RECIRCULATION EFFECTS ON TOTAL NITROGEN AND TOTAL PHOSPHORUS REMOVAL IN A FULL-SCALE SUBSURFACE FLOW CONSTRUCTED WETLAND
Abstract (Summary)The main objective of this study was to test effluent recirculation effects on total nitrogen and total phosphorus removal based on concentration and mass in a full-scale subsurface horizontal flow constructed wetland. The wetland treats approximately 4,550 L·d-1 of domestic wastewater from septic tank effluent before it discharges to a soil adsorption field. Plastic walls were added through the gravel and plant media of the wetland to simulate five independent parallel channels for replication. Each channel was designed with an average width of 1.83 m, water depth of 0.61 m, length of 15.15 m, and a porosity of 36.2%. Two of the wetland channels recirculated 42% of the effluent wastewater volume by pumping through a closed loop to the inlet. Removals based on mass were calculated from measurements of flow, precipitation, and weekly nutrient analysis over an 11-week period. Results show that effluent recirculation did not enhance nutrient treatment. Therefore, unamended effluent recirculation alone does not appear to be an effective option for performance enhancement of constructed wetlands. Mass based calculations were better suited for performance assessment because this treatment system did not meet the steady flow assumption implicit in concentration based removal estimates. Significant positive correlations between precipitation and differences between removal calculation methods also indicate that the wetland does not meet the assumption of ideal mixing during precipitation events.
School:University of Cincinnati
School Location:USA - Ohio
Source Type:Master's Thesis
Date of Publication:01/01/2005