Application Of Advanced Oxidation Processes Research Articles

Pilot-scale regeneration of wastewater through intensified sulfate radical-based advanced oxidation processes (PMS/UV-A, PMS/H2O2/UV-A, and PMS/O3): Inactivation of bacteria and mechanistic considerations

This research addresses the application of advanced oxidation processes (AOPs) for wastewater reclamation at pilot scale, one of the main limitations usually observed in this type of technology. Although interest in sulfate radical-based AOPs (SR-AOPs) has increased considerably in recent years, pilot-scale application studies are very scarce. The generation of free radicals by activation of peroxymonosulfate (PMS) can be enhanced by the introduction of UV-A radiation, or other oxidants such as hydrogen peroxide (H2O2) or ozone (O3), increasing the efficiency of the processes with lower reagent consumption.The combination of 0.5 mM PMS and 0.25 g·h−1 O3 was the fastest process in inactivation of Enterococcus faecalis, achieving inactivation in less than 45 min. Significant synergies were also observed for the combination of PMS, H2O2 and UV-A radiation, achieving total inactivation in less than 120 min, a performance significantly lower than that of the PMS/O3 system. Mechanistic studies showed that the sulfate radical (SO4•-) was responsible for bacterial inactivation in the PMS/O3 system, while in the PMS/H2O2/UV-A system the predominant species varies according to the molar ratio of the oxidants. Thus, the hydroxyl radical (•OH) is predominant in a 1:1 ratio, and SO4•- is predominant in a 1:3 ratio. This phenomenon occurs because an excess of PMS acts as a sink for radicals, preventing their interaction with bacteria.The treatments studied have been shown to be effective in the simultaneous elimination of several pathogenic microorganisms such as Enterococcus faecalis, Escherichia coli, and Staphylococcus aureus, making this technology an alternative to conventional disinfection treatments.

Magnetic photocatalysts based on graphene oxide: synthesis, characterization, application in advanced oxidation processes and response surface analysis

The decomposition rate of methyl orange (MO) is studied in aqueous solution of magnetic photocatalysts based on graphene oxide (GO). ZnO photocatalytic nanoparticles are synthesized with controlled amounts on magnetized graphene oxide and two photocatalytic samples including GFZ1 and GFZ2 are prepared for use in advanced oxidation process. The characterization of the synthesized photocatalysts is done by XRD, FTIR and VSM. The crystal structure of magnetic Fe3O4 nanoparticles as well as photocatalytic ZnO nanoparticles on the graphene oxide network has been confirmed by XRD analysis in both synthesized samples. FTIR analysis of both GFZ1 and GFZ2 also shows the stretching vibration of Fe–O and Zn–O bonds in Fe3O4 and ZnO, respectively. The superparamagnetic properties of both samples can be confirmed using VSM analysis. It is also observed that with the increase of ZnO nanoparticles in GFZ2, the magnetic properties decrease compared to GFZ1. The effect of irradiation time time (between 5 and 40 min), weight fraction of the synthesized photocatalysts (0.1%wt, 0.2%wt, and 0.3%wt) and pH of the suspension (3, 7, and 11) on the changes in MO decomposition rate was investigated and the response surface method (RSM) was used to study the effect of the simultaneous change of two parameters of the mentioned factors on the MO removal efficiency. The results show that with the increase of irradiation time and also the weight fraction of both photocatalysts, the decomposition rate of MO also increases significantly. So that in all time intervals and weight fractions, the photocatalytic activity of GFZ2 is much higher than that of GFZ1. The effect of pH also shows that the maximum and minimum decomposition rates occur in acidic and neutral conditions, respectively.

Application of Advanced Oxidation Processes for the Treatment of Color and Chemical Oxygen Demand of Pulp and Paper Wastewater

The present study was conducted in order to investigate the efficiency of different advanced oxidation processes both individually and in combination with the biological method for the removal of color and chemical oxygen demand (COD) from wastewater in the pulp and paper industry. Advanced oxidation processes include ozone, Fenton, hydrogen peroxide, and photo-Fenton. Biologically treated wastewater was successively subjected to advanced oxidation processes (AOPs). The optimum conditions for the ozone treatment of raw wastewater were found to be a contact time of 9 min and a pH of 5 at a fixed dose of ozone for a removal efficiency of 41.22% for color and 88.53% for COD. Similar optimum conditions for the ozone treatment of biologically treated wastewater showed a removal efficiency of 46.36% for color and 95.92% for COD. The photo-Fenton process also showed an efficiency comparable to the ozone treatment for both raw wastewater and biologically treated wastewater, resulting in a removal efficiency of 39.85% (color) and 90.13% (COD) for raw wastewater, and of 41.34% (color) and 94.29% (COD) for biologically treated wastewater. Each had a contact time of 12 h. The Fenton oxidation of raw wastewater showed a removal efficiency of more than 26.30% for color and 86.33% for COD. Fenton oxidation, however, showed an efficiency of 26.62% for color and 84.49% for COD removal from biologically treated wastewater. Hydrogen peroxide showed an efficiency of 28.45% for color and 85.13% for COD removal from raw wastewater, and 39.48% for color and 86.53% for COD removal from biologically treated wastewater. The results for the raw wastewater treatments indicated that higher removal efficiencies can be achieved when they are used as pre-treatments. Biological treatment is a cost-effective method but it has less efficiency for color removal. In combination with one of the AOPs, either as a pre- or post-treatment under a controlled time and dose, biological treatment increased the efficiency, making treatment feasible at larger scales.

Evaluation of the olive mill wastewater treatment based on advanced oxidation processes (AOPs), flocculation, and filtration

Different eco-friendly processes are under study to treat olive mill wastewater in the line with European 2024 zero-waste plan. This study is focused on the application of advanced oxidation processes, flocculation, and filtration to determine the best operational condition to obtain high-quality regenerated water in a simple and fast process. In this sense, after photo-Fenton high organic matter removal percentages were obtained: turbidity = 78.3 ± 6.4 %, chemical oxygen demand = 82.9 ± 0.1 %, total organic carbon = 68.9 ± 8.2 %, total phenolic compound = 20.8 ± 9.1 %, and total nitrogen = 64.1 ± 2.1 %. However, the total iron was increased to 792 ± 71 mg/L generating toxicity in the wastewater (100 % mortality in D. magna toxicity test). The subsequent flocculation and filtration steps, refine the water quality. In this sense, different flocculants have been studied to optimize regenerated treated water and the operations time, determining the sedimentation rate in a typical Kynch curve. In quality terms, adjusting the oxidized water to pH = 6 showed the best option to determine lowest values of COD = 131 mg O2/L, TPCs = 0.110 mg/L, and total iron = 0.380 mg/L but with high values for sodium = 1320 mg/L and chloride ions = 473 mg/L. However, with a minimum amount of Nalco 9913 (10 mg/L) and Nalco GR-204 (50 mg/L) highest sedimentation rate was achieved. After three filtration steps, regenerated water for irrigation purposes with the following quality parameters pH = 7.0, electric conductivity = 6.04 mS/cm, turbidity = 0.66 FTU, COD = 451 mg O2/L, TOC = 142 mg/L, TPCs = 0.13 mg/L; sodium ions = 1.50 mg/L, chloride ions = 221 mg/L, total iron = 0.247 mg/L, and no toxicity was obtained.

Hydroxyl radical induced Cr flocculation via redox reaction: The extending application of heterogeneous advanced oxidation processes on Cr removal

Flocculation is a traditional and effective method to remove Cr from wastewater, but the addition of flocculants inevitably leads to secondary pollution. In this study, Cr flocculation was induced using hydroxyl radical (•OH) (•OH flocculation) generated in an electro-Fenton-like system, achieving total Cr removal of 98.68% at initial pH = 8 within 40 min. The obtained Cr flocs showed significantly higher Cr content, lower sludge yield, and good settling properties compared to alkali precipitation and polyaluminum chloride flocculation. •OH flocculation behaved like a typical flocculant, introducing electrostatic neutralization and bridging. The mechanism proposed that •OH could overcome the steric hindrance of Cr(H2O)63+ and combine with it as an additional ligand. Then Cr(III) was proved to undergo multi-step oxidation to form Cr(IV) and Cr(V). After these oxidation reactions, •OH flocculation took precedence over Cr(VI) generation. As a result, Cr(VI) didn’t accumulate in solution until •OH flocculation was completed. This work provided a clean and eco-friendly strategy for Cr flocculation instead of flocculants and extended the application of advanced oxidation processes (AOPs), which is expected to enrich existing strategies of AOPs towards Cr removal.

Insight into iron oxychloride composite bone char for peroxymonosulfate activation: Mechanism of singlet oxygen evolution for selective degradation of organic pollutants

The activity of iron-based catalysts in advanced oxidation processes (AOPs) is limited by the redox cycle of Fe(III) and Fe(II). In this work, iron oxychloride (FeOCl) with a unique layered structure was loaded on the bone char (BC) to enhance the activation of peroxymonosulfate (PMS). Characterization of the FeOCl-BC catalyst reveals that the loading of FeOCl changed the composition and structure of BC and BC reduced the bond gap of FeOCl. Acetaminophen (APAP) as a target pollutant could be almost completely degraded at neutral pH, and the removal rate reached 0.6597 min−1. APAP could also be selectively oxidized by FeOCl-BC/PMS system in the presence of some inorganic anions (SO42−, NO3−, and Cl−) and humic acid. Quenching experiments, electron paramagnetic resonance (EPR), chemical probes, and linear sweep voltammetry (LSV) confirm that the primary oxidation mechanism of the FeOCl-BC/PMS system was dominated by 1O2. The 1O2 was generated from the conversion of O2•− and the self-dissociation of PMS, involving the formation of metastable iron intermediates and the redox cycle of Fe(III) and Fe(II). The unique structure of FeOCl, the transport of lattice oxygen and the enrichment of electrons by carbon defects play an essential role in generating reactive species. In this work, the limitation of the redox cycle of Fe(III) and Fe(II) was broken by loading FeOCl on the surface of BC, and a new catalytic mechanism was proposed. This work provides a new perspective for the construction of efficient iron-based catalysts and the practical application of PMS-based AOPs.

An application of advanced oxidation process on industrial crude oily wastewater treatment

Advanced oxidation process, via photo-catalytic oxidation process was demonstrated in this study as one of the promising techniques of simulated oily wastewater treatment. Several effective factors such as initial oil concentration, catalyst dose, stirring speed (rpm), pH value and hydrogen peroxide (H2O2) dose influencing on the photo-catalytic degradation rate of oily wastewater were investigated. The catalyst used in this work was titanium dioxide (TiO2). The solubility of oil in water was increased using emulsifier. Results indicated that the photo-catalytic oxidation process has a good removal percentage of oil from oily wastewater reached to 98.43% at optimum operating parameters of 1 g/L initial oil concentration, 850 rpm, 8 pH, 3 mL H2O2 and 1.5 g/L of TiO2 after 40 min of irradiation time. The degradation reaction follows a first order kinetics with a correlation coefficient (R2) of 93.7%. Ultimately, the application of photo-catalytic oxidation processes at these optimum operating parameters on an industrial oily wastewater collected from an effluent stream of Ras Shukair at Red See supplied by Asuit Petrochemical Company was done in Egypt. The results showed that the best oil removal (99%) was achieved after adding 3 mL of H2O2 in a reaction time of 40 min compared to without adding H2O2.

Switching of radical and nonradical pathways through the surface defects of Fe3O4/MoOxSy in a Fenton-like reaction

Coexistence of radical and nonradical reaction pathways during advanced oxidation processes (AOPs) makes it challenging to obtain flexible regulation of high efficiency and selectivity for the requirement of diverse degradation. Herein, a series of Fe3O4/MoOxSy samples coupling peroxymonosulfate (PMS) systems enabled the switching of radical and nonradical pathways through the inclusion of defects and adjustment of Mo4+/Mo6+ ratios. The silicon cladding operation introduced defects by disrupting the original lattice of Fe3O4 and MoOxS. Meanwhile, the abundance of defective electrons increased the amount of Mo4+ on the catalyst surface, promoting PMS decomposition with a maximum k value up to 1.530 min−1 and a maximum free radical contribution of 81.33%. The Mo4+/Mo6+ ratio in the catalyst was similarly altered by different Fe contents, and Mo6+ contributed to the production of 1O2, allowing the whole system to attain a nonradical species–dominated (68.26%) pathway. The radical species-dominated system has a high chemical oxygen demand (COD) removal rate for actual wastewater treatment. Conversely, the nonradical species-dominated system can considerably improve the biodegradability of wastewater (biochemical oxygen demand (BOD)/COD = 0.997). The tunable hybrid reaction pathways will expand the targeted applications of AOPs.

Original nanostructured bacterial cellulose/pyrite composite: Photocatalytic application in advanced oxidation processes

The development of an original catalytic composite of bacterial cellulose (BC) and pyrite (FeS2) for environmental application was the objective of this study. Nanoparticles of the FeS2 were synthesized from the hydrothermal method and immobilized on the BC structure using ex situ methodology. In the BC, the FTIR and XRD analyzes showed the absorption band associated with the Fe–S bond and crystalline peaks attributed to the pyrite. Thus, the immobilization of the iron particles on the biopolymer was proven, producing the composite BC/FeS2. The use of the SEM technique also ratifies the composite production by identifying the fibrillar structure morphology of the cellulose covered by FeS2 particles. The total iron concentration was 54.76 ± 1.69 mg L−1, determined by flame atomic absorption analysis. TG analysis and degradation tests showed respectively the thermal stability of the new material and its high catalytic potential. A multi-component solution of textile dyes was used as the matrix to be treated via advanced oxidative processes. The composite acted as the catalyst for the Fenton and photo-Fenton processes, with degradations of 52.87 and 96.82%, respectively. The material proved stability by showing low iron leaching (2.02 ± 0.09 and 2.11 ± 0.11 mg L−1 for the respective processes). Thus, its high potential for reuse is presumed, given the remaining concentration of this metal in the BC. The results showed that the BC/FeS2 composite is suitable to solve the problems associated with using catalysts in suspension form.

A review on superior advanced oxidation and photocatalytic degradation techniques for perfluorooctanoic acid (PFOA) elimination from wastewater

Perfluorooctanoic acid (PFOA) has been identified as the most toxic specie of the family of perfluorinated carboxylic acids (PFCAs). It has been widely distributed and frequently detected in environmental wastewater. The compound's unique features such as inherent stability, rigidity, and resistance to harsh chemical and thermal conditions, due to its multiple and strong C–F bonds have resulted in its resistance to conventional wastewater remediations. Photolysis and bioremediation methods have been proven to be inefficient in their elimination, hence this article presents intensive literature studies and summarized findings reported on the application of advanced oxidation processes (AOPs) and photocatalytic degradation techniques as the best alternatives for the PFOA elimination from wastewater. Techniques of persulfate, photo-Fenton, electrochemical, photoelectrochemical and photocatalytic degradation have been explored and their mechanisms for the degradation and defluorination of the PFOA have been demonstrated. The major advantage of AOPs techniques has been centralized on the generation of active radicals such as sulfate (SO4•-) hydroxyl (•OH). While for the photocatalytic process, photogenerated species (electron (e) and holes (h + vb)) initiated the process. These active radicals and photogenerated species possessed potentiality to attack the PFOA molecule and caused the cleavage of the C–C and C–F bonds, resulting in its efficient degradation. Shorter-chain PFCAs have been identified as the major intermediates detected and the final stage entails its complete mineralization to carbon dioxide (CO2) and fluoride ion (F−). The prospects and challenges associated with the outlined techniques have been highlighted for better understanding of the subject matter for the PFOA elimination from real wastewaters.

Advanced Oxidation Processes for Removal of Emerging Contaminants in Water

This Special Issue includes manuscripts on mechanistic understanding, development, and implementation of advanced oxidation processes (AOPs) for the removal of contaminants of emerging concern in water and wastewater treatment. The main goal was successfully achieved under the joint effort of authors, anonymous reviewers, and editorial managers. Totally, one review and 15 research papers are included in the Special Issue. These are mainly focused on catalyst synthesis, reactor design, treatment performance, kinetic modeling, reaction mechanisms, and by-product formation during electrochemical, photocatalytic, plasma, persulfate, chlorine, ozone-based, and Fenton-related AOPs at different scales. This Special Issue received attention from researchers from different parts of the world such as Argentina, Brazil, Canada, China, Germany, India, Mexico, and the USA. The guest editors are happy to see that all papers presented are innovative and meaningful, and hope that this Special Issue can promote mechanistic understanding and engineering applications of AOPs for the removal of contaminants of emerging concern in water.

Oxygen-Deficient Engineering for Perovskite Oxides in the Application of AOPs: Regulation, Detection, and Reduction Mechanism

A perovskite catalyst combined with various advanced oxidation processes (AOPs) to treat organic wastewater attracted extensive attention. The physical and chemical catalytic properties of perovskite were largely related to oxygen vacancies (OVs). In this paper, the recent advances in the regulation of OVs in perovskite for enhancing the functionality of the catalyst was reviewed, such as substitution, doping, heat treatment, wet-chemical redox reaction, exsolution, and etching. The techniques of detecting the OVs were also reviewed. An insight was provided into the OVs of perovskite and reduction mechanism in AOPs in this review, which is helpful for the reader to better understand the methods of regulating and detecting OVs in various AOPs.

The roles of the oxygen vacancies caused by the ion doping method in catalytic materials and their applications in advanced oxidation processes

We review the principles of oxygen vacancy formation induced by dopant ions, their mechanism of action and their application in advanced oxidation processes.

Treatment of nanofiltration concentrate of landfill leachate using advanced oxidation processes incorporated with bioaugmentation

Advanced oxidation processes have been broadly applied in wastewater treatment, but few studies have focused on its degradative effect on refractory organic contaminants in membrane concentrates of landfill leachate. In this study, the treatment effects of advanced oxidation processes including electrocoagulation (EC), ozone (OZ), anodic oxidation (AO) and electro-Fenton (EF) incorporated with genetically engineered nitrifying bacteria Rhodococcus erythropolis expressing Nirs and AMO (rRho-NM) on nanofiltration concentrate (NFC) of old landfill leachate were investigated in a lab-scale experiment. The results showed that advanced oxidation processes degraded the refractory organic contaminants including coagulation-resistant substances (CRS), humic acid (HA), fulvic acid (FvA), macro molecular organics (MMOs) and benzene ring compounds (BRCs) and increased the biodegradability in NFC of old landfill leachate. Compared to activated sludge (AS), rRho-NM exhibited an excellent removal performance for total organic carbon (TOC), ammonia nitrogen (NH4–N), total nitrogen (TN), biochemical oxygen demand (BOD) and chemical oxygen demand (COD) for advanced oxidation processes-treated NFC of old landfill leachate. Advanced oxidation processes incorporated with bioaugmentation demonstrated an outstanding degradation performance for removing refractory organic contaminants, TOC, NH4–N, TN, BOD, COD and heavy metal in NFC of old landfill leachate. In addition, OZ incorporated with rRho-NM (OZ-rRho-NM) showed the optimal removal efficacy in reduction of refractory organic contaminants, TOC, NH4–N, TN, BOD and COD, the shortest hydraulic retention time (HRT) and the minimum energy consumption in NFC of landfill leachate. Furthermore, the cheapest treatment cost for NFC could be achieved by EC incorporated with rRho-NM (EC-rRho-NM). More impressively, rRho-NM remained stable in expressing Nirs and AMO genes, increased nitrification and denitrification rate, and improved MBR effluent quality in the treatment of NFC. In conclusion, this work provides new insights into the application of advanced oxidation processes incorporated with bioaugmentation using rRho-NM for the treatment of NFC of old landfill leachate.

Co–Mn spinel oxides trigger peracetic acid activation for ultrafast degradation of sulfonamide antibiotics: Unveiling critical role of Mn species in boosting Co activity

Activation of peracetic acid (PAA) to generate powerful oxidizing species has become a promising advanced oxidation processes (AOPs) in wastewater treatment, yet the development of low-cost and high-performance activators is still a primary challenge. Herein, a range of Co–Mn spinel oxides (Co3-xMnxO4) with varying levels of Co and Mn were successfully elaborated, in which Co1.1Mn1.9O4 exhibited remarkable performance in PAA activation, outperforming most reported heterogeneous catalysts. Extensive quenching experiments and electron spin resonance (ESR) analysis indicated that acetylperoxyl radical (CH3C(O)OO●) was the predominated oxidizing species responsible for sulfamethoxazole (SMX) degradation. Density functional theory (DFT) calculations revealed that doping with Mn not only promoted the electron transfer and accelerated reduction of Co(III) to Co(II), but also lowered the energy barrier for PAA activation. Moreover, the prominent chemisorption and activation of PAA with Co1.1Mn1.9O4 was also benefitted from the significant role of Mn in optimizing the distribution of bonding and antibonding states on Co 3d orbitals. Unexpectedly, high levels of Cl−greatly facilitated SMX degradation due to the mass production of HOCl from the chain reactions of various radicals with Cl−. This work provides new insights into bimetallic activation of PAA, and the knowledge obtained will further advance the application of PAA-based AOPs.

Sedum Plumbizincicola Derived Functional Carbon for Activation of Peroxymonosulfate to Eliminate Bisphenol A: Performance and Reaction Mechanisms

Carbon-based functional materials are deemed to be excellent candidates to adsorb contaminants from wastewater, yet their catalytic roles in advanced oxidation processes (AOPs) are still ambiguous. Therefore, four functional carbons (SPFCx) were fabricated in this study under various pyrolysis temperatures by using Sedum plumbizincicola (SP) residues (a kind of phytoremediation plant) as the precursors. Notably, SPFC800 exhibited the best adsorption capacity (qe = 26.081 mg g−1) toward bisphenol A (BPA) due to its having the largest specific surface area (121.57 m2 g−1). By injecting peroxymonosulfate (PMS, 5.0 mM), BPA (10 mg L−1) could be completely removed within 70 min. More importantly, the BPA removal was stable and effective even in complex wastewater. Interestingly, radicals played minor roles in the SPFC800/PMS system, while nonradical mechanisms (i.e., 1O2 and electron-transfer regime) were responsible for the BPA elimination, which was verified by quenching tests, solvent exchange experiments (H2O2→D2O), and electrochemical experiments. Overall, this work may provide a facile and green method for BPA contaminated-wastewater purification and promote the application of AOPs in environmental remediation.

ПРОЦЕС “СОНОПЕРОКСАТ” ДЛЯ ОКИСНЮВАЛЬНОЇ ДЕГРАДАЦІЇ МЕТИЛОВОГО ОРАНЖЕВОГО

The efficiency of application of advanced oxidation processes for removal of methyl orange mono azo dye from wastewater is considered. For intensive oxidative degradation of methyl orange, it was proposed to use a combination of ultrasonic cavitation and “Peroxate” process – the “Sonoperoxate” process. Rational conditions for oxidative degradation of methyl orange at its initial concentration in an aqueous solution of 25 mg/dm3 (76.5·10-6 mol/dm3) were established: the molar ratio of methyl orange:hydrogen pero- xide:potassium metaperiodate = 1:50:10; pH of the reaction medium – 3; temperature – 293 K; specific power of cavitation ultrasonic treatment – 68 W/dm3. Under such conditions, the degradation degree of methyl orange of 89.4 % was achieved for 1800 s.

Catalytic ozonation for imazapic degradation over kelp-derived biochar: Promotional role of N- and S-based active sites

It is a feasible strategy to prepare reliable biochar catalysts for heterogeneous catalytic ozonation (HCO) processes by using inexpensive, high quality, and easily available raw materials. Here, an environmentally friendly, simple, and green biochar catalyst rich in nitrogen (N) and sulfur (S) has been prepared by the pyrolysis of kelp. Compared with directly carbonized kelp biomass (KB), acid-activated KB (KBA) and base-activated KB (KBB) have higher specific surface areas and more extensive porous structures, although only KBB displays effective ozone activation. Imazapic (IMZC), a refractory organic herbicide, was chosen as the target pollutant, which has apparently not hitherto been investigated in the HCO process. Second-order rate constants (k) for the reactions of IMZC with three different reactive oxygen species (ROS), specifically kO3, IMZC, kOH, IMZC, and k1O2, IMZC, have been determined as 0.974, 2.48 × 109, and 6.23 × 105 M−1 s−1, respectively. The amounts of graphitic N and thiophene S derived from the intrinsic N and S showed good correlations with the IMZC degradation rate, implicating them as the main active sites. OH and O2− and 1O2 were identified as main ROS in heterogeneous catalytic ozonation system for IMZC degradation. This study exemplified the utilization of endogenous N and S in biological carbon, and provided more options for the application of advanced oxidation processes and the development of marine resources.

Applications of advanced oxidation processes (Electro‑Fenton and sono‑electro‑Fenton) for COD removal from hospital wastewater: Optimization using response surface methodology

This study investigates the feasibility of applying electro-Fenton (EF) and sono-electro-Fenton (SEF) processes for the removal of chemical oxygen demand (COD) from the hospital wastewater generated by the Al-Diwaniyah hospital located in Iraq. The effect of various operational parameters on COD removal was studied based on the response surface methodology (RSM). The optimal conditions for maximum removal of COD using EF were found to be a current density of 19.293 mA/cm2, an H2O2/COD ratio of 1.4, and a time duration of 46.67 min, in which 96.27% COD removal was obtained at a specific energy consumption rate of 7.325 kWh/kg COD. In the EF process, results showed that the H2O2/COD ratio has the most effect on COD removal, with a 61.76% contribution, followed by the current density, which contributed 22.78%. The suitability of the model equation was confirmed by its high R2 value (98.90%). For the SEF system, the best operating conditions were found to be a current density of 10 mA/cm2, an H2O2/COD ratio of 0.2, and a time duration of 46.67 min, in which 88.31% COD removal was obtained at a specific energy consumption of 2.082kWh/kg COD. Adopting the SEF process showed that the specific energy, H2O2, and iron consumptions are lowered by 1/3.5, 1/7, and 1/2, respectively, compared to those observed at the optimum conditions for maximizing EF alone. Results revealed a significant improvement in the EF system when combined with the ultrasonic (US) technique, wherein a considerable amount of COD removal with a final value of COD less than 100 ppm was observed at a lower cost in terms of energy consumption and the chemicals used, thus confirming the role of SEF for treating hospital wastewater using a more efficient and cost-effective approach.

Dual-functional Mo2C quantum dots enriched N-doped graphitic carbon layers in advanced oxidation processes (AOPs)

Advanced oxidation processes (AOPs) are reckoned effective for removing persistent and recalcitrant pollutants by reactive oxygen species (ROSs), including hydroxyl radicals (•OH), sulfate radicals (SO4•-), and superoxide radicals (•O2-), as well as singlet oxygen (1O2). In this work, the Mo2C quantum dots enriched N-doped graphitic carbon layers (Mo2C QDs/NGCLs) were constructed via a facile two-step methodology. Interestingly, the Mo2C QDs/NGCLs acted as a highly efficient cocatalyst and/or catalyst simultaneously in AOPs, in particular visible-light-driven (VLD) Fenton and VLD PMS activation. In the hydroxyl radical-based AOPs (•OH-AOPs), it exhibited a remarkable removal efficiency for a range of aromatic organic pollutants, including rhodamine B (RhB) (99.9 %), phenol (90 %), benzophenone-3 (BZP) (83 %), methyl orange (MO) (58 %), methyl blue (MB) (89 %), ibuprofen (IBU) (100 %), and carbamazepine (CBZ) (50 %). Sulfate radicals-based AOPs (SR-AOPs) effectively degrade RhB (72 %), MO (83 %), IBU (70 %), and BZP (100 %). Thus, the present findings confirmed the potential of transition metal carbides for AOP applications and established a solid theoretical and technical basis for further research.