Degradation Of Diatrizoate Research Articles

Bubble-less photocatalytic ozonation with ceramic membranes and static mixers enhances the total organic carbon removal and degradation of iodinated X-ray contrast agents

Conventional bubble-based ozonation of wastewater creates several issues, e.g., the low degradation of certain micropollutants like X-ray contrast agents, mass transfer limitations due to inhomogeneous mixing, and the waste of undissolved ozone. In contrast, this work uses tubular ceramic membranes for bubble-free and bubble-less ozonation. Static mixers are placed around the membrane to enhance the radial mixing of ozone, creating homogeneous reaction conditions throughout the membrane contactor. Additionally, the ozone mass transfer significantly increases with static mixers. Furthermore, the membrane is made of a photocatalyst (TiO2) on the shell-side to improve the micropollutant degradation by photocatalytic ozonation. An ozone-stable hydrophobic treatment method is developed to use ceramic membranes as a membrane contactor for the ozonation of water. After hydrophobic treatment, the ozone mass transfer coefficient is in the order of 1.3 ⋅ 10−6 ms−1 using bubble-less operation resulting in an ozone concentration up to 4.0 mg L−1. Overall, bubble-less operation significantly increases the ozone mass transfer compared to bubble-free operation. Photocatalytic ozonation in a membrane contactor with static mixers increases the degradation of diatrizoate by 37% compared to sole ozonation in the same membrane contactor. Furthermore, this process increases the removal of total organic carbon in experiments with a water matrix consisting of four different micropollutants by 115% compared to sole ozonation.

Enhanced peroxymonosulfate activation for degradation of iodinated contrast media by microwave-induced bimetallic carbon-based catalysts: Insight into the synergistic mechanism between microwaves and bimetallic sites

Microwave-assisted catalytic oxidation process was a promising wastewater treatment technology for the disposal of refractory organic contaminants. Nevertheless, its practical implementation was limited by the high energy consumption of microwaves and the poor sustainable reactivity of catalysts. To address these issues, the microwave-assisted dielectric-activation double-responsive Co/Fe carbon-based catalyst (CoFe/NC-3) was used to activate peroxymonosulfate (PMS) for oxidative degradation of refractory diatrizoate (DTZ). The results showed that the DTZ was completely degraded within 6 min in the MW/CoFe/NC-3/PMS reaction system, and the degradation efficiency increased by 82.38% compared with the MW/Fe/NC/PMS system. It was attributed to the enriched active sites and prolonged redox cycling capability of the bimetallic catalysts. Moreover, microwave enhanced electron migration ability to accelerate the circulation of Fe3+/Fe2+/Fe0 and Co3+/Co2+ and generate more reactive oxygen species (ROSs) for the high-efficiency degradation of DTZ. The degradation pathways of DTZ were elucidated by LC-MS in combination with DFT calculation and the product toxicity was evaluated using ecological structure-activity relationship software (ECOSAR). The results showed that the majority of intermediate degradation products were not acute or chronic toxicity to fish, daphnia, and green algae. Overall, these results revealed that the MW/CoFe/NC-3/PMS system was a cost-effective and stable method for wastewater treatment.

Catalysis of cupric and cuprous oxides in copper pipes on the diatrizoate transformation with peroxymonosulfate as a disinfectant

Cupric and cuprous oxides (CuO and Cu2O) are the main corrosion products of copper pipes; peroxymonosulfate (PMS) is a good drinking water disinfectant; micropollutants are ubiquitous in the factory waters. Corrosion products influence the micropollutant transformation under the action of disinfectants. This study compared the conversion of diatrizoate (DTZ) with PMS as a disinfectant under the catalysis of CuO (Cu(II)PS) and Cu2O (Cu(I)PS). The pseudo-first-order constant (kobs) for the DTZ degradation in the Cu(II)PS was 11.8 times that in the Cu(I)PS, with values of 0.092 and 0.0078 min−1, respectively. SO4− and HO played dominant roles in the Cu(II)PS, while O2− and 1O2 were the primary contributors in the Cu(I)PS. The yield ratio of reactive species were 92.8% and 69.6% in the Cu(II)PS and Cu(I)PS, respectively. The DTZ degradation was promoted by the increase of CuO dose, while inhibited by the increase of Cu2O dose (0.1–1.0 g L−1). In both Cu(II)PS and Cu(I)PS, the DTZ degradation was enhanced by the increasing PMS dose (10–100 mg L−1) and neutral pH (7.0), whereas weakened by water matrix (NOM, HCO3− and Cl−). The total organic iodine was mainly converted to IO3− with a ratio of 45.3 and 7.4% in the Cu(II)PS and Cu(I)PS, respectively. In the Cu(II)PS, the DTZ transformation was mainly through the amide hydrolysis followed by amino oxidation and stepwise deiodination followed by hydroxyl addition. However, hydroxyl addition is not thought to occur in the Cu(I)PS since the related intermediates have not been identified. The study helps to comprehensively understand the conversion of iodine-containing micropollutants in copper pipes when PMS is a disinfectant.

Enhanced degradation and deiodination of diatrizoate in a sulfite mediated photolytic system: performance, products and possible pathways

This study systematically investigated the performance of a sulfite mediated photolytic system on diatrizoate (DTZ) degradation and deiodization under different UV intensity, sulfite dosage, initial solution pH, initial DTZ concentration and co-present constituents. As compared with sole UV photolysis and sole sulfite reduction system, the UV/sulfite system performed a higher efficiency of DTZ degradation and deiodization. At the same time, the scavenging experiments were conducted by respectively adding KNO3, KNO2, MeOH and TBA, which indicated eaq− was the dominant active species responsible for the enhanced degradation and deiodination of DTZ. Effects of reaction factors showed that the UV/sulfite system was a promising technique for DTZ degradation. A complete removal of DTZ (40 µM) could be obtained under the UV intensity of I0 (6.67 × 10−7 einstein/cm2∙s), sulfite dosage of 0.50 mM and pH ranging from 8∼10. In addition, the intermediate products of DTZ degradation were identified and possible degradation mechanism was proposed. Four possible products including TP504, TP488, TP486 and TP236 were obtained in this study. The main degradation pathways might include protonation, deiodination, substitution and heterocyclic formation.

Kinetics of diatrizoate degradation by ozone and the formation of disinfection by-products in the sequential chlorination

Abstract In this study, we studied the degradation kinetics of a common iodine contrast agent, diatrizoate, by ozone and the formation of disinfection by-products (DBPs) in the sequential chlorination. Effects of ozone concentration, solution pH, and bromide concentration on diatrizoate degradation were evaluated. The results indicate that diatrizoate can be effectively degraded (over 80% within 1 h) by ozone, and the degradation kinetics can be well described using the pseudo-first-order kinetic model. The pseudo-first-order rate constant (kobs) of diatrizoate degradation significantly increased with increasing ozone concentration and decreasing bromide concentration. The kobs kept increasing with the increase of pH value and reached a maximum of 6.5 (±0.05) × 10−2 min−1 at pH 9. As the ozone concentration gradually increased from 0.342 to 1.316 mg/L, the corresponding kobs of diatrizoate degradation increased from 1.76 (±0.20) × 10−3 to 4.22 (±0.3) × 10−2 min−1. The bromide concentration exhibited a strong inhibitory effect on diatrizoate degradation because of the competition for ozone with diatrizoate. Trichloromethane was the only detected DBP in the subsequent chlorination in the absence of bromide. However, in the presence of bromide, six other DBPs were detected, and bromochloroiodomethane and tribromomethane became the major products with concentrations 1–2 orders higher than those of the other DBPs. In order to provide safe drinking water to the public, water should be maintained at circumneutral pH values and low bromine concentrations (<5 μM) before reaching the chlorine disinfection process to effectively control the formation of DBPs.

Thiourea Dioxide Coupled with Trace Cu(II): An Effective Process for the Reductive Degradation of Diatrizoate.

Diatrizoate, a refractory ionic iodinated X-ray contrast media (ICM) compound, cannot be efficiently degraded in a complex wastewater matrix even by advanced oxidation processes. We report in this research that a homogeneous process, thiourea dioxide (TDO) coupled with trace Cu(II) (several micromoles, ubiquitous in some wastewater), is effective for reductive deiodination and degradation of diatrizoate at neutral pH values. Specifically, the molar ratio of iodide released to TDO consumed reached 2 under ideal experimental conditions. TDO eventually decomposed into urea and sulfite/sulfate. Based on the results of diatrizoate degradation, TDO decomposition, and Cu(I) generation and consumption during the TDO-Cu(II) reaction, we confirmed that Cu(I) is responsible for diatrizoate degradation. However, free Cu(I) alone did not work. It was proposed that Cu(I) complexes are actual reactive species toward diatrizoate. Inorganic anions and effluent organic matter negatively influence diatrizoate degradation, but by increasing the TDO dosage, as well as extending the reaction time, its degradation efficiency can still be guaranteed for real hospital wastewater. This reduction reaction could be potentially useful for in situ deiodination and degradation of diatrizoate in hospital wastewater before discharge into municipal sewage networks.

Unexpected degradation and deiodination of diatrizoate by the Cu(II)/S(IV) system under anaerobic conditions

Transition metal catalyzed sulfite auto-oxidation is a promising technology used in water and wastewater treatment for the elimination of contaminants. In the literature, this process has been reported to be efficient only in the presence of oxygen. However, in this study, we unexpectedly found that the degradation of diatrizoate (DTZ) by a system based on the combination of copper ion and sulfite (Cu(II)/S(IV)) reached over 95% under anaerobic conditions, but was considerably retarded under aerobic conditions at pH 7. Furthermore, it was found that Cu(I), generated from the cleavage of the CuSO3 complex, was the main reactive species responsible for the degradation of DTZ by the Cu(II)/S(IV) system under anaerobic conditions. In fact, the absence of oxygen promoted the accumulation of Cu(I). The concomitant release of the iodide ion with the degradation of DTZ indicated that the anaerobic degradation of DTZ by the Cu(II)/S(IV) system mainly proceeded through the deiodination pathway, which was also confirmed by the detection of deiodinated products. The anaerobic degradation of DTZ was favored at higher initial concentrations of Cu(II) or sulfite in this system. Since the CuSO3 complex, the precursor of Cu(I), was formed mainly at pH 7, the highest anaerobic degradation of DTZ was achieved at pH 7. An increase in reaction temperature considerably enhanced the degradation of DTZ by the Cu(II)/S(IV) system with an apparent activation energy of 119.4 kJ/mol. The presence of chloride, bicarbonate and humic acid slightly influenced the anaerobic degradation of DTZ. The experiments with real water samples also demonstrated the effectiveness of the degradation of DTZ by the Cu(II)/S(IV) system under anaerobic conditions.

Degradation of diatrizoate in a pin-to-liquid plasma reactor, its transformation products and their residual toxicity

Diatrizoate, a recalcitrant iodinated contrast medium, has been detected in wastewaters and water bodies worldwide, with concentrations in hospital wastewaters in the μg/L range. Considering that conventional wastewater treatment technologies and ozonation fail to adequately remove diatrizoate, there is a need for researching alternative treatment technologies. In the present work, aqueous solutions of diatrizoate were treated in a compact (7.5 mL liquid volume) non-thermal plasma–liquid reactor. Oxygen and air plasmas were used for diatrizoate removal, with oxygen plasma performing better. After 20 min of treatment of 200 μg/L diatrizoate in pure water, oxygen led to 90% degradation whereas air achieved only 20% degradation. Two diatrizoate concentrations were studied: 10 mg/L to facilitate the identification of transformation products when using an oxygen plasma and 200 μg/L, a concentration in the range expected in hospital wastewater. For the oxygen plasma treatment, the energy efficiency for removing diatrizoate was 0.140 g/kWh for C0 = 10 mg/L and 0.006 g/kWh for C0 = 200 μg/L. The following transformation products of diatrizoate were identified: m/z 486A, 504A, 504B, 628, 630A, 630B (previously described in literature) and m/z 486B, 550, 555, 565, 578 (novel). Acute toxicity tests on Aliivibrio fischeri revealed no residual toxicity associated to transformation products. Since diatrizoate is a particularly recalcitrant aqueous organic pollutant, its successful removal and the lack of formation of toxic transformation products indicates that the developed plasma-based technology is promising for treating challenging wastewaters, such as hospital wastewaters.

Accelerated Degradation of Aqueous Recalcitrant Iodinated Contrasting Media Using a UV/SO32- Advanced Reduction Process

Based on the formation of free radical-hydrated electrons by the activation of sulfite (SO32-), the UV/SO32- process is an advanced reduction process that can reduce pollutants. This study investigated the degradation kinetics, mechanism, influencing factors, and degradation pathways of sodium diatrizoate (DTZ), an iodinated contrasting media, during the UV/SO32- process. The degradation kinetics of DTZ were well fitted by the pseudo-first-order model, the degradation rate of which was higher than that of UV only and UV/H2 O2. The degradation rate of DTZ during the UV/SO32- process was positively correlated with the initial SO32- concentration. Weakly alkaline and alkaline conditions promoted the degradation of DTZ, while organic matter inhibited degradation during the UV/SO32- process. The degradation mechanism included direct photolysis and free radical attack, whereby free radical attack played a more important role than direct photolysis. Sulfite radicals dominated DTZ degradation efficiency, and hydrated electrons controlled the deiodination efficiency. The degradation pathways of DTZ during the UV/SO32- process included substitution, decarboxylation-hydroxylation, and amide bond cleavage.

Electrochemical Processes Coupled to a Biological Treatment for the Removal of Iodinated X-ray Contrast Media Compounds.

Iodinated X-ray contrast media (ICM) compounds are a form of intravenous radiocontrast containing iodine, which are rapidly eliminated via urine or feces. The issue with the accumulation of ICM has received considerable critical attention since they are ubiquitously distributed in municipal wastewater effluents and in the aquatic environment and are not significantly eliminated by most biological sewage treatment processes. Among the methods that have been tested to eliminate ICM, electrochemical methods have significant advantages, since they can selectively cut the carbon-iodine bonds that are suspected to decrease their biodegradability. On the production sites, the recovery of iodine ions due to the carbon-iodine cleavage can be envisaged, which is particularly interesting to reduce the cost of the ICM production process. The coupling of an electrochemical process and a biological treatment can be carried out to mineralize the organic part of the formed by-products, allowing the recovery of the iodide ions. Therefore, the degradation of diatrizoate, a typical ionic ICM compound, by an electrochemical process was the purpose of this study. The electrochemical reduction of diatrizoate was performed using a flow cell with a graphite felt electrode at different potentials. The removal yield of diatrizoate reached ~100% in 2 h and the main product, 3,5-diacetamidobenzoic acid, was quantitatively formed, showing that diatrizoate was almost completely deiodinated. According to the BOD5/COD ratio, the biodegradability of diatrizoate after electrolysis was considerably improved. Cyclic voltammetry analysis of the electroreduced solution showed several oxidation peaks. The electrochemical oxidation of the by-products formed after the first treatment by electroreduction was then performed at three different potentials to study the influence of electrochemical oxidation on biodegradability. Results showed that the degradation yield of the deiodinated by-products increased with the potential and reached 100% at 1.3 V/SCE. Four different biological treatments were implemented during 21 days in stirred flasks with fresh activated sludge. The evolution of the mineralization during the biological treatment highlighted the biorecalcitrance of diatrizoate as previously estimated by the BOD5/COD ratio. Interestingly, the mineralization yield increased from 41 to 60% when electrochemical oxidation at 1.3 V/SCE was implemented after electroreduction.

Comparison of diatrizoate degradation by UV/chlorine and UV/chloramine processes: Kinetic mechanisms and iodinated disinfection byproducts formation

This study compared the degradation efficiency of diatrizoate (DTA) by UV/chlorine and UV/chloramine processes. DTA could be effectively degraded by the UV/chlorine and UV/chloramine processes compared with chlorination and chloramination solely. Although the UV/chlorine process was more sensitive to the variations of oxidant dosages, solution pH, the concentration of bicarbonate and chloride, UV/chlorine degraded DTA more efficiently than UV/chloramine process. The reactive chlorine species (RCS) and hydroxyl radical (HO) are predominant contributors to DTA degradation in the UV/chlorine and UV/chloramine processes respectively, and the specific contribution of each reactive specie changed with solution pH. The performance of UV/chlorine and UV/chloramine processes on DTA degradation was obviously inhibited in natural waters (e.g., wastewater, rainwater, river water and tap water), however, degradation of DTA in the UV/chlorine are still satisfactory compared with UV/chloramine process. Formation of chloroform, dichloroacetonitrile, and iodoform (IF) from DTA was observed in both UV/chlorine and UV/chloramine processes. It is notable that formation potential of IF from DTA was significantly enhanced in UV/chloramine process, and thus the overall cytotoxicity of generated DBPs in UV/chloramine process is far greater than that in UV/chlorine process.

Aerobic removal of iodinated contrast medium by nano-sized zero-valent iron: A combination of oxidation and reduction.

The removal performance and mechanisms of diatrizoate (DTA), a typical iodinated contrast medium, from water by nano-sized zero-valent iron (nZVI) under aerobic conditions were investigated in this study. Reactive oxygen species (ROS) and transformation products were detected with electron spin resonance and liquid chromatography electrospray ionization tandem mass spectrometry, respectively. Furthermore, the effects of several operational parameters on DTA removal were illustrated. The results showed that nZVI had a much higher DTA removal ability compared to microscale zero-valent iron (mZVI) in the presence of oxygen. Moreover, the detection of ROS and I- as well as the analysis of intermediate products suggested a combination of oxidation and reduction pathways for DTA removal by nZVI under aerobic conditions. Additionally, a high dosage of nZVI and acidic conditions led to the enhancement of DTA removal, while nZVI aging, as well as chloride and nitrate ions in the solution, had negative effects on the degradation of DTA by nZVI in the presence of oxygen.

Degradation of diatrizoate in water by Fe(II)-activated persulfate oxidation

As a type of iodinated contrast medium (ICM), the diatrizoate (DTZ) found in aquatic systems has posed a serious threat to the ecosystem and to human health. In this study, Fe(II)-activated persulfate (Fe2+/PS) oxidation was employed to degrade DTZ, and the optimal operating conditions were determined. Electron paramagnetic resonance (EPR) spectra and density functional theory (DFT) calculations were adopted to determine the dominant radicals and analyze the degradation paths, respectively. It was found that a PS concentration of 10 mmol/L, an n(Fe2+)/n(PS) ratio of 1:10, an initial pH of 3.0, and a high temperature increased the degradation efficiency of DTZ. After suppression of the oxidation process by tertiary butyl alcohol (TBA) and methanol (MtOH), the EPR spectra demonstrated that DTZ degradation was attributed to the combined effects of SO4− and OH and that OH played a more important role. Based on the theoretical calculation and comparison of the reduction energies of possible degradation products, the path from DTZ to TP630 and then to TP628 and finally to TP602 was recognized as the main DTZ degradation pathway during the Fe2+/PS oxidation process. These findings validated and demonstrated that DTZ could be effectively degraded by Fe2+/PS oxidation, which is a promising approach to remove DTZ from water.

Degradation kinetics of diatrizoate during UV photolysis and UV/chlorination

The degradation kinetics of the widely used iodinated X-ray contrast medium, namely diatrizoate, was investigated during ultraviolet (UV) photolysis and UV/chlorination. Factors influencing diatrizoate degradation, such as pH, chlorine dosage, and bromide concentration, were also evaluated. Diatrizoate was not degraded during chlorination. However, the degradation of diatrizoate during UV photolysis and UV/chlorination complied with the pseudo-first-order kinetics. At pH 7, the pseudo-first-order rate constant during UV/chlorination was 9.3 times higher than that during UV photolysis. The results of a radical quenching test using excessive tert-butanol suggested that the contribution of Cl, a type of reactive chlorine species (RCS), was limited. The contributions ofUV direct photolysis, hydroxyl radicals (OH), and RCS to diatrizoate degradation during UV/chlorination at pH 7 were estimated to be 12.8%, 1.2%, and 85.9%, respectively. Results of further experiment suggested that OCl primarily caused diatrizoate degradation. As the chlorine concentration gradually increased from 25 to 150 μM, the corresponding pseudo-first-order rate constant of UV/chlorination increased from 8.37 (±0.42) × 10−3 to 5.52 (±0.28) × 10−2 s−1. When the pH value was increased from 5 to 9, the rate of diatrizoate degradation reached the maximum at pH 7 and gradually decreased during UV/chlorination; however, the rate of diatrizoate degradation remained stable during UV photolysis. The degradation of diatrizoate was inhibited when the bromide concentration was increased due to the competition for chlorine between bromide and diatrizoate; thus, the generation of OCl was limited. Compared with UV irradiation, UV/chlorination could reduce the formation of iodinated trihalomethanes (I-THM) after chlorination. However, dichloroacetonitrile (C2HCl2N), which is carcinogenic, was generated during UV/chlorination.

A novel method for photo-oxidative degradation of diatrizoate in water via electromagnetic induction electrodeless lamp

In this study, an electromagnetic induction electrodeless lamp (EIEL) was first introduced into UV advanced oxidation processes (AOPs) for photodegradation of Diatrizoate (DTZ), which was the most persistent iodinated X-ray contrast medium (ICM), and traditional Hg lamps were taken as references. Direct photolysis rate of DTZ under EIEL irradiation was 1.34 times as that under Hg irradiation, but the electric energy consumption was 0.87 times. In this sense, the combination of EIEL and oxidants (O2, H2O2 and S2O82−(PS)) was further investigated. The remarkably increased photodegradation rates were observed in UV/PS system due to primary contribution rate of SO4− (62.5%) based on the results of radical concentrations and second-order rate constants of DTZ with SO4− and OH. Inorganic ions influencing the photodegradation process were investigated. The effect of natural organic materials (NOMs) in UV/PS system was studied based on contribution ratios of light screening effect and quenching. Transformation mechanisms of DTZ in UV/PS system included deiodination, intramolecular cyclization, decarboxylation, deacetylation and deamination, which were further confirmed by frontier electron density calculations. The study indicated that UV/PS with EIEL irradiation has the potential to remove pharmaceuticals in contaminated aquatic environments.

Effective degradation of diatrizoate by electro-peroxone process using ferrite/carbon nanotubes based gas diffusion cathode

In this study, ferrite modified carbon nanotubes (MFe2O4/CNTs, M: Fe, Mn) were prepared and employed as cathodic catalysts to assist electro-peroxone (i.e., combined ozonation with electrolysis process using a carbon-polytetrafluoroethylene cathode) treatment of emerging pollutant diatrizoate (DTZ) in aqueous solution. The structural and surface property of synthesized catalysts was studied, and the performance of electro-peroxone process using MFe2O4/CNTs based gas diffusion cathode (GDC) was systematically investigated from the kinetic and mechanistic viewpoints. Results show that the combination of ozonation and electrolysis exhibited synergistic degradation of DTZ. Approximately 71.9% DTZ had been degraded with MFe2O4/CNTs based GDC after 10min, 13.2% higher than with bare CNTs based GDC, implying that the combined treatment efficiency could be enhanced by the presence of MFe2O4. The performance of MFe2O4/CNTs catalytic electro-peroxone process was positively correlated with inlet ozone concentration (10–30mg/L), and an increase in applied current stimulated DTZ degradation at a low cathodic current density (5–40mA/cm2) but inhibited the degradation at a high cathodic current density (40–60mA/cm2). The MFe2O4/CNTs catalytic electro-peroxone treatment also showed a significant dependence on initial pH and reaction temperature, but was little affected by supporting electrolyte concentration. Higher removal efficiency was obtained at a lower initial DTZ concentration. The comparison tests reveal that peroxone reaction was the main pathway of hydroxyl radicals (HO) production in the present system, and the presence of MFe2O4 at the cathode could promote HO generation. These observations suggest that electro-peroxone is efficient for DTZ degradation in aqueous solution, and MFe2O4/CNTs are good and promising cathodic materials and catalysts for this process.

Investigations of diatrizoate degradation by photo-activated persulfate

The widespread occurrence of iodinated X-ray contrast media (ICMs) in aquatic systems poses potential risks to ecologic system and human health. The present study investigated the degradation kinetics and mechanisms of a typical ICMs, diatrizoate (DTZ), by using simulated sunlight (from a solar simulator Suntest CPS+) activated persulfate (PS) oxidation process. The influence of key kinetic factors, such as PS concentrations, pH, dissolved organic matter (DOM), bicarbonate and chloride ions was evaluated. The reaction pathways and mechanisms were proposed based on photoproducts identification using HPLC-MS. UV/PS was found to be more efficient than UV/H2O2. Sulfate radicals (SO4·-) was the dominant reactive species in the oxidation process, and the second-order rate constant of sulfate radical with DTZ was calculated as1.90×109M−1s−1 based on laser flash photolysis (LFP) experiments. The results indicated that increasing initial PS concentration favored the decomposition of DTZ; whereas, degradation of DTZ was not affected by pH change ranging from 4.5 to 8.5. DOM inhibited DTZ removal rate, while, bicarbonate enhanced it, and chloride ions induced a negative effect above 500mM. Major oxidation pathways including deiodination-hydroxylation, decarboxylation- hydroxylation and side chain cleavage were proposed, and detailed underlying mechanisms were also discussed. We suggest a direct photodegradation of primary intermediates generated by SO4·- attack. These findings demonstrate that halogenated pollutants can readily react with SO4·- to form light-absorbing intermediates (ranging from 350 to 500nm). Thus, this activation method could be a promising approach in the removal of ICMs.

Oxidation of diatrizoate in aqueous phase by advanced oxidation processes based on solar radiation

Abstract The aim of this study was to investigate the use of solar radiation to treat recalcitrant pollutants, using sodium diatrizoate (DTZ), an ionic X-ray contrast media, as reference compound. The effectiveness in DTZ removal was compared among solar radiation, H2O2, solar radiation/H2O2, K2S2O8, solar radiation/K2S2O8, Fenton, solar radiation/Fenton, Fenton-Like, and solar radiation/Fenton-Like systems. Using direct DTZ photolysis, the percentage DTZ degradation is low and independent of the medium pH, but not of the irradiance level. However, in the presence of radical-promoting species, 100% DTZ degradation is achieved. Results obtained with solar radiation/Fenton and solar radiation/Fenton-like systems suggest that the formation of peroxo and iron hydroperoxy complexes susceptible of absorbing radiation in the solar radiation area represents a new source of OH and/or OH2 radicals in the medium, favoring DTZ degradation. The byproducts formed in each process and the post-treatment medium toxicity were studied, observing an increased toxicity after all oxidation treatments, indicating that the degradation products generated are more toxic than DTZ. Moreover, a direct relationship was found between percentage DTZ degradation and aqueous medium toxicity.

Photocatalytic Elimination of Diatrizoate and I<sup>-</sup> Formation: Influence of Dissolved Oxygen, Metal Ions and Natural Organic Matter (NOM)

A simplified model of environmental conditions was developed to evaluate the effect of natural organic matter (NOM) and metal ions on the Pt/TiO2 photocatalytic degradation of diatrizoate and I - formation in the presence of different dissolved oxygen (DO) level. The results showed that the photocatalytic degradation of diatrizoate was strongly influenced by the amount of DO present and by the presence of metal ions. The DO concentration and the presence of NOM severely affected the formation of I - . The high R 2 values of the model signify that the models obtained are able to give a reasonably good estimate of response for the system in the range studied.

Comparative study of oxidative degradation of sodium diatrizoate in aqueous solution by H2O2/Fe2+, H2O2/Fe3+, Fe (VI) and UV, H2O2/UV, K2S2O8/UV

This study centers on Advanced Oxidation Processes (AOPs) based on the use of iron salts and ultraviolet (UV) radiation for the removal of diatrizoate (DTZ) contrast medium, selected as a model compound resistant to all conventional natural and waste water treatment methods. We studied the effectiveness of Fenton’s reagent, Iron (III) and Iron (VI) salts, and oxidation processes based on the use of UV radiation, UV/H2O2 and UV/K2S2O8, for the degradation of DTZ in aqueous medium. With Fenton’s reagent, the percentage DTZ removal was independent of the initial Fe2+ concentration and was most influenced by the initial hydrogen peroxide concentration. In contrast, the Fenton-like system was affected by both initial Fe3+ and H2O2 concentration. The effects of ferrate salt-bases methods were highly dependent on the solution pH, and a higher rate constant (1.74×102M−1s−1) was obtained when dihydrogen ferrate species predominated in the medium. The UV/H2O2 system was strongly dependent on the pH and initial H2O2 concentration, showing a favorable synergic effect at H2O2 concentrations <10.0mM. The UV/K2S2O8 system proved to be more effective than the UV/H2O2 system, with higher rate constants, which were 24.0% higher for pH=6.5 and [DTZ]0=25mgL−1. Study of the influence of the matrix on these AOPs revealed a markedly higher percentage DTZ removal and reaction rate in surface water with the UV radiation-based systems than with the iron salt-based systems. According to the total organic carbon values obtained, a high degree of mineralization was only attained with the UV/K2S2O8 system.