3.2.1. Adsorption isotherms
The adsorption data of PCDD/Fs are shown in Table 2. An increasing dosage of activated carbon could reduce the dioxins concentration to lower levels. As the dosage of activated carbon in-
creases from 0.02 g to 0.51 g, the residual concentration (Ce ) reduces from 9.04 ng/L to 1.38 ng/L for PCDDs, and from 65.36 ng/L to 5.20 ng/L for PCDFs. However, the adsorbed dioxins per gram of
activated carbon (Qe ) decreased significantly. Therefore, it is essential to take both removal efficiencies of dioxins and optimal use of activated carbon into consideration. So, the adsorption isotherms of PCDD/Fs should be investigated. Such adsorption isotherms represent the amount of adsorbed PCDD/Fs per gram of activated carbon (Qe ) as a function of the dioxins concentrations after adsorption (Ce ). The experimental results were modeled by both Henry linear isotherm and Freundlich isotherm (Doretto and Rath, 2013; Foo and Hameed, 2010; Limousin et al., 2007).
The Freundlich isotherm describes non-ideal and reversible adsorption, not restricted to the formation of monolayer (Foo and Hameed, 2010). It is defined by the following exponential equation: