Effect Of Iron On Low Temperature Nitrogen Removal Performance And Microbial Community Of Anammox

The anammox process is a biological process in which ammonia nitrogen and nitrite nitrogen are converted into nitrogen by anammox bacteria under anaerobic conditions.It has the advantages of energy saving,low operating cost and less excess sludge,and is a research hotspot in the field of wastewater denitrification in recent years.As the main functional microorganism of anammox,anammox bacteria is an autotrophic microorganism with slow growth rate and low enrichment degree,which is easily disturbed by environmental factors.Among them,the deterioration of nitrogen removal efficiency caused by low temperature environment is the main bottleneck problem in the popularization and application of anammox technology.Iron is not only a ubiquitous metal element in the environment,but also one of the nutrient elements needed for microbial growth.In this study,batch experiments were conducted to optimize the dosage of Fe²⁺and nZVI at low temperature,and then a continuous anaerobic test device was set up to investigate the effects of Fe²⁺and nZVI on the activity of anammox bacteria and microbial community under low temperature stress(15?).The main conclusions are as follows:(1)the effect of Fe²⁺on the low temperature activity of anammox.The results of batch experiments show that the demand for iron by anammox bacteria increases at low temperature;At 15?,the optimal dosage of Fe²⁺is 10 mg Fe²⁺/g VSS,and the SAA value of anammox sludge(0.04 g N/g VSS/d)increases by about 40%.Continuous dosing of 10 mg Fe²⁺/g VSS can significantly improve the nitrogen removal efficiency,and the promotion effect on nitrogen removal of anammox shows a periodic change of first significant promotion,then fluctuation and then decline.Fe²⁺can effectively adjust p H in water environment.Maintain?NO₂^--N/?NH₄⁺-N at about 1.32;And participate in denitrification process so that?NO₃^--N/?NH₄⁺-N is basically less than 0.26.The only anammox functional bacteria in the system is Candidatus Brocadia.(2)The effect of nZVI on low temperature activity of anammox.There is an optimal demand for nZVI by anammox bacteria at low temperature.At low temperature(10?-15?),10 mgnZVI/g VSS can significantly improve the SAA value of anammox sludge in a short time,and the SAA can be increased by up to 30%.In the continuous test process of adding 10 mgnZVI/g VSS,the nitrogen removal efficiency is significantly improved in the first to fourth cycles,and decreased from the fifth cycle.The analysis of nZVI's promotion effect on nitrogen removal rate was more reflected in instantaneous stimulation and long-term inhibition.Adding Fe²⁺can effectively restore nitrogen removal performance of nZVI-Anammox system.The relative abundance of anammox bacteria in nZVI-Anammox system was higher than that in control group.(3)Analysis of the differential action mechanism of Fe²⁺and nZVI on anammox nitrogen removal process at low temperature.At 15?,compared with nZVI,Fe²⁺is more beneficial to the increase of sludge concentration and sludge particle size,but the ratio of MLVSS/MLSS in Fe²⁺-Anammox test group is lower.SEM results showed that there were a lot of pores on the sludge surface in Fe²⁺-Anammox test group,while needle-like aggregates were observed in the sludge of nZVI-Anammox test group.XRD results show that Fe₂O₃ is the main iron oxide in sludge.Iron is mainly accumulated in Pellet components of sludge,and granular sludge enriched with Fe²⁺has the greatest contribution to nitrogen removal efficiency at low temperature.While the number of functional genes hzs B in nZVI-Anammox test group is the largest,the anammox sludge activity of the system is poor,resulting in poor nitrogen removal effect.Adding Fe²⁺can improve the relative abundance of Psychrobacter,Pseudomonas and Aquabacterium in microbial community.