Enzyme‐linked immunosorbent assay (ELISA) and liquid chromatography/tandem mass spectrometry (LC/MS/MS) were compared for analyzing microcystins in water. ELISA results of microcystin‐LR spiked into raw water samples were close to the spike concentrations, but method variability was ±25%. However, ELISA‐derived microcystin‐LA concentrations were two to three times higher than the spike concentrations obtained using the kit‐provided microcystin‐LR standards, indicating the need for variant‐appropriate ELISA standards. LC/MS/MS results agreed with spike concentrations for all variants in reagent water, but matrix suppression was observed in some raw waters. In bench‐scale studies, ozonated microcystins generated low‐level positive responses by ELISA and a protein phosphatase inhibition assay, even though microcystins were not detected by LC/MS/MS. These findings indicate that ELISA results—particularly in treated water—should be interpreted with caution because of the possibility of false‐positives, relatively high variability, and differential detection of some variants.

These two processes effectively remove MTBE but may also increase bromate. Initial pilot‐scale investigations demonstrated that both ozone alone and a combination of ozone and hydrogen peroxide (known as peroxone) can remove methyl tertiary butyl ether (MTBE) from water sources used by the Metropolitan Water District of Southern California. Under the tested conditions, peroxone more effectively removed MTBE than did ozone alone. In pilot tests, peroxone (here, 4 mg/L ozone and 1.3 mg/L hydrogen peroxide) removed an average of about 78 percent of the MTBE from water samples taken from the California State Water Project and the Colorado River. However, in peroxone‐treated samples from both water sources at ambient conditions, bromate was produced at concentrations above the maximum contaminant level of 10 μg/L for bromate in drinking water. A lower pH of 6.5 reduced bromate formation by about 20 percent in samples from both water sources, but it did not reduce the bromate concentration below 10 μg/L (the water sources contained about 0.1 mg/L bromide). Further optimization of the peroxone process may minimize bromate formation while providing acceptable MTBE removal and disinfection.

Ozonation of waters containing moderate to high levels of bromide at ambient pH can form bromate at levels that may exceed the United States maximum contaminant level (MCL) of 10 μg/L. A proven technology for minimizing the formation of bromate is ozonation of the water at a reduced (typically acidic) pH. However, in waters with moderate or high alkalinity, the cost of acid and base addition to lower and subsequently raise the pH of the water can be higher than the cost of generating the ozone. To lower costs (minimize the amount of acid and base addition), Metropolitan Water District of Southern California has been conducting a long-term evaluation of alternative bromate-control strategies. Test results indicate that, depending on a utility's by-product goals, that the addition of chlorine/ammonia, ammonia/chlorine or chlorine dioxide upstream of the ozone can be used to significantly minimize bromate formation. This paper provides new insights into emerging bromate-control strategies, as well as potential fatal flaws-the increased formation of other by-products of concern (chlorate, trihalomethanes, N-nitrosodimethylamine) in treated water.

A combination of ozone and hydrogen peroxide (known as peroxone) was studied as a treatment alternative for removing methyl tertiary butyl ether (MTBE), a common fuel oxygenate. The authors investigated the effects of oxidation of ozone and peroxone on MTBE in Santa Monica, Calif., groundwater. Experiments conducted in a large‐scale, semibatch reactor demonstrated that peroxone (at a peroxone ratio of 1.0, with applied ozone doses of ≤10 mg/L) was more consistently effective in oxidizing MTBE than was ozone alone. To achieve MTBE levels below the California secondary standard of 5 μg/L for drinking water, however, applied ozone doses of > 10 mg/L would be necessary for spiked MTBE concentrations of approximately 200 and 2,000 μg/L. Both ozone and peroxone can degrade MTBE into biodegradable products such as t‐butyl formate, t‐butyl alcohol, acetone, and aldehydes (including formaldehyde, acetaldehyde, heptaldehyde, glyoxal, and methyl glyoxal). In addition, peroxone can oxidize MTBE more rapidly than can ozone alone. When peroxone was used, the concentrations of bromate formed ranged from nondetected to 13 μg/L (in water containing ~0.3 mg/L bromide), exceeding the maximum contaminant level of 10 μg/L. Results indicated that bromate formation could be effectively controlled with hydrogen peroxide‐to‐ozone ratios > 1.0.

No abstract