Study On Start-up Of Anammox Process And Enhancement Of Sludge Purification Efficiency

Antibiotics are widely used to improve public health,prevent disease and increase productivity on animal farms.However,antibiotics discharged into the environment by pharmaceutical industry and its application sources may cause potential ecological risks to the environment.Meanwhile,excessive nitrogen discharge will also lead to eutrophication of water.Biological nitrogen removal is an effective way to reduce nitrogen in water.Anaerobic ammonia oxidation（anammox）process is a new biological nitrogen removal process with broad application prospects,which can achieve simultaneous removal of NH₄⁺-N and NO₂^--N under anaerobic conditions.However,the application of anammox process in practical engineering is limited by the problems such as long start-up time,lack of inoculated bacteria source and easy to be affected by external environmental conditions（such as antibiotics and dissolved oxygen）.It is an important subject to further accelerate the engineering application of anammox process to explore the strategies suitable for the enrichment of anammox bacteria and to study the appropriate measures to reduce the sensitivity of anammox bacteria to external conditions.Based on the optimization of the effect of stirring method on the start-up of anammox reactor,the feasibility of starting anammox reactor with paddy soil as bacteria source was stu died in this paper.The effects of applied magnetic fields and iron-loaded sludge-based hydrothermal carbon（Fe-BC）on the efficiency of anammox were studied.The effect of Fe-BC on improving anammox efficiency and alleviating tetracycline（TC）stress was further explored,and its influencing mechanism was analyzed from the perspective of functional gene abundance,functional microbial population changes,extracellular polymeric substances（EPS）and electron transfer ability.In order to enrich the source of anammox bacteria,the anammox reactor was successfully started with paddy soil with abundant source and rich anammox bacteria as inoculation source.Based on the analysis of the influences of built-in submersible pump,external circulating pump and built-in agitator on the start-up process of anammox,the paddy soil source reactor and activated sludge source reactor realized the start-up of anammox process in 75 days with built-in agitator.Although the total nitrogen（TN）removal rate of sludge source reactor（81.37%）was higher than that of the paddy soil source reactor（70.37%）,the average TN removal rate under the optimal hydraulic retention time（HRT）（22 h）was similar to that of the sludge source reactor.Compared with sludge source reactor（1.52%）,paddy soil source reactor（9.01%）has higher relative abundance of Planctomycetota.The relative abundance of Candidatus Brocadia in sludge source reactor and paddy soil source reactor were 1.19%and 7.61%,respectively.The applied magnetic field can improve the efficiency of anammox reactor in short term,but the long-term operation effect was not good.The experimental results of the influence of external magnetic field on anammox efficiency showed that external magnetic field could not improve the efficiency of the anammox reactor in the long term.The addition of external magnetic field in the short term increased the TN removal rate of the reactor by 8.39%.However,long-term operation results showed that external magnetic field reduced the TN removal efficiency of the anammox reactor by 18.25%compared with the control group.The applied magnetic field decreased the contents of protein（from 14.35 mg/g MLSS to 7.47 mg/g MLSS）and polysaccharide in EPS,and the relative abundance of Candidatus Brocadia decreased from 4.5%to 0.8%in the control group.The Fe-BC prepared by hydrothermal carbonization method as exogenous additives can improve the efficiency of anammox by promoting EPS secretion,increasing the content of intermediate electron transfer components of EPS,accelerating electron transfer and improving functional bacteria.The addition of 2.5 and 5.0 g/L Fe-BC increased the TN removal rate by10.62%and 17.14%,respectively,while 5.0 g/L Fe-BC reactor increased the specific anammox activity（SAA）by 49.58%compared with 0 g/L Fe-BC reactor.Fe-BC enhanced the activity of anammox sludge by increasing the content of protein and polysaccharide in EPS,promoting the secretion of humic acid and cytochrome c,and mediating the electron transfer process of anammox.After removing EPS and simultaneously enzymolizing polysaccharide and protein,the SAA in 5.0g/L Fe-BC reactor decreased by 61.38%and 79.99%,respectively,which was significantly higher than that in 0 g/L Fe-BC reactor.In addition,the relative abundance of Candidatus Brocadia in the anammox reactor supplemented with Fe-BC was increased by 35.56-55.56%compared with 0 g/L Fe-BC reactor.The relative abundance of key functional genes related to nitrogen conversion（e.g.,hao,nir S,and nap A）and EPS formation functional genes（e.g.,rfb A,rfb B,rfb D,gale,and pgm）has increased.The addition of Fe-BC is an effective way to alleviate the inhibition effect of TC on anammox process.Fe-BC can alleviate the inhibition effect of antibiotics on anammox bacteria by promoting EPS secretion,increasing the content of intermediate electron transfer components in EPS,accelerating electron transfer,improving the abundance of functional bacteria and functional genes.The 1.0 mg/L TC reduced the SAA of TC reactor by 4.31 mg TN/（g MLSS·d）compared with that of the blank reactor,and reduced the TN removal rate by 5.86%compared with the blank reacto by inhibiting the electron transfer process.At the same time,microorganisms reduced the toxic effect by increasing the EPS.The addition of Fe-BC increased the amount of EPS secreted by microorganisms from 91.78 mg/g VSS in the blank reactor to 117.56 mg/g VSS,in which protein and polysaccharide increased 32.93 mg/g VSS and 7.62 mg/g VSS,respectively.At the same time,it increased the secretion of humic acid and cytochrome c,and promoted the electron transfer process to improve the efficiency of anammox.EPS mediated anammox process,after extracellular protein was removed by protease K enzymatic hydrolysis,the SAA was decreased by 49.78%,while the ability of polysaccharide to improve the SAA was related to the treated enzymes.In addition,compared with TC reactor,the absolute abundance of hdh and hzs B increased by 2.77 and1.18 times,respectively,and the relative abundance of Candidatus Brocadia increased from 8.22%to 10.24%.In addition,Fe-BC can reduce the TC content in the reactor through adsorption to alleviate the toxic effect of TC on anammox bacteria,thus improving the nitrogen removal efficiency of anammox.