Start-up And Mechanism Of Snad Process In Up-flow Reactor Under Micro-oxygen Condition

Simultaneous partial nitrification,ANAMMOX and denitrification process(SNAD)is a new type of biological synchr-onous decarburization and nitrogen removal technology developed on the basis of CANON process for wastewater with lower C/N ratio.It has many advantages such as small footprint,low sludge yield,efficient remove of carbon and nitrogen etc.And it has a broad growing outlook in project applications.In this experiment,the lower C/N fertilizer wastewater was used as the research object,and the micro-oxygen technology was applied to the membrane bioreactor to achieve successful start-up and stable operation of the SNAD process at a higher mixed licquicd suspended solids.In addition,the research on the effects of nitrogen and carbon and the changes in bacterial structure to provide a theoretical basis and data support for the application of the SNAD process in practical engineering.The main work is as follows:(1)Simulate the industrial wastewater with a laboratory scale as the research object,and explore the impact of different C/N on the start-up process of SNAD in the upflow reactor under micro-oxygen conditions.Finding the optimal control parameters to meet the requirements of the system to remove ammonia nitrogen,total nitrogen and COD are gradually enhanced and stabilized by adjusting the dissolved oxygen and alkalinity.The test proved that the optional dissolved oxygen and alkalinity concentration is 0.4mg/L and 1400mg/L-1700mg/L,respectively.The effluent NHS+-N,TN and COD concentrations were 20 mg/L,50 mg/L and 22 mg/L,respectively,with removal rates of 90%,76%and 95%,respectively.And the denitrification process was traditionally denitrified and short-denitrification dominates.(2)In the case of C/N=1.5(COD=300mg/L,NH4+-N=200mg/L),the SNAD process was started in a manner with low ammonia nitrogen concentration and high nitrous oxide concentration.The effluent concentrations of NH4+-N,TN,and COD were 10 mg/L,67 mg/L and 38 mg/L,with the removal rates were 96%,67%,and 87%respectively.Although the nitrogen removal effect did not increase significantly,the results of high-throughput sequencing showed that a small amount of anaerobic ammonia-oxidizing bacterial populations appeared.At this stage,nitrogen removal was still dominated by short-term denitrification.(3)When C/N=1,the SNAD process is started successfully by adjusting the concentration ratio of ammonia nitrogen and nitrous Nitrogen in the outflow and sdding to the influent nitrogen load.The NH4+-N,N02--N,NO3--N and COD concentrations in effluent were 7 mg/L,10 mg/L,7 mg/L,and 22 mg/L respectively.The removal rate of NH4+-N is above 96%,and the removal rate of TN is 86%,the removal rate of COD is about 90%finally.In addition,38%of nitrogen was removed by anaerobic ammonia oxidation,and 62%of nitrogen was removed by short-cut denitrification through the analysis of the nitrogen removal path.(4)The activity of the functional flora in different stages was determined through batch tests.The activity of AOB was 2.18 mg-NH4+-N/(gVSS·h)and 9.35 mg-NH4+-N/(gVSS·h)during the initial stage and stable stage of short-cut nitrification and denitrification,respectively.Compared with the start-up sludge,the activity of AOB in the stable operation stage of short-cut nitrification and short-cut denitrification was 4.3 times that of' the start-up sludge.NOB activity was effectively suppressed,which proved that the short-cut nitrification prcess was achieved.The activity of-short-cut denitrifing bacteria did not change much.The activity of ANAMMOX bacteria was 1.78 mg-TN/(gVSS·h)during the stable stage of-SNAD.(5)To explore the changes in physicochemical properties such as sludge status,particle size,and extracellular polymer during the start-up of SNAD process.The lower protein and polysaccharide content in EPS reduces the probability of filter cake plugging,making membrane fouling more light.(6)Samples were taken at different stages of the SNAD start-up process for high-throughput sequencing.The results showed that two anaerobic ammonia-oxidizing species were present,their names were:Candidatus Brocadia and Candidatus Jettenia,and microscopically proved the SNAD process was started successfuly.In addition,the functional bacteria of short-cut nitrification,anaerobic ammonia oxidation was Phaedactylibacter and Nitrosomonas;Saprospiraceae,Comamonadaceae and PHOS-HE51;Candidatus Brocadia,and Candidatus Jettenia,respectively.