Bio-sorption of toxic metals from industrial wastewater by algae strains Spirulina platensis and Chlorella vulgaris: Application of isotherm, kinetic models and process optimization

The present study evaluates the effect of an acidic treatment on the improvement of the percentage removal of toxic metal (%TMrem) from wastewater by algae strains (Spirulina platensis (SP) and Chlorella vulgar (CV)) under different adsorbent dosages (0.2–2.5 g), a pH of (4–8) and contact time (5–100 min). The acidic treatment (Ac-T) altered the functional groups on the surface of algae promoting more electronegative groups and improved the %TMrem of Al, Ni and Cu. Treated SP removed up to 95.0 ± 0.3% (Std. Dev = 0.24), 87.0 ± 0.2% (Std. Dev = 0.34)%, and 63.0 ± 0.3% (Std. Dev = 0.14) of Al, Ni, and Cu at the optimum pH of 5.5, 6.0, and, 7.0 and an adsorbent dosage of = 2.5 ± 0.1 g/L (Std. Dev = 0.14) g/L, respectively. Lower %TMrem of 87.0% ± 0.2 (Std. Dev = 0.09), 79.1 ± 0.4% (Std. Dev = 0.08), and 80.0 ± 0.2% (Std. Dev = 0.04) were achieved with treated CV, respectively. The optimum operational conditions for maximum %TMrem were determined at (Calgae = 4.8 ± 0.2 gMNPs.L−1, Ct = 88 ± 1, and pH = 6) using the response surface methodology (RSM). The adsorption of TMs on algae is endothermic, spontaneous, and follows Langmuir and second-order kinetics. Zeta potential measurements indicated that the adsorption mechanism between the toxic metal (TM) and algal strains is controlled by electrostatic interaction. As such, bio-sorption is a sustainable and efficient technology for the removal of TM from wastewater. [Display omitted] •Acidic treatment (Ac-T) enhanced toxic metal (TMs) removal ability by algae strains.•Ac-T reformed surface functional groups and increased TMs the removal efficiency.•Response surface methodology predicted optimum conditions for maximum %TMrem.•The biosorption mechanism were a combined electrostatic attraction and ion-exchange.•Up to 95% TM removal efficiency was achieved by treated Spirulina platensis.