Atrazine removal by powdered activated carbon in floc blanket reactors

The application of powdered activated carbon (PAC) to upflow flee blanket r eactors (FBR) is widely used to reduce the concentration of organic compoun ds present in drinking water sources. Long carbon retention limes can be re ached due to the high solids concentrations attainable in the blanket. pote ntially resulting in organic loadings close to the maximum adsorptive capac ity predicted by the isotherm. However, some operating parameters can compr omise both carbon retention time and adsorption capacity, leading to poor a dsorption performance. The objective of this study was to point out these p arameters and to determine whether the carbon capacity determined by the bo ttle point isotherm test can be used to predict the removal of organic micr opollutants by PAC applied in FBRs. For this purpose, a laboratory-scale up flow FBR was used to evaluate the steady-state removal of atrazine spiked i n a natural water. The results of this study showed that the PAC was not us ed at its maximum capacity predicted by batch isotherm experiments, which c annot be attributable to the fact that carbon retention times were lower th an 20 h. It is hypothesized that carbon capacity for micropollutants in con tinuous-flow systems, where the carbon retention time is higher than the hy draulic retention time, is a function of the DOC throughput. This study als o showed that carbon retention time decreases with increasing carbon dose, or hydraulic loading rate. (C) 2000 Elsevier Science Ltd. All rights reserv ed.