Removal of basic dyes using green macroalga caulerpa lentillifera

Abstract

A macroalga Caulerpa lentillifera was found to have high adsorption capacity for basic dyes. For the sorption of a basic dye Astrazon® Blue FGRL, the adsorption reached equilibrium within the first hour for whole range of concentrations employed in this work (20-1,280 mg l-1). The kinetic data corresponded well with the pseudo second-order kinetic model where the rate constants decreased as initial dye concentrations increased. At low dye concentrations (20-80 mg l-1), an increase in the adsorbent dosage resulted in a higher removal percentage of the dye, but a lower amount of dye adsorbed per unit mass (q). The adsorption isotherm followed both the Langmuir and Freundlich models within the temperature range of 18-70oC. The highest maximum adsorption capacity (qm) was obtained at 50oC. The enthalpy of adsorption was estimated at 14.87 kJ mol-1 suggesting a chemical adsorption mechanism. The results were compared to the sorption performance of a commercial activated carbon. The comparison studies were done using 3 basic dyes, i.e. Astrazon® Blue FGRL, Astrazon® Red GTLN, and methylene blue. The evaluation revealed that the alga exhibited greater sorption capacity than activated carbon for all types of basic dyes. Further investigation showed that the sorption process obeyed the pseudo second order kinetic model. The sorption processes were controlled by both film and pore-diffusion. BDST and Thomas models were used to analyze experimental data from continuous flow study and the model parameters were evaluated. Good agreement of experimental results on breakthrough characteristics with the model prediction was observed. In the study of binary dye mixture, shifts of spectral peaks were observed when the composition of the mixture changed and the area beneath the light absorbance curve corresponded to the quantity of the dyes in the mixture. Then the new, simple analytical method was proposed for the measurement of individual dye component in the mixture of two dyes.