Bioremoval capacity of Co⁺² using Phormidium tenue and Chlorella vulgaris as biosorbents

Microalgae sorbents are microalgae that have the potential to passively bind heavy metals/contaminants to their cellular structures in a process called biosorption. This study investigates the use of two species of microalgae to remove the toxic heavy metal cobalt from aqueous solution. Two microalgae isolates, Phormidium tenue and Chlorella vulgaris, were collected from the Wadi Hanifah Stream in Riyadh, the Kingdom of Saudi Arabia. We determined the capacity of both isolates to bioremove Co⁺² ions and the optimum conditions under which this occurs. The two isolates were additionally characterized by microscopic and Fourier transform infrared spectroscopy (FTIR). In the current investigation, Phormidium tenue removed 94% of Co⁺² under ideal conditions of pH 6, contact duration (30 min), starting concentration (50 mgL⁻¹) and biosorbent dose (1gL^-1); while Chlorella vulgaris removed 87% of Co⁺² under the same parameters except pH 5.5 and contact duration (60 min). Fourier transform infrared spectroscopy (FTIR) confirms the binding of Co⁺² to the biomass, which comprises many of the functional groups. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed some alterations to the shape of algal cells and cellular components for both microalgae studied. In addition, equilibrium study by both Langmuir and Freundlich models was performed to detect the effect of certain equilibrium factors on the capacity of the biosorption mechanism. Finally, Phormidium tenue and Chlorella vulgaris were discovered to be promising microalgae for effective cobalt biosorption in aquatic conditions.