Effect of co-existing parameters on the adsorption of perfluorooctanoic acid (PFOA) on powdered activated charcoal

In this study the adsorption of PFOA on three different commercial Powdered Activated Charcoal (PACs), wood-based, bamboo-based and coconut-shell-based activated charcoals, was explored. The influence of PACs characteristics on adsorption has been evaluated and the presence of oxygen containing functional groups significantly affect the adsorption mechanism. The adsorption equilibrium of PFOA, the initial concentration of 1 mg/L was achieved in 2 hours by the doses of 1.2 g/L of PACs. The effect of pH, adsorbent types, hardness ions and temperature in adsorption efficiency of PAC was investigated by batch experiments. The results of adsorption kinetic showed that PFOA adsorption on PACs fitted better with the pseudo second order model (R2 > 0.9). It elucidated that the adsorption of PFOA on PACs surface comprised of physisorption and chemosorption as a rate-limiting step of PFOA adsorption mechanism. Additionally, the adsorption isotherms models illustrated that the adsorption of PFOA on all PACs was consistent with Langmuir model (R2 > 0.9), showing that the adsorption depends on mono-layer adsorption. The adsorption capacity decreased with an increasing pH for wood-based PAC while bamboo-based and coconut-shell -based PACs increased when the solution pH increase and the adsorption of PFOA was pH dependent. It Could be observed that the adsorption was exothermic process as the association amount of PFOA onto PAC decrease as the temperature went down. The presence of hardness ions hindered the adsorption behavior of PFOA adsorption onto PACs due to the reduction in electrostatic interaction between PFOA and the protonated surfaces of PACs. These conditions, therefore, may enhance or diminish the PFOA adsorption capacity on PACs where the mechanism was mainly controlled and influenced by the electrostatic attraction and hydrogen bonding and other forces such as Van Der Waals forces might also be included. This study showed PAC is a potential absorbent for PFOA removal in engineering application commercially because of its high adsorption capacity and high adsorption kinetics.