Powdered activated carbon (PAC) has been used extensively in the water treatment industry for the removal of organic compounds. Innovative application of PAC to unique water treatment processes has recently increased its usefulness. The use of PAC with ultrafiltration (UF) membranes, collectively called the PAC-UF system, may replace conventional treatment in some situations. The UF membranes remove turbidity, microorganisms, and some organic compounds, while the PAC enhances the removal of organic matter. The application of PAC in a floc blanket reactor (FBR) has also been investigated for the removal of organic matter. The long solids retention time of the blanket allows the PAC to approach equilibrium, which increases the amount of organic matter it can adsorb. The combination of PAC with a FBR and UF membrane, the FBR-PAC-UF process as described in this paper, can decrease the PAC dose to achieve an effluent goal for organic matter. The PAC is first applied to the UF process; the partially spent PAC from the UF is then transferred to the FBR where it tends to equilibrate at the effluent concentration from the FBR. This paper discusses the advantages and feasibility of this countercurrent application of PAC in the FBR-PAC-UF process. Small scale pilot plant experiments were conducted in the laboratory to assess the removal of natural organic matter (NOM) by the FBR-PAC-UF system. A mathematical model of this system was developed to predict the performance of PAC for the removal of dissolved organic carbon (DOC). The model's predictions are compared to experimental results.
