پديد آورندگان :
خطايي، بهنوش دانشگاه تربيت مدرس - دانشكده مهندسي عمران و محيط زيست , مختاراني، نادر دانشگاه تربيت مدرس - دانشكده مهندسي عمران و محيط زيست , گنجي دوست، حسين دانشگاه تربيت مدرس - دانشكده مهندسي عمران و محيط زيست
كليدواژه :
نفت خام , خاك رسي , روش بيوالكتروسينتيك , مدلسازي , حل عددي
چكيده فارسي :
وش بيوالكتروسينتيك جهت كاهش محدوديت‌هاي هر يك از فرايند‌هاي بيولوژيكي و الكتروسينتيك تنها در تصفيه آلاينده هاي آلي از خاكهاي ريزدانه، كاربرد دارد. در اين روش تلفيقي، فرايند بيولوژيكي در تجزيه آلاينده‌ها و فرايند الكتروسينتيك در تسريع و جهت‌دهي انتقال آلاينده‌ها و ميكروارگانيسم‌ها نقش دارند. هدف از انجام اين تحقيق، تعيين معادلات و شرايط حاكم بر فرايند بيوالكتروسينتيك در تصفيه خاك رسي آلوده به نفت خام مي‌باشد. به منظور توسعه و صحت سنجي مدل، ابتدا به راه اندازي سيستم تلفيقي بيوالكتروسينتيك در مقياس آزمايشگاهي پرداخته شد. آزمايش‌هاي بيوالكتروسينتيك در راكتورهاي استوانه‌اي از جنس پلكسي گلاس به طول 55 و قطر 5 سانتي‌متر و با استفاده از خاك آلوده به نفت خام و اعمال ميدان الكتريكي با شدت مشخص، در حضور سويه Pseudomonas Putida انجام شدند. از سوي ديگر، پس از تعيين و تلفيق معادلات حاكم بر فرايند الكتروسينتيك و سينتيك تجزيه زيستي، با كدنويسي در نرم افزار متلب حل عددي معادله مورد نظر انجام شد. در ادامه، ضمن مقايسه نتايج حاصل از حل عددي مدل پيشنهادي با نتايج آزمايشگاهي، روند يكساني در تغييرات غلظت نفت خام بين اين دو مشاهده گرديد. به علت وجود اختلاف بين نتايج مدل و داده‌هاي آزمايشگاهي و به منظور تطابق بيشتر بين اين دو، از ضريب اصلاحي مربوط به فاكتور انتقال ميكروارگانيسم‌ها تحت ميدان الكتريكي استفاده گرديد. بدين صورت تطابق بهتري بين نتايج حل عددي و داده هاي آزمايشگاهي روش تلفيقي مشاهده شد. طبق نتايج حاصل مدل پيشنهادي توانسته ميزان غلظت باقيمانده نفت خام پس از تصفيه به روش بيوالكتروسينتيك را با تطابق خوبي پيش‌بيني نمايد.
چكيده لاتين :
Removal of petroleum hydrocarbons from soil using electrokinetic method or biological processes has been considered in recent century. The most limiting factors in the electrokinetic process are extreme changes in pH around the electrodes and non-polarity of some pollutants. On the other hand, the key factor of biological treatment is simultaneous presence of microorganisms, pollutants, electron acceptors, and essential nutrients for microorganisms’ growth. But in fine-grained soils with low permeability, it is difficult to uniformly distribute bacteria, electron acceptors and nutrients, or making pollutants available for microorganisms. To solve these problems, bioelectrokinetic method is used to eliminate the limitations of both biological and electrokinetic processes in treatment of fine-grained soil contaminated with organic compounds. The aim of this study is determining the equations and conditions governing on bioelectrokinetic process in removal of crude oil from clayey soil. For this reason, the numerical method of FTCS finite-difference was applied for modeling the pollutant biodegradation and transmission in clayey soil under electric field. In order to develop and validate the model, the first step was to set up a bioelectrokinetic system in a laboratory scale. In this study, each test was conducted in cylindrical cell made of Plexiglas with the length and diameter equal to 55 and 5 cm respectively, for 35 days. They were performed in various conditions of pollution amount and electric field intensity in the presence of Pseudomonas putida strain. Experimental results showed the removal efficiency was obtained about 34% in minimum voltage gradient (1.25 V/cm) and initial concentration of oil (4000mg/kg). While, increasing the voltage gradient and oil initial concentration respectively to 1.5 V/cm and 10000 mg/kg could remove about 48% of pollutant. After determining and combining the governing equations on the electrokinetic and biodegradation system, the numerical solution of the equation was coded using Mat-lab software. In suggested mathematical model, the parameters like initial concentration of crude oil, voltage gradient, time step and spatial step were assumed as variables and parameters related to reactor, soil and pollutant such as the length of reactor, soil porosity and tortuosity, ion mobility, diffusion coefficient and electroosmosis permeability coefficient were considered as constants. In continue, by comparison the result of numerical solution of the suggested model with the experimental results, the same trend was observed in changes in crude oil concentration between the two. Because of differences between the model results and laboratory data and to make more accordance between the two, the modifying factor was used as the factor of microorganism transfer under electric field. In this way, a better accordance between them was observed and this difference reduced to minimum. Modeling results showed that electroosmosis, diffusion and electromigration mechanisms, unlike biodegradation, had little impact on the transmission and removal of crude oil from soil. According to the numerical solution, similar to bioelectrokinetic data, increasing the initial concentration of crude oil and voltage gradient caused the increase in removal efficiency of crude oil. In addition, the model has been able to predict the residual crude oil concentration after bioelectrokinetic treatment with a good accordance.
