Reusable chitosan beads for nitrogen removal in urban stormwater bioretention systems

Overview

Urban stormwater runoff carries complex forms of nitrogen that conventional bioretention systems struggle to remove effectively. This solution introduces porous chitosan biopolymer beads as a supportive treatment layer beneath the ponding or soil zone of a bioretention system. The beads absorb nitrogen and slowly release it during dry periods to support plant growth, creating a more complete nutrient management cycle. Made from waste shellfish products, the beads are fully biodegradable and reusable for many cycles without loss of absorption capacity.

Technical specifications

• Material: Chitosan biopolymer derived from waste shellfish, fully biodegradable
• Nitrogen removal efficiency: 98% in lab tests (60 ppm reduced to 1.3 ppm)
• Phosphate removal efficiency: 99% in lab tests (1.2 ppm reduced to 0.004 ppm)
• Reusability: Validated regeneration capability across many cycles with no diminishing of original capacity
• Integration: Designed as a porous layer beneath the ponding zone or soil layer of existing bioretention infrastructure
• Dual function: Absorbs nitrogen and phosphorus during wet events; slowly releases stored nitrogen to support vegetation during dry seasons

Technology readiness level

The bio-beads have been validated at laboratory scale with various environmental water samples containing high concentrations of nitrogen and solids similar to stormwater runoff. Biodegradability and regeneration performance have been fully characterized. The next validation phase involves engineering a realistic wetland bioretention model incorporating the beads, followed by testing with spiked water samples, contaminated site water, and actual stormwater collected from nearby communities.