LAB-SCALE SUBSURFACE FLOW CONSTRUCTED WETLANDS FOR NITROGEN REMOVAL FROM MUNICIPAL WASTEWATER

Conventional biological nitrification-denitrification technology is cost prohibitive for small communities. Constructed wetlands have been subjected to considerable research for nitrogen removal. Research findings have shown that constructed wetland nitrification is oxygen-limited, and denitrification is carbon-limited. In this study the effectiveness of two modified lab-scale subsurface flow constructed wetland systems for total nitrogen removal had been evaluated. The wetlands had no net removal of nitrogen when there was no artificial aeration. However, 49–87% total nitrogen removal was achieved when the wetlands were aerated with compressed air. The wetland operated for autotrophic denitrification (Reactor 1) performed very well for all feed concentrations (20, 30, 35 and 40 mg NH4+-N/1) resulting in effluent total nitrogen (TN) less than 8 mg N/1. However, at 40 mg NH4+-N/l feed concentration the effluent NH4+-N was relatively high (2.87 mg N/1). The wetland operated for heterotrophic denitrification with recycling resulted in effluent TN generally greater than 15 mg N/1 (20 mg NH4+-N/1 feed concentration resulted in effluent of 8.29 mg TN/1). The effluent NH4+-N in this reactor was always less than 1 mg N/1 for all feed concentrations except at 40 mg NH4+-N/1 feed concentration when effluent NH4+-N was 1.41 mg/1. Sulfate reduction was targeted in one of the wetlands, and about 50% sulfate removal was achieved in the anaerobic polishing zone. BOD5/SCOD removal was almost 100% under all loading conditions.