AWWA ACE95080

Pesticide pollution episodes, which typically occur in surface waters during spring runoff, have become a major concern in the production of safe drinking water. Utilities located in member countries of the European Union (EU) face especially strict regulations that limit the concentrations of individual pesticides to 0.1 ug/L and the total concentration of all pesticides to 0.5 ug/L. Granular activated carbon (GAC) filters are often employed as a barrier to abate such pollution. GAC is used either as the primary treatment method or in a polishing step during which pesticides are adsorbed that escaped previous treatment such as powdered activated carbon adsorption and/or advanced oxidation. Often, GAC filters are in service over a period of several years before the GAC is regenerated. During the time of operation, the GAC becomes preloaded with background organic matter (BOM), which results in a decreased removal efficiency of the GAC adsorber for trace organic compounds such as pesticides. To quantify the BOM preloading effect, utilities are interested in performing laboratory tests prior to the spring runoff period to determine whether the remaining GAC life is sufficient to adequately control the anticipated pesticide levels. This study describes the technique for measuring the remaining life of an operating GAC adsorber for pesticides; and makes and validates predictions for the life of fresh GAC and the remaining life of operating GAC columns.