Advancing Biofiltration Design for Pollutant-Specific Effluent Limits and Enhanced System Longevity
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Biofiltration (aka bioretention with underdrains) has emerged as a preferred stormwater treatment option in many MS4 permits and has been demonstrated to meet many stormwater management goals. However, substantial questions remain about biofiltration design for specific pollutants and site conditions. Additionally, field scale monitoring studies have indicated the potential for export of pollutants from biofiltration, even when carefully designed and constructed to modern specifications.

Prompted in part by these concerns, recent and ongoing research in Washington, California, and elsewhere have begun to reevaluate conventional biofiltration design assumptions and test the performance of innovative designs. Specifically, this research includes surveys and testing of media components, column studies of individual components and combinations, and full-scale design and monitoring projects of innovative systems. Information from these studies, as well as review of past studies in the International Stormwater BMP Database, provides the basis for advancing biofiltration design to achieve higher and more consistent performance for specific pollutant, as well as improving system longevity.

This presentation will provide a summary of recent and ongoing research, including the practical findings that can be transferred to projects in the Pacific Northwest. The discussion will be organized into three primary topics:

(1) Biofiltration media composition: How does media composition influence performance? What are we learning about the unit treatment processes that are effective in biofiltration media, and how can we exploit this knowledge to improve performance? What aspects of media specifications are most important? How can we manage the construction quality issues associated with variability in material supply stocks and differences in material availability by region?

(2) Alternative approaches for controlling system hydraulics: The conventional approach has been to control media contact time by controlling the permeability of the media. What are the advantages and disadvantages of this approach? How could a paradigm shift to an outlet-controlled filtration design with a high rate media mixture improve both longevity and performance?

(3) Role of plants in biofiltration performance and longevity: Vegetation can improve performance and enhance longevity – but it can be costly to install and maintain. What role do plants (and associated symbiotic fungal communities) play in biofiltration operations? Can the absence of plants be mitigated in cases where a non-vegetated design is preferred? In addition to summarizing recent research findings, the presentation will also identify future research needs and provide practical lessons learned from implementing biofiltration, including specifying and acquiring media and working with construction contractors.

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Publication Summary

  • Geosyntec Authors: Aaron Poresky, Eric Strecker, Brandon Steets
  • Title: Advancing Biofiltration Design for Pollutant-Specific Effluent Limits and Enhanced System Longevity
  • Event or Publication: CASQA Conference 2013
  • Practice Areas: Watershed and Stormwater Management, Water and Natural Resources Assessment, Management, and Restoration
  • Date: 2013
  • Location: Tahoe, CA