Activated carbon from pineapple waste biomass for the removal of methylene blue

Abstract

Environmental pollution especially pigment-containing wastewater from industrial sources are of concern nowadays. Conventional treatment techniques are efficient but they are not economically feasible for large-scale application. Utilization of agricultural waste biomass such as from the pineapple (Ananas comosus) industry offers an interesting alternative to remove pigment as it can be converted into activated carbon. In this study, activated carbon was prepared from the pyrolysis (500 oC, 1 hour) of pineapple waste biomass (leaves, stem, crown) impregnated with zinc chloride (ZnCl2). The activated carbon was prepared with different impregnation ratios (50, 100 and 150 wt %) and designated as PLAC A, PLAC B and PLAC C in which the resulting activated carbon with the highest surface area was chosen for subsequent studies. It was characterized for its surface area, surface chemistry, point of zero charge (pH pzc), functional groups, porosity and surface morphology. The dye removal performance of PLACs was investigated using methylene blue (MB) taking into consideration of the following parameters; contact time, initial concentration of MB, pH, temperature and PLAC dosage. In addition, maximum uptake (qmax) of MB by PLACs were determined based on goodness-of-fit obtained from mathematical models, including Langmuir, Freundlich and Redlich Peterson adsorption isotherm models as well as kinetic models (pseudo first order and second order). The adsorption equilibrium data was best fitted with the Langmuir adsorption isotherm with r2 of 0.969 and qmax at 288.34 mg/g. The adsorption kinetics showed two distinct phases of adsorption indicating a pseudo second order reaction at higher MB concentration of 300 to 400 mg/L, and a pseudo first order kinetic model at lower MB concentration of 100 to 200 mg/L. Based on the data obtained, it can be concluded that PLAC B has the highest dye removal capacity due to its properties of high surface area (914.67 m2/g), pH (6.12) and adsorption capacity at 288.34 mg/g. This study has shown that, pineapple waste biomass can be turned into an adsorbent which can be used for dye removal in wastewater.