Biological treatment method is one of the best and most cost-effective methods for the treatment ofcontaminated wastewaters. The purpose of this study was to evaluate the effect of retention time andtemperature on the efficiency of stabilization ponds in removing organic compounds, N-NH3 and PO4from oil refinery wastewater.Materials and Methods:The method used in the present study was of an experimental type, in which an anaerobic stabilizationpond with dimensions of 1 × 0.2× 1 m and a laboratory scale facultative pond with the capacity of 400L were designed, set up and operated, using fiberglass sheet with a thickness of 6 mm. In this study,the hydraulic retention time of 2 and 5 days for anaerobic pond and 5 and 10 days for facultative pondwere set in both hot and cold temperatures. Then, N-NH3 and PO4 parameters were measured at thewavelengths of 425 and 690 nm respectively. Also, TCOD, SCOD, TBOD, SBOD and pH of sampleswere measured according to the standard methods for water and wastewater tests.Results and Discussion:These results indicated that the retention time and temperature had a significant effect on theefficiency of stabilization ponds, so that the efficiency of anaerobic and facultative stabilization pondsin the removal of organic compounds was significantly increased with the increase of retention timeand temperature (p<0.05). The maximum removal efficiency for COD, BOD, N-NH3 and PO4 wasobtained to be 93.31, 93.66, 88.15 and 73.17 % respectively (at the retention time of 5 days ofanaerobic and 10 days of facultative and hot temperature), and the minimum removal efficiency for1-Department of Environmental Health Engineering, School of Khalkhal Medical, Ardabil University ofMedical Sciences, Ardabil, Iran2-Department of Environmental Health Engineering, School of Public Health, Kermanshah University ofMedical Sciences, Kermanshah, Iran3- Department of Nursing, School of Khalkhal Medical, Ardabil University of Medical Sciences, Ardabil, Iran4-Department of Environmental Health Engineering, School of Public Health, Ardabil University of MedicalSciences, Ardabil, Iran5- Department of Environmental Health Engineering, School of Public Health, Alborz University of MedicalSciences, Karaj, IranJ.Env.Sci,TechJ.Env. Sci. Tech., Vol 16, No.2, Summer 2014153the same parameters was obtained to be 41.47, 40.55, 34.26 and 22.46% respectively (at the retentiontime of 2 days of anaerobic and 5 days of facultative and hot temperature). Also, the single algaavailable in the facultative pond was formidiom and it was able to grow in high concentrations ofsulfur.The results of this study showed that the pilot-scale stabilization ponds in hot temperature, if operatedproprly, have the ability to remove organic compounds with a high efficiency. However, in coldweather, its efficiency is low but in acceptable level.
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