Biomedical Engineering Reference
In-Depth Information
TABLE 2.4 Selected Types of Aerobic and Anaerobic Respiration
Involved in Microbial Metabolism of Organic Matter
Electron
Acceptor
Metabolic
Products
Relative Potential
Energy
Process
Aerobic
respiration
O
2
CO
2
,H
2
O
High
"
NO
3
Denitrification
CO
2
,N
2
Fe
3
þ
CO
2
,Fe
2
þ
Iron reduction
SO
4
2
Sulfate
reduction
CO
2
,H
2
S
Methanogenesis
CO
2
CO
2
,CH
4
Low
Source: Taken from Suflita and Sewell (1991).
usually present in and around groundwater recharge areas as a result of
infiltrating rainwater. When oxygen is not available, the following
electron acceptors are preferentially utilized by microbes in the order
shown: nitrate
>
Fe(III)
>
sulfate
>
carbon dioxide (Brock and
Madigan, 1991). The redox potential (i.e., available electron acceptors)
in subsurface environments is highly site-dependent.
Methanol biodegradation has been shown to take place under both
aerobic (oxygen as the electron acceptor) and anaerobic (all electron
acceptors besides oxygen) conditions. The aerobic biodegradation of
methanol is the most energetically favored mechanism for methanol-
degraders and leads to the mineralization of methanol. Microbial
growth on methanol with nitrate as the electron acceptor by faculta-
tively anaerobic nitrate-reducing bacteria is the second most energeti-
cally favored mode of methanol metabolism (Metcalf and Eddy, Inc.,
2003). There are nearly 200 wastewater treatment plants in the United
States that currently use methanol as a carbon source to remove nitrate
(NO
3
) fromwater by anoxic denitrification (Methanol Institute, 2008).
Methanol is the most commonly used external carbon source and is
dosed at wastewater treatment plants based on the amount of nitrate to
be removed as well as dissolved oxygen concentrations. Methanol is
used at plants operating a variety of denitritification processes, includ-
ing tertiary filtration, biological aerated filtration, and moving-bed
