Research On Denitrification Efficiency And Microbial Community Characteristics Of Sulfur Autotrophic Denitrification Biofilter

The municipal tailwater is an important unconventional water resource,it can cause eutrophication for its high relative nutrients.In view of the problems of high concentration of NO₃^--N and low C/N ratio in the municipal tailwater,the sulfur-based autotrophic denitrification?SAD?biofilter was established in this research,and pilot-scale reactor was carried out on-site to systematically evaluate the operation efficiency of the system at low temperature.The microbial community structure and copy abundance of denitrification functional gene in the reaction system were further investigated.The main achievements are as follows:The lab-scale and pilot-scale?height diameter ratio:1.5:1,filler:1200mm,effective volume:1100L?SAD biofilter were established.The biofilter were filled with the mixture of sulfur,zeolite,limestone and volcanic rock with a volume ratio of 3:3:1:1.The results of lab-scale experiments showed that the removal efficiency of NO₃^--N were higher than 90%when influent NO₃^--N was arranging from 15 to 45 mg/L,temperature was?20?,and HRT?Hydraulic retention time?was 3 h.The results showed the SAD system has a good resistance to shock loads.When the gas-water radio was 1:1,the removal efficiency of NO₃^--N was reduced to 45.42%,and the removal efficiency of NO₃^--N was 93.72%when reactor run with non-aeration.In addition,it was found that the addition of organic carbon had a significant effect on the operation efficiency of sulfur autotrophic system,when the system was constructed by adding methanol with 12,24 and 36 mg/L,the removal efficiency of NO₃^--N was 85.66%,95.96%and 98.64%respectively,the proportion of heterotrophic denitrification proportion increased from 10.6%to 31.5%,the results suggested that the increase of carbon source can improve denitrification ability and promote the synergism of autotrophic and heterotrophic.The process parameters of long-term stable operation of the SAD system at low temperature were proposed.The operation results of pilot-scale system showed,TN and NO₃^--N removal efficiency were70.6%and 74.2%,respectively,with HRT of 3 h at the temperature ranging from 19.2 to 16.9°C;TN and NO₃^--N removal efficiency were 53.7%and 52.4%,respectively,with HRT of 6 h at the temperature ranging from 14.5 to 10.5°C;TN and NO₃^--N removal efficiency reached 81.1%and 85.3%,respectively,with HRT of 9 h at the temperature ranging from 6.4 to 9.8°C.According to the difference value between the theoretical and the measured value of SO₄^2-,the contribution proportion of autotrophic denitrification process to total NO₃^--N removal in these three different stages were 78.4%,83.7%and 67.3%respectively,which suggested that heterotrophic and autotrophic denitrification processes occurred simultaneously and have synergistic effect.Furthermore,the structure and function of microbial community,the expression of functional genes in the sulfur autotrophic denitrification system were revealed,respectively.Proteobacteria and Chloroflexi were two dominant phyla,Thiobacillus and Ferritrophicum were two dominant genus in different system,Thiobacillus,which was the main sulfur autotrophic denitrification bacteria,increased and then decreased along the reactor,Ferritrophicum,which promotes sulfur autotrophic denitrification,increased significantly.The results of quantitative PCR showed that nir S gene and nos Z gene had more high copy abundance in denitrification process.