Remediation Of Diesel-contaminated Soil By Aeration Enhanced Washing With Nonionic Surfactant

Diesel is an important fuel, which is present in the energetic matrix of the majority of countries. Transportation between production and consumption centers and establishment of proper storge conditions are important issues related to diesel oil. Unfortunately, despite safety precautions, diesel oil spills still occur, large amount of diesel will through various channels to enter into the soil and water environment, a direct result is the contamination of the vadose zone, with the migration and transformation of pollutants, it will not only destory the ecosystem, but also posed a big potential threat to people’s health. It’s urgent to form a simple and cost-effective technology system for treatment of diesel-contaminated soil.Aeration-enhanced nonionic surfactant washing is a new kind of remediation method, the apply of aeration can reduce the usage of nonionic surfactant, which will bring down the cost, the foam that produced by aeration can enlarge the contact area between surfactant and soil, which will improve the washing efficiency. Besides, the nonionic surfactants have good property of biodegradable, soil that after repaired has the very good biological adaptability. This method has showed great potential for the treatment of organic-contaminated soil and groundwater.Remediation of soils contaminated with diesel was investigated in bench-scale experiments. Three types of nonionic surfactants: polyoxyethylene laurel ether(Brij-35), polyethylene glycol tertoctylphenyl ether(TX-100), polyoxyethyenesorbitan monooleate(Tw-80) were used to wash dieselcontaminated soil in different experimental conditions, respectively. Mainly studied:(1) Effect of aeration on the washing efficiency;(2) Effect of three types of surfactant on the washing efficiency;(3)Adsorption behavior of the three types of surfactants on the soil;(4)Concentration of surfactants in the leaching solution;(5)Test of surface tension of the surfactant solution and contact angle of the soil. The parameters of aeration, surfactant concentration, solid-liquid ratio, washing time, pH, aeration intensity and soil particle size were studied, Analysised the surface tensions of the three types of nonionic surfactants solution and the contact angle of the soil paricals that before and after washing were studied, combined with the adsorption and desorption behavior of the three types of nonionic surfactants on the surface of the soil, aimed at providing a know-how for the remediation of diesel-contaminated soil.the conclusions were as follows:(1) The aeration enhanced ex-site washing method can improve the remove rate of 10-17 percent. Under the optimized conditions: 1 times the CMC of concentration, 1 hour washing time, pH 11, aeration rate was 7.5 L/min, the remove rate of the three types of nonionic surfactants Brij-35, TX-100, Tw-80 were 77.4%, 66.18%, 59.84%, respectivily. The optimal nonionic surfactant is Brij-35, the oil content of contaminated soil samples that after washed can be reduced to 1.58% from 7%, and the contact angle of the soil sample was decreased to 6.65 ° from 24.12 °.(2) The adsorption isotherm of the three types of nonionic surfactants Brij-35, TX-100, Tw-80 showed that the saturated adsorption amount on the soil samples were 8000μg/g, 1800μg/g, 19000μg/g, respectively. When the contaminated soil washed under the optimized condition, the leaching concentrations of the three types of nonionic surfactants Brij-35, TX-100, Tw-80 were 2.718 mg/L, 1.022 mg/L, 0.004 mg/L, respectively. The leaching concentrations of the three types of nonionic surfactants were higher than that without aeration.(3) The surface tension of the three types of the nonionic surfactants solution were decreased as the increase of the concentration, but was not affected by pH. At 1 time of the CMC, the surface tension of the three types of nonionic surfactants Brij-35, TX-100, Tw-80 were 50.45 mN/m、39.22 mN/m、61.40mN/m, respectively. For the same type of nonionic surfatant, the smaller the surface tension, the bigger the remove rate.(4) After the soil samples were contaminated by the diesel, the contact angle of the soil particle on the surface were increased, which reflected through the variation of the hydrophilic of the soil partical. The contact angle decreased after the diesel-contaminated soil been washed by nonionic surfactants, the contact angle that under the condition of aeration is less than that of without aeration, washing process that with aeration can better restore the hydrophilic of the soil.