Functionalized Waste-Derived Cellulose for Simultaneous Phosphate and Nitrate Recovery from Secondary-Treated Wastewater and Its Repurposing as a Slow-Release Fertilizer

Abstract

Global population growth and urbanization are driving the need for higher agricultural productivity, which necessitates sustainable and efficient nutrient management. Integrating nutrient recovery from wastewater with the reuse in agriculture can be a viable way to save the environment from nutrient-induced eutrophication problems and, at the same time, would help maintain food security by ensuring easy availability of quality nutrients. However, existing approaches have so far not been successful because most focus only on nutrient removal rather than recovery and reuse, thereby creating a gap in the circular nutrient management. In this study, a sustainable solution addressing these challenges was developed by synthesizing a biodegradable polymeric hybrid adsorbent derived from cellulose, which would simultaneously recover nitrate and phosphate from secondary-treated wastewater and then act as a slow-release fertilizer. Waste biomass-derived cellulose nanofibers were cross-linked to form a structural network dispersed with hydrated ferric oxide nanoparticles and functionalized with tributylamine groups to selectively adsorb phosphate and nitrate, respectively. The adsorbent demonstrated adsorption capacities of 10 mg of NO^–₃–N/g for nitrate and 4 mg of PO^3–₄–P/g for phosphate. When a nitrate- and phosphate-saturated adsorbent was applied as a fertilizer, it improved seed germination and plant growth compared to conventional fertilizers by providing a slow-release nutrient source.