Biomedical Engineering Reference
In-Depth Information
site in Canada, the fate and persistence of anM85 fuel was investigated in
an aerobic shallow sandy aquifer (Barker et al., 1990). The average
concentration of methanol introduced into the aquifer was 7030 ppm. By
Day 476 of the experiment, about 99% of the methanol was degraded
(Table 2.5 includes the effective first-order degradation rate). Insufficient
oxygen was present in the plume to account for the removal of the
methanol; the researchers therefore concluded that themethanol degraded
first aerobically, then anaerobically (Hubbard et al., 1994).
In a laboratory study, methanol biodegradation was investigated in soils
from three different subsurface sites under various redox conditions (Novak
et al., 1985). The first site was aerobic and also had high nitrate levels, the
second site was anoxic and had low nitrate but high sulfate concentrations,
and the third site was anoxic and had low nitrate and sulfate levels.
Rapid biodegradation took place in the microcosms at the first site from
both the saturated (4.19-4.55 ppm/day) and unsaturated zones (4.44-
5.15 ppm/day), although the amount of methanol added was sufficient
to create anaerobic conditions. Rapid methanol biodegradation was also
observed in the microcosms from the saturated zone of the second site
(1.33-3.18 ppm/day) and the third site (1.0 to 2 ppm/day). This study
concluded that methanol concentrations up to 1000 ppm were removed in
less than a year at temperatures of 10-11
C and at a pH range of 4.5-7.8.
Methanol was found to be readily biodegradable in all subsurface soils
examined, with biodegradation proceeding more rapidly in the saturated
region. This research suggests that methanol contamination in groundwater
is unlikely to persist for lengthy periods of time because of its susceptibility
to biodegradation under both aerobic and anaerobic conditions.
In another laboratory study, Suflita and Mormile (1993) measured
acclimation periods (periods before degradation proceeded) and bio-
degradation rates of methanol and various other alcohols and fuel
oxygenates in anaerobic aquifer slurries at organic concentrations of
50 ppm. These researchers reported a methanol acclimation period of
5 days, the shortest among the alcohols tested (the other alcohols being
ethanol, 2-propanol, and tert-butanol), as well as an anaerobic methanol
biodegradation rate of 7.4
0.7 ppm/day. In a later study, these
researchers investigated methanol biodegradation under a range of
redox conditions (Mormile et al., 1994). Under nitrate-reducing
