| In recent years,with the acceleration of the global industrialization and urbanization,the organic pollutant components in water are becoming more and more complicated,proportion of pollutants and the nutrient content is increasing,which challenges the conventional water pollution control technologies.Over the past decade,the coupling process has been widely used due to the advantages of removal of organic carbon,nitrogen and phosphorous and sulfur together,effectively process-shorten,reduce of resources and energy consumption.Coupled treatment technology,especially anaerobic simultaneous denitrification and methanogenesis(SDM)process,which achieved the coupling of denitrification and methanogenesis in a single reactor,effectively enhanced stability and pollutant removal efficiency of the treatment system.However,at present,the metabolic characteristics of the coupling process,characteristics of corresponding sludge and microbial structure and diversity,coupling mechanism and so on are still unclear,which limited the application of the SDM process.In this study,the COD/NO3--N ratio was used as the control object.The metabolic characteristics,characteristics of the granular sludge and dynamics of the microbial community were investigated by the short-term test and long-term continuous experiments,to reveal its coupling mechanism.The main contents and results of this paper are as follows:(1).Study on metabolic properties of treatment process under different COD/NO3--N ratio.Short-term tests were conducted with the addition of nitrate.pH and ORP values,degradation of nitrogen and methane production rate selected as the metabolic characteristic indexes.Results show that coupling of the denitrification and methanogenesis was happened under different COD/NO3--N ratio,and the coupling proportion showed an inverse relationship.Under the low COD/NO3--N ratio(3 and 5),methanogensis was almost completely suppressed,and under the high COD/NO3--N ratio(50 and 100),denitrification was coupled little and the methanogenesis was still the main metabolism process of the process.With glucose as the carbon source,COD/NO3--N ratio of 8 could be used as a boundary condition for simultaneous denitrification and methanogenesis(SDM).(2).Physical and chemical properties of granular sludge at the COD/NO3--N ratio of 8.0.Results indicated granular sludge samples significantly changed before and after the short-term test,which showed that smoothness of particles was decreased,the sludge particles were rougher and fluffy.Color of granules was changed to light brown or white,the settling velocities of granular sludge was 52.7±3.2 m/h,and the average size was 1.4±0.5 mm,which decreased about 37.4% and 22.1% compared with the control group.Outer surface of granular sludge was attached to short rod-shaped and spherical strains,including the Streptococcus.The FT-IR spectrum showed a peak at 1745 cm-1,which might be related to the death of bacteria during the SDM process,the adsorption performance and stability of the SDMGS were decreased,and the enzyme activities changed significantly.Overall,with the nitrate adding in a sudden could be taken an adverse effect to the methanogenesis sludge.(3).Similarities and differences of microbial structure and diversity in the conventional granulated sludge and the coupling sludge(SDMGS)were discussed with denaturing gradient gel electrophoresis and high-throughput sequencing.Proteobacteria,Bacteroidetes and Firmicutes were the three major bacterial groups in the SDMGS samples.?-Proteobacteria,Enterobacteriales,Enterobacteriaceae and Bacteroides were the most important bacterial groups,which might be associated with the SMD process.Compared with the control group,the composition of the archaeal communites of the SDMGS samples were like that of the control group,Methanosaeta and Methanobacterium are the main methanogens.(4).Metabolic characteristics of the process and differences of physical and chemical properties between granular sludge under different coupling degree in the long-term experiments were studied.During long-term experiments,the degradation of carbon was not affected,and nitrate nitrogen was almost completely degraded.A small amount of nitrite was accumulated during the process.Metabolic rate of methanogenesis is greatly reduced from 3.5 L/h to 0.8~0.9 L/h.,and content of methane in the biogas has a significant decrease Change of the chemical functional group of the granular sludge is not obvious under different COD/NO3--N ratio,but its external structure and internal structure was likely to be disintegrated with increasing COD/NO3--N ratio,which could be releated to the SDM process.(5).Structure and diversity of microbial communities and functional micorbes in different coupled granular sludge were explored.With the help of high throughput sequencing method,structure and diversity of microbial communities in different coupled granular sludge were researched,and differences and succession of microbial communities and functional microbes,and the corresponding number were also investigated.Continuous experiments show that the structure and quantities of bacterial communities fluctuates under different COD/NO3--N ratios.Proteobacteria,Bacteroidetes,Firmicutes,Chloroflexi and Spirochaetes are the main dominant bacterial communities in all the coupling processes.Number of the Smithella(at COD/NO3--N ratio of 15.18 and 8.00)was increased,which might be related to degradation of propionic and butyric acid during the SMD process.Methanosaeta and Methanobacterium were closely related to the methane production process during the coupling process,and results also showed that the Methanebacteria were more likely to be adapt to nitrate-containing nitrogen systems,especially in high concentrations of nitrate.Results of metagenomic analysis showed that Methanosaeta concilii GP6 was closely related to the methane production process during the SDM process.Alicycliphilus denitrificans BC,Alicycliphilus denitrificans K601,Thauera sp.MZ1 T and Acidovorax sp.JS42 were related to the denitrification during the SDM process. |
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