Study On The Effect Of Nitrate Nitrogen Concentration On The Denitrification Performance Of Biological Contanct Oxidation Process

The factors affecting the biological nitrogen removal efficiency include dissolved oxygen,carbon nitrogen ratio,temperature and other process parameters.Although there have been a lot of studies on the above process parameters in the literature,with the continuous improvement of sewage nitrogen discharge standard,how to improve the biological nitrogen removal efficiency is still a research hotspot.Biological contact oxidation process is a typical wastewater treatment process,which uses a large number of microorganisms attached to the filler to form a biofilm to adsorb and purify wastewater.Compared with the activated sludge process,microorganisms grow on the filler and have strong impact load,which can make the slow growing microorganisms such as ammonia oxidizing bacteria,nitrifying bacteria and denitrifying bacteria grow in large quantities.At the same time,it also provides a good carrier and unit for the study of denitrification rate.In this study,polyurethane sponge was selected as biological filler,and the reaction device of anoxic and micro aeration was used to treat the mixed wastewater of nitrate nitrogen and ammonia nitrogen.The main conclusions are as follows:1.After more than 200 days of continuous operation,the content of ammonia nitrogen in the effluent of reaction column No.1(anoxic column)is about 19 mg/L,the content of nitrate nitrogen is about 8 mg/L,the content of ammonia nitrogen in the effluent of reaction column No.2(micro oxygen column)is about 1 mg/L,and the content of nitrate nitrogen is about 3 mg/L.After more than 180 days of operation,the system reached a stable state.The ammonia nitrogen,nitrite nitrogen and nitrate nitrogen content in the final effluent of the reactor were below lmg/L,1 mg/L and 3 mg/L.The removal rates of ammonia nitrogen and total nitrogen were about 95%and 92%,respectively,and the removal rates were above 90%,the denitrification efficiency of the system was very good.By comparing the changes of the media before and after culture,it was found that the filler changed from white to black brown,and a large number of microorganisms attached to it to form a stable biofilm;2.In the stable stage,100 mature fillers were taken from the anoxic reactor for batch kinetics experiment.The concentration of different forms of nitrogen in water was measured by changing the initial concentration of nitrate nitrogen,and the nitrite accumulation rate and denitrification rate were calculated.When the concentration of nitrate in the influent is lower than 10 mgN/L,no nitrite is detected.When the concentration of nitrate in the influent is greater than 10 mgN/L,the accumulation of nitrite begins to appear.With the further increase of nitrate concentration in the influent,the nitrite accumulation first increases to nearly 100%,and then gradually decreases and stabilizes in the range of 70%-80%.When the concentration of nitrate in the influent increased from 0 to 20 mgN/L,the denitrification rate increased from 0 to 0.37 mgN/(Lhn),and the change trend was linear.As the nitrate concentration continued to increase to 200 mg/L,the denitrification rate began to decrease to 0.28 mgN/(Lhn).When the nitrate concentration continued to increase,the denitrification rate did not change with the nitrate concentration.The Monod equation was used to simulate the denitrification kinetics,and the equation of nitrate nitrogen concentration and denitrification rate was obtained;3.The diversity of microbial community composition was analyzed by highthroughput sequencing technology,and the difference of denitrifying bacteria in the two columns was compared.In reaction column No.l,Proteobacteria accounted for 36.1%and Chloroflexi accounted for 21.8%,while Bacteroidetes accounted for 32.4%and Proteobacteria accounted for 27.5%in reaction column No.2.Comparative analysis showed that Proteobacteria was the dominant bacteria in denitrification process,and the main denitrification was denitrification The proportion of Thauera in reaction column No.1 and No.2 was 6.3%and 0.3%,Combined with the operation of the reactor,the reasons are as follows:the situation of the two reaction columns and the concentration of influent nitrate nitrogen are different.The influent nitrate nitrogen concentration of reaction column No.1 is high,the influent nitrate nitrogen concentration of reaction column No.2 is low,which results in the high proportion of denitrifying bacteria in reaction column No.1.