Malachite Green Adsorption Using Industrial Waste Coffee Husk: Isotherm, Kinetic and Response Surface Methodology

Abstract

The industrial waste coffee husk serves as cost-effective adsorbent for malachite green adsorption is investigated. This study investigates the optimisation of malachite green batch system adsorption using industrial waste coffee husk through conventional method and Surface Response Methodology. Two outputs of removal and uptake were examined. In addition, evaluation of result through isotherm and kinetic studies was conducted. The malachite green exhibited 50% removal at 8 mg coffee husk adsorbent and selected optimum conditions were pH 4-6, 60 minutes at concentration of 20 mg/L. The result was better fit to Langmuir and Pseudo-second-order kinetic. The calculated maximum uptake from Langmuir model was 78 mg/g. The isotherm and kinetic studies revealed that the homogeneous monolayer adsorption and the chemisorption is the rate limiting factor. The Surface Response Methodology Box Behnken Design approach generally showed similar trend of observation for removal and uptake of malachite green adsorption. The ANOVA summarized that adsorbent amount and time were significant parameters for removal, but adsorbent amount was the only significant parameter for uptake. The generated equations that had poor regression analysis (r²) and models were lack of fit significantly for removal and uptake of malachite green using industrial waste coffee husk. Furthermore, the predicted versus actual data plot and validation study showed poor findings. Through this study, it is recommended that the conventional method is more reliable than Response Surface Methodology. With respect to high performance in malachite green adsorption, industrial waste coffee husk is a potential cost-effective adsorbent.

Keywords: coffee husk, isotherm, kinetic, malachite green, optimisation, Surface Response Methodology