A survey of disinfection byproduct (DBP) occurrence in the United States was conducted at 12 drinking water treatment plants. In addition to currently regulated DBPs, more than 50 DBPs that rated a high priority for potential toxicity were studied. These priority DBPs included iodinated trihalomethanes (THMs), other halomethanes, a nonregulated haloacid, haloacetonitriles, haloketones, halonitromethanes, haloaldehydes, halogenated furanones, haloamides, and nonhalogenated carbonyls. The purpose of this study was to obtain quantitative occurrence information for new DBPs (beyond those currently regulated and/or studied) for prioritizing future health effects studies. An effort was made to select plants treating water that was high in total organic carbon and/or bromide to enable the detection of priority DBPs that contained bromine and/or iodine. THMs and haloacetic acids (HAAs) represented the two major classes of halogenated DBPs formed on a weight basis. Haloacetaldehydes represented the third major class formed in many of the waters. In addition to obtaining quantitative occurrence data, important new information was discovered or confirmed at full-scale plants on the formation and control of DBPs with alternative disinfectants to chlorine. Although the use of alternative disinfectants (ozone, chlorine dioxide, and chloramines) minimized the formation of the four regulated THMs, trihalogenated HAAs, and total organic halogen (TOX), several priority DBPs were formed at higher levels with the alternative disinfectants as compared with chlorine. For example, the highest levels of iodinated THMs-which are not part of the four regulated THMs-were found at a plant that used chloramination with no prechlorination. The highest concentration of dichloroacetaldehyde was at a plant that used chloramines and ozone; however, this disinfection scheme reduced the formation of trichloroacetaldehyde. Preozonation was found to increase the formation of trihalonitromethanes. In addition to the chlorinated furanones that have been measured previously, brominated furanones-which have seldom been analyzed-were detected, especially in high-bromide waters. The presence of bromide resulted in a shift to the formation of other bromine-containing DBPs not normally measured (e.g., brominated ketones, acetaldehydes, nitromethanes, acetamides). Collectively, -30 and 39% of the TOX and total organic bromine, respectively, were accounted for (on a median basis) bythe sum of the measured halogenated DBPs. In addition, 28 new, previously unidentified DBPs were detected. These included brominated and iodinated haloacids, a brominated ketone, and chlorinated and iodinated aldehydes.

In the absence of bromide ion (Br−), method 5710B from Standard Methods is adequate for measuring trihalomethane (THM) precursor concentrations, provided a free available chlorine (FAC) residual of 3 mg/L is maintained at the end of incubation, and method 5710E from Standard Methods is appropriate for predicting THM concentrations at the consumer's tap. In the presence of Br−, method 5710B is adequate for measuring THM precursor concentrations provided only total precursor is desired. Because the initial Br−/average FAC dosage molar ratio influences bromine substitution, THM species concentrations cannot be predicted using method 5710B. Instead, method 5710E must be used. This is particularly important when evaluating THM precursor removal unit processes when the use of method 5710B may indicate greater bromine substitution in the unit process effluent than in the influet.

Recently developed analytical techniques allow for the quantification of C1‐C1O straight‐chain aliphatic aldehydes, benzaldehyde, and the dialdehydes glyoxal and methylglyoxal down to 1 μg/L. These compounds are formed as the partial oxidation products of the reaction between disinfectants (particularly ozone) and naturally occurring organic matter. Various full‐scale and pilot treatment plants in North America that employ ozonation were surveyed using these techniques, which showed a trend toward both monoaldehyde and dialdehyde formation. Once formed, aldehydes can persist in the water and their concentrations may even increase following postdisinfection. An effective means of aldehyde removal appears to be the use of biologically active granular activated carbon filters, whose filtration mode determines the actual degree of removal. Dialdehydes require a slower filtration rate for their removal than formaldehyde and acetaldehyde.

This pilot‐plant study was initiated to evaluate biological filtration for the removal of aldehydes formed during ozonation. An additional objective of this testing was to demonstrate that aldehyde measurements could be used as a surrogate for analysis of assimilable organic carbon (AOC). The use of granular activated carbon (GAC) as an alternative to anthracite coal as the filter medium was also investigated, and it was observed that GAC filters developed biological activity sooner and showed longer‐term stability. Although biological activity was established sooner on slow‐rate filters, the high‐rate filters in time achieved a comparable capability. Data for formaldehyde and glyoxal provide information on removal of readily biodegradable and more recalcitrant ozone by‐products, respectively, and demonstrate trends similar to those for the removal of AOC.

The results of these studies of the Sacramento–San Joaquin River Delta demonstrate that DBP control strategies should include watershed management as well as treatment processes in other regions of the United States.During development of the draft Disinfectants‐Disinfection Byproducts (D‐DBP) Rule, the issue of watershed management for DBP precursor control was discussed but not included in the rule. This article focuses on a major California watershed, describing examples of the types of studies that utilities can use to determine precursor sources and develop solutions for control. In addition, a chlorination and ozonation study of a five‐by‐five matrix of total organic carbon and bromide levels—which spanned a wide range of concentrations that can be expected in many US waters—provided insights into the effects of organic and inorganic precursors and disinfectants in DBP formation.