Kinetic Simulation of Hexavalent Chromium Adsorption on Granular Activated Carbon Columns from Continuous Flow of Water

With regard to the carcinogenic, mutagenic, and pulmonary effects of hexavalent chromium [Cr(VI)] and its impact on the kidney and liver, a study of different methods of its removal from drinking water is essential. In this regard, although the adsorption process has been introduced as an effective method for the removal of chromium, no Iranian study has ever investigated the simulation of the adsorption process with granular activated carbon (GAC) for the removal of Cr(VI) using the Bohart–Adams model. Hence, the aim of the present study was to simulate the kinetics of GAC columns for the adsorption of Cr(VI) from the continuous flow of water.
In this experimental-interventional study, the Bohart-Adams model was used to determine the rate coefficient and adsorption capacity of GAC columns in Cr(VI) removal from aqueous solutions in continuous flow. In this regard, three GAC columns in laboratory scale with bed depths of 31, 45, and 62 cm were operated to treat water containing 20 mg/l Cr(VI) in overflow rates of 1.41, 2.43, and 3.85 ml/cm2.minute. The longevity of columns was considered up to the moment of providing maximum acceptable concentration of chromium in water. Chromium concentration was determined using the standard method of diphenylcarbazide.
Findings: By changing the depth of columns from 31 cm to 62 cm in the overflow rate of 1.41 ml/cm2.minute, the longevity of GAC columns increased from 2.5 hours to 6 hours. By increasing the overflow rate to 3.85 ml/cm2.minute, the longevity of these columns was reduced to 0.5 hour and 1.5 hours, respectively. By changing the overflow from 1.41 ml/cm2.minute to 3.85 ml/cm2.minute, the adsorption capacity of the columns declined from 191.31 mg/l to 148.57 mg/l. This procedure was consistent with the change in adsorption rate coefficient of GAC from 0.005 l/mg.minute to 0.01 l/mg.minute.
GAC columns can be used to treat the continuous flow of water containing 20 mg/l Cr(VI) to the extent of providing the relevant standards.