Total petroleum hydrocarbons (TPH) have been used as fuels as their spills have occurred in various routes such as leaks and spills on the surface soils, leaks through under storage tanks, and spills through the aged oil pipes, etc. These accidental releases of TPH frequently ended up with soil and ground water pollution. In most cases, TPH have toxicity against numerous biota as animals and plants in the environment as well as humans. TPH may be degraded through physicochemical and biological processes in the environment but with relatively slow rates. Currently, chemical and biological treatment technologies are used independently for TPH decontamination in soil. In this study an integrated chemical and biological treatment technology has been developed to eventually establish an efficient and environment-friendly restoration technology for TPH contaminated soils.
Fenton-like reactions were employed as a chemical treatment process and subsequently a bioaugmentation process utilizing diesel fuel degraders was applied as a biological treatment process. TPH concentrations were monitored for samples taken weekly for at least one month. Heterotrophic and TPH degradative bacterial communities were monitored and analyzed based upon viable cell counting, MPN and PCR-DGGE techniques.
Most efficient chemical removal of TPH from soils occurred where the surfactant OP-10S (0.05%) and oxidants (FeSO4 4%, and H2O2 5%) were used. The inoculation of diesel fuel degraders into the soil slurry led to an increase in their population density at lease two orders of magnitude, indicating a good survival of the degradative populations in the contaminated soils. However, an adverse effect in the TPH removal has been observed in the chemically treated soils, potentially due to the presence of free radicals and other oxidative products generated in the process where a lower treatment efficiency (65%) was observed. A similar treatment made in the diesel fuel contaminated field showed a successful removal of TPH under the conditions (soil temperature 20℃, moisture 45% and pH 7.0). The TPH degraders in the field have been successfully monitored by viable counting method and Microplate MPN technique. The PCR-DGGE technique was successfully applied to monitor the degraders and their associated indigenous bacterial populations in the soil bioslurry treatment conditions for treatability study at lab scale. The findings in this study will contribute to development of bioslurry treatment technologies for TPH-contaminated soils and sediments in the environment.