ARS | Publication request: Treatment of Nitrogen in Animal Wastewater Via Constructed Wetlands

Submitted to: Water Environment Federation
Publication Type: Abstract Only
Publication Acceptance Date: March 22, 1999
Publication Date: N/A

Technical Abstract: Swine production is an important part of the US agricultural economy with increased manure management challenges. To solve these challenges, we assessed constructed wetlands (surface flow) in Duplin Co., North Carolina, as part of a USDA Water Quality Demonstration project. They were used for treatment of swine manure effluent after it was treated in an anaerobic lagoon but prior to land application. They consisted of six 3.6-m x 33.5-m cells, in sets of two cells connected in series. The vegetative community of the three systems were: 1) rush and bulrushes, 2) bur-reed and cattails, and 3) soybean grown in saturated-soil culture in one cell connected to a second cell with flooded rice. Nitrogen loading rate during the first year was 3 kg/ha/day but increased to 25 kg/ha/day in the subsequent years. At the lowest loading rate, 94% of the nitrogen was removed; moreover, at the highest loading rate, 80 to 90% was removed. During the growing seasons with N loading <10 kg/ha/day, nitrogen reduction rates were similar between wetland plants and agronomic crops. Wetland plants had a mean above-ground dry matter production of 21 Mg/ha/yr. Rice grain yield was 3.7 Mg/ha/yr, and soybean yielded up to 4.3 Mg/ha/yr. The redox conditions of the wetland soils were highly reducing, generally 100 to -200 mV. Denitrification enzyme assays indicated that nitrate was the limiting factor and that denitrification could be increased by pre-wetland nitrification of wastewater.