Activated Carbon Promotes the Formation of Bromated Byproducts during Chlorination with the Presence of Bromide

The exposure of activated carbon (AC) to chlorine can produce more toxic byproducts, but their interactions and byproducts in the presence of bromide have never been investigated yet. Therefore, this work first studied the effects of AC on the disinfection byproduct (DBP) formation with bromide and free radical-mediated reaction process. The results indicated that the proportion of brominated trihalomethanes/brominated haloacetic acids in the effluent was increased by 3-10% with AC and toxicity also increased. Fourier transform ion cyclotron resonance mass spectrometry results suggested that the relative intensity of halogenated byproducts including unknown brominated DBPs (Br-DBPs) was increased by 21%. In addition, the free radical-mediated reaction activated by AC also contributed to the generation of aliphatic halogenated and nonhalogenated compounds. The chlorine and bromide free radicals were activated by the AC. Though the reactive bromide species did not lead to the Br-DBP formation, HOBr or Br2 generated during the free radical chain reaction and the modification of the DOM properties through free radical reaction were responsible for the increase of Br-DBPs. Therefore, this study could provide a novel insight into the control of the risk of the toxic byproducts when using chlorine and AC simultaneously.