Synthesis of Green Algal-Based Biochar for Remediation of Arsenic from Contaminated Waters

Abstract

Arsenic (As) contamination of freshwater poses a major global public-health challenge. This study evaluated locally isolated freshwater green macroalgae as a feedstock for producing low-cost biochar for As(III) removal from aqueous solutions. Four filamentous chlorophytes, Basicladia kosterae, Stigeoclonium tenue, Cladophora dalmatica, and Spirogyra fluviatalis, were isolated from the Korang River (Islamabad, Pakistan), cultivated in BG11 medium, and combined in equal proportions to form a composite feedstock. The biomass was pyrolyzed at 500 °C under an N₂ atmosphere to produce composite algal biochar. FTIR analysis revealed O–H, C=O, and aromatic C–H functional groups that may contribute to arsenic adsorption, while XRF analysis indicated a high Fe content (~33 wt%), suggesting a role of Fe-(hydr)oxide phases in arsenic immobilization. Batch adsorption experiments were conducted at a biochar dosage of 10 g L⁻¹ using initial As(III) concentrations of 0.05 to 0.5 ppm and contact times of 12 to 72 h. The highest removal efficiency (88 ± 3.5%) was achieved at 0.5 ppm after 12 h. These findings demonstrate the potential of indigenous freshwater algal biochar as an economical adsorbent for arsenic remediation. Further studies involving BET characterization, arsenic speciation, pH effects, post-adsorption analyses, and column-scale testing are needed to clarify adsorption mechanisms and practical applicability.