Activated Persulfate Oxidation Research Articles

The in situ catalytic oxidation of sulfamethoxazole via peroxydisufate activation operated in a NG/rGO/CNTs composite membrane filtration.

Metal-free carbonaceous composite membranes have been proven to effectively drive novel in situ catalytic oxidation for the degradation of organic pollutants via persulfates activation. In this study, nitrogen-doped graphene (NG) was employed as a modifier to enhance the catalytic activity of the carbon mats by assembly with reduced graphene oxide (rGO) and carbon nanotubes (CNTs) on the top of a nylon supporter. The morphology and performance of the NG/rGO/CNTs composite membrane were compared to those obtained without the addition of NG (rGO/CNTs). Owing to the larger nanochannels for water delivery and stronger hydrophobicity on the surface, the NG/rGO/CNTs composite membrane shows a superior low-pressure filtration performance in favor of energy-saving operation. For the in situ catalytic oxidation of the NG/rGO/CNTs composite membrane through the activation of peroxydisufate (PDS), the average removal rate of sulfamethoxazole (SMX), one of frequently detected sulfonamide antibiotics in water, can reach 21.7 mg·m-2·h-1 under continuous filtration mode, which was 17% more rapid than that of the rGO/CNTs, resulting in significant detoxifying of the oxidation intermediates. Owing to the addition of NG into the carbon mats, the reactive nitrogen-doped sites identified by X-Ray photoelectron spectroscopy (XPS), such as pyridinic and graphitic N, played important roles in PDS activation, while both the radical and non-radical pathways were involved in in situ catalytic oxidation. According to the experimental evidence of the effects that solution environment has on the SMX removal and transmembrane pressure, the NG/rGO/CNTs composite membrane shows a relatively high resistance to changes in the solution pH, chloride ion inhibition, and background organics fouling. These results suggest a new approach to the application of activated persulfate oxidation in water treatment, such that improvements to the reaction stability warrant further investigation.

Degradation of imidazolium ionic liquids in a thermally activated persulfate system

Thermally activated persulfate (PS) oxidation, a clean source of sulfate radicals (SO4•–), has been used as a promising advanced oxidation method for the treatment of organic contaminants. In this study, the degradation of ionic liquids (ILs) by thermally activated PS was investigated with 1-alkyl-3-methylimidazolium bromides (C4mimBr) as a model compound. The effects of various factors including temperature, initial IL and PS concentrations, solution pH, alkyl chain length of imidazolium cation, and common water constituents such as humic acid (HA), HCO3-and Cl- were evaluated. Results showed that C4mimBr can be completely degraded in 2 h at 60 °C, indicating effective removal of C4mimBr by thermally activated PS oxidation. The oxidation followed a pseudo-first-order kinetics model, and the rate constant increased with increasing temperature, PS concentration and initial solution pH. Alkyl chain length had no effect on the degradation. HA and Cl- had negative effects on C4mimBr removal, while 5 mM HCO3- increased C4mimBr degradation. Multiple intermediate products were identified by HPLC-MS/MS and the degradation pathway and mechanism were proposed. The free radicals generated in the activated PS system (e.g., SO4•– and •OH) showed different effects on the degradation. SO4•– radicals select to attack the substituted side chain of ILs cation, producing more chance for •OH to attack the imidazolium core. Moreover, toxicity tests using bioluminescent bacteria Vibrio Qinghaiensis sp.-Q67 and nematode C. elegans demonstrated efficient detoxification of CnmimBr treatment. These findings may offer an environmentally friendly approach for ILs treatment in aqueous solution.

Enhanced activated persulfate oxidation of ciprofloxacin using a low-grade titanium ore under sunlight: influence of the irradiation source on its transformation products.

In this work, the activated persulfate oxidation of ciprofloxacin (CIP) using a low-grade titanium ore under sunlight or simulated sunlight were conducted to analyze the CIP degradation efficiency and to identify the transformation products (TPs) generated during oxidation under both types of irradiation sources by using liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF-MS). All advance oxidation process experiments were performed in a 2700-mL raceway reactor at a pH value of ~ 6.5 and an initial CIP concentration of 1mg/L, during 90min of reaction time. The control experiments carried out under simulated sunlight achieved a 97.7 ± 0.6% degradation efficiency, using 385W/m2 of irradiation with an average temperature increase of 11.7 ± 0.6°C. While, the experiments under sunlight reached a 91.2 ± 1.3% degradation efficiency, under an average irradiation value of 19.2 ± 0.3W/m2 in October-November 2019 at hours between 11:00 am and 3:00 pm with an average temperature increase of 1.4 ± 0.8°C. Mass spectrometry results indicated that 14 of the 108 possible TPs reported in the literature were detected. The calculated exact mass, measured accurate mass, and its characteristic diagnostic fragment ions were listed, and two new TPs were tentative identified. The TP generation analysis showed that some specific compounds were detected in different time intervals with kinetic variations depending on the irradiation used. Consequently, two CIP degradation pathways were proposed, since the type of irradiation determines the CIP degradation mechanism. Graphical abstract.

Microwave activated persulfate oxidation of leachate subsequent to optimized chemical coagulation

Microwave activated persulfate oxidation of leachate subsequent to optimized chemical coagulation

Degradation of pyrene in contaminated water and soil by Fe2+-activated persulfate oxidation: Performance, kinetics, and background electrolytes (Cl-, HCO3- and humic acid) effects

SO4−-based oxidation technologies have been considered as key solution in polycyclic aromatic hydrocarbons (PAHs) degradation. This study constructed Fe2+-activated persulfate oxidation to degrade pyrene in water and soil by using batch and column experiments. Pyrene degradation kinetic in polluted water and effects of soil background electrolytes (Cl−, HCO3− and humic acid) on pyrene degradation were both investigated. The variation of soil properties during pyrene degradation in soil was evaluated. Polluted water remediation results showed that approximately 93.2 % of pyrene was degraded by 65 mM of persulfate with Fe2+/persulfate molar ratio of 0.25. In soil, 88.5 % of pyrene was degraded under the same persulfate concentration and Fe2+/persulfate molar ratio, and there was a slight decrease of soil pH (from 6.7 to 5.4). Cl−, HCO3− and humic acid in soil brought an adverse effect to pyrene degradation through scavenging SO4−. Column study of soil remediation proved the superiority of Fe2+ in activating persulfate, whose application in soil remediation can finally reduce soil pollution and simultaneously avoid the excessive soil acidification in in-situ remediation. In addition, by evaluating the soil organic matter and total organic carbon during the remediation process, it was found that the soil properties have been improved. Therefore, Fe2+-activated persulfate oxidation would be a feasible way to remediate pyrene polluted water/soil.

Fe(II)-activated persulfate oxidation to degrade iopamidol in water: parameters optimization and degradation paths

Iodinated contrast media (ICM), which was widely used in medical imaging and was difficult to remove by conventional wastewater treatment methods, attained much attention due to its potential environmental impacts. Herein, iopamidol (IPM), one typical compound of ICM, was found to be rapidly degraded by ferrous activated persulfate oxidation (Fe(II)/PS) as compared with PS or Fe(II) alone. With a persulfate concentration of 1 mmol L−1, n(Fe(II))/n(PS) of 1:10, and a pH of 3.0, 78% IPM was degraded within 60 min, with a degradation rate of 0.1266 min−1. It was demonstrated that IPM degradation and deiodination were favored by a high temperature, while affected positively by acidic and neutral conditions. Radical quenching experiments and Electron Paramagnetic Resonace (EPR) spectra showed that the combined effects of SO4−· and ·OH contributed dominantly to degrade IPM, while the ·OH played an essential role during the degradation reaction. Through the Discrete Fourier Transform quantum chemical calculation, the possible reaction pathways for the oxidation of IPM by ·OH are as follows: IPM-TP651-TP667-TP541-TP557, IPM-TP651-TP525-TP557, IPM-TP705-TP631-TP661, and IPM-TP705-TP735. The obtained results showed that IPM could be degraded effectively by Fe(II)/PS system, giving a promising technique for IPM removal from water.

P-Nitrophenol degradation by activated persulfate

The degradation of p-nitrophenol (PNP), which is listed as a priority pollutant by the Environmental Protection Agency (EPA), was investigated in this work by the activated persulfate oxidation. Different forms of persulfate activation (namely thermal, by medium basification and with an iron salt catalyst) were evaluated, apart from founding the best operating conditions for maximizing process performance (assessed in terms of PNP removal and mineralization — evaluated by the overall total organic carbon (TOC) reduction). For the thermal and alkaline activation of persulfate, the temperature was varied in the range of 30 to 90 ºC and the pH between 3.0 to 9.0, respectively, being found that best performances exist for a reaction temperature of 70 ºC while pH above 7.0 is not necessary. In short reaction times (≤10 min) the oxidation of PNP, mineralization and consumption of persulfate were successfully fitted to a second-order kinetic model and the apparent activation energies determined. The effect of persulfate concentration was determined in the range of 0.8 g/L to 9.6 g/L, being noticed that an increase in its concentration above 6.4 g/L led to worst process performances. An additional improvement was observed with the presence of iron in solution, indicating that the metal salt plays an important role in catalyzing the persulfate activation — again, an optimal iron dose was observed (80 mg/L). The combination of the three ways to activated the persulfate allowed obtaining the highest PNP (94%) and TOC (66%) removals, showing that the process is promising in the degradation of PNP and organics mineralization. Radical scavenging runs allowed concluding that both radicals, sulfate and hydroxyl, are forming during the oxidation process, however the role of SO4•− predominates. The identification and quantification of reaction intermediates was also assessed and the contribution of carboxylic acids (oxalic, maleic and pyruvic) in TOC measured was found to be higher than 95%. Finally, the effect of the matrix was evaluated, and for this purpose a domestic wastewater was spiked with 500 mg/L of PNP; it was found that the degradation of the pollutant was almost not affected by the water matrix.

Synergistic heat/UV activated persulfate for the treatment of nanofiltration concentrated leachate

Nanofiltration concentration leachate is a high concentration organic wastewater with low biodegradability and high toxicity. To explore the feasibility of a combined Heat/UV activated persulfate process on nanofiltration concentrated leachate, the effects of persulfate concentration, initial solution pH before reaction, UV-lamp power and reaction temperature on the removal of organic pollutant were systematically investigated. Results indicated that the maximum rate of chemical oxygen demand (COD), ammonia-nitrogen (NH3-N) and absorbance of organic matter under UV light at 254 nm (UV254) removal from the leachate were 65.4%, 51.4% and 98.1%, respectively, at a persulfate concentration of 18 g L−1, initial solution pH before reaction of 9.0, UV-lamp power of 60 W and temperature of 80 °C. The results of three-dimensional fluorescence and UV254 showed that the removal rates of humic substances contained in the nanofiltration concentrated leachate were over 98%. In addition, the results of free radical scavenging showed that hydroxyl radicals were dominant under alkaline conditions. The results of this study demonstrated that coupling heat and ultraviolet activated persulfate oxidation is a promising technique for the treatment of nanofiltration concentrated leachate.

Different non-radical oxidation processes of persulfate and peroxymonosulfate activation by nitrogen-doped mesoporous carbon

Activated persulfate oxidation is an emerging advanced oxidation process for organic pollutant degradation. Own to different molecular structures and oxidation potentials, persulfate (PDS) and peroxymonosulfate (PMS) may show different degradation performances due to various catalytic mechanisms even by the same catalysts. In this study, the nitrogen-doped mesoporous carbon (N-OMC) was applied to activate PDS and PMS for degrading a model organic pollutant phenol to reveal their activation mechanisms. Results show that both PDS and PMS could be efficiently activated by N-OMC. The degradation of phenol fitted well with pseudo-first-order kinetics, whose kinetic constants increased with the increase of pH, PDS/PMS dosage, and N-OMC dosage. Based on quenching experiments and electron spin resonance spin-trapping technique, the N-OMC was found to activate PDS and PMS via non-radical process of electron transfer and singlet oxygen formation, respectively, instead of the commonly observed radical process. This work will be useful to understand the activation processes of PDS and PMS, and benefit for the development of catalysts for pollutant degradation.

Formation of nitrophenolic byproducts in soils subjected to sulfate radical oxidation

Activated persulfate oxidation is an emerging technology with great prospects for soil remediation. For the first time, the present study demonstrated that application of this technology to soils with nitrite (NO2−) presence yielded nitrophenolic byproducts, including 3-nitrophenol, 4-nitrophenol, 2-hydroxy-5-nitrobenzoic acid, and 4-hydroxy-3-nitrobenzoic acid. Their yields were positively related to the contents of soil organic matter (SOM). Most of these byproducts were distributed in soil waters, suggesting that they are readily transported to other places, thus can contaminate a larger area. Nitrated byproducts presumably formed by oxidation of NO2− by SO4−, which generates NO2. This generated NO2 then reacted with phenolic moieties in SOM and was transformed to organic nitrogen. In addition, ammonia nitrogen in soils was oxidized by SO4− and contributed to the formation of nitrophenolic byproducts. Considering the omnipresence of nitrite and ammonia in subsurface soils, this study identified potential risks of persulfate use for in situ soil remediation. These results are relevant to devise strategies to avoid inappropriate use of oxidative reagents and the resulting formation of toxic byproducts.

Nitrogen-doped reduced graphene oxide – PVDF nanocomposite membrane for persulfate activation and degradation of water organic micropollutants

Metal-free carbon-based polymer nanocomposite membranes were employed for the first time for activated persulfate oxidation in continuous mode of operation. For that purpose, reduced graphene oxide doped with nitrogen by using melamine as source (rGO-M) was included as catalytic active phase in a poly(vinylidene fluoride) matrix (PVDF). The performance of the resulting composite membrane (rGO-M-PVDF) was compared against that obtained with supported membranes prepared by simple filtration of rGO-M into a PTFE substrate. The uniform distribution of rGO-M within both the surface pores and cross-sectional channels of the composite rGO-M-PVDF membrane (with a thickness of 292 ± 20 μm) was confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), while its main structural features were studied by X-ray diffraction (XRD) and Raman spectroscopy. The quite good performance of this composite membrane was demonstrated by the degradation of three fluoroquinolone antibiotics at ppb level in ultrapure water (100 μg L−1 each), leading to average pollutant mass removal rates in the range 2.05–2.73 mg m−2 h−1. Conversions of the pharmaceuticals in the range 54–91% were obtained even after 24 h of operation in full continuous mode. Persulfate conversion was confirmed and high resistance to fouling was observed with this novel catalytic membrane. Average pollutant mass removal rates in the range 0.34–0.77 mg m−2 h−1 were obtained in preliminary experiments performed with surface water instead of ultrapure water, highlighting the need for additional studies on both water matrix effects and process optimization.

Improving solid–liquid separation performance of anaerobic digestate from food waste by thermally activated persulfate oxidation

Anaerobic digestion is a promising ecofriendly technology for the management of the continuous increasing food waste (FW). However, the large amount of resulting anaerobic digestate are very difficult to be purified due to high concentration of suspended colloids. Solid–liquid separation is a pivotal step for the subsequent biological treatment of the digestate by activated sludge process. The dewaterability of digestate could directly reflect the solid–liquid separation performance. In this study, a thermally-activated persulfate (PDS) conditioning method was utilized to enhance the digestate dewaterability. Results revealed that PDS thermally conditioning significantly improved the dewaterability by decreasing digestate pH and decomposing organic substances in digestate. The decline of pH, which was resulted from PDS thermally activation reaction, facilitated filterability improvement via reducing the surface negative charges and prompting the oxidizing ability of PDS-relevant radicals. Protein, the main organic component in digestate, was most closely correlated with digestate dewaterability. Fortunately, they were also the most vulnerable constituent under the oxidation attack. PDS thermal conditioning at 80°C was proven to be the most suitable for improving the solid–liquid separation performance of anaerobic. For practical application in conditioning the anaerobic digestate from FW, the conditions should be further optimized according to the digestate characteristic.

Dewatering efficiency of sewage sludge during Fe2+-activated persulfate oxidation: Effect of hydrophobic/hydrophilic properties of sludge EPS

To clarify the effect of the hydrophobic/hydrophilic polarity of extracellular polymeric substances (EPS) on sludge filterability improvement during S2O82-/Fe2+ oxidation, waste activated sludge (WAS), glucose-fed hydrophilic sludge (HPI-WAS), and sodium acetate-fed hydrophobic sludge (HPO-WAS) samples were cultivated, and their dewatering behaviors were individually explored. Experimental results showed that S2O82- oxidation effectively disintegrated the polymeric EPS and led to a more significant reduction in the water content for HPO-WAS than for HPI-WAS (12.87–15.23% vs 9.31–12.12%), especially regarding the bound water (Wb) content. After oxidation, as high as 38.88–42.61% of the Wb within HPO-WAS samples were declined, much higher than the HPI-WAS samples (19.27–29.20%). Specifically, carbohydrates within sludge EPS negatively influenced the dewatering process of S2O82-/Fe2+ oxidation. By contrast, abundant existence of humic acids and polymeric proteinaceous components (especially those hydrophilic proteins and transitional humic acids) within the sludge EPS exhibited a converse trend. FT-IR and EEM spectral, as well as particle sizes variation for the sludge samples before and after S2O82-/Fe2+ oxidation was also evaluated. This study provides new insight into the enhancement of S2O82-/Fe2+ oxidation for sludge dewatering based on polarity analysis of EPS.

Removal of antibiotic resistant microbes by Fe(II)-activated persulfate oxidation

Sewage in WWTPs is one of main way to spread antibiotic resistant microbes (ARMs), and beach bay water is in direct contact with human skin. It is necessary to pay attention to remove the ARMs in WWTP sewage and bay water. Our results showed that ARMs and total microbes (TMs) can be effectively removed by S2O82-/Fe2+ in the effluent stage of WWTPs and bay water. Quenching experiments using tert-butyl alcohol, dimethyl sulfoxide and Al2O3 as scavengers confirmed that the primary reactive oxidants responsible for microbes removal during the Fe(II)-activated persulfate oxidation process might be SO4•- and Fe(IV), rather than •OH. The bacterial community shifted and the alpha diversity significantly reduced after treatment. In WWTP group, relative abundance of Firmicutes increased to 8.56%, and potential pathogens such as genus Vibrio decreased to 0.03% in bay water after treatment. The ecological toxicity to the environment of S2O82-/Fe2+ further illustrated that the mortality of indicator species Oryzias latipes did not increase after treatment, and the dosage of 60/30 μM can be potentially ideal dosage of S2O82-/Fe2+. This study revealed Fe(II)-activated persulfate oxidation as an eco-friendly and economical method could reduce TMs and ARMs in WWTP sewage and bay water.

Formation of chloronitrophenols upon sulfate radical-based oxidation of 2-chlorophenol in the presence of nitrite

Sulfate radical (SO4−)-based advanced oxidation processes (SR-AOPs) are promising in-situ chemical oxidation technologies widely applied for soil/groundwater remediation. The presence of non-target water constituents may interfere the abatement of contaminants by SR-AOPs as well as result in the formation of unintended byproducts. Herein, we reported the formation of toxic chloronitrophenols during thermally activated persulfate oxidation of 2-chlorophenol (2CP) in the presence of nitrite (NO2−). 2-Chloro-4-nitrophenol (2C4NP) and 2-chloro-6-nitrophenol (2C6NP) were identified as nitrated byproducts of 2CP with total yield up to 90%. The formation of nitrated byproducts is a result of coupling reaction between 2CP phenoxyl radical (ClPhO) and nitrogen dioxide radical (NO2). As a critical step, the formation of ClPhO was supported by density functional theory (DFT) computation. Both 2C4NP and 2C6NP could convert to 2-chloro-4,6-dinitrophenol (2C46DNP) upon further treatment via a denitration-renitration process. The formation rate of 2C4NP and 2C6NP was closely dependent on the concentration of NO2−, solution pH, and natural water constituents. ECOSAR calculation suggests that chloronitrophenols are generally more hydrophobic and ecotoxic than 2CP. Our result therefore reveals the potential risks in the abatement of chlorophenols by SR-AOP, particularly when high level of NO2− is present in water matrix.

Fe (II)-activated persulfate oxidation effectively degrades iodoform in water: Influential factors and kinetics analysis

Iodoform (CHI3) is one of the disinfection by-products (DBPs) that is formed in the pre-oxidation and disinfection processes of drinking water treatment. In this study, Fe(II)-activated persulfate oxidation (Fe2+/PS) was employed to degrade iodoform, the effects of initial reactants concentration, reaction parameters, kinetics model were investigated, and the underlying mechanisms of CHI3 degradation in Fe2+/PS oxidation process was unveiled. The results showed that the mole ratio Fe2+/PS of 1:5, initial PS concentration of 15 μmmol/L, and pH of 3.0 were identified as the optimum operating parameters. In addition, a relatively higher temperature could enhance CHI3 removal and deiodination. The kinetic model has two different reaction steps: a fast one during the first ten minutes of reaction; then followed by a much slower one. Suppression of the reaction by TBA and MeOH showed that the combined effects of SO4−· and ·OH contributed to the degradation of CHI3, but ·OH played a dominant role. The degradation pathways and the products of total liberated iodine species demonstrate that the applicability of the Fe2+/PS oxidation process for CHI3 degradation. These results indicated that the Fe2+/PS oxidation process is an effective advanced oxidation process for CHI3 removal in water treatment.

Heat activated persulfate oxidation of Reactive Black 5

Heat activated persulfate oxidation of Reactive Black 5

Degradation of phenol in water by Fe(II)-citrate activated persulfate oxidation

To enhance the degradation efficiency, complexing agent citric acid (CA) and trisodium citrate (TC) were introduced into the Fe(II)-persulfate (Fe2+/PS) oxidation system to degrade phenol. And the optimal operating conditions were determined. The results showed that Fe2+-citrate/PS system had higher degradation efficiency than the others. The optimal operating conditions to degrade phenol in water were: a PS concentration of 0.06 mol/L, a Fe2+ concentration of 0.02 mol/L and a TC concentration of 0.01 mol/L, while reaction temperature and the initial pH values had little influence on the phenol degradation.

Inactivation of water pathogens with solar photo-activated persulfate oxidation

The effect of solar activated persulfate oxidation and solar mild thermal heating on water disinfection (PS/solar) was demonstrated for the inactivation of E. coli and E. faecalis in both isotonic water (IW) and synthetic urban wastewater (SUWW). The process was studied in both bench-scale and pilot-scale (60 L CPC solar compound parabolic collector) reactors. The impact of solar ultraviolet (UV) and thermal increase on bacterial inactivation were separately studied. The thermal inactivation at 40 °C and 0.5 mM-PS shows a 3-log reduction value (LRV) for E. coli without lag phase and 5-LRV for E. faecalis with a lag phase of 1 h, during 4 h solar exposure. The thermal effect at 50 °C played a dominant role, with fast bacterial decay for both bacteria, which dominates the kinetics over the thermal activation of PS. In the presence of PS and solar irradiation, the combined thermal and UVA effects, accelerated the bacterial process. 6-LRV in E. coli and E. faecalis was observed after solar exposure periods of 20 min (solar dose), using 0.5 and 0.7 mM of PS in IW, respectively. Longer solar exposure times were required to attain similar LRV in synthetic urban wastewater, in the presence of 25 mg/L of organic matter, i.e. 80 and 100 min (solar dose) for E. coli and E. faecalis, respectively. These results were confirmed at pilot scale, where 60 L of IW were treated with 0.5 mM of PS in 50 min (solar dose). The PS/solar process uses low cost chemical reagents (0.5 mM-PS) and a free source of energy (solar radiation) for the treatment of wastewater and is able to achieve the high removals (6-LRV) of the two model faecal indicators of water contamination. This process opens a clear alternative to treat polluted water with organic matter and pathogens with implications in water-energy reclamation field.

Strengthened dewaterability of coke-oven plant oily sludge by altering extracellular organics using Fe(II)-activated persulfate oxidation

Although oily sludge has tremendous resource recovery value, its high water content has hindered its treatment and reuse. This study systematically explored the technical feasibility of using Fe(II)-activated persulfate oxidation (Fe2+/S2O82−) to enhance the dewaterability of oily sludge. To identify the main factors controlling sludge dewatering, this study measured changes in chemical oxygen demand, ammonia nitrogen (NH4+-N) and extracellular polymeric substances (EPS). Results showed that at 0.1 mmol-Fe2+/g-VSS and 0.08 mmol-S2O82−/g-VSS, capillary suction time (s) was reduced by roughly 36.1% within 1 min and dewaterability was strengthened strongly. Sulfate radicals originating from Fe2+/S2O82− oxidized a large amount of EPS, leading to liberation of EPS-bound water. A similar declining trend in NH4+-N was evident as a result of the strong oxidizing ability of sulfate radicals. Further analysis via scanning electron microscopy and thermogravimetric-Fourier transform infrared spectrometry revealed that Fe2+/S2O82− oxidation destroyed the water-oil-gel-like structure of the oily sludge, thereby accelerating the separation of solids and water while reducing CO2 emissions during the subsequent pyrolysis. Therefore, oily sludge dewatering was enhanced significantly by the Fe2+/S2O82− process.