Functionalized organosolv lignin grafted with 3-aminopropyltriethoxysilane: A bio-based adsorbent for phosphate recovery from dairy wastewater

Wastewater rich in phosphates and nitrates causes eutrophication and leads to the impairment of freshwater resources. Out of various methods used, adsorption is the immaculate and economical for removing and recovering phosphates and nitrates from wastewater streams in a single-step process. This study explores the potential of bio-based adsorbent, functionalized organosolv lignin [OL], chemically modified by grafting with 3-aminopropyltriethoxysilane [APTES], as an effective bio-based adsorbent [OL-APTES-H+] for phosphate recovery from aqueous solutions and industrial wastewater. The characterization of OL-APTES-H+ was performed using multiple analytical techniques, providing comprehensive information on the material morphology, elemental composition, functional groups, thermal stability, surface charge, and electrokinetic behavior. The adsorption efficiency of OL-APTES-H+ was assessed under varying experimental conditions, including pH, contact time, and initial phosphate concentration. The adsorption capacity of OL-APTES-H+ depended on pH, with different forms of phosphate species being preferentially adsorbed at different pH values. A maximum adsorption capacity of 21.12 mg/g was achieved at pH 5. Kinetic studies indicated that the adsorption process followed a combination of electrostatic interactions, chemisorption and surface interaction, as evidenced by SEM and EDS analyses. XPS results confirm phosphorus incorporation on the adsorbent surface, reinforcing chemisorption. Adsorption isotherm analysis revealed that the data fitted well to the Langmuir isotherm model, suggesting a monolayer adsorption mechanism. The adsorption performance of OL-APTES-H+ was enhanced in the presence of monovalent ions, while a slight reduction in efficiency was observed in the presence of divalent anions. When applied to industrial dairy wastewater, OL-APTES-H+ exhibited phosphate removal efficiencies ranging from 30 % to 58 %. Overall, OL-APTES-H+ demonstrates considerable potential as a bio-based adsorbent for phosphate recovery, effectively mitigating environmental pollution in wastewater bodies and providing an eco-friendly source of phosphates for sustainable agricultural practices.