بررسي فرآيند حذف فنانترن از خاك با استفاده از فرآيند الكتروكينتيك_فنتون

Investigation of phenanthrene removal from contaminated soil using elektokinetic combined with fenton

تصفيه و پاكسازي خاكهاي آلوده به مواد هيدروكربني به دليل ارتباط با چرخه غذايي امري مهم است. روشهاي متنوعي براي حذف اين نوع از آلايندهها مورد استفاده قرار گرفته است كه هريك داراي نقاط قوت و ضعف متعددي هستند. از جمله اين روشها، روش الكتروكينتيك است كه در سالهاي اخير به دليل سادگي، هزينه پايين، عدم توليد پسماند ثانويه و توانايي حذف چند نوع آلاينده از خاك مورد توجه قرار گرفته است. در اين پژوهش به منظور حذف آلاينده آلي فنانترن از خاك رسي از روش الكتروكينتيك در دو بازه زماني هفت و ده روزه بهره گرفته شده است و تأثير مدت زمان فرآيند در حذف فنانترن از خاك در مقياس آزمايشگاهي بررسيشده است. غلظت فنانترن در خاك در فرآيند هفت روزه از 580 رسيده، كه mg ⁄ kg 600 كاهش يافته است و با افزايش مدت زمان فرآيند به ده روز غلظت آلاينده به mg ⁄kg 1000 به mg ⁄ kg برابر با 2 درصد افزايش است. در ادامه به منظور بهبود فرآيند از تلفيق الكتروكينتيك با تكنيك فنتون، كه يك تكنيك اكسيدكننده است، استفاده 500 كاهش داده است و در mg ⁄ kg شده است. تلفيق فنتون و الكتروكينتيك در مدت پنج روز غلظت آلاينده را در خاك به 50 درصد يعني 460 رسيده است. mg ⁄ kg مدت زمان ده روز اين مقدار به كمتر از 46 درصد يعني

Polycyclic aromatic hydrocarbons are hydrocarbons that composed of two or more benzene rings. These compounds are produced by incomplete burning or pyrolysis of organic matter. Phenanthrene is a type of aromatic hydrocarbon composed of three benzene rings, whose known effects can be attributed to its stimulating effect and skin sensitivity. The remediation of contaminated soil with hydrocarbon pollutants is crucial issue due to the soil connection with the food cycle. There are several methods for contaminated soil remediation. Electrokinetic (EK) is considered as one of the innovative technique that capable to remove both heavy metals and hydrocarbon contaminant from the soil matrix. The oxidation and reduction agents are added to change the chemical and microbiological properties of the soil that improve the extraction of pollutants or reduce their toxicity through the oxidation-reduction reactions. Oxidation agents can include air or oxygen, or chemical oxidants (such as hydrogen peroxide, sodium or potassium permanganate, ozone, chlorine, or oxygenated compounds). On the other hand, Fe􀬶􀬾, Fe􀬴, Calcium Polysulfide, and Sodium Ditonite are used as reducing agents. Fenton is one of the subsets of oxidation-reduction methods that has been considered by researchers for the last few years to remove pollutants from the soil. In the present study, the capability of EK combined with the Fenton was investigated to remove phenanthrene from contaminated soil. The effect of soil remediation time was studied for the EK only and EK combined with Fenton. The applied soil was characterized through the XRF and XRD. Based on the XRF, BaSO􀬸, SiO􀬶 , Al􀬶Si􀬶O􀬹(OH)􀬸 are the most prevalent component. Noteworthy is the presence of 6% hematite in the soil composition tested. Iron as a catalyst in the Fenton process plays an important role, which should be in contact with hydrogen peroxide to complete this process. Because of the proper percentage of hematite in the soil, it is not necessary to add iron from the outside of the system to complete the Fenton process. Based on the obtained results, the intensity of the electric current in all experiments rises rapidly at 1 to 20 hours of each test, reaching its peak of about 810 mA, then decreases and becomes almost constant. The reason for the rapid increase in the intensity of electric current in the early hours of the experiment, which was also observed in other researches, is the presence of metal salts and ions in the pore-water of the soil, which causes high electrical conductivity in the soil. With the increasing of the time, due to the electrical migration of these ions to the electrolyte reservoirs and the precipitation of a non-conducting layer on the surface of the electrodes, the intensity of the current decreases after 20 hours. In all experiments, the electroosmosis flow was from the anode to the cathode is due to the positive zeta potential of the soil. In experiments 3 and 4, using the Fenton technique, the rate of electroosmosis flow decreased due to the precipitation of the catalyst particles in the soil. Despite the reduction of the electroosmosis flow rate (test 3 and 4), the percentage of phenanthrene removal from soil has increased, which is due to the decomposition of pollutants into simple compounds during the Fenton technique. Overall, results revealed that, when the EK without any enhancement was applied in the seven days the phenanthrene concentration was decreased from 1000 to 600 mg/Kg. However, with the increasing time to 10 days, the phenanthrene concentration was decreased to 580 mg/Kg. When the EK combined with Fenton was conducted, the phenanthrene concentration was reduced to 500 mg/Kg after 5 days. However, with the increasing time to 10 days, the phenathrene removal was increased to 540 mg/Kg. Moreover, the energy consumed in experiment 3, where 50% of the pollutant was removed from the soil environment, was the lowest. Also, experiment 4 has eliminated 54% of the phenanthrene in the soil, had the most energy during the process.