Determining the actual hydraulic retention time of a constructed wetland cell for comparison with the theoretical hydraulic retention time
Hunt, Brandy Noreen
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The design of constructed wetlands for wastewater treatment is based on the hydraulic retention time, which is the most easily changed operational variable in the design. This can be changed by the flow rate, decaying plant matter, or sludge accumulation, because of changes in volume and depth. A tracer study was conducted to determine the hydraulic retention time for cell one of the Tignall Water Treatment Facility. According to the results of the study, the average hydraulic retention time is approximately 7.7 days which indicates that the hydraulic efficiency of the system is approximately 0.50, which is average according to Persson et al. (1999), but other findings of the study, such as plant density, indicate that the system may be beginning to decline. It is recommended that wetland cell one be drained, dredged, and replanted.