Effects of the suspended sediment concentration and oil type on the formation of sunken and suspended oils in the Bohai Sea

Abstract

The unsourced oil contamination on the coast of Bohai Sea has recently attracted scholars to study the formation of sunken and suspended oils (SSO) from oil slicks on the sea surface. In this research, batch experiments have been conducted to study the time-scale effect of the different concentrations of suspended sediments on the formation of sunken oils and suspended oils using three oils (Oman crude oil, Merey crude oil, and 380# fuel oil) and two sediments (sand and silt) at different temperatures. The results showed that the sunken and suspended oils formed quickly within the mixing time and reached a maximum at the equilibrium time, te, and that te had a wide range of variation with sediment concentration and type. The oil sinking and submerging efficiency could reach up to 6.33%, 43.82% and 44.44% for 380# fuel oil, Oman crude oil and Merey crude oil, respectively. It is noted that the increase in sediment concentration and environmental temperature could enhance the formation of SSO but that it had a close relationship with the oil type. Overall, hydrophobic sand had a significantly higher oil sedimentation effect than silt.

Distribution of Polycyclic Aromatic Hydrocarbons in Sunken Oils in the Presence of Chemical Dispersant and Sediment

“…The size distribution of the quartz sand was measured and shown in Figure 2. as previously described [32]. Briefly, sunken oils were prepared using 400 mL natural seawater, 100 mg HFO 380, and predefined amounts of quartz sand in 500 mL Erlenmeyer flasks closed by silicone stoppers wrapped with aluminum foil to avoid the evaporation of light compounds.…”

“…After the shaking time, the mixtures were placed to settle for 18 h in a refrigerator. Negatively buoyant sunken oils were separated from the suspensions for oil extraction, and then total petroleum hydrocarbons (TPH) analysis was performed using the analytical procedure as previously described [32].…”

“…The improved BFT method could provide sufficient mixing energy for dispersion, akin to that observed in the field and better reproducibility [47]. The procedure used to prepare sunken oils was performed as previously described [32]. Briefly, sunken oils were prepared using 400 mL natural seawater, 100 mg HFO 380, and predefined amounts of quartz sand in 500 mL Erlenmeyer flasks closed by silicone stoppers wrapped with aluminum foil to avoid the evaporation of light compounds.…”

“…Coastal sediment has been regarded as an important transport medium and repository for environmental pollutants [29][30][31]. After many major oil spills, such as Tsesis, Ixtoc-I, Vista Bella, and others, the formation of sunken oils was mainly dominated by the interaction between spilled oils and sediments [6,9,32,33]. Several studies have been conducted to understand the formation and characteristics of sunken oils in the presence of sediment [34][35][36][37].…”

“…At present, there is still a significant knowledge gap concerning the synergistic effect of chemical dispersants and sediments on the formation and characteristics of the sunken oils. Most of the previous bench-scale studies have focused on the oil sinking efficiency (OSE) in the presence of dispersants and sediments [3,32,[34][35][36]43]. Few studies were conducted on the quantitative distribution of polycyclic aromatic hydrocarbons (PAHs) in the sunken oils.…”