Conventional Advanced Oxidation Processes Research Articles

A single-atom manganese nanozyme mediated membrane reactor for water decontamination

Single-atom nanozymes possess high catalytic activity and selectivity, and are emerging as advanced heterogeneous catalysts for environmental applications. Herein, we present the innovative synthesis and characterization of a single-atom manganese-doped carbon nitride (SA-Mn-CN) nanozyme, integrated into a polyvinylidene fluoride (PVDF) membrane for advanced water treatment applications. The SA-Mn-CN nanozyme demonstrates high peroxidase-like activity, efficiently catalyzing the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) and generating reactive oxygen species (ROS) for effective antibacterial action. Notably, the SA-Mn-CN/PVDF membrane showcases enhanced water permeability, superior antifouling properties, and ultra-fast degradation kinetics of organic pollutants. Mechanistic studies reveal that the nanozyme selectively generates Mn(IV)-oxo species via peroxymonosulfate (PMS) activation, crucial for the efficient oxidation processes. Our integrated membrane system effectively removes (within 1 min, > 92 % removal) a variety of organic micropollutants in continuous-flow operations, demonstrating excellent stability and minimal manganese leaching. Compared to conventional advanced oxidation process (AOPs)/membrane system, the SA-Mn-CN/PVDF/PMS system holds the advantages of high catalytic activity and selectivity for generation of reactive species, wide working pH range (pH3–11) and excellent stability and reusability under the backwashing conditions. The developed device-scale AOPs/membrane system was proven to be effective in bacterial inactivation and pollutants degradation, verifying the vast application potential of the SA-Mn-CN/PVDF membrane for practical water decontamination. This work pioneers the development of enzyme-mimicking nanozyme membranes, offering a sustainable and high-performance solution for wastewater treatment, and sets a new benchmark for the design of nanozyme-based catalytic membranes in environmental applications.

High-efficiency phosphorus recovery from hypophosphite and phosphite-containing wastewater via a new electrodialysis enrichment and hydrothermal oxidation coupling process

Hypophosphite is an ideal reducing agent used in industries such as electroplating. However, the presence of high concentrations of hypophosphite and phosphite in industrial wastewater necessitates the consumption of large amounts of strong oxidants to oxidize hypophosphite to phosphate for subsequent removal by precipitation. This study introduces an innovative application of green hydrothermal process for the oxidation treatment of inorganic materials, combined with the ion enrichment advantages of electrodialysis. This novel coupling process achieves efficient enrichment and rapid oxidation of high-concentration hypophosphite and phosphite with minimal chemical consumption and more economical operating costs, yielding high-quality phosphate resources. Under electrodialysis conditions with a particle electrode dosage of 3 %, a voltage of 20 V, and a residence time of 10 h, the total phosphorus in the middle chamber was reduced from 2801.17 mg/L to 119.05 mg/L, achieving an anodic enrichment rate of 95.75 %. Under hydrothermal conditions of 400 °C for 15 min, with an H2O2 doping ratio of 7 % and a Ca(OH)2 doping ratio of 35 g/L, the peak oxidation rates of H2PO2− and HPO32− reached 99.38 %, and 99.39 % of phosphorus was transferred from the liquid phase to the solid phase in recyclable forms such as Ca5(PO4)3OH, Ca3(PO4)2, and FePO4. H2O2 enhances the hydrothermal oxidation process by increasing the concentration of free radicals. Ca(OH)2 acted as a catalyst to enhance •OH generation during the hydrothermal reaction, provided Ca2+ required for phosphorus recycling, and increased the pH to obtain crystalline products with a high Ca/P molar ratio. Compared to conventional advanced oxidation processes, the electrodialysis and hydrothermal coupling process offers a clean alternative for treating high-concentration hypophosphite and phosphite in plating wastewaters, achieving a cost saving of 22.99 %.

Simultaneous Emerging Contaminant Removal and H2O2 Generation Through Electron Transfer Carrier Effect of Bi─O─Ce Bond Bridge Without External Energy Consumption.

Conventional advanced oxidation processes (AOPs) require significant external energy consumption to eliminate emerging contaminants (ECs) with stable structures. Herein, a catalyst consisting of nanocube BiCeO particles (BCO-NCs) prepared by an impregnation-hydrothermal process is reported for the first time, which is used for removing ECs without light/electricity or any other external energy input in water and simultaneous in situ generation of H2O2. A series of characterizations and experiments reveal that dual reaction centers (DRC) which are similar to the valence band/conducting band structure are formed on the surface of BCO-NCs. Under natural conditions without any external energy consumption, the BCO-NCs self-purification system can remove more than 80% of ECs within 30min, and complete removal of ECs within 30min in the presence of abundant electron acceptors, the corresponding second-order kinetic constant is increased to 3.62 times. It is found that O2 can capture electrons from ECs through the Bi─O─Ce bond bridge during the reaction process, leading to the in situ production of H2O2. This work will be a key advance in reducing energy consumption for deep wastewater treatment and generating important chemical raw materials.

Wastewater treatment, hydrogen and energy recovery using electrochemical advanced oxidation

Electrochemical advanced oxidation processes (EAOPs) offer several advantages over conventional Advanced Oxidation Processes (AOPs) such as UV/H2O2 and H2O2/O3. This includes the absence of chemical additives and ease of control. However, high energy consumption hampers the industrial application of EAOPs. Currently, the hydrogen generated at the cathode is vented and wasted, because of its low gas purity and difficulty in collecting it. But it also underscores an opportunity where the reactor design can be improved to facilitate the collection of high-purity hydrogen for energy savings. In our study, The EAOPs reactor was designed with a proton exchange membrane (PEM) for hydrogen generation. The hydrogen at the cathode chamber is then supplied to a fuel cell to generate electricity. The energy efficiency of the EAOPs-fuel cell system is evaluated through the wastewater treatment performance and energy saving that fuel cells achieve. To optimize the EAOPs-fuel cell system, various operational conditions, including different anode types, salt concentrations, and target organic compounds, were examined to optimize the system. Our experimental results indicate that the EAOPs-fuel cell system exhibits energy-efficient performance across various operational conditions. Notably, the highest energy efficiency and recovery ratio were achieved when operating at 3 V with boron-doped diamond (BDD) as the anode. Furthermore, we investigated the impact of mass transfer on the system's energy efficiency, considering both the initial organic concentration and flow velocity. This study provided valuable insights into combining the effect of EAOPs and hydrogen fuel cells, contributing to the understanding and optimizing the oxidation performance. It also contributes to developing sustainable and cost-effective advanced oxidation technologies with wide-ranging water treatment applications.

UV/H2O2 produced degradation of 2,4-D and 4-CPA

2,4-dichlorophenoxyacetic (2,4-D) acid and 4-chlorophenoxyacetic acid (4-CPA), as widely utilized organochlorine pesticides, are normally detected in wastewater and atmosphere. Their harmfulness to the ecosystem cannot be ignored. UV/H2O2 is one of the most conventional advanced oxidation processes, which has remarkable advantages for the removal of refractory organic pollutants in wastewater. However, the reaction mechanisms and pathways of pollutants with reactive radicals are still unclear. In this study, the degradation efficacy and mechanisms during the photodegradation of 2,4-D and 4-CPA in UV/H2O2 processes were investigated by experiments and density functional theory calculations. The results showed that 2,4-D was more likely to be degraded by UV/H2O2 treatment than UV photolysis alone. In contrast, 4-CPA can be degraded effectively and rapidly under UV irradiation alone. By LC-MS analysis, the degradation products of 2,4-D and 4-CPA in the UV/H2O2 processes were identified and they were produced by hydroxylation and photolysis. Therefore, we speculated a competition mechanism presented between direct photolysis and indirect photolysis in the UV/H2O2 degradation of 2,4-D and 4-CPA. The OH-initiated reaction mechanisms of 2,4-D and 4-CPA in aqueous environments were investigated using quantum chemical methods SMD/M06–2X/6–311++G (3df, 2p)//SMD/M06–2X/6-311 + G (d,p). The pH dependence of the reaction mechanisms and rate constants in their degradation process induced by ·OH was also investigated. The calculation results showed that the ionic forms (2,4-D- and 4-CPA-) were more prone to react with ·OH in comparison to the corresponding molecular forms (2,4-D and 4-CPA). The total rate constants of 2,4-D and 4-CPA with OH increased with the pH from 1 to 10, and decreased with continued pH increase. The toxicities of 2,4-D, 4-CPA and their products were assessed by the QSAR-based toxicity evaluation software. The results showed that several products were more toxic than their parent compounds, such as 2,4-dichlorophenol, 3,5-dichlorocatechol, 4-chlorophenol and hydroquinone. This work can contribute to clarifying the environmental risks of 2,4-D and 4-CPA and offer a complete understanding for the photodegradation behavior of 2,4-D and 4-CPA in aqueous ecosystems.

Critical perspective on the elimination of emerging contaminants from industrial wastewater via microbial electrochemical technologies

AbstractIndustrial water pollution originating from various industries like textile, dairy, oil, and petrochemical industries, etc. is a huge concern globally and has led to devastating effects on the environment due to the release of refractory emerging contaminants (ECs). These ECs of concern have attracted wide devotion from the scientific community due to their recalcitrant nature and disastrous effects on plants, aquatic life forms, and humans. In this regard, conventional wastewater treatment technologies such as coagulation, flocculation, membrane technologies, electrocoagulation, and other biological technologies like sequencing batch reactor, anaerobic up‐flow sludge blanket reactor, etc., are inefficient in removing ECs from the industrial effluent, while conventional advanced oxidation processes incur high cost due to the extensive requirement of energy for the degradation of ECs. To overcome this issue, microbial electrochemical technologies (METs) can be employed. For instance, METs have shown promising results in the degradation of various ECs, such as microbial fuel cells, which have shown nearly 92% to 98% removal of sulfamethoxazole with simultaneous power recovery. Alizarin yellow R, nitrobenzene, and Congo red were degraded by microbial electrolysis cells with removal efficiency in the range of 88% to 98%, demonstrating their superiority in the elimination of trace contaminants. Similarly, almost 100% mineralization of pyraclostrobin was noticed for the bio‐electro‐Fenton process, showing the elevated potential of these neoteric technologies for the remediation of recalcitrant pollutants. Thus, the current review article aims to critically analyze the intervention of METs for the elimination of ECs from industrial wastewater.

Chloride ion enhanced oxidant-free in situ degradation of Ni-EDTA by electrochemical process with boron-doped diamond electrodes

Conventional advanced oxidation processes were used to treat heavy metal complexes. However, a considerable amount of oxidants was required to enable effective oxidative degradation, which led to a significant increase of the treatment costs and subsequent difficulties in the sludge disposal. Based on the abundance of anions in heavy metal wastewater, the effects of anions on the in-situ degradation of Ni-EDTA in an oxidant-free electrochemical system with boron-doped diamond (BDD) as the anode were investigated. The presence of Cl- was found to exert a significant effect on improving the degradation process. Moreover, pH had little effect on the removal of nickel (Ni) and Ni-EDTA within a specific pH range (1 < pH < 9). The removal efficiencies of Ni and TOC reached 100 % and 77.45 %, respectively, at pH 2.16 with 0.4 M NaCl electrolyte, 2 mM Ni-EDTA concentration, and a current density of 50 mA/cm2. •OH and Cl• played crucial roles in the removal of Ni-EDTA by disrupting the chelation sites of Ni and EDTA molecules. The released Ni2+ ions could active the H2O2 in-situ generated at the cathode to produce •OH. The formation of the precipitation products such as NiOOH, Ni(OH)2, and NiCO3 in the Cl-/BDD system were conform based on the XRD and XPS analyses, which suggested the possible pathways for the removal of Ni2+ and Ni3+. Finally, the possible degradation pathways of Ni-EDTA were proposed based on the identification of intermediate products using UPLC-MS.

Insight into the selective oxidation behavior of organic pollutants via Ni-N4-C mediated electron transfer pathway

Advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS) is a hopeful method for organic pollutants degradation. However, conventional AOPs often suffer from various disturbances in applications, such as organic matter, inorganic ions, pH, etc. Herein, a novel Ni(Ⅱ)-doped g-C3N4 (Ni4.60CN) catalyst with Ni-N4-C structure was prepared, which exhibited outstanding PMS activation ability. The Ni-N4-C active sites facilitated the electron transfer from pollutants to PMS and achieving high selectivity toward pollutant degradation. Then, integrating experimental and theoretical results, the origin of this selectivity was revealed, indicating that organic pollutants with low vertical ionization potential (VIP), high the highest occupied molecular orbital energy (EHOMO), and low potential differences between organics and Ni4.60CN (marked as EPD) are more beneficial to be degraded. This study unravels the electron transfer mechanism induced by Ni-N4-C sites in Ni4.60CN /PMS activation system and provides a comprehensive insight into the selective oxidation behavior of various pollutants.

Treatment of Effluent Containing p-Cresol through an Advanced Oxidation Process in a Batch Reactor: Kinetic Optimization

The present research is related to the study of p-cresol oxidation reaction in aqueous phase. Firstly, the conventional advanced oxidation process (AOP) in a lab-scale batch reactor was used, seeking to identify the most impacting process variables and then to propose an optimization approach for ensuring the complete p-cresol degradation and the highest total organic carbon (TOC) conversion. In the AOP with the use of hydrogen peroxide as the oxidizing agent, the oxidation reaction was optimized with the aid of a factorial design, and a maximum TOC conversion of 63% was obtained. The Lumped Kinetic Model (LKM) was used to describe the profile of residual TOC concentration due to chemical species, which were categorized into two groups (refractory and non-refractory compounds). The model was able to satisfactorily describe the profile of the residual fractions of these two classes of organic compounds and allowed estimating the related kinetic constants (k) at two different temperatures, namely (a) 3.19 × 10−1 and 2.82 × 10−3 min−1 for non-refractory and refractory compounds at 80 °C and (b) 4.73 × 10−1 and 5.09 × 10−3 min−1 for the same compound classes at 90 °C, while the activation energy (Ea) of the process was 42.02 and 62.09 kJ mol−1, respectively. The kinetic modeling of organic pollutants oxidation in liquid effluents would allow to perform in situ seawater treatment on vertical reactors installed in offshore platforms and to properly release treated water into the oceans. In this way, ocean contamination caused by the exploration on offshore platforms of oil and natural gas, the main energy sources and vectors in the current world, may be remarkably reduced, thus favoring a more eco-friendly energy production.

Controlling contaminants using a far-UVC-based advanced oxidation process for potable reuse

Increasing the efficiency of the processing units used to purify municipal wastewater to potable quality would enhance the sustainability of potable reuse. Conventional advanced oxidation processes using 254 nm UV light degrade contaminants by both direct photolysis and reaction with radicals produced by hydrogen peroxide photolysis. Treatment goals include 0.5-log removal of 1,4-dioxane, reducing N-nitrosodimethylamine to <10 ng l−1 and 6-log virus inactivation. Using three potable reuse waters, we demonstrate here that a switch from 254 to 222 nm (far-UVC) achieved all three treatment goals at ~320 mJ cm−2 UV fluence, which is around four-fold less than is needed at 254 nm. Developing and validating a kinetic model, we determined that the increased energy efficiency arises from a 2.1- to 7.5-fold increase in direct photolysis and a 3.6-fold increase in radical concentrations. Compared with switching to far-UVC wavelengths, alternative efforts to switch from H2O2 to chlorine have been frustrated by the need to increase UV fluence to control N-nitrosodimethylamine. Enhancing the advanced oxidation processes used in potable reuse treatment trains represents an attractive target for reducing the energy intensity of the train. Switching the UV wavelength from 254 nm to 222 nm improves contaminant degradation by both direct photolysis and reaction with radicals, offering substantial efficiency gains.

Amorphous zirconium oxide activates peroxymonosulfate for selective degradation of organic compounds: Performance, mechanisms and structure-activity relationship

Application of heterogeneous advanced oxidation processes (AOPs) for wastewater treatment suffers from the low oxidant utilization efficiency, slow catalytic cycling and severe matrix interference. Herein, we report that amorphous zirconium dioxide (aZrO2), a redox-inert metal oxide, can efficiently activate peroxymonosulfate (PMS) to degrade organic micropollutants under very low oxidant doses and complex coexisting matrices. Distinct from conventional AOPs where radicals are formed, the surface Zr(IV)-PMS* complex was identified as the principal reactive species, and primarily conducted oxygen-atom-transfer route with selected molecules. Quantitative structure-activity relationship analysis indicated that the formation of Zr(IV)-PMS* complex was governed by the density of the surface hydroxyl groups. The strong interaction between the Zr atom and PMS caused the deviation of the negative charge from Zr(IV) metal sites to the oxidant. As a result, the O-O bond of the adsorbed PMS was prolonged and its oxidation potential elevated, which enabled it to directly react with contaminants. This study indicates the potential of aZrO2 as a novel and eco-friendly catalyst that activates PMS to selectively tackle organic contaminants, and sheds light on the designing of Fenton-like catalysts using redox-inert metals.

Electric field-enhanced coupled with metal-free peroxymonosulfate activactor: The selective oxidation of nonradical species-dominated system

Nowadays metal-free persulfate-based advanced oxidation processes (AOPs) have been intensively investigated, however, the catalysts are often too complex to fully consider their application potential. Conventional AOPs usually suffer from severe interference in real water matrix, thus, selective oxidation is practically and scientifically challenging as it could avoid unnecessary inputs of energy and possible secondary pollutants. In this study, a remarkably synergistic effect was achieved when conventional amorphous boron/peroxymonosulfate (Boron/PMS, 0.67 × 10−2 min−1) system was combined with electrolysis (E-Boron/PMS, 1.54 × 10−2 min−1) to degrade sulfamethoxazole (SMX). Evidenced by selectively quenching tests with kinetic evaluation, electron paramagnetic resonance (EPR), solvent-exchange experiment and electrochemical analysis, the dominated reactive oxygen species in E-Boron/PMS system tended to be 1O2, instead of the •OH and SO4•−. Mechanistic study unveiled that 1O2 was generated via accelerated PMS self-decomposition, triggered by interface alkalization and hydroxyl radicals transfer at the cathode interface. 1O2 is considered to be selective to the electron-rich organic compounds, thus E-Boron/PMS system was superior to conventional radical-dominated system (Boron/PMS) for SMX removal in the co-presence of common inorganic anions, showing the great merits of selective oxidation in nonradical system. These findings provided new insights into effective and selective oxidation of SMX via E-Boron/PMS system, which shed new light on the development of nonradical system.

Electrocatalytic membrane containing CuFeO2/nanoporous carbon for organic dye removal application

Decolorizations, degradation and mineralization of wastewater containing dyes utilizing an electrocatalytic membrane reactor (ECMR) is a beneficial development to conventional advanced oxidation processes (AOPs) caused of its robust efficiency and sustainability and environmental appropriateness. We herein developed a stainless-steel mesh (SSM) electrode supported a porous membrane via incorporation of a PVDF casting solution containing CuFeO2 delafossite nanoparticles impregnated in nanoporous carbon (NPC) biomass derived from apple powder as a critical electrocatalytic and chemical confinement active sites. The SSM membrane electrode was applied as the anode in a gravity-driven ECMR with deep-permeation and self-cleaning function and its concept-of-proof were investigated by methyl orange (MO, as typical azo dyes) electrocatalytic oxidation/filtration. As-designed system exhibiting a robust degradation efficiency of over 98.72% toward MO due to the heterointerfacial structure of CuFeO2 and NPC, which provided the fast electron transfer and low recombination rate, the superior generation rate of the hydroxyl radicals, large effective surface area, self-regenerability, and the least fouling and concentration polarization. The TOC and COD analysis validated that the treatment by as-prepared ECM is proficient for effluent-treatment than the industrial physico-chemical treatments. This strategy beacon paves the headlight for the substantial understanding and designing of novel extremely effective and economic ECMs for several potential applications, including environmental remediation.

Boosting reactive oxygen species generation over Bi3O4Br/CuBi2O4 by activating peroxymonosulfate under visible light irradiation

Given the limitations of conventional advanced oxidation processes (AOPs), a coupling system by integrating sulfate radical-based AOPs (SO4--AOPs) with photocatalysis for boosting the peroxymonosulfate (PMS) activation under visible light was established. Herein, we developed a novel 5 %Bi3O4Br/CuBi2O4 catalyst for rapid and efficient degradation of tetracycline (TC). The rate constant (k) for degrading TC in 5 %Bi3O4Br/CuBi2O4 + PMS + Vis system was 3.69 min−1, which is 30.62, 2.18 times higher than that of photocatalysis and SO4--AOPs alone, respectively. The quenching experiments verified that h+, OH, O2– and 1O2 were dominant contributors for the degradation of TC. EPR and quantitative analysis further implied illumination was favor in achieving mass production of OH and 1O2. Moreover, O2– and SO4- might convert into 1O2 in the 5 %Bi3O4Br/CuBi2O4 + PMS + Vis system. The degradation pathways of TC were proposed and the toxicity of intermediates was much lower than that of untreated TC. Besides, the 5 %Bi3O4Br/CuBi2O4 + PMS + Vis system showed over 90% removal rate in a wide pH range (3–11) or different concentrations of inorganic anions. This work provided a worthy reference in developing an environmentally-friendly system for the high-efficiency degradation of antibiotics.

Self-Enhanced Selective Oxidation of Phosphonate into Phosphate by Cu(II)/H2O2: Performance, Mechanism, and Validation.

Phosphonate is an important category of highly soluble organophosphorus in contaminated waters, and its oxidative transformation into phosphate is usually a prerequisite step to achieve the in-depth removal of the total phosphorus. Currently, selective oxidation of phosphonate into phosphate is urgently desired as conventional advanced oxidation processes suffer from severe matrix interferences. Herein, we employed 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) as a model phosphonate and demonstrated its efficient and selective oxidation by the Cu(II)/H2O2 process at alkaline pH. In the presence of trace Cu(II) (0.020 mM), 90.8% of HEDP (0.10 mM) was converted to phosphate by H2O2 in 30 min at pH 9.5, whereas negligible conversion was observed by UV/H2O2 or a Fenton reaction (pH = 3.0). The oxidation of HEDP by Cu(II)/H2O2 was insignificantly affected by natural organic matters (10.0 mg TOC/L) and various anions including chloride, sulfate, and nitrate (10.0 mM). The complexation of Cu(II) with HEDP coupling Cu(III) produced in situ enabled an intramolecular electron transfer process, which features high selective oxidation. Selective degradation of HEDP was further validated by adding stoichiometric H2O2 into an industrial effluent, where the existing Cu(II) could serve as the catalyst. This study also provides a successful case to trigger selective oxidation of trace pollutants of concern upon synergizing with the nature of the contaminated water.

Enhanced Chlorinated Pollutant Degradation by the Synergistic Effect between Dechlorination and Hydroxyl Radical Oxidation on a Bimetallic Single-Atom Catalyst.

Chlorinated organic pollutants are highly toxic and widespread in the environment, which cause ecological risk and threaten the human health. Chlorinated pollutants are difficult to degrade and mineralize by the conventional advanced oxidation process as the C-Cl bond is resistant to reactive oxygen species oxidation. Herein, we designed a bifunctional Fe/Cu bimetallic single-atom catalyst anchored on N-doped porous carbon (FeCuSA-NPC) for the electro-Fenton process, in which chlorinated pollutants are dechlorinated on single-atom Cu and subsequently oxidized by the ·OH radical produced from O2 conversion on single-atom Fe. Benefitting from the synergistic effect between dechlorination on single-atom Cu and ·OH oxidation on single-atom Fe, the chlorinated organic pollutants can be efficiently degraded and mineralized. The mass activity for chlorinated organic pollutant degradation by FeCuSA-NPC is 545.1-1374 min-1 gmetal-1, excessing the highest value of the reported electrocatalyst. Moreover, FeCuSA-NPC is demonstrated to be pH-universal, long-term stable, and environment friendly. This work provides a new insight into the rational design of a bifunctional electrocatalyst for efficient removal of chlorinated organic pollutants.

H2S Removal from Groundwater by Chemical Free Advanced Oxidation Process Using UV-C/VUV Radiation.

Sulfide species may be present in groundwater due to natural processes or due to anthropogenic activity. H2S contamination poses odor nuisance and may also lead to adverse health effects. Advanced oxidation processes (AOPs) are considered promising treatments for hydrogen-sulfide removal from water, but conventional AOPs usually require continuous chemical dosing, as well as post-treatment, when solid catalysts are applied. Vacuum-UV (VUV) radiation can generate ·OH in situ via water photolysis, initiating chemical-free AOP. The present study investigated the applicability of VUV-based AOP for removal of H2S both in synthetic solutions and in real groundwater, comparing combined UV-C/VUV and UV-C only radiation in a continuous-flow reactor. In deionized water, H2S degradation was much faster under the combined radiation, dominated by indirect photolysis, and indicated the formation of sulfite intermediates that convert to sulfate at high radiation doses. Sulfide was efficiently removed from natural groundwater by the two examined lamps, with no clear preference between them. However, in anoxic conditions, common in sulfide-containing groundwater, a small advantage for the combined lamp was observed. These results demonstrate the potential of utilizing VUV-based AOP for treating H2S contamination in groundwater as a chemical-free treatment, which can be especially attractive to remote small treatment facilities.

Efficacy of a two-compartment electrochemical flow cell introduced into a reagent-free UV/chlorine advanced oxidation process

As the advanced oxidation process of ultraviolet photolysis of chlorine (UV/chlorine) is more effective under an acidic condition than under a basic one, it requires reagent addition to keep the solution pH acidic and to supply free chlorine. In this study, a two-compartment electrochemical flow cell with an anion exchange membrane as a diaphragm was introduced into a UV/chlorine reactor for realizing a reagent-free operation using anodically produced protons and free chlorine. As a result, wastewater in the anodic compartment was successfully acidified by the protons generated through the water discharge at the anode, by the hydrolysis of electrochemically generated chlorine, and by the inhibition of the hydroxide ion supply from the cathodic compartment by the diaphragm. Furthermore, the electrochemical chlorine production was enhanced by increasing the chloride ion concentration in the anodic compartment through the electrodialysis effect. As the acidic effluent from the reactor was finally neutralized by hydroxide ions generated by the water discharge at the cathode, it was demonstrated that the proposed UV/electro-chlorine advanced oxidation process could work well without reagent addition. The electrical energy per order (EEO) of the process was estimated to be 15.7 kWh/(m3 order), which was comparable to that of the conventional advanced oxidation processes.

Formation of DBPs during chlorination of antibiotics and control with permanganate/bisulfite pretreatment

Abstract Antibiotics are widespread in water and wastewater, which could react with chlorine to produce disinfection byproducts (DBPs) during disinfection process. Activation of permanganate by bisulfite generates a permanganate/bisulfite (PM/BS) ultra-fast oxidation system, which exhibits more complete oxidation of refractory organics than conventional advanced oxidation processes. This study explored the formation and speciation of trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles, haloketones and trichloronitromethane during chlorination of antibiotics (chloramphenicol, ciprofloxacin and sulfamerazine), as well as the impact of Br - . PM/BS pre-oxidation was further applied to control DBP formation from antibiotics. Only THMs and HAAs were quantifiable. Trichloromethane was dominant in THMs. HAAs derived from ciprofloxacin and sulfamerazine were mostly constituted by monochloroacetic acid, while trichloroacetic acid was dominate in chlorinated chloramphenicol. Sulfamerazine exhibited the highest DBP formation potential (DBPFP), of which trihalomethane formation potential (THMFP) was 997.14 ± 13.96 μg L−1 and haloacetic acid formation potential (HAAFP) was 3767.86 ± 325.09 μg L−1. Chloramphenicol had very low THMFP, but high HAAFP (1560.29 ± 56.55 μg L−1), which was six times higher than that of ciprofloxacin. Adding Br - increased DBPFP and yields of brominated species. PM/BS pre-oxidation (KMnO4/HSO3− was 1.0/2.5 mM/mM) significantly reduced the DBPFP and chlorine reactivity, and inhibited the utilization of bromine into DBPs with the presence of Br - . After PM/BS treatment, over 50% of the ciprofloxacin in real drug manufacturing wastewater were degraded, and the THMFP decreased by about 50%. Overall. PM/BS process is a promising advanced oxidation technology for antibiotic wastewater treatment and control of DBP formation.

Application of Fe-MOFs in advanced oxidation processes

Metal organic frameworks (MOFs) are novel porous materials formed by the link-up of transition metal ions through organic bridges. Fe-based metal organic frameworks (Fe-MOFs), an important branch of MOFs, not only have the characteristics of porous channels, exceptionally high specific surface area and multiple active sites like most MOFs, but are more environmentally friendly than other MOFs. Therefore, Fe-MOFs are more suitable for environmental restoration. This paper focuses on the application of Fe-MOFs in advanced oxidation processes (AOPs). The heterogeneous catalysts used in conventional AOPs are generally less efficient due to the difficulty in balancing specific surface area and stability. Therefore, MOFs, a novel multifunctional material with exceptionally high surface area, multiple active sites, acid-base stability and thermal stability, are expected to be heterogeneous catalysts for next-generation AOPs. By surveying the application of MOFs in different AOPs (Fenton-like, photocatalysis and sulfate radical (SO4·−)-mediated oxidation), it was found that MOFs not only exhibited excellent catalytic performance in various AOPs, but also improved the pH range for AOPs. The non-specificity of MOFs and the wide adaptability to pH (3.0–6.5) have contributed to the tremendous development of heterogeneous catalysts, while the mechanism of MOFs synthesis, how to convert sulfate ions in natural water into sulfate radicals, and how to reduce the cost of synthesis remain to be further studied. AOPs with Fe-MOFs are similar to Santa Claus with reindeer, in that Fe-MOFs help AOPs do their job (i.e., treat water pollution) more efficiently.