Monitoring TPH biodegradation in soil around Ray oil refinery by natural attenuation, biostimulation and bioaugmentation treatments

Abstract

In this study, total petroleum hydrocarbons (TPHs) decontaminating mechanisms for soils around the Rey refinery complex (South of Tehran, Iran) was investigated. Natural attenuation, biostimulation and bioaugmentation (separately and in combination) methods were evaluated TPHs and soil microbial respiration in 210 days, using laboratory treatments The modified methods were applied through 13 different treatments, including improving the environmental conditions for native bacteria (natural attenuation for treatments 1-8), adding non-native bacterial complex (bioaugmentation for treatment 9) and intensifying and stimulating growth while adding non-native bacterial complex (biostimulation-bioaugmentation for treatments 10-13). Although, overall of the treatments, a significant decreasing TPHs concentration were observed over the time, biostimulation-bioaugmentation treatments had the highest amount of TPHs decomposition, the highest rate of bio-respiration, the lowest half-life times (t1/2), and the highest remediation efficiency and biodegradation constants rate. Among natural attenuation treatments, modifiers with manure and sawdust had the greatest effect on reducing the TPHs concentration and the highest rate of bio-respiration. The first-order kinetic model was fitted to the data related to biodegradation in a satisfactory manner. The results showed that there was a strong and positive linear correlation between decreasing TPHs concentration and microbial respiration in all modifiers. Although for the bacterial treatments and at the early stages of inoculation, the rate of total respiration was low, but as the time passed and with adaptation of the effective inoculated bacteria to contaminated soil, the respiration rate gradually was increased. Due to its low cost and low environmental risk, the proposed bioremediation technique for oil contaminated soil can be recommended to the region.