Adding PAC to remove DOC

The hybrid process resulting from adding powdered activated carbon (PAC) to ultrafiltration (UF) reactors is being used to remove organic compounds in full-scale drinking water treatment plants. One way to increase the adsorption efficiency of PAC is to add it to continuously stirred tank reactors (CSTRs) or to plug flow reactors installed upstream of the membranes. Additionally, the PAC that is recovered from the membrane backwash can be recycled to a floc blanket reactor (FBR) installed upstream of the PAC/CSTR-UF process. This study developed an adsorption model that predicts the removal of dissolved organic carbon (DOC) in the FBR-PAC/CSTR-UF system. The model was verified experimentally using two commercially available PACs in a laboratory-scale pilot unit. Removal of DOC by coagulation with aluminum salts and adsorption on the recycled PAC in the FBR substantially reduced carbon use. The model was used to assess the effect of various operating parameters on DOC adsorption efficiency and to determine optimal operating conditions.