Study On Mechanism Of Nitrogen Removal By Anammox Coupled MBR Process

Nitrogen pollution is one of the main causes of water quality deterioration.Traditional nitrification and denitrification process can effectively remove nitrogen,but needs to consume a lot of energy and chemicals.The anaerobic ammonia oxidation(anammox)discovered in the 1990 s is based on the microbial action of anaerobic ammonia oxidizing bacteria(An AOB)to convert NH4+-N and NO2--N to N2,which has the advantages of low energy consumption and high efficiency.However,it is difficult to meet the current sewage discharge standards by using the anammox process alone.Therefore,combining anammox process with other processes is a realistic choice for engineering applications.MBR is a wastewater treatment process combining activated sludge process and membrane separation technology.It has simple operation,stable effluent and high treatment efficiency.Based on the previous research,this study took the domestic sewage of Yanshan Campus of Guilin University of Technology as the influent,and studied the mechanism of nitrogen removal by an anammox coupled MBR process.By monitoring the concentration changes of NH4+-N,NO2--N,TN,COD,and dissolved organic matter in the influent and effluent under different operating conditions(temperature,DO,reflux ratio).The denitrification contribution rate dominated by the anammox was calculated.15 N isotope-labeled batch experiments were used to verify the results,and the results of microbial community structure analysis during process operation were used to explore the nitrogen removal mechanism of the coupled process.The main conclusions are as follows.(1)The DO concentration had an important effect on the start of the process.The experimental results of the previous operation showed that the anammox reaction could achieve high-efficiency denitrification under the appropriate DO concentration.The average TN removal rate of stage Ⅲ reached 86.53%.(2)The temperature had a great influence on the process.The experimental results showed that when the temperature was between 5 and 30 ℃,the removal rates of NH4+-N and TN decreased with decreasing temperature.The effect of temperature on the removal of TN was greater than that of NH4+-N.In addition,the effect of low temperature on microbial activity in the coupling process was irreversible.(3)Increasing the reflux ratio could effectively improve the nitrogen removal efficiency.The effect of changing the reflux ratio on TN removal was greater than that of NH4+-N.The experimental results of this study showed that when the TN in the water was 76.24 ~ 94.19 mg / L and the reflux ratio was 4: 1,The indicators of effluent such as NH4+-N,TN and COD can meet the first-class A standard of the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant(GB18918-2002).(4)The removal of organic matter was selective.By analyzing the dissolved organic matter of the influent and effluent,the fluorescence intensity of protein-like substances was related to the system’s ability to remove nitrogen,and the removal rate of protein-like substances by the process reached 72.4%.(5)The anammox reaction had a higher contribution rate to the nitrogen removal of the process.15 N stable isotope experiments showed that the denitrification contribution rate of anammox reaction was 60.11~69.83%,while the denitrification contribution rate was 30.17~39.89%.The small-scale experimental experiments have obtained the denitrification contribution rate of 64.4~74.4% for the anammox reaction,the results were basically consistent with the 15 N stable isotope experiment.(6)The abundance of ammonia oxidizing bacteria and An AOB occupied a certain proportion.At the genus level,the results showed that the nitrogen cycle related Nitrospira and Aridibacter were relatively stable,and the community composition were both 2% to 4%.The abundance of Nitrosomonas genus gradually decreased from the initial 1% until it finally disappeared,and Candidatus Kuenenia associated with An AOB always occupied a certain proportion,and finally maintained a 0.58% proportion.The results of high-throughput sequencing provided a theoretical basis for the presence of anammox in the process.