This article synthesizes work done over the past few decades to better understand the removal of organic contaminants by the coagulation process, alone and in combination with other processes. Published data demonstrate that coagulation can substantially reduce the concentration of certain organic contaminants found in drinking water supplies, and that an understanding of the fundamental mechanisms by which coagulation removes organic contaminants facilitates qualitative prediction of the types of contaminants likely to be removed and the effects of process control variables. Data also demonstrate that removal of organic contaminants by coagulation can be influenced by other processes, such as preozonation, and that coagulation can influence the removal of organic contaminants by subsequent treatment processes, such as filtration and activated carbon adsorption.

GAC adsorption and membrane processes offer alternatives to enhanced coagulation for removing NOM.As a result of the anticipated Disinfectants/Disinfection By‐product Rule, there has been increasing emphasis by the water industry on the removal of natural organic matter (NOM) from raw‐water supplies. Three important NOM removal options are coagulation, granular activated carbon (GAC) absorption, and membrane filtration. Of these three processes, coagulation is the most widely used in the water industry. But when coagulation cannot remove adequate concentrations of NOM so that disinfection by‐products can be controlled, other treatment technologies such as GAC and nanofiltration may need to be used Various aspects of each of these technologies are discussed.

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Potential sources of error in evaluating the adsorptive capacity of granular activated carbon (GAC) are identified and discussed, with special attention given to carbon sampling and preparation, preparation of test solutions, and selection of GAC dosages, adsorbate concentration, and equilibration time. Adsorptive capacity can vary with particle size, but data are presented to show that this may not always occur. Heterogeneous solutions require careful selection of GAC dosages and adsorbate concentration, and the data for such solutions require careful interpretation. Model simulations are used to illustrate the importance of closely approaching equilibrium and to estimate the time required to approach equilibrium under various conditions. For large GAC particles and slowly diffusing adsorbates, several years may be required to reach equilibrium. Failure to reach equilibrium can result in a significant underestimation of adsorptive capacity. Pulverizing GAC greatly reduces the time required to reach equilibrium, thus reducing the possibility of biodegradation of the adsorbate.