Advanced Reduction Processes Research Articles

Advanced reduction processes initiated by oxidative radicals for trichloroacetic acid degradation: Performance, radical generation, and mechanism

The degradation of haloacetic acids (HAAs) in aqueous environments poses a challenge due to their oxidative resistance. Given that HAAs are highly carcinogenic disinfection byproducts, it is imperative to develop effective degradation methods to reduce their potential health risk. In this study, we found that only 27.2% of 200 μM trichloroacetic acid (TCA) was removed in the UV-activated persulfate (PS) system after 2 h, while complete removal was achieved with the addition of 15 mM formic acid (FA). The main products of TCA degradation were dichloroacetic acid and monochloroacetic acid. Results from free radical quenching experiments and electron paramagnetic resonance spectroscopy analyses indicated that reductive carbon dioxide radical (CO2•−) was the main active species responsible for TCA reduction. Oxidative radicals (i.e., SO4•− and •OH) generated from PS activation reacted with FA to form CO2•−, efficiently degrading TCA. The effects of PS and FA concentrations, solution pH, anions (e.g., Cl−, SO42−, and HCO3−), and small organic molecules (e.g., methanol, ethanol, and acetic acid) on degradation efficiency were examined. Overall, this study proposes a simple and efficient method to improve the degradation efficiency of HAAs in the UV/PS system and provides new insights into the advanced reduction processes used for water treatments.

Ciprofloxacin removal as an emerging contaminant using electrochemical advanced reduction process: Mechanism, degradation pathway and reaction kinetic

The introduction of emerging contaminants (ECs), particularly antibiotics to the water resources has grown in recent years. Due to its widespread application and their toxicity, the ECs are one of the major environmental concerns. The present study is to evaluate the electrochemical removal of ciprofloxacin (CIP) as an emerging contaminant through the advanced reduction process (ARP). Moreover, the degradation pathway, mechanism and its kinetics have provided. In this study, the impacts of main operating variables were evaluated including pH, current density, initial pollutant concentration, sodium sulfite (Na2SO3) concentration, and time on the CIP removal through electrochemical process based-ARP. The obtained results revealed the 94.15 % CIP degradation rate under optimal conditions, at the concentration of 20 mg/L and pH 5 during 60 min. The CIP reduction followed the first-order kinetics with the rate of 0.99. In addition, the ARP along with electrochemical systems as a novel process were suggested as suitable and high efficiency technique for the CIP removal.

Unveiling the role of artificial intelligence in tetracycline antibiotics removal using UV/sulfite/phenol advanced reduction process

UV/sulfite-based advanced reduction processes (ARP) have attracted increasing attention due to their high capability for removing a wide range of pollutants. Therefore, developing UV/sulfite ARP systems with assisted Artificial Intelligence (AI) models is considered an efficient strategy for sustainable pollutant removal. The present study delves into modeling and optimizing photodegradation of tetracycline (TC) antibiotics under UV/sulfite/рhenol reԁuсtion рroсess (UV/SPAP) using integrаteԁ Artifiсiаl Neurаl Networks (ANN), Suррort Veсtor Regression (SVR), аnԁ Genetiс Algorithm (GA). The сonсentrаtions of рhenol (X1) аnԁ sulfite (X2), рH (X3), reасtion time (X4), аnԁ TC сonсentrаtion (X5) in our exрerimentаl setuр were varied, аnԁ use the generаteԁ ԁаtа to trаin AI moԁels. The findings revealed that the AI-optimized performance is very effective in predicting and optimizing the removal of TC, thereby providing a sustainable water treatment approach. In general, SVR performed better based on scaling coefficients and ANN using different criteria indicated that X4 and X5 parameters were statistically significant. Oрtimаl rаnges for X1, X2, X3, X4, аnԁ X5 аre ԁetermineԁ to be 6.34, 3, 8.45, 80.13, аnԁ 1, resрeсtively. This аррroасh highlights the imрortаnсe of integrаting AI аnԁ ARP for sustаinаble environmentаl mаnаgement.

Enhanced sorption and destruction of PFAS by biochar-enabled advanced reduction process

The biochar-enabled advanced reduction process (ARP) was developed for enhanced sorption (by biochar) and destruction of PFAS (by ARP) in water. First, the biochar (BC) was functionalized by iron oxide (Fe3O4), zero valent iron (ZVI), and chitosan (chi) to produce four biochars (BC, Fe3O4-BC, ZVI-chi-BC, and chi-BC) with improved physicochemical properties (e.g., specific surface area, pore structure, hydrophobicity, and surface functional groups). Batch sorption experimental results revealed that compared to unmodified biochar, all modified biochars showed greater sorption efficiency, and the chi-BC performed the best for PFAS sorption. The chi-BC was then selected to facilitate reductive destruction and defluorination of PFAS in water by ARP in the UV-sulfite system. Adding chi-BC in UV-sulfite ARP system significantly enhanced both degradation and defluorination efficiencies of PFAS (up to ∼100% degradation and ∼85% defluorination efficiencies). Radical analysis using electron paramagnetic resonance (EPR) spectroscopy showed that sulfite radicals dominated at neutral pH (7.0), while hydrated electrons (eaq–) were abundant at higher pH (11) for the efficient destruction of PFAS in the ARP system. Our findings elucidate the synergies of biochar and ARP in enhancing PFAS sorption and degradation, providing new insights into PFAS reductive destruction and defluorination by different reducing radical species at varying pH conditions.

Significant roles of reactive bromine intermediates on organic co-contaminants degradation during bromate reduction in electrochemically activated (bi)sulfite process

(Bi)sulfite radical-based advanced reduction process (HSO3/SO3−-ARP) was an emerging technology to simultaneously reduce BrO3− and oxidize organic co-contaminants. However, the evolution of reactive bromine intermediates (RBrIs) and their role on degradation of organics has not been investigated. This study utilized an electrochemically activated (bi)sulfite process, a novel HSO3/SO3−-ARP for BrO3− reduction (EA-S (IV)-BrO3− process), to confirm the generation of RBrIs and elaborate the degradation mechanism of organic contaminants. Firstly, the generated RBrIs responsible for organic pollutants degradation were bromine dioxide (BrO2), bromine monoxide (BrO) and free bromine (HBrO/BrO−). Then, the species-specific second-order rate constants for RBrIs reacting with structurally diverse phenolic contaminants (PCs) (kBrO2, PCs = 107−1010 M−1 s−1 and kBrO, PCs = 106−1010 M−1 s−1) were obtained by fitting with the experimental data using a first-principle-based kinetic model of EA-S (IV)-BrO3− process in anaerobic condition. Notably, at pH 2 and 6, HSO3 (33–95 %) and BrO2 (5–66 %) dominated PCs degradation. Conversely, at pH 10, BrO (48–66 %), SO3− (27–42 %) and BrO2 (5–12 %) were the major radicals due to high reaction rates between RBrIs and dissociated PCs. The role of HBrO/BrO− was minimal (<1 %). Finally, negative linear relationships between kBrO2/BrO/HBrO, PCs and Hammett constants (Σσ+) indicated that PCs with electron-donating groups were more sensitive to RBrIs. BrO and BrO2 dominated oxidation of PCs via electron transfer, hydroxylation and ketonization, while the formation of brominated products attributed to HOBr/BrO− were negligible. This study advanced the understanding of BrO3− reduction process and the significant role of RBrIs on degradation of organic co-contaminants.

Comparative analysis of UV-initiated ARPs for degradation of the emerging substitute of perfluorinated compounds: Does defluorination mean the sole factor?

Due to the increasing attention for the residual of per- and polyfluorinated compounds in environmental water, Sodium p-Perfluorous Nonenoxybenzenesulfonate (OBS) have been considered as an alternative solution for perfluorooctane sulfonic acid (PFOS). However, recent detections of elevated OBS concentrations in oil fields and Frontal polymerization foams have raised environmental concerns leading to the decontamination exploration for this compound. In this study, three advanced reduction processes including UV-Sulfate (UV-SF), UV-Iodide (UV-KI) and UV-Nitrilotriacetic acid (UV-NTA) were selected to evaluate the removal for OBS. Results revealed that hydrated electrons (eaq−) dominated the degradation and defluorination of OBS. Remarkably, the UV-KI exhibited the highest removal rate (0.005 s−1) and defluorination efficiency (35 %) along with the highest concentration of eaq− (K = −4.651). Despite that nucleophilic attack from eaq− on sp2 carbon and H/F exchange were discovered as the general mechanism, high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (HPLC/Q-TOF-MS) analysis with density functional theory (DFT) calculations revealed the diversified products and routes. Intermediates with lowest fluorine content for UV-KI were identified, the presence nitrogen-containing intermediates were revealed in the UV-NTA. Notably, the nitrogen-containing intermediates displayed the enhanced toxicity, and the iodine poly-fluorinated intermediates could be a potential-threat compared to the superior defluorination performance for UV-KI.

UV/Sulfite reduction kinetics of perfluorobutane sulfonic acid (PFBS), perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA)

Reduction of persistent perfluorinated compounds (PFCs) by UV-activated sulfite (SF) has been recognized as one of the most effective advanced reduction processes (ARPs). With the UV/SF ARP, PFBS degradation reached 66.6 % at 25 °C after 6 h, while PFOS and PFOA were completely degraded within 80 and 20 mins, respectively. PFOA has the largest defluorination efficiency of 77.5 %, greater than 57.8 % for PFOS and 42.7 % for PFBS after 6 h. With the UV/SF system operated at 15, 25, 35 and 45 °C, activation energy (Ea) of PFBS defluorination was determined to be 360.8 kJ/mol, larger than those of PFOS and PFOA (319.4 and 67.3 kJ/mol, respectively), which implies that PFBS is more persistent and difficult to be degraded in the natural environment. Based on the consumption of SF, secondary-order kinetics models were developed to describe the degradation and defluorination of PFBS, PFOS, and PFOA at various reaction times. Concentrations of various intermediate species were determined by liquid chromatography quadrupole time-of-flight mass spectrometry (LC/QTOF-MS) during the PFBS degradation to investigate the reaction pathways in the UV/SF ARP. The proposed reaction mechanisms for PFBS degradation include desulfonation, H/F exchange, and chain shortening via direct C − C bond cleavage.

Positive profile of natural small molecule organic matters on emerging antivirus pharmaceutical elimination in advance reduction process: A deep dive into the photosensitive mechanism of triplet excited state compounds

Natural small molecular organic matter (NSOM), ubiquitous in natural waters and distinct from humic acid or fulvic acid, is a special type of dissolved organic matter (DOM) which is characterized as strong photosensitivity and simple molecular structure. However, little study had been directed on the role of NSOM in eliminating emerging contaminants in advanced reduction process (ARP). This study took three small molecular isomeric organic acids (p−hydroxybenzoic acid, pHBA; salicylic acid, SA; m−hydroxybenzoic acid, mHBA) as the representative substances of NSOM to explore these mechanisms on promoting Ribavirin (RBV, an anti COVID−19 medicine) degradation in ultraviolet activated sulfite (UV/Sulfite) process. The results demonstrated that the observed degradation rate constant of RBV (kobs-RBV) was 7.56 × 10−6 s−1 in UV/Sulfite process, indicating that hydrated electron (eaq−) from UV/Sulfite process could not effectively degrade RBV, while it increased by 178 and 38 times when pHBA and SA were introduced into UV/Sulfite process respectively, suggesting that pHBA and SA strongly promoted RBV degradation while mHBA had no promotion on RBV abatement in UV/Sulfite process. Transient absorption spectra and reactive intermediates scavenging experiment indicated that the triplet excited state pHBA and SA (3pHBA* and 3SA*) contributed to the degradation of RBV through non−radical process. Notably, eaq− played the role of key initiator in transforming pHBA and SA into their triplet states. The difference of kobs-RBV in UV/Sulfite/pHBA and UV/Sulfite/SA process was attributed to different generation pathways of 3pHBA* and 3SA* (high molar absorptivity at the wavelength of 254 nm and photosensitive cycle, respectively) and their second order rate constants towards RBV (kRBV-3pHBA* = 8.60 × 108 M−1 s−1 and kRBV-3SA* = 6.81 × 107 M−1 s−1). mHBA could not degrade RBV for its lack of intramolecular hydrogen bond and low molar absorptivity at 254 nm to abundantly transform into its triplet state. kobs-RBV increased as pH increased from 5.0 to 11.0 in UV/Sulfite/SA process, due to the high yield of eaq− in alkaline condition which promoted the generation of 3SA* and the stable of the absorbance of SA at 254 nm. By contrast, kobs-RBV underwent a process of first increasing and then decreasing in UV/Sulfite/pHBA process as the increase of pH, and its highest value achieved in a neutral condition. This lied in the exposure of eaq− increased as the increase of pH which promoted the generation of 3pHBA*, while the molar absorptivity of pHBA at 254 nm decreased as the increase of pH in an alkaline condition which inhibited the yield of 3pHBA*. The RBV degradation pathways and products toxicity assessment indicated that UV/Sulfite/pHBA had better detoxification performance on RBV than UV/Sulfite/SA process. This study disclosed a novel mechanism of emerging contaminants abatement through non-radical process in NSOM mediated ARP, and provide a wide insight into positive profile of DOM in water treatment process, instead of only taking DOM as a quencher of reactive intermediates.

Simultaneous Degradation, Dehalogenation, and Detoxification of Halogenated Antibiotics by Carbon Dioxide Radical Anions

Despite the extensive application of advanced oxidation processes (AOPs) in water treatment, the efficiency of AOPs in eliminating various emerging contaminants such as halogenated antibiotics is constrained by a number of factors. Halogen moieties exhibit strong resistance to oxidative radicals, affecting the dehalogenation and detoxification efficiencies. To address these limitations of AOPs, advanced reduction processes (ARPs) have been proposed. Herein, a novel nucleophilic reductant—namely, the carbon dioxide radical anion (CO2−)—is introduced for the simultaneous degradation, dehalogenation, and detoxification of florfenicol (FF), a typical halogenated antibiotic. The results demonstrate that FF is completely eliminated by CO2−, with approximately 100% of Cl− and 46% of F− released after 120 min of treatment. Simultaneous detoxification is observed, which exhibits a linear response to the release of free inorganic halogen ions (R2 = 0.97, p < 0.01). The formation of halogen-free products is the primary reason for the superior detoxification performance of this method, in comparison with conventional hydroxyl-radical-based AOPs. Products identification and density functional theory (DFT) calculations reveal the underlying dehalogenation mechanism, in which the chlorine moiety of FF is more susceptible than other moieties to nucleophilic attack by CO2−. Moreover, CO2−-based ARPs exhibit superior dehalogenation efficiencies (> 75%) in degrading a series of halogenated antibiotics, including chloramphenicol (CAP), thiamphenicol (THA), diclofenac (DLF), triclosan (TCS), and ciprofloxacin (CIP). The system shows high tolerance to the pH of the solution and the presence of natural water constituents, and demonstrates an excellent degradation performance in actual groundwater, indicating the strong application potential of CO2−-based ARPs in real life. Overall, this study elucidates the feasibility of CO2− for the simultaneous degradation, dehalogenation, and detoxification of halogenated antibiotics and provides a promising method for their regulation during water or wastewater treatment.

Photoreduction of atrazine from aqueous solution using sulfite/iodide/UV process, degradation, kinetics and by-products pathway

Due to its widespread use in agriculture, atrazine has entered aquatic environments and thus poses potential risks to public health. Therefore, researchers have done many studies to remove it. Advanced reduction process (ARP) is an emerging technology for degrading organic contaminants from aqueous solutions. This study was aimed at evaluating the degradation of atrazine via sulfite/iodide/UV process. The best performance (96% of atrazine degradation) was observed in the neutral pH at 60 min of reaction time, with atrazine concentration of 10 mg/L and concentration of sulfite and iodide of 1 mM. The kinetic study revealed that the removal of atrazine was matched with the pseudo-first-order model. Results have shown that reduction induced by eaq-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\ ext{e}}}_{{\ ext{aq}}}^{-}$$\\end{document} and direct photolysis dominated the degradation of atrazine. The presence of anions (Cl-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\ ext{Cl}}}^{-}$$\\end{document},CO32-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\ ext{CO}}}_{3}^{2-}$$\\end{document} and SO42-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\ ext{SO}}}_{4}^{2-}$$\\end{document}) did not have a significant effect on the degradation efficiency. In optimal conditions, COD and TOC removal efficiency were obtained at 32% and 4%, respectively. Atrazine degradation intermediates were generated by de-chlorination, hydroxylation, de-alkylation, and oxidation reactions. Overall, this research illustrated that Sulfite/iodide/UV process could be a promising approach for atrazine removal and similar contaminants from aqueous solutions.

Biochar and surfactant synergistically enhanced PFAS destruction in UV/sulfite system at neutral pH

The UV/sulfite-based advanced reduction process (ARP) emerges as an effective strategy to combat per- and polyfluoroalkyl substances (PFAS) pollution in water. Yet, the UV/sulfite-ARP typically operates at highly alkaline conditions (e.g., pH > 9 or even higher) since the generated reductive radicals for PFAS degradation can be quickly sequestered by protons (H+). To overcome the associated challenges, we prototyped a biochar-surfactant-system (BSS) to synergistically enhance PFAS sorption and degradation by UV/sulfite-ARP. The degradation and defluorination efficiencies of perfluorooctanoic acid (PFOA) depended on solution pH, and concentrations of surfactant (cetyltrimethylammonium bromide; CTAB), sulfite, and biochar. At high pH (8–10), adding biochar and BSS showed no or even small inhibitory effect on PFOA degradation, since the degradation efficiencies were already high enough that cannot be differentiated. However, at acidic and neutral pH (6–7), an evident enhancement of PFOA degradation and defluorination efficiencies occurred. This is due to the synergies between biochar and CTAB that create favorable microenvironments for enhanced PFOA sorption and deeper destruction by prolonging the longevity of reductive radicals (e.g., SO3•−), which is less affected by ambient pH conditions. The performance of UV/sulfite/BSS was further optimized and used for the degradation of four PFAS. At the optimal experimental condition, the UV/sulfite/BSS system can completely degrade PFOA with >30% defluorination efficiency for up to five continuous cycles (n = 5). Overall, our BSS provides a cost-effective and sustainable technique to effectively degrade PFAS in water under environmentally relevant pH conditions. The BSS-enabled ARP technique can be easily tied into PFAS treatment train technology (e.g., advanced oxidation process) for more efficient and deeper defluorination of various PFAS in water.

Insights into the photo-reduction of nitrate in the presence of CaSO3: Performance and mechanism

S(IV)-based advanced reduction processes have been viewed as effective strategies to eliminate nitrate (NO3−) from water. In this work, CaSO3 was introduced as the slow-release source of S(IV), and the combination of UV and CaSO3 was applied for NO3− reduction. 30 mg N/L of NO3− could be removed in the UV/CaSO3 process after 60 min reaction; UV irradiation and hydrated electrons (eaq−) reduction were responsible for the NO3− removal. The generated nitrite (NO2−) could further be removed in this process (UV/CaSO3). The degradation of NO3− increased from 65.8% to 100% with elevating CaSO3 dosage from 0.2 to 2 g/L, and the accumulation of NO2− decreased accordingly. Almost 100% removal of NO3− was achieved with initial pH being 3–12 without NO2− accumulation after reaction. The effects of anions (Cl−, CO32−, and SO42−) on the NO3− degradation and NO2− accumulation in UV/CaSO3 were negligible. Nitrogen (N2) was demonstrated as the major gaseous product during the NO3− reduction, and nitrogen-sulfur compounds (not NO2− or NH4+) remained the final liquid reduction products of NO3−. This study revealed that UV/CaSO3 would be a promising approach to remove NO3− chemically and simultaneously control the NO2− accumulation.

How I– alters UV and UV/VUV processes' redox capacities: Evidences from iodine species evolution, hydrogen peroxide formation, and oxyhalides degradation?

Although UV and/or VUV tandem I– are often proposed as advanced reduction processes (ARPs) to eliminate micropollutants by generating eaq–, the fate of I– and its byproducts formation remain to be explored. Therefore, this study investigated the iodine species evolution during UV/I– and UV/VUV/I– processes under different influencing factors. Results show that UV/VUV oxidized most of I– to IO3– whereas UV only oxidized a portion of I– to intermediate reactive iodine species (RISs, including I2, HOI, and I3–); meanwhile, substantial H2O2 was generated only in UV/VUV/I– process but not in UV/I– process, proving that UV/VUV owns stronger oxidation ability than UV alone. Spiking I– into water exerted triple-sided effects by consuming •OH, generating eaq–, and shielding light, thus complicating the systems. Holistically, increasing pH or decreasing dissolved oxygen converted oxidizing environment into reducing condition and caused less RISs formation, especially for UV/VUV/I–. For oxyhalides, neither UV/I– nor UV/VUV/I– degraded ClO4–. While UV/I– cannot remove ClO3–, UV/VUV/I– reduced ClO3– to Cl–. Expectedly, both UV/I– and UV/VUV/I– reduced BrO3– to Br– more efficiently than UV and UV/VUV, confirming that I– can enhance the reduction capacities of UV/VUV and UV technologies.

The utility of ultraviolet beam in advanced oxidation-reduction processes: a review on the mechanism of processes and possible production free radicals.

Advanced oxidation processes (AOPs) and advanced reduction processes (ARPs) are a set of chemical treatment procedures designed to eliminate organic (sometimes inorganic) contamination in water and wastewater by producing free reactive radicals (FRR). UV irradiation is one of the factors that are effectively used in oxidation-reduction processes. Not only does the UV beam cause the photolysis of contamination, but it also leads to the product of FRR by affecting oxidants-reductant, and the pollutant decomposition occurs by FRR. UV rays produce active radical species indirectly in an advanced redox process by affecting an oxidant (O3, H2O2), persulfate (PS), or reducer (dithionite, sulfite, sulfide, iodide, ferrous). Produced FRR with high redox potential (including oxidized or reduced radicals) causes detoxification and degradation of target contaminants by attacking them. In this review, it was found that ultraviolet radiation is one of the important and practical parameters in redox processes, which can be used to control a wide range of impurities.

Highly efficient reduction of bromate by vacuum UV/sulfite system

Bromate (BrO3-), a worldwide regulated by-product after ozone disinfection, is often detected in bromide-containing water, and has a strict limit of 10 μg L−1 in potable water. BrO3- degradation by advanced reduction processes (ARPs) has gained much attention because of efficient removal and easy integration with ultraviolet disinfection (UV at 254 nm). In the vacuum UV (VUV, 185/254 nm)/sulfite system, the elimination kinetics of BrO3− increased by 9-fold and 15-fold comparing with VUV alone and UV/sulfite system. This study further demonstrated the hydrated electron (eaq-) works as the dominant species in BrO3- degradation in alkaline solution, while in the acidic solution the H• became a secondary reactive species besides eaq−. Hence, the influences of pH, sulfite concentration, dissolved gas and water matrix on effectiveness of degradation kinetics of BrO3- was explored in details. With increasing pH, the proportion of SO32− species increased and even became the major ones, which also correlated well with the kobs (min−1) of BrO3− degradation. The stability of eaq− also climbs with increasing pH, while that of H• drops significantly. Higher sulfite dosage favored a more rapid degradation of BrO3−. The presence of dissolved oxygen inhibited BrO3- removal due to the scavenging effect of O2 toward eaq− and transformed VUV/sulfite-based ARP to an advanced oxidation process (AOP), which was ineffective for BrO3- removal. BrO3- removal was inhibited to varying degrees after anions (e.g., bicarbonate (HCO3−), chloride (Cl−), nitrate (NO3−)) and humic acid (HA) being added.

First highly effective non-catalytic nitrobenzene reduction in UV/dithionite system with aniline production – Advanced reduction process (ARP) approach

Advanced reduction processes (ARPs) are currently intensively investigated as an alternative to Advanced Oxidation Processes (AOPs). The study presents efficient reduction of nitrobenzene under non-catalytic conditions through reaction with free radicals having reductive potential. Effective conversion of nitrobenzene in a model wastewater solution, was obtained for sodium dithionite (SDT)/ dithionite (DTN). The developed process provide a nitrobenzene reduction efficiency of > 99.9 % within 10 min under neutral conditions, ambient temperature, with a molar ratio of reductant to pollutant (rred) of 3. Additional UV radiation lowered by 10 % the dose of DTN. Interestingly, addition of titanium dioxide (TiO2) as a photocatalyst did not show a positive effect. An extremely significant conclusion of this study is the observed excellent resistance of the reaction system to the negative influence of inorganic anions, with a reduction in efficiency in the following order: CO32-22%>NO3-6%>SO42-2%>Cl-2%>NO2-<1%>S2O32-<1%>N3-<1% and dissolved organic matter (DOM) (<13%). The study showed that the process works effectively across the pH range from 3 to 12. Studies on the reaction mechanism revealed that sulfur dioxide anion radical (SO2∙-)) was responsible for the main reduction effect. The main product of nitrobenzene reduction was aniline (>99.9 %). The total cost of purification process was USD 0.77/m3. The high efficiency, short process time, low cost, and lack of need for complicated equipment make this developed process potentially widely applicable in the industry. The developed method for the reduction of nitrobenzene to aniline is the first non-catalytic method with such high efficiency and without the formation of intermediate reaction products.

Determination of Optimum Conditions for the Degradation of 2,4,6-Trinitrotoluene (TNT) by Advanced Reduction Processes

Determination of Optimum Conditions for the Degradation of 2,4,6-Trinitrotoluene (TNT) by Advanced Reduction Processes

Silver nanocluster-based colorimetric/fluorimetric dual-mode sensor for the detection of bromide and sulfite in waters and wastewaters

In this work, the development of a fluorimetric/colorimetric dual-mode nanosensor for the determination of sulfite and fluorimetric determination of bromide involving silver nanoclusters (AgNCs) is reported. SO2 and Br2 were found to significantly modify the optical properties of AgNCs. Particularly, both volatiles weakened the fluorescence of AgNCs, whereas a color change from nearly colorless to yellowish/brown upon exposure of AgNCs to SO2. Accordingly, three smartphone-based optical assays were devised for sulfite and bromide determination, involving in situ volatile generation and enrichment/trapping of the selectively formed volatiles by AgNCs confined in a droplet and exposed to the headspace above the sample. A hydrophobized cellulose substrate acting as drop holder enabled integrating both the enrichment and the subsequent smartphone-based optical detection in a straightforward manner. Smartphone-based digitization of the enriched AgNCs microdrops and subsequent image processing using a smartphone and its integrated App, respectively, were used for quantitative purposes. Under optimal conditions, limits of detection (LODs) of 1.1 µM and 1.5 µM were achieved for the fluorimetric determination of sulfite and bromide, respectively, whereas sulfite was alternatively determined by colorimetric readout, yielding a LOD of 37.0 µM. The repeatability, expressed as relative standard deviation, was found to be in the range of 5.1–5.9 % in all cases (N = 8). The applicability of the method was demonstrated in aqueous samples of increasing complexity, with recoveries in the range 91–109 %. In addition, the responsiveness of AgNCs to SO2 and Br2 rendered them suitable for the monitoring of bromide and sulfite in increasingly relevant advanced reduction processes such as the UV/sulfite system, as demonstrated in this work.

Reductive Degradation of N-Nitrosodimethylamine via UV/Sulfite Advanced Reduction Process: Efficiency, Influencing Factors and Mechanism

N-nitrosodimethylamine (NDMA), as an emerging nitrogenous disinfection byproduct, is strictly controlled by multiple countries due to its high toxicity in drinking water. Advanced reduction processes (ARPs) are a new type of water treatment technology that can generate highly reactive reducing radicals and make environmental contaminants degrade rapidly and innocuously. In this study, a systematic investigation on the kinetics of the NDMA degradation via the chosen UV/sulfite ARP and the impacts of some key parameters of reaction system was conducted. The results indicated that the UV/sulfite ARP was an efficient and energy saving method for the reductive degradation of NDMA. A total of 94.40% of NDMA was removed using the UV/sulfite ARP, while only 45.48% of NDMA was removed via direct UV photolysis under the same reaction conditions. The degradation of NDMA via the UV/sulfite ARP followed pseudo-first-order kinetics. Increasing both the UV light intensity and sulfite dosage led to a proportional increase in the NDMA removal efficiency. The alkaline condition favored the degradation of NDMA, with the removal efficiency increasing from 21.57% to 66.79% within the initial 5 min of the reaction when the pH increased from 3 to 11. The presence of dissolved oxygen substantially decreased the removal efficiency of NDMA due to the formation of oxidizing superoxide radicals, which competed with NDMA by capturing the reducing active radicals during the reaction. An analysis of the degradation products indicated that several refractory intermediates such as dimethylamine, methylamine and nitrite were completely decomposed via the UV/sulfite ARP, and the final degradation products were formate, ammonia and nitrogen.

Enhanced coagulation coupled with cyclic IX adsorption-ARP regeneration for removal of PFOA in drinking water treatment.

Laboratory investigations were conducted to demonstrate a potentially transformative, cost-efficient per- and polyfluoroalkyl substances (PFAS) treatment approach, consisting of enhanced coagulation and repeated ion exchange (IX)-advanced reduction process (ARP) for concurrent PFAS removal and IX resin regeneration. Enhanced alum coagulation at the optimal conditions (pH6.0, 60 mg/L alum) could preferentially remove high molecular-weight, hydrophobic natural organic matter (NOM) from 5.0- to ~1.2-mg/L DOC in simulated natural water. This facilitated subsequent IX adsorption of perfluorooctanoic acid (PFOA, a model PFAS in this study) (20 μg/L) using IRA67 resin by minimizing the competition of NOM for functional sites on the resin. The PFOA/NOM-laden resin was then treated by ARP, generating hydrated electrons (eaq - ) that effectively degraded PFOA. The combined IX-ARP regeneration process was applied over six cycles to treat PFOA in pre-coagulated simulated natural water, nearly doubling the PFOA removal compared with the control group without ARP regeneration. This study underscores the potential of enhanced coagulation coupled with cyclic IX-ARP regeneration as a promising, cost-effective solution for addressing PFOA pollution in water. PRACTITIONER POINTS: Enhanced alum coagulation can substantially mitigate NOM to favor the following IX removal of PFOA in water. Cyclic IX adsorption-ARP regeneration offers an effective, potentially economical solution to the PFOA pollution in water. ARP can effectively degrade PFOA during the ARP regeneration of PFOA/NOM-laden resin.