Total Organic Carbon Removal Efficiency Research Articles

Ultrasound, Hydrogen Peroxide, and Persulfate in Hybrid Advanced Oxidation Processes(AOPs): A Comparative Study for the Reuse of Sewage Treatment Effluent

Objectives : As the variety and quantity of recalcitrant pollutants such as pharmaceuticals, pesticides, endocrine disruptors, and cosmetic products discharged into water bodies steadily increase, the need for AOPs following biological wastewater treatment processes is growing. In this study, we compared the Total Organic Carbon (TOC) removal capabilities of conventional AOPs, ultrasound, hydrogen peroxide, and persulfate-based multiple AOPs on the final effluent of S wastewater treatment plant. The study also evaluated the feasibility of wastewater reuse by examining the optimal operating conditions of the applied AOPs.Methods : The removal characteristics of TOC were investigated based on reaction time, US frequency, and oxidant dosage for the following conditions: ultrasound (US) alone, individual treatments with hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) and persulfate (PS) as oxidants, combined US/H<sub>2</sub>O<sub>2</sub> and US/PS dual AOPs, and a US/PS/H<sub>2</sub>O<sub>2</sub> multi-AOPs system.Results and Discussion : Only US oxidation treatment at 80 kHz for 60 minutes resulted in a 14.4% TOC removal efficiency. Individual treatment with H<sub>2</sub>O<sub>2</sub> at 174 mM showed 69.2% removal efficiency, while persulfate oxidation treatment at 43.5 mM showed 13.8%. The PS/H<sub>2</sub>O<sub>2</sub> oxidation treatment showed 68.5% removal efficiency at 174 mM H<sub>2</sub>O<sub>2</sub> and 0.52 mM PS, and an 85.3% removal efficiency at 2.08 mM PS and 350 mM H<sub>2</sub>O<sub>2</sub> conditions. Under the same 80 kHz ultrasound conditions, the combined US and other oxidant treatment resulted in an increased TOC removal efficiency: 87.8% for US/H<sub>2</sub>O<sub>2</sub> at 174 mM H<sub>2</sub>O<sub>2</sub>, and 81.9% for US/PS at 43.5 mM PS. Additionally, the multi-treatment with US, PS, and H<sub>2</sub>O<sub>2</sub> showed a removal efficiency of 87.0% at 2.08 mM PS and 350 mM H<sub>2</sub>O<sub>2</sub>, and 91.1% at 174 mM H<sub>2</sub>O<sub>2</sub> and 0.52 mM PS conditions.Conclusion : In this study, among the AOPs, the oxidation treatment with US/PS/H<sub>2</sub>O<sub>2</sub> exhibited the highest TOC removal efficiency at 91.1%. The integration of chemical oxidants with US demonstrated significant improvement in TOC removal capabilities, with PS showing superior performance at the same concentration conditions among the utilized chemical oxidants in the multi-AOPs. Although H<sub>2</sub>O<sub>2</sub> also displayed commendable TOC removal abilities, its oxidation efficiency was lower at low concentration injections, whereas higher concentrations of H<sub>2</sub>O<sub>2</sub> injections proved to be more effective in oxidation.

Preparation of CeO2 Supported on Graphite Catalyst and Its Catalytic Performance for Diethyl Phthalate Degradation during Ozonation

Catalysts for the efficient catalytic decomposition of ozone to generate reactive free radicals to oxidize pollutants are needed. The graphite-supported CeO2 catalyst was optimally prepared, and its activity in ozonation was evaluated using the degradation of diethyl phthalate (DEP) as an index. The stability of CeO2/graphite catalyst and the influence of operating conditions on its catalytic activity were investigated, and the mechanism of CeO2/graphite catalytic ozonation was analyzed. CeO2/graphite had the highest catalytic activity at a Ce load of 3.5% and a pyrolysis temperature of 400 °C with the DEP degradation efficiency of 75.0% and the total organic carbon (TOC) removal efficiency of 48.3%. No dissolution of active components was found during the repeated use of CeO2/graphite catalyst. The ozone dosage, catalyst dosage, initial pH, and reaction temperature have positive effects on the DEP degradation by CeO2/graphite catalytic ozonation. The presence of tert-butanol significantly inhibits the degradation of DEP at an initial pH of 3.0, 5.8, or 9.0, and the experimental results of the •OH probe compound pCBA indicate that the CeO2/graphite catalyst can efficiently convert ozone into •OH in solution. The DEP degradation in the CeO2/graphite catalytic ozonation mainly depends on the •OH in the bulk solution formed by ozone decomposition.

Floating MIL-88A(Fe)@expanded perlites catalyst for continuous photo-Fenton degradation toward tetracyclines under artificial light and real solar light

In this work, MIL-88A(Fe) was immobilized onto the expanded perlites to fabricate the floating MIL-88A(Fe)@expanded perlites (M@EP) catalyst via high throughput batch synthesis method under room temperature. The as-prepared M@EP could efficiently activate H2O2 to achieve 100% tetracycline antibiotics (TCs) removal under both artificial low power UV light (UVL) and real sunlight (SL) irradiation. The toxicological evaluation, growth experiment of mung beans and antimicrobial estimation revealed the decreasing aquatic toxicity of the TCs intermediates compared to those of the pristine TCs. A self-designed continuous bed reactor was employed to investigate the long-term operation of the M@EP. The findings demonstrated that the antibiotics mixture can be continuously degraded up to 7 days under UVL and 5 daytimes under SL irradiation, respectively. More importantly, ca. 76.9% and 81.6% of total organic carbon (TOC) removal efficiencies were accomplished in continuous bed reactor under UVL and SL irradiation, respectively. This work advances the immobilized MOFs on floating supports for their practical application in large-scale wastewater purification through advanced oxidation processes. Environmental implicationThis work presented the high throughput production and photo-Fenton degradation application of floating MIL-88A(Fe)@expanded perlites (M@EP). Three tetracycline antibiotics (TCs) were selected as model pollutants to test the degradation ability of M@EP in batch experiment and continuous operation under artificial light and solar light. The complete TCs degradation could be accomplished in self-designed device up to 7 d under UV light and 5 d under real solar light. This work tapped a new door to push MOFs-based functional materials in the real water purification.

Fabrication of N-doped graphitic carbon encapsulated Fe3C/Fe nanoparticles with dual-reaction centers for highly effective Fenton-like degradation of organic pollutants

The highly active and durable design of heterogeneous catalysts holds vital importance in the popularization of Fenton-like process for wastewater remediation. In this study, we successfully fabricated magnetic N-doped graphitic carbon (NC) encapsulated Fe3C/Fe nanoparticles, designated as Fe3C/Fe@NC-2.8, with a two-step pyrolysis method. We employed chitosan as a green precursor of NC, which is used as a heterogeneous Fenton-like catalyst to degrade refractory organic pollutants. Density functional theory (DFT) calculations revealed that the built-in electric field from the shell to core promoted electron transfer from NC to Fe3C/Fe, and thereby improved regeneration of Fe(II) and H2O2 activation. Because of the strong synergistic effects of the dual-reaction regions of Fe and Fe3C, as well as the core-shell structure advantages, the optimized Fe3C/Fe@NC rapidly degraded the typical refractory organic pollutants, and showed a much higher activity than the reference Fe2O3 and Fe3O4 samples. The total organic carbon removal efficiency of bisphenol A reached 70 % after reaction for 60 min. In addition, Fe3C/Fe@NC-2.8 possessed trace Fe leaching and satisfactory magnetically separable ability. This work provides mechanistic and practical perspectives for the development of advanced catalysts for recalcitrant pollutant treatment.

The Fabrication and Property Characterization of a Ho2YSbO7/Bi2MoO6 Heterojunction Photocatalyst and the Application of the Photodegradation of Diuron under Visible Light Irradiation.

A novel photocatalytic nanomaterial, Ho2YSbO7, was successfully synthesized for the first time using the solvothermal synthesis technique. In addition, a Ho2YSbO7/Bi2MoO6 heterojunction photocatalyst (HBHP) was prepared via the hydrothermal fabrication technique. Extensive characterizations of the synthesized samples were conducted using various instruments, such as an X-ray diffractometer, a Fourier transform infrared spectrometer, a Raman spectrometer, a UV-visible spectrophotometer, an X-ray photoelectron spectrometer, and a transmission electron microscope, as well as X-ray energy dispersive spectroscopy, photoluminescence spectroscopy, a photocurrent test, electrochemical impedance spectroscopy, ultraviolet photoelectron spectroscopy, and electron paramagnetic resonance. The photocatalytic activity of the HBHP was evaluated for the degradation of diuron (DRN) and the mineralization of total organic carbon (TOC) under visible light exposure for 152 min. Remarkable removal efficiencies were achieved, with 99.78% for DRN and 97.19% for TOC. Comparative analysis demonstrated that the HBHP exhibited markedly higher removal efficiencies for DRN compared to Ho2YSbO7, Bi2MoO6, or N-doped TiO2 photocatalyst, with removal efficiencies 1.13 times, 1.21 times, or 2.95 times higher, respectively. Similarly, the HBHP demonstrated significantly higher removal efficiencies for TOC compared to Ho2YSbO7, Bi2MoO6, or N-doped TiO2 photocatalyst, with removal efficiencies 1.17 times, 1.25 times, or 3.39 times higher, respectively. Furthermore, the HBHP demonstrated excellent stability and reusability. The mechanisms which could enhance the photocatalytic activity remarkably and the involvement of the major active species were comprehensively discussed, with superoxide radicals identified as the primary active species, followed by hydroxyl radicals and holes. The results of this study contribute to the advancement of efficient heterostructural materials and offer valuable insights into the development of sustainable remediation strategies for addressing DRN contamination.

Exploring effects of carbon, nitrogen, and phosphorus on greywater treatment by polyculture microalgae using response surface methodology and machine learning

The microalgae-based wastewater treatment is a promising technique that contribute to achieving sustainable development goals (SDGs), such as SDG-6, “Clean Water and Sanitation”. However, it is strongly influenced by the initial composition of wastewater. In this study, the impact of initial organics and nutrient concentration on the removal of total organic carbon (TOC), total carbon (TC), ammonium (NH4+), total nitrogen (TN), and phosphate (PO43−) from greywater using native polyculture microalgae was explored. Response surface methodology was employed along with two machine learning approaches, AdaBoost and XGBoost, to evaluate the interactions among three main factors: TOC, NH4+, and PO43−, and their effects on treatment efficiency. The C/N ratios for achieving maximum TOC and TC removal efficiency of 99.2% and 97.7% were determined to be 10.3, and 65.4–73.6, respectively. Notably, the N/P ratio did not significantly affect their removal. The highest NH4+ removal efficiency, reaching 96.2%, was attained at C/N ratios of 4.3, 24.0, 38.2, and 212.9, coupled with N/P ratios of 0.3, 2.6, and 23.4. Highest TN removal efficiency of 77.2% was achieved at C/N and N/P ratios of 12.2 and 2.0, respectively. Highest PO43− removal of 78.8% was obtained at N/P ratio 12.8. However, C/N ratio did not affect the removal efficiency. Maintaining these specified C/N and N/P ratios in the influent greywater would ensure that the treated greywater meets the required standards for various reuse applications, including flushing, groundwater recharge, and surface water discharge. The integration of RSM with AdaBoost and XGBoost provided accurate predictions of removal efficiencies. For all the models, XGBoost had the highest R2, and lowest MAE and MSE values. The cross validation of RSM models with AdaBoost and XGBoost further reinforced the reliability of these models in predicting treatment outcomes.

Harmonizing the cyano-group and Na to enhance selective photocatalytic O2 activation on carbon nitride for refractory pollutant degradation

Manipulating exciton dissociation and charge-carrier transfer processes to selectively generate free radicals of more robust photocatalytic oxidation capacity for mineralizing refractory pollutants remains challenging. Herein, we propose a strategy by simultaneously introducing the cyano-group and Na into graphitic carbon nitride (CN) to obtain CN-Cy-Na, which makes the charge-carrier transfer pathways the dominant process and consequently achieves the selective generation of free radicals. Briefly, the cyano-group intensifies the local charge density of CN, offering a potential well to attract the hole of exciton, which accelerates the exciton dissociation. Meanwhile, the separated electron transfers efficiently under the robust built-in electric field induced by the cyano-group and Na, and eventually accumulates in the heptazine ring of CN for the following O2 reduction due to the reinforced electron sink effect caused by Na. As a result, CN-Cy-Na exhibits 4.42 mmol L-1 h-1 productivity with 97.6% selectivity for free radicals and achieves 82.1% total organic carbon removal efficiency in the tetracycline photodegradation within 6 h. Additionally, CN-Cy-Na also shows outstanding photodegradation efficiency of refractory pollutants, including antibiotics, pesticide plastic additives, and dyes. This work presents an innovative approach to manipulating the exciton effect and enhancing charge-carrier mobility within two-dimensional photocatalysts, opening an avenue for precise control of free radical generation.

Remediation of oil-drilling cuttings by ozonation in a bubble flow reactor

Oil-drilling cuttings (ODCs) are the major wastes generated during oil/gas exploration and extraction. In the present work, a new method based on ozonation is suggested for the remediation of ODCs at ambient conditions, without pre-drying. During the ozonation process, the pressure drop across the gas phase along with the pH, redox potential, and temperature of liquid phase are monitored with the aid of built-in sensors. Occasionally, solid and liquid samples are collected to measure the total organic carbon (TOC) of each phase as a function of time, while the concentration of the total petroleum hydrocarbons (TPH) is measured before and after the completion of treatment. The maximum TOC removal efficiency for the solid phase reached ∼60% and that of TPH ∼ 40% whereas the energy efficiency was ∼ 0.1 kWh/g-TOC. The main mechanisms of ODC remediation are the mass-transfer of organic species from the solid to aqueous phase, and the direct oxidation by dissolved ozone, whereas their synergistic action is reflected in fluctuations of TOC concentration in liquid phase. The TOC removal efficiency of the solid phase increases with the flow rate decreasing, the ozone concentration increasing, and the mass ratio of ODC to seawater (SW) increasing. Ozonation in the liquid phase after its separation from treated ODC proceeds very fast through the direct oxidation by ozone. The process energy efficiency is favoured for low ozone concentration, low gas flow rate, high ODC to SW mass ratio, oxygen as feed gas, and without the addition of sodium dodecyl sulphate (SDS) as surfactant.

Optimization of Vancomycin Antibiotic Removal from Synthetic and Real Wastewater Using UV/Fe3 O4 @Alg-ZnO Nanocomposite Photocatalysis: Response Surface Methodology Based on a Box-Behnken Design

Background: Vancomycin (VCM) is a critical antibiotic due to its high consumption and side effects, including increased bacterial resistance affecting treatment processes. This research investigated the efficiency of VCM antibiotic removal from an aqueous solution using a UV/Fe3 O4 @Alg-ZnO integrated process. Methods: Response surface methodology (RSM) and a Box-Behnken design were applied using Design-Expert software to optimize the number of samples and simultaneously understand the interactive effects between variables. X-ray diffraction (XRD), a vibrating-sample magnetometer (VSM), field effect scanning electron microscopy (FE-SEM), and Fourier transform infrared (FTIR) analyses were used to check the structural characteristics. The effects of initial catalyst concentration (0.1, 0.3, and 0.5 g/L), initial pollutant concentration (10, 30, and 50 mg/L), contact time (10, 30, and 50 minutes), and pH (3, 7, and 11) on VCM decomposition rate were investigated. Spectrophotometry, total organic carbon (TOC), and GC-MS analyses were used to check the efficiency of the process. Results: In this study, VCM and TOC removal efficiency was 92.64% and 85.38%, respectively, under optimal conditions. The reason for the reduction in the efficiency of the combined UV/Fe3 O4 @Alg-ZnO process in real raw sewage, after activated sludge (13%) and after activated sludge and stabilization ponds (24%), is the high COD, which causes the active radicals produced to be spent on other species instead of the VCM antibiotic. Conclusion: The current study showed that the UV/Fe3 O4 @Alg-ZnO process performs well in removing VCM and TOC. In real wastewater, this efficiency was significantly reduced.

Insights into behaviors of functional groups in biomass derived products during aqueous phase reforming over Ni/α-MoO3 catalysts

Aqueous phase reforming (APR) of biomass-derived products has been widely applied for hydrogen generation, chemicals production, and wastewater treatment. Despite its widespread application, the complexity of the raw materials and reaction mechanisms significantly complicates the APR process, impeding its development. This study investigated the APR performance of biomass-derived products using Ni/α-MoO3 catalysts toward hydrogen production and pollutant control, conducted at a temperature of 225 °C and a residence time of 30 min, thus comprehensively understanding the effect of different functional groups. The results showed that the amide (R–HCON) exhibited superior hydrogen production potential during APR. In terms of total organic carbon (TOC) removal, ether showed a 98.10% removal efficiency without a catalyst, whereas the presence of catalyst greatly enhanced the TOC removal efficiency of acetaldehyde (-CHO) from 62.26% to 86.68%. The performed APR of biomass-derived products on Ni/α-MoO3 catalysts primary resulted in the presence of N, N-Dimethylformamide (HCON-(CH3)2), and aminobenzene (Ph-NH2) for Ni leaching with a lower concentration. The carbon deposition on the catalyst primarily resulted from the combined effects of various compounds and the oxygen vacancies within the catalysts. This study aims to provide novel insights into the APR process for both biomass and biomass-derived materials.

Interface engineering in a nitrogen-rich COF/BiOBr S-scheme heterojunction triggering efficient photocatalytic degradation of tetracycline antibiotics

Tetracycline (TC) antibiotics, extensively utilized in livestock farming and aquaculture, pose significant environmental challenges. Photocatalysis, leveraging renewable sunlight and reusable photocatalysts, offers a promising avenue for mitigating TC pollution. However, identifying robust photocatalysts remains a formidable challenge. This study introduces a novel hollow-flower-ball-like nanoheterojunction composed of a nitrogen-rich covalent organic framework (N-COF) coupled with BiOBr (BOB), a semiconductor with a higher Fermi level. The synthesized N-COF/BOB S-scheme nanoheterojunction features an expanded contact interface, strengthened chemical bonding, and unique band topologies. The N-COF/BOB composites showcased exceptional TC degradation performance, achieving an 81.2% removal of 60 mg/L TC within 2 h, markedly surpassing the individual efficiencies of N-COF and BOB by factors of 3.80 and 5.96, respectively. Furthermore, the total organic carbon (TOC) removal efficiency highlights a superior mineralization capacity in the N-COF/BOB composite compared to the individual components, N-COF and BOB. The toxicity assessment revealed that the degradation intermediates possess diminished environmental toxicity. This enhanced performance is ascribed to the robust S-scheme nanoheterojunction structure, which promotes efficient photoinduced electron transfer from BOB to N-COF. This process also augments the separation of photogenerated charge carriers, resulting in an increased yield of superoxide radicals (∙O2−) and hydroxyl radicals (∙OH). These reactive species significantly contribute to the degradation and mineralization of TC. Consequently, this study introduces a sustainable approach for addressing emerging antibiotic contaminants, employing COF-based photocatalysts.

NH2-MIL-101(Fe)-mediated photo-Fenton reaction enhanced simultaneous removal of nitrogen and refractory organics in anammox process through interfacial electron transfer

In this study, H2O2 (0.1 ‰) and NH2-MIL-101(Fe)-driven (150 mg/L) photo-Fenton-coupled anammox were proposed to simultaneously improve the removal efficiency of nitrogen and humic acid. Long-term experiments showed that the total nitrogen removal efficiency was increased by the photo-Fenton reaction to 91.9 ± 1.5 % by altering the bioavailability of refractory organics. Correspondingly, the total organic carbon removal efficiency was significantly increased. Microbial community analyses indicated that Candidatus_Brocadia maintained high activity during photo-Fenton reaction and was the most abundant genus in the reactor. Dissimilatory nitrate reduction to ammonium process and denitrification process were enhanced, resulting in reduced NO3–-N production. The establishment of electron transfer between microorganisms and NH2-MIL-101 (Fe) improved the charge separation efficiency of the quantum dots and increased the intracellular adenosine triphosphate content of anammox bacteria. These results indicated that photo-Fenton-anammox process promoted the removal of nitrogen and refractory organics in one reactor which had good economic value and application prospects.

Degradation of residual dyes in actual textile wastewater using UV/H<sub>2</sub>O<sub>2</sub>: Evaluation of the impact of operating variables through multi-layer perceptron analysis

UV/H<sub>2</sub>O<sub>2</sub> is a commonly used advanced oxidation process for removing non-biodegradable organic compounds. However, additional efforts are needed to understand the relative significance of operational factors during the UV/H<sub>2</sub>O<sub>2</sub>. Here, we investigated the effect and specific contribution of crucial factors such as H<sub>2</sub>O<sub>2</sub> concentration, UV intensity, and reaction time on the color and total organic carbon (TOC) removal efficiency in textile wastewater using the one-factor-at-a-time method and multi-layer perceptron (MLP) analysis. The results showed that color removal was enhanced with high H<sub>2</sub>O<sub>2</sub> concentration, high UV intensity, and long reaction time. Overall, more than 99% removal of color was achieved by the UV/H<sub>2</sub>O<sub>2</sub>, utilizing the following parameters: H<sub>2</sub>O<sub>2</sub> concentration of 5 mM, UV intensity of 26.6 W/m<sup>2</sup>, and reaction time of 180 min. On the other hand, the removal of TOC was increased by high H<sub>2</sub>O<sub>2</sub> concentration and long reaction time, but not by high UV intensity. In the MLP analysis, the H<sub>2</sub>O<sub>2</sub> concentration was identified as the primary factor affecting both color and TOC removal, accounting for 43% and 50% reduction of the color and TOC, respectively. Overall, this study helps to understand the relative importance of the most critical operating factors in treating actual textile wastewater by the UV/H<sub>2</sub>O<sub>2</sub>.

Impact of source water quality on total organic carbon and trihalomethane removal efficiency in a water treatment plant: A case study of Upper Awash, Ethiopia.

This study addresses the limited understanding of factors affecting the efficiency of water treatment plants in reducing trihalomethane (THM) formation through total organic carbon (TOC) removal, highlighting significant challenges in improving treatment effectiveness. The aim of this study was to examine the influence of water quality on the efficiency of water treatment plants to remove TOC and reduce THM formation. Linear regression and correlation analyses were conducted to examine the relationship between water quality parameters and THM concentrations. The results showed that there was a negative relationship between turbidity, metals, and TOC concentration with TOC removal efficiency. Positive correlations were found between parameters and the formation of THMs in water. Of these parameters, water temperature was observed to have relatively less influence on THM formation. It was observed that seasonal variations in water quality affect the efficiency of TOC removal and THM content in treated water. THM levels in chlorinated water were found to be within the permissible range of the World Health Organization's drinking water quality guidelines. However, it is still important to maintain continuous monitoring and take measures to reduce THMs. The model demonstrated a strong correlation (R2 = 0.906) between predicted and measured THM values.

Insights on dielectric barrier discharge plasma treatment of oil drilling cuttings

Oil drilling cuttings produced during oil exploration and extraction contain a high percentage of crude oil, ranging from 5% to 20% weight ratio (w/w) on a dry basis, and must be managed and treated properly before their release to the environment. In this study, non-thermal plasma (NTP) was investigated as an advanced oxidation process for the efficient, sustainable and cost-effective treatment of oil drilling cuttings. To this end, a plane-to-grid dielectric barrier discharge (DBD) reactor operating at atmospheric pressure was tested under different plasma conditions. The effect of treatment time, DBD power and air flow rate on the total organic carbon (TOC) removal efficiency was assessed and the energy efficiency of the process was determined. Within 10 min of plasma treatment, a very high TOC and total petroleum hydrocarbons (TPH) removal (∼90% and ∼99%, respectively) was achieved, while polycyclic aromatic hydrocarbons (PAHs) were degraded by ∼50% within 2 min of treatment. Depending on the experimental conditions, the energy efficiency of the process varied from 5 to 35 mg/kJ. From GC-MS analysis, several byproducts of the oxidation of oil drilling cuttings were identified, while the analysis of exhaust gases revealed that ∼85.1% of the removed organics from oil drilling cuttings was transformed to CO2 and CO. This study provides critical information on the effectiveness of the NTP process for the treatment of heavily contaminated solid wastes and can be considered as the critical step for its application for the treatment of solid wastes from the oil industry.

Design and investigation of photoelectrochemical water treatment using self-standing Fe3O4/NiCo2O4 photoanode: In-situ H2O2 generation and fenton-like activation

Photoelectrocatalytic advanced oxidation processes (PEC AOPs) show great promise for solar-driven water treatment due to their energy efficiency and environmental compatibility. This study focuses on two key aspects: 1) creating an efficient photoanode and 2) utilizing the cathodic process simultaneously to enhance water treatment. Herein, a self-standing photoanode with stemmed nanospikes made from Fe3O4@NiCo2O4 (FNCO) was developed and seamlessly integrated into a PEC system. FNCO photoanode significantly improves PEC cell performance, using half the energy (12 Wh/g-pollutant) and achieving a four-fold higher rate constant (7.9×10−2 s−1) compared to NiCo2O4 (NCO). The in-situ generation of H2O2 and its Fenton-like activation amplifies the generation of reactive oxygen species (ROS), contributing to the PEC degradation activity. Detailed analysis reveals that the presence of surface-Fe3O4 enhances surface hydrophilicity and contributes to the high density of catalytically active sites in FNCO. We conducted a comprehensive investigation into the in-situ formation and activation pathways of H2O2 molecules through a series of experiments. The designed PEC water treatment system achieved almost 60 % total organic carbon (TOC) removal efficiency with consistent performance across a range of real-world water treatment scenarios, underscoring its versatility and robustness.

Bioaugmentation treatment of coal chemical reverse osmosis concentrate in biological contact oxidation system coupled with ozone pretreatment

With the zero discharge requirements of coal chemical industry in China, reverse osmosis technology and fractional crystallization technology have been applied to recover water and valuable salts. Organic matter significantly inhibits salt crystallization, therefore it is urgent to remove organic matter from coal chemical reverse osmosis concentrate (CCROC) efficiently and economically. Common biological systems have the bottlenecks of long start-up period and poor pollutants removal efficiency due to the inhibition of toxic compounds and high salinity to the microorganisms. In this work, a self-prepared halotolerant bacteria preparation (HBP, mixture of screened Bacillus, Pseudomonas, and Halomonas with strong degrading capacity of CCROC) was inoculated into different biochemical systems (activated sludge and biological contact oxidation in sequencing batch reactor) to try to enhance the pollutants removal of extremely refractory CCROC (BOD5/COD of 0.05). The results showed that HBP increased the total organic carbon (TOC) removal efficiency from 8% to 15% in activated sludge system. In addition, biological contact oxidation reactor (BCOR) could better retain the HBP, leading to a higher TOC removal efficiency (20%). Typically, the inoculation of HBP without activated sludge in BCOR contributed to the highest TOC removal (28%). The class Bacilli (genus Bacillus) was dominant during the start-up and stable period of this bioaugmented treatment process. To further increase the pollutants removal, ozone oxidation pretreatment was conducted prior to biological treatment to break the ring structures. The total TOC removal increased to 42% under the combined treatment, while the dominant classes in biofilms shifted to Actinobacteria, Gammaproteobacteria, Alphaproteobacteria, and Bacteroidia. This study provided an effective approach for CCROC treatment with industrial application potentials.

High-efficient degradation of ibuprofen as typical PPCP through a novel electrochemical approach of traditional peroxone method

An electrogenerated peroxone process was innovatively structured to effectively degrade the antiphlogistic ibuprofen (IBU) representing typical refractory pharmaceutical. The process involved electrogenerated O3 from H2O oxidation using a Ti mesh/SnO2-F anode in membrane electrode assembly (MEA) and electrogenerated H2O2 from O2 reduction using a carbon-polytetrafluoroethylene (C/PTFE) cathode. The synergetic system of H2O2 and O3 formed in situ could generate hydroxyl radical (OH) to achieve IBU degradation and total organic carbon (TOC) removal. The effects of current density, aqueous initial pH, and coexisting anions on IBU removal efficiencies were investigated and then optimized as 30 mA/cm2 and neutral condition. As a result, IBU decomposition and TOC mineralization could be finished after 10 min and 120 min electrolysis, respectively. The stability of the synergetic system combining MEA with C/PTFE-O2 was also evaluated and confirmed through multiple cycles of electrogenerated peroxone based on TOC removal efficiency. In addition, IBU degradation pathways were proposed according to the identification of intermediates (e.g. hydroxylated IBU, phenolics, and carboxylic acids) by HPLC-MS/MS. These results manifested that this synergetic system is a promising technology to remove aqueous recalcitrant pharmaceuticals.

Waste coconut shell-derived carbon monolith as an efficient binder-free cathode for electrochemical advanced oxidation treatment of endocrine-disrupting compounds

Discharge of endocrine-disrupting compounds such as methylparaben (MePa) into natural water bodies deteriorates the aquatic ecosystem. In this regard, electrochemical oxidation (EO) and electro-Fenton (EF) processes are acknowledged as effective methods to eliminate biorecalcitrant compounds from different wastewater matrices. In these systems, the H2O2-producing ability of carbon-based cathodes is put to advantage for producing homogenous hydroxyl radicals by simulating Fenton's reaction, which dramatically augments the contaminant removal efficiency. However, commercial carbon based cathodes are not economically affordable, especially for voluminous treatment. Hence in the present work, waste-derived carbonised coconut shell (CCS) monolith was employed as a cathode in EO and EF treatment of MePa. Almost the entire MePa with initial concentration of 10 mg/L was removed in 60 min by EO and 45 min by EF process at neutral pH, applied current density of 7.5 mA/cm2, NaCl concentration of 1.0 g/L and 10 mg/L of Fe2O3 dosing. The MePa removal efficiency of the CCS cathode-fitted system after 60 min was better than the commercial graphite plate and Ti-based mixed metal oxide employing system due to higher H2O2 electrosynthesis (H2O2 = 9.0 ± 0.6 mg/L after 60 min). Moreover, the same setup was used for treating 10 mg/L of MePa-spiked real sewage and demonstrated MePa and total organic carbon removal efficiency of 80.16 ± 2.31% and 37.42 ± 3.50%, respectively, in 45 min. Further, the CCS-mediated EF treatment achieved >90% removal of MePa for eight continuous batch cycles and recorded a current density drop of just 0.23% per cycle. The degradation pathway and toxicity assessment of the intermediates using the Ecological Structure Activity Relationships (ECOSAR) tool supported the eco-friendliness of the current treatment scheme.

Performances and mechanisms of the peroxymonosulfate/ferrate(VI) oxidation process in real shale gas flowback water treatment

Shale gas flowback water (SGFW), which is an inevitable waste product generated after hydraulic fracturing during development, poses a severe threat to the environment and human health. Managing high-salinity wastewater with complex physicochemical compositions is critical for ensuring environmental sustainability of shale gas development. Desalination processes have been recommended to treat SGFW to adhere to the discharge limits. However, organic fouling has become a significant concern in the steady operation of desalination processes, and the effective removal of organic compounds is challenging. This study aimed to develop an effective oxidation method to mitigate membrane fouling in real SGFW treatment process. It adopted the peroxymonosulfate (PMS)/ferrate (Fe(VI)) process, involving both free and non-free radical pathways that can alleviate the negative effects of high-salinity environments on oxidation. The operating parameters were optimized and removal effects were examined, while the synergistic oxidation mechanism and organic conversion of the PMS/Fe(VI) process were also analyzed. The results showed that the PMS/Fe(VI) process exhibited a synergistic effect compared with the PMS and Fe(VI) processes alone, with a total organic carbon (TOC) removal efficiency of 46.8% under optimal reaction conditions in real SGFW. In the Fe(VI)/PMS process, active species such as Fe(V)/Fe(IV), ·OH, and SO4−· were jointly involved in the oxidation of organic matter. Additionally, 99.5% of the total suspended solids and 95.2% of Ba2+ in the SGFW were removed owing to the formation of a coagulant (Fe3+) and SO42− during the reaction. Finally, an ultrafiltration membrane fouling experiment proved that oxidation processes can increase the membrane-specific flux and alleviate fouling resistance. This study can serve as a reference for the design of real SGFW treatment processes and is significant for the environmental management of shale gas development.