Yafteh

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Background : Nitrogen-containing ions such as nitrate and nitrite occur widely in a variety of water sources. This pollutant causes health problems such as the blue-baby syndrome, and possible formation of carcinogenic compounds in the digestive tract. Thus, removing them from water sources seems necessary. Biological denitrification is a method used in the treatment of nitrate contaminated water. Numerous biological denitrification processes such as fluidized bed reactors (FBR) have been reported. This bench-scale research describes the operation of granular activated carbon (GAC) based fluidized bed reactors (FBR) for nitrate removal from water. Materials and Methods: The GAC was inoculated with a denitrifing culture isolated from Khorramabad milk industry wastewater. In addition, characteristics of GAC were analyzed using scanning electron microscopy (SEM). A mixed bacterial culture was acclimated to the removal of 50-200 mg NO3-N. L–1 at 1-3 h retention time from water. The experiments were carried out under anoxic conditions. The effects of various operating conditions such as hydraulic retention time (HRT), Nitrate loading rate and initial concentrations of nitrate on the denitrification were demonstrated experimentally. Results: The experimental results demonstrated that the over 94% of NO3-N was removed in the 2-3 h retention time, almost no NO2-N accumulated in treated water when the concentration of NO3-N was around 50-100 mg/L in influent. Under the experimental conditions, drinking water quality was achieved at a nitrogen loading lower than 2.4 kgNO3-N•m-3•day-1 with an influent COD/N ratio of 3 if ethanol was used as the carbon source. The denitrification rate increased up to a maximal value of 3.45 kgNO3-N•m-3•day-1 with increasing nitrogen loading rate (4.8 kgNO3-N•m-3•day-1). Conclusion: This study demonstrates that GAC offers favorable attachment sites for bacteria on the surfaces of GAC for Nitrate removal and denitrification of water was carried out in a fluidized bed reactor (FBR) using Activated carbon-immobilized cell beads as support carriers.

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Background : Pseudomonus stutzeri bactrerium is one of the most important and effective denitrifier bacteria in wastewater. With regard to the importance of effects of nitrate on water resources and human health and role of metronidazole inhibition, this study was done with the aim of survey of effect of metronidazole different concentrations on biological denitrification of Pesudomonas stutzeri in wastwater. Materials and Methods: This research was an experimental study. After sampling from raw wastewater, identification and isolation of pseudomonus stutzeri bactrerium were done. Bacteria suspension in specific culture medium and metronidazole different concentrations in deionized water and nitrate different concentrations for experimentals of nitrate removal under anoxic conditions was prepared and metronidazole inhibition experiments on activity of denitrification by pseudomonus stutzeri in synthetic and real wastewater were conducted. Results: Metronidazole at concentrations of 100, 200, 300 and 400mg/l, in synthetic wastewater containing nitrate concentrations to 500mg/l, had no inhibitory effect on activity of denitrification by pseudomonus stutzeri. Metronidazole at concentrations of higher than 800mg/l in synthetic wastewater and higher than 500mg/l in domestic wastewater had inhibitory effect. In 800mg/l metronidazole concentrations, with increasing the concentration of substrate(nitrate), significant reduction in the rate of nitrate removal by pseudomonus stutzeri was observed. This bacterium was added to three samples of domestic sewage, but had no effect on the rate of nitrate removal. Conclusion: With ergard to strong ability of Pseudomonus stutzeri to remove nitrate high concentrations and high resistance of this bacterium against metrinidazole, biological denitrification process can have a high potential to be used for removal of nitrates high concentrations from industrial wastewater, particularly pharmaceutical industries wastewater.

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