SERDP 2021 Project of the Year Award for Weapons Systems and Platforms

Oils, fuels, and lubricants are critical to the mission of every ship and watercraft used across the Department of Defense (DoD). As a result, oily water is generated on all military vessels in bilgewater, compensated ballast tanks, or oily waste holding tanks. The treatment of this contaminated water is complicated by the emulsions created by mixing water with oils, fuels, and lubricants. Preventing the discharge of oil and water emulsions from the ship into the environment requires costly secondary treatment systems that divert resources away from the vessels’ primary mission. Secondary treatment of bilgewater could be rendered unnecessary with improvements to primary treatment systems that are informed by a better understanding of the physical and chemical properties of emulsions. While the formation of oil and water emulsions has been widely studied in other applications, these specific properties have not been thoroughly investigated for bilgewater generated by military vessels.

To address these issues, Dr. Cari Dutcher and her team from the University of Minnesota, Twin Cities executed a study to provide an understanding of the generation, stabilization, and worsening of shipboard oil and water emulsions in the presence of complex hydrodynamic fields with varied chemical conditions (Project Overview). In addition, the team set out to explore emulsion governing factors, including shear and mixing, interfacial tension, the ratios of water to oil and surfactants, salinity, and size distribution in complementary macro- and micro-scale tasks.

As a result of this project Dr. Dutcher’s team made substantial progress in improving the overall understanding of oil and water emulsions in military vessels. The team optimized the design of microfluidic devices for dynamic interfacial tension (IFT) measurement and successfully executed droplet coalescence experiments using surface treatment to yield hydrophilic walls suitable for oil-in-water systems. Dynamic IFT measurement of simulated bilgewater with detergent mix and model surfactants for oil-in-water systems were proven to result in different time-dependent profiles than those obtained in water-in-oil systems, suggesting a curvature dependent surfactant transport mechanism. The characterization of surfactant parameters using different isotherm models revealed the fundamental properties of both model and commercial surfactants in bilgewater system. The preliminary results of Stokes’ trap experiments have shown successful trap and coalescence of droplets in water-in-oil systems. Static emulsion stability tests found the non-monotonic relations for emulsion destabilization times with both oil and surfactant concentration. For oil contents greater than 10% oil, flow-induced destabilization was observed in rheometric shear flows. Similar flow-induced destabilization was observed for lower oil contents, down to 0.1% oil, when exposed to more complex Taylor Couette (TC) flows. The changes in stability were determined through changes in droplet size distributions. Finally, the preliminary results with in-situ injection in TC flows enables further advanced studies of the dynamics of emulsion formation and destabilization in flow.

The results of this project provide a new understanding of the effects of water to oil to surfactant ratios on time-dependent properties that impact emulsion formation, stability, and worsening. Additionally, the results provide a new understanding of hydrodynamic effects on the transient emulsification and destabilization processes. Ultimately, the results of this project can inform improvements to bilgewater treatment strategies that will reduce DoD’s potential to release contaminated bilgewater into the environment and allow vessels to focus more resources on their mission.

For their efforts on the project Understanding Shipboard Oil/Water Emulsions Using Macro- and Micro-scale Flows, Dr. Cari Dutcher and her team have been awarded the 2021 SERDP Project of the Year for Weapons Systems and Platforms.