A custom-designed experimental constructed wetland for removal of targeted pollutants during tertiary treatment of wastewater effluent

In cooperation with the City of Iowa City, a 1-acre free water surface experimental constructed wetland was designed and built at the city's South Wastewater Plant to provide information about: the utility of this technology for polishing secondary effluent; construction and maintenance issues; and about the effects of the wetland on the local water table.; The system consisted of four cells, each planted with seven different native hydrophytes and having two open water areas. Chlorinated secondary effluent was delivered using one of two inlet designs: a perforated horizontal pipe; or a 5-foot tall vertical pipe topped with a sprinkler head. Washed limestone or river rock was placed around the inlet in each cell. One part of this study determined if variations in the chemistry of the effluent from different cells could be attributed to the different filter material or to the method of water delivery.; Wetland water quality was monitored from November 1999 through November 2000. Water flow rates and depths were varied to determine if the resulting retention times had any effect on pollutant removal Water parameters measured in the wetland were: carbonaceous biochemical oxygen demand (CBOD), total suspended solids (TSS), nitrate-N, ammonia-N, phosphorus, temperature, pH, zinc, copper, mercury, alkalinity, dissolved oxygen, free and residual chlorine, fecal coliforms, and conductivity. Six groundwater wells were installed in and around the facility for monitoring groundwater elevations. Elevations were monitored biweekly through the study period. Groundwater samples were analyzed for nitrate-N, pH, alkalinity, temperature, chlorine, and Zn.; This system removed nitrate, ammonia, metals, phosphorus, and CBOD, whereas TSS and fecal coliforms, at times, increased through the system. The cell design variations appeared to have made no significant difference in the wetland water quality. Groundwater analysis showed that the water from the wetland infiltrating shallow groundwater was not adversely affecting the groundwater quality, nor causing mounding of the local water table.; The wetland provided new habitat for a variety of mammals, birds, amphibians, and insects and is located in an area where most wetlands had been converted to farmland many years ago.