Development of a high-performance alginate-based composite aerogel for adsorption and recovery of phosphate and nitrate from livestock wastewater

Abstract

Developing efficient technologies to recover valuable nutrients from livestock wastewater can reduce costs and improve environmental impacts of dairy production. Herein, a composite alginate aerogel was fabricated by embedding montmorillonite particles containing cationic cetylpyridinium (MT⁺) using a lanthanum salt as a crosslinker of alginate. The cationic charge density of the aerogel composite (MT⁺@Alg) was further increased by graft polymerizing a quaternary ammonium (QA) vinyl monomer to form MT⁺@QAlg with polycationic structures. The resulting MT⁺@QAlg aerogel, possessing a high BET surface area of 180 m2.g⁻¹ with a uniform porous structure and multiple cationic centers including MT⁺ nanoparticles and polycationic side chains, demonstrated remarkable properties of high adsorption efficiencies and capacities of phosphate (600 mg.g⁻¹) and nitrate ions (800 mg.L⁻¹) within 30 min, good elasticity, and stable composite aerogel structures sustaining 50 compression cycles with only 10 % plastic deformation. The adsorbed phosphate could be extracted with an enrichment factor of 9.5. Furthermore, the MT⁺@QAlg aerogel exhibited superior dynamic adsorption and enrichment performance for phosphate from environmental manure wastewater at a flow rate of 300 mL.min⁻¹. The enhanced adsorption efficiency was attributed to multiple adsorption mechanisms (La-Phosphate complexation, ion exchange and hydrophobic-hydrophobic interactions) which were confirmed through XPS, FTIR, and confocal analyses. The successfully MT⁺@QAlg aerogel shows great promise for applications in separation and recovery of nitrate and phosphate particularly from agricultural wastewater.