Filter Media Additives for Phosphorus Removal

Design innovations to improve water quality treatment performance of filter media mixtures involve the incorporation of additives to enhance retention of reactive or dissolved pollutants. A number of granular amendments have been demonstrated to improve nutrient removal from discharge water in BMPs such as bioretention systems, stormwater planters, absorbent landscapes, sand filters or green roofs. 
There are two primary processes involved, chemical precipitation and adsorption. Both mechanisms are ultimately finite, but have been shown in some cases to make significant improvements on the discharged water quality over several years. For instance, a two year STEP research study that compared standard bioretention media, to the same media amended with Sorbtive™ in one plot and iron enriched sand (aka red sand) in another showed statistically significant improvements in effluent phosphorus concentrations from the two media amended plots (STEP, 2019)STEP. 2019. Improving nutrient retention in bioretention. Technical Brief. Accessed: https://sustainabletechnologies.ca/app/uploads/2019/06/improving-nutrient-retention-in-bioretention-tech-brief.pdf.
Determining when additive enhanced filter media needs replacing or maintenance represents a new challenge for stormwater asset managers, as there are no suitable visual indicators. Erickson et al. (2018) suggest effluent sampling and laboratory testing to identify when enhanced filter media pollutant retention is waning, or periodic sampling and batch (laboratory) testing of filter media to directly measure its capacity to retain the targeted pollutantsErickson, A.J., Taguchi, V.J., Gulliver, J.S. 2018. The Challenge of Maintaining Stormwater Control Measures: A Synthesis of Recent Research and Practitioner Experience. Sustainability. 2018, 10, 3666. https://www.mdpi.com/2071-1050/10/10/3666 . Periodic replacement of filter media at inlet locations should be considered as an operation and maintenance best practice to maintain treatment performance.
 Filter Media Additives
Material 	Benefits 	Potential concerns
Biochar 	Renewable Enhances soil aggregation, water holding capacity and organic carbon content 	Currently expensive Energy intensive to produce Some sources say ineffective for phosphorus removal
Bold & GoldTM 	Documented total phosphorus removal of up to 71%Hood A, Chopra M, Wanielista M. Assessment of Biosorption Activated Media Under Roadside Swales for the Removal of Phosphorus from Stormwater. Water. 2013;5(1):53-66. doi:10.3390/w5010053.	Proprietary
Iron filings or Zero valent iron (ZVI)	Proven phosphorus retention Retained phosphorus is stable 	May harm plantsLogsdon SD, Sauer PA. Iron Filings Cement Engineered Soil Mix. Agron J. 2016;108(4):1753. doi:10.2134/agronj2015.0427. Removal efficiency declines with increased concentration of incoming phosphorus
Red sand or Iron-enriched sand 	Proven phosphorus removal Also removes TSS 	Poor orthophosphate removal in hypoxic or anoxic conditions
Smart SpongeTM 	Removes phosphorus, as well as TSS, fecal coliform bacteria and heavy metals Non-leaching 	1-3 year lifespan, after which the product is removed as solid waste Proprietary
Sorbtive MediaTM 	High phosphorus removal efficiency 	Proprietary
Water treatment residuals 	Waste product reuse 	Quality control (capabilities depend on source, treatment methods, storage time)
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category: materials
category: Phosphorus
category: Water quality