Critical Review on Bromate Formation during Ozonation and Control Options for Its Minimization

A comparative study of reactive manganese species and electron transfer pathway in oxidation efficiency and environmental impact: Which activation route for potassium permanganate is optimal?

Various methods have been explored to activate potassium permanganate (Mn(VII)) for the elimination of organic compounds, typically by generating highly-reactive manganese species (RMnS) or mediated by electron transfer process (ETP). However, the oxidation selectivity, transformation pathways, toxicity byproduct potential, and efficacy in complicated water matrices associated with RMnS and ETP have not been comprehensively evaluated and compared, which is important for selecting a fit-of-purpose mechanism for water remediation. This study selected Mn(VII)/graphite process and ultraviolet (UV)/Mn(VII) process as the model ETP-dominated system and RMnS-dominated system, respectively. RMnS demonstrated significantly higher degradation efficiency for bromophenols, with oxidation rate constants 2.69-6.28 times higher than ETP. The oxidation efficiency of RMnS could be enhance under alkaline condition, whereas the degradation efficiency of ETP is dependent on the combined effects of solution pH and pKa of compounds. Furthermore, RMnS exhibited a stronger dehalogenation capacity, enabling the almost complete release of bromide ions from bromophenols with the formation of non-brominated organic product. Correspondingly, the RMnS process obviously reduced the brominated disinfection byproducts formation potential (DBPFPs). Mass spectrometry results revealed that the ETP process tended to form more polymeric brominated dimer products during the oxidation of bromophenol, leading to more DBPFPs production. ETP process showed superior degradation efficiency in real water backgrounds due to robustness against complicated water matrices, and displayed lower energy and oxidant consumption. Findings of this study elucidated the efficiency and mechanistic differences between RMnS and ETP, providing guidance for selecting activation methods to enhance KMnO4-based water treatment process.

Decreased bromate formation but inadvertently increased toxicity in the chloramination-ozonation process: Essential roles of halamines in generating halogenated and nitrogenous byproducts

The prechloramination followed by post-ozonation (NH2Cl-O3) process has been widely recognized for its effectiveness in suppressing bromate (BrO3-) formation. However, the presence of bromide (Br-) during NH2Cl treatment results in the formation of various halamines. This study reveals that while the NH2Cl-O3 process reduces BrO3- formation, it leads to a substantial increase in overall cytotoxicity (from 2.01-4.10 to 4.30-12.05 mg-Phenol/L) and genotoxicity (from 0.29 to 0.88 µg-4-NQO/L) to mammalian cells at the condition of 3 mg/L NH2Cl and 1 mg-O3/mg-C. Total organic halogen, especially total organic bromine, markedly increases during the NH2Cl-O3 process, with TOBr rising from 7.2 μg/L in SE to 72.5 μg/L with 3 mg/L NH2Cl, and to 75.7 μg/L with 5 mg/L NH2Cl. By employing Ultra-Performance Liquid Chromatography-Orbitrap Mass Spectrometry (UPLCOrbitrap MS) combined with halogenated isotopic feature detection and 15N-labeled isotope techniques, we precisely identified the molecular formulas of these disinfection byproducts (DBPs), demonstrating that the NH2Cl-O3 process promotes the formation of a broader range of both halogenated DBPs and nitrogenous byproducts (N-DBPs). In the presence of Br-, after prechloramination, various halamines such as bromochloramine (NHBrCl), monobromamine (NH2Br), and dibromamine (NHBr2) were formed. Prechloramination inadvertently enhances a synergistic halamines/O3 process, amplifying DBP formation. These halamines can all contribute to an increase in toxicity, particularly when combined with O3 treatment. While effectively controlling BrO3-, our findings highlight the need to consider overall toxicity and evaluate the formation of other potentially toxic DBPs.

Increased formation of brominated disinfection by-products and toxicities during low-H2O2-mediated ozonation of reclaimed water

Reusing reclaimed water requires stringent disinfection but inevitably generates disinfection by-products (DBPs). H2O2/O3 treatment is an efficient and environmentally benign disinfection method. For the first time, our bioassay results elucidate that low H2O2/O3 ratio (molar) treated water increased unignorable toxicity effect compared to that of the high H2O2/O3 ratio. To clarify this finding, individual organic brominated DBPs (Br-DBPs), bromate, and adsorbable organic bromine (AOBr) were considered due to their potential risk. Organic Br-DBPs were mainly generated from ozone-induced pathways. Individual organic Br-DBPs were not the primary concern in this scenario because they are typically only produced in observable quantities at bromide concentrations exceeding 500 μg/L, and even then, they often remain below detection limits when treated with H2O2/O3. On the contrary, both bromate and AOBr were detectable at low H2O2/O3 ratios. Furthermore, bromate is produced from HOBr and bromine radicals induced by HO•. Moreover, bromate formation was promoted because of increased HO• formation, particularly at H2O2/O3 ratios <0.24. To prevent HO•-induced pathways from being dominant, higher H2O2/O3 ratios (>0.48) were required. Toxicity assays revealed that AOBr-included organic extracts of ozonated reclaimed water induced more toxic effects. The toxicity induced by the organic fraction resulted from its decreased oxidation level, which was, in turn, driven by the increased formation of bromate. Enhanced toxicity effects were observed when cells were exposed to a bromate and organic extract mixture. It indicates that both the AOBr and bromate present in low-H2O2-O3-treated reclaimed water pose potential risks, and their coexistence further elevates these risks. Increasing the H2O2/O3 ratio markedly decreased the generation of intracellular oxidative substances and oxidative damage. In conclusion, when treated with H2O2/O3, shifting from HO•-induced pathways to ozone-induced pathways by a relatively high H2O2/O3 ratio decreased the amounts of DBPs produced and controlled the toxic effects to ensure the safety of ozonated reclaimed water.

Hybrid modelling framework for ozonation and biological activated carbon in tertiary wastewater treatment

Despite water being a significant output of water and resource recovery facilities (WRRFs), tertiary wastewater treatment processes are often underrepresented in integrated WRRF models. This study critically reviews the approaches used in comprehensive models for ozone (O3) and biological activated carbon (BAC) operation units for wastewater tertiary treatment systems. The current models are characterised by limitations in the mechanisms that describe O3 disinfection and disinfection by-product formation, and BAC adsorption in multi-component solutes. Drawing from the insights from the current O3, BAC, and WRRF modelling approaches, we propose an integrated O3-BAC model suitable for simulating dissolved organic carbon (DOC) and micropollutants removal in the O3-BAC systems. We recommend a hybrid modelling approach in which data-driven models can be integrated to compensate for structural limitations in mechanistic models. The model is developed within the activated sludge model (ASM) framework for flexibility in coupling with other WRRF models and hence facilitates developing system-wide WRRF models for wastewater reclamation and reuse systems.

Effectiveness of ozone nanobubble treatments on high biomass cyanobacterial blooms: A mesocosm experiment and field trial

Cyanobacterial harmful algae blooms (cyanoHABs) are a global threat to water resources, and lake managers need effective strategies to suppress or control them. Algaecides may have negative environmental impacts, and their use is becoming restricted. Nanobubble ozone technology (NBOT) is an emerging water treatment option with potentially fewer negative impacts. We assessed the effectiveness of NBOT in treating Planktothrix cyanoHAB from Grand Lake St Marys (GLSM, Ohio USA) in a mesocosm (2,000L) experiment and two 4-week trials in a GLSM embayment (Sunset Beach, SBE; ∼4.7∗107 L). In mesocosms, the medium (1.21 ± 0.08 ozone to dissolved organic carbon ratio, O3:DOC) and high (2.04 ± 0.07 O3:DOC) doses decreased both chlorophyll a (chl-a) and phycocyanin by 98-99% and microcystins by 62% and 92%, respectively. The low dose (0.68 ± 0.05 O3:DOC) decreased chl-a and phycocyanin by over 70%. No effect was observed for chl-a nor microcystins in both oxygen-only nanobubble mesocosm treatments and the SBE NBOT trial. The average O3:DOC at SBE was less than the low NBOT mesocosm experiment dose, and the percentage of water treated was lower. DOC chemistry, as indicated by SUVA254, was more oxidized at the NBOT outlet than the inlet in the SBE trial, suggesting interaction with ozone. However, no differences were observed 3m from the outlet, indicating minimal treatment reach. The mesocosm experiment highlighted NBOT's ability to control cyanoHABs, but the limited effectiveness of NBOT at SBE was likely due to high cyanobacteria biomass and DOC at the onset of treatment, low O3:DOC, and low percentage of lake water instantaneously treated.

Homogeneous versus heterogeneous Mn(II) oxidation in peroxymonosulfate assisting chlorination: Synergistic role for enhanced Mn(II) oxidation in water treatment

Removal of Mn(II) is an essential step for addressing water discoloration in water treatment utilities worldwide. However, conventional chlorination suffers from poor oxidation of Mn(II) due to its low homogeneous oxidation kinetics. This study explored the oxidation capability of a new chemical dosing strategy employing peroxymonosulfate (PMS) to assist the chlorination process (PMS@Cl2) for effective Mn(II) oxidation. The study comprehensively explored both oxidation kinetics and underlying mechanisms associated with homogeneous and heterogeneous oxidation within the PMS@Cl2 system. At an [Mn(II)]0 of 1 mg/L, chlorination demonstrated inability in oxidizing Mn(II), with <10 % oxidation even at an elevated [Cl2] of 150 μM (∼10 mg/L). By contrast, PMS completely oxidized 100 % Mn(II) within a 30-minute reaction at a much lower [PMS] of 60 μM (kobs = 0.07 min-1 and t1/2 = 9 min), demonstrating its superior Mn(II) oxidation kinetics (over one order of magnitude faster than conventional chlorine). PMS@Cl2 exhibited an interesting synergistic benefit when combining a lower dose PMS with a higher routine dose Cl2 (loPMS@hiCl2), e.g. [PMS]:[Cl2] at 15:30 or 30:30 μM. Both conditions achieved 100 % Mn(II) oxidation, with even better values of kobs and t1/2 (0.16-0.17 min-1 and ∼4 min) relative to PMS alone at 60 µM. The synergic benefit of PMS@Cl2 was attributed to distinct functions played by PMS and Cl2 in both homogeneous and heterogeneous oxidation processes. Reactive species identification excluded the possible involvement of SO4•-, OH•, or chlorine radicals in the homogeneous oxidation of the PMS@Cl2 system. Instead, the dominant species was O2•- radical generated during the reaction of Mn(II) and PMS. Furthermore, the heterogeneous oxidation emphasized the important role of combining Cl2 dosing, which demonstrated an increased reactivity and electron transfer with the Mn-O-Mn complex, surpassing PMS. Overall, heterogeneous oxidation accelerated the oxidation kinetics of the PMS@Cl2 system by 1.1-2 orders of magnitude relative to the homogeneous oxidation of Cl2 alone. We here demonstrated that PMS@Cl2 could offer a more efficient mean of soluble Mn(II) mitigation, achieved with a relatively low routine dose of oxidant in a short reaction period. The outcomes of this study would address the existing limitations of traditional chlorine oxidation, minimizing the trade-offs associated with high residual chlorine levels after treatments for soluble manganese-containing water.

Ozonation and catalytic ozonation - Sources of error. What do we need to know?

Due to the increasing contamination of the environment, including water pollution by numerous emerging contaminants, there is a growing interest in advanced water purification/treatment processes. A technique of particular and growing interest over the years is ozonation in its broadest sense. It is a complex process, and its course, both in the version without and with the participation of a catalyst, depends on a number of factors that can affect its efficiency and the correct interpretation of the obtained results. The paper discusses the importance of the most relevant of these factors: ozone initiation and decomposition, proper catalyst preparation, potential sources enhancing the ozonation process (H2O2 and 1O2), the influence of commonly used buffers and natural water admixtures, and the importance of adsorption processes. The paper also explains how the structure of the ozonated compound can affect its oxidation efficiency and identifies the most common sources of errors having the influence on the interpretation of experimental data.

A novel simultaneous abatement of bromate and diphenyl phosphate using the freezing process

The purification of bromate (BrO3-)-contaminated water has become a challenge because of its persistence and adverse effects. Furthermore, there has been concern over the release of byproducts, such as diphenyl phosphate (DPHP), from flame retardants in wastewater treatment plant (WWTP). In this study, we designed the water treatment system for the oxidation of DPHP accompanied by bromate (BrO3-) reduction via freezing the solution. A sample containing 10 μM DPHP, 100 μM Br-, and 50 μM BrO3-, with a pH of 3 was frozen at -20oC, approximately 25 μM BrO3- was reduced, and DPHP was fully eliminated after a 0.5 h reaction time. Conversely, these reactions did not advance in water at 20oC. This increase in the rate of chemical reaction in ice is the consequence of the freeze concentration effect, which refers to the extraction of dissolved chemical species into the liquid-like regions of the polycrystalline ice micro-structure during the freezing of the solution. The redox reactions among DPHP, Br-, and BrO3- become thermodynamically favorable due to the distinctive environment in the liquid brine in ice. The efficiency of the DPHP oxidation significantly increased with an increase in BrO3- concentration, and vice versa. The Br-/BrO3--induced HOBr production is proposed as a primary oxidant for DPHP degradation. The proton activity (pH) has a significant influence on the reaction efficiency. The low freezing temperature accelerated the reaction kinetics of DPHP degradation and BrO3- reduction. The results of this study indicate the possibility of utilizing ice chemistry for the BrO3- reduction that concomitantly removes DPHP for water treatment. This environmentally friendly water treatment method can be considered to implement in regions with a cold climate.

Prediction of hydroxyl radical exposure during ozonation using different machine learning methods with ozone decay kinetic parameters

The abatement of micropollutants by ozonation can be accurately calculated by measuring the exposures of molecular ozone (O3) and hydroxyl radical (•OH) (i.e., ∫[O3]dt and ∫[•OH]dt). In the actual ozonation process, ∫[O3]dt values can be calculated by monitoring the O3 decay during the process. However, calculating ∫[•OH]dt is challenging in the field, which necessitates developing models to predict ∫[•OH]dt from measurable parameters. This study demonstrates the development of machine learning models to predict ∫[•OH]dt (the output variable) from five basic input variables (pH, dissolved organic carbon concentration, alkalinity, temperature, and O3 dose) and two optional ones (∫[O3]dt and instantaneous ozone demand, IOD). To develop the models, four different machine learning methods (random forest, support vector regression, artificial neural network, and Gaussian process regression) were employed using the input and output variables measured (or determined) in 130 different natural water samples. The results indicated that incorporating ∫[O3]dt as an input variable significantly improved the accuracy of prediction models, increasing overall R2 by 0.01-0.09, depending on the machine learning method. This suggests that ∫[O3]dt plays a crucial role as a key variable reflecting the •OH-yielding characteristics of dissolved organic matter. Conversely, IOD had a minimal impact on the accuracy of the prediction models. Generally, machine-learning-based prediction models outperformed those based on the response surface methodology developed as a control. Notably, models utilizing the Gaussian process regression algorithm demonstrated the highest coefficients of determination (overall R2 = 0.91-0.95) among the prediction models.

Achieving realistic ozonation conditions with synthetic water matrices comprising low-molecular-weight scavenger compounds

Ozonation is used worldwide for drinking water disinfection and increasingly also for micropollutant abatement from wastewater. Identification of transformation products formed during the ozonation of micropollutants is challenging due to several factors including (i) the reactions of both oxidants, ozone and hydroxyl radicals with the micropollutants, as well as with intermediate transformation products, (ii) effects of the water matrix on the ozone and hydroxyl radical chemistry and (iii) the generation of oxidation by-products. In this study, a simple approach to achieve realistic ozonation conditions in the absence of dissolved organic matter has been developed. It is based on composing synthetic water matrices with low-molecular-weight scavenger compounds (phenol, methanol, acetate, and carbonate) that mimic the chemical interactions of ozone and hydroxyl radicals with real water matrices. Synthetic waters composed of only four low-molecular-weight compounds successfully replicated two lake waters and two secondary wastewater effluents, matching instantaneous ozone demand, ozone and hydroxyl radical exposures in the initial phase, as well as the ozone evolution in the second phase of the ozonation process. The synthetic water matrices also reproduced the effects of temperature and pH changes observed in real waters. The abatement of two micropollutants, bezafibrate and atrazine, and the formation of the corresponding transformation products during ozonation were in agreement for synthetic and real waters. Furthermore, the kinetics and extent of bromate formation during ozonation in synthetic water were comparable to real lake water and wastewater. This supports the robustness of the proposed approach because bromate formation is very sensitive to the interplay of ozone and hydroxyl radicals. Furthermore, with the novel reaction system, a significant effect of hydroxyl radicals scavenging by carbonate on bromate formation was demonstrated. Overall, the herein-developed approach based on synthetic water matrices allows to perform realistic ozonation studies including both oxidants, ozone and hydroxyl radicals, without the constraints of using dissolved organic matter.

Virus inactivation in low ozone exposure water reuse applications

In drinking water applications, an ozone exposure (Ct) based framework has been historically used to validate ozone disinfection. However, significant viral inactivation can be achieved with little to no measurable ozone exposure. Additionally, ozone exposure depends on multiple water quality variables as well as the calculation/ozone measurement method used. In this study, we evaluated alternative ozone monitoring frameworks as well as the impact of water quality variables on ozone decay kinetics and virus/coliform inactivation. Here we show that both change in UV254 absorbance and applied O3:TOC were well correlated with viral inactivation and these frameworks were resilient to changes in water quality. Both increasing temperature (12-30 ⁰C) and pH (5.5-8.4) was shown to significantly increase the ozone decay rate and decreased the resulting ozone exposure by as much as ∼90% in the case of pH. However, due to the increased reaction rate of ozone with viruses at elevated temperature and pH, there was only a minor impact (∼20% in the case of pH) in overall disinfection performance for a given O3:TOC. These frameworks were also considered for variable source water with TOC (5-11 mg/L) and TSS (1.2-5.8 mg/L). Change in UV254 absorbance or applied ozone dose (mg/L) were the strongest indicators of disinfection performance for source waters of variable TOC, however site-specific testing may be needed to apply this framework. Challenge testing with influent nitrite indicated that ozone disinfection performance is significantly impacted (>50% reduction in inactivation) in the presence of nitrite thus enforcing the importance of accounting for this value in the applied ozone dose. Multi-point ozone dissolution was investigated as an alternative ozone application method that may present a benefit with respect to overall disinfection performance especially if nitrite was present. Developing and validating these alternative monitoring frameworks and ozone application methods is imperative in water reuse applications where unnecessary elevated ozone exposure may lead to harmful byproduct formation.

Robust Activity and Stability of P-Doped Fe-Carbon Composites Derived from MOF for Bromate Reduction

Iron-based materials are effective for the reductive removal of the disinfection byproduct bromate in water, while the construction of highly stable and active Fe-based materials with wide pH adaptability remains greatly challenging. In this study, highly dispersed iron phosphide-decorated porous carbon (Fe2P(x)@P(z)NC-y) was prepared via the thermal hydrolysis of Fe@ZIF-8, followed by phosphorus doping (P-doping) and pyrolysis. The reduction performances of Fe2P(x)@P(z)NC-y for bromate reduction were evaluated. Characterization results showed that the Fe, P, and N elements were homogeneously distributed in the carbonaceous matrix. P-doping regulated the coordination environment of Fe atoms and enhanced the conductivity, porosity, and wettability of the carbonaceous matrix. As a result, Fe2P(x)@P(1.0)NC-950 exhibited enhanced reactivity and stability with an intrinsic reduction kinetic constant (kint) 1.53-1.85 times higher than Fe(x)@NC-950 without P-doping. Furthermore, Fe2P(0.125)@P(1.0)NC-950 displayed superior reduction efficiency and prominent stability with very low Fe leaching (4.53-22.98 μg L-1) in a wide pH range of 4.0-10.0. The used Fe2P(0.125)@P(1.0)NC-950 could be regenerated by phosphating, and the regenerated Fe2P(0.125)@P(1.0)NC-950 maintained 85% of its primary reduction activity after five reuse cycles. The study clearly demonstrates that Fe2P-decorated porous carbon can be applied as a robust and stable Fe-based material in aqueous bromate reduction.

Kinetic modelling assisted balancing of organic pollutant removal and bromate formation during peroxone treatment of bromide-containing waters

The peroxone process (O3/H2O2) is reported to be a more effective process than the ozonation process due to an increased rate of generation of hydroxyl radicals (•OH) and inhibition of bromate (BrO3-) formation which is otherwise formed on ozonation of bromide containing waters. However, the trade-off between the H2O2 dosage required for minimization of BrO3- formation and effective pollutant removal has not been clearly delineated. In this study, employing experimental investigations as well as chemical modelling, we show that the concentration of H2O2 required to achieve maximum pollutant removal may not be the same as that required for minimization of BrO3- formation. At the H2O2 dosage required to minimize BrO3- formation (<10 µg/L), only pollutants with high to moderate reactivity towards O3 and •OH are effectively removed. For pollutants with low reactivity towards O3/•OH, high O3 (O3:DOC>>1 g/g) and high H2O2 dosages (O3:H2O2 ∼1 (g/g)) are required for minimizing BrO3- formation along with effective pollutant removal which may result in a very high residual of H2O2 in the effluent, causing secondary pollution. On balance, we conclude that the peroxone process is not effective for the removal of low reactivity micropollutants if minimization of BrO3- formation is also required.

PFAS removal from landfill leachate by ozone foam fractionation: System optimization and adsorption quantification

Landfills are the primary endpoint for the disposal of PFAS-laden waste, which subsequently releases PFAS to the surrounding environments through landfill leachate. Ozone foam fractionation emerges as a promising technology for PFAS removal to address the issue. This study aims to (i) assess the effectiveness of the ozone foam fractionation system to remove PFAS from landfill leachate, and (ii) quantify equilibrium PFAS adsorption onto the gas-water interface of ozone bubbles, followed by a comparison with air foam fractionation. The results show that ozone foam fractionation is effective for PFAS removal from landfill leachate, with more than 90 % long-chain PFAS removed. The identified operating conditions provide valuable insights for industrial applications, guiding the optimization of ozone flow rates (1 L/min), dosing (43 mg/L) and minimizing foamate production (4 % wettability). The equilibrium modelling reveals that the surface excess of air bubbles exceeds that of ozone bubbles by 20-40 % at a corresponding PFAS concentration. However, the overall removal of PFAS from landfill leachate by ozone foam fractionation remains substantial. Notably, ozone foam fractionation generates foamate volumes 2 - 4 times less, resulting in significant cost savings for the final disposal of waste products and reduced site storage requirements.

Oxidation processes and me

This publication summarizes my journey in the field of chemical oxidation processes for water treatment over the last 30+ years. Initially, the efficiency of the application of chemical oxidants for micropollutant abatement was assessed by the abatement of the target compounds only. This is controlled by reaction kinetics and therefore, second-order rate constant for these reactions are the pre-requisite to assess the efficiency and feasibility of such processes. Due to the tremendous efforts in this area, we currently have a good experimental data base for second-order rate constants for many chemical oxidants, including radicals. Based on this, predictions can be made for compounds without experimental data with Quantitative Structure Activity Relationships with Hammet/Taft constants or energies of highest occupied molecular orbitals from quantum chemical computations. Chemical oxidation in water treatment has to be economically feasible and therefore, the extent of transformation of micropollutants is often limited and mineralization of target compounds cannot be achieved under realistic conditions. The formation of transformation products from the reactions of the target compounds with chemical oxidants is inherent to oxidation processes and the following questions have evolved over the years: Are the formed transformation products biologically less active than the target compounds? Is there a new toxicity associated with transformation products? Are transformation products more biodegradable than the corresponding target compounds? In addition to the positive effects on water quality related to abatement of micropollutants, chemical oxidants react mainly with water matrix components such as the dissolved organic matter (DOM), bromide and iodide. As a matter of fact, the fraction of oxidants consumed by the DOM is typically > 99%, which makes such processes inherently inefficient. The consequences are loss of oxidation capacity and the formation of organic and inorganic disinfection byproducts also involving bromide and iodide, which can be oxidized to reactive bromine and iodine with their ensuing reactions with DOM. Overall, it has turned out in the last three decades, that chemical oxidation processes are complex to understand and to manage. However, the tremendous research efforts have led to a good understanding of the underlying processes and allow a widespread and optimized application of such processes in water treatment practice such as drinking water, municipal and industrial wastewater and water reuse systems.

Highly efficient reduction of bromate by vacuum UV/sulfite system

Bromate (BrO3-), a worldwide regulated by-product after ozone disinfection, is often detected in bromide-containing water, and has a strict limit of 10 μg L-1 in potable water. BrO3- degradation by advanced reduction processes (ARPs) has gained much attention because of efficient removal and easy integration with ultraviolet disinfection (UV at 254 nm). In the vacuum UV (VUV, 185/254 nm)/sulfite system, the elimination kinetics of BrO3- increased by 9-fold and 15-fold comparing with VUV alone and UV/sulfite system. This study further demonstrated the hydrated electron (eaq-) works as the dominant species in BrO3- degradation in alkaline solution, while in the acidic solution the H• became a secondary reactive species besides eaq-. Hence, the influences of pH, sulfite concentration, dissolved gas and water matrix on effectiveness of degradation kinetics of BrO3- was explored in details. With increasing pH, the proportion of SO32- species increased and even became the major ones, which also correlated well with the kobs (min-1) of BrO3- degradation. The stability of eaq- also climbs with increasing pH, while that of H• drops significantly. Higher sulfite dosage favored a more rapid degradation of BrO3-. The presence of dissolved oxygen inhibited BrO3- removal due to the scavenging effect of O2 toward eaq- and transformed VUV/sulfite-based ARP to an advanced oxidation process (AOP), which was ineffective for BrO3- removal. BrO3- removal was inhibited to varying degrees after anions (e.g., bicarbonate (HCO3-), chloride (Cl-), nitrate (NO3-)) and humic acid (HA) being added.