Impact of bromide and iodide during drinking water disinfection and potential treatment processes for their removal or mitigation

In this study, the impact of bromide and iodide on disinfected waters was examined and potential treatment technologies for their removal or mitigation were investigated. Distributed waters from two Western Australian drinking water sources were evaluated in terms of their bromide and iodide concentrations, disinfection by-product (DBP) formation, halogen-specific adsorbable organic halogen (AOX) formation and chlorinous odours after disinfection. In both systems, the brominated DBPs dominated the measured DBPs and, in both cases, the known DSPs accounted for only 30% of total organohalogens. Chloramination with a sufficient free chlorine contact time followed by ammonia addition, rather than preformed monochloramine, may be a viable mitigation strategy for the minimisation of I-OBPs, since exposure to free chlorine should promote the conversion of iodide to iodate, a safe form of iodine. This study has shown that bromide plays an important role in this process, mainly by enhancing the preferred conversion' of iodide to iodate. Ozone pre-treatment selectively oxidised iodide to iodate and minimised the formation of I-OB Ps. Complete conversion of iodide to iodate, while minimising the bromate formation to below the guideline value of 10 µg L-1 was achieved for a wide range of ozone concentrations in raw waters, including raw waters with high bromide concentrations

Photodecomposition of iodinated contrast media and subsequent formation of toxic iodinated moieties during final disinfection with chlorinated oxidants

Large amount of iodinated contrast media (ICM) are found in natural waters (up to µg.L-1 levels) due to their worldwide use in medical imaging and their poor removal by conventional wastewater treatment. Synthetic water samples containing different ICM and natural organic matter (NOM) extracts were subjected to UV254 irradiation followed by the addition of chlorine (HOCl) or chloramine (NH2Cl) to simulate final disinfection. In this study, two new quantum yields were determined for diatrizoic acid (0.071 mol.Einstein-1) and iotalamic acid (0.038 mol.Einstein-1) while values for iopromide (IOP) (0.039 mol.Einstein-1), iopamidol (0.034 mol.Einstein-1) and iohexol (0.041 mol.Einstein-1) were consistent with published data. The photodegradation of IOP led to an increasing release of iodide with increasing UV doses. Iodide is oxidized to hypoiodous acid (HOI) either by HOCl or NH2Cl. In presence of NOM, the addition of oxidant increased the formation of iodinated disinfection by-products (I-DBPs). On one hand, when the concentration of HOCl was increased, the formation of I-DBPs decreased since HOI was converted to iodate. On the other hand, when NH2Cl was used the formation of I-DBPs was constant for all concentration since HOI reacted only with NOM to form I-DBPs. Increasing the NOM concentration has two effects, it decreased the photodegradation of IOP by screening effect but it increased the number of reactive sites available for reaction with HOI.For experiments carried out with HOCl, increasing the NOM concentration led to a lower formation of I-DBPs since less IOP are photodegraded and iodate are formed. For NH2Cl the lower photodegradation of IOP is compensated by the higher amount of NOM reactive sites, therefore, I-DBPs concentrations were constant for all NOM concentrations. 7 different NOM extracts were tested and almost no differences in IOP degradation and I-DBPs formation was observed. Similar behaviour was observed for the 5 ICM tested. Both oxidant poorly degraded the ICM and a higher formation of I-DBPs was observed for the chloramination experiments compared to the chlorination experiment. Results from toxicity testing showed that the photodegradation products of IOP are toxic and confirmed that the formation of I-DBPs leads to higher toxicity. Therefore, for the experiment with HOCl where iodate are formed the toxicity was lower than for the experiments with NH2Cl where a high formation of I-DBPs was observed

Fate of iodide in oxidative water treatment

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Reaction pathway of the degradation of the <i>p</i>-hydroxybenzoic acid by sulfate radical generated by ionizing radiations

International audienceThe degradation of p-hydroxybenzoic acid (HBA) in aqueous solutions by ionizing radiation was studied. The phenolic pollutant was easily removed by the electron beam irradiation, as more than 80% of the initial 100 µM introduced was degraded for a dose of 600 Gy. It was shown that the addition of persulfate, producing the sulfate radical as additional reactive species, induced a change in the reaction pathway. LC–MS analyses were performed in order to identify the different by-products formed. In the absence of persulfate, the main by-product formed was 3,4-dihydroxybenzoic acid, while in presence of persulfate, 1,4-benzoquinone was detected and the hydroxylated by-products were not present. A reaction pathway of HBA degradation by hydroxyl and sulfate radicals was proposed from the identification of the chemical structure of the different by-products detected.The influences of pH and dissolved oxygen were also studied. A high decline of HBA degradation was observed at pH 11 compared to pH 4.5, this decrease was minimized in the presence of persulfate. The dissolved oxygen concentration was found to be a limiting parameter of HBA degradation, however an excess of dissolved oxygen in solution did not improve the degradation to a large extent

Degradation of acetic acid with sulfate radical generated by persulfate ions photolysis

International audienceThe photolysis of S2O82- was studied for the removal of acetic acid in aqueous solution and compared with the H2O2/UV system. The SO4-• radicals generated from the UV irradiation of S2O82- ions yield a greater mineralization of acetic acid than the •OH radicals. Acetic acid is oxidized by SO4-• radicals without significant formation of intermediate by-products. Increasing system pH results in the formation of •OH radicals from SO4-• radicals. Maximum acetic acid degradation occurred at pH 5. The results suggest that above this pH, competitive reactions with the carbon mineralized inhibit the reaction of the solute with SO4-• and also •OH radicals. Scavenging effects of two naturally occurring ions were tested; in contrast to HCO3- ions, the presence of Cl- ions enhances the efficiency of the S2O82-/UV process towards the acetate removal. It is attributed to the formation of the Cl• radical and its great reactivity towards acetate

Radiolysis of acetic acid aqueous solutions—Effect of pH and persulfate addition

The degradation of acetic acid in aqueous solution by ionizing radiation was studied. The radiolysis of acetic acid solution induces the almost complete degradation and mineralization of this compound. The high yield of acetic acid mineralization is explained by the degradation of oxalic acid by solvated electron. The degradation of acetic acid depends on the pH of the solution. The best degradation is observed at pH 4.5 due to the higher rate constant of reaction of acetate with hydroxyl radicals and the competitive reactions of inorganic carbon which occur at higher pH. The influence of persulfate ion (S2O82−) addition that forms the sulfate radical (SO4 −) during irradiation in solution was examined. The persulfate addition induces an almost constant degradation of acetic acid whatever the initial pH of the solution. The decrease of pH during the persulfate radiolysis partly explains the high degradation observed. But the additional radicals formed by the persulfate introduction also improve the degradation

Electron beam irradiation of citric acid aqueous solutions containing persulfate

International audienceThe electron beam irradiation of aqueous solutions of citric acid was studied. The results showed the effectiveness of the degradation of the carboxylic acid by the radiation process. The impact of pH was examined. It was demonstrated that the increase of pH induces a drop of the degradation due to the scavenging of radicals by the inorganic carbon. Moreover the interest of persulfate () addition that induces the formation of sulfate radicals () by the reaction of persulfate with the hydrated electrons was studied. The addition of persulfate leads to a great enhancement of the degradation of the carboxylic acid and also a large increase of the mineralization of the solution. Effectively, it was shown that the particular reactivity of the sulfate radical causes an enhancement of the mineralization yiel

Electron beam irradiation of aqueous solution of persulfate ions

The radiolysis of persulfate (S2O8 2-) aqueous solution was studied for the enhancement of electron beam process applied to water treatment. It was shown that the persulfate ion reacts with aqueous electron and produces additional radical species in aqueous solution. The oxidative radical species formed (sulfate radical SO4 -•) is a very strong oxidant able to react with various recalcitrant pollutants. A model of the evolution of persulfate concentration in solution was performed. It was shown that the presence of persulfate induces a decrease of pH and also an increase of dissolved oxygen concentration in solution during irradiation. Moreover the interest of persulfate addition for the improvement of an organic compound degradation by radiolysis was shown

Oxidative treatment of bromide-containing waters: Formation of bromine and its reactions with inorganic and organic compounds - a critical review

Bromide (Br-) is present in all water sources at concentrations ranging from ~10 to &gt;1000 µg L-1 in fresh waters and about 67 mg L-1 in seawater. During oxidative water treatment bromide is oxidized to hypobromous acid/hypobromite (HOBr/OBr-) and other bromine species. A systematic and critical literature review has been conducted on the reactivity of HOBr/OBr- and other bromine species with inorganic and organic compounds, including micropollutants.The speciation of bromine in the absence and presence of chloride and chlorine has been calculated and it could be shown that HOBr/OBr- are the dominant species in fresh waters. In ocean waters, other bromine species such as Br2, BrCl, and Br2O gain importance and may have to be considered under certain conditions.HOBr reacts fast with many inorganic compounds such as ammonia, iodide, sulfite, nitrite, cyanide and thiocyanide with apparent second-order rate constants in the order of 104–109 M-1 s-1 at pH 7. No rate constants for the reactions with Fe(II) and As(III) are available. Mn(II) oxidation by bromine is controlled by a Mn(III,IV) oxide-catalyzed process involving Br2O and BrCl.Bromine shows a very high reactivity toward phenolic groups (apparent second-order rate constants kapp ˜ 103–105 M-1 s-1 at pH 7), amines and sulfamides (kapp ˜ 105–106 M-1 s-1 at pH 7) and S-containing compounds (kapp ˜ 105–107 M-1 s-1 at pH 7). For phenolic moieties, it is possible to derive second-order rate constants with a Hammett-s-based QSAR approach with log(k(HOBr/-PhO))=7.8-3.5Sslog(k(HOBr/PhO-))=7.8-3.5Ss. A negative slope is typical for electrophilic substitution reactions.In general, kapp of bromine reactions at pH 7 are up to three orders of magnitude greater than for chlorine. In the case of amines, these rate constants are even higher than for ozone. Model calculations show that depending on the bromide concentration and the pH, the high reactivity of bromine may outweigh the reactions of chlorine during chlorination of bromide-containing waters

Identification of disinfection by-product precursors by natural organic matter fractionation: a review

International audienceDuring disinfection of drinking water, natural organic matter reacts with chlorine to produce harmful disinfection by-products. The identification of precursors of disinfection by-products in natural organic matter is challenging because natural organic matter is very complex and poorly known. Therefore, scientists have focused on the fractionation of natural organic matter with membranes or resins to better understand how and which organic matter fractions react during chlorination. Here, we compared the reactivity of various organic fractions with disinfection by-products. For that we did a meta-analysis of 400 water samples published in 80 publications, with focus on chlorination time and dose, SUVA254 and the column capacity factor used during resin fractionation. SUVA254 refers to the ultraviolet absorbance at 254 nm divided by the organic matter concentration. We found that hydrophobic compounds have 10–20% higher reactivity to both trihalomethane and haloacetic acid formation compared to hydrophilic compounds in waters with SUVA254 above 2L/(mg∙m), while hydrophobic and hydrophilic compounds have equal reactivity in waters with low SUVA254. On the other hand, hydrophilic compounds are 20–80% more reactive towards emerging disinfection by-products, regardless of SUVA254. Chlorination time and dose do not influence the reactivity ratio between the different fractions. An increase in column capacity factor can shift the reactivity ratio from hydrophobic to hydrophilic fractions. Dead-end, stirred cell ultrafiltration membrane fractionation might not always produce sharply separated fractions, which is mainly due to fouling. Therefore, no clear correlation could be found between membrane fractions and all investigated disinfection by-product groups