme
structures capable of functioning in aerobic environments
ANAEROBIC RESPIRATION
Anaerobic respiration occurs in the absence of free dissolved oxygen. Oxygen is still required for
respiration, but is derived from nitrate (NO3-), Sulfate (S04-2) and Carbonate (CO3-2)
Bound Oxygen Molecule
Nitrate
Sulfate
Carbonate
End Product
Nitrogen Gas
Hydrogen Sulfide
Methane
WHAT’S THE DIFFERENCE BETWEEN ANOXIC AND ANAEROBIC?
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Anaerobic: A condition in which free of combined oxygen is not available
Anoxic: A condition in which oxygen is available in combined forms only
o While technically anaerobic, reactions that involve using inorganic electron
acceptors (nitrate and sulfate) are often referred to as anoxic
TYPES OF ORGANISMS
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Aerobic Organisms: Use aerobic respiration only
Anaerobic organisms: Use anaerobic respiration only
Facultative Organisms: Can use both aerobic and anaerobic respiration. They will use
aerobic respiration in the presence of free dissolved oxygen.
REFERENCES
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Activated Sludge Processes, METC Group Incorporated, 1999
Operation of Municipal Wastewater Treatment Plants, Volume II: Liquid Processes Sixth
Edition, WEF