Soil Remediation Demonstration Project:
Biodegradation of Heavy Fuel Oils
CHARLES M. REYNOLDS, PRASANTA BHUNIA, AND BRENT A. KOENEN
expensive than adding air. The approximate trade-
INTRODUCTION
off among air-injection technologies, passive bio-
degradation, and anaerobic biodegradation is time
Background
versus resources (Fig. 1).
There have been numerous petroleum releases
Bioremediation treatments are successful when
in cold, remote regions. Alternatives for cleanup
limitations are overcome. The key problem, how-
are limited by the remote locations, difficulties in
ever, is identifying and implementing the most
mobilization of heavy equipment, inability to ef-
cost-effective means of doing this at isolated, cold
fectively monitor the biotreatment processes, and
sites. Two important aspects in comparing low-
the costs of site operation. To remediate petroleum-
cost to more costlier alternatives are time con-
contaminated sites, we need a low-cost, low-
straints and monitoring difficulties.
input treatment alternative to use in conjunction
In comparing treatments, it is important to
with existing methods.
measure effectiveness over time. In applying a
In general, indigenous soil microbiota can de-
bioremediation technology to a particular site, it
grade petroleum compounds. When soils fail to
is also important to consider contaminant trans-
bioremediate at optimum rates, it is often a func-
port, leaching, and the location of the problem. The
tion of the water solubility of the compound and
rate of treatment must be compared to the rate of
environmental limitations imposed on the mi-
leaching and the distance between the contami-
crobes. Major limitations to the microbiota are tem-
nated soil and the area where it might cause
peratures that are too high or too low, excess or
harm--the potential receptor. For many sites,
deficient water, insufficient or excessive nutrients,
transport rates and distance to receptors are such
insufficient carbon in a form that microorganisms
that remediation need not be immediate. If a
can use, poor mixing or distribution of the petro-
longer time is acceptable for remediation, more
leum in the soil, and, for aerobic microorganisms,
treatment options and lower costs can be consid-
lack of oxygen (O2).
ered.
The relative effectiveness of different treatment
A final difficulty in comparing the effectiveness
systems will vary over time. For example, lack of
of treatments is that of obtaining accurate mea-
oxygen has been believed to be the primary limi-
surements in the field. Limitations to effective
tation at depth; thus, air-injection technologies are
bioremediation have been identified primarily
commonly employed to overcome this. However,
through laboratory studies. Measuring rates in the
it is now well established that subsurface (rela-
field is much more difficult because we cannot
tively deep) microbial activity is common, and
control field conditions effectively. In a field study,
anaerobic biodegradation of water-soluble petro-
where we tried to measure bioremediation rates
leum takes place without the need to inject air if
in a 1-acre (0.4-ha) landfarm that we had treated
alternate electron acceptors, such as oxidized spe-
uniformly, we found that the bioremediation rates
cies of iron or nitrogen (such as nitrate), are avail-
varied up to seven-fold (Reynolds 1993b).
able. The anaerobic processes are significantly
Diesel-contaminated soils have been shown to
slower than aerobic processes, but they are less
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