Using Floating Vegetation to Remove Nutrients from An Anaerobic Swine Wastewater Lagoon.

Methods are needed for utilizing nutrients contained within animal wastewater lagoons.  One potential method for removing nutrients is to have vegetation growing in the lagoon.  A study was conducted from 2005-2007 to determine the feasibility of growing vegetation on floating platforms on a single stage anaerobic wastewater lagoon.  Following prototype testing of different plant species and floating platforms five plant species were selected as having potential for growth on an anaerobic wastewater lagoon.  The platforms selected as most durable for such caustic water were devised in cooperation with Maryland Aquatic Nurseries and Charleston Aquatic Nurseries. The study consisted of four replicated vegetated platforms per plant species placed in completely randomized design on the lagoon.  The plants were Giant Reed (Arundo donox, common bermudagrass (Cynodon dactylon L. Pers.), Tifton 85 bermudagrass (Cynodon dactylon L. Pers.), St. Augustine grass (Stenotaphrum secundatum), and wild millet (Panicum milliaceum).  The platforms were periodically harvested and the biomass was weighed and analyzed for N, P, and K.  Two of the species (Giant Reed and St. Augustine grass) were found to be unsuitable for long-term growth on the wastewater lagoon.  Giant Reed grew well during 2005-2006 but by 2007 most of the platforms were devoid of Reed and there were none to be harvested at the final cutting.  The St. Augustine grass survived on only one of the four floats for the duration of the study, and growth was minimal.  The greatest biomass production (sum of six cuttings) was 0.36 g cm^-2 dry matter from the Tifton 85 bermudagrass.  The common bermudagrass produced a total of 0.32 g cm^-2 dry matter while the wild millet produced a total of 0.31 g cm^-2 dry matter.  Nutrient uptake and removal from the wastewater was primarily a function of biomass produced.  The study showed that plant species exist which can grow and thrive on anaerobic wastewater lagoons on floating platforms while removing N, P, and K from the wastewater.