SUBSURFACE FLOW CONSTRUCTED WETLANDS TREATING MUNICIPAL WASTE-WATER FOR NITROGEN TRANSFORMATION AND REMOVAL

Research was conducted on pilot-scale, subsurface how constructed wetl and systems treating municipal wastewater. Increasing tile hydraulic r etention time (HRT) from 1.7 days to 4.3 days reduced the mean effluen t NH4 concentration by 2.7 mp N/L. Hydroperiod manipulation caused a 2 .9-mg N/L decrease in effluent NH4. The influent NH4 concentration for the 9-month study period averaged 21 mg N/L. The lowest average efflu ent NH4 concentration observed in single-stage treatment cells was 13 mg N/L. The mean effluent NH4 concentration from the second-stage cell s of two wetland cells in series was 10 ma N/L. During the period from May through September, the second-stage cells produced an effluent NH 4 concentration of 6 mg N/L. A variable-order kinetic model for sizing the second-stage cells of a series system yielded a coefficient of de termination, r(2), of 0.94 for the summer NH4 removal data. The predic ted HRT to reduce NH4 from 20 mg N/L to 5 mg N/L was 3.9 days, if the cells were subjected to cyclic draw and fill.