Two-stage Partial Nitrification-anaerobic Ammonium Oxidation Denitrification Performance And Its N₂O Production Pathway

In recent years,some new denitrification processes have been developed in succession,especially the short-cut nitrification-anaerobic ammonia oxidation process.Comparedwiththetraditionaldenitrificationprocess,theshort-cut nitrification-anaerobic ammonia oxidation process not only saves 50%of aeration,but also eliminates the need for additional Carbon source,sludge production is low.The short-cut nitrification process has not studied in depth how to maintain stable nitrite nitrogen accumulation in low C/N municipal wastewater.Therefore,it is necessary to study the stability and nitrogen transformation pathway under different operating conditions.Since anaerobic ammonia-oxidizing bacteria grow slowly for a long time,and biological filter is a combination of biological oxidation and physical trapping,it can effectively prevent the loss of anaerobic ammonia oxidizing bacteria.The anaerobic ammonia oxidizing bacteria have strict requirements on their growth environment and are easily affected by changes in environmental conditions.The influence of environmental factors such as DO on the denitrification performance is discussed,and it has certain significance in the regulation of practical applications.In the process of biological denitrification,the greenhouse gas-N₂O is emitted,and its harm to the environment cannot be ignored.However,there are few researches on the release of N₂O in the mainstream anaerobic ammoxidation process and its generation pathways.The purpose of N₂O reduction can be achieved by studying the generation mechanism of N₂O and regulating the operating parameters.This project takes actual domestic sewage as the research object,and inoculates the sludge in the stable short-run nitrifying SBR in the pilot plant.After 11 days,the nitrous acid accumulation rate reaches over 95%,and the short-cut nitrification starts quickly.When the DO concentration was reduced to 0.5 mg/L,the ammonia oxidation rate gradually decreased,and the NAR decreased from 91.8%to 71.7%.The oxygen half-saturation constants of AOB were 0.146 mg O₂/L and 0.307 mg O₂/L for high DO and low DO operating phases,respectively.AOB had higher affinity for dissolved oxygen under long-term high DO conditions.Under low DO conditions,Nitrospira's growth tends to gain advantages,and Nitrospira is an important factor affecting short-run nitrification stability.Studying its nitrogen transformation pathway,under different dissolved oxygen conditions,different degrees of short-cut nitrification,simultaneous nitrification and denitrification and anaerobic ammonia oxidation occur in the system.The main way to produce N₂O by short-cut nitrification process is nitrification bacteria denitrification.The anaerobic ammonium oxidizing bacteria were cultured and enriched using a biofilter.After 173 days of anaerobic ammonia oxidation filter,the TN removal rate was over 83.6%,and the maximum total nitrogen removal load was 0.75 kg/m³/d^-1.The anaerobic ammonia filter was not heated at the initial stage of start-up.On the138th day,when the filter temperature decreased to 16°C,the Anammox bacteria was active,but the activity was low,the TN removal rate was reduced to 50%,and the temperature was gradually increased to 25°C.After°C,its activity gradually recovered.After 173d,the removal rate of TN reached more than 80%.It can be seen that lowering the temperature inhibits Anammox bacteria reversibly.The influent oxygen concentration in the influent was 4.0-5.0 mg/L.Due to the presence of some nitrifying bacteria in the anaerobic ammonium biofilm inoculation sludge,the dissolved oxygen in the filter tank could be removed and the system TN removal rate was maintained at over 78%.During the two-stage short-cut nitrification-anaerobic ammonia oxidation,short-cut nitrification SBR increased the pre-denitrification,which could further inhibit the activity of NOB and was beneficial to the growth of AOB.The control temperature was 25°C;the filtration rate was 0.25m/h,and the influent NH₄⁺-N concentration was 16-20mg/L.After 10 days,the TN removal rate increased from46.73%to 78%,and the anaerobic ammonia oxidation filter was successfully started.When the temperature is 25°C,the filtration rate is gradually increased,after 218 days,and the controlled filtration rate is 0.5 m/h.After 10 days,the removal rate of the filter pool is increased from 65%to 90%,and the total nitrogen volume load is 0.75 kg/m³/d,the average anaerobic ammonium oxide effluent TN concentration was 8 mg/L.The successful implementation of the two-stage short-cut nitrification-anaerobic ammonia oxidation process for the stable and efficient treatment of domestic sewage.