Analyzing the removal effect of nitrogen before and after enhanced aeration in constructed wetlands

Abstract

In this research, constructed wetlands were applied to remove the nitrogen of lightly polluted wastewater from a wastewater treatment plant in Tangshan. The results showed that a favorable removal effect of nitrogen could be obtained through constructed wetland. Moreover, the aeration device added to the bottom could increase the removal rates of ammonia nitrogen in lightly polluted wastewater, but the removal of total nitrogen was not satisfactory under this operational condition. In addition, when the bottom aeration device was added, the optimal operation condition was evaluated by three-dimensional (2D and 3D) contour plots. The results showed that in a horizontal zeolite subsurface constructed wetland (HZSW), the optimal removal rates for ammonia nitrogen (which could reach above 98%) were obtained when the average daily aeration time was about 7-17 h and hydraulic loadings were 0.05-0.20 m3/(m2·d). Meanwhile, the optimal removal rates of total nitrogen could reach 56.40-62.60% when the average daily aeration time was less than 5 h and the hydraulic loadings were less than 0.11 m3/(m2·d). In contrast, in a horizontal limestone subsurface constructed wetland (HLSW) the optimal removal rates of ammonia nitrogen (namely 96.44-97.10%) could be obtained when the average daily aeration time was more than 11 h and hydraulic loadings were about 0.10-0.45 m3/(m2·d); meanwhile, the optimal removal effects of total nitrogen, namely 49.25-55.00%, were obtained when the average daily aeration time was less than 8.5 h and the hydraulic loadings were less than 0.13 m3/(m2·d). In summary, the removal effects of ammonia nitrogen increased obviously and that of total nitrogen were depressed apparently after the bottom aeration device was added.