Heavy-Metal Removal from Simulated Multimetal Wastewater Using Suspended and Biofilm-Derived Microalgal Biomass: Time Dependence, Dosage Effects, and Biomass Characterization

Heavy-metal contamination from industrial and mining activities poses a persistent environmental challenge. This study compared post-harvested suspended and revolving algal biofilm (RAB)-derived biomass in batch tests with simulated wastewater containing Ni(II), Zn(II), Co(II), and Cr (nominally Cr(III)). The reported profiles showed rapid initial decreases in aqueous metal concentrations. At 16 g/L, the reported biofilm treatment values corresponded to more than 90% Ni removal and more than 95% Co removal. Increasing biomass dosage generally increased apparent percentage removal while decreasing liquid-depletion-based uptake per unit biomass. The linearized kinetic estimates and dosage-dependent model coefficients are treated as descriptive outputs, not as validated model selection or intrinsic adsorption constants. The biofilm sample had a higher reported mean polysaccharide content than the suspended sample; this comparison is descriptive rather than statistically established. FTIR identifies candidate biomass functional groups, and XPS shows Ni-, Co-, and Cr-associated surface signals after exposure, but these observations do not distinguish adsorption from surface-associated precipitation or establish a dominant mechanism. Incomplete operating-condition and harvest records, unverified low-level Zn quantification, and the absence of independently demonstrated control-corrected removal and mass-balance closure limit attribution of the observed differences. The findings provide a preliminary comparison of the tested biomass preparations rather than validation of an intrinsic biosorption advantage or a treatment process.