Denitrification in Marsh‐Pond‐Marsh Constructed Wetlands Treating Swine Wastewater at Different Loading Rates

Abstract

Denitrification in constructed wetlands can be very important in the treatment of swine lagoon effluent when land application areas are limited. The objectives of this investigation were to determine (i) the denitrification enzyme activity (DEA) in the marsh sediments of marshpond-marsh (MPM) constructed wetlands, (ii) changes in DEA with additions of carbon and nitrate, and (iii) the response of DEA to different wastewater N loading rates. Swine wastewater was applied to six MPM wetlands located at North Carolina A&T State University, Greensboro, NC, at rates of 4 to 35 kg N ha 21 d 21 . Soil samples were obtained from the top 25 mm of the marsh sections on four dates for determination of DEA via the acetylene blockage method (blocked at N 2 O). Headspace N 2 O was measured via gas chromatography. In the control treatment, they ranged from 0.06 to 1.13 and 0.16 to 0.79 mg N 2 O-N kg 21 soil hr 21 in the first and second marshes, respectively. In both marshes, the DEA rate was significantly increased with the addition of nitrate but not by glucose, indicating that nitrate was a clear limiting factor for denitrification. The DEA in both the control and the amended treatments increased dramatically with increased wastewater N loading, and the increases were generally more pronounced in the first marsh. The DEA values produced in the absence of acetylene blockage did not increase with wastewater N loading rate. Denitrification enzyme activity levels in the marsh sections of the MPM were generally consistent with a highly denitrifying environment. C ONSTRUCTED WETLANDS have been investigated and used for treatment of animal waste in the USA and around the world for over 10 yr (Cathcart et al., 1994;McCaskey et al., 1994). The understanding of their treatment processes, designs, and operations have advanced significantly (Kadlec and Knight, 1995;Knight et al., 2000;Hunt et al., 2002;Stone et al., 2002). Constructed wetlands have been found to generally provide somewhat limited P removal capacities but significant N removal capacities (Knight et al., 2000;Hunt et al., 2002). The effectiveness of N removal has varied considerably with wetland design and loading rates (Poach et al., 2003(Poach et al., , 2004b. Their research indicated that the continuous marsh wetlands were able to treat higher loads of N than the MPM wetlands. Furthermore, the continuous marshes were subject to less ammonia volatilization than the MPM wetlands (Poach et al., 2002(Poach et al., , 2004a.While soil accumulation and plant uptake of N were important at low N loading rates , they were responsible for smaller portions of the removal at higher N loading rates ($10 kg ha 21 d 21) . At the higher loading rates, denitrification became the apparent predominant pathway for N removal. Hunt et al. (2003) reported high levels of DEA in continuous marsh wetlands used to treat swine wastewater. These wetlands had sloped bottoms, and denitrification was higher at the upper slope area where oxygen was more available to facilitate nitrification of ...

Fate of nitrate in seepage from a restored wetland receiving agricultural tailwater

“…DNP measured in this study, ranged from non-detectable to over 15,000 mg NO 3 -N m À2 d À1 (Table 6), which spans the range of DNP rates reported by several studies (Gale et al, 1993;Hunt et al, 2006;Zaman et al, 2008). Average DNP in the main flowpath zone (2437 mg NO 3 -N m À2 d À1 in 10-cm soil depth of N amended treatment) was higher than rates reported from wetlands receiving agricultural runoff in other regions, however, DNP in fingers and uplands (20-104 mg NO 3 -N m À2 d À1 in 10-cm soil depth of N amended treatments) was similar to that in other studies (Xue et al, 1999;Smith et al, 2000;Poe et al, 2003).…”

“…Samples were taken with an auger adjacent to the piezometer sites (n = 12), at depths of 10, 50 and 100 cm, placed on ice upon collection and maintained at 3 C until analysis (<3 days). DNP was measured using the acetylene block technique (Tiedje, 1982;Hunt et al, 2006). Duplicate field moist subsamples (25 g) were placed in 125 mL Erlenmeyer flasks.…”

Denitrification of agricultural drainage line water via immobilized denitrification sludge

“…[21,[24][25][26]36,39] Relative to carbon and nitrogen concentration, all 3 of the methanol:nitrate concentrations (2:1, 10:1, and 20:1) seemed to function adequately. However, pushing the ratio lower could result in either lower denitrification or potentially incomplete denitrification.…”

“…These reaction rates were 10 3 greater than the denitrification rate of floating sludge of constructed wetlands that treated swine wastewater. [36,38,39] They were nearly 10 4 greater than the denitrification of the wetland detritus layer and 10 5 greater than denitrification of the wetland soil. [38] The reaction rate was in the range observed by Tchobanoglous and Burton.…”

Effect of variations in the nitrogen loading rate and seasonality on the operation of a free water surface constructed wetland for treatment of swine wastewater

“…[2,3] Several studies have discussed the effects of variations in the nitrogen loading rate (NLR) and seasonality on the operational efficiency of FWS wetlands. [2,[4][5][6][7] Hunt et al [4] found total nitrogen (TN) removal in a range of 70 to 95% with NLRs between 3.0-36.0 kg TN ha ¡1 ¢d ¡1 , with the highest efficiency levels (>75%) at NLRs below 25.0 kg TN ha ¡1 ¢d ¡1 in a FWS fed with swine wastewater from an anaerobic lagoon. Plaza de los Reyes et al [8] indicated that this type of configuration can only remove between 20.0-40.0% of the applied TN, with a NLR between 7.1-14.3 kg TN ha ¡1 ¢d ¡1 .…”