Study On Performance Of Autotrophic Denitrification Filler In Constructed Wetland For Nitrogen And Phosphorus Removal

In recent years,the discharge standard of tail water of sewage treatment plant has been continuously improved by the state.The concentration of NO₃^--N in tail water is high and C/N is low.Carbon source is required in traditional heterotrophic denitrification,which is costly and prone to secondary pollution.On the contrary,carbon source is not required in sulfur autotrophic denitrification,which has higher nitrogen removal efficiency.And the substrate has the function of phosphorus removal.The combination of sulfur autotrophic denitrification and constructed wetland is an efficient,economic and eco-friendly method for advanced treatment of tail water.In order to improve the efficiency of nitrogen and phosphorus removal by sulfur autotrophic denitrification,the study mainly focused on the problem of tail water not meeting the standard through performance comparison and proportion optimization of filler.Sulfur autotrophic denitrification technology was applied to subsurface constructed wetland to investigate the purification effect of wetl and on actual sewage.（1）The SLAD system had the highest denitrification efficiency.When the HRT was 4 h and the TN concentration in the influent was 16～23 mg/L,the average concentration of the effluent was 2.6 mg/L.However,its performance of TP removal was poor,and the average removal rate was only 33.21%.On the contrary,the PLAD system had significant advantages in phosphorus removal.When the TP concentration in the influent was 1.6～2.7 mg/L,the effluent could meet the environmental quality standard of surface water class V（0.4 mg/L）.However,its performance of TN removal was low,and the average removal rate was only 55.31%.As a sulfur source,sulfur had obvious denitrification effect,while pyrite had significant advantages in phosphorus removal,and limestone could provide sufficient alkalinity and was cheap and easy to obtain.It was speculated that the combination of the three could achieve the purpose of high-efficiency nitrogen and phosphorus removal at the same time.（2）When the volume ratio of limestone,sulfur and pyrite was 5:3:2,the removal effect of NO₃^--N was the best.When the concentration of the influent was about 11.70mg/L,the average concentration of the effluent was 0.21 mg/L,and the removal rate was stable at about 98%.When the volume ratio of limestone,sulfur and pyrite was5:1:4,the removal effect of PO₄^3--P was the best.When the concentration of the influent was about 3.50 mg/L,the average concentration of the effluent was 0.11mg/L,and the removal rate was stable at about 95%.When the ratio was 5:3:2,the removal rate of PO₄^3--P was 89%,and the p H of the effluent was between 7.00 and7.15,which was suitable for the growth of sulfur autotrophic denitrifying bacteria.The removal efficiency of TN and TP by the system（5:3:2）decreased with the decrease of HRT.When the HRT was 4 h,the average removal rates of TN and TP were 90.40%and 91.51%,respectively.（3）Constructed wetland A was filled with limestone,sulfur and pyrite（5:3:2 of volume ratio）.And constructed wetland B was filled with limestone,sulfur and gravel（5:3:2 of volume ratio）.In this experiment,two wetlands were operated at the same time with HRT of 4 h.In wetland A,when the TN concentration of the influent was16.18～23.50 mg/L,the average removal rate was 95.42%.When the TP concentration of the influent was 1.71～2.31 mg/L,the average removal rate was 94.57%.The removal efficiency of TN and TP in wetland A was greater than that in wetland B.This showed that adding 20%volume of pyrite could improve the efficiency of the original system（sulfur:limestone=1:1 of volume ratio）for nitrogen and phosphorus removal,the TN concentration of the effluent could be reduced from the original 2.0to 1.5 mg/L,and the TP concentration of the effluent could be increased from the environmental quality standard of surface water class V（0.4 mg/L）to IV（0.3 mg/L）.（4）The microbial community diversity of seed sludge was the highest,and the denitrification microorganisms had been enriched in wetlands A and B.The dominant bacteria phylum in wetlands A and B were Proteobacteria with abundances of95.92%and 83.68%,respectively.The dominant bacteria class were Betaproteobacteria with abundances of 89.55%and 67.03%,respectively.The dominant bacteria genus were Proteobacteria with abundances of 86.45%and49.63%,respectively.At the phylum,class and genus levels,the abundance of dominant bacteria in wetland A was higher than that in wetland B.These dominant bacteria played a major role in denitrification in wetland.Therefore,wetland A had more efficient and stable performance of nitrogen removal than wetland B.