Phycoremediation of heavy metals and resource recovery of rare earth elements using green algae from eutrophic freshwater bodies

Abstract

Biosorption is an emerging and or complementary technology to the conventional treatment methods for industrial wastewater. Biosorption involves the use of dead biological material to sequester inorganics and or organic pollutants. Micro algae have a diversity of algal species found mostly in freshwater bodies of which only a few were investigated for their biosorption potential. This study focussed on the utilisation of green algal sorbents for the recovery of rare earth elements (REE) and removal of heavy metals. The algal samples were collected from Hartbeespoort dam in South Africa and isolated using streak plating method. The pure algal species were identified using molecular methods and found to have 95-98% identities to Chloroidium saccharophilum, Desmodesmus multivariabilis, Scenedesmus acuminutus and Stichococcus bacillaris. Chlorella vulgaris and Chlamydomonas reinhardtii were purchased for comparison purposes. The species were cultured in the laboratory under controlled conditions and dried to obtain dead algal cells for biosorption studies. Adsorption and desorption experiments were carried out to determine the sorption capacity and possible recovery in single metallic studies of lanthanum (La), thallium (Tl) and cadmium (Cd). Kinetic studies were also investigated to determine the potential rate controlling steps that are useful when designing a full scale biosorption process. Surface characterisation of algae was carried out to determine the possible mechanisms involved in biosorption processes. Multi-metallic studies were investigated to better understand the influence of competing ions in the actual environment.