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 (SO₄^2-) 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), SO₄^2- (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.

Keywords: Advanced reduction processes; Bromate reduction; Inorganic species; Natural organic matter; Photocatalytic thin films; Real waters.