Enhanced biological desalination by Arthrospira platensis: Role of extracellular polymeric substances in ion adsorption and salt removal

This study investigates the impact of operating conditions on the salt removal efficacy of Arthrospira platensis fresh biomass, highlighting the mechanisms involved in algal biological desalination. The optimal bio-desalination rate of 28.03% was attained with a 20% (v/v) biomass volume, 30 ppt salinity, and a 30-min incubation period. The study emphasizes the significant impact of extracellular polymeric substances (EPS) in enhancing bio-desalination efficiency. Whole-cell treatments resulted in markedly greater decreases in salinity (28.13%) and chloride (27.1%) compared to EPS-reduced cells (2.9% and 5.2%), thus affirming the functional significance of surface-bound EPS. Analysis indicated that EPS has a substantial overall yield (280 mg L^-1), predominantly consisting of carbohydrates and proteins, which offer numerous binding sites for ions. Fourier-transform infrared (FTIR) spectroscopy identified functional groups (hydroxyl, amino, carbonyl, carboxylate, and amides) associated with ion adsorption, while SEM-EDS provided direct visualization of Na⁺ and Cl^- accumulation on the cell surface post-desalination. To further elucidate the adsorption mechanism, equilibrium data were fitted to Langmuir and Freundlich isotherm models; the Freundlich model (R² = 0.93) provided the best fit, indicating favorable heterogeneous, multilayer adsorption consistent with the complex EPS-cell wall architecture. Collectively, these findings demonstrate that intact EPS matrices of A. platensis markedly improve desalination, offering a sustainable approach for saline water treatment and advancing our understanding of algae-based desalination mechanisms.