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Simulation Evaluation of the Effects of Non‐Uniform Flow and Degradation Parameter Uncertainty on Subsurface‐Flow Constructed Wetland Performance
Author(s) -
Grismer Mark E.
Publication year - 2005
Publication title -
water environment research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.356
H-Index - 73
eISSN - 1554-7531
pISSN - 1061-4303
DOI - 10.2175/106143005x73938
Subject(s) - environmental science , flow (mathematics) , residence time distribution , wetland , constructed wetland , subsurface flow , tracer , dispersion (optics) , flow conditions , environmental engineering , residence time (fluid dynamics) , soil science , degradation (telecommunications) , hydrology (agriculture) , mechanics , geotechnical engineering , groundwater , engineering , sewage treatment , ecology , physics , optics , nuclear physics , biology , telecommunications
Although constructed wetland treatment systems have been used in a variety of applications, uncertainty in adequately determining flow conditions or hydraulic residence times (“hydraulic efficiencies”) and degradation model parameters remains a problem with their design. Breakthrough or impulse‐type tracer studies in constructed wetlands often result in residence‐time distributions exhibiting long skewed “tails” suggesting multiple flow channels or perhaps unrealistically large dispersion factors. A fractional‐flow analysis is developed here to quantify possible flow non‐uniformity in a subsurface‐flow constructed wetland and is then used to assess the effects of non‐uniformity and degradation model parameter variability on constituent (for example, chemical oxygen demand) removal. A model application to tracer data developed previously demonstrates how flow non‐uniformity alone can account for significant “tailing” and can be related to even moderate estimated dispersion numbers. From the analysis, it is evident that flow non‐uniformity is of greater concern than decay parameter uncertainty, and that, from a constructed wetland design and operation perspective, every effort should be made to ensure relative flow uniformity across the constructed wetland.