The effect of metronidazole on biological denitrification of Pesudomonas stutzeri in wastewater

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.