Evaluation of the use of powdered activated carbon for the control of organic compounds during drinking water treatment

Powdered activated carbon (PAC) is commonly used in drinking water treatment plants to control taste and odor, and it is available to remove synthetic organic chemicals (SOCs) that must be controlled to meet drinking water standards. The objective of this study was to show how the adsorptive properties of PAC could more effectively be used in both conventional and unconventional treatment processes to control organic compounds.; A major finding of this study involved the competitive effect of natural organic matter (NOM) on the the adsorption of organic compounds on activated carbon. Isotherm data show that the adsorption capacity of a compound is highly dependent on the initial compound concentration due to the competition of NOM for adsorption sites on the surface of the carbon. The equilibrium carbon capacity at a certain aqueous concentration decreases with decreasing initial organic compound concentration in the isotherm test when the initial NOM concentration is constant. An easy-to-use method was developed in this study to determine the isotherm of an organic compound when present in natural water at any initial concentration. The method approximates the complex mixture of NOM as a single compound referred to as the equivalent background compound (EBC). The initial concentration and single solute isotherm constants of the EBC are solved for based on the NOM's competitive effect on the adsorption of the organic compound on activated carbon, and these data can be used to accurately predict the adsorption capacity for conditions of relevance in operating plants.; The performance of PAC in a floc-blanket reactor (FBR) for the adsorption of TCP, NOM and trichloroethylene (TCE) from natural water was investigated. Laboratory and field data were collected. PAC residence times as high as 30 hrs can be achieved in the floc blanket under laboratory conditions. Comparison of the PAC adsorption capacity in the reactor to the equilibrium adsorption capacity of TCP, TCE, and NOM in central Illinois groundwater and surface water showed that full utilization of the adsorption capacity of the carbon can be achieved with such high residence times. However, the PAC performance has to be compared to an isotherm conducted with an initial SOC concentration comparable to the SOC concentration in the influent to the reactor. This is due to the finding of decreasing isotherm capacity with decreasing initial concentration.