Alternative methods for determining the percentage regeneration of activated carbon

The percent regeneration (PR) of activated carbon (AC) regenerated under various conditions is frequently assessed via batch equilibrium adsorption (loading) tests followed by regeneration and reloading. Newly developed and existing methods for calculating PR, which are based on different experimental protocols, were assessed. The PRs for methods 1–3 are based on the ratio of the solid phase concentrations (or loadings) obtained using regenerated AC to that obtained using virgin AC. Method 1 requires multiple reloading tests with different initial conditions to estimate the regenerated AC loading in equilibrium with the same liquid phase concentration as the virgin AC. Method 2, which uses identical initial conditions in the adsorption and re-adsorption tests, yields loadings that are in equilibrium with different liquid phase concentrations. Method 3 uses the virgin AC isotherm to calculate the ratio between loadings at the liquid phase concentration reached during the reloading test. Methods 1 and 3 are more correct because they compare isotherm loadings at the same equilibrium liquid phase concentrations. Method 2 should be avoided and the results of studies using it need to be re-evaluated. Methods 1–3 yielded unrealistically high PR values for the control (ineffective regenerations) experiments, because they do not account for contaminant left on the AC. PR4, developed to consider residual contaminant, described the control experiments well and should also be the most appropriate for low-intensity regenerations. Unfortunately, it is impossible to establish a priori the degree of the intensity of a regeneration. In addition, if the regeneration greatly reduces the adsorption capacity of the AC, PR4 will yield nonsensical values, so it must be used with extreme care. A sensitivity analysis showed that, although PR3 is not as consistent as PR4, on average their values are relatively close. For intense regenerations, method 1 is the correct method to evaluate PR; however, it requires more experimental effort than the alternatives. A methodology was proposed for exploratory regeneration research involving many conditions to reduce the experimental effort required to calculate PR so as not to limit the scope of the regeneration study.