Biomedical Engineering Reference
In-Depth Information
biofilm reactor processes. Methanol can also be added to activated
sludge biological nutrient removal processes, either directly to the
anoxic or postanoxic zone(s) depending on plant configuration and
operations. Storage of methanol must consider local code requirements
because of its flammability (Metcalf and Eddy, 2003; WEF et al., 2005).
Other modes of anaerobic biodegradation of methanol have been
studied extensively, resulting in the identification of at least 11 species
of methanogenic bacteria that can grow on methanol (Brock and
Madigan, 1991).
Other types of anaerobic metabolism include acidogenesis (resulting
in the production of acetate or butyrate) (Florencio et al., 1995) and
sulfidogenesis (Heijthuijsen and Hansen, 1990). The ability of sulfate-
reducing bacteria to oxidize methanol was rarely reported in earlier
studies (Esnault et al., 1988; Ward and Winfrey, 1985), but since then
evidence has accumulated that suggests that sulfate-reducing bacteria
are involved in anaerobic degradation of methanol in sediments,
particularly in marine environments (Nanninga and Gottschal, 1986;
Esnault et al., 1988). Sulfidogenic methanol-utilizing microorganisms
have been shown to oxidize methanol by reducing sulfate to hydrogen
sulfide (Heijthuijsen and Hansen, 1990). Finally, some methanol-
degrading strains have been shown to utilize hydrogen (Heijthuijsen
and Hansen, 1990).
A
VAILABILITY OF
N
UTRIENTS
Most microorganisms require nutrients
such as nitrogen and phosphorus for cell growth. In general, microbial
growth in most subsoils is not limited by nitrogen and phosphorus as
long as the contaminant concentrations are in the sub-ppm range
(Tiedje, 1993). As stated previously, for M100 releases into the
subsurface, methanol concentrations would often exceed 1 ppm, result-
ing in potentially nutrient-limited conditions. However, as methanol is
advected away from the source area, concentrations would decrease and
microbial activity would not likely be nutrient-limited.
A
PPROPRIATE
pH
AND
T
EMPERATURE
L
EVELS
Most microorganisms grow
best in a relatively narrow pH range around neutrality (6-8) (LaGrega
et al., 1994). The characteristic range of pH found in groundwater
