Bilgewater, an oil and grease mixture with water, may affect many aquatic species. Thus, development of methods and techniques to treat or to mitigate the formation and undesired consequences of shipboard emulsions are urgently needed. This research investigated the fundamental physicochemical processes in the formation, stabilization, and breaking of shipboard relevant emulsions. Understanding shipboard emulsions at evolving interfaces is a key scientific challenge. The underpinning hypothesis was that surface chemical changes at the liquid-liquid (l-l) interface are critical for mass and charge transfer leading to emulsion formation, stabilization, and worsening. Using unique in situ chemical imaging capabilities developed at Pacific Northwest National Laboratory, the research team answered the following questions: 1) How do ionic, nonionic, and solid emulsifiers affect emulsion stabilization in ship bilgewater conditions? 2) How does microbial activity affect emulsion formation, stabilization, and breaking? A unique vacuum compatible microreactor, System for Analysis at the Liquid Vacuum Interface (SALVI), was used to achieve multi-scale imaging and obtain a more fundamental understanding of these physiochemical multi-phase processes.

This project had the following objectives: 1) study the emulsion formation mechanism in synthetic and actual bilgewater using novel multimodal imaging approaches; 2) obtain molecular distribution of key species at the droplet surface and interface; and 3) set the technical foundation for the development of cost-effective solutions to reduce, prevent, and treat ship-relevant emulsions.

The key technical approach was to use SALVI, a unique vacuum and ambient compatible microfluidic interface and multimodal imaging to study emulsion. The research team employed in situ liquid chemical imaging to study various liquid surfaces, solid-liquid (s-l), and l-l interfaces. SALVI, as a portable microfluidic reactor, was suitable for a multitude of analytical instruments, including Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS), scanning electron microscope (SEM), and nuclear magnetic resonance, allowing chemical insight into the complex l-l interface. This project studied the l-l interactions at the molecular level and provided unprecedented insight into the physicochemical processes of bilgewater emulsions.

SERDP-recommended emulsion systems were used as the base models for synthetic bilgewater studies. Specifically, synthetic bilgewater is similar to Marine Environment Protection Committee 107(49) test fluid Carbon emulsion. More importantly, real bilgewater samples as well as a Naval Surface Warfare Center Carderock surrogate sample from SERDP funded labs were shared and studied in this project complementing other ongoing bilgewater emulsion research. Emulsions prepared by mechanical means were used to serve as the surrogate and be analyzed using multiple imaging techniques to understand their surface properties, size, morphology, aggregation, and l-l interactions.

Besides bulk approaches to study emulsions, the unique multiplexed chemical imaging capability was employed to decipher the complex interfacial process in emulsion formation, breaking, and separation. Specifically, the approach captured the l-l interface and studied how stressors affect emulsion formation and transformation. Two analyses were performed. First the team sought to establish feasibility of multimodal imaging applications to study bilgewater emulsions and demonstrate how different measurement results can be integrated to understand the l-l interface transformation. Building upon the team’s expertise in biofilm imaging and optimal bilgewater analysis conditions, the research team aimed to investigate the effect of microbes on bilgewater stabilization or breaking.

The researchers demonstrated that the in situ correlative imaging of bilge emulsion is possible using the advance chemical imaging techniques such as SEM and ToF-SIMS. First, droplet size distribution of bilge emulsion seems to grow from fresh to aged particles in water based on optical and in situ SEM imaging. Moreover, unique oil and water interfacial information and evolution can be captured using in situ liquid SIMS. The researchers also illustrated that biofilm effects on bilge could be probed using ToF-SIMS. Furthermore, both planktonic cells and biofilms influence the oil-in-water bilge changes. These results set the technical and scientific foundations for further systematic studies of bilgewater stabilization, breaking, and mitigation.

This research provides a fundamental understanding of the underlying principles of bilgewater emulsion formation, stabilization, and breaking using multiplexed in situ chemical imaging techniques to study, at the molecular level, the l-l interactions and liquid surface modifications under ship-relevant conditions. Findings, based on direct observations, provide physical and chemical knowledge underpinning these complex interfacial phenomena and lead to solutions for oil-in-water (O/W) emulsion reduction, improved wastewater treatment, waste-oil-holding capacities, and fuel holding capacities onboard ships. Microfluidic-based strategies for stabilization, effective separation, and treatment of O/W emulsions, developed based on the findings of this research, will reduce maintenance burden, increase oily water separator treatment efficiency, and lower the cost of wastewater treatment for the Department of Defense.