Assessment of TPH attenuation during remediation of gasoil-contaminated Soil using active carbon modifier in pilot study

Abstract

Background and objectives: In the oil-rich country of Iran, pollution of soil with petroleum compounds is a very important factor for pollution. Gasoil is one of the major products of crude oil and is a major source of environmental pollution. Currently, there is an urgent need to prevent the expansion and distribution of oil pollutions as well as their derivatives.Organic carbon has gained attention as an effective compound in applied management programs of environment conservation. The present study aimed to evaluate the refining of total petroleum hydrocarbon content, determining its kinetic model during the application of refiner and quantitative investigation of the effect of active carbon weight and grain size on the attenuation rate of total petroleum hydrocarbon. Materials and methods: The soil polluted with gasoil was collected from the vicinity of the gasoil tanker located in Shiraz refinery. Then, after measurement of the amount initial total petroleum hydrocarbon content and physical and chemical properties of the polluted soil, 700 gram soil samples containing active carbon at 0.05 and 2.05 mm sizes and 20, 40, 60, 80 and 100 g kg-1 weight doses were prepared as pilot. The samples were then rested in a 50% constant humidity for four weeks at 28 ± 2 °C, and were aerated and incubated two times a week. Finally, the results of the changes in the total petroleum hydrocarbon and microbial activity over time were reported after statistical analysis. Results: The results showed that the application of active carbon had a significant effect on the reduction of gasoil pollution of the soil. The results related to determination of the kinetic model for the reduction of pollution during the biochar application process showed that the kinetic of reduction in total petroleum hydrocarbon was of first order equation; so that in 100 g kg-1 active carbon treatment, the lowest half- life was 21.13 days, and the half- life of control soil was 78.76. The results of total petroleum hydrocarbon showed that there was a significant reduction of total petroleum hydrocarbon content in all active carbon treatments. Investigation of bio- respiration (activity index of degrading microorganisms) showed that the application of active carbon in smaller sizes and amount higher weights led to improved hydrocarbon degradation. The biological efficiency of active carbon was calculated 38 percent at the end of the 60 day period. Conclusion: Application of active carbon refiner in the gasoil- polluted soil is a cheap, effective and environment- compatible method which provides a suitable environment for the plants and soil microorganisms if utilized properly in the polluted soil. This method may be utilized in remediation of the polluted soils as a pre-refining method alone or along with other biological methods (depending on the extent of the pollution and the required remediation).