Persulfate Research Articles

Modi-Red Mud Loaded CoCatalyst Activated Persulfate Degradation of Ofloxacin

As an abundant potentially dangerous waste, red mud (RM) requires a straightforward method of resource management. In this paper, an RM catalyst loaded with cobalt (Co-RM) was prepared by the coprecipitation method for the efficient activation of persulfate (PS). Its degradation performance and mechanism of ofloxacin (OFL) were investigated. The characterization results of scanning electron microscopy, X-ray diffractometer, and energy dispersive spectrometer showed cobalt was successfully loaded onto the surface of RM, and the catalyst produced could effectively activate PS. Under the conditions of 15 mg/L OFL, 0.4 g/L Co-RM, 4 g/L PDS, 3.0 pH, and 40 °C temperature, the maximum removal rate of OFL by the Co-RM/PDS system was 80.06%. Free radical scavenging experiments confirmed sulfate radicals were the main active substances in the reaction system. The intermediates in OFL degradation were further identified by gas chromatography-mass spectrometry, and a possible degradation pathway was proposed. Finally, the relationship between defluorination rate and time in the Co-RM/PDS degradation OFL system was described by the first-order kinetic equation. This work reports an economical, environmental solution to the use of waste RM and provides a research basis for the further exploration of RM-based catalysts.

Microwave assisted zirconium oxide based catalytic activation of persulfate for methyl orange dye degradation

In this investigation, zirconium oxide (ZrO2) based activation of persulfate (PS) under microwave (MW) irradiation for methyl orange (MO) dye degradation was studied. ZrO2 was synthesized using facile hydrothermal method and it was characterized via XRD, FTIR, SEM, and TGA techniques. Subsequently, MW/ZrO2/PS experiments were conducted to explore the effect of ZrO2 dosage (0–1.5 g/L), initial MO concentration (15–250 mg/L), MW reactor temperature (60–90 ℃), MW power (240–700 W), PS dosage (50–250 mg/L), and presence of NaCl (0–5000 mg/L) on MO removal at pH ~ 7. Under the optimal conditions (ZrO2 ~ 0.5 g/L, MO concentration ~ 25 mg/L, MW temperature ~ 90 ℃, MW power ~ 560 W, and PS dose~250 mg/L), 99 % of MO removal and 85.9 % of TOC removal were observed. Moreover, the toxicity of the initial sample was reduced by 72.9 %. Interestingly, the catalytic oxidation of MO was not affected due to the presence of NaCl. Radical studies confirmed that SO4−⦁ radical was the major active species responsible for MO degradation. Subsequently, the central composite design (CCD) approach was used to find out the interaction effects between MO concentration (10–250 mg/L), PS dosage (50–500 mg/L), and MW treatment time (5–20 min) on MO removal. The CCD based response surface model was found to be significant and reliable (p < 0.0001). Moreover, the chemical cost and energy cost for MW/ZrO2/PS experiments under optimized condition was estimated as $22.5 and $30.3 per kg of MO removal. Overall, transition metal-based PS activation under MW irradiation could be one of the potential alternatives for dye wastewater treatment.

Efficient removal of sulfamethoxazole by biomass phosphorus-derived Cu3P/biochar catalyst combined with persulfate

Sulfamethoxazole (SMX) is ubiquitous in environments with concentrations ranging from nano-gram per liter to milli-gram per liter in practice, especially in water matrices (surface water and wastewater), posing a grave threat to ecosystems for its antibacterial and persistent characteristics. Efficient SMX removal is critical for water purification. Herein, the nano and micron Cu3P particles are synthesized on biochar utilizing phytic acid (PA) doped rice brans. PA facilitates the transformation of Cu-containing precursors to Cu3P on biochar, promoting catalytic performance. Under the conditions of 0.15 g/L catalyst (6PA-Cu11), 3.0 mM persulfate (PS), and pH 7.00, sulfamethoxazole (SMX) at a concentration of 0.25, 0.50, 1.00, and 10.00 mg/L can be completely removed within 30, 60, and 180 min, respectively. Moreover, the combination of Cu3P/biochar and persulfate exhibits preferable catalytic performances for SMX removal in sodium humate solution and surface water matrices, demonstrating the broad applicability of such a catalytic system for water purification. Sulfate radical (SO4−•) and hydroxy radical (•OH) play vital roles in the oxidation of SMX, with 1O2 assisting in. Except for cuprous ion (≡Cu+), partially charged copper ions (≡Cuδ+) and phosphorus ions (≡Pγ−) in Cu3P, owning the electron-donating ability, are found to participate in the activation of PS or the reduction of high-valent copper ions depending on density functional theory (DFT) calculations. Biochar carrier enhances the catalytic role of copper ions in Cu3P and facilitates the recovery of active sites by improving the desorption of the activation product (SO42−) from the Cu3P surface. This research promotes the practicability of the Cu3P/biochar catalyst in the advanced oxidation process for refractory organic pollutant removal and deepens the perception of its catalytic mechanisms.

Efficient persulfate activation by photo-excited organic dyes: Mechanism and application for actual dyeing wastewater self-purification

Sulfate Radical-Advanced Oxidation Processes are considered an efficient way for purifying dyeing wastewater, which commonly resists conventional treatment processes owing to the complex components, low biodegradability and high toxicity. However, this emerging technique is associated with issues of secondary pollution and great energy consumption during peroxymonosulfate (PMS) or persulfate (PS) activation processes. Herein, a dye pollutant/PS/visible light self-catalytic system was constructed, based on the photosensitive property of organic dyes for PS activation without catalyst and energy input. In this system, the degradation ratio of 100 mL 10 mg L−1 basic fuchsin, rhodamine B and eosin Y significantly increased by 60%, 76% and 50%, compared with the process without light irradiation. Such improvements were attributable to an efficient photo-induced electron transfer from photo-excited dyes to PS, which has the precondition that the lowest unoccupied molecular orbital (LUMO) energy level of the dye is higher than that of PS, thereby generating oxidizing species like ·SO4−, ·OH and 1O2 for pollutants degradation. Due to the high performance of pollutants simultaneous removal, wide pH adaptability and anti-interference, the complex self-catalytic system consisted of nine dyes and bis-phenol A exhibited the possibility for practical application. Expectedly, the actual dyeing wastewater self-purification system featured a decolorization efficiency of 54% accompanied by the removal of co-existing aromatic proteins and tryptophan-like substances; moreover, the acute bio-toxicity of the raw wastewater greatly decreased by 61.6%. Owing to its high efficiency, eco-friendliness and low consumption, the constructed “using waste to treat waste” system provides a promising way for wastewater treatment.

Efficient degradation of thiamethoxam pesticide in water by iron and manganese oxide composite biochar activated persulfate

Neonicotinoid pesticides in aquatic environments pose a risk to the sustainability of ecosystems and human health. However, there is limited research on the removal of these pesticides from aquatic systems. In this study, biochar doped with different Fe/Mn ratios (FeMn­BC) were prepared at various pyrolysis temperatures and used for the degradation of a typical neonicotinoid pesticide, thiamethoxam (TMX), by activated persulfate (PS). From the experimental results, it is known that the biochar with a Fe/Mn ratio of 3/1 prepared at 600 °C has the most excellent removal efficiency. Optimal degradation conditions were investigated, and under these conditions, TMX removal rates of up to 99.0 % in 90 min were achieved. The applicability of this system in natural surroundings were tested by investigating the effects of inorganic anions and humic acid and in real water samples on TMX removal. In addition, the TMX removal remainly reach to 90.0 % by FeMn-BC activated PS and basically no change after five reuse cycles. Free radical quenching experiments and electron paramagnetic resonance analysis revealed that SO4− and OH radicals on the catalyst surface were the main radicals promoting TMX degradation. Combining the catalyst characterization and experimental results, the possible mechanisms were proposed: the interaction of iron and manganese ions and the oxygen-containing functional groups on the catalyst surface together promote the generation of reactive radicals. This study provides a novel approach for removing neonicotinoid pesticides using modified biochar.

Degradation of 2-Chlorophenol in Aqueous Solutions Using Persulfate Activated by Biochar Supported Sulfide-Modified Nanoscale Zero-Valent Iron: Performance and Mechanisms

In this work, soybean biochar-supported sulfide-modified nanoscale zero-valent iron (BC@S-nZVI) was synthesized and used to activate persulfate (PS) to degrade 2-chlorophenol (2-CP) in aqueous solutions. Batch experiments were carried out to investigate the degradation effects under different conditions, including initial mass ratios among 2-CP, PS, and BC@S-nZVI, initial pH values, temperature, and anions. The results showed that the mass ratio of PS to 2-CP equal to 70 and the mass ratio of BC@S-nZVI to PS equal to 0.4 were the optimum mass ratios in the degradation system. The degradation efficiency of 2-CP was higher under acidic and alkaline conditions than the neutral condition, and the effect was best at a pH of 3; meanwhile, it increased with the increase in temperature. Moreover, the degradation rate was restrained with the addition of Cl−, promoted with the addition of NO3− and CO32−. Both free radical and material functions played leading roles in the degradation of 2-CP, and the stability of BC@S-nZVI was better than nZVI and S-nZVI. The experimental results showed that it was promising to remove 2-CP and other organic pollutants from groundwater by PS activated with BC@S-nZVI.

Novel application of Fe-Mg-Mt-SS activated persulfate for the disinfection of Escherichia coli in water: Performance and mechanism

New technology is required for the effective disinfection of pathogenic bacteria in water. A novel type of activator material (Fe-Mg-Mt-SS) was prepared using bimetallic iron-magnesium (Fe-Mg), montmorillonite (Mt), and sewage sludge carbon (SS) and applied it for disinfection. The specific surface area of Fe-Mg-Mt-SS was 115.72 m2/g, and the spatial structure of Fe-Mg-Mt-SS was orderly and layered. Mt played a role in frame support, and Fe-Mg was integrated into the structure in an orderly manner. Fe-Mg-Mt-SS effectively activated persulfate (PS) to disinfect Escherichia coli (E. coli) in water, with a disinfection rate of 7.00 lg of E. coli within 80 min in the PS/Fe-Mg-Mt-SS system, and the high disinfection rate was stable under different pH and elevated temperatures. Fe-Mg-Mt-SS showed broad spectrum disinfectant efficiency against other bacteria (Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus subtilis). Fe-Mg-Mt-SS activated PS killed E. coli mainly by producing hydroxyl and oxygen radicals, which damaged the E. coli cell membrane. Bimetallic activation with Fe and Mg synergistically activated PS, graphitised SS had more orderly spatial and laminar structures, and Mt improved the thermal stability and layer spacing of Fe-Mg-Mt-SS, which facilitated better metal insertion and improved its activation properties. The preparation of Fe-Mg-Mt-SS and activation of PS provide a new technology for the disinfection of pathogenic bacteria in water.

Merits and Limitations of Radical vs. Nonradical Pathways in Persulfate-Based Advanced Oxidation Processes.

Urbanization and industrialization have exerted significant adverse effects on water quality, resulting in a growing need for reliable and eco-friendly treatment technologies. Persulfate (PS)-based advanced oxidation processes (AOPs) are emerging as viable technologies to treat challenging industrial wastewaters or remediate groundwater impacted by hazardous wastes. While the generated reactive species can degrade a variety of priority organic contaminants through radical and nonradical pathways, there is a lack of systematic and in-depth comparison of these pathways for practical implementation in different treatment scenarios. Our comparative analysis of reaction rate constants for radical vs. nonradical species indicates that radical-based AOPs may achieve high removal efficiency of organic contaminants with relatively short contact time. Nonradical AOPs feature advantages with minimal water matrix interference for complex wastewater treatments. Nonradical species (e.g., singlet oxygen, high-valent metals, and surface activated PS) preferentially react with contaminants bearing electron-donating groups, allowing enhancement of degradation efficiency of known target contaminants. For byproduct formation, analytical limitations and computational chemistry applications are also considered. Finally, we propose a holistically estimated electrical energy per order of reaction (EE/O) parameter and show significantly higher energy requirements for the nonradical pathways. Overall, these critical comparisons help prioritize basic research on PS-based AOPs and inform the merits and limitations of system-specific applications.

Removal of insecticides from waters and soils by sulfate radical‐based advanced oxidation processes

AbstractInsecticides are toxic compounds widely used to prevent, destroy, and control any insect pests. A larger food production with increasing agricultural activity has been ensured from their application to farmlands. Insecticides have been detected in waters and soils being dangerous for living beings. Due to their high biorecalcitrance and stability at ambient conditions, they cannot be destroyed in conventional wastewater treatment plants (WWTPs) and powerful advanced oxidation processes (AOPs) are being developed for their removal. This review presents a detailed and critical analysis over the application of sulfate radical‐based AOPs to the remediation of waters and soils polluted with insecticides. Persulfate (PS) and peroxymonosulfate (PMS) are used as parent oxidants but they need to be activated to produce strong effective oxidizing radicals such as sulfate radical (SO4●−) and hydroxyl radical (●OH). Alkaline, thermal, catalytic, UV, UV with Fe, photocatalytic, and other methods applied as activators of PS and/or PMS are separately analyzed in waters and soils. For each hybrid procedure, the fundamentals are briefly detailed and the best results reported in the literature are summarized and discussed. The effect of operating parameters on the oxidation power of treatments in pure water, real waters, WWTPs effluents, and contaminated soils are remarked to show the viability of sulfate radical‐based AOPs for insecticides removal from waters and soils. The effect of added common anions and natural organic matter, the detection of oxidizing radicals by selective scavengers and electron paramagnetic resonance, and the identification of the generated by‐products in waters are described. Comparisons with analogous treatments with H2O2 and Fenton are discussed as well. Further research efforts should consider a deeper study of PS‐ and/or PMS‐based processes of insecticides not only in actual agricultural and real wastewaters, but also in many soils to confirm their possible suitability at the industrial level.

Fe-MOF-derived carbon compounds as catalysts for trichloroethylene degradation via persulfate oxidation: Role of precursor template and pyrolysis temperature

Trichloroethylene (TCE) commonly exists in contaminated water as a persistent toxic pollutant. The advanced oxidation of persulfate (PS) is a promising method for degrading organic pollutants. Heterogeneous Fe-carbon composites prepared by pyrolysis with metal–organic frameworks (MOFs) have attracted attention. However, the intrinsic relationship between the physicochemical properties and catalytic performance of MOF-derived carbon compounds via PS is unclear. This study investigates TCE removal by Fe-MOF-derived carbon (MFC) with PS. The effects of the precursor template structure, pyrolysis temperature, and coexisting substances on TCE removal over the MFC/PS system are examined. Fe-MOF-derived from different precursor templates presented different TCE removal rates of 75.2–85.0%. The pyrolysis temperature of MFC alters the pore size, phase composition, and other properties, thereby affecting electron transport in the materials and catalyzing the degradation process. The total TCE removal reached 85.8% with MFC600, derived from MF88B and pyrolyzed at 600 ℃. This catalyst demonstrated excellent performance for PS degradation over a wide pH range (3−9). Moreover, free-radical and nonradical pathways coexist in the MFC600/PS system. During the TCE degradation process, oxygen vacancies, Fe species (Fe0, Fe3N, Fe3C, and Fe3O4), and N species (pyridinic N and graphitic N) were active centers in the material and played a major role in catalytic degradation. They participated in the subsequent generation of HO•, SO4•-, and •O2-, and 1O2. Furthermore, a possible degradation mechanism is proposed. This study elucidates the control of the physicochemical properties of carbon-based catalysts by exploiting MOF diversity.

Oxalic acid enhanced ferrous/persulfate process for the degradation of triclosan in soil: Efficiency, mechanism and a column study

Triclosan (TCS) is a compound in pharmaceutical and personal care products (PPCPs) that preferentially accumulates in soil and may threaten human health. Iron-based persulfate activation processes (Fe-PAPs) are a promising technique in soil remediation but are limited by their narrow pH application range and resultant iron precipitation. In this study, oxalic acid (OA) was specifically introduced to improve the efficiency of Fe2+-activated persulfate (PS) processes for TCS degradation in soil. The complexation of OA and Fe2+ improved the total iron concentration in the Fe2+/OA/PS system and prevented iron precipitation. Fe-minerals in soil were also dissolved by OA, which participated in PS activation. The most appropriate proportion of Fe2+/OA/PS is 1:1:1, and approximately 85% of the TCS was degraded within 240 min compared with 45% in the Fe2+/PS system. SO4•- and 1O2 played important roles on TCS oxidation, while O2•- and CO2•- mainly participated in the iron cycle. The weak stretch of Fe-O in OA containing treatments in ATR-FTIR measurements provided evidence that OA dissolved the Fe-minerals. The introduction of OA in the Fe2+/PS system in four different soils reduced the negative effect of soil organic matter on TCS degradation. Three types of intermediates including hydroxylation, cleavage of ether bonds and cyclization products, were identified by LC-Q-TOF-MS. Column experiments were used to study the feasibility of in situ chemical oxidation (ISCO) remediation of TCS in the Fe2+/OA/PS system. Our findings indicated the ability of OA to be used as a cheating agent in Fe-PAPs for TCS soil remediation.

Mechanism of iron salt impregnated biowaste biochar with a prevailing free radical initiator for effective removal of toxic thallium from solution

Thallium is an emerging metallic pollutant with extremely high toxicity which resulted in worldwide water pollution in the past decades. It is critical to develop multiple alternative methods for Tl removal to enrich control strategy towards Tl pollution in aquatic environment. It is proposed herein a highly effective and environmental-friendly Tl removal method by applying iron salt-impregnated biochar (BC) combined with persulfate (PS), using two most common iron salts (FeCl3 and Fe(NO3)3). It was found that FeCl3@BC-PS system achieved higher Tl removal capacity (164.42 mg/g), which exhibited a comparative preponderance relative to the reported iron based adsorbent composites, partially owing to significantly enhanced specific surface area (854.48 m2/g). The dominant Tl removal mechanisms include free radical based oxidation and chemical adsorption. Radical quenching experiments confirmed that SO4− and OH served as vital radicals for FeCl3@BC-PS and Fe(NO3)3@BC-PS, respectively. The study provides a reliable alternative for Tl-wastewater treatment with PS activation by catalyst based on the synergistic effect of biochar and iron salts.

Conversion of agricultural waste to porous hydrochar for non-metallic activation of persulfate to phenol degradation via non-radical-dominated processes: Singlet oxygen and electron transfer

Recently, non-radical oxidation was served as an efficient approach during pollutant degradation due to its excellent environmental applicability. However, designing a green and low-cost non-metallic catalyst to activate persulfate (PS) for removal of hazardous organic contaminants via non-radical-dominated processes is still challenging. Herein, porous hydrochar (PHC) was synthesized with agricultural waste of corn straw (CS) as precursor and KHCO3 as pore-forming agent, which contained mesoporous structures with defects, thus facilitating phenol adsorption (117.14 mg/g). Moreover, 20 mg/L of phenol could achieve 100% removal at a wide pH range (7.0–11.0) within 10 min by PHC/PS system. The radical pathways induced by O·H and O2·− had certain effect on phenol removal, while non-radical pathways (1O2 and electron transfer process) played dominant contributions. Among them, 1O2 was produced from the reaction between surface functional groups on PHC and PS, and electron transfer process occurred from phenol to PS via PHC as the conductor. Whether under the interference of co-existing substances or in different water matrixes, the degradation efficiency of phenol could reach above 80%, exhibiting the excellent adaptability of PHC/PS system. This study proposed a potential resource utilization method of agricultural waste to prepare non-metallic catalyst for effective water remediation.

Nitrogen-rich magnetic biochar prepared by urea was used as an efficient catalyst to activate persulfate to degrade organic pollutants

In order to fully exploit the potential of magnetic biochar-based persulfate (PS) systems, N was utilized to modify the magnetic biochar-based catalysts through impregnation-pyrolysis method. A typical antifungal drug, metronidazole (MNZ), is selected as the target pollutant to score the reactivity of as-synthetic nitrogen-rich magnetic biochar (NMBC) catalysts. In the modified system, 99.6% of MNZ was removed, 13.6 times of that in the unmodified system. Active radical verification experiments showed that 1O2 was the key active radical. Various characterization showed that the nitrogen-rich significantly improved the persistent free radical, defect degree, content of oxygen-containing groups, electrochemical conductivity and other catalytic activity related properties. Physicochemical characterization, Fe(II) semi-quantitative analysis and masking experiments confirmed that the doping of magnetic biochar with nitrogen increased its Fe(II) content (23.79 mg/g), approximately 2.6 times higher than that of pristine magnetic biochar. Moreover, N induces strong electron accretion of Fe atom through coordination bond, which leads to the increase of electron density on the Fe atom, which increases the content of Fe (II) in the material, thus improving the ability of the material to activate PS to generate 1O2, and promoting the degradation reaction of MNZ. This paper provides a method to improve the activation performance of magnetic biochar.

Efficient remediation of PAHs contaminated site soil using the novel slow-release oxidant material

The eco-friendly slow-release material for persulfate (PS) using chitosan (CS) and urea (U) composite as frame structure (CS-U@PS) was firstly used to remediate the site soil contaminated by polycyclic aromatic hydrocarbons (PAHs) from Hefei city, China. The influences of glutaraldehyde dosage and urea dosage on the slow released properties of CS-U@PS was investigated and a longer release time of 190.0 d to 591.0 d was achieved, indicating the promising tunability according to the contents of pollutants in site soil. The effects of various factors (cross-linking agent dosage, initial PAHs concentration, CS-U@PS dosage, hydrogen peroxide dosage, etc.) on the degradation of soil spiked with PAHs (80 and 8 mg·kg−1) by CS-U@PS were studied, and the degradation pathway of PAHs was speculated. According to the EPR results, urea played an important role in promoting the 1O2 generation, which was the main reactive oxidative species. Finally, the long-term remediation of the industrial site soil with total PAHs of 553.2 mg·kg−1 was performed using 50 mg·g−1soil CS-U@PS and 90.22% removal rate was obtained after nine months. Moreover, the monitoring results of soil respiration gas show that, in addition to CO2, there is no additional greenhouse gas generated in the process of soil remediation, suggesting that the remediation of site soil using CS-U@PS has an excellent application prospect.

Phytic acid-modulated iron phosphide/biochar catalyst activates persulfate for rapid sulfamethoxazole removal: Synergy between iron phosphides and biochar

The efficient activation of persulfate (PS) is essential for rapidly degrading refractory organic pollutants in water. Traditional metal-based catalysts are limited by defects such as the metal ion redox cycle and secondary pollution, resulting in insufficient catalytic performances. In this research, highly active micron-sized iron phosphides (FeP and Fe2P) are in-situ synthesized on biochar, and the primary crystal phase can be switched by adjusting the phytic acid (PA) amount. Under the conditions of 0.15 g/L catalyst, 0.5 mM PS, and pH 7, sulfamethoxazole (SMX) at concentrations of 0.25, 0.50, 1.00, and 10.00 mg/L can be completely oxidized within 3, 5, 15, and 180 min, respectively. The leached ferric ion amount is below 0.020 mg/L. Meanwhile, ideal SMX abatements are achieved in sodium humate solution and surface water matrices, demonstrating the potential of this catalytic system for drinking water and wastewater treatment. Moreover, SO4-•, •OH, and 1O2 are crucial reactive oxygen species for SMX removal. Based on density functional theory (DFT) calculations, it is found that the partially charged Fe ion (≡Feδ+) is the pivotal site for PS activation and ≡Fe2+ regeneration. FeP and Fe2P are typically semi-metallic. Biochar can enhance the catalytic efficacies of FeP and Fe2P by shifting d-band centers (spin up and down) towards fermi level and reducing band gaps (spin down). Besides, biochar may donate electrons to iron phosphides when activating PS. The enhancement of FeP by biochar is more significant, which is why FeP/biochar is superior to Fe2P/biochar in PS activation.

Rapid degradation of organic pollutants by enhanced persulfate activation using CeO2-MnFe2O4 nanostructures: A polymetallic synergistic effect

Persulfate-based advanced oxidation processes (AOPs) have attracted considerable attention in the treatment of organic wastewater with high performance and long lifetime. The construction of efficient, environmentally-friend, and stable nanocatalysts has been recognized as a promising approach to activate persulfate. Herein, magnetic CeO2-MnFe2O4 nanomaterials fabricated via a simple sol-gel method were used for the first time to enhanced activate persulfate (PS) for the removal of the organic pollutant enrofloxacin (ENR). It was demonstrated that 97.2% of ENR (10 mg L−1) was efficiently degraded. 63.3% of TOC decreased within 35 min under a neutral solution (pH 6.81) in the PS+CeO2-0.2MnFe2O4 system using a catalyst dosage of 0.25 g L−1 and 0.18 mM PS. The magnetic CeO2-MnFe2O4 nanostructures maintained excellent recovery as well as recyclability ENR removal efficiency was 90% after recycling five times. EPR and quenching tests indicated that sulfate radicals (SO4•−) and hydroxyl radicals (•OH) significantly contributed to ENR removal. XPS analysis showed that the synergistic redox cycles of Ce3+/Ce4+, Mn2+/Mn3+, and Fe2+/Fe3+ are essential to activate PS for ENR degradation. DFT calculations also revealed that PS molecules preferred to adsorb to and dissociate on CeO2-MnFe2O4 surfaces rather than just CeO2 and MnFe2O4 surfaces. CeO2 plays a dual role in the charge transfer from CeO2-MnFe2O4 to PS molecules, i.e., both electron storage and donor. This work also provides a new interpretation to explain the activation mechanism of PS. The developed CeO2-MnFe2O4 nanostructures with rapid removal efficiency, high degradation efficiency and good recyclability may provide potential guidance for the design of polymetallic oxide nanocatalysts in PS-based AOPs.

Remediating thiacloprid-contaminated soil utilizing straw biochar-loaded iron and manganese oxides activated persulfate: Removal effects and soil environment changes

Thiacloprid (THI) has accumulated significantly in agricultural soil. Herein, a novel approach to removing THI was explored by straw biochar-loaded iron and manganese oxides (FeMn@BC) to activate the persulfate (PS). The factors influencing the removal of 5 mg kg−1 THI from the soil by FeMn@BC/PS were investigated, including FeMn@BC dosing, PS dosing, temperature, and soil microorganisms. The feasibility was demonstrated by the 75.22% removal rate of THI with 3% FeMn@BC and 2% PS at 7 days and a 92.50% removal rate within 60 days. Compared to the THI, NH4+-N and available potassium were 3.96 and 3.25 times, and urease and phosphatase activities were increased by 22.54% and 33.28% in the FeMn@BC/PS at the 15 days, respectively. THI was found to seriously alter the structure of the genus in the 15 days by 16 S rRNA analysis; however, the FeMn@BC/PS group alleviated the damage, compared to the THI with 658 more operational taxonomic units. Actinobacteriota accounted for 51.48% of the microbial community in the FeMn@BC/PS group after 60 days, possibly converting transition products of THI into smaller molecules. This article provides a novel insight into advanced oxidative remediation of soils.

Kinetic modeling and cost analysis of coupled ultrasonic processes for the treatment of dairy wastewater

Sonolysis with bubble cavitation is an effective tool for the degradation of complex, recalcitrant organic compounds. Thermal and cavitation effects are additive to the breaking of complex bonds in organic contaminants by hydroxyl radicals. Strong oxidants such as persulfate (PS) and hydrogen peroxide (H2O2), with their high redox potentials (2.01 and 1.8 V, respectively), are coupled with ultrasound energy for the degradation of contaminants. PS and H2O2 generate SO4̇ and ȮH radicals, respectively with higher redox potentials (2.6 and 2.8 V, respectively). Consequently, the radicals are even more active at breaking the strong covalent bonds of the contaminants. Coupled methods in different combinations of coagulation-flocculation, chemical oxidation, and sonication are investigated for the treatment of organic content dairy wastewater. The doses of PS and H2O2 are optimized at 0.75 g/L and 25.5 g/L, respectively. The kinetic study reveals that pseudo-second-order kinetic fits experimental data with a R2 value of 0.99. The oxidation by PS and H2O2, along with ultrasound application, facilitates the removal of COD up to 84.3 % at an economically feasible treatment cost of $5.635 per kg of COD removal. Coupled process is found able to qualify dairy wastewater as dischargeable at a feasible cost of treatment.

A walnut shell biochar-nano zero-valent iron composite membrane for the degradation of carbamazepine via persulfate activation

In this study, novel walnut shell biochar-nano zero-valent iron nanocomposites (WSBC-nZVI) were synthesized using a combined pyrolysis/reduction process. WSBC-nZVI displayed a high removal efficiency (86 %) for carbamazepine (CBZ) compared with walnut shell biochar (70 %) and nano zero-valent iron (76 %) in the presence of persulfate (PS) (0.5 g/L catalyst, 10 mg/L CBZ, 1 mM persulfate). Subsequently, WSBC-nZVI was applied for the fabrication of the membrane using a phase inversion method. The membrane demonstrated an excellent removal efficiency of 91 % for CBZ in a dead-end system (2 mg/L CBZ, 1 mM persulfate). In addition, the effect of various operating conditions on the degradation efficiency in the membrane/persulfate system was investigated. The optimum pH was close to neutral, and an increase in CBZ concentration from 1 mg/L to 10 mg/L led to a drop in removal efficiency from 100 % to 24 %. The degradation mechanisms indicated that oxidative species, including 1O2, OH, SO4−, and O2−, all contribute to the degradation of CBZ, while the role of 1O2 is highlighted. The CBZ degradation products were also investigated, and the possible pathways and the predicted toxicity of intermediates were proposed. Furthermore, the practical use of the membrane was validated by the treatment of real wastewater.