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

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.

Contaminants of emerging concern reduction and microbial community characterization across a three-barrier advanced water treatment system

This research investigated the removal of contaminants of emerging concern (CECs) and characterized the microbial community across an advanced water treatment (AWT) train consisting of Coagulation/Flocculation/Clarification/Granular Media Filtration (CFCGMF), Ozone-Biological Activated Carbon Filtration (O3/BAC), Granular Activated Carbon filtration, Ultraviolet Disinfection, and Cartridge Filtration (GAC/UV/CF). The AWT train successfully met the goals of CECs and bulk organics removal. The microbial community at each treatment step of the AWT train was characterized using 16S rRNA sequencing on the Illumina MiSeq platform generated from DNA extracted from liquid and solid (treatment media) samples taken along the treatment train. Differences in the microbial community structure were observed. The dominant operational taxonomic units (OTU) decreased along the treatment train, but the treatment steps did impact the microbial community composition downstream of each unit process. These results provide insights into microbial ecology in advanced water treatment systems, which are influenced and shaped by each treatment step, the microbial community interactions, and their potential metabolic contribution to CECs degradation.

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

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

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.

A comparative study on adsorption behavior of iodinated X-ray contrast media iohexol and amidotrizoic acid by magnetic-activated carbon

As persistent and ubiquitous contaminants in water, iodinated X-ray contrast media (ICM) pose a non-negligible risk to the environment and human health. In this study, we investigated the adsorption behavior of two typical ICM compounds, iohexol (IOH) and amidotrizoic acid (DTZ), on magnetic activated carbon. Theoretical investigations, using density functional theory, identified the molecule structures and calculated the molecular diameters of IOH (1.68 nm) and DTZ (1.16 nm), which revealed that ICM could be adsorbed by mesopores and larger micropores. Therefore, magnetic activated carbon with a porous structure was prepared by the co-precipitation method to investigate the adsorption mechanism of IOH and DTZ. MAC--5 (magnetic activated carbon with a theoretical iron oxide content of 37%) showed the best adsorption ability for both IOH and DTZ, with maximum adsorption capacities of 86.05 and 43.00 mg g^-1, respectively. Adsorption kinetics and isotherm models were applied to explore the mechanisms involved, and the effects of solution pH, initial concentration, temperature, ionic strength, and natural organic matter were also investigated. The pore filling effect, π-π stacking, hydrogen bonding, and electrostatic interaction, were found to be the main adsorption mechanisms. The co-adsorption data showed that competition may occur in ICM coexisting environments. Interestingly, the used MAC--5 could be successfully regenerated and its adsorption efficiency did not decrease significantly after five cycles, indicating that it is a promising adsorbent for ICM. The results from this study provide some new insights for the treatment of water containing ICM.

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.

Application of UV-activated persulfate and peroxymonosulfate processes for the degradation of 1,2,3-trichlorobenzene in different water matrices

The presence of a large number of micropollutants in the environment, including priority and emerging substances, poses a significant risk to surface and groundwater quality. Among them, trichlorobenzenes are widely used in the syntheses of dyes, pesticides, solvents, and other chemicals and have been identified as priority pollutants by the European Water Framework Directive. The main goal of this study was to investigate the behavior of 1,2,3-trichlorobenzene (TCB) during the sulfate radical-based advanced oxidation processes (SR-AOPs) involving UV activation of persulfate or peroxymonosulfate (UV/S₂O₈^2- and UV/HSO₅^- processes). For this purpose, TCB was subjected to SR-AOPs in synthetic water matrices containing humic acids or hydrogencarbonate and natural water samples and a comparative evaluation of the degradation process was made. The toxicity of the oxidation by-products was also assessed. The evaluation of TCB degradation kinetics results using principal component analysis indicates that the efficacy of the SR-AOPs was highly dependent on the pH, initial oxidant concentration, UV fluence, and matrix characteristics. In natural waters, TCB degradation by the UV/S₂O₈^2- process proved to be most effective in acidic conditions (pH 5), while the UV/HSO₅^- process showed the highest efficacy in basic conditions (pH 9.5), achieving a maximum TCB degradations of 97-99%. The obtained results indicate that UV/S₂O₈^2- and UV/HSO₅^- as new generation oxidation processes have significant potential for TCB removal from water and result in only minor toxicity after treatment (14-23% of Vibrio fischeri bioluminescence inhibition).

Mineralization of sulfonamides from wastewater using ozone-based systems

Ozone, UV/ozone, ozone/persulfate (PS) and UV/ozone/PS systems were used to mineralize sulfonamides. Sulfadiazine (SDZ), sulfamerazine (SMR) and sulfamethazine (SMZ) were the target compounds. The novel contribution of this study is its determination of the effects of PS addition, sulfonamide structure, pH and salinity on sulfonamide mineralization in ozone-based systems. The mineralization rate of sulfonamides satisfied pseudo-first-order kinetics. The SMZ mineralization rate constant in ozone, UV/ozone, ozone/PS and UV/ozone/PS systems at pH 5 were 0.0058; 0.0101; 0.0069 and 0.0802 min^-1, respectively, and those at pH 7 were 0.0075; 0.0116; 0.0083 and 0.0873 min^-1, respectively. The increase in the number of methyl substituents in the heterocyclic group of SMZ and the corresponding increase in the steric hindrance of radical addition, reduced mineralization rates below those of SMR and SDZ. The addition of PS promoted sulfonamide mineralization in the ozone-based systems; conversely, salinity inhibited sulfonamide mineralization.

Demonstration-scale evaluation of ozone-biofiltration-granular activated carbon advanced water treatment for managed aquifer recharge

The Sustainable Water Initiative for Tomorrow (SWIFT) program is the effort of the Hampton Roads Sanitation District to implement indirect potable reuse to recharge the depleted Potomac Aquifer. This initiative is being demonstrated at the 1-MGD SWIFT Research Center with a treatment train including coagulation/flocculation/sedimentation (floc/sed), ozonation, biofiltration (BAF), granular activated carbon (GAC) adsorption, and UV disinfection, followed by managed aquifer recharge. Bulk total organic carbon (TOC) removal occurred via multiple treatment barriers including, floc/sed (26% removal), ozone/BAF (30% removal), and adsorption by GAC. BAF acclimation was observed during the first months of plant operation which coincided with the establishment of biological nitrification and dissolved metal removal. Bromate formation during ozonation was efficiently controlled below 10 µg/L using preformed monochloramine and preoxidation with free chlorine. N-nitrosodimethylamine (NDMA) was formed at an average concentration of 53 ng/L post-ozonation and was removed >70% by the BAFs after several months of operation. Contaminants of emerging concern were removed by multiple treatment barriers including oxidation, biological degradation, and adsorption. The breakthrough of these contaminants and bulk TOC will likely determine the replacement interval of GAC. The ozone/BAC/GAC treatment process was shown to meet all defined treatment goals for managed aquifer recharge. PRACTITIONER POINTS: Floc/sed, biofiltration, and GAC adsorption provide important barriers in carbon-based treatment trains for bulk TOC and trace organic contaminant removal. Biofilter acclimation was observed during the first three months of operation in each operating period as evidenced by the establishment of nitrification. Bromate was effectively controlled during ozonation of a high bromide water with monochloramine doses of 3-5 mg/L. NDMA was formed at an average concentration of 53 ng/L by ozonation and complete removal was achieved by BAFs after several months of biological acclimation. An average 25% removal of 1,4-dioxane was achieved via oxidation by hydroxyl radicals during ozonation.

The application of UV-C laser in persulfate activation for micropollutant removal: Case study with iodinated X-ray contrast medias

A novel light source UV-C laser was applied in persulfate (PS) activation to effectively remove iodinated X-ray contrast medias (ICMs) including iohexol (IOX), iopamidol (IPM) and diatrizoate (DTZ) in this study. Significant ICMs degradation was observed in UV-C laser/PS systems with pseudo first-order rate constants of 0.022-0.067 s^-1. Sulfate radicals (SO₄^•-) were the main active species in the three ICMs degradation, and the steady-state concentrations ([SO₄^•-]_ss) were 3.629 × 10^-11 M (IOX), 1.702 × 10^-11 M (IPM) and 1.148 × 10^-11 M (DTZ), respectively. Under the high intensity of UV-C laser, the optimal reaction efficiency was achieved at pH = 7.0 with PS concentration of 1.0 mM, and the degradation efficiency for IOX reached 93.8% within only 40 s. Both bicarbonate and chloride ions could inhibit the three ICMs degradation and the inhibition rate increased with the increase of ions concentration. The kinetic models were established and the steady-state concentrations of radicals were calculated. Density functional theory (DFT) calculations combined with experiments were used to derive the reaction pathways for three ICMs. Cyclic voltammetry measurements detected a lower redox potential peak in IOX degradation, revealing the existence of electron shuttles under the UV-C laser irradiation to promote the redox reaction. This study is the first report of UV-C laser activation of persulfate. It is a new advanced oxidation process mediated by very effective photolysis and active species formation.

Kinetics and mechanism of 4-methylbenzylidene camphor degradation by UV-activated persulfate oxidation

4-Methylbenzylidene camphor (4-MBC), a widely used ultraviolet (UV) filter detected in various aquatic environments, has been shown to evoke estrogenic activity. In this study, the use of UV light-activated persulfate for 4-MBC degradation is evaluated for the first time. Our results showed that the combination of UV and persulfate (UV/persulfate) can significantly remove 4-MBC, with a pseudo-first-order rate constant (k_obs) of 0.1349 min^-1 under the conditions of [4-MBC]₀ = 0.4 μM, [persulfate]₀ = 12.6 μM, and initial pH = 7. The k_obs and persulfate dose exhibited a linear proportional relationship in the persulfate dose range of 4.2-42 μM. The k_obs remained similar at pH 5 and pH 7 but significantly decreased at pH 9. A radical scavenging test indicated that SO₄^-• was the dominant species in 4-MBC degradation; the second-order rate constant of SO₄^-• with 4-MBC was calculated to be (2.82 ± 0.05) × 10⁹ M^-1 s^-1. During the UV/persulfate reaction, 4-MBC was continuously degraded, while SO₄^-• was gradually converted to SO₄^2-. 4-MBC degradation involved the hydroxylation and demethylation pathways, resulting in the generation of transformation byproducts P1 (m/z 271) and P2 (m/z 243), respectively. The Microtox® acute toxicity test (Vibrio fischeri) showed increasing toxicity during the UV/persulfate degradation of 4-MBC. The 4-MBC degradation rate was markedly lower in outdoor swimming pool water than in deionized water. Graphical abstract.

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.

Adsorption of Heavy Metals on Soil Collected from Lixisol of Typical Karst Areas in the Presence of CaCO3 and Soil Clay and Their Competition Behavior

The content of heavy metals in the soil in Guizhou Province, which is a high-risk area for heavy metal exposure, is significantly higher than that in other areas in China. Therefore, the objective of this study was to evaluate the ability of CaCO3 and clay to accumulate heavy metals in topsoil sample collected from Lixisol using the method of indoor simulation. The results showed that the contents of Cu, Zn, Cd, Cr, Pb, Hg and As in the soil sample were 10.8 mg/kg, 125 mg/kg, 0.489 mg/kg, 23.5 mg/kg, 22.7 mg/kg, 58.3 mg/kg and 45.4 mg/kg, respectively. The soil pH values increased with the CaCO3 concentration in the soil, and the fluctuation of the soil pH values was weak after the CaCO3 concentrations reached 100 g/kg. The adsorption capacity of lime soil increased by approximately 10 mg/kg on average, and the desorption capacity decreased by approximately 300 mg/kg on average. The desorption of all heavy metals in this study did not change with increasing clay content. Pseudo-second-order kinetics were more suitable for describing the adsorption kinetics of heavy metals on the soil material, as evidenced by the higher R2 value. The Freundlich model can better describe the adsorption process of As on lime soil. The process of As, Cr, Cd and Hg adsorption on the soil sample was spontaneous and entropy-driven. Additionally, the process of Cu and Pb adsorption on the soil materials was spontaneous and enthalpy-driven. Generally, the adsorption and desorption of heavy metals in polluted soil increased and decreased, respectively, with increasing CaCO3 content. The effect of calcium carbonate on the accumulation of heavy metals in soil was greater than that of clay. In summary, CaCO3 and pH values in soil can be appropriately added in several areas polluted by heavy metals to enhance the crop yield and reduce the adsorption of heavy metals in soils.

Degradation of refractory organic compounds from dinitrodiazophenol containing industrial wastewater through UV/H2O2 and UV/PS processes

In this study, refractory organic compounds from dinitrodiazophenol (DDNP) containing industrial wastewater were degraded through two ultraviolet (UV)-based advanced oxidation processes: UV/hydrogen peroxide (UV/H₂O₂) and UV/potassium persulfate (UV/PS) processes. In both processes, the synergistic effects, operational parameters (i.e., oxidant dosage and initial pH value), and pseudo first-order constant k were systematically studied. Moreover, the reactive oxygen species formed in the UV/H₂O₂ and UV/PS processes were identified, and the degradation of refractory organic compounds was characterized through UV-visible spectra analysis. The improvement in biodegradability of DDNP industrial wastewater after treatment by different processes was compared. Both the UV/H₂O₂ (synergistic coefficient F = 61.34) and UV/PS (synergistic coefficient F = 54.85) processes showed significant, highly synergistic effects. The increase in oxidant dosage was beneficial in organic compound removal in both the UV/H₂O₂ and UV/PS processes, but excessive H₂O₂ showed a stronger inhibition of the increase in organic compound removal than that in the UV/PS process. In addition, an acidic environment was more conducive to organic compound degradation in the UV/H₂O₂ process, whereas the initial pH value had less of an influence on the UV/PS process. Under optimal conditions for the UV/H₂O₂ and UV/PS processes, the CN and COD removal efficiencies were 99.71%, 66.35%, 99.69%, and 70.81%, respectively, and the k values for COD removal were 0.0804 and 0.0824 min^-1. Tests to identify reactive oxygen species showed that the hydroxyl radical was the predominant oxidizing species in the UV/H₂O₂ process, whereas the hydroxyl and sulfate radicals were both identified in the UV/PS process, and the sulfate radical contributed the most to the degradation of organic compounds. In addition, spectrum analysis revealed that the complex structure (e.g., benzene ring, nitro group, and diazo group) of refractory organic compounds from DDNP industrial wastewater was effectively destroyed by the UV/H₂O₂ and UV/PS processes, and both processes improved the biodegradability (biochemical oxygen demand for 5 days/chemical oxygen demand (BOD₅/COD)) of DDNP industrial wastewater from 0.052 to 0.665 and 0.717, respectively. Overall, both the UV/H₂O₂ and UV/PS processes effectively degraded the refractory organic compounds from DDNP industrial wastewater, and the UV/PS process exhibited a higher organic compound removal efficiency and better applicability.

Removal of refractory organics in dinitrodiazophenol industrial wastewater by an ultraviolet-coupled Fenton process

A significant amount of biorefractory organic wastewater is generated during the production of dinitrodiazophenol (DDNP). In this study, ultraviolet light (254 nm) that was coupled with the Fenton (UV-Fenton) process was applied to treat refractory organics in DDNP industrial wastewater. The effects of key parameters (i.e., H₂O₂ dose, Fe²⁺ dosage, and initial pH) on the treatment efficacy for DDNP industrial wastewater by the UV-Fenton process was investigated systematically. Alcohol quenching experiments were carried out to identify reactive oxygen species in the UV-Fenton process. The treatment efficacy and degradation characteristics of refractory organics were studied and compared by using control experiments. Increasing H₂O₂ and Fe²⁺ doses could lead to improved treatment results to a different extent. A more intense reaction and better treatment results were achieved by using the UV-Fenton process at lower pH conditions. Under optimal conditions of H₂O₂ dose = 7.5 mL L⁻¹, Fe²⁺ dosage = 0.05 mM, and initial pH = 5.0, the pseudo-first order constants k for chemical oxygen demand removal and color number removal were 0.18 min⁻¹ and 1.24 min⁻¹, and the chemical oxygen demand and color number removal efficiencies were 74.24% and 99.94%, respectively. The treatment results for the UV-Fenton process were better than other processes under the same conditions, and a significant synergetic effect was observed for the UV-Fenton process. Alcohol quenching experiments indicated that the predominant reactive oxygen species in the UV-Fenton process was the hydroxyl radical (·OH). Because more ·OH was produced, the UV-Fenton process exhibited a much better treatment performance in degrading and destroying organic structures (i.e., benzene rings, –NO₂, and –N Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N–). Furthermore, the biodegradability indicated by the biological oxygen demand/chemical oxygen demand ratio was improved considerably to 0.48 from 0.054. The good treatment performance by UV-Fenton allowed for a more efficient electrical energy consumption compared with the UV and UV-H₂O₂. This study provides a theoretical reference for DDNP industrial wastewater treatment by using the UV-Fenton process.

In this study, ultraviolet-Fenton process was applied to degrade refractory organics in dinitrodiazophenol industrial wastewater. In addition, the treatment efficiency and reaction mechanism were systematically investigated.