Performance of TPP-Crosslinked Nano-chitosan for Simultaneous Nutrient Adsorption in Nutrient-Rich Wastewater

Excessive dissolved nitrogen and phosphorus drive aquatic eutrophication, yet conventional treatments such as biological nitrification–denitrification and chemical precipitation are costly, generate secondary waste, and are not well suited to simultaneous multi-nutrient removal in a single step. Despite growing interest in chitosan-based adsorbents, the competitive adsorption behavior of ammonium nitrogen (NH4+–N), nitrate nitrogen (NO3––N), and phosphate (PO4–P) coexisting in a single matrix has not been systematically evaluated under optimized conditions. This study synthesized nano-chitosan crosslinked with tripolyphosphate (NCS) via ionotropic gelation and evaluated its simultaneous removal of these nutrients from synthetic wet-market wastewater. Physicochemical characterization (FTIR, Transmission Electron Microscopy, Scanning Electron Microscopy, Dynamic Light Scattering, and zeta potential) confirmed stable nanoscale particles with surface properties favorable for ionic interaction. Adsorbent dose (0.05–0.10 g), nutrient concentration (30–90 mg L–1), and contact time (1–3 h) were optimized using Response Surface Methodology; all reduced models were significant (p < 0.001, R2 = 0.950–0.973). Kinetic analysis showed NH4+–N was best described empirically by the PSO model, while NO3––N uptake was slower. Single-solute modified Langmuir qmax values were 50.4, 90.2, and 48.5 mg g–1 for NH4+–N, NO3––N, and PO4–P, respectively; capacities decreased substantially under multi-nutrient conditions due to competitive adsorption, underscoring the need to evaluate adsorbents under both single and multi-solute conditions for realistic performance assessment.