Use of floating vegetation to remove nutrients from swine lagoon wastewater

Methods are needed to remove nutrients contained within wastewater lagoons. Potential exists for nutrient removal directly from lagoons if vegetation can be grown on floating mats in the lagoon and periodically harvested and removed. Vegetative cover of lagoons may also help reduce odor problems. A study was conducted to determine the feasibility of using floating mats of vegetation on swine lagoon wastewater. Wastewater from the University of Georgia swine wastewater lagoons was pumped to replicated tanks (1285 L) in which floating mats of vegetation were grown. The floating platforms were made of PVC pipe with attached wire screen and fibrous material into which the vegetation was sprigged. Three different wetland species were tested: cattail (Typha latifolia L.), soft rush (Juncus effuses), and maidencane (Panicum hematomon Schult 'Halifax'). Full-strength wastewater, 1/2-strength wastewater, and an inorganic nutrient solution (1/4-strength Hoaglund solution) as a control were tested. The test was conducted as a modified batch process as opposed to a continuous flow through process. The modification was that every two weeks half of the volume of each tank was replaced with the appropriate solution of full-strength wastewater, 1/2-strength wastewater, or 1/4-strength Hoaglund solution so that nutrient concentrations would not be depleted. There were four replicate tanks of each nutrient solution for each wetland species, for a total of 36 tanks. Vegetation from the floating mats was harvested periodically by removing all vegetation above 5 cm of the base of the floating mat. Measurements were made at each cutting of the total biomass per tank, leaf area, and nutrient content (N, P, K) of the vegetative tissue. Growth responses were quite different among the three species. The cattail had tremendous growth during the spring and summer months. The growth rate of the rush was slow for the first year. It then died during summer of 2002 at both the 1/2-strength and full-strength wastewater, indicating that this species is not suitable for growth on floating mats in swine lagoon wastewater. Total nutrient removal by both the cattail and maidencane was primarily a function of total biomass produced. Over the length of the study, on full-strength wastewater, the cattail produced 16,511 g m(-2) biomass and removed 534, 79, and 563 g m(-2) of N, P, and K, respectively, while the maidencane produced 9751 g m(-2) of biomass and removed 323, 48, and 223 g m(-2) of N, P, and K, respectively. Results from this study indicate that potential exists for using floating platforms to grow cattail, maidencane, or possibly other yet to be identified plant species in wastewater lagoons for nutrient removal.