Plant Growth and Elemental Uptake by Floating Vegetation on a Single-Stage Swine Wastewater Lagoon

Abstract

Methods are needed for utilizing nutrients contained within animal wastewater lagoons. One potential method for capturing nutrients in a useful form is to grow vegetation on the lagoon. A study was conducted from 2005 to 2008 to determine the feasibility of growing vegetation on floating platforms on a single-stage swine wastewater lagoon. Five species were selected from earlier studies as having potential for growth on a commercial swine farm wastewater lagoon: common bermuda grass (Cynodon dactylon (L.) Pers.), Tifton 85 bermuda grass (Cynodon dactylon (L.) Pers.), St. Augustine grass (Stenotaphrum secundatum (Walter Kuntze)), fall panicum (Panicum dichotomiflorum (L.) Michx.), and giant reed (Arundo donax L.). The plants were periodically harvested as needed, and the biomass was weighed and analyzed for N, P, K, Ca, Mg, S, Al, B, Cd, Cr, Cu, Fe, Mn, Mo, Na, Ni, Pb, and Zn. Giant reed and St. Augustine grass were found to be unsuitable for long-term growth on the wastewater lagoon. The greatest biomass production (sum of six cuttings) was 3.6 kg m-2 dry matter from Tifton 85 bermuda grass, followed by common bermuda grass (3.2 kg m-2 dry matter) and fall panicum (3.1 kg m-2 dry matter). All of the plant species accumulated greater than 1000 ppm Na. Nutrient (N, P, and K) uptake and removal from the wastewater with biomass harvesting was primarily a function of biomass produced. The greatest annual uptake and removal of N and P from the wastewater was by Tifton 85 bermuda grass in 2006, where three cuttings of the floating vegetation removed totals of 69 and 25 g m-2 N and P, respectively. Annual uptake and removal of K was greatest by fall panicum, where uptake and removal by three cuttings in 2007 totaled 78 g m-2. In 2008, weeds that had populated the mats were harvested for biomass and elemental uptake. Uptake and total removal of nutrients in two cuttings of the weeds in 2008 was lower than what was observed with the planted species. Total uptake and removal of N, P, and K by the weeds in 2008 was approximately 30, 10, and 30 g m-2. The study showed that plant species exist that can grow and thrive on single-stage anaerobic wastewater lagoons on floating platforms for at least two years while taking up N, P, and K from the wastewater. Harvesting of biomass (which could potentially be used as a soil amendment or as cellulosic feedstock for bioenergy) from floating mats hence could be a mechanism for animal producers to both remove and productively use nutrients contained in the wastewater.