Study On Sulfur/Sulfur-iron Coupling Carrierfor Advanced Removal Of Nitrogen And Phosphorous From Municipal Wastewater

The nitrogen and phosphorus in the effluent from municipal wastewater treatment plant(WWTP) could cause eutrophication in sensitive waters. Therefore, efficient and low-cost methods to remove them have been becoming essential research hotspots. The sulfur-iron coupling carrier packed bed is an effective technology to remove the nitrogen and phosphorous in the effluent from WWTP. However, the blockage constraints its engineering application. Based on the analysis on the blockage mechanism, some methods, such as deoxygenation, changing the filling form and backwash, were adopted to prevent the blockage. In this study, a pilot-scale reactor of sulfur-iron packed bed was set up for further engineering application.A packed bed with fillings of sulfur tablets was firstly employed to remove the dissolved oxygen(DO) in the secondary effluent. As the flow rate changed from 0.55 m/h to 1.37 m/h, the DO concentration was decreased to less than 0.4 mg/L, with a removal efficiency of 90%. The highest nitrogen removal rate was 2000 mg NO3--N/(L·d). Moreover, the DO concentration did not affect the zero-valent iron’s performance in phosphorus removal.Then two kinds of packed beds with fillings of both sulfur and iron were operated following the packed bed with sulfur only, respectively. The sulfur and iron fillings were completely mixed in one packed bed, and in the other were placed by layers. For the completely mixed one, the concentration of NO3--N in the effluent could reach 1.9 mg/L with varied flow rates, and the highest nitrogen removal rate was 910 mg NO3--N/(L·d). In the other one with layers, the concentration of NO3--N in the effluent was 0.34 mg/L and the highest nitrogen removal rate was 1100 mg NO3--N/(L·d). For both of the reactors, the total phosphorus(TP) concentrations were lower than 0.2 mg/L. The blockage gradually occurred in the mixing packed reactor after 50 days whereas the blockage did not occur in the layer packed reactor after 100 days. It strongly proved that the sulfur-iron coupling carrier packed reactor was effective to delay the blockage.In the pilot-scale reactor with the sulfur and sulfur-iron coupling carrier packed beds, the reactor successfully had a stable performance after 130 days, and the DO removal efficiency was over 90%. With the influent rate of 0.5~1.5 m3/h, the concentration of NO3--N in the effluent remained less than 3 mg/L and that of TP was less than 0.2 mg/L.