Total Organic Carbon Removal Rate Research Articles

Enhanced photocatalytic activity of porous TiO2 containing C/P/K derived from grapefruit peel.

Grapefruit peel possesses a porous structure and a significant specific surface area. In this study, we introduce an innovative and eco-friendly approach for synthesizing porous TiO2. This was accomplished by employing grapefruit peel as a bio-template and tetrabutyl titanate as the precursor, utilizing a two-step rotary impregnation-calcination process. The TiO2 faithfully reproduced the structural characteristics of the grapefruit peel across different scales, simultaneously incorporating C, P, K elements from the original grapefruit peel into the final samples. The fabricated samples were analyzed using XRD, XPS, SEM, TEM, BET, and UV-vis DRS. The results showed that the TiO2 displays an anatase phase, and possesses a high specific surface area. The investigation of photocatalytic performance demonstrated that the CPK-TiO2-10 sample exhibited outstanding photocatalytic activity against Rhodamine B (RhB) solution, achieving complete degradation within 60 minutes. Additionally, the total organic carbon (TOC) removal rate reached 91.34% after 60 minutes of irradiation. The sample maintained a high degradation efficiency, even after five recycling cycles. This exceptional performance can be attributed to its porous structure, enriched with pores and a larger surface area, as well as the beneficial effects of doping with C, P, K elements in TiO2.

Activating the lattice oxygen of low-cost Ni/WO2 nanoparticles on carbon paper for electrocatalytic oxidation of 2, 4-dichlorophenoxyacetic acid

Electrocatalysis is a promising method for removing harmful substances because it does not involve toxic agents and has low energy consumption. Herein, we have developed a low-cost nickel-tungsten dioxide (Ni/WO2) grown on carbon paper for the first time. Ni/WO2/CP demonstrates remarkable catalytic efficiency for the electrocatalytic oxidation of 2,4-dichlorophenoxyacetic acid (2,4-D), achieving a conversion rate of 100 % within 3 h and a total organic carbon (TOC) removal rate of 57 %. After four reaction cycles, the electrode can still achieve a conversion rate of 90.49 %. The exceptional activity of Ni/WO2 could be attributed to the activation of lattice oxygen in WO2 by coupled Ni, leading to the generation of a significant amount of superoxide free radicals (O2−) and creating numerous oxygen vacancies that serve as the active sites for subsequent 2,4-D oxidation. This work highlights the impact of lattice oxygen on electrocatalytic oxidation and material modification, offering a noble metal-free catalyst for converting harmful substances.

Enhancing degradation of sulfapyridine by magnetic Fe2O3-CoFe2O4@NC prepared through a facile solid phase coordination-calcination method for peroxymonosulfate activation

In this study, a facile and environmentally friendly solid phase coordination combined with calcination method was designed and ultra-efficient nitrogen carbon coated bimetallic composites (Fe2O3-CoFe2O4@NC) was fabricated to activate PMS for sulfapyridine (SPY) antibiotic elimination. A series of materials after calcined under different temperature and with different metal ratios were synthesized and Co/Fe carbon-based material calcined under 500 °C with 2:1 Co/Fe molar ratios (Fe2O3-CoFe2O4@NC) was demonstrated to be superior to rapidly remove 10 mg L−1 SPY within 10 min by activating 0.6 mM PMS. Meanwhile, the main reasons why different catalysts possessed different degradation efficiency were explored. The magnetic Fe2O3-CoFe2O4@NC showed a superior catalytic activity with kobs of 0.5314 min−1, which was 13.5-, 18.5- and 12.6 times than that of Co3O4@NC/PMS, Fe2O3@NC/PMS and CoFe/PMS systems, respectively. This was attributed to the synergistic effect of Co and Fe and accelerated electron transfer, which resulted in the generation of SO4−, 1O2, O2− and OH. The Fe2O3-CoFe2O4@NC/PMS system exhibited strong environment tolerance to most anions and humic acid, as well as high stability and recyclability. In detail, Cl−, NO3−, H2PO4− and humic acid (HA) showed promoting effect on SPY degradation, and the excellent removal efficiency maintained in actual water matrix. Moreover, the SPY degradation rate could reach 90 % after the fifth cycle and the mineralization rate was preferable, with 56.4 % of total organic carbon (TOC) removal rate. Generally, the degradation of SPY mainly involved bonds cleavage and hydroxyl addition, and five possible degradation pathways were proposed. This work provided an environmentally friendly, facile and promising route to synthesize nitrogen carbon coated bimetallic catalysts with sufficient properties for pollutant removal.

Mechanism and application of enhanced degradation of phenol through peroxymonosulfate activation by sulfur-doped biochar prepared with sodium thiosulfate as activator and sulfur dopant

Na2S2O3 was used as activator and sulfur dopant for preparation of sulfur-doped biochar (SBC) with high specific surface area and sulfur content, and its performance to activate peroxymonosulfate (PMS) for phenol degradation was studied. In the presence of 0.3 g/L S4BC-800 and 1 g/L PMS, 20 mg/L phenol could be removed completely in 30 min. S doping improved the electron transfer performance of the composite and enhanced the activation property of PMS for phenol degradation. Free radical quenching experiment and electron paramagnetic resonance analysis indicated that SO4•−, •OH, and 1O2 were involved in phenol degradation. In addition, the current oxidation process confirmed that there was also direct oxidation based on electron transfer between PMS and phenol with S4BC-800 as mediator. The S4BC-800/PMS system could effectively decompose the recalcitrant organic pollutants in the effluent of sewage treatment plant, achieving the total organic carbon removal rate of 83.26 %.

Enhanced treatment of p-nitrophenol and coking wastewater through electrochemical and electrochemical-ozonation coupling process utilizing a novel Ti4O7 reactive electrochemical membrane anode

Organic pollutants in water could be removed by electrochemical treatment using a reactive electrochemical membrane (REM) with Magnéli phase Ti4O7, yet it is challenging to design suitable porosity to realize effective mass transfer and enhance the reactivity. Here, a novel Ti4O7 REM was prepared by a spark plasma sintering (SPS) method, which showed excellent electrochemical reactivity and mass transfer rate for organic pollutants in water. Compared to other Ti4O7 REMs, the novel Ti4O7 REM achieved a 140–9000-fold decrease in charge transfer resistance and a 5–110-fold increase in mass transfer rate. The p-nitrophenol in water can be completely removed in the REM system, with a maximum total organic carbon (TOC) removal rate of 85%. Then the REM system obtained an amazing removal rate of TOC (50.1%) and UV254 (89.6%) in the electrochemical treatment of real coking wastewater. In addition, to further enhance the removal efficiency, a coupled oxidation process with the novel Ti4O7 REM and O3 aeration was investigated. The TOC removal rate and energy consumption were 57.1% and 165.2 kWh (kg TOC)−1 at the optimal conditions within a short treating time. Our findings highlighted an innovative REM for a broad range of potential environmental applications.

Assembling an S-type heterojunction comprising vacancy-rich CeO2-x and CuBi2O4 for improved photocatalytic oxidation of gaseous toluene

The exploration of highly efficient methods for degrading VOCs, with concurrent low energy consumption and lasting reusability, holds significant appeal. In this regard, an S-type CuBi2O4/CeO2-x heterojunction with the robust interfacial interactions is presented as an active photocatalyst for the efficient decomposition of gaseous toluene under full-spectrum irradiation. The optimal sample CC15 effectively degrades gaseous toluene at a high concentration of 1800 ppm within 2 h, achieving a notable CO2 yield of 87.05 %, and a TOC (total organic carbon) removal rate of 89.33 %. Furthermore, CuBi2O4/CeO2-x exhibits exceptional stability, maintaining its 100 % degradation capability over 32 cycles for nearly 64 h. Comparative characterization reveals that the superior performance derives from an abundance of oxygen vacancies and effective pre-adsorption capabilities, which facilitate rapid adsorption of VOCs on the catalyst surface, thereby increasing the likelihood of degradation reactions. Additionally, the formation of an S-type heterojunction, valence pairing between Bi3+ and Ce3+/4+ ions, and strong interfacial interactions serve as the primary pathways for the efficient separation of photogenerated carriers, contributing to the high CO2 production rate and prolonged cycle stability. The present investigation underscores the significant potential of vacancy-rich S-type heterojunctions and interfacial interactions between composite components, offering excellent activity and long-term availability for VOCs removal.

Cobalt-doped iron-based metal–organic gels as efficient visible-light-driven peroxymonosulfate activators for the efficient degradation of norfloxacin with simultaneous antibacterial activity

A strategically fabricated cobalt-doped iron-based metal–organic gel (CFM) synergistically promotes peroxymonosulfate (PMS) activation and visible light-induced photocatalysis to remove norfloxacin (NOR). Cobalt incorporation into the metal–organic gel significantly optimizes its electronic structure, leading to the exceptional performance of CFM in synergistically activating PMS, amplifying visible light absorption, and enhancing photoinduced charge separation efficiency. The Vis/50 %-CFM/PMS system enables a NOR removal rate of up to 96.8 % within 60 min and a total organic carbon (TOC) removal rate of 78.3 %, signifying excellent decontamination performance. Exhibiting robust mineralization potential, the Vis/CFM/PMS system has undergone comprehensive analysis of the intermediary degradation process using Density Functional Theory (DFT) calculations. The toxicity of degradation intermediates was assessed employing the quantitative structure–activity relationship (QSAR) model. In addition, the Vis/CFM/PMS system showed antibacterial effects against E. coli and S. aureus. This investigation furnishes a novel perspective toward developing innovative PMS activation photocatalyst coupling systems for environmental remediation.

Preparation of catalyst of cobalt‐ and/or iron‐doped strontium zirconate and its performance in removal of m‐cresol using ozone as oxidant

AbstractBACKGROUNDWastewater containing m‐cresol has become a global water environmental problem because its degradation is difficult, and it is highly toxic to plants, animals, and humans. The heterogeneous catalytic ozonation process has been widely used in the treatment of environmental pollution, so it is very important to study efficient catalysts. Perovskite catalysts have been widely investigated and applied in catalytic ozonation processes. Among them, strontium zirconate is a promising perovskite catalyst owing to its high oxidation efficiency and environmental friendliness.RESULTSStrontium zirconate was successfully synthesized via the co‐precipitation method. To improve strontium zirconate catalytic performance, some methods such as changing the doping ratio of cobalt and iron, changing the amount of polyethylene glycol added, changing the calcination temperature, and changing the aging time were carried out during the synthesis process. Finally, the optimal conditions were determined. 0.4 g L−1 Sr2Co0.4Fe0.6ZrO6 prepared under the optimal conditions was used for catalytic ozonation of 100 ppm m‐cresol, which achieved the optimum degradation (0.136 min−1), m‐cresol conversion rate (92.2%) and total organic carbon removal rate (12.1%) within 20 min.CONCLUSIONThis work provides the best preparation conditions. The Sr2Co0.4Fe0.6ZrO6 catalyst, as prepared, is the optimal catalyst for catalytic ozonation of m‐cresol among the investigated Sr2CoxFe1−xZrO6 catalysts. © 2024 Society of Chemical Industry (SCI).

Degradation of tannic acid using monopersulfate activated CuO particles

A Copper(II) oxide material was synthesized and its efficiency in degrading Tannic acid (TA) was investigated using ultraviolet (UV) irradiation and CuO activated peroxymonosulfate (PMS). The CuO particle catalyst exhibited exceptional activity and was characterized using XRD, SEM, Raman spectroscopy, and laser diffraction particle size analysis (LDPS). The influence of calcination temperature, UV power, PMS dosage, CuO dosage, and coexisting anions on the degradation rate of TA was examined. The research results demonstrate that the addition of a structural guide enhances the catalytic performance of CuO. Among the different calcination temperatures investigated, CuO calcined at 500 °C demonstrates the best catalytic performance and achieves the highest degradation efficiency under neutral conditions. Under the optimal conditions of 0.1 g/L CuO and 1.2 mmol/L PMS, the TA degradation rate of 15 mg/L within 40 min was 97.69%, and the total organic carbon removal rate was 69.85%. Quenching experiments confirmed the participation of multiple active species in the decomposition process. After five experimental cycles, the CuO material maintained a TA removal rate above 92%. Furthermore, HPLC-MS analysis was employed to identify potential intermediates in the degradation of TA.

Degradation of tannic acid in heterogeneous Fenton system and persulfate system using iron(III) modified attapulgite: Influencing factors and degradation mechanism analysis

The redox cycle of iron is a well-known rate-determining step for radical generation in advanced oxidation system. In this study, iron(III) modified attapulgite (Fe-ATP) was employed as a regulator to enhance the degradation of tannic acid (TA) in heterogeneous Fenton and persulfate (PS) systems. Results showed that under the conditions of pH 3 and 0.5 g·L−1 of Fe-ATP, the maximum removal rate of TA was 82.2% and the removal rate of total organic carbon (TOC) was 31.7% in heterogeneous Fenton system with 5 mM H2O2 and 90 min reaction, and the maximum removal rate of TA was 78.5% and removal rate of TOC was 28.9% in PS system with 1 g·L−1 Na2S2O8 and 60 min reaction. Among commonly inorganic anions (Cl-, NO3-, HCO3-, CO32-, SO42-, HPO42- and H2PO4-), only HPO42- and H2PO4- significantly inhibited the TA removal by Fe-ATP. Radical quenching tests indicated that hydroxyl radical (∙OH) and sulfate radical (SO4∙-) were the main active species in the heterogeneous Fenton system and PS system, respectively. Moreover, the TA removal rate could still reach 40% after four times of recycling. Hence, the Fe-ATP could be a good catalyzer for treating tannic acid contaminated waters in heterogeneous Fenton system and persulfate system.

Labile oxygen-driven catalytic ozonation via surface peroxide pathway for efficient wastewater treatment

The aluminosilicate-based heterogeneous catalysts hold great promise for industrial catalytic ozonation; however, the lack of exploration into novel active sites and mechanism studies has impeded their development. In this work, we demonstrate that labile oxygen (Olab) can be generated in mullite (mullite-Olab) by the introduction of extra Al-O4 tetrahedral units. In our experiments, mullite-Olab exhibits excellent performance in terms of catalytic ozone activation, with a degradation rate of 87.4 % within 15 min for nonbiodegradable atrazine, corresponding to a high quasi-first-order rate constant (k, 0.112 min−1), while the degradation constant is close to 0 for mullite without Olab. Operando Raman and density functional theory (DFT) simulations further reveal that Olab activates ozone via a novel surface peroxide pathway to generate surface Olab-O* species with a high oxidizing ability. The mullite-Olab is stable with an average Al3+ leaching of 0.339 ppm during cycling, meeting the effluent discharge standard of the total Al. Moreover, we achieve the kilogram synthesis of mullite-Olab, which shows promising activity in the catalytic ozonation of acrylic fiber wastewater, with the chemical oxygen demand (COD) and total organic carbon (TOC) removal rates of 46.0 %±4.8 % and 24.9 %±2.8 % for 5 cycles. This work is the first to demonstrate the role of Olab in ozone activation and provides an advanced mullite-Olab catalyst for future nonbiodegradable wastewater treatment.

Reduced electron/hole recombination in Z-scheme nanostructure of zeolitic imidazolate framework-11/graphitic carbon nitride as photocatalyst under visible light

In this research, for the first time, the synthesis of nanostructure of zeolitic imidazolate framework-11/graphitic carbon nitride (ZIF-11/g-C3N4 X) with different weight of g-C3N4 (X: 0.01, 0.1, 0.3 g) is reported. Their performance was compared in photocatalytic degradation of MB under visible light. Synthetic samples were characterized by X-Ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectrometer (XPS), diffused reflectance spectroscopy (DRS), Field emission scanning electron microscopy (FE-SEM), Transmission electron microscope (TEM), Brunauer–Emmett–Teller (BET), Electrochemical Impedance Spectroscopy (EIS) and Photoluminescence (PL) analysis. Based on the results, Z-scheme ZIF-11/g-C3N4 0.3 was selected as the best sample. FESEM and TEM images indicated that g-C3N4 sheets were complicated on the surface of ZIF-11 with rhombic dodecahedron (RHO) morphology. The surface area and band gap of ZIF-11/g-C3N4 0.3 was determined as 174.5 m2/g and 2.58 eV, respectively. The recombination of charge carriers in the ZIF-11/g-C3N4 0.3 nanostructure was reduced. Photocatalytic degradation efficiency of MB (5 ppm), pH = 7, visible irradiation (120 W-60 min) using 0.1 g of ZIF-11/g-C3N4 0.3 was achieved 72.7% with first-order kinetic model and acceptable stability in three consecutive cycles. Further, the total organic carbon (TOC) removal rate by ZIF-11/g-C3N4 0.3 after 5 h were 66.5%.

An efficient, recyclable and stable immobilized enzyme cascade catalytic system with visible-light driven for the removal of organic matter in water

A novel photo-enzyme composite catalyst based on modified carbon nitride was constructed and applied in the removal of antibiotics and phenolic pollutants in water. This composite catalyst (Cyt c/C/CN) has high catalytic activity and stability under acidic or alkaline conditions, which broadens the application range of cytochrome c (Cyt c). In addition, it has A high degradation rate and mineralized rate for sulfadiazine (SDZ) and bisphenol A (BPA). Among them, the degradation and total organic carbon (TOC) removal rate of SDZ were 65.53% and 40.44% respectively, which were much higher than that of pure CN (50.83% and 9.76%). Moreover, the degradation and TOC removal rate of BPA were 72.53% and 44.66%, which were 1.3 times and 2.5 times that of pure CN, respectively. The findings provide insights for designing photo-enzyme coupling systems to efficiently and at a high level remove sulfonamides antibiotics and phenolic agricultural organic pollutants in a simple step.

Metagenomic Insight Reveals the Microbial Structure and Function of the Full-scale Coking Wastewater Treatment System: Gene-based Nitrogen Removal

Microbial communities play crucial roles in pollutant removal and system stability in biological systems for coking wastewater (CWW) treatment, but a comprehensive understanding of their structure and functions is still lacking. A five-month survey of four sequential bioreactors, anoxic 1/oxic 1/anoxic 2/oxic 2 (A1/O1/A2/O2), was carried out in a full-scale CWW treatment system in China to elucidate operational performance and microbial ecology. The results showed that A1/O1/A2/O2 had excellent and stable performance for nitrogen removal. Both total nitrogen (TN; (17.38 ± 6.89) mg·L−1) and ammonium–nitrogen (NH4+-N; (2.10 ± 1.34) mg·L−1) in the final biological effluent satisfied the Chinese national standards for CWW. Integrated analysis of 16S ribosome RNA (rRNA) sequencing and metagenomic sequencing showed that the bacterial communities and metagenomic function profiles of A1 and O1 shared similar functional structures, while those of A2 significantly varied from those of other bioreactors (p < 0.05). The results indicated that microbial activity was strongly connected with activated sludge function. Nitrosospira, Nitrosomonas, and SM1A02 were responsible for nitrification during the primary anoxic–oxic (AO) stage and Azoarcus and Thauera acted as important denitrifiers in A2. Nitrogen cycling-related enzymes and genes work in the A1/O1/A2/O2 system. Moreover, the hao genes catalyzing hydroxylamine dehydrogenase (EC 1.7.2.6) and the napA and napB genes catalyzing nitrate reductase (EC 1.9.6.1) played important roles in the nitrification and denitrification processes in the primary and secondary AO stages, respectively. The mixed liquor suspended solids (MLSS)/total solids (TS), TN removal rate, total organic carbon (TOC) removal rate, and NH4+-N removal rate were the most important environmental factors for regulating the structure of core bacterial genera and nitrogen-cycling genes. Proteobacteria were the potential main participants in nitrogen metabolism in the A1/O1/A2/O2 system for CWW treatment. This study provides an original and comprehensive understanding of the microbial community and functions at the gene level, which is crucial for the efficient and stable operation of the full-scale biological process for CWW treatment.

Intrinsic Polarized Electric Field Induces a Storing Mechanism to Achieve Energy Storing Catalysis in V2 C MXene.

Efficient storage and separation of holes and electrons pose significant challenges for catalytic reactions, particularly in the context of single-phase catalysis. Herein, V2 C MXene, with its intrinsic polarized electric field, successfully overcomes this obstacle. To enhance hole storage, a multistep etching process is employed under reducing conditions to control the content of surface termination groups, thus exposing more defective active sites. The intrinsically polarized electric field confines holes to the surface of the layer and free electrons within the layer, leading to a lag in e- release compared to h+ . The quantities of stored holes and electrons are measured to be 18.13µmolg-1 and 106.37 µmol g-1 , respectively. Under dark, V2 C demonstrates excellent and stable dark-catalytic performance, degrading 57.91% of tetracycline (TC 40mg L-1 ) and removing 23% of total organic carbon (TOC) after 140 min. In simulated sunlight and near-infrared light, the corresponding degradation rates reach 72.24% and 79.54%, with corresponding TOC removal rates of 49% and 48%, respectively. The hole and electron induced localized surface plasmon resonance (LSPR) effects contribute to a long-lasting and enhanced broad-spectrum mineralization of V2 C MXene. This study provides valuable insights into the research and application of all-weather MXene energy storage catalytic materials.

Synthesis of Bi4O5I2 coupled with Sb2WO6 boosts the photocatalytic degradation of tetracyclines under simulated sunlight

For this study, a Sb2WO6/Bi4O5I2 composite material was successfully prepared via a precipitation-calcination method. The Sb2WO6/Bi4O5I2 heterostructure enhanced the light absorption and facilitated the separation of charge carriers. Under simulated sunlight exposure, the removal rates of tetracycline (TC) and doxycycline hyclate (DOX·HCl) reached 88.2% and 83.9%, respectively, over an optimized SWB2 composite (theoretical mole ratio of Sb2WO6: BiOI was 1.5:10). Further, the total organic carbon (TOC) removal rates were 37.6% and 33.7%, respectively. The experiments explored various parameters including catalyst dosage, initial concentrations of TC and DOX·HCl, solution pH, and common inorganic ions. The TC and DOX·HCl degradation pathways were speculated. Furthermore, SWB2 demonstrated remarkable stability and cyclability under simulated sunlight. Trapping experiments and electron paramagnetic resonance (EPR) tests revealed that •O2- played a major role as a free radical in the photocatalytic process, while h+ and •OH also had significant contributions. Based on in-situ XPS, trapping experiments, EPR test, band bending analysis, and SPV tests, the formation of S-scheme heterojunction between Sb2WO6 and Bi4O5I2 was inferred. This study provides insights into the design strategy of S-scheme heterojunctions between Aurivillius-type compounds and bismuth-rich halide bismuth oxide, which is informative for the development of advanced environmental remediation concepts.

Porous pie-like nitrogen-doped biochar as a metal-free peroxymonosulfate activator for sulfamethoxazole degradation: Performance, DFT calculation and mechanism

Design and development of low-cost, high-efficient, metal-free persulfate heterogeneous catalysts was a hot research topic. Herein, porous pie-like nitrogen-doped biochar (NBC) was prepared by one step high temperature pyrolysis of rape straw, urea and ZnCl2 mixture, and applied for peroxymonosulfate (PMS) activation toward sulfamethoxazole (SMX) degradation. Among these as-prepared catalysts, the NBC2.0 sample presented the best catalytic activity, with the 99.8 % SMX degradation efficiency in 5 mins and the 81.7 % total organic carbon (TOC) removal rate in 30 mins. Additionally, it could realize an excellent SMX degradation in the wide pH range of 3.0 to 9.0, and possessed the high degradation efficiency in presence of various organic pollutants or in real water environments, indicating its good pH adaptability, universality and practicality. Mechanistic investigations disclosed that the NBC2.0/PMS/SMX system involved both radical and non-radical degradation pathways, with singlet oxygen (1O2) and the direct electron transfer mechanism being the main contributors. The main active reaction sites of NBC were graphitic N, pyridinic N and C = O group, as corroborated by density functional theory (DFT) calculation and X-ray photoelectron spectroscopy (XPS) measurement. The possible SMX breakdown routes were determined by intermediate identification. This work provides a promising metal-free persulfate catalyst for environment remediation.

Efficient visible-light photocatalysis of chloramphenicol using novel engineered biochar-based Ti-doped Bi2WO6 composite: Mechanisms, degradation pathways, and applications

A novel engineered biochar (ACB)-based Ti-doped Bi2WO6 composite (Ti-Bi2WO6@ACB) was synthesized via a one-step hydrothermal reaction for the efficient degradation of chloramphenicol (CAP) and extensive environmental applications. Multiple characterization techniques, CAP degradation effects, total organic carbon (TOC) removal, effects of environmental factors, recycling tests, actual wastewater treatment, enhancement strategies, and disinfection effects were systematically evaluated. It was found that Ti-Bi2WO6@ACB is a Ti3+ self-doped TiO2/Bi2WO6/ACB ternary heterogeneous photocatalyst. The introduction of ACB and Ti doping enhanced the elemental composition, oxygen-containing functional groups, defect structure (oxygen vacancies), visible-light absorption, and active sites. Moreover, Ti-Bi2WO6@ACB effectively inhibited the recombination of photogenerated carriers. The removal efficiency of Ti-Bi2WO6@ACB for 50 mg⋅L−1 CAP was 92.44 % at 120 min of irradiation, and the TOC removal rate was 67.72 %, which was significantly higher than that of the control treatment. Ti-Bi2WO6@ACB is reusable and photostable, with approximately 99 % sterilization of Staphylococcus aureus and Escherichia coli within 10 min of light irradiation and 48 h of cultivation. The addition of H2O2, ultrasonication, heating, and blowing air in the system improved the photocatalytic efficiency. The ultrasound enhancement mechanisms are related to the effects of cavitation, microjets, and photocatalysis coupled with sonocatalysis. CAP degradation was dominated by OH, O2−, and h+. The doping of Ti3+/TiO2 generated more defects and O2−, and the ACB acted as a carrier to prevent the agglomeration of TiO2 and Bi2WO6. Further, the degradation process of CAP was documented and the degradation pathways may include hydroxylation addition, methanol denaturation, substitution, C–N bond breaking, oxidation, hydrolysis, and decarboxylation reactions. The research presents fresh insights into the development of high-performance engineered biochar-based composite for environmental detoxification.

UV/persulfate processes for the removal of total organic carbon from coagulation-treated industrial wastewaters

Sulfate radical-based oxidation processes were investigated to understand the relationship between persulfate (PS) consumption and total organic carbon (TOC) removal from industrial wastewater under various PS concentrations. First, the degradation and mineralization of Bisphenol A (BPA) (initial concentration: 11 mg/L) were investigated in ultraviolet (UV)/PS systems. Complete degradation was achieved within 30 min of UV irradiation, and 41%–72% TOC removal was achieved at PS concentrations of 200 and 400 mg/L. The consumed concentration of S2O82− and generated concentration of SO42− increased gradually to similar levels. The ratio of the PS consumption to TOC removal based on the mass concentration (mg/L) was 14.5 and 23.2 at 180 min for 200 and 400 mg/L of S2O82−, respectively. Three types of coagulation-treated industrial wastewater from metal-processing, food-processing, and adhesive-producing plants were obtained, and TOC removal was analyzed using the same UV/PS systems (initial TOC concentration: 100 mg/L). The TOC removal rates ranged from 16.9% to 94.4% after 180 min of UV irradiation at PS concentrations of 1,000, 2,000, 4,000, and 8,000 mg S2O82−/L. Despite the higher TOC removal at higher PS concentrations, the PS activation efficiency decreased significantly as the PS concentration increased. Only approximately 30%–40% activation efficiency was achieved at a PS concentration of 8,000 mg/L. In this study, the ratio of PS consumption to TOC removal ranged from 20.6 to 43.9.

Evaluation of nitrous oxide emission during ammonia retention from simulated industrial wastewater by microaerobic activated sludge process

Considering the reciprocating processes of nitrogen gas (N2) fixation to ammonia (NH4-N) and NH4-N removal to N2 through nitrification and denitrification during wastewater treatment, a microaerobic activated sludge process (MAS) is proposed in this study as a pretreatment to retain NH4-N from high-strength nitrogenous wastewater for further NH4-N recovery through membrane technology, that is, inhibit nitrification, with sufficient removal of total organic carbon (TOC). With DO and pH control, the 3-reactor bench-scale MAS systems successfully realized an NH4-N retention rate of over 80 %, with TOC removal rates of over 90 %. In addition, the emissions of carbon dioxide (CO2) and nitrous oxide (N2O) during MAS were evaluated. The total N2O emissions were 407 and 475 mg-N/day when pH was controlled at 6.2 (S1) and 6.8 (S2), respectively, with average emission factors to total nitrogen load over 2 % in both systems. Also, the global warming potential of N2O is one order of magnitude larger than that of CO2, indicating the significance of N2O in the MAS process. Therefore, the mechanisms of N2O emission from each reactor were investigated. The first reactor, where most of the TOC was adsorbed, emitted only 1.98 % (S1) and 2.43 % (S2) of the total N2O emissions through the denitrification of nitrite and nitrate (NOx) from the return sludge. The second reactor emitted 79.9 % (S1) and 69.0 % (S2) of the total N2O with the emission rates the same order of magnitude as the NOx production rates. Multiple pathways were considered to contribute to the high N2O emissions, and biotic NH2OH oxidation was one potential pathway at pH 6.2. Finally, the third reactor emitted 9.98 % (S1) and 16.8 % (S2) of the total N2O by nitrifier denitrification. Overall, this study showed that the large N2O emissions under nitrification-inhibiting conditions of the MAS process owed to the incomplete nitrification under acidic conditions and large abundances of denitrifiers. On the other hand, the lower N2O emissions at pH 6.2 evidenced the potential N2O mitigation under slightly more acidic conditions, underlining the necessity of further study on N2O mitigation when adapting to the trend of NH4-N recovery.