Effects of Salinity on Dispersant/ Oil Particle Size

Clair Hollingsworth

Shahidul Islam

Dr. Cheryl Page

Dr. Temitope Ojo

Dr. Jim Bonner

Department of Civil Engineering

Texas A&M University

Most oil spills occur in near-shore coastal environments, posing both ecological and economic effects.  One method of oil spill response is the use of chemical dispersants.  Chemical dispersants contain surfactants, which are molecules with both hydrophilic and hydrophobic components that stabilize the oil droplets in the water column.  The rationale fir dispersant use is that if an oil slick is incorporated into the water column as oil droplets where it can be diluted, it is less likely to be washed ashore. 

One concern for dispersant use in coastal environments is that salinity concentrations may be variable.  Most dispersants are designed to for optimum effectiveness at 30‰ salinity (typical ocean concentration).  Another concern is the lower mixing-energy levels found in many near-shore environments.   Application of dispersants on oil slicks in these low-energy environments may also render lower effectiveness.   

In order to test the effectiveness of dispersant Corexit 9500 on Arabian Medium Crude oil at varying salinities (10‰, 20‰, & 30‰), a lab-scale reactor (with accompanying mixer) was employed.  The mixer provided a constant low-energy input (mean shear rate of 15 sec^-1).  A series of four-hour experiments were conducted for both premixed and non-premixed oil/dispersant.  A LISST-100X particle sizer instrument collected oil droplet data in real-time.  In general, the premixed dispersant/oil scenario was more effective than the non-premixed oil/dispersant scenario for all salinities.  Also, when considering the non-premixed scenario only, the higher-salinity condition was more effective than lower salinities. 

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