Bromate Formation Research Articles

CuO Promotes the Formation of Halogenated Disinfection Byproducts during Chlorination via an Enhanced Oxidation Pathway.

Previous studies showed that cupric oxide (CuO) can enhance the formation of trihalomethanes (THMs), haloacetic acids, and bromate during chlorination of bromide-containing waters. In this study, the impact of CuO on the formation kinetics and mechanisms of halogenated disinfection byproducts (DBPs) during chlorination was investigated. CuO does not enhance the formation of DBPs (i.e., 1,1,1-trichloropropanone, chloroform, and trichloroacetaldehyde (TCAL) /dichloroacetonitrile) during chlorination of acetone, 3-oxopentanedioic acid (3-OPA), and aspartic acid, respectively. This indicates that the halogen substitution pathway cannot be enhanced by CuO. Instead, CuO (0.1 g L-1) accelerates the second-order rate constants for reactions of chlorine (HOCl) with TCAL, citric acid, and oxalic acid at pH 8.0 and 21 °C from <0.1 to 29.4, 7.2, and 15.8 M-1 s-1, respectively. Oxidation pathway predominates based on the quantification of oxidation products (e.g., a trichloroacetic acid yield of ∼100% from TCAL) and kinetic modeling. CuO can enhance the formation of DBPs (e.g., THMs, haloacetaldehydes, and haloacetonitriles) during chlorination of model compounds and dissolved organic matter, of which both halogen substitution and oxidation pathways are required. Reaction rate constants of rate-limiting steps (e.g., citric acid to 3-OPA, aromatic ring cleavage) could be enhanced by CuO via an oxidation pathway since CuO-HOCl complex is more oxidative toward a range of substrates than HOCl in water. These findings provide novel insights into the DBP formation pathway in copper-containing distribution systems.

Reduction of bromate formation in electrochemical production of hypobromite for water disinfection

Hypohalites are powerful water disinfectants for many applications. Continuous production of hypobromite was studied using an undivided electrochemical cell operating at 20 A cell current (28.9 mA cm−2) and an electrolyte flow of 50 L h−1. With 34 mM NaBr as electrolyte current efficiency is between 25 and 42 %. Anodic oxidation and disproportionation of hypobromite led to formation of substantial concentrations of BrO3− in the electrolyte. BrO3− concentrations up to 1 mM (22.6 mg L−1) were formed during anodic Br− oxidation. Replacement of NaBr by mixtures of NaCl and NaBr as electrolyte led to reduction of BrO3− concentration to 0.5 mM (11.3 mg L−1). By combination of NaCl electrolysis with following dosage of NaBr solution the BrO3− concentration could be reduced below the detection limit of the analytical method which was used to quantify BrO3− and hypobromite. In a freshly prepared 5 mM hypobromite solution the BrO3− concentrations remained below 0.1 mM (2.2 mg L−1). When applied in typical dosage for halogen based disinfectants (10−3 mM and 10−2 mM hypohalite) the BrO3− concentration dilutes to 0.02 μM – 0.2 μM. The optimised process thus leads to BrO3− concentrations below the legal limit for BrO3− in drinking water (10 μg L−1 BrO3−).

A Perspective on Removal of Cyanotoxins from Water Through Advanced Oxidation Processes.

This perspective discusses the challenges associated with the removal of cyanotoxins from raw water sources for drinking water treatment and the emergence of sulfate radical-based advanced oxidation processes (SR-AOPs) as an effective treatment technique. The advantage of SR-AOPs is that they can be activated using a variety of methods, including heat, UV radiation, and transition metal catalysts, allowing for greater flexibility in treatment design and optimization. In addition, the byproducts of SR-AOPs are less harmful than those generated by •OH-AOPs, which reduces the risk of secondary contamination. SR-AOPs generate sulfate radicals (SO4 •-) that are highly selective to certain organic contaminants and have lower reactivity to background water constituents, resulting in higher efficiency and selectivity of the process. The presence of natural organic matter and transition metals in the natural water body increases the degradation efficiency of SR-AOPs for the cyanotoxins. The bromate formation is also suppressed when the water contaminated with cyanotoxins is treated with SR-AOPs.

Oxidation of the N-containing phosphonate antiscalants NTMP and DTPMP in reverse osmosis concentrates: Reaction kinetics and degradation rate

N-containing organophosphonate antiscalants such as Aminotris (methylene phosphonic acid) (NTMP/ATMP) and Diethylenetriamine penta(methylene phosphonic acid) (DTPMP) are commonly used in reverse osmosis (RO) to prevent scaling, as well as to increase permeate yields. However, the concentrate in RO still contains antiscalants which can cause adverse effects in the environment such as mobilization of heavy metals. The abatement of antiscalants from RO concentrate can promote the precipitation of oversaturated scale-forming substances and reduce the risk of adverse environmental effects. In the present study, the degradation of NTMP and DTPMP as representatives for N-containing organophosphonate by ozone, hydroxyl radicals (•OH), and sulfate radicals (SO4•-) are studied regarding reaction kinetics and degradation in different matrices. The results show that NTMP and DTPMP react fast with ozone and sulfate radicals (formed in UV/persulfate). Reaction rate constants of ozone showed a strong pH dependency due to the dissociation of the amine. The apparent reaction rates for pH 7 have been determined to be kapp(NTMP + ozone) = 1.44 × 105 M−1 s−1 and kapp(DTPMP + ozone) = 1.16 × 106 M−1 s−1. Reaction kinetics of •OH and SO4•- did not play a distinctive pH dependency (k(•OH) = 109-1010 M−1 s−1 and k(SO4•-) = 107-108 M−1 s−1). Furthermore, real water experiments have shown that ozonation and UV/persulfate are effective tools to abate organophosphonates in RO concentrates. The formation of carcinogenic bromate in ozonation is minimized by the presence of N-containing organophosphonates presumably due to enhanced ozone consumption and scavenging of free bromine.

Optimizing Ozone Disinfection in Water Reuse: Controlling Bromate Formation and Enhancing Trace Organic Contaminant Oxidation.

The use of ozone/biofiltration advanced treatment has become more prevalent in recent years, with many utilities seeking an alternative to membrane/RO based treatment for water reuse. Ensuring efficient pathogen reduction while controlling disinfection byproducts and maximizing oxidation of trace organic contaminants remains a major barrier to implementing ozone in reuse applications. Navigating these challenges is imperative in order to allow for the more widespread application of ozonation. Here, we demonstrate the effectiveness of ozone for virus, coliform bacteria, and spore forming bacteria inactivation in unfiltered secondary effluent, all the while controlling the disinfection byproduct bromate. A greater than 6-log reduction of both male specific and somatic coliphages was seen at specific ozone doses as low as 0.75 O3:TOC. This study compared monochloramine and hydrogen peroxide as chemical bromate control measures in high bromide water (Br- = 0.35 ± 0.07 mg/L). On average, monochloramine and hydrogen peroxide resulted in an 80% and 36% decrease of bromate formation, respectively. Neither bromate control method had any appreciable impact on virus or coliform bacteria disinfection by ozone; however, the use of hydrogen peroxide would require a non-Ct disinfection framework. Maintaining ozone residual was shown to be critical for achieving disinfection of more resilient microorganisms, such as spore forming bacteria. While extremely effective at controlling bromate, monochloramine was shown to inhibit TrOC oxidation, whereas hydrogen peroxide enhanced TrOC oxidation.

Bromate Formation by the Oxidation of Bromide in the Electrochemically Activated Persulfate Process: Mechanism and Influencing Factors

Bromate Formation by the Oxidation of Bromide in the Electrochemically Activated Persulfate Process: Mechanism and Influencing Factors

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

Ozone is a commonly applied disinfectant and oxidant in drinking water and has more recently been implemented for enhanced municipal wastewater treatment for potable reuse and ecosystem protection. One drawback is the potential formation of bromate, a possible human carcinogen with a strict drinking water standard of 10 μg/L. The formation of bromate from bromide during ozonation is complex and involves reactions with both ozone and secondary oxidants formed from ozone decomposition, i.e., hydroxyl radical. The underlying mechanism has been elucidated over the past several decades, and the extent of many parallel reactions occurring with either ozone or hydroxyl radicals depends strongly on the concentration, type of dissolved organic matter (DOM), and carbonate. On the basis of mechanistic considerations, several approaches minimizing bromate formation during ozonation can be applied. Removal of bromate after ozonation is less feasible. We recommend that bromate control strategies be prioritized in the following order: (1) control bromide discharge at the source and ensure optimal ozone mass-transfer design to minimize bromate formation, (2) minimize bromate formation during ozonation by chemical control strategies, such as ammonium with or without chlorine addition or hydrogen peroxide addition, which interfere with specific bromate formation steps and/or mask bromide, (3) implement a pretreatment strategy to reduce bromide and/or DOM prior to ozonation, and (4) assess the suitability of ozonation altogether or utilize a downstream treatment process that may already be in place, such as reverse osmosis, for post-ozone bromate abatement. A one-size-fits-all approach to bromate control does not exist, and treatment objectives, such as disinfection and micropollutant abatement, must also be considered.

Removal of micropollutants and ecotoxicity during combined biological activated carbon and ozone (BO3) treatment

Ozonation is a viable option to improve the removal of micropollutants (MPs) in wastewater treatment plants (WWTPs). Nevertheless, the application of ozonation is hindered by its high energy requirements and by the uncertainties regarding the formation of toxic transformation products in the process. Energy requirements of ozonation can be reduced with a pre-ozone treatment, such as a biological activated carbon (BAC) filter, that removes part of the effluent organic matter before ozonation. This study investigated a combination of BAC filtration followed by ozonation (the BO3 process) to remove MPs at low ozone doses and low energy input, and focused on the formation of toxic organic and inorganic products during ozonation. Effluent from a WWTP was collected, spiked with MPs (approximately 1 µg/L) and treated with the BO3 process. Different flowrates (0.25–4 L/h) and specific ozone doses (0.2–0.6 g O3/g TOC) were tested and MPs, ecotoxicity and bromate were analyzed. For ecotoxicity assessment, three in vivo (daphnia, algae and bacteria) and six in vitro CALUX assays (Era, GR, PAH, P53, PR, andNrf2 CALUX) were used.Results show that the combination of BAC filtration and ozonation has higher MP removal and higher ecotoxicity removal than only BAC filtration and only ozonation. The in vivo assays show a low ecotoxicity in the initial WWTP effluent samples and no clear trend with increasing ozone doses, while most of the in vitro assays show a decrease in ecotoxicity with increasing ozone dose. This suggests that for the tested bioassays, feed water and ozone doses, the overall ecotoxicity of the formed transformation products during ozonation was lower than the overall ecotoxicity of the parent compounds. In the experiments with bromide spiking, relevant formation of bromate was observed above specific ozone doses of approximately 0.4 O3/g TOC and more bromate was formed for the samples with BAC pre-treatment. This indirectly indicates the effectivity of the pre-treatment in removing organic matter and making ozone more available to react with other compounds (such as MPs, but also bromide), but also underlines the importance of controlling the ozone dose to be below the threshold to avoid formation of bromate. It was concluded that treatment of the tested WWTP effluent in the BO3 process at a specific ozone dose of 0.2 g O3/g TOC, results in high MP removal at limited energy input while no increase in ecotoxicity, nor formation of bromate was observed under this condition. This indicates that the hybrid BO3 process can be implemented to remove MPs and improve the ecological quality of this WWTP effluent with a lower energy demand than conventional MP removal processes such as standalone ozonation.

Inhibition of bromate formation in plasmon-enhanced catalytic ozonation over silver-doped spinel ferrite

High energy consumption and formation of harmful byproducts are two challenges faced by advanced oxidation processes (AOPs). While much research efforts have been devoted to improving the treatment efficiency, byproduct formation and control calls for more attention. In this study, the underlying mechanism of bromate formation inhibition during a novel plasmon-enhanced catalytic ozonation process with silver-doped spinel ferrite (0.5wt%Ag/MnFe2O4) as the catalysts was investigated. By scrutinizing the effects of each factor (i.e. irradiation, catalyst, ozone) as well as the combinations of different factors on major Br species involved in bromate formation, examining the distribution of Br species, and probing the reactive oxygen species partaking in the reactions, it was found that accelerated ozone decomposition which inhibited two main bromate formation pathways and surface reduction of Br species (e.g. HOBr/OBr− and BrO3−) contributed to the inhibition of bromate formation, both of which can be enhanced by the plasmonic effects of Ag and the good affinity between Ag and Br. A kinetic model was developed by simultaneously solving 95 reactions to predict the aqueous concentrations of Br species during different ozonation processes. The good agreement between the model prediction and experimental data further corroborated the hypothesized reaction mechanism.

Enhancing Ferrate Oxidation of Micropollutants via Inducing Fe(V)/Fe(IV) Formation Needs Caution: Increased Conversion of Bromide to Bromate.

This study explores the formation of bromate (BrO3-) in the copresence of Fe(VI) and bromide (Br-). It challenges previous beliefs about the role of Fe(VI) as a green oxidant and highlights the crucial role of intermediates Fe(V) and Fe(IV) in the conversion of Br- to BrO3-. The results show that the maximum concentration of BrO3- of 48.3 μg/L was obtained at 16 mg/L Br- and that the contribution of Fe(V)/Fe(IV) to the conversion was positively related to pH. The study suggests that a single-electron transfer from Br- to Fe(V)/Fe(IV) along with the generation of reactive bromine radicals is the first step of Br- conversion, followed by the formation of OBr- which was then oxidized to BrO3- by Fe(VI) and Fe(V)/Fe(IV). Some common background water constituents (e.g., DOM, HCO3-, and Cl-) significantly inhibited BrO3- formation by consuming Fe(V)/Fe(IV) and/or scavenging the reactive bromine species. While investigations proposing to promote Fe(V)/Fe(IV) formation in Fe(VI)-based oxidation to enhance its oxidation capacity have been rapidly accumulated recently, this work called attention to the considerable formation of BrO3- in this process.

Unexpected trends for the formation of chlorate and bromate during the photolysis of chlorine in bromide-containing water

Solar photolysis of free chlorine (solar/chlorine) in bromide-containing water occurs under various scenarios, such as chlorinated reservoirs and outdoor swimming pools, and the formation of chlorate and bromate is an important issue in the system. We reported unexpected trends for the formation of chlorate and bromate in the solar/chlorine system. Excess chlorine inhibited the formation of bromate, i.e., increasing chlorine dosages from 50 to 100 μM reduced the bromate yield from 6.4 to 1.2 μM in solar/chlorine at 50 μM bromide and pH 7. The yield of bromate in solar/chlorine at 100 μM chlorine and 50 μM bromide in 240 min was 18.8% of that at 50 μM bromine only. The underlying mechanism was that HOCl can react with bromite (BrO2−) to form HOClOBrO−, whose multi-step transformation finally formed chlorate as the major product and bromate as the minor product. This reaction overwhelmed the oxidation of bromite to form bromate by reactive species, such as •OH, BrO• and ozone. On the other hand, the presence of bromide greatly enhanced the formation of chlorate. Increasing bromide concentrations from 0 to 50 μM enhanced the chlorate yields from 2.2 to 7.0 μM at 100 μM chlorine. The absorbance of bromine was higher than that of chlorine, thus the photolysis of bromine formed higher levels of bromite at higher bromide concentrations. Then, bromite rapidly reacted with HOCl to form HOClOBrO− and it further transformed to chlorate. Additionally, 1 mg L−1 NOM had a negligible effect on bromate yields in solar/chlorine at 50 μM bromide, 100 μM chlorine and pH 7. This study demonstrated a new pathway of chlorate and bromate formation in the solar/chlorine system with bromide.

Efficiency of ozonation and O3/H2O2 as enhanced wastewater treatment processes for micropollutant abatement and disinfection with minimized byproduct formation

Ozonation, a viable option for improving wastewater effluent quality, requires process optimization to ensure the organic micropollutants (OMPs) elimination and disinfection under minimized byproduct formation. This study assessed and compared the efficiencies of ozonation (O3) and ozone with hydrogen peroxide (O3/H2O2) for 70 OMPs elimination, inactivation of three bacteria and three viruses, and formation of bromate and biodegradable organics during the bench-scale O3 and O3/H2O2 treatment of municipal wastewater effluent. 39 OMPs were fully eliminated, and 22 OMPs were considerably eliminated (54 ± 14%) at an ozone dosage of 0.5 gO3/gDOC for their high reactivity to ozone or •OH. The chemical kinetics approach accurately predicted the OMP elimination levels based on the rate constants and exposures of ozone and •OH, where the quantum chemical calculation and group contribution method successfully predicted the ozone and •OH rate constants, respectively. Microbial inactivation levels increased with increasing ozone dosage up to ∼3.1 (bacteria) and ∼2.6 (virus) log10 reductions at 0.7 gO3/gDOC. O3/H2O2 minimized bromate formation but significantly decreased bacteria/virus inactivation, whereas its impact on OMP elimination was insignificant. Ozonation produced biodegradable organics that were removed by a post-biodegradation treatment, achieving up to 24% DOM mineralization. These results can be useful for optimizing O3 and O3/H2O2 processes for enhanced wastewater treatment.

Linear and Non-Linear Modelling of Bromate Formation during Ozonation of Surface Water in Drinking Water Production

Bromate formation is a complex process that depends on the properties of water and the ozone used. Due to fluctuations in quality, surface waters require major adjustments to the treatment process. In this work, we investigated how the time of year, ozone dose and duration, and ammonium affect bromides, bromates, absorbance at 254 nm (UV254), near-infrared (NIR) spectra, and fluorescent components (humic-like and tyrosine-like) during surface water ozonation. Linear and non-linear models were used to determine and predict the relationships between input and output variables. Season, ozonation dose and time were correlated with the output variables, while ammonium affected only bromates. All coefficients of determination (R2) for the multiple linear regression models were &gt;0.64, while R2 for the piecewise linear regression models was &gt;0.89. The season had no effect on bromate formation in either model, while ammonium only affected bromides and bromates. Three input variables influenced UV254 in both models. The artificial neural network (ANN) model with the season, ozonation dose and time, ammonium, and NIR spectra was an effective way to describe water ozonation results. The multilayer perception neural network 14-14-5 had the lowest errors and was the best ANN model with R2 values for training, testing, and validation of 0.9916, 0.9826, and 0.9732, respectively.

Control of N-nitrosodimethylamine (NDMA) formation from N,N-dimethylhydrazine compounds by ozone-based advanced oxidation processes

N-nitrosodimethylamine (NDMA) is formed during ozonation of model compounds with dimethylhydrazine groups, such as daminozide (DMZ) and 2-furaldehyde 2,2-dimethylhydrazone (2-F-DMH) at pH 7 with yields of 100 % and 87 %, respectively. In this study, ozone/hydrogen peroxide (O3/H2O2) and ozone/peroxymonosulfate (O3/PMS) were investigated to control NDMA formation, and O3/PMS (50–65 %) was more effective than O3/H2O2 (10–25 %) with a ratio of H2O2 or PMS to O3 of 8:1. The reaction of PMS or H2O2 to decompose ozone could not compete with the ozonation of model compound because of the high second-order rate constants of the ozonation of DMZ (5 ×105 M−1 s−1) or 2-F-DMH (1.6 ×107 M−1 s−1). The Rct value of the sulfate radical (SO4•−) showed a linear relationship with NDMA formation, indicating that SO4•− significantly contributed to its control. NDMA formation could be further controlled by injecting small quantities of ozone numerous times to minimize the dissolved ozone concentration. The effects of tannic acid, bromide and bicarbonate on NDMA formation were also investigated during ozonation, O3/H2O2, and O3/PMS processes. Bromate formation was more pronounced in the O3/PMS process than in the O3/H2O2 process. Therefore, in practical applications of O3/H2O2 or O3/PMS processes, the generation of NDMA and bromate should be detected.

Screening of technologies for limiting the occurrence of disinfection by-products in urban water systems

Providing safe tap water while limiting the occurrence of disinfection by-products (DBPs) is probably one of the most challenging aspects of environmental chemical engineering within the urban water cycle. In the present work, an investigation about this challenge for the real water conditions of a full-scale drinking water treatment plant has been carried out. Five different and well-known technologies (four different aeration procedures, coagulation, hydrogen peroxide dosage, ion exchange and ultrafiltration) were studied in a real surface water matrix from an engineering point of view. A preliminary estimation of operation costs was also included. The study was focused primarily on trihalomethanes (THMs) and bromate, the DBPs currently regulated by the Spanish legislation, under the real treatment conditions of a drinking water treatment plant that distributes water to 100,000 inhabitants from a surface water reservoir. Based on the results, agitation aeration exhibited the greatest performance to remove THMs directly (86.46 % of removal). Ion exchange resin showed the best potential to inhibit their formation by 100 % bromide removal. Moreover, hydrogen peroxide dosage showed outstanding results in tests performed at full-scale for preventing the formation of bromate in the ozonation stage by 60 %. This was also the cheapest technology according to the dosage cost analysis performed, with 0.01 €·m−3. Thus, this investigation about the elimination of DBPs can be used as a reference to select the optimal treatment technology for limiting their occurrence under real working conditions for full-scale drinking water treatment plants.

Catalytic ozonation performance of graphene quantum dot doped MnOOH nanorod for effective treatment of ciprofloxacin and bromate formation control in water

A catalyst GQDs@MnOOH was successfully synthesized by attaching graphene quantum dots (GQDs) on the surface of MnOOH nanorods to boost catalytic ozonation of antibiotic, exemplified by ciprofloxacin (CIP). The result demonstrated that the GQDs@MnOOH/O3 system had the greatest CIP removal effectiveness, followed by that of MnOOH/O3 and O3 only. The 0.02 mM CIP was degraded with 99.9% efficiency in 30 min in the presence 9.6 mg L-1 of O3 catalyzed by 12.5 mg L-1 of GQDs@MnOOH. The kinetic rate constants ​​were in the order: GQDs@MnOOH/O3 (0.161 min−1) > MnOOH/O3 (0.079 min−1) > O3 (0.055 min−1). The GQDs@MnOOH could enhance CIP degradation and inhibit BrO3- formation in different water sources. Results of scavenger and electron paramagnetic resonance (EPR) experiments demonstrated that oxygen radical (O2•-), singlet oxygen (1O2), and hydroxyl radicals (•OH) were involved in CIP degradation by the GQDs@MnOOH/O3 system. Accordingly, the degradation pathways of CIP and mechanism of catalytic ozonation over GQDs@MnOOH were investigated and proposed. This research is expected to shed light on the connection between carbonaceous material and metal hydroxide in catalytic ozonation.

A novel strategy using sulfite for bromate control during UV/persulfate oxidation of bromide-containing waters

The ultraviolet/persulfate (UV/PS) process has attracted more and more attention for water treatment. However, it runs the risk of producing bromate in the presence of bromide ions. In this work, we propose a new strategy using sulfite to inhibit bromate formation. The results show that the addition of sulfite significantly reduced the formed bromate in the UV/PS system by 61.2% and 24.5% in 30 min and 120 min, respectively. Increasing sulfite dosage or pH could enhance bromate control. From the standpoint of reaction kinetics, sulfite is likely to inhibit bromate formation by reducing bromine radicals (Br) back to bromide ions, the energy profile of which was quantified by density functional theory (DFT) calculations. In the UV/PS/sulfite system, the conversion of SO3− to HO was observed, indicating that sulfite also served as a source of reactive radicals. Moreover, sulfite apparently promoted the degradation of benzoic acid and phenol in a UV/PS system, showing advantages over other inorganic reductants. As a result, we discovered that sulfite could not only help control bromate formation in UV/PS but also improve the system’s oxidation capacity.

Efficient liquid-phase hydrogenation of bromate over nanosized Pd catalysts supported on TpBD-Me2 covalent organic framework

The formation of toxic and carcinogenic bromate, BrO3–, during the disinfection of fresh or seawater by ozonation poses a threat to the human health, and therefore the development of methodologies for its removal from water is of high importance. Heterocatalytic bromate hydrogenation has been widely employed to decrease the BrO3– ion concentration in water below the strict legal limit imposed. In this work, we evaluate for the first time the performance of a covalent organic framework (COF) for this reaction. TpBD-Me2 COF was synthesized on gram scale and used as both catalyst and support for Pd nanocatalysts with different Pd loadings for bromate hydrogenation reaction.TpBD-Me2 was found to present considerable catalytic activity for BrO3– reduction with 60% conversion after 180 min. The conversion increased with increasing Pd loading of the COF, with the sample with 5% Pd on COF reaching 93% conversion after 180 min. The catalytic activity was further improved by performing an in situ pre-reduction step before the reaction, resulting in complete conversion of BrO3– already after 60 min of reaction. These results show that COF materials are efficient catalysts for this application.

Overlooked Cytotoxicity and Genotoxicity to Mammalian Cells Caused by the Oxidant Peroxymonosulfate during Wastewater Treatment Compared with the Sulfate Radical-Based Ultraviolet/Peroxymonosulfate Process.

Byproduct formation (chlorate, bromate, organic halogen, etc.) during sulfate radical (SO4•-)-based processes like ultraviolet/peroxymonosulfate (UV/PMS) has aroused widespread concern. However, hypohalous acid (HOCl and HOBr) can form via two-electron transfer directly from PMS, thus leading to the formation of organic halogenated byproducts as well. This study found both PMS alone and UV/PMS can increase the toxicity to mammalian cells of wastewater, while the UV/H2O2 decreased the toxicity. Cytotoxicity of two wastewater samples increased from 5.6-8.3 to 15.7-29.9 mg-phenol/L, and genotoxicity increased from 2.8-3.1 to 5.8-12.8 μg 4-NQO/L after PMS treatment because of organic halogen formation. Organic halogen formation from bromide rather than chloride was found to dominate the toxicity increase. The SO4•--based process UV/PMS led to the formation of both organic halogen and inorganic bromate and chlorate. However, because of the very low concentration (<20 μg/L) and relatively low toxicity of bromate and chlorate, contributions of inorganic byproducts to toxicity increase were negligible. PMS would not form chlorate and bromate, but it generated a higher concentration of total organic halogen, thus leading to a more toxic treated wastewater than UV/PMS. UV/PMS formed less organic halogen and toxicity because of the destruction of byproducts by UV irradiation and the removal of byproduct precursors. Currently, many studies focused on the byproducts bromate and chlorate during SO4•--based oxidation processes. This work revealed that the oxidant PMS even needs more attention because it caused higher toxicity due to more organic halogen formation.

Ozone Diffusion through a Hollow Fiber Membrane Contactor for Pharmaceuticals Removal and Bromate Minimization

Recently, ozonation has been advocated as a solution to tackle emerging contaminants. Hollow fiber membrane contactors (HFMC) have a lower residual ozone concentration than bubble reactors that could limit the formation of potential ozonation by-products, especially bromates that are regulated in drinking water. The aim of this study was to evaluate ozonation with HFMC for pharmaceutical abatement and bromate minimization compared to bubble columns in wastewater. A HFMC, composed of 65 polytetrafluoroethylene hollow fibers with a 0.45 mm/0.87 mm inner/external diameter and a 0.107 m² exchange surface, was used for the ozonation of real-treated wastewater spiked with 2 µM of p-chlorobenzoic acid (p-CBA) and 3 mg.L-1 of bromide. p-CBA was tracked to monitor the production of strongly-oxidant hydroxyl radicals from the decomposition of the molecular ozone. At 100% p-CBA abatement, 1600 µg.L-1 of bromate was formed with the HFMC, whereas 3486 µg.L-1 was formed with the bubble column. These results demonstrate that HFMC can produce a significant amount of hydroxyl radicals while limiting bromate formation in real-treated wastewater. The test water was also spiked with carbamazepine and sulfamethoxazole to evaluate the abatement efficiency of the process. Short contact times (approximately 2s) achieved high rates of pharmaceuticals removal without bromate formation.