Adsorption Equilibria of Natural Organic Matter After Ozonation

The equilibrium adsorption behavior of natural organic matter (NOM) subjected to coagulation and various levels of ozonation and biostabilization was investigated in benchscale experiments. The overall adsorbability of NOM increased with coagulation but decreased if coagulation was followed by ozonation and biostabilization. Without adsorption, ozonation was shown to enhance the biodegradability of coagulated NOM, up to 46 percent of total organic carbon was removed at the highest ozone dosage. The adsorption of NOM was described quantitatively by accounting for competitive adsorption among pseudocomponents and by applying concepts of polymer adsorption. Neither approach was entirely satisfactory for obtaining a systematic relationship between adsorbability and ozone dosage. Granular activated carbon (GAC) ad- contaminant level (MCL)for total THMs sorbers are considered a best available and the addition of MCLs for SOCs and technology for many synthetic organic disinfection by-products will increase chemicals (SOCs) and, as noted in the the use of GAC adsorbers in drinking Code of Federal Regulations, are consid- water treatment. At the same time, more ered suitable for the removal of trihalo- stringent disinfection regulations will methane (THM) precursors.’ Thus, the require improved removal of natural proposed lowering of the maximum organic matter (NOM) and may also lead to the increased use of alternative disinfectants such as ozone. Because coagulation and ozonation typically precede GAC adsorbers in water treatment practice, an understanding of how these processes affect the adsorption of NOM is essential. This is important because NOM is known to compete with SOCs for adsorption sites in GAC systems. In addition, the large cost of ozonation and GAC adsorption requires that design combinations of these and other processes for removal of both NOM and SOCs be optimized. Bench-scale tests were used in this study to examine the effects of alum coagulation, different ozone dosages, and biostabilization on the equilibrium ad