ARS | Publication request: DENITRIFICATION IN CONSTRUCTED WETLANDS USED FOR SWINE WASTEWATER TREATMENT

Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: October 21, 2001
Publication Date: N/A

Technical Abstract: Constructed wetlands are useful for treating nitrogen in swine wastewater. Their predominant treatment mechanism is denitrification, when the nitrogen loading rates are high (>10 kg N/ha/day). Consequently, it is important to better understand denitrification function in these constructed treatment wetlands. In a study at North Carolina A&TSU, six marsh-pond-marsh wetland cells were loaded with 50, 41, 32, 23, 14, or 5 kg N/ha/day. Denitrification was highest (5.4 g N m**2/day) with the 32 kg N/ha/day loading rate. Denitrification potential was highest (6.9 ug N g/soil/hour) at the 50-kg N/ha/day loading rate. In a separate study on continuous marsh wetlands in Duplin Co., NC, partially nitrified swine wastewater ( approx. 140 mg NO3-N/L and 100 mg NH4-N/L) was applied to one wetland and untreated swine wastewater (approx. 240 mg NH4-N/L) was applied to a second wetland. All of the applied NO3-N was removed within the first 3 m of the first wetland. However, even after 33 m, 25% of the applied NH3-N remained in the second wetland. Denitrification was higher with the floating sludge layer (72 ug N g/sludge/hour) than with the wetland soil (0.5 ug N g/soil/hour) or the detritus layer (4 ug N g/detritus/hour). Denitrification potential of the floating sludge was similar to that of denitrifying bacteria immobilized in polyvinyl alcohol pellets (34 ug N gm/pellet/hour).