Bromine is a trace element in the Earth's crust and is commonly detected in natural waters at various levels. In water treatment plants bromide (Br-) reacts directly to produce disinfection byproducts (DBPs) and will form intermediates in the formation of organic DBPs (e.g., THM, HAA, and haloacetonitriles).  The toxicity of brominated DBPs are concerning. However, very few studies directly consider Br- removal  from natural waters because of its low concentration relative to chloride and the poor selectivity of separation processes. Thus, Br- poses a harm to consumers and can limit the capacity of water utilities to be compliant with current DBP regulations.

Capacitive deionization (CDI) has recently gained popularity as an alternative way of deionizing natural waters. Unlike reverse osmosis and distillation, the CDI process does not require high pressures or temperatures. It can operate at room temperature with the application of a small voltage (e.g., 1.0 - 1.2 V) and process can be reversed by lifting the electric current. During operation, raw water is passed through porous electrodes while a potential difference is applied to the cell. Applied voltage forms the electric double layer, causing ions to migrate towards the electrodes, which leads to adsorption of ions and decreases the overall ionic strength of water. The main objective of this study is to utilize the principles of capacitive deionization and the difference in electrochemical oxidation of bromide and chloride ions to selectively remove bromide from natural waters. Our results indicate that it is possible to selectively remove bromide from natural waters utilizing the lower electrochemical formation potential of bromine gas (1.09 V vs. standard hydrogen electrode) compared to chlorine formation (1.36 V vs. standard hydrogen electrode).