# Treatment of Aqueous Bromate by Superparamagnetic BiOCl-Mediated Advanced Reduction Process
## 2 Results and Discussion
### Influence of Common Electron Acceptors  
For reduction, electron acceptors, such as oxygen (O\({}_{2}\)) and nitrate (NO\({}_{3}^{-}\)), usually show significant suppressive effects [13; 23]. Therefore, the effects of common electron acceptors (O\({}_{2}\), NO\({}_{3}^{-}\), and Fe\({}^{3+}\)) at a concentration level of drinking water on bromate degradation by UV/BiOCl-HAP\({}_{\rm SM}\)/ formate was evaluated (Figure 11). No significant influence was noted from 30-120 mg\(\cdot\)L\({}^{-1}\) NO\({}_{3}^{-}\) until the NO\({}_{3}^{-}\) concentration increased to 240 mg\(\cdot\)L\({}^{-1}\). Moreover, 1-4 \(\mu\)M Fe\({}^{3+}\) (FeEDTA\({}^{-}\)) exerted a slight effect on BrO\({}_{3}^{-}\) degradation. As regards the DO ((O\({}_{2}\))\({}_{\rm aq}\)), 8.3 mg\(\cdot\)L\({}^{-1}\) DO cause about 20% decrease in BrO\({}_{3}^{-}\) degradation relative to that in the absence of DO. After comparing the scavenging rate of CO\({}_{2}^{\bullet-}\) by NO\({}_{3}^{-}\) ((0.3-1.3) \(\times\) 10\({}^{3}\) s\({}^{-1}\)), Fe\({}^{3+}\) ((0.1-2.0) \(\times\) 10\({}^{2}\) s\({}^{-1}\)), DO (6.0 \(\times\) 10\({}^{5}\) s\({}^{-1}\)), and BrO\({}_{3}^{-}\) (9.24 \(\times\) 10\({}^{3}\) s\({}^{-1}\)) (Table 1), one can easily understand the inconspicuous influence of NO\({}_{3}^{-}\) and Fe\({}^{3+}\). However, CO\({}_{2}^{\bullet-}\) scavenging kinetics could not explain the DO-induced \(\sim\)20% inhibition. The 8.3 mg\(\cdot\)L\({}^{-1}\) DO should completely suppress BrO\({}_{3}^{-}\) degradation theoretically because the scavenging rate of CO\({}_{2}^{\bullet-}\) by DO is 65 times that by BrO\({}_{3}^{-}\). Thus, besides scavenging CO\({}_{2}^{\bullet-}\), DO may also play a positive role in the photoreduction of BrO\({}_{3}^{-}\) by UV/BiOCl-HAP\({}_{\rm SM}\)/formate. The electroreduction of DO ((O\({}_{2}\))\({}_{\rm aq}\)) by e\({}_{\rm CB}^{-}\) is accepted to generate the superoxide radical (O\({}_{2}^{\bullet-}\)), and O\({}_{2}^{\bullet-}\) may convert into H\({}_{2}\)O\({}_{2}\) through disproportionation (Equations (12)-(15), [38]). H\({}_{2}\)O\({}_{2}\) can easily transform into free HO- (HO\(\cdot\)_t_) through UV photolysis and catalysed decomposition by surface metal ion of photocatalyst [50]. As discussed above, HO\({}_{\rm f}\), rather than HO-s near the surface of BiOCl-HAP\({}_{\rm SM}\) (HO-s), contributed to the formation of CO\({}_{2}^{\bullet-}\). The \(\sim\)20% inhibition of BrO\({}_{3}^{-}\) degradation indicates that the DO's positive effect outcompetes its negative effect. Obviously, UV/BiOCl-HAP\({}_{\rm SM}\)/formate was more resistant to common electron acceptors than the typical hydrated electron based-ARPs. For example, 95 \(\mu\)M NO\({}_{3}^{-}\) (5.9 mg\(\cdot\)L\({}^{-1}\)) induced a 75% inhibition of MCAA degradation by typical ARP UV/SO\({}_{3}^{-}\)[51]. Besides O\({}_{2}\), NO\({}_{3}^{-}\), and  
Figure 10: Removal of bromate by UV/BiOCl-HAP\({}_{\rm SM}\)/formate and element releasing for 10 successive cycles. Conditions: [Formate]\({}_{0}\) = 4 mM; BiOCl-HAP\({}_{\rm SM}\) dosage 0.5 g\(\cdot\)L\({}^{-1}\), [BrO\({}_{3}^{-}\)]\({}_{0}\) = 6.63 \(\mu\)M, pH = 7.0 \(\pm\) 0.1, 25 \({}^{\circ}\)C, reaction time 15 min.  
Fe\({}^{3+}\), residual chlorine (also an electron acceptor) is usually found in the drinking water to depress the microorganism growth. To decrease the influence of residual chlorine, pretreatment by UV photolysis is feasible and convenient:  
\[\mathrm{e}_{\mathrm{CB}}^{-}+\left(\mathrm{O}_{2}\right)_{\mathrm{aq}}\to \mathrm{O}_{2}^{\bullet-}\,, \tag{12}\]  
\[2\mathrm{O}_{2}^{\bullet-}+\mathrm{H}^{+}\to\mathrm{HO}_{2}^{-}+\mathrm{O}_{2}\,, \tag{13}\]  
\[\mathrm{O}_{2}^{\bullet-}+\mathrm{H}^{+}+\mathrm{e}_{\mathrm{CB}}^{-}\to \mathrm{HO}_{2}^{-}\,, \tag{14}\]  
\[\mathrm{HO}_{2}^{-}+\mathrm{H}^{+}\to\mathrm{H}_{2}\mathrm{O}_{2}\,. \tag{15}\]