Abstract
IntroductionPetroleum hydrocarbons are among the most important soil pollutants. The main purpose of this study was to investigate hexadecane removal as a representative of petroleum hydrocarbons in slurry bioreactors with the help of bio-enhancement and bio-stimulation. MethodIn this study, hexadecane degrading bacteria were first isolated from soil and compost and were identified by Polymerase Chain Reaction (PCR). After that, using the Taguchi test, the effects of such parameters as salinity, pH, bacteria type, inoculated bacteria number, C:N:P ratio, micronutrient content, soil-to-water ratio, and the initial concentration of hexadecane on hexadecane removal rate were assessed using a Gas Chromatography-Flame Ionization Detector (FID-GC). ResultsThe results indicated that the two bacterial species (Ochrobactrum oryzae and Acinetobacter radioresistence) resulted in the highest removal of hexadecane. Salt had an inhibitory effect on the biodegradation of hexadecane, and microbial consortium was more effective in removing hexadecane compared to pure bacteria. Due to the presence of sufficient amounts of phosphorus and nitrogen in the primary soil, addition of these compounds had no effects on hexadecane removal. Nevertheless, addition of micronutrients enhanced the removal of contaminants. As the water-to-soil ratio increased, the bacteria’s access to food increased, as well, which resulted in a higher biodegradation rate. The initial concentration of hexadecane was the most important factor in its removal. DiscussionThe isolated bacteria from compost removed hexadecane from soil more efficiently compared to the bacteria isolated from soil. Furthermore, increase in the variety of bacteria types in the consortium resulted in an increase in the removal efficiency and a decrease in the retention time for bioremediation. Overall, hexadecane was removed by biological processes, ultrasound waves, soil adsorption, and chemical processes where evaporation had no effects. The initial concentration of hexadecane and bio-enhancement were among the important factors influencing the removal of hexadecane from the soil.
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