Optimization, modeling and its conformity with the reality of physico-chemical and microbial processes of petroleum hydrocarbons reduction in soil: a case study of Tehran oil refinery

Abstract

The present study was carried out in Tehran oil refinery, and HYDRUS-1Dsoftware was used to model the changes of PAHs concentration in the soil column. This investigation was conducted in three steps: at first, the ecological characteristics of Tehran oil refinery were identified, and then the water quality of its wastewater treatment plant was briefly evaluated. Then, a rectangular pilot plant was prepared to compare the potential of PAHs adsorption on soil and the five different adsorbents and optimized the adsorption process. So that, it was layered with various grain sizes of sand from coarse to fine up to 25 cm as a drainage layer. Then, it was packed with a specific measured weight of each of the adsorbents and the soil sample in 15 cm height at separate steps, and the synthetic wastewater began to influence on it. In all experiments, the steady-state regime was achieved by a constant pressure drop. The column pressure head and its conditions were stable during experiments. The adsorption of PAHs on these adsorbents and soil was estimated by measuring the concentration of PAHs in effluences of the drainage every 30 min intervals up to 4 h. In the next steps, the experiments were carried out to separate the PAHs degrading bacteria from soil, to optimize the conditions influencing on the biodegradation of PAH compounds in the laboratory. Finally, HYDRUS-1D was used to model the changes of PAHs concentration in the soil column. The results showed: the soil of the studied area has a high capacity to absorb PAHs. Bentonite has the highest capacity to absorb PAH compounds. Due to the adaptations of indigenous microorganisms in oil-polluted soils, their population increases with the biodegradation of PAH compounds by microorganisms. The maximum bacterial growth was observed at 30 °C and at pH 7.5. The optimum ratio of C:N:P for urea, nitrate and ammonium sulfate were 1:5:100, 1:5:100 and 1:10:100, respectively. There is a good conformity between experimental and laboratory data, and with the passage of time from the second week onwards, the conformity increases.