Formation Of Iodinated Trihalomethanes Research Articles

Sequential combination of pre-chlorination and powdered activated carbon adsorption on iodine removal and I-THMs control in drinking water

Combining pre-oxidation with activated carbon adsorption was explored as an ideal approach for removing iodine from water source to eliminate the formation of Iodinated trihalomethanes (I-THMs). Compared with permanganate and monochloramine, chlorine is more suitable as pre-oxidant to obtain higher active iodine species (HOI/I2). Active iodine species adsorption using both powdered activated carbon (PAC) and granular activated carbon (GAC) can be well fitted the pseudo-second-order kinetic model indicating that chemical adsorption was the dominant mechanism for HOI/I2 adsorption. The average pore size of activated carbons was the most strongly correlated with the adsorption capacity (R2 > 0.98), followed by methylene blue (R2 > 0.76), pore volume (R2 > 0.70) and iodine number (R2 > 0.67). Moreover, three models, including intraparticle diffusion, Byod kinetic, and diffusion-chemisorption were used to illustrate the mechanisms of HOI/I2 adsorption. Chemical adsorption was the dominant mechanism for HOI/I2 adsorption. In summary, at the molar ratio of [NaClO] and [I−] as 1.2, pre-chloriantion time of 5 min, subsequently dosage of 15 mg/L of PAC E with 20 min adsorption can remove 79.8% iodine. In addition, the combined process can eliminate 61%–87.2% of I-THMs in the subsequent chlor(am)ination. The results indicate that pre-chlorination combined with PAC can effectively removed HOI/I2 and attenuate I-THMs formation in the subsequent disinfection process.

Insight into the formation of iodinated trihalomethanes during chlorination, monochloramination, and dichloramination of iodide-containing water

In this study, the formation of iodinated trihalomethanes (I-THMs) was systematically evaluated and compared for three treatment processes - (i) chlorination, (ii) monochloramine, and (iii) dichloramination - under different pH conditions. The results demonstrated that I-THM formation decreased in the order of monochloramination > dichloramination > chlorination in acidic and neutral pH. However, the generation of I-THMs increased in the dichloramination < chlorination < monochloramination order in alkaline condition. Specifically, the formation of I-THMs increased as pH increased from 5 to 9 during chlorination and monochloramination processes, while the maximum I-THM formation occurred at pH 7 during dichloramination. The discrepancy could be mainly related to the stability of the three chlor (am) ine disinfectants at different pH conditions. Moreover, in order to gain a thorough insight into the mechanisms of I-THM formation during dichloramination, further investigation was conducted on the influencing factors of DOC concentration and Br−/I− molar ratio. I-THM formation exhibited an increasing and then decreasing trend as the concentration of DOC increased from 1 to 7 mg-C/L, while the yield of I-THMs increased with increasing Br−/I− molar ratio from 5:0 to 5:10. During the three processes mentioned above, similar I-THM formation results were also obtained in real water, which indicates that the excessive generation of I-THMs should be paid special attention during the disinfection of iodide-containing water.

Generation of iodinated trihalomethanes during chloramination in the presence of solid copper corrosion products

Copper water pipelines are widely used in water distribution systems, but the effects of solid copper corrosion products (CCPs) including CuO, Cu2O and Cu2(OH)2CO3 on the generation of iodinated trihalomethanes (I-THMs) during chloramination remain unknown. This study found that the formation of I-THMs during chloramination of humic acid (HA) was inhibited by the presence of CuO and Cu2O, but promoted with the addition of Cu2(OH)2CO3. The negative effect of CuO and Cu2O is mainly exerted by promoting the decay of both NH2Cl and HOI. Although Cu2(OH)2CO3 also accelerated the decomposition of NH2Cl and HOI, it was found that the complexes formed between Cu2(OH)2CO3 and HA facilitated, through carboxyl functional groups, the reaction between HA and HOI, leading to an enhancement of I-THM generation during chloramination, which was further confirmed by model compound experiments. Additionally, this study demonstrated that the effects of solid CCPs on I-THM generation during chloramination were solid CCP- and HA-concentration dependent, but almost unaffected by different initial I− and Br− concentrations. This study provides new insights into the health risks caused by the corrosion of copper water pipelines, especially in areas intruded by sea water.

Enhanced formation of iodinated trihalomethanes in a mixed chlorine/chloramine system and attenuation by UV-activated process

Iodinated trihalomethanes (I-THMs) have drawn increasing concerns due to their higher toxicity than those of their chlorinated and brominated analogues. In this study, I-THM formation was firstly evaluated for three treatment scenarios - (i) chlorine alone, (ii) chloramine alone, and (iii) mixed chlorine/chloramine - in the presence and absence of UV irradiation for the iodide-containing humic acid solution or natural water. The results indicated that I-THM formation decreased in the order of mixed chlorination/chloramination > chloramination > > chlorination, which fitted the trend of toxicity evaluation results using Chinese hamster ovary cells. Conversely, total organic halide concentration decreased in the order of chlorination > > chloramination ≈ mixed chlorination/chloramination. Besides, I-THM formation can be efficiently controlled in a UV-activated mixed chlorine/chloramine system. Influencing factors including pH values and Br-/I- molar ratios were also systematically investigated in a mixed chlorine/chloramine system. Enhanced I-THM formation was observed with increasing pH values (6.0–8.0) and Br-/I- molar ratios (1: 1–10: 1). The results obtained in this study can provide new insights into the increasing risk of I-THM formation in a mixed chlorine/chloramine system and the effective control of I-THMs in the iodide-containing water using UV irradiation.

Treatment of iodine-containing water by the UV/NH2Cl process: Dissolved organic matters transformation, iodinated trihalomethane formation and toxicity variation

UV/NH2Cl process is becoming increasingly important for water treatment, while its impact on iodine-containing water remains unknown. In this study, the structure transformation of dissolved organic matters (DOMs), generation of iodinated trihalomethanes (I-THMs), and variation of acute toxicity were evaulated during the UV/NH2Cl treatment of iodine-containing water. The combination of exciation emission matrix-parallel factor analysis and two-dimensional correlation spectroscopy integrated with synchronous fluorescence and infrared absorption spectroscopy showed that fulvic-like fraction of DOM was more susceptible to UV/NH2Cl process and particularly iodo and polysaccharide groups gave the fastest resopnses. Consequently, UV fluence lower than 60 mJ/cm2 promoted the production of I-THMs, while excessive UV exhausted NH2Cl and reactive iodine species and subsequently reduced I-THM generation. Moreover, DOM concentration and source, NH2Cl dosage, and I− concentration had significant impacts on I-THM formation in the UV/NH2Cl process. Additionally, a positive correlation was found between acute toxicity variation and I-THM formation when treating iodine-containing waters with UV/NH2Cl. These results together provide a comprehensive understanding on UV/NH2Cl treatment of iodine-containing water.

Photodegradation pathway of iodate and formation of I-THMs during subsequent chloramination in iodate-iodide-containing water

This study investigated the mechanisms of mixed IO3−/I− system under UV irradiation in drinking water and compared the iodinated trihalomethanes (I-THMs) formation of a mixed IO3−/I− system to that of single I− and IO3− systems during subsequent chloramination. The effects of initial I−/IO3− molar ratio, pH, and UV intensity on a mixed IO3−/I− system were studied. The introduction of I− enhanced the conversion rate of IO3− to reactive iodine species (RIS). Besides, IO3− degradation rate increased with the increase of initial I− concentration and UV intensity and the decrease of pH value. In a mixed IO3−/I− system, IO3− could undergo direct photolysis and photoreduction by hydrated electron (eaq−). Moreover, the enhancement of I-THM formation in a mixed IO3−/I− system during subsequent chloramination was observed. The I-THM yields in a mixed IO3−/I− system were higher than the sum of I-THMs produced in a single IO3− and I− systems at all the evaluated initial I− concentrations and pH values. The difference between I-THM formation in a mixed IO3−/I− system and the sum of I-THMs in a single IO3− and I− systems increased with the increase of initial I− concentration. As the initial pH decreased from 9 to 5, the difference of I-THM yields enhanced, while the total I-THM yield of a mixed IO3−/I− system and single I− and IO3− systems decreased slightly. Besides, IO3−-I−-containing water with DOC concentration of 2.5-4.5 mg-C/L, which mainly contained humic-acid substances, had a higher risk in I-THMs formation than individual I−-containing and IO3−-containing water.

Iodinated trihalomethanes formation in iopamidol-contained water during ferrate/chlor(am)ination treatment

Iopamidol is a commonly used iodinated X-ray contrast media in medical field, and its residue in water can react with disinfectants to form highly toxic iodinated disinfection by-products (I-DBPs). This study investigated the degradation of iopamidol and formation of DBPs, especially iodinated trihalomethanes (I-THMs), during ferrate (Fe(VI)) pre-oxidation and subsequent chlor(am)ination under raw water background. It was found that iopamidol degradation efficiency in raw water by Fe(VI) at pH 9 could reach about 80%, which was much higher than that at pH 5 and pH 7 (both about 25%). With Fe(VI) dose increasing, iopamidol removal efficiency increased obviously. During the iopamidol degradation by Fe(VI), IO3− was the dominant product among all the iodine species. After pre-treated by Fe(VI), yields of THM4 and I-THMs can be reduced in subsequent chlor(am)ination. Besides, pH was a crucial factor for Fe(VI) pre-oxidition controlling DBPs. With the pH increasing from 5 to 9, the yield of THM4 kept increasing in subsequent chlorination but showed the highest amount at pH 6 in subsequent chloramination. The yield of I-THMs increased first and then decreased with the increase of pH in both subsequent chlorination and chloramination. I-THM concentrations in chlorinated samples were lower than chloraminated ones under acidic conditions but became higher under neutral and alkaline conditions. The total CTI of THMs during Fe(VI)-chloramination was higher than that during Fe(VI)-chlorination under neutral condition, but sharply decreased under alkaline conditions. In summary, Fe(VI)-chloramination subsequent treatment under alkaline conditions should be an effective method for iopamidol removal and DBP control.

Removal of disinfection by-product precursors by ion exchange resins

The removal of dissolved organic carbon (DOC) is a key factor in the control of disinfection by-product (DBP) formation in drinking water. Ion exchange process deals with the removal of naturally negatively charged organic matter. A fluidized bed column test has been chosen to test in parallel the efficiency of 4 different anionic exchange resins (Purolite PPA860S, Dowex TAN-1, Amberlite IRA-958 and IRA-410) in terms of DOC fraction removal and related DBP formation reduction. IRA-410 was shown to be the best performing resin in terms of DOC and DBP formation potential reduction followed by PPA860S. These resins removed respectively 41 and 37 % of DOC, with humic substances as the main target of the two resins (68 and 72 % reduction, respectively, based on size exclusion chromatography with an organic carbon detector). The UV absorbance was reduced in a higher proportion than the DOC demonstrating a preference of the resins for the relatively hydrophobic compounds. The reduction in trihalomethane and haloacetic acid formation was higher than the DOC removal for IRA-410 and PPA860S (53 and 59 %, respectively); whereas IRA-958 on the other hand showed a lower reduction in DBP formation potential than its DOC removal. All the resins showed a much higher reduction of iodinated trihalomethanes formation potential (66–96% reduction compared to raw water) due to the removals of iodide in addition of organic precursors. However, in a context of increasing halide concentrations, the different resins showed a reduction of their efficiency to control the formation of DBPs.

Formation of emerging iodinated disinfection by-products during ballast water treatment based on ozonation processes

Disinfection by-products (DBPs) generated by ballast water treatment pose a potential threat to marine environment which aroused widespread concern. In recent years, emerging iodinated DBPs have attracted widespread attention because of their stronger cytotoxicity and genotoxicity than brominated/chlorinated DBPs. In this study, the effects of different natural organic matter species, total residual oxidant (TRO) concentrations, storage time, temperature, pH, bromide and iodide concentrations on the generation of iodinated trihalomethanes (I-THMs) during ozonation process of ballast water were investigated. The results showed that bromochloroiodomethane and diiodochloromethane (DICM) were not detected under all conditions during ozonation of humaic acid (HA). Different kinds of precursors had a significantly effect on the formation of I-THMs. For algal cells as precursor, DICM were detected (1.22 μg/L), while DICM were not detected from oxidation of 1,3-etonedicarboxylic acid, fulvic acid (FA), phenol, resorcinol, hydroquinone and HA as precursors. The yields of I-THMs from oxidation of algal cells, FA and phenol were higher than other precursors. Linear relationships were observed between the formation of I-THMs and TRO concentrations. The yields of I-THMs reached a peak at 48 h (180 μg/L) after ozonation treatment of ballast water, and then decreased with storage time extension. An increase in temperature enhanced the formation of dibromoiodomethane and bromodiiodomethane, while wakened the formation of iodoform and dichloroiodomethane. The formation of I-THMs was complicatedly affected by different pH values in the range from 4 to 9. The more bromide concentrations, the more brominated I-THMs were formed. The concentrations of I-THMs increased with increasing iodide concentrations, and low concentrations of iodide had greater effect on the production of I-THMs than high concentrations of iodide.

Organic Amines Enhance the Formation of Iodinated Trihalomethanes during Chlorination of Iodide-Containing Waters

The effects of organic amines (OAs) including glycine (Gly), sarcosine (Sar), and triethanolamine (Tea), representing primary, secondary, and tertiary amines, respectively, on iodinated trihalomethanes (I-THMs) formation during chlorination of iodide (I-)-containing waters were investigated. The total concentration of I-THMs formed in the co-presence of an OA and natural organic matter (NOM) was more than 3 times the sum of those formed in the presence of an OA alone and NOM alone, as OAs competed for free chlorine (FC) to form organic chloramines. Taking Gly as an example, the transformation of I- was determined. In the absence of NOM, the yields of iodate (IO3-) were 89%, 60%, and nearly 0 at [Gly]o/[FC]o = 0:1, 3:4, and 1:1, but 0, 2%, and 43% for hypoiodous acid (HOI), respectively. In the presence of NOM, as [Gly]o/[FC]o increased from 0:1 to 1:1, the yield of IO3- decreased from 66% to 0, while that of I-THMs increased from 2.9% to 16.1%. The competition of FC by OAs inhibited the oxidation of HOI to IO3-, and the formed organic chloramines can oxidize I- to HOI, thus promoting I-DBPs formation. Finally, the enhanced I-THMs formation was verified in real waters.

Accelerated oxidation of iopamidol by ozone/peroxymonosulfate (O3/PMS) process: Kinetics, mechanism, and simultaneous reduction of iodinated disinfection by-product formation potential

Iopamidol (IPM) is a potential source of toxic iodinated byproducts (I-DBPs) during water disinfection. In this work, we determined the kinetics and mechanism of degradation of IPM by a combination of ozone (O3) and peroxymonosulfate (PMS, HSO5−), and assessed its effect on the formation of iodinated trihalomethanes (I-THMs) during chlorination treatment. The degradation of IPM was accelerated by the O3/PMS process, and the hydroxyl (HO•) and sulfate (SO4•−) radicals were major contributors to the degradation. Using identification of the second order reaction rate between SO4•− and IPM (kSO4•−, IPM = 1.6 × 109 M−1 s−1), the contribution of HO• to the degradation was determined to be 78.3%. The degradation of IPM was facilitated by pH > 7, and natural organic matter (NOM) and alkalinity had limited effects on the degradation of IPM in the O3/PMS process. The transformation products of IPM were determined and inferred by QTOF-MS/MS, and the degradation pathways were elucidated. These include amide hydrolysis, amino oxidation, hydrogen abstraction, deiodination, and hydroxyl radical addition. Interestingly, oxidation of IPM by O3/PMS also decreased its potential for formation of I-THMs. After oxidation of IPM, the I-THMs formed from 5-μΜ IPM decreased from 14.7 μg L−1 to 3.3 μg L−1 during chlorination. Although the presence of NOM provided the precursor of I-THMs during chlorination of IPM, the O3/PMS process decreased I-THMs formation by 71%, because oxidation of released iodide into iodate effectively inhibited I-THMs formation. This study provides a new approach for the accelerated degradation of IPM and control of the formation of I-DBPs.

Formation and removal of disinfection by-products in a full scale drinking water treatment plant

In this case study, high sensitivity simple methods for the analysis of trihalomethanes (THM4), iodinated-trihalomethanes (I-THMs), haloacetic acids (HAAs), bromide, iodide and iodate have been developed. A one-step procedure for the analysis of haloacetic acids by head-space GC–MS provides good reproducibility and low limits of quantification (≤50 ng L−1). These methods were applied to characterize the formation of disinfection by-products (DBPs) in a full scale drinking water treatment plant. In this treatment plant, the incorporation of bromine into THMs increases throughout the water treatment line, due to the formation of bromine reactive species favored by the decrease of competition between dissolved organic carbon (DOC) and bromide towards chlorine. A linear correlation has been observed between the bromine incorporation factor and the Br-/DOC mass ratio. The conversion of iodine to iodate by chlorination occurs in this water due to the relatively high bromide concentration. Moreover, a higher formation of iodate compared to iodide levels in the raw water is observed indicating a degradation of organic iodinated compounds. The formation of I-THMs was constant in terms of quantity and speciation between campaigns despite fluctuating concentrations of DOC and total iodine in the raw water. A preferential removal of DBPs formed by the intermediate chlorination in the order I-DBPs > Br-DBPs > Cl-DBPs occurs during the subsequent activated carbon filtration. The removal rates range from 25 to 36% for the regulated THM4, from 82 to 93% for the ∑I-THMs and 95% for haloacetic acids. The assessment of the relative toxicity shows that despite a much lower concentration of HAAs (<10% of the total mass of measured DBPs) compared to THMs, these compounds are responsible for 75% of the relative cytotoxicity of the treated water. Bromoacetic acid on its own accounts for more than 60% of the overall toxicity of the 17 compounds included in this study.

Chloramination of iodide-containing waters: Formation of iodinated disinfection byproducts and toxicity correlation with total organic halides of treated waters

The formation of iodinated disinfection byproducts (I-DBPs) in drinking waters is of a concern due to their higher cyto- and genotoxicity than their chlorinated and brominated analogues. This study investigated the formation of I-DBPs under chloramination conditions using preformed chloramine and associated cyto- and geno-toxicities obtained with Chinese Hamster Ovary (CHO) cell assay. Cyto- and geno-toxicity of the samples were also calculated using DBP toxicity index values and correlated with total organic halide (TOX) formation. In low iodide (I-) (0.32 μM, 40 μg L−1) water, increasing dissolved organic carbon (DOC) concentration of selected waters from 0.1 to 0.25 mg L−1 increased the formation of iodinated trihalomethanes (I-THMs), while further increases from 0.25 to 4 mg L−1 produced an opposite trend. In high iodide water (3.2 μM, 400 μg L−1), increasing DOC from 0.5 to 4 mg L−1 gradually increased the I-THM formation, while a decrease was observed at 5.4 mg L−1 DOC. Iodoform was the most influenced species from the changes in DOC concentration. While increasing the initial iodide concentration from 0 to 5 μM increased the formation of iodoform, it did not make any considerable impact on the formation of other I-THMs. The measured cytotoxicity of samples was significantly correlated with increasing DOC concentration. Unknown TOCl and TOI showed a high correlation with measured cytotoxicity, while calculated total organic chlorine (TOCl) and total organic iodine (TOI) did not correlate. The comparison of measured and calculated cytotoxicity values showed that the calculated values do not always represent the overall cytotoxicity, since the formation of unknown DBPs are not taken into consideration during the toxicity calculations.

Formation of iodinated trihalomethanes and noniodinated disinfection byproducts during chloramination of algal organic matter extracted from Microcystis aeruginosa

The increasing occurrence of harmful algal blooms in surface waters may increase the input of algal organic matter (AOM) to the dissolved organic matter pool. The formation of iodinated trihalomethanes (I-THMs) and noniodinated disinfection byproducts (DBPs) in synthetic waters containing AOM extracted from Microcystis aeruginosa was investigated in chloramination (preformed and in-situ formed chloramine, NH2Cl and Cl2-NH2Cl, respectively) and chlorination (Cl2) processes. AOM is much more favorable for iodine incorporation than natural organic matter (NOM). For example, the formation of I-THM from AOM is much higher than NOM isolate extracted from treated water (e.g., 3.5 times higher in the NH2Cl process), and thus higher iodine utilization and substitution factors from AOM were observed. Short contact time (2 min) chlorination in Cl2-NH2Cl process leading to the formation of halogenated intermediates favored I-THM formation, compared with NH2Cl process. However, further increasing chlorine contact time from 5 min to 24 h facilitated the conversion from iodide to iodate and thus I-THM formation decreased. Meanwhile, the formation of noniodinated THM4, haloacetonitriles (HANs), and haloacetaldehydes (HALs) increased. Factors including concentrations of AOM and bromide, pH, and chlorine/nitrogen ratios influenced the formation of I-THMs and noniodinated DBPs. To evaluate the benefit of mitigating I-THM formation over the risk of noniodinated DBP formation, measured DBPs were weighed against their mammalian cell toxicity indexes. Increasing the chlorine exposure increased the calculated cytotoxicity based on concentrations of measured I-THMs and noniodinated DBPs since unregulated HANs and HALs were the controlling agents.

Evaluating iopamidol degradation performance and potential dual-wavelength synergy by UV-LED irradiation and UV-LED/chlorine treatment

This study revealed the iopamidol degradation performance and the synergistic effect of dual-wavelength ultraviolet light-emitting diodes (UV-LEDs). It was found that the dual-wavelength irradiation (265 and 280 nm) can promote iopamidol degradation during both UV-LED alone and UV-LED/chlorine processes (p < 0.05). The effects of key experimental parameters including pH, chlorine dosage and water matrix during UV-LED/chlorine process were evaluated. Peak degradation rate was observed at pH 7.0 due to the combined effects of the quantum yield of aquatic chlorine photolysis (Φchlorine) and absorptivity of chlorine. The destruction pathways of iopamidol in the UV-LED/chlorine process were proposed by Ultra Performance Liquid Chromatography-Electrospray Ionization-mass spectrometry. Additionally, an opposite trend of iodinated trihalomethane (I-THM) formation during subsequent chlorination between Milli-Q and real waters with prolonging irradiation time was observed, while other detected disinfection by-product (DBP) formation showed the same variation in Milli-Q and real waters. The UV-LED/chlorine treatment using dual-wavelength can enhance iopamidol degradation significantly, but it also promoted I-THM formation in real water, indicating the need for evaluating DBPs before the application of UV-LED/chlorine process in drinking water treatment.

Formation of iodinated trihalomethanes during chlorination of amino acid in waters

Chlorination is essential to provide safe drinking water. However, this process leads to the formation of disinfection byproducts (DBPs). In this study, tryptophan (Trp) has been selected as a precursor to conduct the chlorine disinfection. Moreover, the factors that affect the formation of trihalomethanes (THMs) and iodinated trihalomethanes (I-THMs) are investigated. The formation pathway of Trp chlorination is proposed based on the intermediate products identified.According to the experimental results, the formation of THMs and I-THMs during Trp chlorination fitted a new first-order kinetic model. The dosage of chlorine, temperature, pH and the ratio of bromide and iodide had major influence on the formation of THMs and I-THMs during chlorination. In addition, the inhibition of luminescent bacteria Vibrio fischeri in the water sample increased during Trp chlorination.

Effect of UV irradiation on iodinated trihalomethane formation during post-chloramination

Ultraviolet (UV) irradiation has been widely used in drinking water treatment processes, but its influence on the formation of disinfection by-products (DBPs), especially the emerging iodinated trihalomethanes (I-THMs) during post-chloramination remains unclear. This study evaluated the impact of low pressure (LP) UV treatment on the formation of I-THMs during post-chloramination through two pathways. The first pathway is through the transition of DOM structure and composition during UV-chloramination, resulting significant increase of I-THM formation with increasing UV dosage in different dissolved organic matter (DOM)-containing water (49.7%–90.5% at 1160 mJ/cm2). With the application of excitation emission matrix-parallel factor analysis (EEM-PARAFAC), we found that I-THM formation in UV-chloraminated water correlated well with two ratios of three PARAFAC humic-like components (C3/C2 and C1/C2, R2 = 0.958–1.000), suggesting that the ratios of fluorescent components can be used as reliable indicators for I-THM formation. Moreover, the shift in these fluorescent components is crucial for I-THM formation during UV-chloramination. Another pathway for UV irradiation to affect I-THM formation during post-chloramination is through the transformation of iodine species. Large amounts of reactive iodine species (HOI/I2 and I3−) can be generated directly in the mixed iodine system by UV light, leading to the enhancement of iodine utilization factor (IUF) (up to 0.040) after post-chloramination. These results suggest that UV application to DOM-containing water may induce changes in organic precursors and iodine species so as to enhance I-THM formation during post-chloramination.

Formation of iodinated trihalomethanes during breakpoint chlorination of iodide-containing water

This study investigated the formation of toxic iodinated trihalomethanes (I-THMs) during breakpoint chlorination of iodide-containing water. Impact factors including I− concentration, natural organic matter (NOM) concentration and type, pH as well as Br−/I− molar ratio were systematically investigated. Moreover, the incorporation of I− into I-THM formation was also calculated. The results showed that I-THM formation varied in different zones of the breakpoint curves. I-THMs increased with increasing chlorine dosage to breakpoint value and then dropped significantly beyond it. Iodoform (CHI3) and chlorodiiodomethane (CHClI2) were the major I-THMs in the pre-breakpoint zone, while dichloroiodomethane (CHCl2I) was the dominant one in the post-breakpoint zone. The formation of I-THMs increased remarkably with I− and dissolved organic carbon (DOC) concentrations. More bromine-containing species were formed as Br−/I− molar ratio increased from 0.5 to 5. In addition, the major I-THM compound shifted from CHCl2I to the more toxic CHClBrI. As pH increased from 6.0 to 8.0, I-THM formation kept increasing in the pre-breakpoint zone and the speciation of I-THMs changed alongside the breakpoint curves. The incorporation of I− during breakpoint chlorination was highly dependent on chlorine, I−, and NOM concentrations, NOM type, solution pH and Br−/I− molar ratio.

Formation of iodinated THMs during chlorination of water and wastewater in the presence of different iodine sources

The formation potential of iodinated trihalomethanes (I-THMs) during chlorination of different organic precursors in the presence of various iodine sources was studied. Organic precursors included humic acid, natural organic matter from river water and wastewater effluent organic matter. Inorganic iodide and two iodinated X-ray contrast media compounds (iopamidol and diatrizoate) were used as iodine sources. The formation potential of I-THMs under different experimental conditions (chlorination contact time, iodide and bromide concentrations) was investigated. The formation of I-THM species upon chlorination of river water and humic acids rapidly increased up to 24h and then a decreasing trend was observed. Wastewater, showed a rapid formation of I-THMs within the first 6h, followed by a lower rate with extended time. Formation of I-THMs in the presence of iopamidol was more favorable regarding the other two iodine sources. CHBrClI was the dominant specie followed by CHCl2I and CHBr2I. Increasing iodide concentrations result in higher I-THMs formation. The presence of bromide enhanced the I-THMs yields and shifted towards bromine-containing species (CHBrClI and CHBr2I).

Iodinated trihalomethane formation during chloramination of iodate-containing waters in the presence of zero valent iron

Iodide (I−) and iodinated X-ray contrast media (ICM) are the primary iodine sources for the formation of iodinated disinfection byproducts (I-DBPs), and iodate (IO3−) is believed to be a desired sink of iodine in water. This study found that highly cytotoxic iodinated trihalomethanes (I-THMs) also can be generated from iodate-containing waters (without any other iodine sources) in the presence of zero valent iron (ZVI) during chloramination, which could be a big issue in the wide usage of iron pipes. The effect of major factors including ZVI dosage, NH2Cl and IO3− concentrations, initial pH, Br−/IO3− molar ratio, phosphate concentration, iron corrosion scales (goethite and hematite) on the formation of I-THMs were investigated. Formation of I-THMs from IO3− increased with the increase of ZVI dosage, IO3− and NH2Cl concentrations. Chloramines can also remarkably accelerate the reduction of IO3− by ZVI. Peak I-THM formation was found at pH 8. As the Br−/IO3− molar ratio increased from 0 to 20, I-THM formation considerably enhanced, especially for the bromine-incorporated species. Goethite and hematite enhanced the formation of I-THMs in the presence of ZVI. Additionally, a significant suppression on I-THM formation was observed with the addition of phosphate. Considering that a large number of water distribution networks contain unlined cast iron pipes, transformation of IO3− in the presence of ZVI during chloramination may contribute to the formation of I-THMs in such systems.