Comparison of Crude Oil Degradation in Freshwater and Saltwater Environments Using Batch Reactors

Abstract

The degradation of crude oil in freshwater and saltwater was investigated using experimental methods and mathematical modeling for a packed-bed treatment unit. Two tanks of equal capacity were filled with 1.5 m³ of freshwater and saltwater, respectively. Six control valves were installed at uniform depth intervals to allow sample collection over 42 days at 7-day intervals. Collected samples were analyzed for physicochemical properties, total bacterial counts (TBC), and total petroleum hydrocarbon (TPH) concentrations. A dispersion and degradation model was developed, combining first-order degradation kinetics with the Monod equation, to describe TPH diffusion within the water columns. Experimental results showed that TBC gradually increased in both water types up to day 30, followed by a rapid rise between days 35 and 40. TPH concentrations declined over time, though variations occurred with depth. The effect of crude oil contamination was more pronounced in freshwater compared to saltwater. Model validation revealed that predictions based on first-order degradation kinetics closely matched the observed TPH data, whereas the Monod-based model deviated from experimental results. This indicates that Monod kinetics may not be suitable for modeling crude oil degradation in stagnant water environments. The study highlights the differential behavior of crude oil dispersion and degradation in freshwater versus saltwater.