Experimental Research On Simultaneous Nitrification And Denitrification In A/O Biofilter

Excessive nitrogen content is one of the main reasons for water eutrophication.To reduce water pollution effectively,it is necessary to upgrade and reconstruction the wastewater treatment plants?WWTPs?,which could ensure that the effluent quality meet the standards.The presious study shoewd that the national municipal sewage water quality has low-carbon and high-nitrogen characteristics,which caused that the traditional activated sludge process had a poor nitrogen removal effect,and it is difficult to meet the total nitrogen emission standard.Therefore,it is extremely urgent to develop a kind of advanced nitrogen removal processes of the municipal secondary effluent.In addition,the biological filter has many advantages,such as small footprint,high processing efficiency,fast start-up speed and etc.It is easy to combine with anaerobic ammonium oxidation?Anammox?,simultaneous nitrification and denitrification and other emerging denitrification technologies,and has subsequent expansion space,which is in line with the actual needs of modern society.So this test is based on anoxic/aerobic?A/O?biological filter,with A/O biological filter simultaneous nitrification and denitrification as the research focus,to provide theoretical value about improving the removal efficiency of wastewater nitrogen to real operations on WWTPs.Firstly,the experiment started the film-forming of the A/O biological filter for a 34 total days.Thereinto the aerobic column membrane was successfully used for 19 days,at this time,the removal rate of the chemical oxygen demand?COD?,ammonia nitrogen?NH4+-N?and total nitrogen?TN?in the effluent were 64.53%,96.11%and 25.03%,respectively.However,the membrane was hung on the anoxic column by the 31d,at that time,the removal rates of COD,NH₄⁺-N and TN in the effluent of the filter tank were stable at about 69.01%,97.05%and 42.85%,respectively.After the system was successfully started,the pollutant indicators of the reactor in the stable operation phase were investigated.The concentrations of COD,NH4+-N and TN in the effluent were 16.49 mg/L,0.0012 mg/L and 5.02 mg/L,respectively,which was lower than the Class-IA wastewater discharge standard,and the deviation of the test data is small.Secondly,after the A/O biological filter is successfully formed biofilm,the influencing factors?carbon-to-nitrogen ratio?C/N?,reflux ratio,dissolved oxygen?during operation were investigated.The study found that the removal rate of COD and TN in the effluent water gradually increased with the elevation of C/N ratio in the influent,mainly because that the increasing of carbon content in the influent water is helpful to the denitrification reaction in the anoxic biological filter,also could strengthen the denitrification effect of the system and maintain the COD content in the effluent at a low level.When the C/N ratio was higher than4:1,continuing to increase the amount of carbon source added has little impact on the removal effect of various pollutants.With the increase of the influent return ratio,the systematic treatment efficiency for pollutants gradually decreased.On the one hand,with the increase of the recirculation flow,the substrate concentration in the influent was diluted,and the difficulty for microorganisms to ingest the substrate was added,so the reaction rate was reduced.On the other hand,the elevation of hydraulic load has caused an impact on the biofilm on the filter media surface,and result in the shedding of some biofilms and adversely affecting biochemical reactions.The increase of dissolved oxygen content improved the removal rate of NH4+-N in the anoxic column,but the removal rate of other pollutants was declined,mainly because that part of the effluent flows back to the inlet of the anoxic column,resulting in the increasing concentration of dissolved oxygen promotes nitrification in the anoxic column and inhibited denitrification.Further analysis of the experimental data revealed that simultaneous removal of ammonia nitrogen and nitrate nitrogen occurred in the anoxic column,indicating that simultaneous nitrification and denitrification occurred in the A/O biological filter.When the C/N ratio was4:1,the reflux ratio was 100%,and the dissolved oxygen concentration in the aerobic column was controlled at 2 mg/L,at this time,the nitrogen removal efficiency of the A/O biological filter was optimal.That was 12.16 mg/L,0.025 mg/L and 4.08 mg/L,respectively,which totally meet the Chinese Class-IA wastewater discharge standard.In order to extensively explore the denitrification mechanism of the simultaneous nitrification and denitrification in the A/O biological filter,under the optimal operation condition,the Monod equation was used to construct the synchronous nitrification and denitrification?SND?reaction kinetic equation for the anoxic column.According to the variation of the concentration in highly pollutants,the corresponding constants R and Z values were obtained,and the value obtained by fitting analysis was 3.79,which was much higher than the half-saturation constant in the normal denitrification process.That was mainly result from that the process of substrate mass transfer to the anoxic zone was hindered by the biofilm inside the column,so the concentration of NO₃^--N that can really participate in the denitrification reaction was lower than the detected value.The reaction rate of nitrification was lower than the normal denitrification process,which performrd as value larger.