Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2001
Publication Date: 5/1/2002
Citation: HUNT, P.G., SZOGI, A.A., HUMENIK, F.J., RICE, J.M., MATHENY, T.A., STONE, K.C. CONSTRUCTED WETLANDS FOR TREATMENT OF SWINE WASTEWATER FROM AN ANAEROBIC LAGOON. TRANSACTIONS OF THE AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS. 2002. V. 45. P. 639-647. Interpretive Summary: Currently, there is a substantial worldwide problem in balancing the need for animal agriculture and environmental quality. Traditional methods of recycling animal manures to land for crop production are not always satisfactory because of the large concentration of animals. Yet, distribution of animals requires more land and producers, and it may be insufficient to meet future food needs. Consequently, there is much interest in alternative methods of animal waste treatment. One method is the use of constructed wetlands. They are operationally passive and natural in their processes. Treatment wetlands are constructed on upland sites and maintained by the addition of wastewater. As the wastewater passes through the constructed wetland, it is treated by plant uptake, soil accumulation, and microbiological processes. We studied experimental constructed wetlands in North Carolina for five years. We determined that they were very effective in removing nitrogen at rates as high as 40 pounds per acre per day. We also determined that this removal was primarily by the microbiological processes. At these rates of nitrogen removal, one wetland acre could do the job of 45 acres of traditional cropland treatment. Conversely, we found that the wetlands were not as effective in the removal of phosphorus. However, the wetlands could be augmented with chemical treatment for phosphorus removal. This augmentation could be associated with a nitrogen removal enhancement process called nitrification. Thus, wetlands appear to be an alternative to current waste treatment methods, particularly when used in a total waste management system.
Technical Abstract: Animal waste management is a national concern that demands improved but 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. We used four wetland cells (3.5 m x 33.5 m) with two cells connected in series. One set of cells was planted with bulrushes (Scirpus americanus, Scirpus cyperinus, and Scirpus validus) and rushes (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 cells one and two and at the exit of cell two for both the bulrush and cattail wetlands. Nitrogen was effectively removed at loading rates of 3 to 40 kg/ha/day, but P was not consistently removed, particularly at rates > 4 kg/ha/day. Neither plant growth nor plant litter/soil accumulation was a major factor in N removal after the loading rates exceeded 10 kg/ha/day. However, the soil plant litter matrix was important for denitrification because it and the wastewater provided the carbon and reaction sites for microbial respiration. Soil Eh values were indicative of depleted nitrate-N which was generally absent from the wetlands. Denitrification was found to be limited by nitrate availability according to denitrification enzyme analysis. These results show that constructed wetlands can be very effective in the removal of N from swine wastewater. However, they will need to be augmented with some form of enhanced P removal to be effective in treatment of both P and N.