Effect of remediation strategy on crude oil biodegradation kinetics and half life times in shoreline sediment samples

Bioremediation, the process by which microorganisms degrade organic compounds to non-toxic or less toxic substances, has been widely used for cleanup of coastal ecosystems after oil spills. In this study, the hydrocarbon degradation rate and half lives in three bioremediation strategies (natural attenuation, biostimulation, and bioaugmentation) were compared in weathered crude oil (WCO) contaminated sediment samples. Three initial WCO concentrations of 3, 30 and 60 g WCO per kg sediment were investigated. Kinetic evaluations were carried out in a 90-day laboratory scale experiment. All oiled sediments showed decreasing WCO concentrations over time. After two weeks, the rate of degradation in the natural attenuation experiments stayed approximately constant. Bioaugmentation demonstrated higher oil removal than biostimulation or natural attenuation. The results indicated that first order kinetics can describe bioremediation of crude oil in sediments. The values of R2 (coefficient of determination) varied from 0.9552 to 0.9965. The first order kinetic constant for the reactors at different WCO concentrations was between 0.0014 and 0.0159/day. The half life of WCO in sediment reactors was different for each applied method. The minimum WCO half life for natural attenuation, biostimulation and bioaugmentation was 408, 69 and 44 days respectively.