Nitrogen Cycling in Constructed Wetlands as Related to Swine Wastewater G. B. Reddy and Richard Phillips Department of Natural Resources and Environmental Design P. G. Hunt, M. Poach, and Terry Matheny USDA-ARS, Coastal Plains Soil, Water, and Plant Research Center

INTRODUCTION Animal production is a major component of US agriculture for food consumption and nation’s economy NC ranks second in the nation in swine production Managing 42 billion pounds of swine manure per year environmentally friendly is challenging Traditionally swine operators flush the manure from houses into an anaerobic lagoon and spray from the lagoon to the land. Due to continuous application on land, overspills from lagoons, and unexpected hurricanes, the surface and ground water are being contaminated. Many farmers have limited land NC new regulations mandate that lagoons need to be closed and new technologies to treat swine waste need to be implemented in coming years. Of all the technologies available, constructed wetlands are cost effective, passive, easy to maintain, and low cost to operate.

Swine wastewater contains following pollutants: N (total – N, NH4, NO3) P (total –P, Ortho Phosphate) Total solids Suspended solids COD Fecal coliforms

OBJECTIVES To determine N removal rates in MPM constructed wetlands treated with different loads of N in swine wastewater. To investigate denitrification enzyme activity in the marsh sediments of MPM constructed wetlands To determine uptake of N by vegetation To quantify the contribution of NH3 volatilization to the overall N removal of MPM system.

METHODOLOGY

NC A&T State University Swine Unit

Wastewater was flushed in to an anaerobic primary lagoon and overflows into a secondary lagoon

Nitrogen Loading Rates: 5 to 50kg/ha/day Hydraulic loading rate: 7 to 12. 5m3 day

Marsh-Pond-Marsh 75 cm 15 cm 10 m 20 m Inflow Outflow

Wastewater Flow Diagram

Nitrogen Cycle Plants Water Soils Roots/Rhizomes Microbes Volatilization (C & N) Sedimentation and Sorption (5-day BOD, TSS, N & P) Incoming Wastewater Outgoing Wastewater Water Diffusion (N & P) Microbes Sediment/Organic Matter Transformations Soils Roots/Rhizomes

Sampling ISCO 2700 auto samplers were used for sampling on a daily basis combined into weekly composition Six auto samplers were installed. The water sampler combined daily samples into weekly composites. A tipping bucket wired to an electronic totalizer (cycle counter) was installed at the inflow and at the outflow of each wetland cell. Monitoring Equipment Tipping Bucket

Monitoring Equipment

Data Logger

Ammonia volatilization measurements Waste Water Analysis Waste Water Analysis Total-N, NH4 and NO3 were analyzed by using USEPA methods 351.2, 351.2, and 353.1, respectively. Plant Analysis Cattails and bulrushes were sampled in an area of 0.25 m2. The plants were dried at 60 0C for 48 hours or until constant weight obtained, ground and total-N determined by using C-H-N analyzer (Perkin-Elmer model 2400) Ammonia volatilization measurements A special open-ended enclosure was used to measure NH3 volatilization from each section of wetland cell.

Denitrification enzyme activity Sediment samples were collected at the 0-2.5 cm depth from marsh 1 and 2 of each wetland cell. DEA was measured by the acetylene inhibition method (Tiedje, 1994). 10-15 g of field moist sediment was placed in 60 ml serum bottles (five replications). Each bottle received one of the following amendments 5 ml chloramphenicol (1 g /L) 5 ml chloramphenicol with NO3 (200 mg NO3-N/L) 5 ml chloramphenicol with glucose (2 g glucose-C/L) 5 ml chloramphenicol with NO3 and glucose

CALCULATIONS

Weekly N Load Equation L = [(C/106) • F]/Aw Effn = [(Li –Lo)/Li] x 100 Where L = weekly N load (kg ha-1 day-1) C = weekly nutrient concentration of liquid manure (mg L-1) F = weekly average of daily flows of liquid manure (L day -1), and Aw = wetland area (ha) Effn = [(Li –Lo)/Li] x 100 Where Effn = N removal rate (kg ha -1 day -1) Li = mean N load at the inlet (kg ha -1 day -1), and Lo = mean N load at the outlet (kg ha -1 day -1)

Hourly rate of NH3 volatilization equation Va = [ dA • Fd / Ap / D] • [ 1mg / 100mg] Where Va = NH3 volatilization dA = difference in NH3-N captured by outlet and inlet gas- washing bottles in mg, Fd = Air flow through enclosure in L min-1 divided by the air sampling rate of 6 L min-1, Ap = Plot area of 4m2, and D = duration of the test in hours

RESULTS

Nitrogen removal rate vs. N loading rate in M-P-P constructed wetlands

Ammonia volatilization in marsh and pond sections of constructed wetlands. Loaded with different N rates

Denitrification Enzyme Activity (DEA) as Influenced by N Loading Rate

NH3 Volatilization, plant uptake, and % N removal in M-P-M constructed Wetlands. Nitrogen Loaded In Kg ha-1 day-1 Ammonia –N Volatized Marsh-Pond Removed By Plants By Wetlands Nitrogen % 37 11 2.2 18.0 49 31 9 3.0 58 28 8 2.6 15.0 53 17 3 8.0 47 14 1 2.8 57 4 2.0 1.0 25

CONCLUSIONS

Nitrogen removal vs. Nitrogen load Wetlands were less effective in removing N when loaded at > 28 kg ha day. As N load increased, pond sections exhibited a significantly higher rate of NH3 volatilization (p < 0.001) than the marsh sections. Ammonia volatilization was greater than 36 mg NH3-N m2 h, when pond section received greater than 15 kg N ha day. The MPM wetlands are NO3 limited systems. However, partial denitrification existed in the wetlands.

IMPACT This research focused on resolving some fundamental problems in constructed wetlands treated with swine wastewater and finally to provide a low-cost, low operation, and efficient system that small to medium hog operators can use to treat their swine waste. This technology will be environmental and ecological friendly and esthetically appealing. Also, in future we are providing a technology where, farmers not only removing pollutants, but also can recover P to use or sell as fertilizer. Once the whole technology is developed, it will be demonstrated to the hog operators and extension personnel.