Study On Carbon And Nitrogen Removal Of Livestock Wastewater By Methanogenesis And Denitrification Coupling With Anammox

Methanogenesis and denitrification coupling with Anammox is a new process which couples Anammox,anaerobic methanogenesis and denitrification in the same reactor.It has the advantages of low energy consumption and small footprint.And it has a higher COD load while taking into account the removal of NO₂^-and NH₄⁺.So it has the potential to be used as the main process for the treatment of livestock wastewater.However,the flora composition of methanogenesis and denitrification coupling with Anammox in the reactor are complex and diverse,and there are differences and contradictions in the physiological metabolism of different bacterium.There is insufficient research on the reasonable operation of the coupling system.Besides,the antibiotics contained in the livestock wastewater will also have an adverse effect on the microorganisms in the system.At present,there is almost no research on the effect of antibiotics on the system.In this article,the simultaneous methanogenesis and denitrification sludge was domesticated in the continuous stirred tank reactor（CSTR）at first.Then the sludge was added to the expanded granular sludge bed（EGSB）in stages for the coupling,in which Anammox is achieved.And the exploration of the impact of environmental conditions and typical antibiotics on the efficiency of carbon and nitrogen removal in the coupling system was done in order to provide a reference for the treatment of livestock wastewater by methanogenesis and denitrification coupling with Anammox.The main research content and results of this article are as follows:（1）The study of the characteristics of carbon and nitrogen removal,gas production characteristics,microbial activity and community changes in the process of domestication and cultivation of simultaneous methanogenesis and denitrification sludge in the CSTR was implement.The simultaneous methanogenesis and denitrification system was constructed successfully by gradually increasing the influent COD and NO₃^--N concentrations.After the acclimation,The reactor can realize the stable removal rate of COD and NO₃^--N.The average removal rate of COD,NO₃^--N and TN of the system reaches 85%、99.9%、87.4%.The biogas production rate is overall increasing in the process of coupling,and the final biogas production rate reaches 0.17m³·m^-3·d^-1.The content of CH₄and CO₂in the produced gas reaches 31.9%and 6.5%respectively.The results of microbial activity determination show that the methanogenic activity and denitrification activity of the reactor in the final system are 83.4 m L·（g·d）^-1and 0.622 g·（g·d）^-1,respectively.High-throughput sequencing results show that the microbial diversity in the reactor decreased.Denitrifying bacteria（Proteobacteria,Firmicutes）proliferated in large numbers and become the largest dominant phylum in the reactor.The total number of Methanogenic-related bacteria order decreased,but the Methanosarcina order slightly increased.（2）The characteristics of carbon and nitrogen removal,changes in measurement ratio and contribution rate of nitrogen removal,functional flora activity and flora structure changes in the coupling process of methanogenesis and denitrification coupling with Anammox in the EGSB were explored.By batching the simultaneous methanogenesis and denitrification sludge cultivated in the CSTR into the EGSB while simultaneously increasing the COD load,the coupling of simultaneous methanogenesis and denitrification with Anammox was realized.With the progress of the coupling process,the effluent NH₄⁺-N of the reactor gradually rises,and the effluent NO₂^--N and NO₃^--N gradually decrease.After the coupling process completed,the average removal rate of COD,NH₄⁺-N,NO₂^--N and TN of the reactor is 94%,13.3%,99.9%and 64.9%.The denitrification contribution rate of Anammox in the coupling process continues to decline,and the contribution rate of denitrification continues to rise,with the final denitrification contribution rates of 13.1%and 86.9%,respectively.After the coupling process completed,the Anammox activity of the upper and lower sludge of EGSB are0.007 and 0.022 g·（g·d）^-1respectively,and the methane production activity is 69.6 and41.0 m L·（g·d）^-1respectively.The denitrification activity is 0.123 and 0.254 g·（g·d）^-1,respectively.After the coupling process completed,the Anammox-related flora in the reactor is greatly reduced,and the denitrification-related flora increases slightly.The Anammox and denitrification functional flora in the lower part of EGSB are relatively large,with relative abundances of 2.22%and 44.62%respectively.A small amount of methanogenesis-related flora is present in the reactor,and the methanogenesis-related flora number at the upper of the reactor is more,with relative abundance of 0.71%.（3）The effects of temperature,pH and DO,which are three important environmental conditions,on the coupling system were studied.Single factor test results show that the carbon and nitrogen removal rate of the sludge increases with the increase of temperature in 25-35℃.While it decreases with the increase of temperature in40-50℃.When p H<7,the degradation rate decreases with the decrease of p H.When p H>8,it decreases with the increase of p H.The degradation rate decreases slightly with the increase of DO in water.The results of the BBD response surface test show that temperature and p H have a significant effect on the degradation rate of COD,but the effect of DO is not significant.The optimal temperature for COD removal is 37℃.The optimal p H is 7.8,and the optimal DO is 0.2 mg·L^-1.And temperature has a very significant effect on the degradation rate of TN.The effect of p H is generally significant,and the effect of DO is not significant.The optimal temperature for TN removal is 38℃.The optimal p H is 7.9,and the optimal DO is 0.2 mg·L^-1.（4）The effects of penicillin G sodium,sulfamethazine sodium,and oxytetracycline hydrochloride with different antibacterial mechanisms,which are three common antibiotics in livestock wastewater,on the coupling system were studied.Single factor test results show that only the degradation rate of NH₄⁺-N is not affected by sulfamethazine sodium.While penicillin G sodium,sulfamethazine sodium,and oxytetracycline hydrochloride all have obvious inhibitory effects on the carbon and nitrogen removal rate of the sludge.The IC₅₀of penicillin G sodium on the degradation rate of COD,NH₄⁺-N,NO₂^--N and TN are 2256,1994,1612,1316 mg·L^-1,respectively.And the IC₅₀values of oxytetracycline hydrochloride on the degradation rate of COD,NH₄⁺-N,NO₂^--N and TN are 265,597,353,373 mg·L^-1respectively.The IC₅₀values of sulfamethazine sodium on the degradation rate of COD,NO₂^--N and TN are 1247,801,863 mg·L^-1,respectively.Orthogonal test results show that the effects of the three antibiotics on COD degradation rate are all generally significant.The effect of oxytetracycline hydrochloride on the degradation rate of NO₂^--N is very significant.The effect of sulfamethazine sodium is generally significant,and the effect of penicillin G sodium is not significant.The rank of effect of the three antibiotics on the degradation rate of COD and NO₂^--N is oxytetracycline hydrochloride>sulfamethazine sodium>penicillin G sodium.