Chlorine Dioxide Oxidation Research Articles

Byproduct Formation of Chlorination and Chlorine Dioxide Oxidation in Drinking Water Treatment

Increasing water scarcity caused by population growth, climate change, pollution from natural and anthropogenic sources, etc. is likely to impact the occurrence of water-associated infectious diseases. Nowadays, access to clean and safe water is a growing concern worldwide. Therefore, disinfection of drinking water is a vital step in public treatment systems as it ensures the removal of various contaminants, including pathogenic microorganisms (protozoa, viruses, bacteria, and intestinal parasites) that give rise to waterborne diseases. Nevertheless, undesirable disinfection byproducts (DBPs) are formed during disinfection as a result of reactions between chemical disinfectants and natural organic matter (NOM), and/or anthropogenic contaminants, and/or bromide/iodide that are present in the raw water. The chemical complexity and heterogeneity of matters in the raw water makes the characterization and the mechanism of DBPs formation quite difficult and ambiguous regardless of the previous hundreds of studies on DBPs generation. As chlorination is still the most economic and most often used disinfection method, and beside chlorination, the application of chlorine dioxide is becoming more widespread, this paper investigates the possible DBPs generated using chlorine and chlorine dioxide with highlighting their adverse health effects. It overviews the reactions of those disinfectants with inorganic and organic compounds. It is important to note that in order to better understand the performance of disinfectants in water treatment, further investigations on the mechanisms of them with inorganic and organic compounds found in water are critically needed.

Effect of Substituents on Molecular Reactivity during Lignin Oxidation by Chlorine Dioxide: A Density Functional Theory Study.

Lignin is a polymer with a complex structure. It is widely present in lignocellulosic biomass, and it has a variety of functional group substituents and linkage forms. Especially during the oxidation reaction, the positioning effect of the different substituents of the benzene ring leads to differences in lignin reactivity. The position of the benzene ring branched chain with respect to methoxy is important. The study of the effect of benzene substituents on the oxidation reaction's activity is still an unfinished task. In this study, density functional theory (DFT) and the m062x/6-311+g (d) basis set were used. Differences in the processes of phenolic oxygen intermediates formed by phenolic lignin structures (with different substituents) with chlorine dioxide during the chlorine dioxide reaction were investigated. Six phenolic lignin model species with different structures were selected. Bond energies, electrostatic potentials, atomic charges, Fukui functions and double descriptors of lignin model substances and reaction energy barriers are compared. The effects of benzene ring branched chains and methoxy on the mechanism of chlorine dioxide oxidation of lignin were revealed systematically. The results showed that the substituents with shorter branched chains and strong electron-absorbing ability were more stable. Lignin is not easily susceptible to the effects of chlorine dioxide. The substituents with longer branched chains have a significant effect on the flow of electron clouds. The results demonstrate that chlorine dioxide can affect the electron arrangement around the molecule, which directly affects the electrophilic activity of the molecule. The electron-absorbing effect of methoxy leads to a low dissociation energy of the phenolic hydroxyl group. Electrophilic reagents are more likely to attack this reaction site. In addition, the stabilizing effect of methoxy on the molecular structure of lignin was also found.

The treatment of 2,2′,4,4′,6,6′-hexanitrostilbene explosive wastewater by hydrodynamic cavitation combined with chlorine dioxide

2,2′,4,4′,6,6′-hexanitrostilbene (HNS) explosive wastewater must be strictly treated before discharge due to its a large number of acute toxic mutagenic nitroaromatic compounds (NACs). This study investigated the degradation effect of HNS explosive wastewater by hydrodynamic cavitation combined with chlorine dioxide oxidation (HC+ClO2). The surface-response model was used to simulate the experiment, and it was established that the surface-response polynomial model had high reliability. After the model simulation and experimental investigation, it was concluded that with pH 4.45, ClO2 concentration 14.86 mg/L and treatment time 120 min, the degradation rate of HNS reaches 64.51% in explosive wastewater. Furthermore, the kinetics of HNS degradation by HC or ClO2 oxidation alone and HC+ClO2 oxidation were examined. Compared with the degradation method alone, the degradation effect of HNS by HC+ClO2 was more significant, and the enhancement factor was 1.33, which indicates that HC greatly enhances the oxidation capacity of ClO2. Based on the detection results of the liquid chromatography–mass spectrometry (LC–MS), the possible degradation pathways of HNS were analyzed: within the attack of •OH, HNS were directly or indirectly decomposed into trinitrophenol, after which continuous denitroso occurred to obtain 1,2,3,5-tetrahydroxy benzene, followed by epoxidation cracking to obtain small organic acids, H2O, CO2, etc.

Effects of the Preferential Oxidation of Phenolic Lignin Using Chlorine Dioxide on Pulp Bleaching Efficiency.

Chlorine dioxide is widely used for pulp bleaching because of its high delignification selectivity. However, efficient and clean chlorine dioxide bleaching is limited by the complexity of the lignin structure. Herein, the oxidation reactions of phenolic (vanillyl alcohol) and non-phenolic (veratryl alcohol) lignin model species were modulated using chlorine dioxide. The effects of chlorine dioxide concentration, reaction temperature, and reaction time on the consumption rate of the model species were also investigated. The optimal consumption rate for the phenolic species was obtained at a chlorine dioxide concentration of 30 mmol·L-1, a reaction temperature of 40 °C, and a reaction time of 10 min, resulting in the consumption of 96.3% of vanillyl alcohol. Its consumption remained essentially unchanged compared with that of traditional chlorine dioxide oxidation. However, the consumption rate of veratryl alcohol was significantly reduced from 78.0% to 17.3%. Additionally, the production of chlorobenzene via the chlorine dioxide oxidation of veratryl alcohol was inhibited. The structural changes in lignin before and after different treatments were analyzed. The overall structure of lignin remained stable during the optimization of the chlorine dioxide oxidation treatment. The signal intensities of several phenolic units were reduced. The effects of the selective oxidation of lignin by chlorine dioxide on the pulp properties were analyzed. Pulp viscosity significantly increased owing to the preferential oxidation of phenolic lignin by chlorine dioxide. The pollution load of bleached effluent was considerably reduced at similar pulp brightness levels. This study provides a new approach to chlorine dioxide bleaching. An efficient and clean bleaching process of the pulp was developed.

Visible light-driven chlorite activation process for enhanced sulfamethoxazole antibiotics degradation, antimicrobial resistance reduction and biotoxicity elimination

In this study, a visible light-driven chlorite activation process, i.e., the combined ClO2-photocatalysis process, was constructed to efficiently produce chlorine dioxide for the enhanced degradation of the sulfamethoxazole antibiotic from aqueous solutions. The superiority of the combined ClO2-photocatalysis process compared to visible light photocatalytic system, and chlorine dioxide oxidation process was systematically investigated. The addition of chlorite in the BiOI-based visible light photocatalytic system achieved 100% removal of sulfamethoxazole within 30 min, surpassing both the photocatalytic system (16%) and chlorine dioxide oxidation process (70%). The degradation constant rate (k) was 0.0771 min−1, which was 2.7 times and 51.4 times higher than the chlorine dioxide oxidation process and photocatalytic system, respectively. Water matrix conditions including pH, inorganic ions, and organic matter had little effect on the degradation efficiency of sulfamethoxazole in the combined ClO2-photocatalysis process. Moreover, antibiotic-resistant bacteria can be effectively inactivated and the production of toxic chlorine-containing intermediates and disinfection byproducts is significantly inhibited. This combined ClO2-photocatalysis process takes advantage of photogenerated radicals to activate chlorite to chlorine dioxide, which not only promotes electron-hole separation, but also exhibits high efficiency, durability, resistance to external environment disturbances, and environmental safety, making it a good candidate for the efficient, green, and sustainable treatment of pharmaceutical wastewater.

Direct and Activated Chlorine Dioxide Oxidation for Micropollutant Abatement: A Review on Kinetics, Reactive Sites, and Degradation Pathway

Recently, ClO2-based oxidation has attracted increasing attention to micropollutant abatement, due to high oxidation potential, low disinfection byproduct (DBPs) formation, and easy technical implementation. However, the kinetics, reactive sites, activation methods, and degradation pathways involved are not fully understood. Therefore, we reviewed current literature on ClO2-based oxidation in micropollutant abatement. In direct ClO2 oxidation, the reactions of micropollutants with ClO2 followed second-order reaction kinetics (kapp = 10−3–106 M−1 s−1 at neutral pH). The kapp depends significantly on the molecular structures of the micropollutant and solution pH. The reactive sites of micropollutants start with certain functional groups with the highest electron densities including piperazine, sulfonyl amido, amino, aniline, pyrazolone, phenol groups, urea group, etc. The one-electron transfer was the dominant micropollutant degradation pathway, followed by indirect oxidation by superoxide anion radical (O2•−) or hydroxyl radical (•OH). In UV-activated ClO2 oxidation, the reactions of micropollutants followed the pseudo-first-order reaction kinetics with the rates of 1.3 × 10−4–12.9 s−1 at pH 7.0. Their degradation pathways include direct ClO2 oxidation, direct UV photolysis, ozonation, •OH-involved reaction, and reactive chlorine species (RCS)-involved reaction. Finally, we identified the research gaps and provided recommendations for further research. Therefore, this review gives a critical evaluation of ClO2-based oxidation in micropollutant abatement, and provides recommendations for further research.

Free chlorine formation in the process of the chlorine dioxide oxidation of aliphatic amines

Chlorine dioxide (ClO2) is commonly used as an alternative disinfectant to chlorine because it has a high bactericidal effect and may produce limited concentrations of halogenated disinfection byproducts (DBPs). However, previous studies have reported that free available chlorine (FAC) was produced when ClO2 reacted with some compounds, such as phenol, leading to the formation of halogenated DBPs. In this study aliphatic amines was found to react rapidly with ClO2 to form significant amount of FAC and its related DBPs. This study investigated the formation of FAC when ClO2 reacts with six model aliphatic amines (including primary amines, secondary amines and tertiary amines). FAC was formed immediately as ClO2 was added to the precursor solution. The maximum yield of FAC even reached 45% (based on consumed ClO2) when ClO2 reacted with 20 μM methylamine at a dose of 10 μM, which is close to a realistic maximum dose (about 0.8 mg/L) in the U.S.. The reactivity of amines to result FAC follows the sequence tertiary amines < secondary amines < primary amines. It was verified that the addition of aliphatic amines may enhance the formation of FAC during ClO2 oxidation in actual water samples. Organic chloramines and other chlorinated DBPs, such as cyanogen chloride, were detected when ClO2 was used as the sole oxidant of real water samples. This study demonstrated that chlorine-related byproducts may also be formed in the presence of organic amines during ClO2 treatment.

Degradation effect of ultraviolet-induced advanced oxidation of chlorine, chlorine dioxide, and hydrogen peroxide and its impact on coagulation of extracellular organic matter produced by Microcystis aeruginosa

Implementation of an ultraviolet (UV)-induced advanced oxidation process (AOP) before coagulation was found to enhance the removal of algae cells. However, the effect of UV-induced AOPs on extracellular cellular organic matter (EOM) and on its coagulation and removal was neglected. This study investigated the impact of UV-induced AOPs (UV/Cl2, UV/ClO2, and UV/H2O2) on EOM from Microcystis aeruginosa, and its coagulation and removal by a conventional gravity system (CGS), dissolved air flotation, and a low-energy flash-pressurized flotation (FPF) process. The changes in EOM characteristics before and after the UV-induced AOPs were based on UV absorbance (UV254) and liquid chromatography with organic carbon detection analysis. The reduction in UV254 increased with an increasing dose of oxidant and UV irradiation. The reduction in UV254 for UV/Cl2, UV/ClO2 and UV/H2O2 was 59.5%, 26.5%, and 17.5% respectively, for 0.71 mM equimolar concentration of oxidant and 1920 mJ/cm2 UV irradiation, as evident from a pseudo-first order kinetics study. Similarly, degradation of the high molecular weight to low molecular weight (LMW) fraction was pronounced for UV/Cl2. The coagulation efficiency decreased after UV-induced AOP in the following order: UV/H2O2 > UV/ClO2 > UV/Cl2. By contrast, the low-energy FPF process showed a higher removal of LMW fractions than CGS. Thus, low-energy FPF could be an alternative technology for the UV-induced AOP treatment system.

Natural organic matter removal in a full-scale drinking water treatment plant using ClO2 oxidation: Performance of two virgin granular activated carbons

The removal of different natural organic matter (NOM) components from boreal lake water was studied at ambient temperature (0.4–18.5 °C) in a full-scale drinking water treatment plant (DWTP). The specific aim was to compare the performance of granular activated carbon (GAC) filters containing different commercial carbons. Liquid chromatography with organic carbon detection (LC-OCD), fluorescence excitation and emission matrices (FEEM), and biodegradable dissolved organic carbon (BDOC) analyses showed that surface water NOM was dominated by humic substances (HS), had the highest fluorescence intensity at the region associated with fulvic acid-like NOM and contained, on average, 0.2 mg/L of BDOC. Coagulation-flocculation and flotation removed 61–82 % of HS and biopolymers and, on average, 50 % of the BDOC. Chlorine dioxide oxidation increased the proportion of HS with 18–22 % and the concentration of BDOC with, on average, 0.05 mg/L, while it decreased the proportion of low-molecular-weight neutrals (LMWN). Sand and GAC filtration removed BDOC to a level below 0.15 mg/L. The two studied GACs showed a 25 % difference in their cumulative total organic carbon (TOC) removals. The distributions of NOM fractions were similar in the effluents of both filters, with LMWN being the most efficiently removed fraction. NOM removal was due to adsorption rather than biodegradation in the filters. In conclusion, DWTPs benefit from complementary analyses, such as LC-OCD, FEEM and BDOC, for understanding and optimising NOM removal. Comparison of different GACs in full-scale studies is also important due to differences in the TOC removals of GACs with similar product specifications.

Chlorine Dioxide in COVID-19: Hypothesis about the Possible Mechanism of Molecular Action in SARS-CoV-2

Introduction: The aim of this review is to hypothesize the mechanism of action of chlorine dioxide in COVID-19 by studying its mechanism of action in the structure of SARS-CoV-2. Methods: Reviews of research on the mechanism of action of chlorine dioxide in viruses, particularly SARS-CoV-2and influenza viruses at the amino acid level in the viral spike were conducted and these data were transferred to the same structural amino acids of SARS-CoV-2. We used 3D computer reconstructions, use of data through cryo-electronic studies, and previous work based on ChimeraX (UCSF) augmented reality software. Results: The projection and simulation of chlorine dioxide oxidation in structural amino acids of SARS-CoV-2 allows inferring the sites in which chlorine dioxide exerts a denaturalizing action on viral structure and on human ACE2 as well as it is possible to understand the extreme speed with which it acts, which could explain the first findings of clinical observational studies of chlorine dioxide use in COVID-19 carried out by the authors in Bolivia under strict compliance of ethics committee. Conclusion: The oxidation by chlorine dioxide of critical amino acids in the spike of the coronavirus SARS-CoV-2 and in the structure of ACE2 allows us to understand the potentially therapeutic actions of chlorine dioxide dissolved in water by oral way in the COVID-19. We hope to publish clinical application trials of this promising systemic virucide soon.

Chlorine and chlorine dioxide oxidation of natural organic matter in water treatment plants

Chlorine and chlorine dioxide oxidation of natural organic matter in water treatment plants

A new water treatment technology for degradation of B[a]A by hydrodynamic cavitation and chlorine dioxide oxidation.

Managing environmental contamination with Benz[a]anthracene (B[a]A) is essential due to its carcinogenic, teratogenic and mutagenic effects on humans and the environment. At present, the mainly B[a]A degradation methods used are photodegradation, bioremediation and traditional advanced oxidation, although they all have disadvantages. In this study, B[a]A was degraded by hydrodynamic cavitation (HC), chlorine dioxide (ClO2), or an innovative combination of the two methods. According to high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) analysed the degradation products and degradation pathway of B[a]A, with the kinetics of different degradation methods discussed. Under optimal conditions, HC combined with ClO2 oxidation can further degrade products to achieve ring cleavage. Compared with the two separate degradation process methods, the combined method exerts a synergistic effect on the degradation of B[a]A, with an enhancement factor of 1.48. Experimental results showed that the combination method can realize enhanced complete degradation of B[a]A, reduce ClO2 requirements, improve efficiency, reduce energy consumption and produce less harmful products with ring cleavage achieved.

Chlorine dioxide catalytic oxidation by zero valent iron for the degradation of PNP in aqueous solution

In order to evaluate the degradation of p-nitrophenol (PNP) in aqueous solution by chlorine dioxide oxidation process catalyzed by Fe0 micro-particles, the effects of Fe0 dosage (0-5.0 g/L), ClO2 dosage (0-2.0 g/L), initial pH (3.0-13.0) and air flow rate (0-5.0 mL/min) on chemical oxygen demand (COD) removal of PNP in aqueous solution were investigated comprehensively. In particular, the maximum COD removal was obtained under the optimal conditions (i.e., Fe0 dosage of 4.0 g/L, ClO2 dosage of 1.2 g/L, initial pH of 5.0, stirring speed of 300 rpm and reaction time of 30 min). Meanwhile, the two control experiments (i.e., Fe0 alone and ClO2 alone systems) were carried out to confirm the performance of chlorine dioxide oxidation process catalyzed by Fe0 micro-particles. In a word, the study provided an effective and promising catalytic oxidation technology for toxic and refractory pollutants.

Deactivation of wastewater-derived N-nitrosodimethylamine precursors with chlorine dioxide oxidation and the effect of pH

In this study, the effect of chlorine dioxide (ClO2) oxidation on the deactivation of wastewater (WW)-derived N-nitrosodimethylamine (NDMA) precursors was investigated under various conditions (i.e., ClO2 application pH, dose and contact time). At pH 6.0, decreases in NDMA formation potentials (FPs) or occurrences (under uniform formation conditions [UFC]) were relatively low (<25%) with ClO2 oxidation regardless of WW-impact. A negative removal was also observed after ClO2 oxidation in some of the non-impacted waters. However, NDMA FP removals were significant (up to ~85%) under the same oxidation conditions in WW-impacted waters at pH 7.8. This indicates that the majority of WW-derived NDMA precursors can be deactivated with ClO2 oxidation above neutral pH. This was attributed to the better oxidative reaction of ClO2 with amines that have lone pair electrons to be shared at higher oxidation pH conditions. In addition, relatively short oxidation periods with ClO2 (i.e., ≤10 min) or low Ct (concentration × time, ~10 mg ∗ min/L) values were sufficient for the deactivation of WW-derived NDMA precursors. ClO2 oxidation was effective in freshly WW-impacted waters. Natural attenuation processes (e.g., sorption, biodegradation, etc.) can change the reactivity of WW-derived NDMA precursors for oxidation with ClO2. The effect of ClO2 on the removal of THM precursors was low (<25%) and independent of oxidation conditions. Given the low formation of regulated THMs and HAAs, ClO2 oxidation presents a viable option for the simultaneous control of NDMA and regulated DBP formation during water treatment, especially for utilities treating WW-impacted water sources.

Degradation of Methyl Orange Using Hydrodynamic Cavitation Technology Combined with Chlorine Dioxide Oxidation: Optimization Using Box–behnken Design (bbd)

In the present work, the hydrodynamic cavitation technology combined with chlorine dioxide oxidation was proved to be an effective method to degrade the methyl orange (MO). The influencing factors in the main experimental process such as solution temperature (25-45 °C), inlet pressure (0.2-0.6 Mpa), reaction time (20- 60min) were investigated. Response surface methodology (RSM) based on Box-Behnken design (BBD) experiments were employed to optimize the experimental methods. The best performance of combined process for degradation of chlorine dioxide was achieved at temperature of 38.13 °C, inlet pressure of 0.4 Mpa and reaction time of 60min and the optimal degradation rate was 82.97% which was very close to the actual experimental result of 82.8% under the same experimental condition. The experimental results showed that BBD could optimize the experimental results well with high accuracy which may simplify the experimental step and a better experimental result could obtained.

Chlorine dioxide oxidation of Escherichia coli in water – A study of the disinfection kinetics and mechanism

ABSTRACTThis study investigated the kinetics and mechanism of chlorine dioxide (ClO2) inactivation of a Gram-negative bacteria Escherichia coli (ATCC 35218) in oxidant demand free (ODF) water in detail as a function of disinfectant concentration (0.5–5.0 mg/L), water pH (6.5–8.5), temperature variations (4–37°C) and bacterial density (105–107 cfu/mL). The effects of ClO2 on bacterial cell morphology, outer membrane permeability, cytoplasmic membrane disruption and intracellular enzymatic activity were also studied to elucidate the mechanism of action on the cells. Increasing temperature and disinfectant concentration were proportional to the rate of cell killing, but efficacy was found to be significantly subdued at 0.5 mg/L and less dependent on the bacterial density. The bactericidal efficiency was higher at alkaline pH of 8 or above as compared to neutral and slightly acidic pH of 7 and 6.5 respectively. The disinfection kinetic curves followed a biphasic pattern of rapid inactivation within the initial 2 min which were followed by a tailing even in the presence of residual biocide. The curves were adequately described by the Cavg Hom model. Transmission Electron Microscopy images of the bacteria cells exposed to lethal concentrations of ClO2 indicated very little observable morphological damage to the outer membranes of the cells. ClO2 however was found to increase the permeability of the outer and cytoplasmic membranes leading to the leakage of membrane components such as 260 nm absorbing materials and inhibiting the activity of the intracellular enzyme β-D-galactosidase. It is suggested that the disruption of the cytoplasmic membrane and subsequent efflux of intracellular components result in the inactivation of the Gram-negative bacteria.

Combined chlorine dioxide oxidation and biological activated carbon processes for treatment of oxytetracycline wastewater

Combined chlorine dioxide oxidation and biological activated carbon processes for treatment of oxytetracycline wastewater

Oxidative transformation of oxcarbazepine by Cl2, ClO2 and O3: characteristics and pathways

In this research, the degradation efficiency, mechanism and intermediates’ toxicities of oxcarbazepine (OXC) upon chlorination, chlorine dioxide oxidation and ozonation were investigated. Results showed that three degradation approaches followed second-order kinetics, and ozonation had the highest removal efficiency both of OXC and dissolved organic carbon (DOC). Reaction intermediates were evaluated by ultra performance liquid chromatography in combination with time-of-flight mass spectrometry (UPLC-Q-TOF-MS). Totals of 11, six and 10 intermediates were detected during the oxidation processes of chlorination, chlorine dioxide oxidation and ozonation, respectively. Although three oxidation approaches had similar pathways in N-heterocyclic ring cleavage and reorganization, ozonation was much more focused on attacking by hydroxyl radicals (OH•), while chlorination had significant Cl-substitution by-products. Chlorine dioxide oxidation brought about fewer degradation by-products than the other two approaches. The above-mentioned oxidation intermediates according to EPA TEST were predicted to be more toxic than OXC, especially those from chlorination. Further test results of the eco-toxicities of oxidized mixtures to the bioluminescent marine bacterium Vibrio fischeri demonstrated the chlorinated samples could lead to the accumulation of toxic transformation products, while chlorine dioxide oxidation and ozonation had detoxication impacts during these processes.

Effect of chlorine dioxide on cyanobacterial cell integrity, toxin degradation and disinfection by-product formation

Bench scale tests were conducted to study the effect of chlorine dioxide (ClO2) oxidation on cell integrity, toxin degradation and disinfection by-product formation of Microcystis aeruginosa. The simulated cyanobacterial suspension was prepared at a concentration of 1.0×106cells/mL and the cell integrity was measured with flow cytometry. Results indicated that ClO2 can inhibit the photosynthetic capacity of M. aeruginosa cells and almost no integral cells were left after oxidation at a ClO2 dose of 1.0mg/L. The total toxin was degraded more rapidly with the ClO2 dosage increasing from 0.1mg/L to 1.0mg/L. Moreover, the damage on cell structure after oxidation resulted in released intracellular organic matter, which contributed to the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) as disinfection by-products. Therefore, the use of ClO2 as an oxidant for treating algal-rich water should be carefully considered.

A comparison of disinfection by-products formation during sequential or simultaneous disinfection of surface waters with chlorine dioxide and chlor(am)ine

The effect of chlorine dioxide (ClO2) oxidation on the formation of disinfection by-products (DBPs) during sequential (ClO2 pre-oxidation for 30 min) and simultaneous disinfection processes with free chlorine (FC) or monochloramine (MCA) was investigated. The formation of DBPs from synthetic humic acid (HA) water and three natural surface waters containing low bromide levels (11–27 μg/L) was comparatively examined in the FC-based (single FC, sequential ClO2-FC, and simultaneous ClO2/FC) and MCA-based (single MCA, ClO2-MCA, and ClO2/MCA) disinfection processes. The results showed that much more DBPs were formed from the synthetic HA water than from the three natural surface waters with comparative levels of dissolved organic carbon. In the FC-based processes, ClO2 oxidation could reduce trihalomethanes (THMs) by 27–35% and haloacetic acids (HAAs) by 14–22% in the three natural surface waters, but increased THMs by 19% and HAAs by 31% in the synthetic HA water after an FC contact time of 48 h. In the MCA-based processes, similar trends were observed although DBPs were produced at a much lower level. There was an insignificant difference in DBPs formation between the sequential and simultaneous processes. The presence of a high level of bromide (320 μg/L) remarkably promoted the DBPs formation in the FC-based processes. Therefore, the simultaneous disinfection process of ClO2/MCA is recommended particularly for waters with a high bromide level.