بررسی کارایی روش انعقاد الکتریکی در تصفیه فاضلاب شهری ارومیه با استفاده از یک راکتور الکتروشیمیایی لوله ای با جریان برگشتی

نویسندگان

چکیده

آلودگی آب و به تبع ان فاضلاب، سبب بروز مشکلات فرآوانی برای انسان می گردد. در سال های اخیر محققان به بررسی روش هایی مختلف برای حذف الاینده ها از فاضلابهای شهری پرداخته اند که در این میان فرایند انعقاد الکتریکی با دارا بودن بازده مناسب حذف و تولید لجن کم یکی از جدیدترین و مطلوب ترین روش ها به شمار می رود. هدف از این مطالعه ارزیابی راندمان حذفCOD ، BOD? و باکتری کلیفرم از فاضلاب تصفیه خانه ارومیه به کمک فرایند انعقاد الکتریکی می باشد. این مطالعه در مقیاس آزمایشگاهی در یک راکتور الکتروشیمیایی لوله ای با جریان برگشتی انجام گرفت. محل ورودی تصفیه خانه شهری ارومیه برای نمونه برداری انتخاب شد. شرایط بهینه نهایی تصفیه در مدت زمان الکترولیز ?? دقیقه، دانسیته جریان ?.??? آمپر بر مترمربع، pH برابر ?.?، هدایت محلول ???? میکرو زیمنس بر سانتی متر و شدت جریان سیال ورودی ?.?? لیتر بر دقیقه بدست آمد. در این شرایط، راندمان حذف COD حدود ??%، BOD? حدود ??% و باکتری کلیفرم ???% بود که کاملا با استانداردهای زیست محیطی سازگاری دارد. برای تعیین مشخصات لجن حاصل آنالیزهای SEM و BET انجام گردید.

کلیدواژه‌ها


عنوان مقاله [English]

Investigation of efficiency of Electrocoagulation method in treatment of Urmia urban wastewater using a recirculating electrochemical tubular reactor

نویسندگان [English]

  • Kambiz Seyyedi
  • Sina Keramat
چکیده [English]

Municipal wastewater is the mixture of domestic wastewater, small amounts of industrial and storm water, drain water, surface infiltration, and ground water. It usually consists of a number of contaminants, such as suspended solids, biodegradable organics, pathogens, nutrients, refractory organics, heavy metals and dissolved inorganics. Direct discharge of untreated wastewater into the natural water bodies is not desirable, as the decomposition of the organic waste would seriously deteriorate the water quality. In addition, communicable diseases can be transmitted by the pathogenic microorganisms. Nutrients such as nitrogen and phosphorous, along with organic material when discharged to the aquatic environment can also lead to excessive growth of undesirable aquatic life when discharged in excessive amounts on land can also lead to the pollution of groundwater. For these reasons, treatment of wastewater has become necessary for the protection of the environment keeping in view public health, economic, social and political concerns. In recent years, various methods for eliminating pollutants have been investigated, in which the electrocoagulation process with proper removal efficiency and low sludge production is considered as one of the newest and most desirable methods. The purpose of this study was to evaluate the efficiency of removal of COD, BOD? and Coliform bacteria from wastewater of Urmia refinery using electrocoagulation method and optimization of the process. To do so, the effect of different parameters such as time of electrolysis, current density, pH, flow rate and conductivity of solution was investigated. This experimental study was carried out in an electrochemical recirculating tubular reactor with an iron pipe as the cathode and some iron rods inside it as the anode. In order to sampling, the inlet of Urmia wastewater refinery was considered. In order to increase the electrical conductivity of the aqueous solution, sodium chloride was used as the electrolyte. After performing the electrochemical reactions, the treated wastewater was evaluated for clotting and COD and BOD? analysis. To determine the characteristics of the sludge the SEM and BET analysis was done.
Results showed that, increasing the time of electrolysis increases the amount of metal and hydroxide ions produced in the anode and cathode of electrochemical cell. Therefore, with the large amount of hydroxide flocs, the removal efficiency increases. With an increase in current density, the rate of removal increased, and then it did not change significantly, so it can be probably said that there is a limit for the rate of adsorption of pollutants to the flocs. It has been established that the effluent pH is one of the important factors influencing the performance of electrocoagulation process. The maximum removal was observed at a pH around of ?; considering the nature of the reaction between ferrous and hydroxide ions, this was not unexpected. When pH is lower than ?, Fe(OH)? is in its soluble form (Fe+?), and when it is higher than ?, Fe(OH)? is in its soluble form of Fe(OH)?-. Since Fe(OH)? has a major role in removing dye, when pH is ?, the rate of dye removal is the highest. With an increase in electrolyte concentration, electrical conductivity of the solution increases, and the voltage needed for accessing a certain value of electric current density decreases; less electric energy is also consumed. With an increase in the rate of the flow passing through the reactor, the removal efficiency decreases because the high flow rate of circulation of the solution in the reactor causes decrease in retention time of the solution in the reactor; therefore, the solution is not treated completely. The released cations from the electrocoagulation process lead to infertility of the negative electrical charge produced by the cell wall of the bacterium.
The final optimum conditions during electrolysis time ?? min, the current density ?.??? A/m?, pH ?.?, conductivity of solution ???? ms/cm and flow rate ?.?? L/min was obtained. In these conditions the removal efficiency ??% of COD, ??% of BOD? and ???% for Coliform bacteria was determined, which is completely agreeable with the environmental standards. As it is evident, the size of the constituent particles of the sludge as a cluster is about ?.? micrometer. Based on the results of BET analyses, the specific surface area, total pore volume, and mean pore diameter of the sludge are ??.? m?/g, ?.?? cm?/g, and ?? nm respectively.

کلیدواژه‌ها [English]

  • Urmia urban wastewater
  • COD
  • electrocoagulation
  • BOD? and Coliform removal