In other tests, dispersant loss was determined from crude oil slicks for two
conditions: 43 h water soaked process with water current velocity 13 cm/s (sample
I) and 91 h water soaked process with water current velocity 5–6 cm/s (sample II).
Warren Spring Laboratory effectiveness was used to discuss about dispersant loss. In
no-flow conditions by increasing time on the tank water surface, two soaked samples
showed an initial increase in dispersibility because of increasing oil density, after
which its rapid decline was observed due to surfactant loss. While in flow conditions,
the dispersibility decreased with time (more rapid than no current conditions). The
result of the different current speeds on dispersant loss also indicated that dispersion
was faster and more complete for sample II than sample I.
They also studied the combined effects of thickness of oil slick and oil type on
dispersant detriment in calm and flow conditions. The obtained results showed the
important role of slick thickness in the dispersion potential. The 55 h soaked thick
slick (5 mm) had higher dispersant effectiveness than 18 h soaked thin slick
(2.5 mm), for the same oils.
The oil concentration and dispersant agents influence oil removal efficiency. The
impacts on the removal of total petroleum hydrocarbons were investigated by Zahed
et al. (2010). In initial concentrations of crude oil of 100, 500, 1000, and 2000, the
removal efficiency of total petroleum hydrocarbons by dispersant were reported
67.3, 62.5, 56.5, and 44.7%, respectively. Without dispersant, the crude oil removal
decreased to 64.2, 55.7, 48.8, and 37.6% for the mentioned oil concentrations.
According to the presented results, the removal of crude oil increased by use of
dispersant and decreased by increasing concentrations of crude oil.
Dispersant agents are able to effectively and quickly eliminate large volumes of
oil compared with other removal methods but they have some limitations. They do
not have an effective performance for high viscous oil (>2000 cSt), and thick layers
of oil, which are formed in the low temperatures, weathering conditions, and mousse
oil. On the other hand, these agents consist of different chemical materials, the
presence of which causes environmental problems for marine creatures. In addition,
dispersant spraying techniques require a greater understanding of the effective
factors on their performance. For example, the wind can change the amount and
position of dispersants during spraying with helicopter (Al-Majed et al. 2012).
Solidifier
Oil solidifiers (gelling agents) are dry granular materials that can be divided into two
main groups: polymeric and low-molecular-weight solidifiers. The polymeric
solidifiers are produced from high-molecular-weight polymers with porous matrix
and large oleophilic surface area, which are able to physical contact with hydrocarbons. While the low-molecular-weight solidifiers are derived from amino acids,
peptides, sugars, quaternary ammonium salts, metallic soaps, derivatized cholesterols, and hydrocarbons. To improve the solidification process, the combination of
different types of solidifiers is recommended. These chemical agents increase the
oil’s viscosity and form a solid or semi-solid material and prevent oil release in the
air and water.
12 Remediation of Pollution by Oil Spills
405
conditions: 43 h water soaked process with water current velocity 13 cm/s (sample
I) and 91 h water soaked process with water current velocity 5–6 cm/s (sample II).
Warren Spring Laboratory effectiveness was used to discuss about dispersant loss. In
no-flow conditions by increasing time on the tank water surface, two soaked samples
showed an initial increase in dispersibility because of increasing oil density, after
which its rapid decline was observed due to surfactant loss. While in flow conditions,
the dispersibility decreased with time (more rapid than no current conditions). The
result of the different current speeds on dispersant loss also indicated that dispersion
was faster and more complete for sample II than sample I.
They also studied the combined effects of thickness of oil slick and oil type on
dispersant detriment in calm and flow conditions. The obtained results showed the
important role of slick thickness in the dispersion potential. The 55 h soaked thick
slick (5 mm) had higher dispersant effectiveness than 18 h soaked thin slick
(2.5 mm), for the same oils.
The oil concentration and dispersant agents influence oil removal efficiency. The
impacts on the removal of total petroleum hydrocarbons were investigated by Zahed
et al. (2010). In initial concentrations of crude oil of 100, 500, 1000, and 2000, the
removal efficiency of total petroleum hydrocarbons by dispersant were reported
67.3, 62.5, 56.5, and 44.7%, respectively. Without dispersant, the crude oil removal
decreased to 64.2, 55.7, 48.8, and 37.6% for the mentioned oil concentrations.
According to the presented results, the removal of crude oil increased by use of
dispersant and decreased by increasing concentrations of crude oil.
Dispersant agents are able to effectively and quickly eliminate large volumes of
oil compared with other removal methods but they have some limitations. They do
not have an effective performance for high viscous oil (>2000 cSt), and thick layers
of oil, which are formed in the low temperatures, weathering conditions, and mousse
oil. On the other hand, these agents consist of different chemical materials, the
presence of which causes environmental problems for marine creatures. In addition,
dispersant spraying techniques require a greater understanding of the effective
factors on their performance. For example, the wind can change the amount and
position of dispersants during spraying with helicopter (Al-Majed et al. 2012).
Solidifier
Oil solidifiers (gelling agents) are dry granular materials that can be divided into two
main groups: polymeric and low-molecular-weight solidifiers. The polymeric
solidifiers are produced from high-molecular-weight polymers with porous matrix
and large oleophilic surface area, which are able to physical contact with hydrocarbons. While the low-molecular-weight solidifiers are derived from amino acids,
peptides, sugars, quaternary ammonium salts, metallic soaps, derivatized cholesterols, and hydrocarbons. To improve the solidification process, the combination of
different types of solidifiers is recommended. These chemical agents increase the
oil’s viscosity and form a solid or semi-solid material and prevent oil release in the
air and water.
12 Remediation of Pollution by Oil Spills
405