Bromate removal from water intended for human consumption by heterogeneous photocatalysis: Effect of major dissolved water constituents

Abstract

This study focuses on the influence of major dissolved constituents naturally found in waters intended for human consumption on bromate (BrO3−) reduction by heterogeneous photocatalysis. The individual and combined effect of chloride (Cl−), bicarbonate/carbonic acid (HCO3−/H2CO3), nitrate (NO3−), sulphate (SO42−) and humic acids (HAs) on BrO3− reduction was evaluated in synthetic waters (SWs). Additionally, freshwaters (FWs) from a drinking water treatment plant (DWTP) were tested and directly compared to SWs. Cl− was beneficial for contents in the range 0.47–1.4 mM, with negligible influence for lower and higher contents. NO3− had a null effect regardless of its content (0.024–0.81 mM). HCO3−/H2CO3 (0.061/0.45 mM), SO42− (0.12–2.6 mM) and HAs (0.11–1.0 mM C) had a negative effect in the tested contents. The BrO3− reduction rate was 2.8 times lower in SW with a mixture of water constituents compared to SW without constituents addition. This decline on BrO3− reduction rate corresponded to the sum of the individual species contribution and so there was no evidence of synergetic effects. By contrast, the use of FWs provided BrO3− reduction rates only slightly lower than that found for SW without constituents addition (∼1.2-fold), which can be attributed to: (i) the distinct characteristics of the organic matter of FWs (HAs, fulvic acids and humins with distinct molecular weights and functional groups) compared to that of SW (pure HAs), and/or (ii) the presence in FWs of other inorganics in addition to those here addressed. The heterogeneous TiO2 photocatalysis proved to be a promising process for BrO3− reduction in DWTPs.