Bacterial streamers formation and hydrodynamics of a rising oil droplet with natural seawater samples using ecology-on-a-chip (eChip) microfluidics*

During the Deepwater Horizon oil spill, dispersant has been used to break up oil into small droplets within the water column, resulting in the generation of substantial quantities of submillimeter/submicron oil droplets. Most research focus on the transport and fate of pristine droplets. Recent studies reveal that bacteria is capable of forming extracellular polymeric substances (EPS) aggregates around individual droplet to increase its drag. However, the mechanism’s implications and the effect of dispersants in the real world scenario remains unclear. Here, we use eChip microfluidic that enables the observation of EPS streamer formation by natural microbial consortium on a rising oil droplet using natural seawater samples. By applying a layer-by-layer hydrophilic functionalization methodology, a single oil droplet can be pinned in the microfluidic channel, and natural seawater is flowed through the channel. Flow field around the oil droplet with streamers is obtained by micro-PIV with natural seeding. Control volume analysis provides instantaneous drag.