Evaluation of the nutrient removal efficiency of a constructed wetland system

In north central Texas, USA, free-water surface wetlands have been constructed\nto treat pre-treated wastewater effluent from the Trinity River. Water quality and\nvegetation data from the first two years of operation (June 2003 to May 2005) were used\nto determine cell-to-cell and system-wide removal efficiency of total suspended solids\n(TSS), total phosphorus (TP) and total nitrogen (TN). The wetland system consisted of\none non-vegetated sedimentation basin and a series of four connected, vegetated wetland\ncells. Temporal analyses displayed varying monthly, seasonal and yearly trends of the\nwetlands’ concentration of the three parameters. Spatial analysis results confirmed that\nTSS, TP and TN concentrations were greater at the beginning of the system as compared\nto the end of the wetland system. Percent reduction analyses showed that the second\nwetland cell (WC2) was the most efficient in TSS, TP and TN removal, while the last\nwetland cell (WC4) had the lowest reduction of the three parameters. TSS removal was\nsignificant (α = 0.05) moving consecutively among the sites in the wetland system, with\nexception to the last wetland cell. TP removal was only significant (α = 0.05) moving\nfrom the third wetland cell (WC3) to WC4, while TN removal was significant (α = 0.05)\nmoving from the sedimentation basin to the first wetland cell (WC1) and then again\nmoving from WC3 to WC4. Overall removal efficiency of the wetland system (from the\nTrinity River to WC4) was quite high, with reductions over 97% for TSS, 47% for TP\nand 67% for TN. N:P ratios decreased moving consecutively throughout the field-scale\nwetlands. Vegetation analyses found WCs 1 and 3 to contain the greatest vegetation\nspecies richness, while WC2 had the lowest richness. The vegetative composition of the\nfour cells was mostly the same. A comparison was conducted between the nutrient reduction efficiency and vegetation data of this wetland system with data from a pilotscale\nwetland system that was operated from 1992 to 2000. The findings of this study\nsuggest that during the first two years of operation, the wetland system’s performance is\ncomparable to the pilot-scale wetlands which were operated for eight years.