Dispersants as marine oil spill treating agents: a review on mesoscale tests and field trials

The increasing oil demand and busy waterways highlight the importance of oil spill preparedness and responses. Dispersants attract attention as an effective response tool to manage the impacts of major spill incidents. Despite in-depth laboratory evaluations on the effectiveness of chemical dispersants and their impacts on the transportation and fate of spilled oils, how dispersant works at sea remains a question and calls for the tests with greater realism to validate laboratory results, bring in energy impacts, and evaluate dispersant application equipment. Mesoscale studies and field trials have thus been widely conducted to assist better spill response operations. Such research attempts, however, lack a systematic summary. This study tried to fill the knowledge gaps by introducing the mesoscale facilities developed to advance the understanding of dispersant effectiveness on various sea conditions. An up-to-date overview of mesoscale studies and field trial assessments of dispersant effectiveness has also been conducted. We ended this review by highlighting the importance of public perception and future research needs to promote the approval and application of dispersants in spill incidents.

Evaluating Surface Washing Agent Performance

Surface washing agents (SWAs) can be used to enhance removal of spilled oil from shoreline surfaces and structures. There are two classes of SWA products, “lift and float” products which remove the oil from the surfaces to create an oil slick which can be recovered mechanically and “lift and disperse” products which emulsify and disperse the oil into the water column, which are more difficult to remove mechanically. Therefore, information regarding the ability of a product to lift oil from a surface and its mechanism of action once the oil has been removed is important for oil spill responders. The SWA effectiveness (SWAE) of 15 products (conducted and reported blind) listed on the NCP Product Schedule was evaluated by applying oil to a sand substrate, allowing time for the oil to adhere to the substrate, treating with SWA, and washing with artificial seawater to release any oil that has been lifted from the substrate surface. The efficiency of SWAs is calculated based on the mass of oil remaining on the substrate relative to the total mass of oil applied. The Dispersant Effectiveness (DE) of SWA products was determined using the Baffled Flask Test and was used to sort products based on their mechanism of action (“lift and disperse” rather than “lift and float”). Using a sand basket approach, the amount of oil remaining in sand varied from 10 to 95% for the various products tested, where a lower percent signifies a better SWA. The DE varied between 8 and 81%. Though previous studies have concluded that good SWAs are poor dispersants and vice versa, the results from this study demonstrate that this is not a general rule. A stoplight decision framework was developed that considers the relationship between DE and SWAE, and serves to identify products whose primary mechanism is “lift and disperse” rather than “lift and float.” Results suggest that regardless of which test is used to evaluate SWAs, coupling findings with DE can provide useful information for decisions during response operations.

Controlling and Documenting Dispersant Effectiveness During Subsea Dispersant Injection (SSDI) - A Novel System for Dispersant Dosage and In-Situ Monitoring of Oil Droplet and Gas Bubble Sizes

Subsea dispersant injection (SSDI) has been implemented as a response method since it was first used in large-scale during the Macondo subsea blow-out in the Gulf of Mexico in 2010. Oil and gas operators have access to SSDI equipment through multiple suppliers of response equipment. This equipment is a crucial part of the capping and containment package offered in the event of a subsea blow-out. The concept is used to ensure access to the spill site (remove surface oil), improve working conditions (reduce exposure to volatile oil components) and finally be used as a response option to reduce environmental impact form the spill (reduce surfacing & stranding of oil and increase natural biodegradation of dispersed oil as small droplets). However, a subsea blow-out of 12 000 m3/day, would require 800–1600 m3 of dispersant for the first week with a dosage of 1–2%. Controlling the dispersant dosage could be critical, especially, since the initial volume of available dispersants could be limited. This paper presents a new system for automatic dispersant dosage control. The system monitors the size distribution of the released oil droplets and gas bubbles. The injected dosage of dispersant is then automatically adjusted to obtain a desired oil droplet size. The dispersant dosage from a hydraulically operated valve is adjusted based on a real-time signal from a silhouette camera (SilCam) positioned in the rising oil & gas plume. The SilCam is used to quantify oil droplet and gas bubble distributions. The SilCam can be held in place by a Remote operated Vehicle (ROV) and all signals are brought to the operator onboard the supply vessel via the ROV's umbilical cord. The concept is tested by down-scaled experiments at SINTEF and verified in full-scale by Oceaneering in a large ROV test pool. This study was headed by Oceanering in close cooperation with SINTEF and funded by the Norwegian Research Council and multiple Norwegian energy companies; Equinor Petroleum AS, Lundin Norge AS, ENI Norge AS, Total E&P Norge AS and ConocoPhillips Scandinavia AS.

A Decade of GoMRI Dispersant Science: Lessons Learned and Recommendations for the Future

Dispersants are among a number of options available to oil spill responders. The goals of this technique are to remove oil from surface waters in order to reduce exposure of surface-dwelling organisms, to keep oil slicks from impacting sensitive shorelines, and to protect responders from volatile organic compounds. During the Deepwater Horizon response, unprecedented volumes of dispersants (Corexit 9500 and 9527) were both sprayed on surface slicks from airplanes and applied directly at the wellhead (~1,500 m water depth). A decade of research followed, leading to a deeper understanding of dispersant effectiveness, fate, and effects. These studies resulted in new knowledge regarding dispersant formulations, efficacy, and effects on organisms and processes at a broad range of exposure levels, and about potential environmental and human impacts. Future studies should focus on the application of high volumes of dispersants subsea and the long-term fate and effects of dispersants and dispersed oil. In considering effects, the research and applications of the knowledge gained should go beyond concerns for acute toxicity and consider sublethal impacts at all levels of biological organization. Contingency planning for the use of dispersants during oil spill response should consider more deeply the temporal duration, effectiveness (especially of subsurface applications), spatial reach, and volume applied.

A comparison of standard test methods for determining the laboratory effectiveness of oil spill dispersants: their benefits and drawbacks

A comparison of two standard test methods for determining the laboratory effectiveness of oil spill dispersants — ASTM F2059-17 «Standard Test Method for Laboratory Oil Spill Dispersant Effectiveness Using the Swirling Flask» and ASTM F3251-17 «Standard Test Method for Laboratory Oil Spill Dispersant Effectiveness Using the Baffled Flask» — is presented in this article. It is underlined that ASTM F2059-17 and ASTM F3251-17 are almost identical from the methodological and technical points of view. The main differences lie in specific design features of the applied test vessels and mixing energies created inside them. It is reasonably established that ASTM F2059-17 can be defined as a low-energy, but ASTM F3251-17 — as a high-energy laboratory test method. The specific examples of application of the test methods for determining the effectiveness of commercially available dispersants are given. It is also concluded that both test methods are necessary to apply for a correct understanding of the dispersant effectiveness. Herewith, the results obtained according to ASTM F2059-17 should be conditionally considered as the lower limit and those according to ASTM F3251-17 — the upper limit of effectiveness of the dispersant. Moreover, the use of gas chromatography with flame ionization detection (GC-FID) is emphasized to be sometimes impossible as a recommended in both ASTM F2059-17 and ASTM F3251-17 method for analyzing the oil extracts obtained during the test. The UV spectrophotometry is proposed instead of GC-FID as an alternative. However, its application is possible only after mandatory optimization of the measurement parameters for each specific oil.

Experiments and Modeling for Investigation of Oily Sludge Biodegradation in a Wastewater Pond Environment

Historic operating and abandoned refineries frequently contain ponds or lagoons that contain oily sludge from historic wastewater treatment processes and separator sludge disposal activities that occurred prior to the implementation of regulations forbidding such disposal. These oily sludge-containing wastewater ponds represent a long-term liability at older operating refineries or abandoned refinery sites. Dewatering and solidification/stabilization are the most common technologies used to treat these sludges; however, these approaches are labor, equipment, and material-intensive. For sites where the time required to complete treatment is not a high priority, biodegradation treatment may be effective for final site remedy. The objective of this study was to investigate potential improvements in oily material biodegradation using dispersants and petroleum-degrading microbial consortia, along with the modeling of this system. The oil dispersed with mixing or remaining in the bulk aqueous phase with biodegradation was measured using methods from a dispersant effectiveness test. The experimental results indicated that mixing at levels of 200 rpm or higher resulted in positive effects on both the extent of hydrocarbon dispersion (80 to 90% of oil dispersed) and the biodegradation of the oil phase (50 to nearly 100% degraded), while the modeling results, taken along with the experimental results, indicated smaller dispersed phase droplet sizes and promoted more efficient biodegradation.