Abstract
Biophysical cohesive particles in aquatic systems, such as extracellular polymeric substances (EPS) and clay minerals, play an important role in determining the transport of spilled oil contamination and its eventual fate, particularly given that suspended sediment and microbial activities are often prevalent and diverse in natural environments. A series of stirring jar tests have been conducted to understand the multiple structures characteristics of the oil-mineral aggregates (OMAs) and EPS-oil-mineral aggregates (EPS-OMAs). OMAs and EPS-OMAs have been successfully generated in the laboratory within artificial seawater using: Texas crude oil (Dynamic viscosity: 7.27 × 10–3Pa⋅s at 20°C), two natural clay minerals (Bentonite and Kaolin clay), and Xanthan gum powder (a proxy of natural EPS). A magnetic stirrer produced a homogeneous turbulent flow with a high turbulence level similar to that under natural breaking waves. High-resolution microscopy results show that EPS, kaolinite, and bentonite lead to distinguished oil floc structures because of the different stickiness character of EPS and mineral clay particles. With relatively low stickiness, kaolinite particles tend to attach to an oil droplets surface (droplet OMAs) and become dominant in small-sized flocs in the mixture sample. In contrast, the more cohesive bentonite particles stickiness could adsorb with oil droplets and are thus dominated by larger sized flocs. Biological EPS, with the highest stickiness, demonstrated that it could bond multiple small oil droplets and form a web structure trapping oil and minerals. Generally, adding EPS leads to flake/solid OMAs formation, and individual oil droplets are rarely observed. The inclusion of ESP within the matrix, also reduced the dependence of settling velocity on floc size and mineral type.
Highlights
With increasing human activities and industrial development within the marine environment, water resource quality, and subsequent recovery, from contamination by industrial dumping and oil spillages have been a major challenge (Doshi et al, 2018); especially in estuarine and coastal regions where they have high sensitivity to the ecosystem and public health (Barbier et al, 2011).Oil-Mineral Flocculation and SettlingIn recent decades, oil spill contamination has tended to occur more commonly in coastal water systems (Peterson et al, 2003; Radoviæ et al, 2012)
A key finding from the present study further suggests that the sticky web structure provided by extracellular polymeric substances (EPS) dominates the stickiness already provided by the clay mineral, and when EPS is present, the variability of oil-mineral aggregates (OMAs) physical properties may be less pronounced
This study quantitatively reveals that the inclusion of EPS in the suspension matrix, leads to flake/solid OMAs formation and this has a dramatic effect on both the trapping and stabilization of oil droplets in OMAs
Summary
With increasing human activities and industrial development within the marine environment, water resource quality, and subsequent recovery, from contamination by industrial dumping and oil spillages have been a major challenge (Doshi et al, 2018); especially in estuarine and coastal regions where they have high sensitivity to the ecosystem and public health (Barbier et al, 2011).Oil-Mineral Flocculation and SettlingIn recent decades, oil spill contamination has tended to occur more commonly in coastal water systems (Peterson et al, 2003; Radoviæ et al, 2012). With increasing human activities and industrial development within the marine environment, water resource quality, and subsequent recovery, from contamination by industrial dumping and oil spillages have been a major challenge (Doshi et al, 2018); especially in estuarine and coastal regions where they have high sensitivity to the ecosystem and public health (Barbier et al, 2011). Besides the huge negative ecological impact in the nearby regions of the spill site and the shoreline, there was an unexpected sedimentation of oil-associated marine snow throughout the water column and down to the seafloor; this was an additional long-term impact on the benthic zones (Daly et al, 2016; Passow and Ziervogel, 2016; Romero et al, 2017)
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