The primary objective of this project was to advance the current understanding of emulsion science for chemically stable emulsions formed in Armed Forces applications. While commercially available equipment can be implemented for bilgewater emulsion mitigation, there is little knowledge surrounding the physical, chemical and thermodynamic properties of the emulsions created in an Armed Forces vessel environment. Thus, targeted treatment and management of these fluids become conjecture and calls for a deliberate and thorough understanding of fundamental emulsion stability properties. This project focuses on three segments: (1) Scoping Study for Review of Armed Forces Vessels Oil-in-Water Emulsions, (2) Characterization of Prepared and Extracted Bilgewater Emulsions, and (3) Data Analysis, Interpretation and Publication.

Investigators Danielle Paynter and Jared Church, from Naval Surface Warfare Center, discuss characteristics of a prepared bilgewater emulsion. (U.S. Navy photo by Nicholas Brezzell)

This project focused on the systematic characterization of both prepared emulsions and extracted bilgewater to determine emulsion stability under various conditions. First, a scoping study of armed forces vessels oil-in-water emulsions was conducted to help define the analytical techniques, types of cleaners, and environmental conditions used for experimental testing. Next, emulsion solutions were systematically investigated using identified Navy relevant oils and cleaners. In particular, these studies evaluated the impact that environmental parameters, cleaner properties, and oil properties had on emulsion stability. Actual bilgewater samples from three Navy ships were also characterized for water quality and oil properties. Results from experimental tests were interpreted using machine learning methods and used to develop a preliminary emulsion stability prediction model.

Results from this multi-scaled investigation of bilgewater emulsions has furthered the understanding of the formation and stabilization of bilgewater emulsions. A scoping study of emulsifiers used on Armed Forces Vessels resulted in the data driven identification of eight commercial cleaners/emulsifiers, which were tested for critical micelle concentration (CMC), interfacial tension, micelle size, and zeta potential. In addition, over 925 emulsion samples were generated and characterized for emulsion stability based on droplet size distribution, oil separation, and creaming rate. Results indicated that 1) emulsion stability is significantly affected by surfactant type, ionic strength, and temperature, 2) the CMC of commercial cleaners is a good indicator of coalescence stability in simulated bilgewater emulsions, 3) water quality parameters range significantly in actual bilgewater samples, and 4) fuel components play an important role in bilgewater emulsion stability. Based on the results from experimental testing, an emulsion stability model was developed to help disseminate findings to bilge operators. The random forest classifier showed the highest prediction of emulsion stability with an F1 score of 0.8868. Sensitivity analysis showed that salinity and temperature were dominant factors in predicting emulsion stability for the conditions tested.

Current bilgewater treatment methods do not rely on targeted techniques to increase the effectiveness of emulsion removal. Hence, this research focused on discovering the underlying principles of emulsion formation and stability such that informed research decisions can be pursued. The purpose of this work was not to just recommend treatment technologies for bilgewater emulsions; rather, the purpose was to contribute to the current research field and to assist shipboard personnel in identifying why emulsions are creating treatment issues. Knowledge gained from this research has already helped inform bilgewater management decisions within the Armed Forces. Currently, the methods for characterizing bilgewater emulsions, developed under this project is being leveraged by the U.S. Navy for recommending bilge cleaners that prevent the generation of stable bilgewater emulsions. The insights from this work also aid in improving other fields where surface active compounds are prevalent. For example, knowledge gained under this project can also be used to help develop new fluorine free firefighting foams based on the fundamental understanding of how compounds transport between fuel and aqueous phases.