Ferrate(VI) pretreatment before disinfection: An effective approach to controlling unsaturated and aromatic halo-disinfection byproducts in chlorinated and chloraminated drinking waters

Abstract

Disinfection is an essential process of drinking water treatment to eliminate harmful pathogens, but it generates potentially toxic disinfection byproducts (DBPs). Ferrate (FeO 4 2- , Fe(VI)) was used to pre-oxidize natural organic matter (NOM, the precursor of DBPs) in source water to control DBP formation in subsequent chlorine or chloramine disinfection. Currently, it is unclear how Fe(VI) changes the structure of NOM, and no information details the effect of Fe(VI) pretreatment on the aromatic DBPs or the speciation of overall DBPs generated in subsequent disinfection of drinking water. In the present paper, Fe(VI) was applied to pretreat simulated source water samples at a Fe(VI) to dissolved organic carbon mole ratio of 1:1 at pH 8.0. 13 C nuclear magnetic resonance spectroscopy was newly employed to characterize NOM in simulated source waters with and without Fe(VI) treatment, and it was demonstrated that Fe(VI) converted unsaturated aromatic C functional groups in NOM to saturated aliphatic ones. High-resolution mass spectrometry (HRMS) and high performance liquid chromatography/triple quadrupole MS were applied to analyze the DBPs generated in chlorination and chloramination of the source waters with and without Fe(VI) pretreatment. It was confirmed that Fe(VI) pretreatment followed by chlorination (or chloramination), generated DBPs containing less unsaturated, halogenated, and aromatic moieties than chlorination (or chloramination) without pretreatment by Fe(VI). Finally, the cytotoxicity of disinfected drinking water samples were assessed with the human epithelial colorectal adenocarcinoma Caco-2 cell line (a model of the intestinal barrier for ingested toxicants), and the results show that Fe(VI) pretreatment detoxified the chlorinated and chloraminated drinking waters.

Generation of Iron(IV) in the Oxidation of Amines by Ferrate(VI): Theoretical Insight and Implications in Oxidizing Pharmaceuticals

“…However, this effect of amines depends on the concentration of amines compared to that of Fe­(VI) because the formation of the Fe IV –amine complex and its enhanced performance depend on the molar ratio of amine to Fe­(VI). Furthermore, the oxidation of amines will eliminate one of the precursors in water that generate DBPs during chlorination; ,, therefore, the amount of chlorinated DBPs would decrease in the use of Fe­(VI) as a preoxidant before chlorination. Fe­(VI) has been demonstrated to be an effective disinfectant and coagulant. ,− Therefore, application of Fe­(VI) has a potential to have multiple advantages in treatment processes.…”

“…Organic amines are key components in organic synthesis, metalloenzymatic reactions, atmospheric particles, coastal waters, and municipal and industrial wastewater discharges. − Amines are widespread in surface water because their moieties are usually found in dissolved natural organic matter and anthropogenic organic contaminants such as pharmaceuticals, personal care products, dyes, and pesticides . Amines in water resources are of concern because disinfection using chlorine and chloramine results in the formation of potentially toxic disinfection byproducts (DBPs). , Many investigators, including our group, are studying an iron-based oxidant, ferrate­(VI) [Fe VI O 4 2– , Fe­(VI)], as a preoxidant prior to disinfection by chlorination. − The application of Fe­(VI) as a preoxidant and subsequent chlorination decrease the levels of chlorinated DBPs (Cl-DBPs) because the oxidation of amine-containing constituents in water and the resulting oxidized products cannot react fully to generate Cl-DBPs. ,,− Amine moieties in pharmaceuticals also play an important role in their oxidation by Fe­(VI) in water. − For example, in the oxidation of sulfonamides, the amine moieties determined the reaction pathways that yield oxidized products. , …”

Comparison of the impact of ozone, chlorine dioxide, ferrate and permanganate pre-oxidation on organic disinfection byproduct formation during post-chlorination

“…Together with the reduction of the water matrix reactivity, the use of pre-oxidation can have complementary benefits such as a degradation of contaminants, 7,8 disinfection (except for Mn(VII) ), 9,10 or coagulation. [10][11][12] DBP reduction has been achieved by pre-oxidizing various water matrices with ClO 2 , 4,13,14 O 3 , 2,15,16 Fe(VI), 14,[17][18][19] and Mn(VII). 18,20 However, only a few studies compared the efficiency of different pre-oxidants.…”

Application of Fe(VI) in abating contaminants in water: State of art and knowledge gaps

“…Fe(VI) is traditionally considered as a green oxidant without producing any hazardous halogenated byproducts. Previous studies have proposed that it can be used as a preoxidant in source water to control disinfection byproducts (DBPs) formation in subsequent chlorine or chloramine disinfection (Liu et al, 2020). It is often stated in the literature that one major advantage of Fe(VI) oxidation over ozonation is that Fe(VI) can't oxidize bromide (Br -) and thus does not lead to the generation of bromate (BrO 3 -) (Sharma, 2011).…”