OIL SPILLAGE INTO WATER—TREATMENT 815
has a strong driving force to diffuse into the water phase.
In this transport process, a small amount of oil “associated”
with the surfactant is carried into the water phase. A continu-
ation of this process produces a series of fi ne oil droplets
migrating from the oil phase into the water phase as sche-
matically shown by Figure 7.
In the graphical presentation of Figure 7, the surfactant for-
mulation can be seen to be compatible with the crude oil phase
as shown in (A). However, due to the nature of the specifi c
compounds, there is a driving force for part of the formulation
of diffuse into the water phase when it contacts an oil/water
interface (B). During this diffusion, some oil associated with
the surfactant as fi ne oil droplets is carried along with the sur-
factant into the water column as shown in (C). In essence, a
three component system—oil water surfactant is formed
at the interface. As the surfactant diffuses into the water phase,
the associated oil is thrown out of solution.
The migration of the surfactant from the oil into the
water phase-in essence, the source of energy for spontaneous
emulsifi cation comes from the redistribution of materials. It
can be seen that for this system to work in the fi eld as an oil
slick dispersant, the surfactant must be brought into contact
with the oil phase initially.
It is also interesting to observe that as the surfactant dif-
fuses through the interface, a reduction in interfacial tension
occurs. Over the entire oil/water interface, there are dissimi-
lar values of interfacial tension due to the somewhat random
diffusion of the surfactant at varying sites along the interface.
Any difference in interfacial tension produces a spreading
pressure, II, which causes rapid movement of the interface.
This interfacial turbulence also aids in the dispersion of the
oil into the water phase.Field Tests Support the Role of Chemical Dispersants
to Minimize Oil Spill ImpactIn summary, there is an increased awareness and rec-
ognition that there is a role for chemical dispersants in
minimizing damage from oil spills. The improved effective-
ness afforded by the self-mix dispersant system has been
demonstrated.
Over the past 10 years, there have been a number of
major fi eld tests that have demonstrated under real life condi-
tions the effectiveness and biological safety of this approach.
These have been reviewed and summarized in a study by the
National Research Council.^41
In order to establish that the transient, rapidly diluting
concentrations of dispersed oil are not harmful, actual mea-
surements of the biological effects were made during several
controlled oil spills.
For examples, on August 19, 1981 a fi eld experiment was
carried out in Long Cove, Searsport, Maine, which simulated
the dispersal of oil slicks in the nearshore zone.^42 The object
of this experiment was to obtain quantitative information on
the fate and effects of dispersed and non-dispersed oil in the
nearshore area. An upper and lower intertidal sampling are
within a 60 × 100 meter test plot were exposed to dispersed
oil in water resulting from the discharge of 250 gallons ofoil premixed with 25 gallons of COREXIT 9527 dispersant.
Release of treated oil was around high-water slack tide on
the surface of the water. The maximum water depth over the
test areas was 3.5 meters. Untreated crude oil (250 gallons)
was released on an ebbing tide within a separate, boomed-
off 60 × 100 meter test plot. A third test plot served as an oil-
free reference plot. To evaluate the effects on the intertidal
infaunal community structure, chemical and biological anal-
yses were carried out concurrently throughout the pre- and
post-spill periods. The conclusions reached by the Bowdoin
College scientists are quoted as follows:- No evidence of any adverse effects was observed
on infaunal community structure from the expo-
sure of intertidal sediments to dispersed oil under
real spill treatment conditions. - There is clear evidence that the undispersed oil
treatment caused some mortality of a commer-
cially important bivalve and increased densities
of opportunistic polychaetes. - The results seen in the test plot that received
untreated oil, are consistent with studies of real-
world oil spills.
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tanker cargoes, US Patent 3,634,050. Issued January 11, 1992. - Corino, E.R., Chemical gelling agents and dispersants. Paper presented
to the Third Joint Meeting of the American Institute of Chemical
Engineers and Puerto Rican Institute of Chemical Engineers, May 20,
1970. - Department of US Navy, The recovery of bunker C fuel oil from the
sunken tanker, SS ARROW, Navships 0994–008–1010, March 1970. - Lehr, W.E. and J.O. Scheren, Jr., Design requirements for booms, Proc.
of API and FWPCA Joint Conference on Control of Oil Spills, NYC,
New York, December 1969. - Hoult, David P., Containment and collection devices for Oil slicks, Oil
on the Sea, Plenum Press, 1969. - Hoult, David P., Containment of Oil Spills by Physical and Air barriers,
paper presented on the Third Joint Meeting of the American Institute of
Chemical Engineers and the Puerto Rican Institute of Chemical Engi-
neers, May 20, 1970. - Struzeski, E.J., Jr. and R.T. Dewling, Chemical treatment of oil spills,
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dealing with oil pollution preparation of a manual for the guidance of
governments, March 2, 1992. - Chemical Oil Spill Treating Agents MSRC. Technical Report Series
93–015, 1993. - Oil Spill Response Manual, Exxon Production Research Co. page 77,
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on Water Pollution by Oil, Aviemore, Scotland, May 4–8, 1970. - McCaull, Julian, The black tide, Environment, November 1969.
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