Changes

Another group of studies of bioretention facilities examines nutrient removal of these LID installation, with mixed results. Some facilities have been observed to increase total phosphorus in infiltrated water (Dietz and Clausen, 2005<ref>Dietz, M.E. and J.C. Clausen. 2005. A field evaluation of rain garden flow and pollutant treatment. Water Air and Soil Pollution. Vol. 167. No. 2. pp. 201-208.</ref>; Hunt and Lord, 2006<ref>Hunt, W.F. and W.G. Lord. 2006. Bioretention Performance, Design, Construction, and Maintenance. North Carolina Cooperative Extension Service Bulletin. Urban Waterways Series. AG-588-5. North Carolina State University. Raleigh, NC</ref> ; TRCA, 2008<ref>. Toronto and Region Conservation Authority. 2008. Performance Evaluation of Permeable Pavement and a Bioretention Swale, Seneca College, King City, Ontario. Prepared under the Sustainable Technologies Evaluation Program (STEP). Toronto, Ontario. https://sustainabletechnologies.ca/app/uploads/2013/03/PP_FactsheetSept2011-compressed.pdf</ref>). These findings have been attributed to leaching from filter media soil mixtures which contained high phosphorus content. To avoid phosphorus export, the plant-available (extractable) phosphorus content of the filter media soil mixture should be examined prior to installation and kept between 12 to 40 ppm (see [[Bioretention: Filter media | Filter media]]; Hunt and Lord, 2006). A design option to increase phosphorus removal performance of bioretention is to incorporate [[Additives | additives]] into the filter media bed, either blended into the media or as a layer in the aerobic portion of the filter bed, such as iron filings (i.e., zero valent iron)<ref>Erickson, A.J., Gulliver, J.S., Weiss, P.T. 2012. Capturing phosphates with iron enhanced sand filtration. Water Research. 46(9). 3032-3042. https://www.sciencedirect.com/science/article/abs/pii/S0043135412001728 </ref>, fly ash<ref>Zhang, W., Brown, G.O., Storm, D.E., Zhang, H. 2008. Fly-ash amended sand as filter media in bioretention cells to improve phosphorus removal. Water Environment Research. 80(6). 507-516. https://onlinelibrary.wiley.com/doi/abs/10.2175/106143008X266823 </ref> <ref>Kandel, S., Vogel, J., Penn, C., Brown, G. 2017. Phosphorus Retention by Fly Ash Amended Filter Media in Aged Bioretention Cells. Water. 9, 746. https://www.mdpi.com/2073-4441/9/10/746</ref>, iron (ferric) or aluminum hydroxide-based water treatment residuals (by-product from drinking water treatment)<ref>O'Neill, S.W., Davis, A.P. 2012a. Water treatment residual as a bioretention amendment for phosphorus. I. Evaluation studies. Journal of Environmental Engineering. 138(3). pp 318-327. https://ascelibrary.org/doi/10.1061/%28ASCE%29EE.1943-7870.0000409</ref> <ref>O'Neill, S.W., Davis, A.P. 2012b. Water treatment residual as a bioretention amendment for phosphorus. II. long-term column studies. Journal of Environmental Engineering. 138(3). pp 328-336. https://ascelibrary.org/doi/10.1061/%28ASCE%29EE.1943-7870.0000436</ref>, biochar <ref>Nabiul Afrooz, A.R.M., Boehm, A.B. 2017.  Effects of submerged zone, media aging, and antecedent dry period on the performance of biochar-amended biofilters in removing fecal indicators and nutrients from natural stormwater. Ecological Engineering. 102. 320-330. https://www.sciencedirect.com/science/article/abs/pii/S0925857417301209 </ref> <ref>Mohanty, S.K., Valenca, R., Berger, A.W., Yu, I.K.M., Xiong, X., Saunders, T.M., Tsang, D.C.W. 2018. Plenty of room for carbon on the ground: Potential applications of biochar for stormwater treatment. Science of the Total Environment. 625. 1644-1658. https://www.sciencedirect.com/science/article/abs/pii/S0048969718300378 </ref>, proprietary filter media additives or blends, or by using iron-rich sand in the filter media blend.  Read about a field evaluation comparing the phosphorus retention performance of parking lot bioretention cells featuring iron-rich sand and proprietary reactive media additive (Sorptive P^TM) in the STEP [https://sustainabletechnologies.ca/app/uploads/2019/06/improving-nutrient-retention-in-bioretention-tech-brief.pdf technical brief]<ref>Sustainable Technologies Evaluation Program. 2018. Improving nutrient retention in bioretention. Technical Brief. https://sustainabletechnologies.ca/app/uploads/2019/06/improving-nutrient-retention-in-bioretention-tech-brief.pdf</ref>.  While moderate reductions in total nitrogen and ammonia nitrogen have been observed in laboratory studies (Davis ''et al''., 2001<ref>Davis, A., M. Shokouhian, H. Sharma and C. Minami. 2001. Laboratory . Study of Biological Retention for Urban Stormwater Management. Water Environment Research. 73(5): 5-14.</ref>) and field studies (Dietz and Clausen, 2005<ref>Dietz, M.E. and J.C. Clausen. 2005. A field evaluation of rain garden flow and pollutant treatment. Water Air and Soil Pollution. Vol. 167. No. 2. pp. 201-208.</ref>), nitrate nitrogen removal has consistently been observed to be low. Design innovations to enhance nitrate-nitrogen removal performance of bioretention is an area of active research.  Promising results have been observed from laboratory column and field-scale evaluations of underdrained practices featuring [[Bioretention: Internal water storage |internal water storage reservoirs]] containing mixtures of clear stone aggregate and shredded newspaper or wood chips, which creates low oxygen or anoxic conditions and promotes conversion of nitrate-nitrogen to nitrogen gas via denitrification <ref>Kim, H., Seagren, E.A., Davis, A.P. 2003. Engineered bioretention for removal of nitrate from stormwater runoff. Water Environment Research. 75(4). 335-367. https://onlinelibrary.wiley.com/doi/abs/10.2175/106143003X141169 </ref> <ref> Brown, R.A., Hunt, W.F. 2011. Underdrain configuration to enhance bioretention exfiltration to reduce pollutant loads. Journal of Environmental Engineering. 137(11). 1082-1091. https://ascelibrary.org/doi/abs/10.1061/(ASCE)EE.1943-7870.0000437 </ref> <ref> Wang, C., Wang, F., Qin, H., Zeng, X., Li, X. Yu, S. 2018. Effect of Saturated Zone on Nitrogen Removal Processes in Stormwater Bioretention Systems. Water. 10, 162. https://www.mdpi.com/2073-4441/10/2/162 </ref>.  

Another group of studies of bioretention facilities examines nutrient removal of these LID installation, with mixed results. Some facilities have been observed to increase total phosphorus in infiltrated water (Dietz and Clausen, 2005<ref>Dietz, M.E. and J.C. Clausen. 2005. A field evaluation of rain garden flow and pollutant treatment. Water Air and Soil Pollution. Vol. 167. No. 2. pp. 201-208.</ref>; Hunt and Lord, 2006<ref>Hunt, W.F. and W.G. Lord. 2006. Bioretention Performance, Design, Construction, and Maintenance. North Carolina Cooperative Extension Service Bulletin. Urban Waterways Series. AG-588-5. North Carolina State University. Raleigh, NC</ref> ; TRCA, 2008<ref>. Toronto and Region Conservation Authority. 2008. Performance Evaluation of Permeable Pavement and a Bioretention Swale, Seneca College, King City, Ontario. Prepared under the Sustainable Technologies Evaluation Program (STEP). Toronto, Ontario. https://sustainabletechnologies.ca/app/uploads/2013/03/PP_FactsheetSept2011-compressed.pdf</ref>). These findings have been attributed to leaching from filter media soil mixtures which contained high phosphorus content. To avoid phosphorus export, the plant-available (extractable) phosphorus content of the filter media soil mixture should be examined prior to installation and kept between 12 to 40 ppm (see [[Bioretention: Filter media | Filter media]]; Hunt and Lord, 2006). A design option to increase phosphorus removal performance of bioretention is to incorporate [[Additives | additives]] into the filter media bed, either blended into the media or as a layer in the aerobic portion of the filter bed, such as iron filings (i.e., zero valent iron)<ref>Erickson, A.J., Gulliver, J.S., Weiss, P.T. 2012. Capturing phosphates with iron enhanced sand filtration. Water Research. 46(9). 3032-3042. https://www.sciencedirect.com/science/article/abs/pii/S0043135412001728 </ref>, fly ash<ref>Zhang, W., Brown, G.O., Storm, D.E., Zhang, H. 2008. Fly-ash amended sand as filter media in bioretention cells to improve phosphorus removal. Water Environment Research. 80(6). 507-516. https://onlinelibrary.wiley.com/doi/abs/10.2175/106143008X266823 </ref> <ref>Kandel, S., Vogel, J., Penn, C., Brown, G. 2017. Phosphorus Retention by Fly Ash Amended Filter Media in Aged Bioretention Cells. Water. 9, 746. https://www.mdpi.com/2073-4441/9/10/746</ref>, iron (ferric) or aluminum hydroxide-based water treatment residuals (by-product from drinking water treatment)<ref>O'Neill, S.W., Davis, A.P. 2012a. Water treatment residual as a bioretention amendment for phosphorus. I. Evaluation studies. Journal of Environmental Engineering. 138(3). pp 318-327. https://ascelibrary.org/doi/10.1061/%28ASCE%29EE.1943-7870.0000409</ref> <ref>O'Neill, S.W., Davis, A.P. 2012b. Water treatment residual as a bioretention amendment for phosphorus. II. long-term column studies. Journal of Environmental Engineering. 138(3). pp 328-336. https://ascelibrary.org/doi/10.1061/%28ASCE%29EE.1943-7870.0000436</ref>, biochar <ref>Nabiul Afrooz, A.R.M., Boehm, A.B. 2017.  Effects of submerged zone, media aging, and antecedent dry period on the performance of biochar-amended biofilters in removing fecal indicators and nutrients from natural stormwater. Ecological Engineering. 102. 320-330. https://www.sciencedirect.com/science/article/abs/pii/S0925857417301209 </ref> <ref>Mohanty, S.K., Valenca, R., Berger, A.W., Yu, I.K.M., Xiong, X., Saunders, T.M., Tsang, D.C.W. 2018. Plenty of room for carbon on the ground: Potential applications of biochar for stormwater treatment. Science of the Total Environment. 625. 1644-1658. https://www.sciencedirect.com/science/article/abs/pii/S0048969718300378 </ref>, proprietary filter media additives or blends, or by using iron-rich sand in the filter media blend.  Read about a field evaluation comparing the phosphorus retention performance of parking lot bioretention cells featuring iron-rich sand and proprietary reactive media additive (Sorptive P^TM) in the STEP [https://sustainabletechnologies.ca/app/uploads/2019/06/improving-nutrient-retention-in-bioretention-tech-brief.pdf technical brief]<ref>Sustainable Technologies Evaluation Program. 2018. Improving nutrient retention in bioretention. Technical Brief. https://sustainabletechnologies.ca/app/uploads/2019/06/improving-nutrient-retention-in-bioretention-tech-brief.pdf</ref>.  While moderate reductions in total nitrogen and ammonia nitrogen have been observed in laboratory studies (Davis ''et al''., 2001<ref>Davis, A., M. Shokouhian, H. Sharma and C. Minami. 2001. Laboratory . Study of Biological Retention for Urban Stormwater Management. Water Environment Research. 73(5): 5-14.</ref>) and field studies (Dietz and Clausen, 2005<ref>Dietz, M.E. and J.C. Clausen. 2005. A field evaluation of rain garden flow and pollutant treatment. Water Air and Soil Pollution. Vol. 167. No. 2. pp. 201-208.</ref>), nitrate nitrogen removal has consistently been observed to be low. Design innovations to enhance nitrate-nitrogen removal performance of bioretention is an area of active research.  Promising results have been observed from laboratory column and field-scale evaluations of underdrained practices featuring [[Bioretention: Internal water storage |internal water storage reservoirs]] containing mixtures of clear stone aggregate and shredded newspaper or wood chips, which creates low oxygen or anoxic conditions and promotes conversion of nitrate-nitrogen to nitrogen gas via denitrification <ref>Kim, H., Seagren, E.A., Davis, A.P. 2003. Engineered bioretention for removal of nitrate from stormwater runoff. Water Environment Research. 75(4). 335-367. https://onlinelibrary.wiley.com/doi/abs/10.2175/106143003X141169 </ref> <ref> Brown, R.A., Hunt, W.F. 2011. Underdrain configuration to enhance bioretention exfiltration to reduce pollutant loads. Journal of Environmental Engineering. 137(11). 1082-1091. https://ascelibrary.org/doi/abs/10.1061/(ASCE)EE.1943-7870.0000437 </ref> <ref> Wang, C., Wang, F., Qin, H., Zeng, X., Li, X. Yu, S. 2018. Effect of Saturated Zone on Nitrogen Removal Processes in Stormwater Bioretention Systems. Water. 10, 162. https://www.mdpi.com/2073-4441/10/2/162 </ref>.  

Roseen et al. (2013) conducted both field and laboratory testing on the performance of bioretention cells featuring filter media amended with drinking water treatment residuals (WTR) with low solids content (5-10% solids) as an [[Additives| additive]]. Water treatment residuals were included at 10-15% of the total filter media mix by volume. Amended bioretention cells had median orthophosphate removal efficiencies of 90-99%. A second study found a bioretention design featuring WTR amended filter media and an [[Bioretention: Internal water storage|internal water storage zone]] optimized to remove phosphorus and nitrogen had an orthophosphate removal efficiency of 20% and effluent concentrations below 0.02 mg/L.<ref>Roseen, R.M., Stone, R.M. 2013. Evaluation and Optimization of Bioretention Design for Nitrogen and Phosphorus Removal. U.S. Environmental Protection Agency. https://www3.epa.gov/region1/npdes/stormwater/research/epa-final-report-filter-study.pdf</ref>  LeFevre et al. (2015) present a state-of-the-art review of dissolved stormwater pollutant sources (focusing on nutrients, toxic metals and organic compounds), typical concentrations, and removal mechanisms and fate in bioretention, along with design options to enhance their retention <ref> LeFevre, G.H., Paus, K.H., Natarajan, P., Gulliver, J.S., Novak, P.J., Hozalski, R.M. 2015. Review of Dissolved Pollutants in Urban Storm Water and Their Removal and Fate in Bioretention Cells. Journal of Environmental Engineering. 141(1). https://ascelibrary.org/doi/abs/10.1061/(ASCE)EE.1943-7870.0000876 </ref>.<br>

Roseen et al. (2013) conducted both field and laboratory testing on the performance of bioretention cells featuring filter media amended with drinking water treatment residuals (WTR) with low solids content (5-10% solids) as an [[Additives| additive]]. Water treatment residuals were included at 10-15% of the total filter media mix by volume. Amended bioretention cells had median orthophosphate removal efficiencies of 90-99%. A second study found a bioretention design featuring WTR amended filter media and an [[Bioretention: Internal water storage|internal water storage zone]] optimized to remove phosphorus and nitrogen had an orthophosphate removal efficiency of 20% and effluent concentrations below 0.02 mg/L.<ref>Roseen, R.M., Stone, R.M. 2013. Evaluation and Optimization of Bioretention Design for Nitrogen and Phosphorus Removal. U.S. Environmental Protection Agency. https://www3.epa.gov/region1/npdes/stormwater/research/epa-final-report-filter-study.pdf</ref>  More recently, LeFevre et al. (2015) present a state-of-the-art review of dissolved stormwater pollutant sources (focusing on nutrients, toxic metals and organic compounds), typical concentrations, and removal mechanisms and fate in bioretention, along with design options to enhance their retention <ref>LeFevre, G.H., Paus, K.H., Natarajan, P., Gulliver, J.S., Novak, P.J., Hozalski, R.M. 2015. Review of Dissolved Pollutants in Urban Storm Water and Their Removal and Fate in Bioretention Cells. Journal of Environmental Engineering. 141(1). https://ascelibrary.org/doi/abs/10.1061/(ASCE)EE.1943-7870.0000876 </ref>.<br>

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