Palm oil mill effluent sludge ash as adsorbent for methylene blue dye removal

This work was aimed to evaluate the adsorptive nature of palm oil mill effluent sludge ash for methylene blue dye removal in aqueous solution. Two types of palm oil mill effluent sludge collected from different treatment ponds, i.e. anaerobic and biopolishing were burnt to ash, and treated with 5M HCl. The treated and untreated adsorbents were characterized for surface area and morphology. Methylene blue dye adsorption was carried out in laboratory at room temperature, and the adsorption data were analyzed based on equilibrium isotherm and kinetic models. The surface area of ash-adsorbents was found to increase more than 12 times after HCl treatment. The highest surface area recorded was 218 m2/g. Equilibrium data of ash-adsorbents obeyed Langmuir isotherm to linear approximation suggesting the monolayer uptake of methylene blue dye. The highest maximum uptake of 50.7 mg/g methylene blue dye (50% removal) was demonstrated by HCl-treated biopolishing ash-adsorbent at initial concentration of 200 mg/L and pH 5.8 ± 0.1. The kinetic data for selected HCl-treated ash-adsorbent were fitted to Ho’s pseudo-second-order model, indicating chemisorption process. Results showed that ash obtained from palm oil mill effluent sludge after simple treatment with HCl could be employed as effective adsorbent for the removal of methylene blue dye.