806 OIL SPILLAGE INTO WATER—TREATMENT
sorbents are much less effective for oil adsorption if contacted
by water prior to application to the spill.
Although highly effective sorbents are available as
noted above, techniques for harvesting (recovering) the oil
soaked sorbent have been limiting. For example, there have
been prior instances of oil soaked straw recovery by manual
pickup with pitchforks. However, there is development
work underway to mechanize this step as well as the appli-
cation procedure. In this regard, some very practical obser-
vations on the use of sorbents have been made by an IMCO
subcommittee on Marine Pollution. This guidance manual
outlined that “the use^9 of absorbents involves six basic oper-
ations, the supply, storage, and transportation of the mate-
rial and then the application, harvesting and disposal of the
contaminated absorbent.” The manual further observes that
some of the early applications of sorbents such as the Torrey
Canyon and Santa Barbara suffered because of the lack of
effective and effi cient harvesting techniques.
More recently, since the early 1990s a new approach to
oil pickup was conceived by the use of SOLIDIFIERS.
Solidifi ers are products which, when mixed with oil,
turn the oil into a coherent mass. They are usually available
in dry granular form. Unlike sorbents that physically soak
up liquid, solidifi ers bond the liquid into a solid carpet-like
mass with minimal volume increase, and retain the liquid for
easy removal. The bonded material also eliminates dripping-
sponge effect by not allowing the material to be squeezed
out, minimizing residue or contamination. Some polymers,
in suffi cient quantity or of high molecular weight, can actu-
ally convert the oil to a rubber-like substance.
Solidifi ers are most commonly used during very small
oil spills on land or restricted waterways to immobilize
the oil and enhance manual recovery. There has been little
documented use of solidifi ers on large spills or open water.
However, the possibility that they may reduce the spread of
waterborne oil by solidifying it and increase recovery and
removal rates is a concept with signifi cant potential benefi t.
The effectiveness of a solidifi er is based on the amount
of product and time it takes to “fi x” a given volume of oil.
The less effective products require larger amounts to solidify
oil. Fingas et al. (1994) presented results from effectiveness
tests on various solidifi ers and found that generally between
13–44 percent by weight of the product to oil was required to
solidify Alberta Sweet Crude over a 30-minute period.
The entire treatment of solidifi ers as an aid to oil spill
response is well covered in an MSRC publication.^10Physical Removal of the Contained Oil by Oil Pickup
Devices Since oil containment booms have a fi xed capacity
for oil spill containment, it is important to consider means
to physically remove the contained oil from the surface. The
use of sorbents has been discussed. An alternate approach is
to remove the fl uid oil by means of skimming devices.
Oil skimmers have been divided into fi ve categories:^11- Oleophilic surfaces (belts, disc, ropes, and
brushes, either acting independently, mounted on
a vessel or used in combination with a boom)- Weirs (simple, self-leveling, vortex assisted, auger
assisted, vessel-mounted, and weir/boom systems) - Vacuum units (portable units and truck-mounted
units) - Hydrodynamic devices (hydrocyclone and water
jet types) - Other methods (including paddle belt and net
trawl).
- Weirs (simple, self-leveling, vortex assisted, auger
The selection of the optimum skimmer for a particular
spill is based on site conditions such as the sea state and
characteristics of the spilled oil e.g. viscosity and emulsion-
forming tendency.
There are over 100 commercially available skimmers
on the market that fall within the generic types previously
mentioned. These are summarized in publications such
as the WORLD CATALOG OF OIL SPILL RESPONSE
PRODUCTS.
For example, for the principle of oleophilic surfaces,
these can comprise either a sorbent belt, an oleophilic rope
or a solid oleophilic disc that rotates through the surface oil
fi lm. In heavy sea conditions this type would be more effec-
tive than a wier type that is more suited to protected in-shore
areas.Controlled Burning of the Spilled Oil Burning represents
a surface treatment of an oil spill that is attractive in that the
oil is essentially removed from the water. However, some
of the negative aspects of this approach that have hampered
its widespread acceptance and use may be summarized as
follows:
In many spill instances, there is an obvious concern
regarding the combustion of the oil for safety reasons. Spills
near harbors, tankers, offshore platforms would create an
obvious hazard if set afi re.
A minimum thickness of oil is required to establish
combustion.
Air pollution is a concern in some instances. There is
continuing evaluation and development burning of agents.
As reported by Alan Allen,^12 there are fi re retardant
booms and ignition methods available to burn the oil under
proper conditions e.g. oil fi lm thickness and amount of emul-
sifi ed water in the oil. An effective burn after the EXXON
VALDEZ spill on Sat. March 25, 1989 was reported by Allen
in this publication.
The very encouraging burn rate statistics suggest that
only 2% of the original relatively fresh oil remained as
residue.
In this regard, it is relevant to quote the author of this
publication in its entirety because of its concise and suffi -
cient analysis of this technique by one well recognized in
this method.
“It should be recognized that the elimination of spilled oil
using in-situ burning must be considered in light of the full
range of potential impacts (safety, air quality, etc.) associated
with the burning of oil an water. The mechanical removal of
spilled oil is by far the preferred cleanup technique whenever
possible. Burning, on the other hand, may provide a safe,C015_002_r03.indd 806C015_002_r03.indd 806 11/18/2005 10:56:38 AM11/18/2005 10:56:38 AM