Biomedical Engineering Reference
In-Depth Information
groundwater are expected to be biodegradation and advection (i.e.,
transport away from the source area by groundwater flow), with little
loss due to adsorption. These two mechanisms are discussed further in
the following subsections.
Biodegradation In general, microorganisms have been shown to play a
prominent role in governing the fate of fuel hydrocarbons in subsurface
aquatic and soil systems (NRC, 1993). When environmental conditions
are amenable to microbial activity, aerobic microbial populations
oxidize organic contaminants and consume oxygen in the process.
Once the localized area has been depleted of the oxygen necessary
for aerobic respiration, anaerobic conditions develop and anaerobic
biodegradation proceeds. While it is well established in the scientific
literature that methanol would biodegrade readily in the subsurface
under both aerobic and anaerobic conditions, four factors are required
for successful methanol biodegradation: the presence of indigenous
methanol-degrading microbial populations, the availability of electron
acceptors, the availability of nutrients, and appropriate pH and temper-
ature levels conducive to microorganism growth. These four factors are
discussed in the following subsections.
P RESENCE OF I NDIGENOUS M ETHANOL -D EGRADING M ICROBES Methanol is
widely produced in nature by anaerobic microorganisms responsible
for complex aromatic hydrocarbon biodegradation (Heijthuijsen and
Hansen, 1990; Oremland et al., 1982). As a result, methanol molecules
are ubiquitous in nature. Furthermore, owing to methanol's high
solubility in water, methanol molecules are bioavailable to micro-
organisms that can utilize them as a source of carbon and energy. A
wide distribution of methanol-degraders in the environment can there-
fore be expected (e.g., Brock and Madigan, 1991).
Systematics of methanol oxidation: Methylotrophs, organisms that can
grow using only one-carbon compounds such as methanol, are known to
use both methane and methanol as their sole carbon and energy source
under both aerobic and microaerobic (low oxygen) conditions (Brock
and Madigan, 1991). Methylotrophs are of commercial interest in the
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