Effects of oil properties on the formation of oil-particle aggregates at the presence of chemical dispersant in baffled flask tests

Enhancement of oil dispersion and marine oil snow formation by surface-active biomasses from diatom

Following the Deepwater Horizon oil spill event, the formation of marine oil snow (MOS) has attracted much attention from marine environmental scientists. This study investigates the crude oil dispersion as well as the MOS formation in the presence of Phaeodactylum tricornutum and Chaetoceros sp. through laboratory experiments. Results indicate that oil dispersion is enhanced with the increasing oscillation time and diatom concentration. The P. tricornutum exhibits a more significant facilitation of oil dispersion, indicated by a lower oil-water interfacial tension. When the P. tricornutum concentration reached 1.0×106 cells/mL, the oil dispersion efficiency reached 45.8%, and the volumetric mean diameter of the suspended oil was reduced from 90.6μm to 71.6μm. Diatom viability also affects oil dispersion and MOS formation. The diatom death and cell rupture result in the release of intracellular surface-active lipids and proteins, leading to a further reduction of oil-water interfacial tension and a higher quantity of oil dispersion. Much larger MOS is formed with dead diatoms due to the aggregation of cellular debris by the sticky polysaccharides. The outcomes of this study will add more scientific evidence for further understanding the fate and transport of marine oil spill, and direct the research and development of biological dispersant as an environmental friendly oil spill response technology.

Halloysite nanotubes as delivery mechanism for feather protein-based multi-surfactant systems in crude oil dispersion application

Chicken feather protein (CFP), and lecithin (L), Tween 80 (T), and DOSS (D) surfactant systems were loaded onto halloysite nanotubes (HNTs), a natural clay aluminosilicate product to form particulate dispersants at different surfactant concentrations and characterized by Fourier Transform Infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy coupled with EDS. For 24 wt% surfactants concentrations loaded HNTs; 100 wt%CFP-HNTs, 60 wt%CFP- 40 wt%L-HNTs, 20 wt%CFP- 80 wt%T-HNTs, 50 wt%CFP- 25 wt%T-25 wt%L-HNTs and 25 wt %CFP- 25 wt%T-50 wt%D-HNTs showed good interfacial tension lowering abilities by recording 6.39, 2.82, 2.43, 1.68, and 1.55 mN/m at 60s respectively. The CFP-based surfactant-HNTs dispersants formed very stable o/w emulsions against droplet coalescence and showed an increase in interfacial viscosity which contributed to the stability of their respective o/w emulsions. In this study, the US EPA's baffled flask test was deployed to probe the prospects of the CFP-based surfactants-HNTs dispersants in crude oil dispersion at different surfactant concentrations. 100 wt%CFP-HNTs, 60 wt %CFP- 40 wt %L-HNTs, 20 wt %CFP- 80 wt %T-HNTs, 50 wt %CFP- 25 wt%T-25 wt%L-HNTs and 25 wt%CFP- 25 wt%T-50 wt%D-HNTs recorded dispersion effectiveness of 33.9, 74.8, 65.4, 78.6 and 88.2 vol% respectively at 24 wt% surfactant concentration. It can be deduced that an increase in the surfactant concentrations loaded onto HNTs improved the dispersion effectiveness of the produced particulate dispersants. Largely, the 24 wt% CFP-based surfactant-HNTs dispersants showed considerable promise in crude oil dispersion in seawater.

Role of light microplastics in the dispersion process of spilled crude oil in the marine environment

Oil spill and microplastic (MP) pollution are the main problems in the marine environment. After an oil spill, the oil film may be dispersed into the water column in the form of droplets under the action of ocean waves. In this study, the sea condition was simulated through the batch conical flask oscillation experiment. Merey crude oil was selected as experimental oil, and polyethylene (PE) and polystyrene (PS) were used as experimental MP. The effects of MP properties (type, concentration and size) on the dispersion of spilled oil were investigated. It is found that for each MP, the oil dispersion efficiency (ODE) increased rapidly at first and then tended to be stable, which all reached the maximum at 360 min. When the concentrations of PE and PS increased from 0 to 100 mg/L, the maximum ODE decreased from 32.64 % to 13.72 % and 10.75 %, respectively, indicating that the presence of MP inhibits the oil dispersion. At the same oscillation time, the volumetric mean diameter (VMD) of dispersed oil increased with the MP concentration. When the particle size of PE and PS increased from 13 to 1000 μm, the maximum ODE increased from 24.74 % to 31.49 % and 28.60 %, respectively. However, the VMD decreased with the size of MP. In addition, the time series of the oil adsorption rate by the MP were well fitted by the kinetic models. The results of this research deepen the understanding of the migration law of spilled oil to the marine environment in the presence of MP, and may further improve the ability of marine environmental scientists to predict the fate of oil spill.

Assessment of spilled oil dispersion affected by dispersant: Characteristic, stability, and related mechanism

Oil dispersion, a crucial process in oil transport, involves the detachment of oil droplets from slicks and their introduction into the water column, influencing subsequent oil migration and transformation. This study examines oil dispersion, considering characteristics, stability, and mechanisms, while evaluating the impact of dispersants and salinity. Results show the significant role of surfactant type in dispersants on oil dispersion characteristics, with anionic surfactants exhibiting higher sensitivity to salinity changes compared to nonionic surfactants. The dispersion efficiency varies with salinity, with anionic surfactants performing better in low salinity (<20‰) and nonionic surfactants showing superior performance at 30-35‰ salinities. Rheological analysis illustrates the breakup and coalescence of oil droplets within the shear rates of breaking waves. An increase in interfacial film rigidity impedes the coalescence of oil droplets, contributing to the dynamic stability of the oil-water hybrid system. The use of GM-2, a nonionic dispersant, results in the formation of a solid-like interface, characterized by increased elastic modulus, notably at 20‰ salinity. However, stable droplet size distribution (DSD) at 35‰ salinity for 60 h suggests droplets can remain dispersed in seawater. The enhancement of stability of oil dispersion is interpreted as the result of two mechanisms: stabilizing DSD and developing the strength of viscoelastic interfacial film. These findings offer insights into oil dispersion dynamics, highlighting the importance of surfactant selection and salinity in governing dispersion behavior, and elucidating mechanisms underlying dispersion stability.

Mechanism of nearshore sediment-facilitated oil transport: New insights from causal inference analysis

A quantitative understanding of spilled oil transport in a nearshore environment is challenging due to the complex physicochemical processes in aqueous conditions. The physicochemical processes involved in oil sinking mainly include oil dispersion, sediment settling, and oil-sediment interaction. For the first time, this work attempts to address the sinking mechanism in petroleum contaminant transport using structural causal models based on observed data. The effects of nearshore salinity distribution from the estuary to the ocean on those three processes are examined. The causal inference reveals sediment settling is the crucial process for oil sinking. Salinity indirectly affects oil sinking by promoting sediment settling rather than directly affecting oil-sediment interaction. The increase of salinity from 0‰ to 35‰ provides a natural enhancement for sediment settling. Notably, unbiased causal effect estimates demonstrate the strongest positive causal effect on the settling efficiency of sediments is posed by increasing oil dispersion effectiveness, with a normalized value of 1.023. The highest strength of the causal relationship between oil dispersion and sediment settling highlights the importance of the dispersing characteristics of spilled oil to sediment-facilitated oil transport. The employed logic, a data-driven method, will shed light on adopting advanced causal inference tools to unravel the complicated contaminants' transport.

Formation and sedimentation of oil-mineral aggregates in the presence of chemical dispersant

The formation and sedimentation of oil-mineral aggregates (OMAs) is the major method to transport spilled oil to the seafloor. In this study, the formation and sedimentation experiments of OMA using montmorillonite and four crude oils were performed in a wave tank in the presence of chemical dispersant. Most of the formed OMAs were droplet OMAs, and single droplet OMA would aggregate into multiple ones under the action of the dispersant. The size of the oil droplets trapped in the OMA increased with time and was larger for the oil with higher viscosity. The sinking velocities of OMAs formed in this study were between 100-1200 μm s-1 and they were positively correlated with their diameter. The density of OMA was of the same order as that of the crude oil that formed them. An increase in the dispersant dosage could promote the formation of OMAs. The oil content in OMAs was higher for the denser oil in the presence of a dispersant. The maximum oil trapping efficiency of OMAs was 48.05%. This study provides fundamental data on the formation kinetics of OMAs.

Impact of mixing energy and dispersant dosage on oil dispersion and sedimentation with microplastics in the marine environment

Recently, the fate of spilled oil in the presence of microplastics (MPs) in the sea has attracted attention of researchers. Merey crude oil and polyethylene terephthalate (PET) were used as the experimental materials in this study. The effects of mixing energy and dispersant dosage on oil dispersion and sedimentation in the presence of MPs in the water column were investigated by laboratory experiments simulating actual sea conditions. The increase of mixing energy showed a promoting effect on oil dispersion. When the oscillation frequency increased from 140 rpm to 180 rpm, the oil dispersion efficiency (ODE) ranged from 2.1 %-3.7 % to 17.4 %-30.8 %, and the volumetric mean diameter (VMD) of the suspended oil droplets/MPs-oil agglomerates (MOA) decreased from 99.9-131.4 μm to 76.6-88.2 μm after 2 h oscillation. The application of chemical dispersant led to an increase in both the quantity and size of the formed sunken MPs-oil-dispersant agglomerates (MODA). At the dispersant-to-oil ratio (DOR) of 1:5, the ODE declined from 77.7 % to 62.6 % when the MPs concentration increased from 0 to 150 mg/L, while the oil sinking efficiency (OSE) rose from 3.4 % to 15.6 % when the MPs increased from 25 to 150 mg/L; the maximum size of the sunken MODA reached 13.0 mm, and the total volume of the MODA formed per unit volume oil reached 389.7 μL/mL oil at the MPs concentration of 150 mg/L. Meanwhile, the results showed that the presence of MPs inhibited the oil dispersion by increasing the oil-water interfacial tension. The outcomes of this work may provide assistance in predicting the transport of spilled oil and developing emergency measures.

Formation of oil-particle aggregates in the presence of marine algae

After an oil spill, the formation of oil-particle aggregates (OPAs) is associated with the interaction between dispersed oil and marine particulate matter such as phytoplankton, bacteria and mineral particles. Until recently, the combined effect of minerals and marine algae in influencing oil dispersion and OPA formation has rarely been investigated in detail. In this paper, the impacts of a species of flagellate algae Heterosigma akashiwo on oil dispersion and aggregation with montmorillonite were investigated. This study has found that oil coalescence is inhibited due to the adhesion of algal cells on the droplet surface, causing fewer large droplets to be dispersed into the water column and small OPAs to form. Due to the role of biosurfactants in the algae and the inhibition of algae on the swelling of mineral particles, both the oil dispersion efficiency and oil sinking efficiency were improved, which reached 77.6% and 23.5%, respectively at an algal cell concentration (Ca) of 1.0 × 106 cells per mL and a mineral concentration of 300 mg L-1. The volumetric mean diameter of the OPAs decreased from 38.4 μm to 31.5 μm when Ca increased from 0 to 1.0 × 106 cells per mL. At higher turbulent energy, more oil tended to form larger OPAs. The findings may add knowledge about the fate and transport of spilled oil and provide fundamental data for oil spill migration modelling.