Metal-hydroxide composite filter media for passive nitrogen and phosphorus removal from stormwater

Overview

This solution addresses the challenge of removing nitrogen- and phosphorus-containing anions (nitrate, nitrite, and phosphate) from stormwater runoff using passive filtration. Synthetic metal-hydroxide particles are known for their ability to rapidly capture anionic contaminants, but their small particle size makes them difficult to deploy in practical filtration systems. By tuning particle formulations and immobilizing them within a hydrophilic organic structural network, the resulting composite filter media offers high capacity and fast kinetics for stormwater treatment applications. The selectivity for different anions can be adjusted by modifying the metal composition of the particles.

Technical specifications

Key features:

• Layered crystal structure: The metal-hydroxide particles have a unique structure that makes them essentially "all surface," allowing nearly the entire bulk of the material to be accessible to water and anionic contaminants.
• High sorption capacity and kinetics: Significantly higher number of sorption sites per gram compared to conventional media, enabling faster and more efficient anion capture.
• Tunable selectivity: Anion selectivity can be adjusted by varying the metal composition of the particles.
• Immobilized composite format: Particles are embedded in hydrophilic organic networks, solving the practical challenges associated with fine particle handling and deployment.
• Stable and non-toxic: Materials are stable over a wide pH range and contain only earth-abundant, non-toxic metal cations.

Validation approach:

• Batch sorption experiments using UV-vis spectroscopy to measure anion concentrations before and after particle exposure
• Particle stability monitoring via X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX)
• Screening of multiple organic hydrophilic networks for optimal composite performance
• Single-pass filtration configuration testing to evaluate real-world performance
• Long-term monitoring of composite stability and capacity over time

Technology readiness level

This technology is currently at the proof-of-concept stage. The research team has prior experience with ion-selective sorptive media, as well as the preparation, characterization, and evaluation of metal-hydroxide materials for catalysis applications. The technical risk is considered low because this class of metal-hydroxide materials is known to be amenable to immobilization in organic networks without loss of performance. Future R&D efforts will focus on testing with real wastewater and tuning both the composite and particle formulations specifically for stormwater anion removal applications.