Page 207 - Environmental Control in Petroleum Engineering

Waste Treatment Methods 193

most difficult to biodegrade. The speed of bioremediation is often mea-
sured in terms of half-lives of the hydrocarbon, i.e., the time for half of
the hydrocarbon to be biologically degraded. Typical degradation half-lives
range from a few days for low-molecular-weight compounds to a number
of years for complex compounds (American Petroleum Institute, 1984).
When the oil has been degraded and hydrocarbon levels have been
reduced, the bacterial populations return to their initial level.
Specific bioremediation half-lives have been reported as over 48
weeks for bunker C fuel (Song et al., 1990), 37-57 weeks for crude
oil sludge (Loehr et al., 1992), less than 30 days for some normal
alkanes and aromatics (Loehr et al., 1992), five weeks for a Saudi
Arabian crude oil (Whiteside, 1993), eight weeks for crude oil under
optimum conditions (McMillen et al., 1993), and more than two years
for crude oil under nonoptimized conditions (McMillen et al., 1993.
Bioremediation with composting has also been successfully applied
with remediation times of five weeks for sludges and diesel-contami-
nated soils (Martinson et al., 1993).
There are a number of difficulties, however, with applying bioreme-
diation at hydrocarbon-contaminated sites. The presence of dissolved
solids, such as heavy metals or salt in reserves pits, will inhibit
bacterial growth. Bioremediation projects can emit significant levels
of air pollutants. For example, the emission rates of benzene and
naphthalene may be high enough to require that respirators be worn
by workers (Myers and Barnhart, 1990). Such air emissions are
expected to limit the availability of permits for bioremediation projects
in the future. Finally, some bioremediation facilities have required
large amounts of water, which can be a problem in arid areas,

Filtration

If the hydrocarbon content of the solids is high, some of the free
hydrocarbons can be separated from the solids by mechanical filtration.
Filtration, however, is not effective for reducing hydrocarbon concen-
trations to low levels.

6.2.3 Solidification

One way to treat contaminated solids is to solidify the mixture so
that the contaminants become part of the solid. Solidification reduces