The Effect of Plant Harvesting on the Performance of a Free Water Surface Constructed Wetland

Abstract

Upon decomposition, at the end of the summer and during the autumn, Wetland vegetation releases organic carbon into the wetland system. A part of this organic matter remains in the wetland, and is degraded at different rates during the rest of the year. In this study, Municipal wastewater, pretreated in a septic tank and stabilization lagoon, was treated by two surface-flow wetlands. Both wetlands were planted with Typha latifolia with one of the wetlands harvested. Organic matter concentration and nutrients in both harvested and nonharvested wetlands were analyzed from December 2004 until August 2005 (272 days). TKN, NH₄, and TP concentrations were always lower in the effluent of the harvested wetland, indicating nitrogen and phosphorus release by decomposition of vegetation, in the nonharvested system. In addition, harvesting reduced the effluent total suspended solids (TSS) and biological oxygen demand (BOD) concentrations by 37.3 and 49.2%, respectively, when compared to the nonharvested wetland in spring. Seasonal background concentrations (C*) in the wetlands, increased from winter to spring and decreased again in summer. Organic load and nutrients produced per gram of Typha were evaluated by using in situ Typha degradation experiments. Based on the research conducted for this paper, harvesting can be recommended as an operational and management strategy in warm climates and diluted wastewater conditions.