Persulfate Dosage Research Articles

Heat and carbon co-activated persulfate to regenerate gentamicin-laden activated carbon: Performance, mechanism, and safety assessment

Activated carbon enriched with high concentrations of gentamicin (ACG) was generated in the production process of gentamicin. Inappropriate handling methods for ACG not only squanders carbon resource, but also seriously hinders achieving global carbon neutrality and hazardous to human health. In the present work, thermal and carbon co-activated persulfate method (TC-PS) was developed to regenerate ACG with degrading gentamicin. The results showed that ACG was effectively regenerated by TC-PS, restoring the adsorption performance for gentamicin. When the treatment temperature was 80 °C, the persulfate dosage was 20 mM and the initial pH was 3.0, the degradation efficiency of gentamicin reached 100%. The HO• and SO4•- were the major reactive species for gentamicin degradation. The possible degradation routes of gentamicin were proposed and the safety assessment indicated that the produced intermediates during the regeneration process of ACG by TC-PS have insignificant impact on the biological and ecological environment.

Effect of sodium dodecyl sulfate on preferential degradation of naphthalene by thermally activated persulfate: Implications for soil flushing solution reuse

Various flushing solutions that contain hydrophobic organic compounds and surfactants are generated during surfactant-enhanced soil flushing processes. How to effectively remove the target pollutants while minimizing the degradation of surfactants for reuse of the flushing solutions has become a major problem. A series of batch experiments were conducted to investigate the preferential degradation mechanisms of naphthalene by sodium dodecyl sulfate (SDS) as well as the effect of SDS concentration on the degradation efficiency using a competitive kinetic method. In addition, the effects of persulfate (PS) dosage, temperature, and pH on the degradation efficiency of naphthalene were also studied, and a prediction model based on response surface methodology (RSM) was built to optimize the preferential degradation of naphthalene. One-dimensional column flushing experiments were performed to evaluate the feasibility of reusing soil flushing solutions at the predicted PS dosage. Results show that: (i) SDS inhibited naphthalene degradation owing to competitive oxidation and micellar protection, with a decreasing degradation rate constant as SDS concentration increased. However, naphthalene was still degraded by reactive oxygen species (ROS) at a higher rate than SDS, indicating the preferential degradation of naphthalene. When the concentration of SDS increased from 5 to 10 times of critical micelle concentration (CMC; 8.2 mM), the ratio for rate constants of naphthalene to SDS (kNAP/kSDS) decreased significantly from 31.61 to 3.38, illustrating the obvious effect of SDS concentration on preferential degradation of naphthalene; (ii) The formation of single-chambered vesicles with a higher thermodynamic stability was observed at 10 CMC, compared to the spherical micelles formed at 5 CMC. The accessibility of naphthalene to ROS was greatly reduced at 10 CMC, resulting in a significant reduction in kNAP/kSDS value. Moreover, the method in which ROS attacked naphthalene in surfactant micelles varied with SDS concentration, which also impacted the preferential degradation of naphthalene; (iii) Under the optimal PS dosage predicted by the RSM model, a good reusability of SDS was observed in the soil flushing solutions after thermally activated PS oxidation, with a significant reduction on the toxic risk of soil after flushing.

Oxidative degradation of Rhodamine B solution with nZVI persulfate activation

In this study, the researchers evaluated the use of nano-zero-valent iron (nZVI) activated persulfate (PS) for the degradation of Rhodamine B (RhB). The effects of various operating parameters such as initial pH, and dosages of PS, nZVI and citric acid (CA) on the removal rate of RhB were investigated. The results demonstrated that at a PS dosage of 5 mmol·L<sup>-1</sup>, nZVI dosage of 0.3 g·L<sup>-1</sup>, 0.1 mmol·L<sup>-1</sup> CA, and pH of 5, the degradation rate of RhB was 94.970%. The degradation and kinetic analysis of RhB using micron-scale zero-valent iron (mZVI) and nZVI revealed that nZVI exhibited higher activity with PS due to its smaller particle size. The activation of PS by nZVI is higher compared to mZVI, and the ineffective consumption is half that of the mZVI/PS system, the TOC removal rate increased by 18.65%. Kinetic analysis indicated that under the mentioned reaction conditions, the degradation process followed a pseudo-second-order reaction model, with the highest apparent reaction rate constant (kobs). The researchers also identified active radical species in the nZVI/PS system. Additionally, Gas Chromatography-Mass Spectrometry (GC-MS) analysis was used to detect reaction intermediates and propose a possible degradation pathway for RhB.

Underwater bubbling plasma assisted with persulfate activation for the synergistic degradation of tetracycline hydrochloride

The performance and mechanism of persulfate consisting of peroxymonosulfate (PMS) and peroxydisulfate (PDS) activation by underwater bubbling plasma (UBP) for the synergistic removal of tetracycline hydrochloride (TCH) were comparatively investigated. Both PMS and PDS addition significantly promoted the removal of TCH in UBP system, indicating persulfate exhibited highly synergistic effect with UBP. Furthermore, enhancing the persulfate dosage, peak voltage and pulse frequency, as well as reducing initial TCH concentration were favorable for the elimination of TCH. Compared with neutral condition, acidic and alkaline condition were advantageous to TCH removal. The presence of coexisting substances including Cl−, SO42− and humic acid (HA) had an adverse effect on TCH degradation, while Fe2+ could improve the removal of TCH. The degradation of ciprofloxacin and metronidazole proved the applicability for other antibiotics degradation of the reaction system. SO4−·, ·OH, ·O2−, hydrated electrons, O3 and H2O2 were the active substances responsible for TCH removal. The reduction of aqueous O3 concentration and enhancement of H2O2 concentration were observed after persulfate addition. UV–vis spectra and TOC analysis illustrated the addition of PMS or PDS facilitated the degradation and mineralization of TCH. 3D-EEMF spectra visually displayed the degradation process of TCH. Plausible degradation routes were deduced based on LC-MS and the toxicities of TCH and its intermediates were evaluated by Toxicity Estimation Software Tool.

Interfacial heterojunction-engineered magnetic alpha-Fe2O3@NiFe LDH@biotemplate catalyst for heterogeneous photocatalytic activated persulfate removal of organic pollutants

The integration of multiple degradation pathways in a single catalyst has been proposed as a promising strategy for environmental remediation. The successful transition process from MnO2 to alpha-Fe2O3 is used to prepare 1D/2D/3D alpha-Fe2O3 @NiFe LDH@diatomite (FENFD) nanocomposite for improving conversion efficiency during pollutant degradation. The effects of initial pH, pollutant concentration, persulfate (PS) dosage, and catalyst dosage on the degradation rate were systematically investigated. FENFD demonstrated favorable PS activation performance and high degradation efficiency for Rhodamine B, azo dyes, and tetracycline over a broad pH range. Comparative experiments with quenching catalytically active radicals and analysis of electron spin resonance (ESR) spectra reveal that the sulfate radical generated by PS photocatalytic activation has a synergistic effect with superoxide radical and hydroxyl radical to degrade pollutants. Biotemplate-diatomite effectively achieves the dispersion of magnetic nano Fe2O3 and LDH and increases light utilization. Meanwhile, density functional theory (DFT) calculations demonstrate that the in situ grow Fe2O3 @NiFe LDH heterojunctions can efficiently transform the interface band structure to inhibit the recombination of photogenerated electron-hole pairs. The stability and reusability of the magnetic nanocomposites were also evaluated, and the degradation efficiency reached 96.4% even after five cycles, which provides new insight into designing single catalysts with different degradation mechanisms.

Synergistic degradation levofloxacin through dielectric barrier discharge and sodium persulfate

The release of antibiotics that are difficult to degrade by themselves into the environment have received increasing attention because they have posed great threat to natural ecosystem and human health. Sodium persulfate (PS) is used to treat organic wastewater because of its strong oxidation, but it needs to be activated. Dielectric barrier discharge (DBD) can product stable gas discharge plasma that is suitable for activating PS. The synergistic degradation process of levofloxacin (LFX) by air DBD plasma with PS were investigated. The effects on the degradation ratio and energy efficiency of LFX were studied, including input power, air flow rate, original concentration, discharge spacing, and PS dosage. The degradation kinetics and synergistic factors were calculated under different PS additions. After plasma alone treatment 45 min, the maximum degradation ratio of LFX was 58.74 % and 88.63 % via plasma alone and plasma synergistic with PS under 15 W input power and 50 mg·L−1 LFX original concentration. The energy efficiency, the first-order reaction rate constant and the synergistic factor SI was 0.1532 g·(kW·h)−1, 4.116 × 10−2 min−1 and 1.64, respectively. The change of ozone concentration in the reaction system after adding PS was measured. The effects on the synergistic degradation of LFX of two radical scavengers, methanol (MeOH), and tert-butanol (TBA), were investigated. After calculation, the contribution ratios of ·OH and SO4-· were 48.08 % and 26.97 %, respectively. The intermediate products were analyzed by LC-MS in the decomposition process of LFX, and the probable decomposition pathway of LFX was presented.

Thermally activated persulfate oxidation of Basic Fuchsin dye: Effect of different operating parameters, kinetic, and thermodynamic study

AbstractThe present paper aims to investigate the efficiency of thermal activation persulfate in eliminating the organic dye “Basic Fuchsin” (BF). In addition, the study attempts to elucidate the effect of different operating parameters, such as persulfate dosage (0.44–4.4 mM), the initial solution pH of (3–10), and temperature (25–50°C), on the process. The effects of various anions and water matrices on BF discoloration were investigated. Thus, the findings revealed that 94.15% of BF can be eliminated using persulfate at a concentration of 4.4 mM and a temperature equal to 50°C. It occurs under the following operating conditions: oxidation time of 60 min, initial pH equal to 6, the pollutant concentration of 10 ppm, and stirring speed equal to 300 rpm. Furthermore, the kinetic study indicated that the degradation of the BF dye using PS followed a first‐order pattern with rate constants varying within a range of 15.3 × 10−3–43.2 × 10−3 min−1. Based on the Arrhenius equation, the activation energy of the studied process was determined to be 29 kJ mol−1, suggesting that a moderate activation energy is required for BF discoloration. The results of the thermodynamic study confirm that the oxidation process is non‐spontaneous and endothermic. Coexisting inorganic anions delayed BF discoloration to varying degrees, and the inhibitory action followed the following order: carbonate > chloride > sulfate > nitrate. Organic pollutants oxidation by the thermal activation of the persulfate is a simple and effective method for the depollution of waste textile water.

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.

A novel method for the remediation of wastewater containing acid red 131 dye using acoustic cavitation combined with sulphur-doped TiO2 and oxidants.

The present study investigated the degradation of Acid Red 131 (AR131) dye using a combination of ultrasound-induced cavitation, ultraviolet (UV) irradiation, chemical oxidants, and photocatalyst, focusing on the effect of operating parameters. It was established that acidic pH, higher input power, and lower initial concentration resulted in higher degradation. Sulphur-doped titanium dioxide (S-TiO2) synthesized using a novel ultrasound-assisted method showed an optimum dosage of 300ppm for the AR131 degradation with sulphur to titanium ratio of 2:1. In the combination approach, the optimum dosage of hydrogen peroxide (H2O2) and potassium persulfate (KPS) was established as 100ppm and 400ppm respectively. The maximum degradation of 90.3% was obtained using a combined approach of US + KPS + UV/S-TiO2 whereas, a maximum synergetic coefficient of 1.57 was obtained for the approach of US + UV/S-TiO2 with degradation of 86.96%. It was also elucidated that for combination approaches of US + H2O2, US + H2O2 + KPS, and US + H2O2 + KPS + UV/S-TiO2, the synergetic coefficients were lower than one due to undesirable side reactions and radical scavenging. Scale-up studies performed at 15 times of the laboratory scale volume, elucidated that the maximum degradation was obtained as 58.01% for the approach of US + KPS + UV/S-TiO2. Therefore, the approach of US + KPS + UV/S-TiO2 was elucidated as the most efficient in degrading the AR131 dye at both small and large scale of operation. In terms of synergy, the approach of US + UV/S-TiO2 was more efficient. Overall, an optimized combination approach was successfully demonstrated for the effective degradation of AR131 dye with synergism and better results at a large scale.

Activation of persulfate by heterogeneous nano zero-valent iron/halloysite nanotubes: reaction behavior, mechanism, and implication for tetracycline hydrochloride degradation.

A novel composite (nZVI/HNTs) was prepared via incorporating nano zero-valent iron (nZVI) on halloysite nanotubes (HNTs) for degrading tetracycline hydrochloride (TCH) with existence of persulfate (PS). The adsorption process of nZVI/HNTs to TCH conformed to the Freundlich isotherm model and pseudo-second-order kinetic model, and its maximum adsorption capacity was 76.62mg·g-1. Furthermore, the nZVI/HNTs + PS system exhibited satisfactory degradation efficiency (84.21%) for TCH, and stable nZVI/HNTs (Fe leaching < 0.001mg·L-1) could be reused. When nZVI/HNTs dosage, PS dosage and temperature increased, TCH degradation could be enhanced. After four cycling, nZVI/HNTs + PS system had still 65.8% degradation for TCH. The quenching tests and EPR analysis evidenced that SO4•- was predominant instead of •OH in such system. Three possible pathways of TCH degradation were provided through the liquid chromatograph-mass spectrometer (LC-MS) determination. Meanwhile, the biological toxicity prediction analysis indicated that the nZVI/HNTs + PS system would be an environment friendly treatment method toward TCH pollution.

Degradation of endocrine‐disrupting chemicals using various sulfate radical activation methods: kinetics and mechanism

AbstractBACKGROUNDMost studies have focused on the degradation of endocrine‐disrupting chemicals using persulfate activation processes. Therefore, the current study compares various sulfate radical activation processes in an aqueous solution of a mixture of diethyl phthalate, butylparaben and bisphenol A that are present in water and wastewater. The effects of initial persulfate dose and pH variation, the effect of concentration of target endocrine‐disrupting chemicals and degradation efficiency under various processes were studied. Additionally, the toxicity and cost estimation of the systems were also examined.RESULTSThe results showed pseudo‐first‐order kinetics with maximum degradation efficiency of 99% for 1 mg L−1 at pH 7, 2.5 mmol L−1 persulfate dose, 450 W power in 60 min for UV‐activated persulfate oxidation process. A quenching experiment highlights the dominance of both sulfate and hydroxyl radicals in the degradation of mixtures of diethyl phthalate, butylparaben and bisphenol A in an aqueous solution. The transformative products identified using gas chromatography–mass spectrometry were monohydroxylated structures that decompose to form organic acids, indicating efficient degradation capacity with minimal toxicity. Further, the sono‐activated persulfate oxidation process was found to be cost‐effective at 1 mg L−1 with 95% degradation efficiency.CONCLUSIONIt is concluded that an increase in the concentration of target compounds decreases the efficiency of degradation under various activation processes. pH 3 and pH 7 favor thermal and sono‐activated and UV‐activated processes, respectively. Toxicity evaluation shows minimal harm to non‐target species Daphnia magna for all activation processes. These findings can be useful for on‐field application for the degradation of chemicals in mixtures. © 2023 Society of Chemical Industry.

Constructing durable BiFeO3@SrBi2B2O7 p-n heterojunction for persulfate enhanced piezo-photocatalytic water purification

Photoresponse piezoelectric materials have attracted tremendous interest as a new generation of photocatalysts for water purification. However, the development of durable and efficient piezo-photocatalyst remains to be a challenging task. Herein, a novel BiFeO3@SrBi2B2O7 (BFO@SBBO) p-n heterojunction with ultrahigh piezo-photocatalytic ability was fabricated after adjustment of BFO outer layer thickness, and utilized to activate persulfate (PS) for efficient water decontamination. The synergistic effect between the internal electric field across the heterojunction and the PS greatly improves the separation of photogenerated charge carriers. In the presence of ultrasonic mechanical vibration, 10 mg/L bisphenol A (BPA) was completely removed within 20 min with the assistance of a low dosage of PS upon visible light irradiation, which outperform various piezo-photocatalysts. Transformation and contribution of reactive oxygen species (ROSs, i.e., OH, O2−, 1O2 and SO4−) generated in the BFO@SBBO/US/Vis/PS system were evaluated and semi-quantified to understand the mechanism of BPA piezo-photocatalytic degradation. The stability and performance of BFO@SBBO piezo-photocatalysis toward typical organic pollutants and actual phenolic water remediation were evaluated, which confirmed the promising practical potential of BFO@SBBO in water remediation. This study offers a new insight into strategies for highly efficient piezo-photocatalyst for photocatalytic water remediation.

Enhanced catalytic levofloxacin degradation via persulfate activation over amorphous potassium ferricyanide@ZIF‐67 nanocages

AbstractA facile method was used to synthesize amorphous potassium ferricyanide (PF)@ZIF‐67 nanocages, a novel metal–organic framework derivative. The structure, composition and morphology of PF@ZIF‐67 were analysed by scanning electron microscopy, transmission electron microscope, X‐ray diffraction and X‐ray photoelectron spectroscopy. The results show that PF@ZIF‐67 nanoparticles were successfully prepared and its nanostructure has high crystallinity. The prepared materials were employed as heterogeneous persulfate catalysts for the degradation of levofloxacin (LEV). The effects of some key parameters including sodium persulfate (PS) dosage, PF@ZIF‐67, initial solution pH and reaction time on LEV degradation were investigated. PF@ZIF‐67 showed higher catalytic capacity for LEV degradation compared to ZIF‐67, implying the iron‐cobalt synergy in the material. Under the optimized conditions of 8.4‐mM PS, 0.5 g/L PF@ZIF‐67 at an initial solution pH of 7.2, 85.8% of LEV could be removed within 240 min. The quenching experiments suggest that sulfate radicals were the predominant reactive species.

Artificial Neural Networks and Genetic Algorithms: An Efficient Modeling and Optimization Methodology for Degradation of Atenolol Using Activated Persulfate with Ultrasound

Atenolol (ATN) is a slowly biodegradable antagonist β-blocker drug and remains in the environment for a long period of time. This drug has a harmful effect on the environment and human and animal bodies. In this study, using activated persulfate with ultrasound for the degradation of ATN was investigated. The effect of independent variables including pH, ATN concentration, persulfate dose, contact time, and ultrasonic power has been studied at 5 levels. Central composite design (CCD) was used for designing the experiments in Design Expert 11.0 software. The ATN concentration was measured using high-performance liquid chromatography (HPLC). Genetic algorithms (GA) and artificial neural network (ANN) were used for optimization and prediction, respectively. The results indicated that at the optimal conditions for the experiment (pH of 6.79, reaction time of 19 min, initial ATN concentration of 15.92 mg/L, US power of 109.56 W, and PS dose of 1317.88 mg/L), the highest ATN degradation efficiency was 98.9%. The ATN degradation could be represented by the pseudo-zero-order kinetics. Also, the data of ATN were well fitted with the ANN model (R2 = 0.98). The results showed that the best pH range to eliminate ATN is the near neutral range and the GA was found to be an effective tool to optimize the experimental conditions for the removal of ATN. The ultrasonic/persulfate process as a useful technique has a high potential to remove ATN from aqueous solutions.

Bacteria-based biochar as a persulfate activator to degrade organic pollutants.

Carbon-based catalysts for activating persulfate to drive advanced oxidation processes (AOPs) are widely used in wastewater treatment. In this study, Shewanella oneidensis MR-1, a typical ferric reducing electroactive microorganism, was utilized as the raw material of biochar (BC) to prepare a novel green catalyst (MBC). The effect of MBC on activating persulfate (PS) to degrade rhodamine B (RhB) was evaluated. Experimental results showed that MBC could effectively activate PS to degrade RhB to reach 91.70% within 270min, which was 47.4% higher than that of pure strain MR-1. The increasing dosage of PS and MBC could improve the removal of RhB. Meanwhile, MBC/PS can well perform in a wide pH range, and MBC showed good stability, achieving 72.07% removal of RhB with MBC/PS after 5 cycles. Furthermore, the free radical quenching test and EPR experiments confirmed the presence of both free radical and non-free radical mechanisms in the MBC/PS system, with •OH, SO4•- and 1O2 contributing to the effective degradation of RhB. This study successfully provided a new application for bacteria to be used in the biochar field.

Activation of persulfate by iron‐loaded soybean straw biochar for efficient degradation of dye contaminants: Synthesis, performance, and mechanism

AbstractBiochar loaded with metal ions has been widely used to activate persulfate to degrade organic pollutants. However, the preparation conditions of catalysts are always controversial. In this study, the co‐heating conditions of soybean straw with high carbon and low nitrogen and nano‐iron oxide were systematically discussed by response surface method, and an efficient catalyst (Fe@BC) was obtained. Fe@BC can effectively activate sodium persulfate (PS) and degrade three synthetic azo dyes (Methyl orange (MO), Amino black 10B (AB10B), and Orange II) and rhodamine B (RhB). Under the optimum conditions, the removal rate of total organic carbon of these four dyes reached 41.1%–89.8% and the final degradation rate could reach 100%. The physicochemical properties of Fe@BC were studied by SEM, BET, XRD, XPS and TGA. The results revealed that the specific surface area of Fe@BC was 195.6m2/g. Further, reducing iron oxide by C generated C0.09Fe1.91 and zero‐valent iron. Free radical scavenging experiments and electron paramagnetic resonance (EPR) measurements showed that the main reactive oxide species (ROS) in the Fe@BC/PS system were hydroxyl radicals (•OH) and singlet oxygen (1O2). Finally, Several Fe@BC modification systems were explored, the optimum pH of Fe@BC/PS system was analyzed, and the effects of Fe@BC and PS dosage on degradation performance were also studied. This study provides a scientific basis for the production of efficient catalysts and biochar energy, and an effective treatment scheme for printing and dyeing wastewater.

Evaluation of atrazine degradation by iron persulfate activation process in aqueous phase using Taguchi approach

Atrazine (ATZ) is one of the most widely used herbicides for the control of annual broadleaf and grassy weeds in the world. Its residual in the environment is of great concern. This research work primarily focused on examining ATZ degradation by the ferrous ion activated persulfate (PS) oxidation process (Fe2+-AP process) and the influence of oxidative parameters on the degradation of ATZ in aqueous phase. The Taguchi Design of Experiment methodology was used to explore the effects of various operational parameters, including ATZ concentration, dosage of Fe2+, dosage of PS, and pH condition (Taguchi L9 orthogonal array). The optimal operational conditions were then determined based on the results of ANOVA statistical analysis. Operational conditions included ATZ at an initial concentration of 5 mg/L, with initial concentrations of 1 mM Fe2+, 10 mM PS, and pH = 3, at 20oC, for a reaction time period of 3 h. The sensitivity of factors for the ATZ degradation followed the decreasing order: PS concentration, pH, ATZ concentration and Fe2+ dosage. The results of this study provide useful operational conditions for the Fe2+-AP process, for application to field remediation of ATZ contamination.

Process characterization and pretreatment of container and drum cleaning industry wastewater using a heat‐activated persulfate oxidation process

AbstractThe aim of this study was to treat wastewater from washing, cutting or crushing of intermediate bulk containers (IBCs), steel drums and plastic drums, using the sulfate radical‐based oxidation method. In this study, it was planned to make the wastewater suitable for activated sludge treatment by applying neutralization after a sulfate radical‐based oxidation process. Samples were taken from the industry three times to study these treatment processes. To determine the optimum conditions in the study, chemical oxygen demand (COD), removal efficiency was calculated, and optimum temperature, optimum time, and optimum persulfate dose were determined. Since the washing is done with hot water in the industry, the thermal activation method was used for the activation of persulfate. In the results of the study, COD removal efficiency, and total organic carbon (TOC), biochemical oxygen demand (BOD), total nitrogen (TN), total phosphorus (TP), and potentially toxic metal(s) removal efficiency was measured in three wastewater samples. According to the results of the study, the temperature at which the best COD removal efficiency was observed was 70°C, the COD/S2O82− ratio was 1:2, and the contact time was 5 h. As a result of the study, it has been revealed that such wastewater can be given to the activated sludge after sulfate radical‐based oxidation and neutralization in the same existing reactor instead of the existing FeCl3 process.

ZnO Promoted Persulfate Activation in Discharge Plasma System for Ofloxacin Degradation

This paper aims to investigate the promotion of persulfate (PS) activation by ZnO in discharge plasma systems for the degradation of ofloxacin (OFX). Scanning electron microscopy and transmission electron microscopy showed that ZnO nanoparticles were successfully prepared by a hydrothermal method. With an increase in the PS dosage, the removal efficiency of OFX first increased and then decreased. With an increase in the ZnO dosage, the removal efficiency of OFX showed a similar trend. Under the optimum 595 mg/L PS dosage and 295 mg/L ZnO dosage, the removal efficiency of OFX by plasma, plasma/ZnO, and plasma/ZnO/PS systems reached 53.6%, 82.8%, and 98.9%, respectively. Increasing the input power was beneficial to the degradation of OFX. ESR results showed that the addition of ZnO could further stimulate PS to produce more ·OH and ·SO4− than that of plasma alone. The capture agent experiment proved that ·OH, ·SO4−, ·O2−, and 1O2 all participated in the degradation of OFX. A total organic carbon (TOC) removal of 49.6% was obtained in the plasma/ZnO/PS system. Based on liquid chromatography-mass spectrometry (LC-MS) and the Toxicity Estimation Software Tool (TEST), degradation pathways and toxicity were analyzed. Compared to other technologies, it can be concluded that the plasma/ZnO/PS system is a promising technology for pollutant remediation.

Persulfate activation by sulfide-modified nanoscale zero-valent iron for metronidazole degradation: Mechanism, major radicals and toxicity assessment

Sulfide-modified nanoscale zero-valent iron (SnZVI) is considered to be an effective method for persulfate (PS) activation. Here, the catalytic activity was evaluated in view of the potential influencing factors, including the sulfidation regent, Fe/S molar ratio, initial solution pH value, catalyst dosage, PS dosage, initial MNZ concentration and common anion species. The complete removal was obtained when Na2S was chosen at Fe/S molar ratio of 0.05 with 1.5 g·L−1 SnZVI and 1.5 mM PS. SnZVI exhibited a promising application owing to the high pH adaptation and the outstanding reusability. The high and persistent release of Fe2+ and FexSy generated on the surface, which accelerated the electron transfer rate for PS activation. The main reactive oxygen species, including OH, SO4−, O2− and 1O2, were further determined. However, OH rather than SO4− was the dominant reactive radical in our study. Finally, the degradation products and possible pathways were predicted based on the intermediate analysis. The T.E.S.T theoretical calculation indicated that the ecotoxicity of the various intermediate products of MNZ were greatly reduced. These results demonstrated that SnZVI/PS was a promising strategy for practical application in the remediation of MNZ contaminated water.