Optimizing biomat-water exchange for contaminant attenuation in open water engineered wetlands
|Sharp, Jonathan O.
|Bosworth, Lily B.
|Includes bibliographical references.
|Unit process, open-water wetlands are reproducibly colonized by a benthic microbial mat (“biomat”) which accumulates about 2 cm per year in association with geotextile lining and a shallow (∼30 cm), clear water column. The biomat is stratified with a diffuse photosynthetic layer at the mat-water interface that transitions to a more consolidated anoxic zone within the upper ∼5-10 mm. The strata are interconnected but vary in ecological parameters such as light and oxygen availability, resulting in different microbial niches and contaminant removal capabilities. The overlying water is in constant exchange with the biomat where respiratory processes impact aqueous chemistry in the open water column. Previous work has provided nitrate attenuation rates from the Prado Wetlands in Corona, California. However, biomat accretion and resulting shifts in biomat-water exchange over time were not accounted for, leaving contaminant transfer, attenuation, and transformation between the surface water and biomat poorly constrained. A combination of laboratory batch reactors, flow-through reactors, and a steady-state model was employed for predicting nitrate diffusion and attenuation profiles within the biomat using interconnected physical and biogeochemical parameters. Hydraulic residence time, water content, and oxygen and nitrate attenuation rates from batch and flow-through experiments were applied to the model and together indicated there is little difference in nitrate removal once biomat is thicker than about 2 cm. Pore water chemistry observations from the field and flow-through reactors suggest the model slightly overestimates nitrate profiles, but all methods generally agree that nitrate removal is insignificant about 2 to 3 cm below the biomat surface due to the balance between nitrate diffusion and attenuation rates. Given the biomat accretes over time, deepening our understanding of the relationship between biomat thickness and its influence on biomat-water exchange and nitrate removal can help us balance long-term water treatment performance with wetland management. Our model illustrates the trade-offs between biomat thickness, optimal system performance long-term, and maintenance requirements in engineered wetlands that must be weighed based on the goals of each wetland.
|Colorado School of Mines. Arthur Lakes Library
|2022 - Mines Theses & Dissertations
|Copyright of the original work is retained by the author.
|Optimizing biomat-water exchange for contaminant attenuation in open water engineered wetlands
|Munakata Marr, Junko
|Strathmann, Timothy J.
|Master of Science (M.S.)
|Civil and Environmental Engineering
|Colorado School of Mines