Submitted to: Journal of Environmental Science and Health
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/1/2009
Publication Date: 2/10/2010
Citation: Ro, K.S., Hunt, P.G., Johnson, M.H., Matheny, T.A., Forbes, D., Reddy, G.B. 2010. Oxygen transfer in marsh-pond-marsh constructed wetlands treating swine wastewater. Journal of Environmental Science and Health Part A. 45:377-382. Interpretive Summary: Constructed wetlands with marsh plants of cattails and bulrush have been used to treat wastewater from swine lagoons. Some of these wetlands were modified to include an aerated pond in the middle to improve treatment efficiency by increasing the oxygen content of the wetlands. Because of the aeration in the middle ponds, more ammonia was volatilized from these modified treatment wetlands. In order to minimize the ammonia volatilization from the pond surface (and thus reduce the smell), a novel idea was implemented that covered the ponds with wetlands that floated on recycled foam pads. These covered wetlands efficiently removed water quality pollutants without promoting ammonia volatilization. A system analysis of these modified wetlands with both covered and uncovered ponds found that pond aeration was not effective at all for oxygen transfer. This inefficiency was due to shallow depths of the ponds in which aeration devices were installed. In fact, wetlands consisting entirely of the marshes without any ponds effectively removed water quality pollutants and reduced ammonia volatilization.
Technical Abstract: Marsh-pond-marsh (M-P-M) constructed wetlands have been used to treat wastewater from swine anaerobic lagoons. To mitigate undesired ammonia emission from M-P-M, ponds were covered with floating wetlands (M-FB-M). The pond sections of the M-FB-M were covered with floating wetlands consisted of recycled rubber mat on which American bulrush (Schoenoplectus americanus) was planted. Ammonia emissions were measured using a wind tunnel; oxygen transfer efficiencies of the aerated ponds were estimated by conducting the American Society of Civil Engineers (ASCE) standard oxygen transfer tests. Biochemical oxygen demand (BOD) and total nitrogen (TN) loading and escaping rates from each wetlands were used to calculate carbonaceous and nitrogenous oxygen demands. Covering pond water surface with the floating bed slightly decreased oxygen transfer efficiency. The diffused membrane aeration (26.7 kg O2/ha/d) of M-P-M was surprisingly not as effective as plant aeration in marsh (38.9 to 42.0 O2/ha/d). This unusually low oxygen transfer efficiency of the diffused aeration was attributed to its low submergence depth of 0.8 m compared to typical depth of 4.5 m. The wetlands consisting entirely of marsh removed similar amounts of carbon and nitrogen without investing additional equipment and energy costs of aerating ponds in the middle of wetlands.