Evaluation Of The Nitrogen Removal Performance In Activated Sludge Process Based On Nitrogen Stable Isotope Fractionation Principle

nitrogen stable isotope technique(¹⁵N)is applied to environment pollution by Kohl for the first time in1971,which brings increasing concerns over nitrogen stable isotope technique.This technique has been widely applied in medicine,tracer,agricultural research,geology,archaeology,etc.But few scholars research applied the stable nitrogen isotope technology in the of wastewater treatment field.The eutrophication problem of human activity,make people pay more and more attention to the transition and transformation of nitrogen and phosphorus in nature,especially nitrogen removal rate which has become a important indices to measure the denitrification efficiency of a natural or artificial systems.For a long time,the efficiency of denitrification were detected by monitoring the nitrogen content at inlet and outlet of water treatment structures.However,this traditional monitoring method can be highly volatile and susceptible to external environment,so it is difficult to accurately describe the denitrification performance of the ecological or biological system.Therefore,to establish a method of detecting or indicators to evaluate the denitrification performance of microorganism from the point of activated sludge and to feedback the denitrification in the process of sewage treatment according to the indicators changes will have a great significance to accurately grasp and precisely control of denitrification efficiency in the sewage treatment plant.This study proposes a model to evaluate the nitrogen removal performance of reactive sludge based on the Rayleigh fractionation equation and the nitrogen stable isotope fractionation.This model could be used to analyze the efficiency and activity of the microbial denitrification of urban sewage.The main parameters of the model are determined by long-term monitoring of waste water treatment plants.To verify the applicability of the model under the different condition of water inorganic nitrogen,this study monitored the denitrification restriction,nitrification restriction and ammonia restriction waste water treatment plants respectively.The results show that the nitrogen removal performance of these three conditions can be accurately predicted by measuring theδ15N value of activated sludge and using the evaluation model.To verify the adaptability of the model under different nitrogen removal ability,this study set up five reactors with different working condition,theδ¹⁵ N values of activated sludge in each reactor were 13.97‰,8.33‰and 4.47‰respectively.The denitrification efficiency evaluated by model are 96%,71%and 22%respectively as the activity of sludge reduce.The fact that denitrification efficiency arrived by using the evaluation model is the same as the actual removal rate shows that this model can be used for water treatment system with different denitrification ability.The application of evaluation model can avoid the complex process of stationing and monitoring.The whole system denitrification ability and sludge viability can be learned byδ¹⁵N value of activated sludge.The result of the model can also reflect the denitrification activity of activated sludge which has guiding significance for denitrification strengthening.At the same time,this model provides a more convenient and accurate way for evaluating the nitrogen removal efficiency in the wastewater treatment process from the perspective of microorganism stable isotope analysis.