Valorization of Pretreated Salvinia molesta Biomass for Ciprofloxacin Biosorption: Kinetic Performance, pH-Dependent Mechanisms, and Circular Economy Implications.

Abstract

The valorization of pretreated waste Salvinia molesta biomass represents a sustainable and circular strategy to address both water contamination and biomass disposal. This study investigated the biosorption performance of pretreated and powdered S. molesta biomass in controlled aqueous solutions of ciprofloxacin (CIP), a widely detected fluoroquinolone antibiotic, under environmentally relevant conditions. The biomass was characterized by a high cell wall fraction (~61%) and moderate protein and polyphenol content, offering a multifunctional surface for biosorption. Batch experiments were conducted to evaluate the effects of pH (4-8) and contact time (up to 60 min) on CIP removal (initial concentration = 1.5 μg/L). The maximum biosorption efficiency (~95%) occurred at pH 6, which aligned with the biomass's point of zero charge ( pHpzc$$ {pH}_p zc $$  = 6.2) and the CIP zwitterionic speciation. Biosorption was rapid in the first 30 min, although equilibrium was rapidly reached within 30 min, consistent with the classical biosorption behavior of dead biomass at low concentrations. The kinetic model followed a pseudo-second-order trend, which was interpreted empirically rather than mechanistically, reflecting surface-controlled adsorption dynamics. Pearson correlations revealed that the protein and polyphenol contents were positively associated (r > 0.85) with biosorption at pH 6-7, highlighting a multi-mechanistic interaction involving electrostatic, hydrogen bonding, and π-π interactions. These findings suggest that S. molesta is a naturally abundant, low-cost biosorbent suitable for decentralized water remediation, particularly in small-scale or proof-of-concept systems using model aqueous matrices, with potential applications in passive treatment units and community-based sanitation systems. Future studies should evaluate isotherm behavior, thermodynamic parameters, and the regeneration potential of the biosorbent to determine scalability under real wastewater conditions.