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Abstract
Bromide accelerates the formation of carcinogenic disinfection by-products (DBPs) during drinking water disinfection when it reacts with dissolved organic matter and disinfectants. The objective of this study is to develop an effective process to lower the DBP formation by removing bromide from drinking water sources. An innovative bromide removal technology has been evaluated using electrically conductive membranes (ECM). ECM made of carbon nanotubes works as the anode to oxidize bromide to bromine, while stainless steel serves as the cathode. The optimal voltage and flow rate for this process in a bench-scale flow-through system to achieve the best bromide removal were determined to be 2.59V and 1 ml/min, respectively. Common ions present in drinking water sources influence bromide removal through competition for the electrode surface and electrode fouling. To confirm the effects of these ions, several common anions (sulfate, chloride, nitrate, and bicarbonate) were spiked individually at concentrations of 0.1, 2, and 5 meq/L to solutions containing bromide at 8.76 μeq/L. The bromide removal efficiency without anions was 70%. Chloride ion showed the strongest impact on bromide removal and lowered the bromide removal efficiency down to 16% with a 5 meq/L chloride concentration. On the other hand, nitrate and sulfate ions showed less impact than other ions and resulted in 27% and 25% bromide removal efficiency, respectively with 5 meq/L ion concentration. The effect of natural organic matter (humic acid) on bromide removal was also evaluated. The dissolved organic carbon (DOC) concentrations of 2mg/L, 5mg/L, and 15 mg/L reduced the bromide removal efficiency to 63%, 38%, and 25%, respectively. In addition, DBP formation potential before and after the ECM treatment was examined to check if the ECM reduced DBP formation potential. The DBP formation potential of water samples containing both bromide and DOC were predominantly influenced by the DOC levels rather than the bromide levels. Hence, the ECM treatment did not significantly change the formation potential of the two regulated groups of DBPs, trihalomethanes (THM) and haloacetic acids (HAAs), or total DBPs measured as total organic halogens (TOX). However, the ECM treatment did inhibit the formation of more toxic brominated DBPs, reflected by lower bromide incorporation factors (BIF) in THMs and HAAs after the ECM treatment.