Development and validation of convective -diffusion models to analyse the transient behaviour of a packed bed: Factors influencing aqueous phase adsorption of a bisbiguanide

Chlorhexidine gluconate [CHG] in combination with cetrimide [CET], widely used in various pharmaceutical compositions, is potentially hazardous to aquatic ecosystems. Continuous removal of these compounds using commercial [GAC] and functionalized activated carbons [FACs] in a packed bed column, is reported. Transient forms of convective diffusion models are developed with depletion terms being represented by the first and second-order kinetics. Performance of the packed bed is analysed with varying bed height, flow rate, initial concentrations, and estimated Damkohler numbers. On the basis of minimum value of sum of the squares of residuals [SSQ], it is evident that the second-order model fits better for the removal of CHG and CET by FAC -HF and FAC -NH3, while the first-order model fits better for GAC. Damkohler number increases with a decrease in flow rate for both the compounds. Ratio of Damkohler numbers does not change with flow rate. Irrespec-tive of flow rates, for GAC: Da2(CHG):Da2(CET) & AP; 0.0526; for FAC -HF: Da2(CHG):Da2(CET) =0.30; for FAC -NH3: Da2(CHG):Da2(CET) = 0.0076. Changes in the breakthrough volume (??????????????????,??????????????????), causing the analytes to migrate from the front of the adsorbent bed into the back, are in the order: for CHG: ??????????????????,??????????????????(FAC -HF) > ??????????????????,?????? ?????? ?????? (FAC -NH3) > ??????????????????,??????????????????(GAC); for CET: ??????????????????,?????????????????? (FAC-NH3) > ??????????????????,?????? ?????? ?????? (FAC -HF) > ??????????????????,??????????????????(GAC).