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Muñoz, Peter A.

Civil and Environmental Engineering

2005

MS

This research examines flow patterns of a constructed wetland (CW) for treating dairy wastewater in Vermont (United States). The CW established at the University of Vermont (UVM) dairy farm create a 2x2 factorial design consisting of two wetland cells with vegetation and two cells with forced aeration. Research conducted gives insight into effects that aeration and vegetation have on flow behavior in cold climate conditions. Conservative tracer studies and spatial temperature and dissolved oxygen mapping were employed to examine flow patterns within four different treatment wetlands. Four tracer studies were conducted on cell 1 (TS0: Nov. 13-Dec 7, 2004; TS1: Dec. 7, 2004-Jan. 5, 2005; TS2: Feb 25-Mar 16, 2005; TS3: Apr 22-May 22, 2005). All four tracers studies were conducted on wetland cell 1, while tracer studies TS1 and TS2 were conducted on all four wetland cells. Total of 230 mg of KBr was added to each cell for each tracer study. The results revealed that preferential flow pathways did occur more often in all wetland cells during TS2 cold climate conditions. During this study, preferential flows were more prominent in non-aerated wetland cells (1 and 3) indicating that supplemental aeration in subsurface constructed wetlands has potential to decrease clogging and prevent occurrence of preferential flow patterns by increasing temperature and physical mixing. Vegetation while less significant to CW flow patterns contributed as thermal protection during extreme cold climate conditions. A number of variables including pore volume at tracer response periods, number of CTSRs, and man residence time were determined in order to evaluate hydraulic characteristics and behavior of UVM treatment wetlands during the cold winter months. Pore volume at tracer response peak showed to be a better indicator of the preferential flows than the pore volume at center of mass because the elongation of tracer curve tails could skew the mean tracer concentration. Similarly, the volumetric efficiency was a better indicator than volumetric efficiency or number of CTSRs as it is calculated using both parameters. Overall, the use of pore volume in tracer response curves was a valuable tool in research and most useful in comparing multiple wetlands with varying flow rates.