Abstract:
Thallium (Tl) and Cadmium (Cd) are listed among priority metallic pollutants known to cause irreversible
health effects and easily magnify in the higher trophic levels of the food chain. Micro algae has a diversity of
species found in freshwater bodies but only a few have been explored for their biosorption potential as
compared to macro algae. The study sourced microalgae from eutrophic freshwater body (Hartbeespoort
dam) in South Africa and isolated using streak plating technique. The pure strains were identified using
molecular methods of 18S ribosomal RNA gene (rRNA) as Chlorella vulgaris and Scenedesmus acuminutus.
The pure strains were then cultured in the laboratory and used to determine the adsorption potential and
recovery of Tl and Cd. Equilibrium and kinetic experiments were used to estimate sorption capacity and rate of
reaction respectively. The effect of initial concentration on Cd and Tl adsorption was also studied. The algae
was characterized to determine the active functional groups on the algal surface wall using Fourier Transform
Infra-red spectroscopy (FTIR). From the study, removal efficiency was achieved at 100% for lower
concentrations of ≥ 150 mg/L of Tl. At higher concentrations in a range of 250-500 mg/L Tl, the performance of
Chlorella vulgaris and Scenedesmus acuminutus was still high with sorption capacity (
max q ) of 1000 and
833.33 mg/g respectively. Cd removal was highest for Chlorella vulgaris at
max q of 175.44 mg/g and affinity (
b ) of 0.011 L/g. When compared to other studies on Tl and Cd adsorption, the tested algae showed a
relatively better
max q than most adsorbents. The kinetic studies showed better correlation co-efficient of ≤ 0.99
for Pseudo-second order model (PSOM) than the first order model. Recovery of Tl was achieved highest for
Chlorella vulgaris at 93.26% and Cd was highest for Scenedesmus acuminutus at 91.92% using nitric acid.
The strongest functional groups responsible for Tl and Cd binding on the algal cell wall were carboxyl and
amines. Microalgae from freshwater bodies showed significant potential for Tl and Cd removal/recovery from
industrial wastewater.
