<p>Ships, including those in the US
Navy, collect oily wastewater in their bilge due to onboard cleaning and
mechanical operations. Oil-in-water emulsions (O/W) are present in bilgewater,
and their filtration is difficult due to surfactants provided by cleaning
products. Despite cleaning efforts, over 457,000 tons of oil are discharged into
the ocean every year. An often overlooked aspect of bilgewater emulsions is
their evolution, as the ship's movement at sea provides extra energy that can
further emulsify the collected oil. This work aims to understand the effects of
motion on model bilgewater emulsions by tracking their evolution in dynamic
(rocking motion) and static conditions. The model bilgewater emulsion comprises
mineral oil, deionized water with 0.42 M NaCl to mimic the salinity of seawater
and sodium lauryl ether sulfate and Triton X-100, as commonly found anionic and
nonionic surfactants, respectively. A rocker is used to simulate a ship motion;
15 mL of emulsion were placed in 50 mL centrifuge tubes to mimic partially
filled bilgewater tanks. Emulsions were characterized via laser diffraction and
optical microscopy. Model bilgewater emulsions with either SLES or Triton X-100
at concentrations above 100 ppm and 500 ppm, respectively, show long-term
stability in static (no-rocking) conditions up to 20 days of observation. These
concentrations represent the minimum surfactant concentration needed to obtain
stable emulsions under static conditions. Under dynamic conditions, the minimum
surfactant concentration to obtain stable emulsions increases to 500 ppm and
1000 ppm for SLES and Triton X-100, respectively. These results mean that the
ship motion can induce drop coalescence in unstable emulsions with lower
surfactant concentrations. However, the drop size distributions for stable
emulsions under dynamic conditions show further emulsification as the average
drop size decreases. The ship motion can help further reduce the size of the
emulsion drops to diameters < 2.8 µm, which are significantly harder to
filter out using current methods. A bilgewater tank partially filled will likely
show a higher amount of sloshing than a filled one. To understand the effects
of bilgewater storage volume on emulsification, a series of dynamic experiments
were carried out with samples that contained up to 100% of the centrifuge tube
volume occupied by the model bilge water emulsion. Even when 100% of the
centrifuge volume is occupied and sloshing is eliminated, the oil moves due to
density differences, and the shear stress between fluids can induce the
generation of drops < 2.8 µm. In summary, this work shows that the ship
motion provides enough energy for emulsification once a minimum surfactant
concentration is reached regardless of the volume of emulsion stored in the
tanks. The data suggests that the best way to mitigate stable bilgewater
emulsion formation is by reducing surfactant concentration.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/17147681 |
| Date | 08 December 2021 |
| Creators | Rina G Sabatello (11813387) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/IMPACT_OF_DYNAMIC_AGEING_ON_THE_FORMATION_AND_STABILITY_OF_MODEL_BILGE_WATER_OIL-IN-WATER_EMULSIONS/17147681 |
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