A COMPARATIVE STUDY ON CRUDE OIL DEGRADATION DYNAMICS IN SALTWATER AND FRESHWATER UNDER BATCH REACTOR CONDITIONS

Abstract

The fate of crude oil in stagnant aquatic systems was investigated through laboratory experiments supported by mathematical modeling. Two cylindrical batch reactors of equal capacity were filled with 1.5 m³ of freshwater and saltwater, and each system was contaminated with 250 cm³ of crude oil. Six control valves were installed at uniform depth intervals for sequential sampling over a 42-day period at 7-day intervals. Physicochemical parameters, Total Bacterial Counts (TBC), and Total Petroleum Hydrocarbon (TPH) concentrations were assessed. Modeling of hydrocarbon dispersion and degradation was performed using a developed Dispersion–Degradation Model incorporating both first-order biodegradation kinetics and Monod parameters. TBC increased progressively in both systems, with a slow microbial response in saltwater until day 26, followed by exponential growth in both water types between days 35 and 40. First-order kinetic degradation rates (kd) were 0.0034 day⁻¹ in freshwater and 0.00213 day⁻¹ in saltwater, showing greater microbial degradation in freshwater. Monod-based model predictions deviated significantly from measured TPH data, while first-order kinetics closely correlated with experimental values. Findings suggest that crude oil breakdown is more efficient in freshwater due to reduced microbial inhibition relative to salinity effects. The study provides essential information for decision-making on remediation technologies in freshwater versus marine spill sites.