Role of immobilised Chlorophyta algae in form of calcium alginate beads for the removal of phenol: isotherm, kinetic and thermodynamic study

Abstract

In this work, sodium alginate-immobilised Chlorophyta algae were evaluated for phenol uptake. The algae/alginate bead (AAB) characteristics were analysed by means of BET-BJH, FTIR, and SEM-EDX methods, while the adsorption performance of AABs with respect to phenol removal was investigated using batch studies. The parameters found to affect the biosorption capacity of AABs included pH, contact time, initial phenol concentration, adsorbent dosage, stirring rate, particle size, and temperature, with the optimal operating variables identified as a pH of 6, an initial phenol concentration of 50 mg/L, AAB dosage of 5 g/L, and a 200 rpm stirring rate. The adsorption process in such cases reached equilibrium within 120 min, demonstrating a maximum phenol elimination capacity of 9.56 mg/g at 30 °C. The isotherm and kinetic models used to determine this were evaluated using the Chi-square test (X2), the coefficient of determination (R2), and the value of equilibrium capacity, with results that revealed that the Freundlich isotherm provides the best fit for the relevant equilibrium data, as shown by its high R2 value (0.96) and low X2 value (1.16135); the theoretical data produced by that model were thus closer to the experimental data than that from the Langmuir model. Kinetic analysis showed that the phenol adsorption followed a pseudo-second-order kinetic model. The thermodynamic parameters were thus explored, revealing that the phenol biosorption process is based on spontaneous physisorption with an exothermic reaction due to negative (ΔG°) and (ΔH°) values. The low cost, natural origin, biodegradability, and eco-friendliness of algae/alginate bead sorbents also make them ideally suited for phenol removal in aqueous solutions.