(414b) Analysis of the Biodegradation of Dilute Oil-in-Water Emulsions Using a Compound Particle-in-Cell Model

In the aftermath of natural and accidental releases of crude oil in the sea, part of the oil is emulsified and dispersed into the seawater column. The oil droplets may be created either at the sea surface during the breakup of an oil slick by sea waves, or at the seafloor during the extrusion of crude oil from natural cracks and broken wellheads. The fate of subsea droplet populations is determined by natural attenuation processes, mainly dissolution into the seawater and biodegradation by oil-eating microbes. We have recently developed a compound particle model for the microbial degradation of solitary oil droplets moving through a water column^[1]. The compound particle is of the core-shell type and consists of an oily core successively surrounded by an ultrathin skin of oleophilic microbes and another biofilm layer of finite thickness. The model accounts for the effects of oxygen limitation and three major biodegradation modes^[2] (i.e., interfacial uptake, bioreaction in the biofilm layer and bulk seawater). In this work, the model is extended by confining the compound particle in a fluid envelope so as to account for droplet-droplet interactions in the limit of low oil volume fractions (Particle-in-Cell method). In the general case of nonlinear microbial kinetics, the governing set of advection-diffusion-reaction equations is solved numerically for oxygen and multiple oil components, whereas analytical solutions have also been established for certain limiting cases. The model provides estimates for the biodegradation rate, size evolution and residence time of oil droplet populations in a water column as functions of key system parameters (oil volume fraction, initial droplet size distribution, drifting velocity, microbial kinetics, diffusivity, solubility, density). The predictive ability of the model is assessed through a comparison with recent experimental data from the literature, and also in-house experiments, on the microbial degradation of oil-in water emulsions.

Acknowledgement: EU Horizon 2020 MSCA Grant 741799 - "OILY MICROCOSM".

References
[1] Kapellos GE, Paraskeva CA, Kalogerakis N, Doyle PS. (2018). Bioengineering, 5:15.
[2] Kapellos GE. (2017) "Microbial strategies for oil biodegradation", In Modeling of Microscale Transport in Biological Processes; Becker, S.M., Ed.; Academic Press, pp. 19-39.