Bioremediation of toxic metals and recovery of target metals from actual wastewater using Algal sorbents

Abstract

The use of biological material is an emerging and environmentally friendly technology with great prospects to effectively clean up toxic metals at low concentrations and possible recovery for re-use in industry. The living biomass accumulates high levels of metals but possible recovery without cell disruption seems almost impossible. Biosorption is a term often used to refer to the treatment of wastewater containing heavy metals using dead biomass. This study utilised algal samples collected from a eutrophic dam and isolated pure strains for use in biosorption experiments. Two species Chlorella vulgaris and Chlamydomonas reinhardtii were identified and tested for their ability to remove and or reduce the concentration of metals in simulated and industrial wastewater. The algal species were initially tested for their biosorption potential for removal/recovery of Lanthanum (La) and Thallium (Tl) in single metallic studies. In addition, test algae was characterised before and after adsorption using Surface Electron Microscope (SEM). Chlamydomonas reinhardtii showed the highest sorption capacity (qmax) of 143 mg/g compared to Chlorella vulgaris with a qmax of 75 mg/g for removal of La. Both species showed a similar qmax for removal of Tl at 1000mg/g but Chlamydomonas reinhardtii had a higher affinity (b) of 1.67 L/g. Wastewater from the mine beneficiary plant showed complete removal of Cobalt from an initial concentration of 0.316 mg/L by C. vulgaris. Industrial water from smelter clave tailings showed Tl as the highest heavy metal concentration of 2.386 mg/L which was reduced to 0.021 mg/L using C. vulgaris. Potassium was reduced significantly by C.reinhardtii from 2036 to 744.7 mg/L. Smelter return water had the highest level of Cr at 135.56 mg/L and was reduced to 45.67mg/L by C.vulgaris. The tested algal sorbents showed potential for the treatment of actual wastewater with the best adsorbent performance from C. vulgaris.