Performance Data from Model Constructed 

 Wetlands for Wastewater Treatment 



O.R. Stein, J.A. Biederman, P.B. Hook, and W.C. Allen 1 



Abstract 



A study has been initiated to contribute to the development of process-based 

 design approaches for constructed wetlands in cold climates. Eight bench-scale 

 vegetated sub-surface bed wetland cells were placed in the climate-controlled 

 environment of Montana State University's Plant Growth Center. Three each 

 were planted with native cattail and bulrush, while two cells remained unplanted 

 as a control treatment. Since April 1996 the cells have received a stream of 

 synthetic wastewater at a rate of 30 ml/min, resulting in a hydraulic residence 

 time of approximately 5 days. To date, the system has been operated at three 

 separate influent concentrations and at various steady temperatures ranging from 

 4° C to 21° C. Samples drawn from influent and effluent once per residence time 

 have been analyzed for the parameters COD, NH4, P0 4 , and S0 4 . Concentration 

 data are presented as a time series moving average for each water quality 

 parameter. All treatments have displayed 80 to 90% COD removal efficiency at 

 temperatures greater than 12° C. Emergent plants have had significant effects 

 upon ammonia and phosphate removal efficiency. Only planted wetland cells 

 exhibited significant long-term phosphate removal. Substantial sulfate removal 

 was expressed in all treatment types at the higher wastewater strengths. Sulfate 

 treatment efficiency was greatly reduced at the lower strength for planted 

 treatments, attributed to increased oxygenation of the root zone. Due to 

 significant water loss through evapo-transpiration, planted treatments generally 

 display greatly improved removal efficiencies if measured on a mass rather than 

 concentration basis. 



Introduction 



A long-term study has been initiated which will contribute to the 

 development of process-based approaches for designing constructed wetlands 



' Assoc. Prof, and Grad. Res. Asst., Dept. of Civil Engr. and Center for Biofilm Engr.; and Asst. 

 Prof, and Grad. Res. Asst. Dept of Animal and Range Sci.; respectively; Montana State 

 University, Bozeman, MT 59717. 



Stein et al 



