Decomposition of Iodinated Pharmaceuticals by UV-254 nm-assisted Advanced Oxidation Processes

A review on recent advancements in the treatment of polyaromatic hydrocarbons (PAHs) using sulfate radicals based advanced oxidation process

Polyaromatic hydrocarbons (PAHs) are the most persistent compounds that get contaminated in the soil and water. Nearly 16 PAHs was considered to be a very toxic according US protection Agency. Though its concentration level is low in the environments but the effects due to it, is enormous. Advanced Oxidation Process (AOP) is an emergent methodology towards treating such pollutants with low and high molecular weight of complex substances. In this study, sulfate radical (SO4‾•) based AOP is emphasized for purging PAH from different sources. This review essentially concentrated on the mechanism of SO4‾• for the remediation of pollutants from different sources and the effects caused due to these pollutants in the environment was reduced by this mechanism is revealed in this review. It also talks about the SO4‾• precursors like Peroxymonosulfate (PMS) and Persulfate (PS) and their active participation in treating the different sources of toxic pollutants. Though PS and PMS is used for removing different contaminants, the degradation of PAH due to SO4‾• was presented particularly. The hydroxyl radical (•OH) mechanism-based methods are also emphasized in this review along with their limitations. In addition to that, different activation methods of PS and PMS were discussed which highlighted the performance of transition metals in activation. Also this review opened up about the degradation efficiency of contaminants, which was mostly higher than 90% where transition metals were used for activation. Especially, on usage of nanoparticles even 100% of degradation could be able to achieve was clearly showed in this literature study. This study mainly proposed the treatment of PAH present in the soil and water using SO4‾• with different activation methodologies. Particularly, it emphasized about the importance of treating the PAH to overcome the risk associated with the environment and humans due to its contamination.

Efficiency of ozonation and sulfate radical - AOP for removal of pharmaceuticals, corrosion inhibitors, x-ray contrast media and perfluorinated compounds from reverse osmosis concentrates

This study investigated the elimination of pharmaceuticals, corrosion inhibitors, x-ray contrast media and perfluorinated compounds from reverse osmosis concentrates during ozonation and UV/persulfate processes. Second-order rate constants for the reactions of candesartan, irbesartan, methyl-benzotriazole, and chloro‑benzotriazole with sulfate radical (SO4·-) were determined for the first time. Experiments were conducted in buffered pure water, in buffered water added with the matrix substituents chloride, carbonate, NOM, and reverse osmosis concentrate with spiked micropollutants (MP). UV/persulfate eliminated all MP to a higher extent than ozonation in RO concentrates due to the higher yield of oxidative species and photolytic degradation. Compounds with electron-rich moieties such as carbamazepine, diclofenac, metoprolol, and sulfamethoxazole were completely eliminated with small ozone doses (< 0.5 mg O3 / mg DOC) and with a small fluence (< 5000 J m-2) in UV/persulfate processes. Photosensitive compounds with high reactivity towards hydroxyl radicals (·OH) and SO4·- like the x-ray contrast media Iopamidol, Iohexol, and Amidotrizoic acid were successfully eliminated with a reasonable fluence in UV/persulfate, whereas these compounds persist in ozonation at common ozone dosages. However, much higher fluences and ozone dosages were required for the least reactive compounds like the class of benzotriazoles. Comparing the application of both oxidative processes to the RO concentrate, ozonation has the disadvantage of forming bromate. The energy input of both processes strongly depends on the target compounds to be eliminated. For the elimination of compounds such as sulfamethoxazole, ozonation is a feasible technique, whereas UV/persulfate is better suited for the elimination of recalcitrant compounds such as x-ray contrast media. In general, oxidative process treatment of RO concentrate could be applied to partly abate micropollutants before discharge.

MWCNTs Decorated with TiO2 as Highly Performing Filler in the Preparation of Nanocomposite Membranes for Scalable Photocatalytic Degradation of Bisphenol A in Water

Bisphenol A (BPA), an endocrine-disrupting compound with estrogenic behavior, is of great concern within the scientific community due to its high production levels and increasing concentration in various surface aquifers. While several materials exhibit excellent capacity for the photocatalytic degradation of BPA, their powdered nature and poor chemical stability render them unsuitable for practical application in large-scale water decontamination. In this study, a new class of nanocomposite membranes based on sulfonated polyethersulfone (sPES) and multiwalled carbon nanotubes decorated with TiO2 nanoparticles (MWCNTs-TiO2) were investigated as efficient and scalable photocatalysts for the photodegradation of BPA in aqueous solutions. The MWCNTs-TiO2 hybrid material was prepared through a facile and inexpensive hydrothermal method and extensively characterized by XRD, Raman, FTIR, BET, and TGA. Meanwhile, nanocomposite membranes at different filler loadings were prepared by a simple casting procedure. Swelling tests and PFG NMR analyses provided insights into the impact of filler introduction on membrane hydrophilicity and water molecular dynamics, whereas the effectiveness of the various photocatalysts in BPA removal was monitored using HPLC. Among the different MWCNTs-TiO2 content nanocomposites, the one at 10 wt% loading (sP-MT10) showed the best photoactivity. Under UV irradiation at 254 nm and 365 nm for 240 min, photocatalytic oxidation of 5 mg/L bisphenol A by sP-MT10 resulted in 91% and 82% degradation, respectively. Both the effect of BPA concentration and the membrane regenerability were evaluated, revealing that the sP-MT10 maintained its maximum BPA removal capability over more than 10 cycles. Our findings indicate that sP-MT nanocomposite membranes are versatile, scalable, efficient, and highly reusable photocatalysts for the degradation of BPA, as well as potentially for other endocrine disruptors.

Removal of Iodine-Containing X-ray Contrast Media from Environment: The Challenge of a Total Mineralization

Iodinated X-ray contrast media (ICM) as emerging micropollutants have attracted considerable attention in recent years due to their high detected concentration in water systems. It results in environmental issues partly due to the formation of toxic by-products during the disinfection process in water treatment. Consequently, various approaches have been investigated by researchers in order to achieve ICM total mineralization. This review discusses the different methods that have been used to degrade them, with special attention to the mineralization yield and to the nature of formed by-products. The problem of pollution by ICM is discussed in the first part dedicated to the presence of ICM in the environment and its consequences. In the second part, the processes for ICM treatment including biological treatment, advanced oxidation/reductive processes, and coupled processes are reviewed in detail. The main results and mechanisms involved in each approach are described, and by-products identified during the different treatments are listed. Moreover, based on their efficiency and their cost-effectiveness, the prospects and process developments of ICM treatment are discussed.

Oxidative Degradation of Pharmaceutical Waste, Theophylline, from Natural Environment

The elimination of organic contaminants from natural resources is extremely important to ensure their (re-)usability. In this report, the degradation of a model pharmaceutical compound, theophylline, is compared between natural and laboratory-controlled environments. While the concentration of H2O2 variably affected the degradation efficiency (approximately from 8 to 20 min for complete degradation) in the photo-irradiation experiments, the inorganic compounds (NaNO3, KH2PO4 and ZnSO4) present in the medium seemed to affect the degradation by scavenging hydroxyl radicals (•OH). The end-product studies using high-resolution mass spectrometry (HRMS) ruled out the involvement of secondary radicals in the degradation mechanism. The quantitative calculation with the help of authentic standards pointed out the predominant role of hydroxylation pathways, especially in the initial stages. Although a noticeable decline in the degradation efficiency was observed in river water samples (complete degradation after 25 min with an approximately 20% total organic carbon (TOC) removal), appreciable TOC removal (70%) was eventually achieved after prolonged irradiation (1 h) and in the presence of additional H2O2 (5 times), revealing the potential of our technique. The results furnished in this report could be considered as a preliminary step for the construction of •OH-based wastewater treatment methodologies for the remediation of toxic pollutants from the real environment.

Degradation Kinetics and Disinfection By-Product Formation of Iopromide during UV/Chlorination and UV/Persulfate Oxidation

As the detection of micropollutants in various water resources is commonly reported, developing an efficient technology to remove them to maintain water safety has become a major focus in recent years. The degradation kinetics of iopromide, one of a group of iodinated X-ray contrast media (ICM), using advanced oxidation processes of ultraviolet/chlorination (UV/Cl2) and UV/persulfate (UV/PS) oxidation were investigated in this research. The results show that iopromide degradation fitted pseudo-first-order kinetics, and the rate constants were calculated as 2.20 (± 0.01) × 10−1 min−1 and 6.08 (± 0.10) × 10−2 min−1 in UV/Cl2 and UV/PS, respectively. In the two systems, the degradation rates were positively correlated with the initial concentrations of HOCl and PS, respectively. In the UV/Cl2 system, the degradation rate of iopromide reached a maximum at pH 7, while in the UV/PS system, pH had only a slight effect on the degradation rate. Chloride in water had a negligible effect on iopromide degradation, whereas bromide inhibited iopromide degradation in the UV/Cl2 system. The contributions of UV irradiation, •OH, and RCS to iopromide degradation during UV/Cl2 treatment were calculated as 20.8%, 54.1%, and 25.1%, respectively. One carbonated and three nitrogenated disinfection by-products (C-DBP (chloroform) and N-DBPs (dichloroacetonitrile, trichloronitromethane, and trichloroacetone)) were detected at relatively high levels, along with three emerging iodinated DBPs (dichloroiodomethane, monochlorodiiodomethane, and triiodomethane). More C- and N-DBPs were generated in the UV/Cl2 and UV/PS systems than in UV irradiation, while considerably higher I-DBPs were generated in UV irradiation than in the other two systems. Thus, it is essential to pay attention to DBP formation when UV/Cl2 or UV/PS is used to treat iopromide in water. In order to better control the generation of carcinogenic and toxic I-DBPs, Cl2 or PS combined with UV should be adopted for iopromide degradation, instead of UV alone, for providing safe drinking water to the public.

The fate and transformation of iodine species in UV irradiation and UV-based advanced oxidation processes

Iodinated disinfection byproducts (I-DBPs) formed in water treatment are of emerging concern due to their high toxicity and the tase-and-odor problems associated with iodinated trihalomethanes (I-THMs). Iodoacetic acid and dichloroiodomethane are currently regulated in Shenzhen, China and the Ministry of Health of the People's Republic of China has also been considering regulating I-DBPs. Iodide (I^-), organoiodine compounds (e.g., iodinated X-ray contrast media [ICM]), and iodate (IO₃^-) are the three common iodine sources in aquatic environment that lead to I-DBP formation. While UV irradiation effectively inactivate a wide range of microorganisms in water, it induces the transformation of these iodine sources, enabling the formation of I-DBPs. This review focuses on the fate and transformation of these iodine sources in UV-based water treatment (i.e., UV irradiation and UV-based advanced oxidation processes [UV-AOPs]) and the formation of I-DBPs in post-disinfection. I^- released in UV-based treatments of ICM and can be oxidized in subsequent disinfection to hypoiodous acid (HOI), which reacts with natural organic matter (NOM) to produce I-DBPs. Both UV and UV-AOPs are not able to fully mineralize ICM and completely oxidize the released I^- to (except UV/O₃). Results reveal that UV and UV-AOPs are adequate for I-DBP degradation but require high UV doses. While the ideal I-DBP mitigation strategy awaits to be developed, understanding their sources and formation pathways aids in informed selections of water treatment processes, empowers water suppliers to meet drinking water standards, and minimizes consumers' exposure to I-DBPs.

Degradation of micropollutant cephalexin by ultraviolet (UV) and assessment of residual antimicrobial activity of transformation products

Cephalexin (CEX) is an antibiotic commonly used to treat bacterial infections in humans and animals. However, it is also a micropollutant. Thus, this study evaluated the degradation of CEX using ultraviolet irradiation (UV-C) and analyzed the by-products as well as their residual antimicrobial activity. A reactor with a mercury vapor lamp was used for the degradation. Irradiated CEX solutions were collected over a period of 4 hours and analyzed using high-performance liquid chromatography coupled with mass spectrometry. For the residual antimicrobial activity the susceptibility test was performed using Staphylococcus aureus and Escherichia coli microorganisms by broth microdilution. It was found that CEX, after treatment, generated a metabolite with a mass of 150 m/z in 15 min. A four- and eightfold increase in the minimum inhibitory concentration of the drug against S. aureus and E. coli could be observed, respectively, after 20 min. Therefore, this treatment proved to be effective in the degradation of CEX, being able to degrade 81% of the initial molecule of the drug in 20 min. Furthermore, the antimicrobial activity of the CEX solution decreased as the irradiation time increased, indicating loss of antimicrobial function of the initial CEX molecule and the resulting by-products.

Comprehensive review on iodinated X-ray contrast media: Complete fate, occurrence, and formation of disinfection byproducts

Iodinated contrast media (ICM) are drugs which are used in medical examinations for organ imaging purposes. Wastewater treatment plants (WWTPs) have shown incapability to remove ICM, and as a consequence, ICM and their transformation products (TPs) have been detected in environmental waters. ICM show limited biotransformation and low sorption potential. ICM can act as iodine source and can react with commonly used disinfectants such as chlorine in presence of organic matter to yield iodinated disinfection byproducts (IDBPs) which are more cytotoxic and genotoxic than conventionally known disinfection byproducts (DBPs). Even highly efficient advanced treatment systems have failed to completely mineralize ICM, and TPs that are more toxic than parent ICM are produced. This raises issues regarding the efficacy of existing treatment technologies and serious concern over disinfection of ICM containing waters. Realizing this, the current review aims to capture the attention of scientific community on areas of less focus. The review features in depth knowledge regarding complete environmental fate of ICM along with their existing treatment options.

Effects of fulvic acid size on microcystin-LR photodegradation and detoxification in the chlorine/UV process

Microcystin-LR (MC-LR), a polypeptide toxin generated by cyanobacteria, threatens the safety of drinking water supplies. In this study, fulvic acid (FA) was separated into two molecular weight (MW) ranges to evaluate the effects of FA size on MC-LR degradation in the chlorine/UV process. The rates of MC-LR degradation were significantly reduced in FA-containing water (3.7 × 10^-3 s^-1 for small MW FA; 4.3 × 10^-3 s^-1 for large MW FA) as compared with FA free water (4.9 × 10^-3 s^-1). The contributions of ClO• to MC-LR degradation were dramatically lower in small MW FA water (0.4%) than large MW FA (13.9%) and FA free water (17.4%), suggesting inhibition by lignin-like substances in FA in the transformation of Cl• to ClO• and scavenging ClO•. Monochlorination and hydroxylation occurred in the first step of the MC-LR degradation process. The accumulation of intermediate products in the chlorine/UV process indicated that small MW FA inhibited further degradation of MC-LR. Small MW FA, rather than MC-LR degradation, was the dominant factor in minimizing MC-LR cytotoxicity toward a human intestinal epithelial cell line.

Nanomaterial Synthesis in Ionic Liquids and Their Use on the Photocatalytic Degradation of Emerging Pollutants

The unique properties of ionic liquids make them suitable candidates to prepare nanoscale materials. A simple method that uses exclusively a corresponding bulk material and an ionic liquid—in this case, [P_6,6,6,14]Cl—was used to prepare AgCl nanoparticles and AgCl@Fe₃O₄ or TiO₂@Fe₃O₄ magnetic nanocomposites. The prepared nanomaterials were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, ultraviolet–visible spectroscopy, and X-ray photoelectron spectroscopy. The photodegradation of atenolol as a model pharmaceutical pollutant in wastewater was investigated under ultraviolet–visible light irradiation using the different synthesized nanocatalysts. In the presence of 0.75 g·L⁻¹ AgCl nanoparticles, a practically complete degradation of 10 ppm of atenolol was obtained after 30 min, following pseudo-first-order reaction kinetics. The effect of different variables (concentrations, pH, oxidant agents, etc.) was analyzed. The recyclability of the nanocatalyst was tested and found to be successful. A degradation mechanism was also proposed. In order to improve the recovery stage of the nanocatalyst, the use of magnetic nanocomposites is proposed. Under the same experimental conditions, a slightly lower and slower degradation was achieved with an easier separation. The main conclusions of the paper are the suitability of the use of ionic liquids to prepare different nanocatalysts and the effectiveness of these at degrading an emerging pollutant in wastewater treatment.

Sulfite enhanced transformation of iopamidol by UV photolysis in the presence of oxygen: Role of oxysulfur radicals

UV/sulfite process in the absence of oxygen was previously applied as an advanced reduction process for the removal of many halogenated organics and inorganics in water and wastewater. Here, it was found that UV/sulfite process in the presence of oxygen could act as an advanced oxidation process. Specifically, the oxysulfur radicals (including sulfate radical (SO₄^·-) and sulfite/peroxomonosulfate radicals (SO₃^·-/SO₅^·-)) played important roles on the degradation of iopamidol (IPM) as a typical iodinated contrast media (ICM). Furthermore, the contribution of SO₄^·- on IPM removal gradually increased as pH increased from 5 to 7 and that of SO₃^·-/SO₅^·- decreased. Besides, all water quality parameters (i.e., chloride (Cl^-), iodide (I^-) and natural organic matter (NOM)) investigated here exhibited inhibitory effect on IPM removal. Three inorganic iodine species (i.e., I^-, reactive iodine species and iodate (IO₃^-)) were detected in UV/sulfite process in the presence of oxygen, while only I^- was detected in that without oxygen. During UV/sulfite/ethanol, UV photolysis and UV/peroxydisulfate (PDS)/tert-butyl alcohol (TBA) processes, thirteen transformation products including eleven deiodinated products of IPM were identified by ultra HPLC quadrupole time of flight-mass spectrometry (UPLC-Q-TOF-MS). Besides, these products generated by direct UV photolysis, SO₄^·- and SO₃^·-/SO₅^·- were further distinguished. The acute toxicity assay of Vibrio fischeri indicated that transformation products by UV/sulfite under aerobic conditions were less toxic than that by direct UV photolysis.

Transformation of X-ray contrast media by conventional and advanced oxidation processes during water treatment: Efficiency, oxidation intermediates, and formation of iodinated byproducts

X-ray contrast media (ICM), as the most widely used intravascular pharmaceuticals, have been frequently detected in various environmental compartments. ICM have attracted increasingly scientific interest owing to their role as an iodine contributor, resulting in the high risk of forming toxic iodinated byproducts (I-BPs) during water treatment. In this review, we present the state-of-the-art findings relating to the removal efficiency as well as oxidation intermediates of ICM by conventional and advanced oxidation processes. Moreover, formation of specific small-molecular I-BPs (e.g., iodoacetic acid and iodoform) during these processes is also summarized. Conventional oxidants and disinfectants including chlorine (HOCl) and chloramine (NH₂Cl) have low reactivities towards ICM with HOCl being more reactive. Iodinated/deiodinated intermediates are generated from reactions of HOCl/NH₂Cl with ICM, and they can be further transformed into small-molecular I-BPs. Types of disinfectants and ICM as well as solution conditions (e.g., presence of bromide (Br^-) and natural organic matters (NOM)) display significant impact on formation of I-BPs during chlor(am)ination of ICM. Uncatalyzed advanced oxidation process (AOPs) involving ozone (O₃) and ferrate (Fe(VI)) exhibit slow to mild reactivities towards ICM, usually leading to their incomplete removal under typical water treatment conditions. In contrast, UV photolysis and catalyzed AOPs including hydroxyl radical (HO^•) and/or sulfate radical (SO₄^.-) based AOPs (e.g., UV/hydrogen peroxide, UV/persulfate, UV/peroxymonosulfate (PMS), and CuO/PMS) and reactive chlorine species (RCS) involved AOPs (e.g., UV/HOCl and UV/NH₂Cl) can effectively eliminate ICM under various conditions. Components of water matrix (e.g., chloride (Cl^-), Br^-, bicarbonate (HCO₃^-), and NOM) have great impact on oxidation efficiency of ICM by catalyzed AOPs. Generally, similar intermediates are formed from ICM oxidation by UV photolysis and AOPs, mainly resulting from a series reactions of the side chain and/or C-I groups (e.g. cleavage, dealkylation, oxidation, and rearrange). Further oxidation or disinfection of these intermediates leads to formation of small-molecular I-BPs. Pre-oxidation of ICM-containing waters by AOPs tends to increase formation of I-BPs during post-disinfection process, while this trend also depends on the oxidation processes applied and solution conditions. This review summarizes the latest research findings relating to ICM transformation and (by)products formation during disinfection and AOPs in water treatment, which has great implications for the practical applications of these technologies.

Comparison of UV-induced AOPs (UV/Cl2, UV/NH2Cl, UV/ClO2 and UV/H2O2 ) in the degradation of iopamidol: Kinetics, energy requirements and DBPs-related toxicity in sequential disinfection processes

The UV-induced advanced oxidation processes (AOPs, including UV/Cl₂, UV/NH₂Cl, UV/ClO₂ and UV/H₂O₂ ) degradation kinetics and energy requirements of iopamidol as well as DBPs-related toxicity in sequential disinfection were compared in this study. The photodegradation of iopamidol in these processes can be well described by pseudo-first-order model and the removal efficiency ranked in descending order of UV/Cl₂  > UV/H₂O₂  > UV/NH₂Cl > UV/ClO₂  > UV. The synergistic effects could be attributed to diverse radical species generated in each system. Influencing factors of oxidant dosage, UV intensity, solution pH and water matrixes (Cl^- , NH₄ ⁺ and nature organic matter) were evaluated in detail. Higher oxidant dosages and greater UV intensities led to bigger pseudo-first-order rate constants (K_obs) in these processes, but the pH behaviors exhibited quite differently. The presence of Cl^- , NH₄ ⁺ and nature organic matter posed different effects on the degradation rate. The parameter of electrical energy per order (EE/O) was adopted to evaluate the energy requirements of the tested systems and it followed the trend of UV/ClO₂  > UV > UV/NH₂Cl > UV/H₂O₂  > UV/Cl₂ . Pretreatment of iopamidol by UV/Cl₂ and UV/NH₂Cl clearly enhanced the production of classical disinfection by-products (DBPs) and iodo-trihalomethanes (I-THMs) during subsequent oxidation while UV/ClO₂ and UV/H₂O₂ exhibited almost elimination effect. From the perspective of weighted water toxicity, the risk ranking was UV/NH₂Cl > UV/Cl₂ > UV > UV/H₂O₂ > UV/ClO₂ . Among the discussed UV-driven AOPs, UV/Cl₂ was proved to be the most cost-effective one for iopamidol removal while UV/ClO₂ displayed overwhelming advantages in regulating the water toxicity associated with DBPs, especially I-THMs. The present results could provide some insights into the application of UV-activated AOPs technologies in tradeoffs between cost-effectiveness assessment and DBPs-related toxicity control of the disinfected waters containing iopamidol.

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.

Disinfection byproducts and halogen-specific total organic halogen speciation in chlorinated source waters - The impact of iopamidol and bromide

This study investigated the speciation of halogen-specific total organic halogen and disinfection byproducts (DBPs) upon chlorination of natural organic matter (NOM) in the presence of iopamidol and bromide (Br^-). Experiments were conducted with low bromide source waters with different NOM characteristics from Northeast Ohio, USA and varied spiked levels of bromide (2-30 μmol/L) and iopamidol (1-5 μmol/L). Iopamidol was found to be a direct precursor to trihalomethane (THM) and haloacetic acid formation, and in the presence of Br^- favored brominated analogs. The concentration and speciation of DBPs formed were impacted by iopamidol and bromide concentrations, as well as the presence of NOM. As iopamidol increased the concentration of iodinated DBPs (iodo-DBPs) and THMs increased. However, as Br^- concentrations increased, the concentrations of non-brominated iodo- and chloro-DBPs decreased while brominated-DBPs increased. Regardless of the concentration of either iopamidol or bromide, bromochloroiodomethane (CHBrClI) was the most predominant iodo-DBP formed except at the lowest bromide concentration studied. At relevant concentrations of iopamidol (1 μmol/L) and bromide (2 μmol/L), significant quantities of highly toxic iodinated and brominated DBPs were formed. However, the rapid oxidation and incorporation of bromide appear to inhibit iodo-DBP formation under conditions relevant to drinking water treatment.

Non-negligible risk of chloropicrin formation during chlorination with the UV/persulfate pretreatment process in the presence of low concentrations of nitrite

The UV/persulfate (PS) process is a promising water treatment technology, and it can not only effectively degrade contaminants of emerging concern, but also control formation of disinfection byproducts (DBPs). In this study, we investigated the potential and mechanisms of chloropicrin (i.e. trichloronitromethane, TCNM) formation during chlorination that followed UV/PS pretreatment in the presence of low concentrations of nitrite. We found that when nitrite was present in the UV/PS system, unexpected high concentrations of TCNM were formed. The formation potential of TCNM was impacted by operational conditions and water matrix components: (1) high pH enhanced TCNM formation; (2) high UV fluence inhibited TCNM formation; and (3) organic compounds containing phenolic groups enhanced TCNM formation. We discovered that electrophilic substitutions by reactive nitrogen species were favored for phenolic groups, and thus more nitrite-N was transformed to organic nitrogen. We also found that more TCNM was generated from natural organic matter than algal organic matter during chlorination following pretreatment using UV/PS. Accordingly, more attention needs to be paid to TCNM formation, if nitrite is present and the water is pretreated using UV/PS (when applied at upstream of chlorination). For example, we found that if monochloramine was used as a disinfectant downstream of the UV/PS process, the formation of TCNM was reduced.

Kinetics and model development of iohexol degradation during UV/H2O2 and UV/S2O82- oxidation

The degradation rates and kinetics of one commonly used iodinated contrast medium, iohexol, were investigated and compared during ultraviolet (UV) photolysis, UV/H₂O₂ and UV/S₂O₈^2- advanced oxidation processes (AOPs). Results indicate that the iohexol degradation rate increased in the order of UV/H₂O₂ < UV irradiation < UV/S₂O₈^2- and followed pseudo-first-order kinetics. Increasing persulfate concentration significantly increased iohexol degradation rate, whereas increasing H₂O₂ concentration caused reverse effect. Radical scavenging test results show that UV photolysis, OH and radicals all contributed to iohexol degradation during UV/S₂O₈^2-, but OH was the main contributor during UV/H₂O₂ and was consumed by excess H₂O₂. The kinetic models of iohexol degradation by both AOPs were developed, and the reaction rate constants with OH and were calculated as 5.73 (±0.02) × 10⁸ and 3.91 (±0.01) × 10¹⁰ M^-1 s^-1, respectively. Iohexol degradation rate remained stable at pH 5-9 during UV irradiation and UV/H₂O₂, but gradually decreased at pH 5-7 and remained stable at pH 7-9 during UV/S₂O₈^2-. The presence of anions displayed inhibitory effects on iohexol degradation during UV/S₂O₈^2- in the order of Cl^- >HCO₃^- ≫ SO₄^2-. UV/S₂O₈^2- AOP exhibited high degradation efficiency and stability on the basis of UV irradiation, which can be applied as a promising degradation method for iohexol. UV/S₂O₈^2- AOP can effectively mineralize iohexol to CO₂ but promoted the generation of toxic iodoform (CHI₃), and the subsequent chlorination had the potential to reduce the content of disinfection by-products; therefore, further evaluation of possible environmental hazards is warranted.

Comparison of inert and non-inert cathode in cathode/Fe3+/Peroxymonosulfate processes on iohexol degradation

To investigate the effect of cathode materials on organics degradation in a cathode/Fe³⁺/PMS process, different cathode materials (platinum, copper and iron) were selected and their performances were compared with iohexol as target organics. The optimal conditions were found to be different for different cathode/Fe³⁺/PMS processes. With a relatively high cathodic current input (2.0 mA/cm²), similar results were found for all the three cathode/Fe³⁺/PMS processes. With a small cathodic current input (not higher than 1.0 mA/cm²), the iohexol removal followed the order of Fe-cathode/Fe³⁺/PMS > Cu-cathode/Fe³⁺/PMS > Pt-cathode/Fe³⁺/PMS, due to the corrosion of Cu-cathode and Fe-cathode and the more serious corrosion of Fe-cathode than Cu-cathode. The corrosion of non-inert cathode materials (Cu-cathode and Fe-cathode) meant that these cathodes not only transmitted electrons but also participated in aqueous reactions, which complicated the mechanisms of cathode/Fe³⁺/PMS processes. The radical identification experiments indicated that SO₄^- was more important than OH for iohexol degradation in Cu-cathode/Fe³⁺/PMS process, while OH played a major role in Pt-cathode/Fe³⁺/PMS and Fe-cathode/Fe³⁺/PMS processes. The different reaction mechanisms resulted in different iohexol transformation pathways in cathode/Fe³⁺/PMS processes with different cathode materials.

Rate constants of sulfate radical anion reactions with organic molecules: A review

The rate constants of sulfate radical anion reaction (k_SO4-) with about 230 organic molecules of environmental interest are tabulated and discussed, together with both the methods of rate constant determinations and the reaction mechanisms. k_SO4-'s were collected from the original publications. The highest values in the ∼10⁹ M^-1 s^-1 range are published for aromatic molecules. There is a tendency that electron donating substituents increase and electron withdrawing substituents decrease these values. There are just a few compounds with rate constants established using different techniques in different laboratories. k_SO4-'s determined in different laboratories by the direct techniques, pulse radiolysis or laser flash photolysis, in most cases agree reasonably. The values determined by competitive experimental techniques, by complex kinetics calculations, or by modelling show a large scatter. Some of these techniques seem to be questionable for k_SO4- determination. The sulfate radical anion reacts with ketone and amine moieties of molecules by electron transfer. The same mechanism is also suggested for the reaction with aromatic rings. However, in a few cases addition to the double bond and sulfate anion elimination reactions were distinguished. A typical reaction with the aliphatic parts of the molecule is H-abstraction.

Environmental photochemical fate and UVC degradation of sodium levothyroxine in aqueous medium

The synthetic hormone sodium levothyroxine (LTX) is one of the most prescribed drugs in the world and the most effective in hypothyroidism treatment. The presence of LTX in the environment has become a matter of major concern due to the widespread use of this hormone and by the fact that it is only partially removed in conventional water and sewage treatment plants. However, information regarding the photochemical fate of this hormone in environmental or engineered systems is scarce in the literature. In this work, the sunlight-driven direct and indirect LTX degradation was investigated by determining the photolysis quantum yield, Φ_LTX = 3.80 (± 0.02) × 10^-5, as well as the second-order kinetic constants of the reactions with hydroxyl radicals, k_LTX,•OH = 1.50 (± 0.01) × 10¹⁰ L mol^-1 s^-1 and singlet oxygen, k_LTX,1O2 = 1.47 (± 0.66) × 10⁸ L mol^-1 s^-1. Mathematical simulations indicate that LTX photodegradation is favored in shallow, nitrite-rich, and dissolved organic matter (DOM)-poor environments, with LTX half-life times varying from less than 10 days to about 80 days. LTX removals of 85 and 95% were achieved by UVC photolysis and UVC/H₂O₂ after 120 min, respectively. Three transformation products, triiodothyronine, diiodothyronine, and diiodotyrosine, were identified during LTX degradation by the UVC-based processes studied. The results herein regarding photo-induced kinetics coupled with environmental fate simulations may help evaluate LTX persistence and also the design of water and wastewater treatment processes.

Assessment of Sulfate Radical-Based Advanced Oxidation Processes for Water and Wastewater Treatment: A Review

High oxidation potential as well as other advantages over other tertiary wastewater treatments have led in recent years to a focus on the development of advanced oxidation processes based on sulfate radicals (SR-AOPs). These radicals can be generated from peroxymonosulfate (PMS) and persulfate (PS) through various activation methods such as catalytic, radiation or thermal activation. This review manuscript aims to provide a state-of-the-art overview of the different methods for PS and PMS activaton, as well as the different applications of this technology in the field of water and wastewater treatment. Although its most widespread application is the elimination of micropollutants, its use for the disinfection of wastewater is gaining increasing interest. In addition, the possibility of combining this technology with ultrafiltration membranes to improve the water quality and lifespan of the membranes has also been discussed. Finally, a brief economic analysis of this technology has been undertaken and the different attempts made to implement it at full-scale have been summarized. As a result, this review tries to be useful for all those people working in that area.

Insight into carbamazepine degradation by UV/monochloramine: Reaction mechanism, oxidation products, and DBPs formation

UV/monochloramine (NH₂Cl) process has attracted some attention for the elimination of contaminants of emerging concern as a novel advanced oxidation process. However, there is still much uncertainty on the performance and mechanisms of UV/NH₂Cl process because of its complexity and generation of various species of radicals, including NH₂^•, HO^•, Cl^• and other reactive chlorine species (RCS). The mechanism and influence factors of degradation of carbamazepine (CBZ) in the UV/NH₂Cl process were investigated, and a synergistic effect was observed. Degradation of CBZ under all investigated conditions followed pseudo-first order kinetics. The corresponding rate constant increased along with the dosage of NH₂Cl, and was affected significantly by the presence of bicarbonate and natural organic matter. The process has little pH-dependency, while the specific contribution of RCS and HO^• changed with solution pH, and RCS always act as a major contributor to the degradation of CBZ. Eleven byproducts of CBZ were identified and their respective evolution profiles were determined. The participation of UV in chloramination can reduce the formation of nitrogenous DBPs, but promote the formation of carbonaceous DBPs. Furthermore, when influent, sand filtered, and granular activated carbon filtered water was respectively used as background, degradation of CBZ was inhibited to different degree and more disinfection byproducts (DBPs) were generated, compared to deionized water. The electrical energy per order for degradation of CBZ in the UV/NH₂Cl process was also calculated to obtain some preliminary cost information.

Removal of Endocrine Disrupting Chemicals from Water: Adsorption of Bisphenol-A by Biobased Hydrophobic Functionalized Cellulose

The aim of this study is to examine the efficiency of biobased Spanish broom (SB) surface modified cellulose fibers to remove bisphenol A (BPA), a well-known endocrine disruptor, from water. Spanish brooms are flowering plants, which are native and abundant to Mediterranean regions. The functionalized fibers (FF) were found to have the best adsorption efficiency at pH 5, due to the optimal hydrophobic interaction between the FF fiber and BPA. Adsorption kinetics of BPA was found to fit well a pseudo-second order reaction. Equilibrium isotherm data were fitted by Langmuir and Freundlich models. A very fast and simple regeneration method was developed and it was observed that adsorption capacity of the fibers was kept almost unchanged after 3 consecutive uses. Bottled water and synthetic wastewater were also tested to assess the efficiency of the process under more realistic water and wastewater treatment conditions. It was found that BPA removal was slightly decreased from 77% in ultrapure water to 64% in synthetic wastewater matrix, indicating that FF has a high selectivity toward BPA, even in the presence of other organic compounds. Overall, it was observed that SB-modified fibers can be a new promising green biotechnology for water purification.

Susceptibility of the Algal Toxin Microcystin-LR to UV/Chlorine Process: Comparison with Chlorination

Microcystin-LR (MC-LR), an algal toxin (cyanotoxin) common in sources of drinking water, poses a major human health hazard due to its high toxicity. In this study, UV/chlorine was evaluated as a potentially practical and effective process for the degradation of MC-LR. Via mass spectrometry analysis, fewer chlorinated-MC-LR products were detected with UV/chlorine treatment than with chlorination, and a transformation pathway for MC-LR by UV/chlorine was proposed. Different degrees of rapid degradation of MC-LR were observed with varying pH (6-10.4), oxidant dosage (0.5-3 mg L^-1), natural organic matter (0-7 mg L^-1), and natural water sources. In contrast to the formation of primarily chloroform and dichloroacetic acid in deionized water where MC-LR serves as the only carbon source, additional chlorinated disinfection byproducts were produced when sand filtered natural water was used as a background matrix. The UV/chlorine treated samples also showed quantitatively less cytotoxicity in vitro in HepaRG human liver cell line tests than chlorination treated samples. Following 16 min (96 mJ cm^-2) of UV irradiation combined with 1.5 mg L^-1 chlorine treatment, the cell viability of the samples increased from 80% after exposure to 1 mg L^-1 MC-LR to 90%, while chlorination treatment evidenced no reduction in cytotoxicity with the same reaction time.

Photodegradation of sulfasalazine and its human metabolites in water by UV and UV/peroxydisulfate processes

The widespread occurrence of pharmaceuticals and their metabolites in natural waters has raised great concerns about their potential risks on human health and ecological systems. This study systematically investigates the degradation of sulfasalazine (SSZ) and its two human metabolites, sulfapyridine (SPD) and 5-aminosalicylic acid (5-ASA), by UV and UV/peroxydisulfate (UV/PDS) processes. Experimental results show that SPD and 5-ASA were readily degraded upon UV 254 nm direct photolysis, with quantum yields measured to be (8.6 ± 0.8) × 10^-3 and (2.4 ± 0.1) × 10^-2 mol Einstein^-1, respectively. Although SSZ was resistant to direct UV photolysis, it could be effectively removed by both UV/H₂O₂ and UV/PDS processes, with fluence-based pseudo-first-order rate constants determined to be 0.0030 and 0.0038 cm² mJ^-1, respectively. Second-order rate constant between SO₄^•- and SSZ was measured as (1.33 ± 0.01) × 10⁹ M^-1s^-1 by competition kinetic method. A kinetic model was established for predicting the degradation rate of SSZ in the UV/PDS process. Increasing the dosage of PDS significantly enhanced the degradation of SSZ in the UV/PDS process, which can be well predicted by the developed kinetic model. Natural water constituents, such as natural organic matter (NOM) and bicarbonate (HCO₃^-), influenced the degradation of SSZ differently. The azo functional group of SSZ molecule was predicted as the reactive site susceptible to electrophilic attack by SO₄^•- by frontier electron densities (FEDs) calculations. Four intermediate products arising from azo bond cleavage and SO₂ extrusion were identified by solid phase extraction-liquid chromatography-triple quadrupole mass spectrometry (SPE-LC-MS/MS). Based on the products identified, detailed transformation pathways for SSZ degradation in the UV/PDS system were proposed. Results reveal that UV/PDS could be an efficient approach for remediation of water contaminated by SSZ and its metabolites.

Degradation of 5,5-diphenylhydantoin by chlorination and UV/chlorination: kinetics, transformation by-products, and toxicity assessment

This study investigated the reaction kinetics and mechanism of the degradation of 5,5-diphenylhydantoin (DPH) during conventional chlorination and UV/chlorination. DPH is one of the antiepileptic drugs, which has frequently been detected in the aquatic environment. For chlorination, the second-order rate constant for the reaction between DPH and free active chlorine (FAC) was determined at pH 5 to 8. At pH 6 to 8, the efficiency of chlorination in the removal of DPH was found to be dominated by the reaction involving hypochlorous acid (HOCl). The result also showed that anionic species of DPH was more reactive toward FAC as compared with neutral DPH. For UV/chlorination, the effect of FAC dosage and pH on the degradation of DPH was evaluated. UV/chlorination is a more effective method for removing DPH as compared with conventional chlorination and UV irradiation. The DPH degradation rate was found to increase with increasing FAC concentration. On the other hand, the degradation of DPH was found to be more favorable under the acidic condition. Based on the identified transformation by-products, DPH was found to be degraded through the reaction at imidazolidine-2,4-dione moiety of DPH for both chlorination and UV/chlorination. Toxicity study on the chlorination and UV/chlorination-treated DPH solutions suggested that UV/chlorination is a more efficient method for reducing the toxicity of DPH.

Comparative study of the formation of brominated disinfection byproducts in UV/persulfate and UV/H2O2 oxidation processes in the presence of bromide

The objective of this research was to compare the transformation of Br^- and formation of brominated byproducts in UV/persulfate (PS) and UV/H₂O₂ processes. It was revealed that Br^- was efficiently transformed to free bromine which reacted with humic acid (HA) or dihydroxybenzoic acid resulting in the formation of brominated byproducts such as bromoacetic acids (BAAs) in UV/PS system. In contrast, no free bromine and brominated byproducts could be detected in UV/H₂O₂ system, although the oxidization of Br^- was evident. We presumed that the oxidation of Br^- by hydroxyl radicals led to the formation of bromine radicals. However, the bromine radical species could be immediately reduced back to Br^- by H₂O₂ before coupling to each other to form free bromine, which explains the undetection of free bromine and BAAs in UV/H₂O₂. In addition to free bromine, we found that the phenolic functionalities in HA molecules, which served as the principal reactive sites for free chlorine attack, could be in situ generated when HA was exposed to free radicals. This study demonstrates that UV/H₂O₂ is more suitable than UV/PS for the treatment of environmental matrices containing Br^-. Graphical abstract Graphical abstract.