Column optimization of adsorption and evaluation of bed parameters-based on removal of arsenite ion using rice husk.

The objective of this study deals with column optimization of adsorption-based on removal of arsenite ion using rice husk. The parameters affecting the column adsorption study, i.e., influent-concentration, bed depth, and flow rate, were optimized. The range of parameters, i.e., influent-concentration (15-50 mg/L), flow rate (20, 35, 45, and 60 mL/min), and bed depth (15-60 mm), were studied experimentally. Kinetics models Bohart-Adams and Hutchins were studied to measure the amount adsorbed, depth of mass transfer zone, saturated concentration, and time observed at 10% & 90% breakthrough. The percentage amount adsorbed qm enhanced with enhancement in bed depth but got reduced with influent ions concentration and volumetric flow rate. Established model Bohart-Adams and Hutchins equations were used for calculation of mass transfer zone which came out to be 51 mm. An adsorption capacity (qm) of 4.5 mg/g for arsenite ions was achieved at optimum parameter values of 60 mm of bed depth, 20 mL/min volumetric flow rate, and 50 mg/L of influent ions concentration. The adsorption bed parameters were also evaluated using Hutchins and Michaels equations. The column study proved rice husk to be a potential adsorbent for the adsorption of arsenite.

Removal of mercury from water by fixed bed activated carbon columns.

The breakthrough curves for Hg(II) ions on a sample of granulated activated carbon (GAC) and a sample of activated carbon cloth (ACC) are generally S-shaped. The breakthrough time increases with increase in the bed depth but decreases on increasing the hydraulic loading rate (HLR) and the feed concentration. The adsorption of Hg(II) ions increases with HLR and attains a maximum value at HLR around 7m(3)/h/m(2). At low HLR, laminar flow conditions prevail so that the mass transfer takes place across a nearly stationary film of the liquid covering the carbon particles. This high resistance leads to low mass transfer and results in smaller adsorption. On increasing HLR, the interface resistance decreases resulting in an increase in adsorption. Beyond a certain HLR, the rate of adsorption decreases due to decrease in the residence time of the solution within the carbon bed and a lower time available for mass transfer. The adsorption zone parameters of the carbon column have been determined using the carbon bed column data and invoking the mathematical treatment suggested by Michaels. Bed Depth Service Time (BDST) theoretical model has been used to calculate the critical bed depth and the depth of the mass transfer zone. These have been found to be in agreement with the experimental values.