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Constructed Wetlands for Treatment of Swine Wastewater from an Anaerobic Lagoon

Hunt, P.G., Szögi, A.A., Humenik, F.J., Rice, J.M., Matheny,T.A., Stone, K.C.
Transactions of the ASAE 2002 v.45 no.3 pp. 639-647
Juncus effusus, Schoenoplectus americanus, Scirpus validus, Sparganium, Typha angustifolia, Typha latifolia, animal manure management, carbon, clay, constructed wetlands, denitrification, enzyme activity, nitrate nitrogen, nitrates, nitrogen, plant growth, plant litter, planting, sand, swine, swine production, topsoil, wastewater, North Carolina
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 × 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.