نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه مهندسی محیط زیست، دانشکده محیط زیست، پردیس دانشکده های فنی، دانشگاه تهران، تهران، ایران

2 گروه مهندسی محیط زیست، دانشکده محیط زیست، پردیس دانشکده های فنی، دانشگاه تهران، تهزان، ایران

چکیده

سابقه و هدف:
پالایشگاه نفت یکی از مراکز صنعتی است که فاضلاب تولیدی آن شامل بار آلودگی زیادی می­ باشد و دارای میزان مختلفی از آلاینده­ های محیط زیستی است که تهدیدی جدی برای محیط زیست و منبع­ های آب می ­باشند. در این تحقیق از رآکتور انعقاد الکتریکی برای حذف و کاهش میزان COD موجود در فاضلاب خروجی واحد API پالایشگاه نفت شازند اراک که یک جداکننده ثقلی آب-روغن می ­باشد، استفاده شده است.
مواد و روش ­ها:
برای شبیه سازی فرآیند انعقاد الکتریکی در شرایط آزمایشگاهی، پایلوتی با ابعاد cm(15×14×13) از جنس پلکسی گلاس طراحی گردید که در آن 6 الکترود آلومینیومی بعنوان الکترودهای قربانی در طی فرآیند با ابعاد cm(12×10) و ضخامت mm2 قرار داده شد. فاصله الکترودها از یکدیگر cm2 در نظر گرفته شد. آرایش تک قطبی برای الکترودها انتخاب گردید. در هر مرحله از آزمایش پس از اندازه گیری میزان pH و COD و سرب فاضلاب اولیه ، حجم 2 لیتر از آن بعنوان نمونه درون رآکتور انعقاد الکتریکی ریخته شده و پس از فرآیند الکتروانعقاد، دوباره میزان pH و COD و سرب ثانویه اندازه گیری شد تا تاثیر فرآیند انعقاد الکتریکی مشخص شود.
نتایج و بحث:
در این تحقیق اثر پارامترهای زمان، pH و ولتاژ در فرآیند لخته سازی الکتریکی اندازه گیری شده است. میزان COD ، pH و سرب موجود در فاضلاب پالایشگاه به ترتیب برابر با (mg/L)450 ، 5.5 و(mg/L)  5.27 در نمونه اولیه اندازه گیری شد. برای جلوگیری از هم پوشانی اثر پارامترهای زمان، pH و ولتاژ در طول فرآیند، مقدار یکی از پارامترها را تغییر داده و دو پارامتر دیگر ثابت نگهداشته شد و میزان بهینه هر کدام تعیین گردید. بمنظور کمینه سازی درصد خطا در روند آزمایش هر مرحله از آن ۳ بار تکرار شده است. پس از انجام مرحله­های مختلف آزمایش و جمع آوری و تحلیل نتایج به­ دست آمده مدت زمان بهینه آزمایش، pH بهینه و همچنین ولتاژ بهینه به ترتیب 90 دقیقه ، 6 و 30 ولت در این فرآیند در نظر گرفته شد، که در پی آن میزان COD از (mg/L)450 به (mg/L) 193 کاهش پیدا کرد و %99.05 از سرب حذف گردید. نتایج آزمایش ­ها نشان داد که با افزایش مدت زمان الکترولیز میزان حذف نیز افزایش می­یابد. همانطور که از مشاهده نتایج می ­توان استنباط کرد میزان حذف با مقدار ولتاژ اعمالی رابطه مستقیم دارد، دلیل آن، تولید و انحلال بیشتر هیدروکسیدهای آلومینیوم در فاضلاب بوده که نقش ماده منعقد کننده را ایفا می­ کند. همچنین pH، تاثیر مهمی روی نتایج دارد. در pH پایین، گونه ­های مونومریک کاتیونی نظیر Al3+ و Al(OH)2+ از انحلال آند آلومینیومی حاصل می ­شود. از طرفی با افزایش بیش از حد pH محلول، ترکیب­ هایی مانند Al(OH)4- نیز شکل می­ گیرند که موجب ایجاد اختلال و کندی در فرآیند حذف می­ شوند.
نتیجه­ گیری:
بررسی نتایج نشان می­ دهد که هیدروکسیدهای آلومینیوم بعنوان مواد منعقد کننده محلول که از انحلال الکتروشیمیایی الکترودهای قربانی تولید می­ گردند، در فرآیند حذف آلاینده­ ها نقش اصلی را ایفا نموده و هر چه نرخ تولید و انحلال آن­ها بیشتر باشد میزان حذف بیشتری نیز اتفاق خواهد افتاد. برای دستیابی به این امر می­ بایست پارامترهای تأثیرگذار در تولید آن­ها را بصورت بهینه تنظیم نمود. با افزایش مدت زمان الکترولیز میزان تولید هیدروکسیدهای آلومینیوم نیز افزایش می یابد. همچنین تنظیم pH محلول در دامنه مناسب، شرایط تولید و تشکیل پلیمر هیدروکسید آلومینیوم ژلاتینی را فراهم می ­آورد.

کلیدواژه‌ها

عنوان مقاله [English]

Evaluation of the electrocoagulation process in API oil refinery wastewater treatment (case study: Arak , Shazand)

نویسندگان [English]

  • Toktam Shahriari 1
  • Abdolreza Karbasi 1
  • Milad Reihani 2

1 Department of Environmental Engineering, School of Environment, College of Engineering, University of Tehran, Tehran, Iran

2 Department of Environmental Engineering, School of Environment, College of Engineering, University of Tehran, Tehran, Iran

چکیده [English]

Introduction:
Oil refinery is one of the industrial centers and its wastewater has a lot of environmental pollutants which are a serious threat to the environment and water resources. In this study, an electrocoagulation reactor was used to remove and reduce the amount of Chemical Oxygen Demand (COD) in the wastewater from the API unit of the Shazand Oil Refinery in Arak, which is a gravity separator of water and oil.
Material and methods:
In order to simulate the electrocoagulation process in experimental conditions, a 15 × 14 × 13 cm Plexiglas pilot was designed, in which six 10 × 12 cm aluminum electrodes with a thickness of 2 mm were put as sacrificial electrodes during the process. The distance between the electrodes was 2 cm. The monopolar arrangement was selected for electrodes. At each stage of the experiment, after measuring the pH and COD of the initial wastewater, the volume of 2 L was poured out as an internal sample into the coagulation reactor; after the electrochemical process, the secondary pH and COD were measured to determine the effect of the electrocoagulation process.
Results and discussion:
In this research, the effect of time, pH, and voltage in the electro-flocculation process has been evaluated. The amount of COD, pH, and lead were measured 450 mg/L, 5.5 and 5.27 mg/L in initial wastewater, respectively. To avoid the overlapping effect of time, pH, and voltage during the process, the value of one of the parameters was changed and two other parameters were kept constant and the optimum value was determined. In order to minimize the errors during the testing process, each step has been repeated three times. After performing different stages of the test and collecting and analyzing the results, the optimum time of the test, optimum pH, and optimum voltage were considered as 90 min, 6 and 30 V, respectively. Consequently, the COD decreased from 450 to 193 mg/L and 99.05% of lead was removed. The results of the experiments showed that by increasing the duration of electrolysis, the removal rate also increases. The results of other research also showed that the flow density is directly related to the reaction time, and by increasing the time, more removal rate can be obtained. As the results demonstrate, the removal rate is directly related to the applied voltage, which is due to the more production of aluminum hydroxides in the wastewater, which plays the role of coagulant. In previous studies, the results also indicated an increase in the removal rate of pollutants by increasing the applied voltage. The pH also had an important effect on the results. At low pH values, cationic monomeric species such as Al3+ and Al(OH)2+ were obtained from the dissolution of the aluminum anode. On the other hand, with the excessive increase in the pH of the solution, such compounds as Al(OH)4- were formed, which caused disruption and sluggishness in the removal process.
Conclusion:
The results of this study showed that aluminum hydroxides as coagulants, which are produced by the electrochemical dissolution of the sacrificial electrodes, play a major role in the pollutant removal process. The higher their production rates, the more removal will occur. To do this, the optimal parameters for producing them should be optimally set. By increasing the electrolysis time, the amount of aluminum hydroxides also increases. Also, adjusting the pH of the solution at an appropriate range provides optimum conditions for the production and formation of gelatin aluminum hydroxide polymer.

کلیدواژه‌ها [English]

  • Aluminum electrode
  • Electrolysis time
  • Industrial wastewater
  • Mono polar

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