Experimental study on kinetics of oil-suspended particulate matter aggregation

The formation of Oil-Suspended Particulate Matter Aggregates (OSAs) occurs when oil and suspended particulate matter are present in aquatic environments. This process has been recognized for decades to enhance natural cleansing of oiled shorelines. Several studies have been conducted during the last two decades to understand the formation and characteristics of OSAs. However, few studies have addressed the kinetic aspects of OSA formation. Operationally, decision makers lack information on the time scale of this process and its significance to oil dispersion following oil spills in aquatic environments. A laboratory study was conducted to measure the time scale of OSA formation and its variations with mixing conditions. OSAs were prepared using a reciprocating shaker and various oil/sediment mixtures. This paper presents findings from experiments conducted using a natural sediment referred as Standard Reference Material 1941b prepared by the National Institute of Standards and Technology, Arabian Medium crude oil, artificial seawater (salinity of 33‰) and various mixing energies. The sediment-to-oil ratio was kept constant to 1 in all the experiments. Total Petroleum Hydrocarbons (TPH) trapped in negatively buoyant OSAs was measured using Gas Chromatography-Flame Ionization Detector (GC-FID) analysis. Results showed that TPH in OSAs increased exponentially with shaking time and reached an equilibrium value within 3 hours. When the shaking rate increased from 2.0 Hz to 2.3 Hz, the equilibrium time decreased from 3.0 hours to 1.3 hours, the oil trapping efficiency in settled OSAs increased from 24% to 33%, and the oil-to-sediment ratio in settled material increased from 0.29 to 0.38 (mg oil/mg sediment).