| The tail water of urban sewage treatment plants is an important unconventional water resource,however,due to its relatively high nutrient salt level,it is easy to lead to eutrophication of the receiving water body.Aiming at the problems of high NO3--N content and low C/N in the discharge water from urban sewage treatment plants,sulfur autotrophy is widely used to treat urban sewage plant tail water,but different sulfur substrates are used as electron donors for sulfur autotrophic denitrification.In view of the advantages and disadvantages,this study established a small-scale experimental device for sulfur-siderite and sulfur-limestone constructed wetlands;for the problem of elevated NH4+-N in sulfur-autotrophic constructed wetlands,a combined system of sulfur-siderite tandem zeolite steel slag constructed wetlands was constructed.(1)The operation results of the sulphur-siderite and sulphur-limestone pilot plants show that the sulphur-siderite constructed wetland system has a better removal effect on nitrates at HRT of 24,12 and 6 h and different pollution loads.Under these conditions,the removal rate of NO3--N by the sulfur-siderite constructed wetland process was all above 90%,and the removal rate could reach 96% when the HRT was 12 h.When the HRT was 12 and 6 h,the average removal rates of total phosphorus by the sulfur-siderite system were 81.38% and82.53%,respectively;the sulfur-limestone system had no removal effect on total phosphorus,and the total phosphorus in the effluent increased.The two sulfur autotrophic systems had no effect on ammonia nitrogen removal.The sulfate concentration in the effluent of the sulfur-siderite system is lower than that of the sulfur-limestone system,and no sulfide is produced in the effluent.The experimental results show that the sulfur-siderite system can simultaneously achieve high-efficiency removal of nitrogen and phosphorus.Proteobacteria,Bacteroidota and Desulfobacterota were the dominant microorganisms in the sulfur-siderite system.When HRT was 24 h,the relative abundance of Enterobacteriaceae was the highest,and the proportion of heterotrophic denitrification was relatively large;Chlorobaculum and Desulfocapsa became the main functional bacterial genera in stages II to IV.Proteobacteria,Bacteroidota and Chloroflexi were the dominant phyla in the sulfur-limestone system.The relative abundances of Desulfocapsa,Chlorobaculum,Cloacibacterium and Geothrix were significantly higher than in the sulfur-limestone system.This may be the reason for the better denitrification and phosphorus removal efficiency of the sulfur-siderite system.Chloroflexi may be the main reason for the production of sulfide in the effluent of the sulfur-limestone system.(2)The operation results of the combined system of sulfur autotrophy and zeolite steel slag wetland show that under different operating conditions,the removal rate of nitrate by the combined system of constructed wetland is above 90%,and the removal rate of total phosphorus is 84%-89%.The removal rate of ammonia nitrogen reached 97% when HRT was24 h,and the removal rate at each stage was above 80%.The experimental results show that the constructed wetland combined system has a good removal effect on nitrate,total phosphorus and ammonia nitrogen under different HRT and influent pollution load operating conditions.Proteobacteria and Bacteroidota were the dominant bacterial phyla in the sulfur-siderite system,and Sulfurimonas,Thiomonas,Ferritrophicum,Thiobacillus and Desulfocapsa were the main functional genera.The abundance of Ferritrophicum increased with decreasing HRT.In the zeolite steel slag system,the relative abundance of Arthrobacter was the highest,and the system was mainly composed of heterotrophic microorganisms. |
