Activated Persulfate Oxidation Research Articles

Enhanced adsorption of tylosin by ordered multistage porous carbon and efficient in-situ regeneration of saturated adsorbents by activated persulfate oxidation: Performance, mechanism and multiple cycles

In this study, a novel ordered multistage porous carbon (OMPC) with a micro-mesoporous structure was prepared and used for the removal of tylosin (TYL). The porous material, carbonized at 900 °C (OMPC-900), exhibited micro-mesoporous structures with pore sizes of 0.71 nm and 3.63 nm, while had a specific surface area of 1300.02 m2 g−1. OMPC-900 demonstrated a maximum adsorption capacity of 341.28 mg g−1 for TYL in water by electrostatic attraction, hydrogen bonding, π-π interactions, and pore-filling mechanisms, which is 6.41 times higher than that of activated carbon. The TYL-saturated adsorbents could be efficiently regenerated by in-situ oxidation through the activation of persulfate (PDS), achieving a regeneration rate of 94.17%, significantly higher than that of activated carbon (55.22%). The excellent regeneration performance may be attributed to the presence of -C=O and graphitic carbon in the adsorbent, which promotes the production of free radicals (•OH, SO4•- and •O2−) and non-free radicals. Among these, the non-radical pathways (1O2 and electron transfer) played a key role in the degradation of TYL loaded on the adsorbent. OMPC-900 maintained stable regenerative adsorption performance of 80.85% after five in-situ regeneration, and the normalized adsorption capacity per unit surface area increased from 0.21 to 0.39 mg m−2, which may be due to that the increase in oxygen-carbon ratio and surface defects improved the adsorption sites activity of the regenerated adsorbent. In comparison to conventional pyrolysis and organic solvent elution, oxidative regeneration through the activation of PDS is a more efficient and sustainable method.

Phenolic compounds, chemical oxygen demand and total carbon organic removal from olive mill wastewater by activated persulfate oxidation using full factorial design

Abstract This study investigated phenolic compounds (PC), chemical oxygen demand (COD) and total carbon organic total (TOC) removal from olive mill wastewater OMW via activated persulfate oxidation. Persulfate (PS, S 2 O 8 2 − ${\mathrm{S}}_{2}{\mathrm{O}}_{8}^{2-}$ ) was activated by thermal and transition metal to form sulfate radical ( S O 4 · − $\mathrm{S}{\mathrm{O}}_{4}^{{\cdot}-}$ ). A mathematical model was developed, and the process variables, namely oxidant dose (0.05 and 0.1 g L−1), type of catalyst (Fe2+, Cu2+), time of treatment (5 and 20 min) and temperature (25 and 45 °C) and their interaction were examined using a full factorial design methodology 24. The results indicated that activation methods are efficient for reduction of PC and COD in OMW. Under conditions maximizing responses, there was a considerable increase in PC, COD and TOC removal (44.73 %, 62.39 % and 95.13 % respectively). The correlation coefficient values of the polynomial model were found to be 90 % (CP removal) and 86 % (COD removal). The predicted values obtained using the response functions agreed well with the experimental data.

Unexpectedly enhanced degradation of acetaminophen by sulfoxides probe in Fe(II)-activated persulfate oxidation: The mechanism and the selectivity

Sulfoxides are widely recognized as probes for identifying and evaluating the generation and contribution of high-valent metals in advanced oxidation processes. However, this paper was surprising to find that the presence of sulfoxides selectively enhanced the degradation of specific pollutants in the Fe(II)/PS system. Represented by methyl phenyl sulfoxide (PMSO), scavenging experiments for active species showed that the presence of PMSO transformed the mechanism from radical dominated (55.60 %) to nonradical dominated (60.91 %), greatly improving the anti-interference ability of the system. Determining the concentration of Fe(Ⅱ) and total iron (Fetot) in solution revealed that the presence of PMSO improved the utilization efficiency of Fe(II) and PS by enhancing the redox reaction between Fe(II) and PS, and resulted in the generation of Fe(IV) more favorably than the generation of SO4·− and ·OH. Additionally, comparing the proven high-valent iron dominated Fe(II)/PI system with the free radical dominated Fe(II)/PS system of this paper, it was revealed that the selectively enhanced oxidation of PMSO specifically targets the free radical dominated system. Experiments have shown that the degradation of acetaminophen, ibuprofen, phenol, and p-chlorophenol was enhanced by PMSO, while the degradation of norfloxacin, primidone, chloramphenicol, sulfamethoxazole, p-nitrophenol, benzoic acid, and nitrobenzene was inhibited. Based on density functional theory (DFT) calculations, PMSO has a selectively enhanced degradation effect for organic pollutants with ionization potential (IP) below 8.66 eV, and vice versa, it has an inhibitory effect. The present study provides new insights into the contribution of sulfoxide to the assessment of high-valent metals and sheds new light on the mechanism of active species.

Simultaneous removal of antibiotic resistance genes and improved dewatering ability of waste activated sludge by Fe(II)-activated persulfate oxidation

Waste activated sludge properties vary widely with different regions due to the difference in living standards and geographical distribution, making a big challenge to developing a universally effective sludge dewatering technique. The Fe(II)-activated persulfate (S2O82−) oxidation process shows excellent ability to disrupt sludge cells and extracellular polymeric substances (EPS), and release bound water from sludge flocs. In this study, the discrepancies in the physicochemical characteristics of sludge samples from seven representative cities in China (e.g., dewaterability, EPS composition, surface charge, microbial community, relative abundance of antibiotic resistance genes (ARGs), etc.) were investigated, and the role of Fe(II)-S2O82− oxidation in enhancing removal of antibiotic resistance genes and dewatering ability were explored. The results showed significant differences between the EPS distribution and chemical composition of sludge samples due to different treatment processes, effluent sources, and regions. The Fe(II)-S2O82− oxidation pretreatment had a good enhancement of sludge dewatering capacity (up to 76 %). Microbial analysis showed that the microbial community in each sludge varied significantly depending on the types of wastewater, the wastewater treatment processes, and the regions, but Fe(II)-S2O82− oxidation was able to attack and rupture the sludge zoogloea indiscriminately. Genetic analysis further showed that a considerable number of ARGs were detected in all of these sludge samples and that Fe(II)-S2O82− oxidation was effective in removing ARGs by higher than 90 %. The highly active radicals (e.g., SO4−·, ·OH) produced in this process caused drastic damage to sludge microbial cells and DNA stability while liberating the EPS/cell-bound water. Co-occurrence network analysis highlighted a positive correlation between population distribution and ARGs abundance, while variations in microbial communities were linked to regional differences in living standards and level of economic development. Despite these variations, the Fe(II)-S2O82− oxidation consistently achieved excellent performance in both ARGs removal and sludge dewatering. The significant modularity of associations between different microbial communities also confirms its ability to reduce horizontal gene transfer (HGT) by scavenging microbes.

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.

Remediation of PAHs contaminated soil enhanced by nano-zero-valent iron combined with white rot fungi Peniophora incarnata

Polycyclic aromatic hydrocarbons (PAHs) are hazardous organic contaminants commonly found in soils. This study investigated an integrated remediation approach combining white rot fungal augmentation and nano-zero-valent iron (nZVI) activated persulfate oxidation to enhance the degradation of PAHs in soil. The white rot fungus Peniophora incarnata demonstrated efficient degradation of lower molecular weight PAHs including phenanthrene (91% removal) and anthracene (71% removal) in liquid culture, but had limited degradation of high molecular weight benzo[a]pyrene (35% removal). Inoculation of P. incarnata in non-sterilized soil led to 54% phenanthrene and 46% anthracene removal after 42 days. Co-inoculation with Pseudomonas aeruginosa slightly improved the degradation by 15% and 13%, respectively. However, benzo[a]pyrene removal was negligible through bioremediation alone. Direct nZVI/persulfate oxidation removed 55–75% of lower molecular weight PAHs and 68% of benzo[a]pyrene in soil. Integrated treatment combining nZVI/persulfate oxidation followed by P. incarnata inoculation resulted in 92–96% degradation of phenanthrene, anthracene and benzo[a]pyrene after 42 days, which was significantly higher than either approach alone. The enhanced PAH removal was attributed to the coupled effects of chemical oxidation and microbial degradation. P. aeruginosa is capable of directly metabolizing and mineralizing lower molecular weight PAHs such as phenanthrene and anthracene. The presence of this additional PAH-degrading bacterium likely contributed to the increased degradation observed. Overall, the sequential nZVI/persulfate and fungal treatment provides an effective and sustainable option for remediating soils co-contaminated with PAHs and other persistent organics. Further research should optimize treatment parameters and evaluate long-term impacts on soil quality.

Application Potential of Layered Double Hydroxides for The Treatment of Persistent Organic Pollutants

Layered double hydroxides (LDHs) is a widely used emerging material. With its adjustable composition, other ions or materials can be incorporated on the surface or in the layer to synthesize modified materials with stronger ability to capture target pollutants. Persistent organic pollutants (POPs) exist in air, water and soil for a long time, which not only affect the ecosystem and ecological balance, but also endanger human health. Therefore, it is of great significance to study the application potential of LDHs in the treatment of POPs. The removal mechanism of persistent organic pollutants by LDHs includes adsorption and activated persulfate oxidation. The factors affecting the removal of POPs by LDHs include the characteristics of LDHs itself (including the inherent characteristics of composition, structure, morphology, etc.), coexisting substrates, temperature, etc.

Enhanced disintegration mechanism of surplus activated sludge to improve dewatering by thermally activated persulfate oxidation under mild temperature.

The dewatering treatment is an essential process for the treatment and disposal of surplus activated sludge (SAS), and improving sludge dewatering performance is still a challenge and has become a research hotspot in recent years. The oxidation and disintegration of bacterial cells and extracellular polymeric substances (EPS) by active radicals produced by advanced oxidation processes (AOPs) were extremely promising to achieve deep sludge dewatering. This paper systematically studied the efficiency and mechanism of thermally activated persulfate (TAP) oxidation technology to the improvement of SAS dewatering performance. The results showed that the relative filterability (CST0/CST) was increased 2.52 times with 2.0 mmol/g VSS potassium peroxydisulfate (PDS) at 80 °C in 90 min. Under this condition, the Zeta potential of SAS significantly decreased from - 14.8 to - 1.44 mV, while the average particle size (dp50) decreased from 52.981 to 48.259 μm. Thermal treatment disrupted the sludge structure to release large amounts of EPS including polysaccharides and protein. Meanwhile, the results of three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectra showed that the TAP treatment could expedite the disintegration of sludge, facilitating the decrease of total EPS content and conversion of tightly bound EPS (TB-EPS) to loosely bound EPS (LB-EPS) and soluble EPS (S-EPS). The mechanism of TAP process to improve SAS dewatering performance was revealed, which could contribute to breaking the bottleneck of sludge depth dewatering and provide a theoretical and technical basis for its practical application.

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.

Aniline degradation and As (III) oxidation and immobilization by thermally activated persulfate

In the Pearl River Delta of China, many sites are likely contaminated with aniline in the soil and arsenic (As) in the groundwater because of a high As background level and the prevailing printing and dyeing industry. This study is to explore the remediation performance of thermally activated persulfate oxidation for the sites with these two contaminants, aniline and As. The As influence on the aniline degradation and vice versa are also systematically investigated. When the molar ratio of aniline to persulfate is 1: 4.65, over 85% of aniline can be degraded at 40 °C in 24 h, and 100 μg L−1 As(III) in solution can be completely adsorbed by the soil. A higher pH favored the aniline degradation but disfavored the As(III) oxidation. Due to the strong buffer capacity of the soil, aniline in the soil could be more quickly degraded than those in the solution. The As(III), however, seem more easily oxidized in the absence of soil. The coexisting Fe2+ can substantially improve As(III) oxidation and immobilization, although the dilute Fe2+ solution may suppress the aniline degradation. The presence of aniline severely inhibited the As(III) oxidation and adsorption, likely due to the competition for the generated free radicals and the adsorption sites on the soils. In contrast, the existing As(III) has a slight effect on aniline degradation. These findings are believed to provide the theoretical basis for the remediation of aniline-arsenic contaminated sites.

Recent Advancements in the Treatment of Emerging Contaminants Using Activated Persulfate Oxidation Process

Emerging contaminants (ECs) usually refer to pesticides, polycyclic aromatic hydrocarbons (PAHs), dioxins, personal care products, cosmetics, and medications. Due to the strong demand and quick growth of these businesses, the ECs have continuously been found in alarming amounts in groundwater, surface water, and wastewater. These ECs provide a significant non-esthetic threat to the ecosystem as a whole and can cause significant non-esthetic contamination when released into the aquatic environment. The conventional wastewater treatment techniques such as activated sludge, membrane filtration, coagulation, adsorption, and ozonation showed ECs removal performance to a certain extent. In turn, numerous emerging advanced oxidation processes (AOPs), especially activated persulfate oxidation, have garnered a huge amount attention due to their outstanding performance in the remediation of ECs. This article presents a systematic and critical review of electro, sono and thermal activation of persulfate for the treatment of ECs. The effect of key parameters such as electrode materials, solution pH, persulfate concentration, current density, and temperature on electro, sono- and thermal-activated degradation of ECs was discussed. The possible reaction mechanism of ECs degradation was also elucidated in detail. It was closed with a note on the situation now and the future course of electro, sono and thermal activation in ECs degradation applications. Experiments performed in recent studies show that with the aid of persulfate in electro activation, the removal efficiency of chemical oxygen demand can be achieved up to 72.8%. Persulfate activated by sono shows 100% removal efficiency of 1,1,1-trichloroethane and sulfamethoxazole. While for thermal activation of persulfate, 100% removal efficiency of carbamazepine, atrazine and sulfamethazine was achieved. All these vital shreds of evidence are substantial enough to picture the negative impact of ECs on the environment.

UVA and goethite activated persulfate oxidation of landfill leachate

In this study, UVA and goethite activated persulfate oxidation was applied to treat a synthetic (SLL) and a real landfill leachate (RLL) spiked with sulfamethoxazole (SMX). Initially, SLL was used to find the optimum landfill leachate (LL) treatment conditions in terms of total organic carbon (TOC) and SMX removal. The screening experiments were conducted using a two-level, four-factor Plackett-Burman design (PBD) to investigate the effects of UVA irradiation, time, concentrations of persulfate (PS) and goethite, on the removal of TOC and SMX. Dark experiments (PS/Goethite) yielded only a 2% TOC removal. Therefore, further experiments were conducted under UVA (365 nm) using a three-factor Box-Behnken design (BBD) in conjunction with response surface methodology (RSM). Analysis of variance (ANOVA) indicated high regression coefficients for the BBD-RSM model in the case of TOC removal (R2 = 0.9755, adjusted R2 = 0.9314 and predicted R2 = 0.7956). In the case of SLL, RSM predicted an 84.4% TOC removal at the reaction time of 5.33 h, PS concentration of 477.4 mM, and goethite dosage of 755 mg/L under UVA. Experimentally, an 81.8% TOC removal and 100% removal of SMX were obtained under these conditions. Finally, the obtained optimum conditions were recalculated using RLL from the local municipal solid waste landfill, and 87% TOC and 100% SMX removals were obtained for PS concentration of 419.3 mM and goethite dosage of 663 mg/L after 4.68 h under UVA irradiation. Air stripping of RLL at pH 11 was complementarily applied to completely remove ammonia nitrogen after 3 hours. The results demonstrated the efficiency of the UVA/PS/Goethite system for the removal of organic matter from the LL for the first time.

Combination of zero-valent aluminum-acid system and electrochemically activated persulfate oxidation for biologically pre-treated leachate nanofiltration concentrate treatment

This study investigated the performance of combined zero-valent aluminum (ZVAl) and electrochemically activated persulfate (PS) oxidation for the leachate nanofiltration concentrate (NFC) treatment. Firstly, operating parameters in the ZVAl procedure were optimized and under the optimum conditions (ZVAl dose 1 g/L, initial pH 1.5) the removal efficiency of the chemical oxygen demand (COD), UV254, and color were 22.39%, 29.03%, and 48.26%, respectively. Secondly, the effect of various anode types (Ti/RuO2, Ti/IrO2, and Ti/SnO2) within the electrooxidation (EO) process was evaluated. The Ti/RuO2 anode was found to be the most effective one in terms of pollutant removal efficiencies and operation cost. The efficiency of single, binary, and hybrid processes was evaluated by control experiments and the results were ranked as PS < ZVAl < ZVAl + PS < EO < EO + PS < EO + ZVAl < EO + ZVAl + PS. In the following part of the study, the Box-Behnken design was preferred to optimize the operating parameters of the hybrid EO + ZVAl + PS process. The COD, UV254, and color removal efficiencies under optimum conditions (4.88 mM PS dose, 1.6 A current applied, and 120 min reaction time) were 62.1%, 75.2%, and 99.9%, respectively. The estimated and experimentally obtained data were close to each other. The pollutant removal efficiencies increased in parallel with the current density and reaction time; however, the effect of the PS dose remained at a negligible level. The obtained results indicate the effectiveness of the hybrid EO + ZVAl + PS process for the treatment of leachate nanofiltration concentrate under optimized conditions.

Impacts of anions on activated persulfate oxidation of Fe(II) - Rich potassium doped magnetic biochar

The potassium-doped magnetic biochar (KMBC) preparation was inevitably introduced the different anions in the process of modifying magnetic biochar (MBC) with different potassium salts, but the effect and mechanism of different anion on KMBC activation properties has not been reported. Therefore, in this paper, five different KMBCs were prepared using several common potassium salts under the same dosage of K+ and Fe2+, and then was added in the presence of persulfate (PS) for the removal of metronidazole (MNZ). The removal rate of metronidazole was ordered as KMBCK2SO4 (98.40%) > KMBCKNO3 (76.84%) > KMBCKCl (20.79%) > KMBCK2CO3 (19.02%) > KMBCK2C2O4 (14.23%). However, the semi-quantitative of Fe(II) experiments results confirmed that the effectively increase of Fe(II) content by potassium salts modification played the dominant role in improvement of KMBC activation performance. The Fe(II) content of KMBC were ordered as KMBCK2CO3 > KMBCK2SO4 > KMBCKNO3 > KMBCKCl > KMBCK2C2O4, with the Fe(II) content of KMBC of 36.74, 17.70, 8.79, 5.24 and 4.85 mg/g, respectively. The indicated that the introduction of different anions would lead to different optimal Fe(Ⅱ) content in KMBC modified with different potassium salts, which was most directly reflected in 1O2 content in different KMBC/PS systems, and account for the difference in MNZ degradation efficiency. Meanwhile, when the Fe(II) content in KMBC reached the range of 13.7–28.8 mg/g, KMBC had the better performance of activating PS.

Effects of nitrite on the degradation of carbamazepine by sulfate radical oxidation

Activated persulfate oxidation has been demonstrated to be a viable approach to degrade carbamazepine (CBZ). However, the influence of nitrite (NO2−) commonly found in wastewaters and groundwaters on the degradation remains unclear. Herein, we found that the presence of NO2− not only reduced the rate but substantially changed the pathway of CBZ degradation in a heat activated peroxydisulfate (heat/PDS) oxidation process. This was because of the scavenging of sulfate radical (SO4−) by NO2− and the formation of nitrogen dioxide radical (NO2). Acridine was identified as a key intermediate during CBZ degradation. In the presence of NO2−, acridine could be further transformed to nitrated derivatives. During this process, an N-centered acridine radical is the key intermediate which coupled with the NO2 originated from the oxidation of NO2−. Besides nitroacridines, several nitrophenols were identified as well. In contrast to the nitroacridines, the nitro group in these nitrophenols was derived from oxidation of the amine in the parent CBZ. Increasing the NO2− concentration increased the formation of nitroacridines but inhibited the formation of nitrophenols. Since nitroaromatic compounds are usually toxic and persistent, this study highlights the potential environmental risks when SO4− is applied to degrade CBZ in the presence of NO2−.

Thermally activated persulfate oxidation of ampicillin: Kinetics, transformation products and ecotoxicity

The heat-activated persulfate system showed encouraging results for the destruction of the widely used antibiotic Ampicillin (AMP). AMP removal follows exponential decay, and the observed kinetic constant was enhanced with persulfate (PS) dosage at the range 50–500 mg L−1 and temperature (40–60 °C), while AMP thermolysis at 60 °C was almost negligible. The apparent activation energy was estimated to 124.7 kJ mol−1. Alkaline conditions, water matrix constituents like bicarbonates, humic acid, and real water matrices retarded AMP oxidation. Experiments performed with tert-butanol and methanol as scavengers demonstrated the contribution of sulfate radicals as the dominant reactive species. Seven transformation products (TPs) of AMP have been identified from AMP destruction. An EC50 value equal to 187 mg L−1 was calculated for 72 h of exposure of the microalgae Chlorella sorokiniana to AMP. According to the ecotoxicity experiments that conducted after treatment of AMP with PS for different reaction times, no important inhibition of microalgae was noticed for contact time of 72 h and 10 d. These results indicate the formation of no toxic AMP by-products for the applied experimental conditions.

Enhanced thermal activation of persulfate by coupling hydrogen peroxide for efficient degradation of pyrene

In this study, H2O2 was introduced into thermally activated persulfate oxidation system (T-HPS), and the oxidation of pyrene (PYR) was investigated by the combined T-HPS technology. The results showed that H2O2 could significantly improve the reactivity of the thermally activated persulfate system (T-PS), with 240-min PYR degradation ratio increasing from 79.3% to 97.2% at 70 °C. In the T-HPS system, as persulfate initial concentration increased from 5 to 100 μM, the kinetic rate constant (kobs) of PYR degradation increased from 4.70 × 10−3 to 3.01 × 10−2 min−1, but the kobs did not show a positive association with H2O2 concentration with the same range, and the highest kobs was obtained at the H2O2 initial concentration of 20 μM. The optimal ratio of PS and H2O2 was set at 1:1 with the initial concentrations of the two oxidants both being 20 μM. Furthermore, PYR could be removed efficiently in a wide range of pH, and the best PYR degradation performance was obtained under neutral pH. Scavenging experiments demonstrated that OH played a more important role in PYR degradation in the T-HPS system than in the T-PS system. As suggested by the Arrhenius equation, the activation energy decreased from 124.5 to 107.4 kJ mol−1 after adding H2O2 to the T-PS system. This study provides a new oxidation approach that could prompt the T-PS activity by adding a suitable dosage of H2O2.

Aerobic and anaerobic regulation induced different degradation behaviors of parachloronitrobenzene in soil by microwave activated persulfate oxidation

Persulfate (PS) oxidation is a promising soil remediation technology. Information regarding pollutant degradation in soil by PS-based technique under different oxidizing atmospheres is still lacking. In this study, p-chloronitrobenzene (p-CNB) degradation in soil in a microwave (MW) activated persulfate (MW/PS) system was evaluated under aerobic and anaerobic conditions. The experimental results demonstrated that anaerobic condition was more conducive to p-CNB degradation. Only 46% of p-CNB was degarded within 60 min treatment under aerobic conditions, but it increased to more than 80% under anaerobic conditions. The increase of PS dosage and MW temperature both promoted p-CNB degradation. SO4•− and •OH played important roles in p-CNB degradation under aerobic conditions, and p-CNB was mainly converted to hydroxylated byproducts including 4-nitrophenol and hydroquinone. The reductive radical S2O8•- was responsible for p-CNB degradation under anaerobic conditions, and aminated byproducts were generated. The residual toxicities of these byproducts were predicted to be decreased, compared with those of p-CNB. Furthermore, by regulating the aerobic and/or anaerobic conditions, other pollutants including pyrene and ethion were also effectively removed in the MW/PS system. Overall, this study highlighted new insights into degradation behaviors of pollutants by MW/PS treatment via aerobic and anaerobic regulation.

The degradation of Fenuron in water by activated persulfate oxidation: An analysis of efficiency, influential parameters and potential applicability

Fenuron (FEN), a member of phenylurea herbicides can be regarded as water contaminant due to its persistence in environment. Persulfate (PS) oxidation as a highly effective degradation technique was applied to degrade FEN using ferrous sulfate (FeSO4), pyrite (PyR; FeS2) and zero-valent iron (ZVI) to activate PS. The systems’ efficiency followed the order as: ZVI-PS system > PyR-PS system > FeSO4-PS system; where, respective degradation of 0.12 mmol/L FEN was 97.5%, 63.6% and 57.8% after 60 min. Therefore, ZVI-PS system was chosen for subsequent detailed analysis and the effects of several influential parameters including ZVI dosage, PS concentration, initial pH, FEN concentration and initial temperature were examined via kinetic studies. ZVI-PS system induced more than 85.0% degradation of 0.06–0.24 mmol/L FEN at initial pH 2.52 to 9.0. Further, difference in initial temperature had an insignificant effect on degradation. ZVI-PS system induced FEN mineralization of about 86.0% after 360 min. Electron paramagnetic resonance (EPR) analysis and free radical quenching (FRQ) analysis were used to demonstrate degradation mechanism by ZVI-PS system. EPR analysis supported that sulfate (SO4−) as well as hydroxyl (OH) radicals were generated in ZVI-PS system; however, FRQ analysis showed that SO4− was dominant reactive radical to carry out FEN degradation. The degradation efficiency of ZVI-PS system was found higher in real waters, which shows its potent applicability to degrade FEN in field. The study concludes that ZVI-PS system can efficiently degrade FEN and may contribute as basic information for future research for the removal of phenylurea herbicides.

Degradation of methyl orange by pyrite activated persulfate oxidation: mechanism, pathway and influences of water substrates.

Degradation mechanism of methyl orange (MO), a typical azo dye, with pyrite (FeS2) activated persulfate (PS) was explored. The results showed that when the initial concentration of MO was 0.1 mM, FeS2 was 1.6 g/L and PS was 1.0 mM, the removal rate of MO could reach 92.9% in 150 min, and the removal rate of total organic carbon could reach 14.1%. In addition, both pH ≤ 2 and pH ≥ 10 could have an inhibitory effect in the FeS2/PS system. Furthermore, Cl- and low concentrations of HCO-3 had little effect on the degradation of MO with FeS2/PS. However, H2PO-4 and high concentrations of HCO-3 could inhibit the degradation of MO in the system. Besides, MO in river water and tap water were not degraded in FeS2/PS system, but acidification (pH = 4) would greatly promote the degradation. In addition, the removal rate of MO with FeS2/PS could still reach about 90% after five cycles of FeS2. Furthermore, the intermediates and possible degradation pathways were speculated by LC-MS, and the degradation mechanism of MO by FeS2/PS was that the cycle of Fe(III)/Fe(II) could continuously activate persulfate to produce SO4•-. The results could provide technical support for azo dye degradation in the FeS2/PS system.