Competitive Removal of Phenol and 2,4-Dichlorophenol in Biological Activated Carbon System

Effect of type of carbon activation on adsorption and its reversibility

“…This seems to be contrary to an earlier study with another GAC in which it was stated that reversibility of adsorption decreases with carbon dose. 6 In that study, a fixed concentration of adsorbate was used in the preliminary adsorption and the resulting bulk concentrations were smaller at increased carbon doses. However, in our study, in the preliminary adsorption stage of phenol, the initial phenol concentration at the carbon dose of 4000 mg dm −3 was about two times higher than at the dose of 2000 mg dm −3 (Table 4).…”

“…Desorption isotherms were constructed according to a batch-displacement technique. 2,6,7 A known mass of activated carbon (2000 and 4000 mg dm −3 ) was initially contacted with a known concentration of phenol and was agitated until equilibrium was reached, as in adsorption batches. After adsorption equilibration, the supernatant was removed by centrifugation and the sorbate concentration in the supernatant was measured.…”

“…Reversibility of adsorption can be expressed 6 as a degree of hysteresis (w) by using Eqn (6): where 1/n des and 1/n ads are the desorption and adsorption intensities obtained from Freundlich isotherms, respectively. The fact that the 1/n value in desorption isotherms is smaller than the 1/n value in adsorption isotherms implies that desorption is slower 6 or more difficult than adsorption. Hence, it can be stated that the degree of hysteresis is an indicator for adsorption reversibility which is based on the difference between the adsorption and desorption intensities.…”

“…One of them is the high energy bonding of adsorbate molecules to specific functional groups on the active sites of the carbon's surface, resulting in covalent bonding. 6,7 Depending on the type of surface functional group and type of sorbate, a sufficiently strong bond which can resist desorption can be formed. Therefore, chemisorption appears to be the most logical explanation for irreversible adsorption.…”

“…3,5 Such apparent irreversibility is commonly referred to as hysteresis or nonsingularity. 6 Desorbability or reversibility of adsorption is very much related to the type of activated carbon, particularly to the method of activation of the carbon. 7 In biological systems combined with activated carbon, the characteristics of the target compounds are also very important.…”