Persulfate Dosage Research Articles

Atrazine degradation using Fe3O4-sepiolite catalyzed persulfate: Reactivity, mechanism and stability.

In this study, with sepiolite as a support, a novel magnetic Fe3O4-sepiolite composite was fabricated by coprecipitation method. The characterization results reveal that the sepiolite support could anchor Fe3O4 nanoparticles with good dispersion. The composite was used as a catalyst to activate persulfate (PS) for atrazine (ATZ) degradation. 71.6% of ATZ and 20.9% of solution TOC could be removed after 60 min with 92 mmol/L of PS ([ATZ]0 = 10 mmol/L). Due to the good adsorption capacity of Fe3O4-sepiolite composite toward ATZ, the degradation was considered to be facilitated by an adsorption process, since the adsorbed ATZ can be more easily transported to the active sites and be degraded in situ. Operation factors, including PS dose and solution pH, were investigated and found to be influential for the ATZ removal. The Fe3O4-sepiolite composite maintained its catalytic activity and structural stability with negligible Fe leaching during the recycling batch experiments. The intermediate products were further identified and the possible transformation pathway was then proposed based on the results. The findings of this research promote the application of Fe3O4-sepiolite composite as efficient and recyclable heterogeneous catalyst for organic degradation, and provide insights into the development of alternative catalysts with good adsorptive properties.

Removal of methamphetamine by UV-activated persulfate: Kinetics and mechanisms

In this study, removal of methamphetamine (METH) was investigated by UV activated persulfate (PS), and the influence of key factors was evaluated. Results suggested that METH degradation followed pseudo-first order reaction kinetics. The combination of UV and persulfate (UV/PS) could completely degrade 100 μg/L of METH in 30 min with a PS dosage of 200 μM at pH 7. Both hydroxyl radical (OH) and sulfate radical (SO4−) were confirmed to contribute to the degradation of METH. The bimolecular reaction rate constants of METH with OH and SO4− were 7.91 × 109 and 3.29 × 109 M−1 s−1, respectively. The degradation rate constant of METH was proportional to the PS dosage (0–800 μM) and was high at neutral pH condition. The presence of inorganic anions significantly reduced METH degradation to different degrees, with the inhibitory effect order of Cl− > NO3− > HCO3−. The degradation efficiency of METH was suppressed by the presence of humic acid due to the effect of UV absorption and free radical quenching. The degradation intermediates and products were identified by UPLC-MS/MS and possible transformation pathways were proposed. Results suggested that the combination of UV/PS is a promising treatment technique for the removal of METH in the water environment.

Degradation of nitrilotris-methylenephosphonic acid (NTMP) antiscalant via persulfate photolysis: Implications on desalination concentrate treatment

Nitrilotris-methylenephosphonic acid (NTMP) has been widely used as an antiscalant in reverse osmosis (RO) desalination and other industrial processes to inhibit scaling from calcium and other hardness ions. Removal of NTMP from RO concentrate can induce the precipitation of oversaturated scale-forming substances, enable additional water recovery from RO concentrate, and reduce the risk of eutrophication after brine disposal. This study investigated the kinetics and mechanisms of oxidative degradation of NTMP by UV photolysis of persulfate at 254 nm. Results showed that NTMP was effectively degraded by persulfate photolysis and the reaction followed pseudo first-order kinetics. The degradation of NTMP was favorable at circumneutral pHs but significantly inhibited in highly alkaline conditions (e.g., pH of 11.5), mainly due to the reduced concentration of SO4•−. Using a competition reaction kinetics approach, the second-order rate constants of NTMP with SO4•− and HO• were determined to be (2.9 ± 0.6) × 107 M−1s−1 and (1.1 ± 0.1) × 108 M−1s−1, respectively. SO4•− had a predominant contribution to NTMP degradation (62%–95%), because the steady-state concentration of SO4•− was 11–54 times higher than that of HO• at pHs between 4 and 11.5. NTMP degradation rate increased with an increase in persulfate dosage and a decrease in NTMP concentration. In the real RO concentrate, NTMP degradation rate was impacted by the presence of chloride and bicarbonate. The degradation of NTMP started with the cleavage of C–N bonds, and then generated intermediates including iminodi(methylene)phosphonate, hydroxymethylphosphonic acid and aminotris(methylenephosphonic acid), which were eventually mineralized into ammonia, phosphate and carbon dioxide. This study demonstrated that UV/persulfate is a promising technology to remove phosphonate antiscalants from RO concentrate.

Hydroxylamine promoted Fe(III)/Fe(II) cycle on ilmenite surface to enhance persulfate catalytic activation and aqueous pharmaceutical ibuprofen degradation

This study demonstrates a new system for the degradation of emerging pharmaceutical contaminants (e.g., ibuprofen) in water by coupling the naturally occurring ilmenite with hydroxylamine (HA) and persulfate (PS). Ilmenite was able to activate persulfate to generate sulfate radicals (SO4−·) and hydroxyl radicals (HO·). The radical generation was greatly improved by adding small amount of hydroxylamine into the solution, due to the efficient Fe(III)/Fe(II) cycle on the ilmenite surface promoted by HA, which was confirmed by X-ray photoelectron spectroscopy and electron paramagnetic resonance (EPR) spectroscopy analysis. SO4−· and HO· contributed comparably to ibuprofen degradation, which was verified by the radical scavenging tests. The degradation was enhanced with increasing ilmenite, PS and HA dosages, but the HA exhibited strong scavenging effect at its high concentrations. The ilmenite/PS/HA process worked well in the real treated wastewater, because the surface-controlled radical generation was less affected by the water matrix. However, the formation of bromate in the bromide-containing water by this process should be concerned. Ibuprofen was partially mineralized, and the degradation products were identified by ESI-tqMS. A radical-induced degradation pathway was proposed based on the product identification. This work provides the mechanistic insights on persulfate activation based on the surface-controlled catalytic processes. It also offers a new strategy to degrade emerging contaminants in water and sheds light on the environmental functions of natural minerals.

DBP alteration from NOM and model compounds after UV/persulfate treatment with post chlorination

The UV/persulfate process is an effective advanced oxidation process (AOP) for the abatement of a variety of micropollutants via producing sulfate radicals (SO4•-). However, when this technology is used to reduce target pollutants, the precursors of disinfection byproducts (DBPs), such as natural organic matter (NOM) and organic nitrogen compounds, can be altered. This study systematically investigated the DBP formation from NOM and five model compounds after UV/H2O2 and UV/persulfate treatments followed with 24 h chlorination. Compared to chlorination alone, the yields of trichloromethane (TCM) and dichloroacetonitrile (DCAN) from NOM decreased by 50% and 54%, respectively, after UV/persulfate treatment followed with chlorination, whereas those of chloral hydrate (CH), 1,1,1-trichloropropanone (1,1,1-TCP) and trichloronitromethane (TCNM) increased by 217%, 136%, and 153%, respectively. The effect of UV/H2O2 treatment on DBP formation shared a similar trend to that of UV/persulfate treatment, but the DBP formation was higher from the former. As the UV/persulfate treatment time prolonged or the persulfate dosage increased, the formation of TCM and DCAN continuously decreased, while that of CH, 1,1,1-TCP and TCNM presented an increasing and then decreasing pattern. SO4•- activated benzoic acid (BA) to form phenolic compounds that enhanced the formation of TCM and CH, while it deactivated resorcinol to decrease the formation of TCM. SO4•- reacted with aliphatic amines such as methylamine (MA) and dimethylamine (DMA) to form nitro groups, which significantly increased the formation of TCNM in post chlorination, and the rate was determined to be higher than that of HO•. This study illuminated the diverse impacts of the structures of the precursors on DBP formation after UV/persulfate treatment, and DBP alteration depended on the reactivity between SO4•- and specific precursor.

Ofloxacin degradation over Cu–Ce tyre carbon catalysts by the microwave assisted persulfate process

In this study, the degradation of ofloxacin (OFX) over Cu–Ce tyre carbon catalysts by the microwave assisted persulfate process was examined for the first time. The results showed that the Cu–Ce tyre carbon catalysts dramatically improved OFX decay efficiency. The optimal reaction conditions were the Cu–Ce tyre carbon catalysts of 2.0 g/L and the persulfate dosage of 12.0 g/L under microwave power of 400 W at 60 °C. The OFX conversion and total organic carbon (TOC) removal reached 95.8% and 87.6%, respectively, after 60 min catalytic oxidation under optimal conditions. To identify the properties of Cu–Ce tyre carbon catalyst, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), the Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and the ultraviolet–visible (UV–vis) diffuse reflectance spectra studies have been carried out. Eleven kinds of degradation products and five pathways during degradation process of OFX and degradation products were identified by GC–MS and HRMS.

UV-activated persulfate oxidation of sulfamethoxypyridazine: Kinetics, degradation pathways and impact on DBP formation during subsequent chlorination

The kinetics and mechanisms of the degradation of sulfamethoxypyridazine (SMP) by an ultraviolet-activated persulfate (UV/PS) advanced oxidation process (AOP) and the formation of disinfection byproducts (DBPs) during subsequent chlorination were investigated in this study. The UV/PS process can significantly remove SMP through pseudo-first-order reaction kinetics. In a competitive kinetic experiment, the second-order rate constant of SMP with sulfate radical was determined to be 2.73 × 1010 M−1 s−1, while that with hydroxyl radical was 2.22 × 1010 M−1 s−1. Six major transformation products in SMP degradation were recognized by LC/MS/MS analysis. It was assumed that the degradation pathway of SMP involves the hydroxylation of the aromatic ring, cleavage of the sulfonamide bond, oxidation of the aniline moiety and elimination of SO2. The impacts of persulfate dose, pH, anions (HCO3–, SO42−, and Br−) and humic acid (HA) concentration on SMP degradation efficiency and DBP formation during subsequent chlorination were also examined. SMP degradation was accelerated with increasing persulfate dose, HCO3– and Br- concentration as well as decreasing pH and HA concentration. However, the amount of chloroform (CF) formed was reduced under a higher persulfate dosage and lower pH. In contrast, the amount of dichloroacetonitrile (DCAN) formed was enhanced under a higher persulfate dose and lower pH. Adding HA also increased the formation of both CF and DCAN. While, both HCO3– and SO42– had little effects on the formation of CF and DCAN. The presence of Br– had no significant effects on the bromine incorporation factors (BIFs) of trihalomethanes (THMs) and dihaloacetonitriles (DHANs). Raw water experiments showed that the UV/PS process could destroy SMP in natural water as well as control the formation of DBPs.

Enhanced removal of benzothiazole in persulfate promoted wet air oxidation via degradation and synchronous polymerization

Wet air oxidation (WAO) has an obvious advantage in treating wastewater with high concentration of organics, but harsh reaction conditions are required and the treatment efficiency has not reached a satisfactory level. Herein, we developed a low dosage of persulfate promoted WAO process (PWAO) to remove a model heterocyclic pollutant benzothiazole (BTH). The addition of persulfate remarkably enhanced the elimination of benzothiazole (BTH) and COD from water via degradation and polymerization. Under optimized operation condition (with 11.1 mM K2S2O8 addition into WAO), about 65.0% of BTH converted into microsphere polymers and more than 94.6% COD was eliminated from water after polymers separation. Electron paramagnetic resonance (EPR) analysis and quenching experiments revealed that OH was effectively generated in a wide range of reaction temperature and it played the key role in BTH degradation and polymerization, while SO4− was detected at low temperature for its fast decomposition at high temperature. Quantum chemical calculation together with ultra-performance liquid chromatography with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS) analysis confirmed that the degradation and polymerization of BTH mainly started from the heterocyclic ring, followed by further oxidation or polymerization. Comparing with normal WAO process, the PWAO technology had an advantage in lower operating cost in removing per unit COD and carbon resource recycle, which indicates a promising prospect in treating wastewater with high concentration of heterocyclic compounds.

Photo-Fenton like Catalyst System: Activated Carbon/CoFe2O4 Nanocomposite for Reactive Dye Removal from Textile Wastewater

The removal of dye from textile industry wastewater using a photo-Fenton like catalyst system was investigated wherein the removal efficiency of phenol and chemical oxygen demand (COD) was studied by varying various parameters of pH (3–11), reaction time (1–50 min), activated Carbon/CoFe2O4 (AC/CFO) nanocomposite dosage (0.1–0.9 g/L), and persulfate amount (1–9 mM/L). The highest removal rates of reactive red 198 and COD were found to be 100% and 98%, respectively, for real wastewater under the optimal conditions of pH = 6.5, AC/CFO nanocomposite dosage (0.3 g/L), reaction time, 25 min, and persulfate dose of 5 mM/L up on constant UV light irradiation (30 W) at ambient room temperature. The result showed that this system is a viable and highly efficient remediation protocol relative to other advanced oxidation processes; inexpensive nature, the ease of operation, use of earth-abundant materials, and reusability for removal of organic pollutants being the salient attributes.

Synergistic Effect of Photocatalytic Degradation of Hexabromocyclododecane in Water by UV/TiO2/persulfate

In this work, the elimination of hexabromocyclododecane (HBCD) is explored by using photodegradation of the UV/TiO2 system, the UV/potassium persulfate (KPS) system, and the homo/heterogeneous UV/TiO2/KPS system. The experimental results show that the dosages of TiO2 and potassium persulfate have optimum values to increase the degradation degree. HBCD can be almost completely degraded and 74.3% of the total bromine content is achieved in the UV/TiO2/KPS homo/heterogeneous photocatalysis, much more than in the UV/persulfate system and the UV/TiO2 system. Roles of radicals SO4•− and OH• in the photocatalysis systems are discussed based on experimental measurements. The high yield of the concentration of bromide ions and decreased pH value indicates that synergistic effects exist in the UV/TiO2/KPS homo/heterogeneous photocatalysis, which can mineralize HBCD into inorganic small molecules like carboxylic acids, CO2 and H2O, thus much less intermediates are formed. The possible pathways of degradation of HBCD in the UV/TiO2/KPS system were also analyzed by GC/MS. This work will have practical application potential in the fields of pollution control and environmental management.

Effect of sodium persulfate as electron acceptor on antipyrine degradation by solar TiO2 or TiO2/rGO photocatalysis

In this work, a comparative study of solar photocatalytic degradation of the pharmaceutical compound antipyrine, AP, was completed. Different systems such as TiO2 alone, TiO2 modified with reduced graphene oxide (TiO2/rGO), TiO2/rGO with adddition of persulfate (TiO2/rGO/PS), and TiO2/PS were used. The catalysts characterization was carried out by X-ray diffraction, N2 physisorption, transmission electron microscopy (TEM) and Raman spectroscopy. Initially for both TiO2 and TiO2/rGO composites, the AP adsorption kinetics was evaluated above and below their pHZPC. Then, the influences of different variables such as pH, TiO2 concentration, rGO load, and persulfate dosage on antipyrine solar photocatalytic degradation were determined. The solar/TiO2/PS system was found to be more efficient than the solar/TiO2/rGO/PS process. Antipyrine was completely degraded in less than 4 min, and 87% of the total organic carbon (TOC) was removed in 15 min under optimal conditions. Finally, the roles played by different reactive oxygen species, ROS, such as HO, O2− and 1O2, in the solar/TiO2/PS system were evaluated using appropriated scavengers.

Re-evaluation of sulfate radical based–advanced oxidation processes (SR-AOPs) for treatment of raw municipal landfill leachate

Sulfate radical (SO4-) -based advanced oxidation processes (SR-AOPs) have proven effective for simultaneously removing refractory dissolved organic matter (DOM) and ammonia in municipal landfill leachates. However, the knowledge on the competition of leachate DOM and ammonia for SO4-, the utilization efficiency of persulfate, as well as the reaction pathways and final products of ammonia oxidation during the SR-AOP treatment remains little known, thereby leading to a lack of a comprehensive evaluation of the emerging leachate treatment technology. The objective of this study was to further investigate the performance of a thermally activated persulfate system for treatment of a mature landfill leachate and re-evaluate the benefits and restrictions of SR-AOPs for leachate treatment. The laboratory experimental results showed that removal patterns of chemical oxygen demand (COD) and ammonia relied heavily upon the dose of persulfate that could be thermally activated to produce reactive sulfate radicals, reflecting the competition of leachate DOM, ammonia, and non-target leachate constituents for SO4-. The utilization efficiency of the added persulfate could be more efficiently utilized for removing the two target leachate pollutants at a lower persulfate dose, whereas more persulfate was wasted due to the reactions with non-target leachate constituents (e.g. Cl− and CO32−) and/or self-decomposition with the increasing persulfate dose. During the treatment, ammonia was oxidized, via the direct attack of SO4- and/or by molecular chlorine produced from the reactions of chloride and sulfate radicals, into nitrate and nitrogen gas, while nitrite was not detected. Of importance, this study highlighted three potentially negative impacts of SR-AOPs on the quality of treated leachate, including accumulation of total dissolved solids, the production of undesirable nitrate, and the pH decrease due to the continuous formation of hydrochloric acid. Therefore, the three issues should be carefully evaluated when a SR-AOP is selected for leachate treatment. Because these impacts become less pronounced with a decreasing persulfate dose, SR-AOPs as a pre-treatment, which is achieved at a relatively low persulfate dose, may be an appropriate option for the SR-AOP application to leachate treatment.

A new study on photocatalytic degradation of meropenem and ceftriaxone antibiotics based on sulfate radicals: Influential factors, biodegradability, mineralization approach

The removal of meropenem and ceftriaxone antibiotics from solution, as first study, was performed in a photo-Fenton process in which UV light and ferrous ions (Fe2+) were applied as persulfate (PS) activators. The batch tests were performed in various conditions like pH of aqueous solution (2−10), amounts of ferrous (0.1–0.5 g/L), initial antibiotic concentrations (20–100 mg/L), persulfate dosages (1–5 mM), UV light intensities (4, 6 and 8 W), temperatures (20, 35 and 50 °C) and scavengers (TBA and IBA). Based on the results of comparative studies, PS/Fe2+/UV system showed the highest ability to remove both antibiotics, in comparison with the other processes (i.e., UV, PS, PS/UV and PS/Fe2+). In addition, the removal rate of antibiotics has a direct relationship with the iron and PS concentrations, UV light intensity and temperature. While, increasing pH of solution and initial antibiotic concentrations, the removal rate of antibiotics witnessed a significant decline. Quenching tests indicated that sulfate radicals had a dominant species during degradation reactions. The mineralization higher than >54% was obtained for both antibiotics. A slight loss was observed in the degradation efficiencies of antibiotics in binary system, compared to the single one. The experimental data were in good agreement with pseudo-first-order kinetic model. Biodegradability indices were enhanced significantly after treatment, which demonstrates that PS/Fe2+/UV system has a high ability in removing organic matters effectively. Finally, it can be inferred that the integration of ferrous ions and UV irradiations was an appropriate technique for efficient activation of PS, which can be introduced as a promising method to remove high concentrations of antibiotics in a real wastewater sample which shows its high feasibility in natural environment.

Efficient Heterogeneous Activation of Persulfate by Iron-Modified Biochar for Removal of Antibiotic from Aqueous Solution: A Case Study of Tetracycline Removal

Waste reutilization is always highly desired in the environmental engineering and science community. In this study, Fe-SCG biochar was functionalized by modifying spent coffee grounds (SCG) with magnetite (Fe3+) at 700 °C and applied for the oxidative removal of tetracycline (TC) with the presence of persulfate (PS). The effects of pH, dosage of biochar and sodium persulfate and initial TC concentration on TC degradation were investigated in a batch system. Our results show that higher TC degradation efficiency was obtained at low pH, low initial TC concentration, and at high dosages of PS and biochar. The highest removal efficiency (96%) was achieved by Fe-SCG/PS under the conditions of pH = 2.0, [Fe-SCG] = 2.5 g/L, [PS] = 60 mM and [TC] = 1 mM. The proposed Fe-SCG catalyst could be a promising effective biochar for the remediation of other emerging organic contaminants.

Study of O3/S2O82- Advanced Oxidation Processes (AOPs) for Removal of Dye Industrial Effluents

This research was carried out to study the efficiency of O3/S2O82- system in removal of Reactive Red 120 (RR120) dye sample. Different operating parameter such as pH, initial dye concentration and persulfate dosage were studied to evaluate the performance on removing colour and COD. The removal of colour and COD achieved higher efficiency at pH 7, 100 mg/L of initial dye concentration and persulfate dosage of 5 g S2O82-/1 g RR120. O3/S2O82- with the most effective conditions experienced effective decolourization and degradation of organic pollutants than O3 only. Furthermore, it achieved faster breakdown of azo bond and aromatic groups than O3 after treatment as observed with UV-Vis absorption spectra. The FT-IR analysis obtained new absorption peak that represents alkenes after 20 min of O3 treatment whereas mostly of the absorption bands of O3/S2O82- flattened.

Insights into removal of tetracycline by persulfate activation with peanut shell biochar coupled with amorphous Cu-doped FeOOH composite in aqueous solution

Peanut shell biochar (BC) supported on Cu-doped FeOOH composite (Cu-FeOOH/BC) was synthesized using a facile and scalable method. The Cu-FeOOH/BC samples were characterized by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), scanning electron microscopy equipped with an energy-dispersive spectrometer (SEM-EDS), x-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) techniques. Novel catalytic composites with different Cu/Fe molar ratios were compared systematically by activating persulfate (PS) for the tetracycline (TC) degradation. 0.5Cu-1FeOOH/BC (Cu/Fe molar ratio = 0.5:1) was confirmed as the optimum activation material and the removal of TC reached 98.0% after 120min by combining with 20mM PS at pH 7.0 and 25°C. The influencing factors including catalyst loading, PS dosage, water matrix species, and pH on the performance system of 0.5Cu-1FeOOH/BC-PS were investigated, respectively. Reaction rate constants (Kobs) on catalyst dosages (0.05, 0.10, 0.20, and 0.30gL-1) were 0.0072, 0.0101, 0.0244, and 0.0144min-1, and 0.0090, 0.0146, 0.0244, and 0.0178min-1 for the change of PS concentrations (5, 10, 20, and 30mM), which indicated that increasing the concentrations of catalyst and PS appropriately improved TC degradation, but excessive dosages inhibited the reaction process of TC removal. The TC removal rate was inhibited by inorganic anions with the following order of HCO3- > Cl- > HPO42- > SO42- > NO3-. Free radical quenching and capture experiments under different pH values revealed that sulfate radicals existed predominantly in acidic conditions and hydroxyl radicals in alkaline conditions. The catalyst showed an excellent recyclability and stability and the removal efficiency of TC still remained over 90% after five consecutive uses. To conclude, coupling of 0.5Cu-1FeOOH/BC and PS can be successfully applied as an effective and stable technique for the treatment of refractory organic pollutants in wastewater.

Degradation kinetic of phthalate esters and the formation of brominated byproducts in heat-activated persulfate system

The degradation kinetics of two phthalate esters (PAEs) (i.e., diethyl phthalate (DEP) and dibutyl phthalate (DBP)) in heat-activated persulfate (PS) system were studied and followed pseudo-first-order kinetics. Results demonstrated that both sulfate radical (SO4-·) and hydroxyl radical (HO) were responsible for degrading DEP and DBP. The pseudo-first-order rate constant (kobs) enhanced remarkably as reaction temperature and PS dosages increased, while it decreased as the initial PAEs concentrations increased. Lower pH values promoted the degradation over the pH range chosen here (5.0–8.0). Natural organic matter (NOM) and HCO3- showed inhibitory effects on PAEs degradation by quenching SO4-· and HO. At any pH value studied here, Cl− enhanced PAEs degradation at lower concentrations while it suppressed degradation as Cl− concentration further increased. The coexisting Br− hindered the degradation of PAEs mainly by suppressing SO4-·. Significant formation of dibromoacetonitrile (DBAN) and bromoform (TBM) was verified with Br− and NOM in the degradation system, while only TBM was detected without NOM. Bromate was also detected in the Br− containing degradation system. Generally, NOM facilitated the formation of brominated disinfection byproducts (Br-DBPs), while it suppressed the generation of bromate. Additionally, it is noteworthy that the degradation efficiency of DBP was higher than that of DEP probably owing to the longer alkyl side chain of DBP. The DBP degradation system was observed to form slightly more Br-DBPs than DEP, while bromate had an opposite trend. Besides, the potential initial degradation pathways of DEP and DBP were discussed by the computational analysis.

Pretreatment of landfill leachate in near-neutral pH condition by persulfate activated Fe-C micro-electrolysis system

In this study, a novel persulfate combined with iron-carbon microelectrolysis (PS-ICME) system was explored to pretreat the landfill leachate. In the static batch experiments, response surface methodology (RSM) was used to determine the relationship between three independent variables (pH, the ratio of iron to carbon (Fe-C ratio), persulfate dosage) and response values (Chemical oxygen demand (COD) removal efficiency). Experimental results showed that the COD removal efficiency reached to 62.91% under the optimal conditions: initial pH 7, Fe-C ratio 3, and persulfate dosage 85 mM. The dissolved organic matter (DOM) in landfill leachate was characterized by three-dimensional excitation-emission matrix spectroscopy (3D-EEMs). Combined with electron spin resonance (ESR) spectrum investigation, the enhanced mechanism for landfill leachate pretreated by PS-ICE in near-neutral pH was elucidated. In the column continuous flow experiment, it had been confirmed that dissolved oxygen plays an important role in the PS-ICME system. Based on the above conclusions, PS-ICME system has a satisfactory performance on pretreatment of landfill leachate.

Effective degradation of fenitrothion by zero-valent iron powder (Fe0) activated persulfate in aqueous solution: Kinetic study and product identification

Fenitrothion (FNT), a common organophosphorus pesticide, has been regarded as a contaminant because it is adverse to the environment. In this study, we chose the highly effective technique, persulfate (PS) activation by zero-valent iron powder (Fe0), to degrade FNT. The effects of several experimental parameters including PS and Fe0 dosages, pH, temperature, and common natural water constituents were systematically investigated via kinetics studies. We found that the addition of Fe0 significantly enhanced the FNT degradation by PS under any of the studied conditions. Under the optimal conditions of [FNT]:[PS] = 1:500 (molar ratio), Fe0:PS = 1:1.5 (molar ratio), pH = 3.0, and 35 °C, 10 mg L−1 of FNT could be completely degraded in 45 min and 20 μg L−1 FNT was removed 96 ± 0% in 12 h. Sulfate (SO4−) radicals led the degradation of FNT in the Fe0/PS system. Twelve transformation products of FNT were determined by LC-MS/MS analysis, and the vulnerable sites in FNT were predicted by a density-functional-theory-based descriptor, 2∑(CriHOMO)2, to illustrate the generation of initial reaction products. The overall acute and chronic toxicity of FNT and its products, as predicted by the ecological structure–activity relationship model (ECOSAR), decreased in the Fe0/PS process. The present work proves that FNT could be efficiently degraded by Fe0-activated PS, which may also contribute to future research on the removal of other organophosphorus pesticides.

Rapid degradation of tetrabromobisphenol A under the UV/TiO2/KPS systems in alkaline aqueous solutions

In this study, rapid degradation of Tetrabromobisphenol A (TBBPA) is explored by using photocatalysis of homo/heterogeneous UV/TiO2/potassium persulfate (KPS) systems in alkaline solutions. The experimental results show increasing pH values and decreasing the initial concentration of TBBPA could increase the degradation degree, while the loading amount of TiO2 and dosage of potassium persulfate have optimum values to increase the degradation degree. TBBPA can be almost completely degraded and 70% of TOC removal efficiency is achieved in the UV/TiO2/KPS homo/heterogeneous photocatalysis, much more than the UV/KPS system and UV/TiO2 system. Roles of radicals $$\text{SO}_{\text{4}}^{ \cdot - }$$ and OH· in the photocatalysis systems are discussed based on experimental measurements. The significant TOC removal efficiency and increased bromide ion concentration yield show that there exist synergistic effects in the UV/TiO2/KPS homo/heterogeneous photocatalysis, which can mineralize TBBPA into inorganic small molecules relatively thoroughly, thus much less intermediates are formed in the UV/TiO2/KPS homo/heterogeneous photocatalysis.