Sugarcane bagasse pith as a low cost adsorbent for the removal of methylene blue from waste water : experimental and modeling study

Abstract

Contamination of water streams due to discharge of dye containing wastewater is a worldwide problem. Adsorption is an effective and efficient method for removing dye stuff from waste water. However high cost of commercial adsorbents limit its use in wastewater treatment. In this study potential of untreated sugarcane bagasse pith as a low cost adsorbent for removal of Methylene Blue (MB); a basic dye, was investigated. Batch experiments were conducted to determine the factors affecting dye removal. Results revealed that the percentage of dye removal depends on adsorbent dosage, initial dye concentration of the solution, solution pH and contact time. Distinctly low MB removal was observed at low solution pH values (<4). At high pH values (4 to 10), high MB removal was obtained and variation of percentage removal with pH was not significant. Equilibrium data fits to Langmuir isotherm and highest dye uptake of 40mg/g was observed. Adsorption rate was very rapid initially and gradually decreased with time. Fixed bed column experiments were performed to study practical applicability and characteristic ‘S’ shape breakthrough curves were obtained. Increase in breakthrough time and bed capacity was observed when the bed height is increased. Fixed bed column data were fitted to Bed Depth Service Time (BDST) model and Yoon Nelson model for different bed heights. In this work, new mathematical model was developed based on film-pore diffusion in non equilibrium conditions to study the dynamics of the column for methylene blue adsorption. Model consists of a system of partial differential equations (PDEs), accounts for the effects of axial dispersion, film-pore diffusion, and external mass-transfer resistances. External mass transfer coefficient calculated using kinetic data obtained from batch experiments was found to be 0.7096 cm min-1 and this valve was used for model calculations. Using the model, effect of bed height and initial concentration on breakthrough curves were predicted. Further, concentration distribution along the radial direction of bagasse particles at different locations of the bed was analyzed. This model was validated using experimental data obtained by fixed bed column experiments.