T. A. Matheny

Constructed wetlands for treatment of swine wastewater from an anaerobic lagoon

Animal waste management is a national concern that demands effective and affordable methods of treatment. We investigated constructed wetlands from 1993 through 1997 at a swine production facility in North Carolina for their effectiveness in treatment of swine wastewater from an anaerobic lagoon. We used four wetland cells (3.6 U 33.5 m) with two cells connected in series. The cells were constructed by removing topsoil, sealing cell bottoms with 0.30 m of compacted clay, and covering with 0.25 m of loamy sand topsoil. One set of cells was planted with bulrushes (Scirpus americanus, Scirpus cyperinus, and Scirpus validus) and rush (Juncus effusus). The other set of cells was planted with bur–reed (Sparganium americanum)and cattails (Typha angustifolia and Typha latifolia). Wastewater flow and concentrations were measured at the inlet of the first and second cells and at the exit of the second cell for both the bulrush and cattail wetlands. Nitrogen was effectively removed at mean monthly loading rates of 3 to 40 kg N ha –1 day –1 ; removals were generally >75% when loadings were <25 kg ha –1 day –1 . In contrast, P was not consistently removed. Neither plant growth nor plant litter/soil accumulation was a major factor in N removal after the loading rates exceeded 10 kg N ha –1 day –1 . However, the soil–plant–litter matrix was important because it provided carbon and reaction sites for denitrification, the likely major treatment component. Soil Eh (oxidative/reductive potential) values were in the reduced range (<300 mV), and nitrate was generally absent from the wetlands. Furthermore, the wetlands had the capacity to remove more nitrate–N according to denitrification enzyme activity determinations. Our results show that constructed wetlands can be very effective in the removal of N from anaerobic lagoon–treated swine wastewater. However, wetlands will need to be augmented with some form of enhanced P removal to be effective in both P and N treatments at high loading rates.

AMMONIA VOLATILIZATION FROM CONSTRUCTED WETLANDS THAT TREAT SWINE WASTEWATER

Increasingly, large–scale animal production occurs in confinement where large per–unit–area quantities of waste are generated. With the increased scale of production, new environment–friendly technologies are needed to deal with the waste. Constructed wetlands are considered an alternative treatment, but it is not known if volatilization of free ammonia (NH3) governs nitrogen removal in these systems. The objective of this research was to quantify the NH3 volatilization from constructed wetlands that treat swine wastewater. In May and July of 2000, a specially designed enclosure was used to measure NH3 volatilization from constructed wetlands receiving swine wastewater. Laboratory and field calibration tests indicated that the enclosure was effective at measuring NH3 volatilization. Wetland tests indicated that NH3 volatilization was occurring. From average hourly rates, it was estimated that 7% to 16% of the nitrogen load to the wetlands was removed through NH3 volatilization. Although NH3 losses should not be ignored, results indicated that NH3 volatilization was not responsible for removing the majority of nitrogen from the swine wastewater.

Forage Subsurface Drip Irrigation Using Treated Swine Wastewater

The rapid expansion of animal production in the eastern U.S. in the 1990s resulted in large quantities of concentrated animal waste that must be utilized or disposed of in an efficient and environmentally friendly manner. To address these environmental concerns for wastewater utilization, we installed a subsurface drip irrigation system to apply treated swine wastewater effluent for bermudagrass hay production. The overall study objective was to determine the feasibility of using subsurface drip irrigation (SDI) for treated wastewater effluent applications. The specific objectives for the SDI system were to compare bermudagrass hay production using (1) commercial and wastewater effluent for nutrients, (2) two SDI lateral spacings (0.6 and 1.2 m) installed at 0.3 m below the surface, and (3) two irrigation application rates based on calculated evapotranspiration (ETc) requirements (75% or 100%). The two-year study measured hay yields, hay biomass, soil nutrients, and soil water nutrients. The SDI system was successfully operated for two years applying effluent and commercial fertilizer to supply the nutrient requirements of the bermudagrass hay. Bermudagrass hay production for 2004 and 2005 ranged from 5.65 to 14 Mg ha-1. Results from the SDI system indicated no significant differences between the SDI lateral spacings or irrigation application rates. Treatments using wastewater effluent had significantly higher hay yields and significantly higher nutrient biomass removal rates than the commercial fertilizer treatments. Nitrate-N observed in soil water lysimeters increased with depth, indicating the potential for leaching without proper management. Soil nitrogen and carbon were not significantly different for any of the treatments but did vary slightly over the life of the project.

NITRATE-N DISTRIBUTION AND TRENDS IN SHALLOW GROUNDWATER ON AN EASTERN COASTAL PLAINSWATERSHED

Nonpoint source pollution from agriculture has been a major concern, particularly where intensive agricultural operations exist near environmentally sensitive waters. To address these nonpoint source pollution concerns, a Water Quality Demonstration Project (WQDP) was initiated on the Herrings Marsh Run (HMR) watershed in Duplin County, North Carolina. The WQDP was implemented to determine water quality benefits from voluntary adoption of improved management practices. In the WQDP, 84 groundwater monitoring well sites were established on 21 farms selected to represent the major farming practices on the watershed. On the HMR watershed, nitrate-N contamination of groundwater was not a wide spread problem. Seventy-four percent of the groundwater monitoring sites had nitrate-N less than the drinking water standard of 10 mg/L. Mean nitrate-N concentrations were below 10 mg/L on 16 of the 21 farms. Of the four farms with nitrate-N exceeding 10 mg/L, one farm had mean nitrate-N that exceeded 20 mg/L. This farm had an undersized and overloaded swine wastewater spray field. After the spray field was expanded and application rates were reduced, groundwater nitrate-N concentrations declined; but they continued to exceed 20 mg/L. Other farms with swine waste spray fields had mean groundwater nitrate-N concentrations <20 mg/L throughout the study period. Groundwater nitrate-N concentrations under row crops were <10 mg/L on all but two farms. Three of the four farms with nitrate-N concentrations exceeding 10 mg/L were in a subwatershed of the HMR that had the highest concentration of animal waste application and excess nitrogen applied. Of the 21 farms, three farms had a significant increasing trend in groundwater nitrate-N while four farms had a significant decreasing trend. The overloaded swine wastewater spray field had a significant decreasing nitrate-N trend. Most farms with concentrations less than 10 mg/L had no detectable trend in nitrate-N concentration during the study. These findings indicate that nitrate-N contamination of groundwater is not a widespread problem on the HMR watershed even though it is intensively farmed.

Oxygen transfer in marsh-pond-marsh constructed wetlands treating swine wastewater

Oxygen transfer efficiencies of various components of the marsh-pond-marsh (M-P-M) and marsh-floating bed-marsh (M-FB-M) wetlands treating swine wastewater were determined by performing oxygen mass balance around the wetlands. Biological oxygen demand (BOD) and total nitrogen (TN) loading and escaping rates from each wetland were used to calculate carbonaceous and nitrogenous oxygen demands. Ammonia emissions were measured using a wind tunnel. Oxygen transfer efficiencies of the aerated ponds were estimated by conducting the ASCE standard oxygen transfer test in a tank using the same aeration device. Covering pond water surface with the floating bed slightly decreased oxygen transfer efficiency. The diffused membrane aeration (26.7 kg O2 ha-1 d-1) of M-P-M was surprisingly not as effective as plant aeration in the marsh (38.9 to 42.0 kg O2 ha-1 d-1). This unusually low oxygen transfer efficiency of the diffused aeration was attributed to its low submergence depth of 0.8 m compared to typical depth of 4.5 m. The wetlands consisting entirely of marsh removed similar amounts of C and N without investing additional equipment and energy costs of aerating ponds in the middle of wetlands.

Swine Lagoon Wastewater Treatment in Marsh-Pond/Floating Wetland-Marsh Constructed Wetland

Constructed wetlands have been used effectively to reduce the mass loads of organic and nutrient components from swine anaerobic lagoons. Continuous marsh wetlands with gentle slope and intermittent flows seem to be the best for promoting oxidation and minimizing ammonia volatilization. However, the pond section of the marsh-pond-marsh section could potentially be effectively aerated by mechanical means or plant root transport from selected wetland plants. The objective of this research was to determine if covering the pond section with floating wetland vegetation could enhance nitrogen cycling, reduce ammonia volatilization, and lower estrogenic levels. Marsh-pond-marsh wetlands were retrofitted with a floating fabric cover containing slots for wetland plant establishment. Both mechanically aerated and naturally aerated conditions were evaluated for estrogenic component removals, ammonia volatilization, and total nutrient removals. Both the covered and uncovered wetlands reduced the estrogenic levels in the swine wastewater. The floating marsh substantially reduced the ammonia volatilization, but it did not promote significantly greater nitrogen treatment than reported for continuous marsh wetlands.

DENITRIFICATION ENZYME ACTIVITY IN SWINE WASTEWATER EFFLUENT OF A NITRIFICATION/DENITRIFICATION TREATMENT SYSTEM

Intensification of swine production in the U.S. and around the world requires advanced manure management. For swine manure management in the state of North Carolina, one system met all of the required advanced management criteria, and it was qualified as an environmentally superior technology. This investigation was part of the testing for this superior technology. The objectives of this investigation were to assess: (1) the denitrification enzyme activity (DEA) in the treatment system’s homogenization tank and denitrification tank, and (2) the impact of the wastewater characteristics on this DEA. The DEA was measured by the acetylene inhibition method. Wastewater in the homogenization tank was fresh-flushed directly from the swine houses. Consequently, it was more concentrated than wastewaters in either the denitrification tank or typical swine wastewater lagoons; it had soluble biochemical oxygen demand (sBOD) of 676 mg L-1 and an electrical conductivity (EC) of 8.9 mS cm-1. However, the DEA in the homogenization tank was significantly limited by the low level of NO3-N, which was 0.1 mg L-1. Conversely, the DEA of the denitrification tank was limited by its lower level of carbon; it had only 53 mg L-1 sBOD. However, it had a NO3-N concentration of 150 mg L-1. When non-limiting glucose-C and NO3-N were added to the wastewaters of the homogenization and denitrification tanks, the homogenization tank had a significantly higher level of potential DEA: 17,943 vs. 10,055 mg N2O-N m-3 d-1, respectively. The DEA was generally well correlated by stepwise regression to the measured physiochemical characteristics. The findings of this investigation document that the DEA within this treated swine wastewater can be altered by manageable constituents of the processed swine wastewater, in particular soluble carbon and oxidized nitrogen.

Ammonia and Greenhouse Gas Emissions from Constructed Wetlands Treating Swine Wastewater

Ammonia and greenhouse gas emissions from marsh-pond-marsh constructed wetlands treating swine wastewater were measured with closed-chamber technique using a photoacoustic multigas analyzer. Theory behind the technique was discussed and the technique was demonstrated with actual field data. Nitrous oxide emission was negligible for all three constructed wetlands. Methane readings were not reliable due to the interference caused by the moisture and other short hydrocarbons in the PVC chamber headspace. Ammonia volatilization rates of different sections varied from 0.64 to 1.6 kg-N/ha/d, which compared well with the values obtained from previous wind tunnel studies. Carbon dioxide emission rates varied from 10.9 to 56.9 g/m2/d.