Reducing bromate formation with H+-form high silica zeolites during ozonation of bromide-containing water: Effectiveness and mechanisms

This paper investigated the effect of H+-form high silica ZSM-5 (HZSM-5) zeolites on bromate formation. HZSM-5 zeolites with different Si/Al molar ratios (i.e., 25−300) were tested taking ozonation alone as control. The zeolites were more effective in reducing bromate formation for the filtered surface water than CeO2, a former reported oxide that can reduce bromate formation at slightly acidic pH. The reduction efficiencies were not closely related to their Si/Al ratios. The HZSM-5 (Si/Al = 300) selected for detailed studies effectively reduced bromate formation by 58% for the filtered water, and also enhanced the removal of dissolved organic carbon (DOC) during ozonation. The efficiency of the HZSM-5 in reducing bromate formation increased with ozone dose (0.38−1.16 mg O3 mg−1 DOC) and pH (6.6−9.3). The HZSM-5 adsorbed OBr− (one of the critical intermediates in bromate formation) quickly with an adsorption capacity of 54 mg g−1, but had no adsorption for ozone, Br−, HOBr and BrO3-. It also significantly inhibited the formation of trace H2O2 which was generated from ozone decomposition and had been considered promoting bromate formation at low concentrations during ozonation. The reduction of bromate formation in O3/HZSM-5 is possibly ascribed to the selective OBr− adsorption in combination with the inhibited H2O2 formation.