Systematic Evaluation of Materials to Enhance Soluble Phosphorus Removal Using Biofiltration or Bioswale Stormwater Management Controls

Abstract

Significant environmental impact can be caused by surface runoff when it transports excessive phosphorus (P) to downstream surface waters. Excessive P can cause uncontrolled aquatic plant growth, low dissolved oxygen, and increased fish mortality. Urban stormwater is composed of both dissolved and particulate P fractions in roughly equal proportions. Many stormwater management controls (SMCs) like biofiltration and bioswales can remove particulate P easily through sedimentation and filtration processes, but dissolved P is much harder to remove. These SMCs also contain compost, which is excellent for removing many other pollutants but can decompose and release P. This laboratory study systematically evaluated dissolved P removal efficiency of 40 different adsorptive materials through jar tests and adsorption isotherm kinetics, column tests that emulate biofiltration systems, and channel tests to emulate bioinfiltration swales. The jar tests yielded 12 materials for further testing using complete adsorption isotherms. Seven of these 12 materials were tested extensively in the column studies. The best materials for enhancing P removal in the columns were activated alumina, alum-based water treatment residuals (WTRs), layered double hydroxyl (LDH), and zero-valent iron (ZVI) aggregate, all exceeding 90% P removal. Based on performance, three were chosen for the channel study: activated alumina, alum-based WTR, and ZVI aggregate. Results showed that lower compost content could reduce P leaching but not eliminate it completely, while biochar mixes were highly variable. Replacing half of the compost with an adsorptive material in a conventional bioretention/bioswale system gave good P removal results. The alum-based WTR is recommended in this study because it ranked excellently for all tests performed, and as a waste material, it can be recycled at a low cost.