Photoresponsive polysaccharide materials for urban nutrient recycling

Overview

This solution addresses urban stormwater pollution by capturing valuable nitrogen (N) and phosphorus (P) nutrients before they reach waterways. The technology uses polysaccharide-based hydrogel materials coordinated with metal ions such as iron(III) to passively absorb N and P from flowing runoff. Once loaded with nutrients, the hydrogels can be dehydrated and reused as a slow-release fertilizer, triggered by exposure to light. This dual-function approach turns a waste stream into an agricultural input, supporting circular nutrient management in urban and agricultural systems.

Technical specifications

Key features:

• Fe(III)-alginate hydrogel matrices capture P at approximately 90% uptake in model wastewater and real liquid dairy waste
• Nitrate and ammonia uptake demonstrated at approximately 30% in model and real waste streams, with further optimization planned
• Tunable metal ion composition (Fe(III) combined with other metal ions) adjusts ionic interactions, stability, and nutrient selectivity
• Polysaccharide backbone can be varied (alginate and other polysaccharides) to modify pH stability and uptake performance
• Photoresponsive release mechanism enables nutrient liberation upon light exposure for fertilizer reuse
• Designed for passive operation in flowing stormwater systems without active energy input

Technology readiness level

The technology has been validated in published laboratory studies using model wastewater solutions and real liquid dairy waste, demonstrating high phosphorus capture and moderate nitrogen uptake under passive soaking conditions. Future work will test the materials in model urban runoff streams under controlled flow conditions, evaluate total nutrient loading capacity, and optimize polysaccharide and metal combinations to increase nitrogen removal efficiency toward the 50% target.