Atrazine removal by powdered activated carbon in floc blanket reactors

The application of powdered activated carbon (PAC) to upflow floc blanket reactors (FBR) is widely used to reduce the concentration of organic compounds present in drinking water sources. Long carbon retention times can be reached due to the high solids concentrations attainable in the blanket, potentially resulting in organic loadings close to the maximum adsorptive capacity predicted by the isotherm. However, some operating parameters can compromise both carbon retention time and adsorption capacity, leading to poor adsorption performance. The objective of this study was to point out these parameters and to determine whether the carbon capacity determined by the bottle point isotherm test can be used to predict the removal of organic micropollutants by PAC applied in FBRs. For this purpose, a laboratory-scale upflow FBR was used to evaluate the steady-state removal of atrazine spiked in a natural water. The results of this study showed that the PAC was not used at its maximum capacity predicted by batch isotherm experiments, which cannot be attributable to the fact that carbon retention times were lower than 20 h. It is hypothesized that carbon capacity for micropollutants in continuous-flow systems, where the carbon retention time is higher than the hydraulic retention time, is a function of the DOC throughput. This study also showed that carbon retention time decreases with increasing carbon dose, or hydraulic loading rate.