Study On The Nitrogen Removal Performance And Nitrite Accumulation Strategy Of The Pilot-scale AAO-AO Process With Double Sludge Age

The biofilm process has a strong impact load resistance,strong adaptability to changes in sewage water quality and quantity,ideal treatment effect,simple operation and maintenance,no sludge expansion,and can expand biomass on the basis of the original tank capacity.In view of the water quality characteristics of China's urban sewage and the upgrading of urban sewage treatment plants,this paper mainly used the traditional continuous flow AAO-AO pilot test as the research object,and added suspended carriers in the anaerobic zone and anoxic zone to form a double sludge age system,to explore the influence of the overall nitrogen removal and the necessary conditions for achieving a certain proportion of autotrophic nitrogen removal in the continuous flow process.The main contents and conclusions are as follows:?1?According to the results of activity and high-throughput sequencing,T1 polyethylene carrier is more suitable for the enrichment of ANAMMOX than T2 polyurethane carrier.R1 and R2 were successfully started on the day 93^rd and 73^rd respectively.After 150days of long-term operation,the activity of ANAMMOX in units of VSS on a T1 and a T2carrier was 5.70 mg/?g·h?and 3.70 mg/?g·h?,respectively.The Planctomycetes that ANAMMOX belonging to on T1 and T2 carriers increased to 76.92%and 40.83%.The relative abundance of Candidatus anammoxoglobus is 75.29%and 38.23%,respectively.?2?The double sludge pilot system has good nitrogen removal performance and certain impact resistance.The biofilm on the suspended carrier occupies a certain proportion in the nitrogen removal contribution rate of the system.The NH₄⁺-N removal performance of the system is good.When the HRT in the aerobic zone is shortened from 7.53 h to 6.17 h,the average removal rate of NH₄⁺-N can still reach99.06%.By extending the HRT in aerobic zone under low temperature conditions,the nitrification activity of the double sludge age system can be effectively restored.The TN removal rate of the system gradually increased with the operation of the reactor,and was not greatly affected by the drop of temperature.The NH₄⁺-N and TN concentrations of the effluent can stably reach the local standards of Beijing?Discharge standard of pollutants for municipal wastewater treatment plant??DB11/307-2013?during the 159-177d of the reactor operation,the average TN removal rate was 64.55%.The removal of COD was affected by heating and cooling.The heating process was beneficial to the removal of COD in the system.The average removal rate of COD during the reactor operation was 72.95%.Denitrification active batch tests showed that the heterotrophic denitrification contribution rates of suspended carriers in the anaerobic zone and anoxic zone in the system were 4.22%and 1.86%,a total of 6.08%.The results of high-throughput sequencing showed that the total proportion of dominant denitrifying functional bacteria on biofilms in anaerobic zone and anoxic zone were 10.15%and 12.15%,respectively.Parcubacteria?genera?incertae?sedis,Candidatus Brocadia and Armatimonadetes?gp5accounted for 5.98%and 4.83%of the dominant autotrophic denitrification functional bacteria,respectively.Combined with the proportion of microorganisms and the results of the ANAMMOX rate test,it was known that the sufficient supply of nitrite is the key factor that has not yet occurred autotrophic denitrification in the system.?3?Adding hydroxylamine to the continuous flow small-scale aerobic tank to start partial nitrification or adding sodium acetate to the anoxic tank to control carbon-nitrogen ratio to start partial denitrification can both achieve nitrite accumulation.Adding NH₂OH?5mg/L?to the aerobic tank of AAO can achieve partial nitrification,and the NAR of the effluent can reach more than 70%.The AOB/NOB in the dosing phase rised from 0.93 to 1.56 and then continued to rise to 2.47,and the addition of NH₂OH had no obvious inhibitory effect on the denitrification effect of the system.After stopping the dosing,continued the process with the low-DO strategy in the aerobic tank,the partial nitrification was easily destroyed.Taking the activated sludge of AAO with sodium acetate for a long time as the inoculation sludge,partial denitrification can be achieved by adding sodium acetate in the anoxic tank of the small test AAO.The dosage was equivalent to increase the SCOD/TIN in raw water from 3.53 to 6.08,the average NAR of the anoxic tank can reach 50.18%during the operation of the reactor.It can be seen from the partial denitrification activity batch tests with different C/N ratios that C/N is not the most critical factor affecting the accumulation of nitrite when partial denitrification sludge that had been successfully started.With the increase of C/N,the ratio of NO₂^--N accumulation rate and maximum NO₂^--N accumulation amount also gradually increased.