Study On Domestic Wastewater Treatment By Anaerobic-Partial Nitrification-Anammox System

The traditional treatment of domestic sewage needs a lot of energy and material input.To explore a new domestic sewage treatment process with low energy consumption,low material input and low sludge yield is of great significance for ecological environment protection.In this study,the’Anaerobic-Partial Nitrification-Anammox’system was constructed to treat domestic wastewater.The anaerobic reactor removed most of the organic pollutants in sewage,and the partial nitrification reactor converted nearly half of ammonia nitrogen in sewage into nitrite nitrogen and finally entered the anaerobic ammonia oxidation reactor to complete the removal of nitrogen.In this paper,the start-up conditions and operating effects of the anaerobic reactor,partial nitrification reactor and anammox reactor were studied respectively.After successful start-up,it was connected to the simulated domestic wastewater.The treatment effect of the system on COD was studied.The effect of partial nitrification process type selection on system stability was studied.The effects of different aeration rates and hydraulic retention time on the nitrogen removal efficiency of the system were studied.The sludge reduction effect of the system was investigated.The characteristics of microbial diversity and community structure during the stable and destroyed operation of the system were analyzed.The main conclusions are as follows.（1）In this paper,the cultivation methods of nitrifying bacteria were studied,and the nitrifying bacteria were domesticated in the biological aerated filter and the sequencing batch reactor respectively.It was difficult to use biological aerated filter to culture partial nitrification sludge to achieve nitrite accumulation,although it could achieve a high ammonia nitrogen conversion rate.The nitrifying sludge was cultured in a sequencing batch reactor for 48 days.Under the conditions of influent ammonia nitrogen concentration of 150 mg/L,hydraulic retention time of 24 h,and temperature of 35°C,the ammonia nitrogen removal rate could reach 74.7%,the nitrite accumulation rate could reach 86.6%.Stable nitrification could be maintained under the low ammonia nitrogen load of 50 mg/L.After the successful cultivation of partial nitrification sludge,it took 22 days to successfully hang the membrane in the biological aerated filter.Finally,under the condition of hydraulic retention time of 8 h and the dissolved oxygen which was 0.1～0.6 mg/L,half partial nitrification was achieved,and nitrite accumulation rate was 89.4～93.2%.（2）After the successful start-up of the reactor,this paper constructed the anaerobic-biofilm partial nitrification-anammox system and anaerobic-activated sludge partial nitrification-anammox system to treat domestic sewage based on two nitrification systems.The experiment showed that after about 70 days of stable operation of the system based on biofilm method,the partial nitrification could not be maintained gradually,resulting in the imbalance of anammox influent proportion and the increase of total nitrogen concentration in the final effluent.In the experimental process,the system based on activated sludge method can always maintain relatively stable nitrification.The average COD concentration of the final effluent was 26.6 mg/L.The average NH₃-N concentration was 0.2 mg/L.The average TN concentration was 2.1 mg/L,The average nitrogen removal rate was 95.7%.The maximum average volumetric nitrogen removal rate was 0.15kg N/（m~3·d）.（3）The residual sludge yield of the Anaerobic-Partial Nitrification-Anammox System was about 0.033 kg MLVSS/kg COD,which had great sludge reduction effect.In this experiment,about80%of COD was removed in the anaerobic reactor.The autotrophic bacteria were the dominant group in the subsequent reactors,and they all operated under low load conditions,and the amount of residual sludge in the system was greatly reduced.（4）During the stable operation of the partial nitrification reactor,Proteobacteria was the most dominant phylum and Nitrosomonas was the most dominant genus.During the destroyed operation of the partial nitrification reactor,the abundances of Proteobacteria and Nitrosomonas decreased,and the average abundances of Bacteroidetes and Denitratisoma increased.From the stable to destroyed operation of the parital nitrification reactor,the abundances of Candidatus Brocadia in the Anammox reactor decreased.In general,the‘Anaerobic-Partial Nitrification-Anammox’domestic wastewater treatment system constructed in this study has a great removal effect on organic pollutants and nitrogen pollutants.Low energy is consumed in the system when it operates.No extra carbon source is required for autotrophic denitrification.Anaerobic system coupling with high microbial biomass has low sludge yield,which has the potential to become an important component of a new domestic wastewater treatment system in the future.