Effect of zeolite addition on bioretention media infiltration and pollutant removal

Lillie Sweeney

Auburn University

Co-Authors: E. Brantley, T. Knappenberger, and J. Shaw

Bioretention cells are depressed landscape features filled with a permeable media designed to address stormwater toxicity in urban settings. A well designed bioretention soil media must consider aspects of both soil physics and soil chemistry to ensure proper infiltration rates are met while removing dissolved and particulate pollutants. Although bioretention cells are traditionally composed of sand, silt, clay, and organic matter, research on the incorporation of alternative materials has gained popularity. Ecolite is an aluminosilicate and microporous soil amendment with the potential to increase the infiltration rate and cation exchange capacity of soil. The purpose of this study was to determine the ability of Ecolite to improve the pollutant removal and infiltration rate of bioretention media. One mixture of 85% sand, 11% fines, and 4% organic matter (ALMIX) by volume was included and modified by replacing the sand with zeolite at 2% (AUMIX2), 10% (AUMIX10), and 20% (AUMIX20) volume. A control of 100% sand was included. Each mixture was placed in four columns, resulting in a total of 20 columns arranged in a randomized complete block design. Synthetic stormwater with known concentrations of zinc, copper, nitrate, ammonium, and phosphorus was applied to the columns in four simulated storm events and the effluent was collected. Metal and phosphorus concentrations of the effluent were measured by inductively coupled plasma mass spectrometry, and nitrogen concentrations were measured by spectrophotometry. The effluent pollutant concentrations were log-transformed and analyzed by analysis of variance in R statistical software. ALMIX had the highest mean removal of phosphorus across all storm events with 97.27% removal, but the outflow concentrations were not significantly different from any mixtures amended with Ecolite. All mixtures had significantly lower outflow phosphorus concentrations than the control (p< 0.001). AUMIX10 and ALMIX had the highest mean removal of copper with 85.95% removal, but there was no significant difference between any of the mixtures’ mean outflow copper concentrations (p= 0.96). ALMIX had the highest mean removal of zinc with 98.13% removal, but there was no significant difference between any of the mixtures’ mean outflow zinc concentrations (p= 0.94). Infiltration and nitrogen data are being analyzed and will be included on the poster. Conclusions drawn from this project will increase the available knowledge of alternative materials in bioretention media and their potential for targeted pollutant removal.

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5 thoughts on “Effect of zeolite addition on bioretention media infiltration and pollutant removal

  1. Thanks for your presentation, Lillie! Well done! So – zeolite is good for removal of ammonium and phosphorus. I personally like to see graphs rather than tables on posters; they appeal to the visual part of my brain.

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    1. Thank you for viewing my work and giving me feedback. Yes, ammonium was significantly reduced in mixtures containing zeolite. However, Alabama’s standard mix was able to remove as much phosphorus as the mixtures containing zeolite, so zeolite did not improve phosphorus removal. I agree that graphs can be easier to visualize, but I thought providing the results in a table would allow me to include more information while utilizing less space. I will consider how this information could be displayed on graphs for when I share this in the future. Thank you!

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  2. Hey there! Thank you for making this presentation, I love bioretention work!
    I may have missed this, but how does using zeolite compare to the normal media in a bioretention in terms of cost?
    Also, who do you hope will utilize the results of this study? (For example, county officials? Community planners?)
    Thank you!

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    1. Hello! Those are great questions, and I believe they tie into each other.
      Cost is absolutely a factor we thought about when designing this research project. Adding Ecolite into a bioretention mixture will certainly increase the cost, and we hoped that the results could be utilized by city planners and stormwater managers to address this. They can use this information and target areas with impaired watersheds and streams rather than including Ecolite in the average bioretention cell.

      Additionally, how much the Ecolite affects the cost of the media depends on many factors.
      1. Of course, the percentage of Ecolite used will affect the cost. For instance, based on the pollutant results of my study, there does not seem to be a need to increase the Ecolite content to 20%. The mixture with 10% Ecolite had a statistically similar concentration of effluent ammonium as the mixture with 20%.
      2. Cost would also depend on the depth of the media, as many states have different recommendations for media depth, and much deeper media would require more Ecolite.
      3. Finally, I want to add that the cost may change depending on how the Ecolite is incorporated. I mixed it in, but it would be interesting to see Ecolite used in a study that breaks the column into multiple layers that are designed to hold and convert specific types of nitrogen, with the end result being a conversion to N2 gas. Only using Ecolite in one layer of the cell to specifically trap ammonium in this manner may reduce the cost.

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      1. Oh that’s so interesting! Thank you very much for explaining this! I especially like your point that the amount of Ecolite added should vary based on management goals– It seems that counties utilizing GI tend to plan for water volume goals, but employ a “one size fits all” strategy for the media layers rather than adapting them to the conditions of that site. I hope that your findings are incorporated into stormwater management considerations!

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