Removal of nutrients from treated municipal waste water by wetland vegetation

Abstract

Wildwood, Florida, population approxi mately 2 500, has been releasing secondarily treated wastewater effluent into a mixed hard wood swamp for 20 years. Wild wood is located in the central portion of Florida and is sur rounded by the characteristically low, flat topography of the region. Because this land is often inundated, it is not readily adaptable to development. Natural waterways usually consist of the shallow streams which empty into a wetlands area, which in turn often borders a shallow lake. The swamp into which Wildwood releases its wastewater effluent ex tends about 8 km (5 miles) south of Wildwood and borders Lake Panasoffkee. Prior to and during this study, the Wildwood wastewater treatment facility consisted of a trickling filter plant with a capacity of 950 m3/d (0.25 mgd). However, during the last few years, the plant has not operated properly and the effluent has received little more than primary treatment. At the start of this study a new activated sludge treatment plant was under construction. The Florida Department of Environmental Regulation was concerned that nutrients from the wastewater effluent might reach Lake Panasoffkee, making addition of tertiary treat ment facilities at Wildwood desirable. Recent studies 1?2 have shown that spray irrigation of wastewater effluent is one effective method of water recharge involving a natural system. This process, however, does involve some cost in elaborate transport and distribu tion equipment. In Florida these distribution costs can be reduced by using a wetlands sys tem. Wetland systems are well suited ?For receiving large volumes of nutrient-laden water for two reasons: 1) the wetland system dis perses water from a point source over a large area; 2) the vegetation itself is adapted to filter nutrients from the water. Swamp systems have been reported by Carter 3 to have a very high productivity of 990 to 1 170 g/m2-y. High productivity derives from the swamp's acting as a filter to trap nutrients from the water and store them in plant biomass. The high pro ductivity and filtering functions of swamps are characteristics comparable to a salt marsh.4 Studies done in a North Carolina salt marsh by Marshall5 have shown the effectiveness of nu trient uptake by marsh vegetation receiving municipal wastes. The Spartina biomass in the experimental marsh increased significantly in the area receiving municipal wastewater. Kitchens et alG and Wharton 7 report that river floodplain swamps functioned effectively as a nutrient sink for both urban and agricultural waste.