N‐nitrosodimethylamine (NDMA) is a carcinogen known to be present in various foods and industrial products. The US Environmental Protection Agency has established a 10–6 cancer risk level for NDMA of 0.7 ng/L. NDMA has been found in the effluents of various water and wastewater plants, but its formation mechanism is not yet understood. This study evaluated NDMA formation during various water and wastewater treatment processes including chlorination and chloramination, ozonation, and ion exchange. On the basis of the limited results obtained in this study, NDMA appears to be a by‐product of the chloramination of water and wastewater, with the level of NDMA formed directly related to the chloramine dose. In the waters tested, NDMA did not form on contact with free chlorine or ozone. Contact of one water with typical levels of amine‐based polymer did not form any measurable NDMA levels (<2 ng/L). Batch testing was conducted with four strong‐base anion exchange resins contacted with untreated groundwater and with buffered deionized water. Results showed that some resins might leach or form NDMA and the level of NDMA produced is a function of the chemical functional group on the surface of the resin.

The perchlorate anion (ClO4–) has been found in potentially harmful concentrations in numerous water sources. Because perchlorate is not removed by conventional water treatment processes, new treatment processes are needed. Biological perchlorate reduction is a promising alternative. The authors investigated a hydrogen‐oxidizing hollow‐fiber membrane–biofilm reactor system for perchlorate removal. Hydrogen is an ideal electron donor for biological drinking water treatment because it presents no toxicity, is inexpensive, and is unlikely to persist as a source of biological instability in distributions systems. The reactor delivers hydrogen in an efficient and safe manner. Results showed that biological perchlorate reduction takes place concurrently with nitrate reduction, no specialized inoculation is required, and perchlorate can be removed to below the preliminary regulatory standards with no chemical addition other than hydrogen gas. The optimal pH is 8, and the accumulation of intermediates is unlikely. Full denitrification and pH control may be required for excellent perchlorate removal.

One of the main factors affecting the equilibrium capacity of activated carbon for synthetic organic chemicals (SOCs) in natural water is the presence of background organic matter (BOM). However, the initial SOC concentration also plays an important role in determining the capacity of the carbon. The objective of this study was to develop a means of quantifying the effect of initial SOC concentration in different types of waters on its adsorption isotherm. The method used approximates the complex mixture of BOM with a single equivalent background compound (EBC). The initial concentration and single-solute isotherm constants of the EBC were calculated based on the BOM's competitive effect on the adsorption of the SOC on activated carbon. The EBC method was then successfully used to predict the equilibrium capacity of powdered activated carbon for 2,4,6Arichlorophenolin several natural and finished waters when present at different initial concentrations.

Because the performance of powdered activated carbon (PAC) for uses other than taste and odor control is poorly documented, the purpose of this article is to critically review uses that have been reported and to analyze means of employing PAC more efficiently. The extent of adsorption of synthetic organic chemicals on PAC is strongly dependent on the type of compound being removed. The reported removals of trihalomethanes and trihalomethane precursors by PAC range from poor to very good. In selecting the point of addition of PAC, consideration must be given to the degree of mixing, the contact time between the PAC and the water, the PAC residence time, and the minimization of interference of adsorption by treatment chemicals. One of the main advantages of PAC is its low capital cost.

The results of this study show that the ozonation of waters containing bromide may produce bromate, with ozone dosage playing a critical role. The appropriate staging of ozone through two or three chambers, however, has the potential to minimize ozone residual and bromate formation while still meeting C × T criteria. The addition of hydrogen peroxide (the PEROXONE process) may increase the formation of bromate. As the pH of ozonation was lowered, the ozone dosage necessary to meet C × T criteria dropped, and less bromate was produced. The authors conclude that a better understanding of the mechanisms of bromate formation is required before it can be fully controlled.

Data analysis suggests that UV‐254 absorbance is a better indicator than TOC concentration for chlorination by‐product formation in SDS tests—and is substantially easier, faster, and less costly to measure.Each of four low‐bromide waters was coagulated at three pH values (5.5, 7.0, and 8.0), and then simulated distribution system (SDS) chlorination tests were performed. The object of the study was to determine whether total organic carbon (TOC) or UV‐254 absorbance can be employed as an indicator of the trihalomethane (THM) and haloacetic acid (HAA) concentrations formed upon chlorination. Results showed that removal of TOC and UV‐254 always increased with decreasing coagulation pH, but the extent of removal varied with the different waters. Maximum reduction of SDSTHM and SDSHAA5 formation was achieved after coagulation at pH 5.5. UV‐254 proved to be a better surrogate for chlorinated by‐product formation than TOC. The applicability of the correlations to waters with higher bromide levels and different chlorination pH values should be evaluated.

The objectives of this study were to determine the efficiency of adsorption of powdered activated carbon (PAC) for a typical synthetic organic chemical, to evaluate the importance of particle size and background organ& and to develop a procedure to predict the performance of PAC. Results showed that performance can be significantly improved by using smaller-size PAC but that the rate of adsorption and PAC capacity are markedly reduced when naturally occurring humic substances are present in the groundwater. Accurate predictions of the removal of trace organics by PAC in a continuously stirred tank reactor were made by running equilibrium and closed-batch kinetic tests, determining equilibrium and kinetic constants, and using an equation to determine the removal efficiency of the PAC for any contact time.Many synthetic organic chemicals water supplies by water runoff, through (SOCs), including the volatile organic waste discharge, or by chemical spills. chemicals (VOCs), in drinking water are Granular activated carbon (GAC) is of interest because of their potential commonly used in fixed-bed adsorbers to mutagenicity, carcinogenicity, and tox-remove SOCs and organic compounds icity. These compounds enter drinking that cause odor problems. The utilization Figure 1. Effect of particle size on the adsorption isotherm for TCP on PAC 1 (water-deionized-distilled; pH-8 IO.01 M phosphate buffer]) JANUARY 1990of GAC for some applications requires an appreciable investment in equipment, and operation and maintenance costs can be high. Thus, alternatives should be investigated. Little attention has been given to the use of powdered activated carbon (PAC) for the removal of SOCs, although it is widely and successfully used in the United States for taste and odorcontrol.1.z The primary advantages of PAC are its lowcapitalcost and theabilitytoapplyit only when needed. The latter is especially important for systems that do not require an adsorbent for much of the year. Some disadvantages are that it is difficult to apply in a way that will allow its adsorption capacity to be fully utilized and that careful monitoringis needed todetermine when it should be applied.Removal of VOCs by PAC hasgenerally not been very good. Only 20 percent reduction of 70~gcarbon tetrachloride/L was achieved with 30 mg PAC/L in jar tests;:' this was consistent with fullscale plant performance." Full-scale studies" showed minor removals of dichloroethane CC, = 5 pg/L) with up to 27 mg PAC/L. Symons et al" reported that more than 100 mg PAC/L was required to remove about 50 percent of 60 pg chloroform/L in jar tests.The removal of compounds that adsorb as strongly as, or more strongly than, tetrachloroethylene is much better than those of the VOCs previously described.Singley et al7 showed about 90 percent removal of SOCs such as chlorobenzene and several polynuclear aromatic hydrocarbons with PAC doses of IO-15 mg/L and2hofcontacttimeattheSunnyIsles water treatment plant. The odorous

Research with a laboratory prototype and at the pilot scale documents that the hydrogen-based hollow-fiber Membrane-Biofilm Reactor (MBfR) is technically and economically feasible for reduction of nitrate and perchlorate. In the MBfR, H2 gas diffuses through the wall of a composite membrane, and an autotrophic biofilm naturally develops on the outside of the membrane, where the bacteria's electron acceptor is an oxidized contaminant (e.g., NO3− or ClO4−) supplied from the water. The hydrogen pressure to the hollow fibers is a key control parameter that can be adjusted rapidly and easily. For denitrification, partial nitrate removal often is acceptable, and the hydrogen pressure can be low to minimize the costs of H2 supply and the concentration of H2 in the effluent. When perchlorate must be reduced, full nitrate removal is essential, since NO3−-N above about 0.2 mg/L slows perchlorate reduction. Perchlorate reduction is sensitive to the hydrogen pressure, which underscores the critical role of H2 pressure for controlling process performance. Given that H2-oxidizing microorganisms have the potential to reduce many oxidized contaminants, we hypothesize that and are beginning to test how well the MBfR reduces bromate, selenate, chlorinated solvents, and other oxidized contaminants.