Competitive adsorption in a ternary system of toxic metals and rare earth elements using Desmodesmus multivariabilis: empirical and kinetic modelling

Abstract

The presence of competing metals in industrial wastewater creates problems of selectivity for binding sites during biosorption of cationic metallic species on microbial cell surfaces. For this reason, modelling of adsorption and uptake of multimetal solutions based on observation of performance of single metal species since this neglects the competition for reactive sites typical in multimetal solutions. In this study, a culture of the green alga Desmodesmus multivariabilis previously isolated from eutrophic freshwater was used as a biosorbent for adsorption/desorption of different metals in a mixed metal solution under varying environmental conditions. The Extended Langmuir Model (ELM) and Combined Langmuir and Freundlich Model (CLFM) were used to evaluate the data from a ternary metallic system. AQUASIM was used for optimization and simulation of kinetic data in ternary systems. The ELM performed better than CLFM with correlation coefficient of approximately 0.99. The highest uptake was observed for thallium with q max = 909.09 mg g−1 in single metal solution. This value was reduced to q max = 77.278 mg g−1 in the presence of other metals which demonstrated the competitive effects of other metal ions in solution. The q max value of lanthanum (La) decreased from 100 in single metals to 71.3 mg g−1 in multimetal solution; whereas, the q max = of cadmium (Cd) decreased from 48.5 to 40.1 mg g−1. Recovery of metals by D. multivariabilis was the highest for La at 90.92% followed by Cd at 90.15%. Competitive inhibition models provided a better insight on the potential for treatment of actual industrial wastewater with varying environmental factors.