Persulfate Oxidation Research Articles

A Special Hydrated Iron Oxyhydroxide for Catalyzing Persulfate to Control Chemical Wastewater Containing Fluoranthene, Phenanthrene, and Pyrene

Water pollution caused by fluoranthene (FLN), phenanthrene (PHE), and pyrene (PYR) has become an increasingly serious issue in recent years. Consequently, finding effective methods to remove these pollutants from aquatic environments is of paramount importance. This study investigated the removal rate of FLN, PHE, and PYR from simulated wastewater using persulfate (PS) and explored the effects of PS catalyzed by three different forms of schwertmannite (sch): sch-1, sch-2, and sch@BC (schwertmannite-biochar composite), and the BET of sch-1, sch-2, sch@BC has been detected, which were 1.09 cm3/g, 11.30 cm3/g, and 6.10 cm3/g. The results showed varying removal rates after a 1 h reaction time for different treatments: For FLN: sch-1+PS (98.5%), sch-2+PS (54.2%), sch@BC+PS (21.1%), and PS alone (14.8%). For PHE: sch-1+PS (94.3%), sch-2+PS (44.1%), sch@BC+PS (28.4%), and PS alone (7.6%). For PYR: sch-1+PS (97.2%), sch-2+PS (52.5%), sch@BC+PS (14.2%), and PS alone (1.7%). Among the catalysts tested, sch-2 (added 0.36 mL H2O2 five times) demonstrated excellent catalytic ability in enhancing the PS removal of FLN, PHE, and PYR. This research provides theoretical support for treating polycyclic aromatic hydrocarbon (PAH)-containing wastewater via persulfate oxidation catalyzed by schwertmannite.

Real-time in situ monitoring as a tool for comparison of electrochemical advanced oxidation processes for the decolourisation of azo and indigoid dyes.

The widespread use of synthetic dyes has led to the release of substantial amounts of dye-contaminated wastewater, posing significant environmental and health concerns. This study focuses on the use of anodic and electrochemically activated persulfate oxidation for the degradation of organic contaminants. Specifically, the structural variations of nine dyes in the indigoid and azo families, and their impact on the efficiency of electrochemical oxidation were analysed. An in situ continuous monitoring apparatus with a UV-visible detector was employed to collect data in real-time. The electrochemically activated persulfate system demonstrated higher efficiency compared to the anodic oxidation approach. In both systems the efficiency of decolourisation was highly dependent on the structure of the pollutant. Electron-withdrawing substituents in direct conjugation with the chromophore, bulky auxochromes, and extended aromatic systems significantly decreased the decolourisation efficiency. Conversely, changing the location of electron-withdrawing groups and adding electron-donating substituents increased the decolourisation efficiency, even overcoming the detrimental effects of bulky groups and extended conjugation. This type of systematic structural comparison study is essential for highlighting the interconnected nature of pollutant structure and degradation speed so that efficient electrochemical oxidation systems can be designed for the treatment of genuine wastewater effluent containing more than one pollutant.

Remediation of Various Phenanthrene-contaminated Soils using Persulfate-Pseudomonas aeruginosa GZ7: Soil Properties, Radical Formation, and Microbial Community

In this study, the complex interaction of oxidizing conditions, soil composition, microbial activity, and phenanthrene (PHE) degradation was explored in persulfate (PS)-Pseudomonas aeruginosa GZ7 remediation of four PHE-contaminated soils: Paddy soil (PAS), Saline soil (SS), Red soil (RS), and Cinnamon soil (CS). Batch experiments displayed the optimal PS dosage was 0.750% (w/w), except for CS (0.125%), achieving PHE degradation rates of 54.79% ~ 81.92% on the 27-day. The zeta potential of soil clay component after 0.750% PS oxidation was lower than 0.125% and 2.000% PS, resulting in a higher PHE bioavailability and biodegradation. The electron paramagnetic resonance (EPR) spectroscopy analysis showed that the abundance of dominant hydroxyl radicals (·OH) in CS was 3 times higher than in PAS at 0.750% PS and PS to Fe2+ molar ratio of 2:1, indicating that a higher soil organic matter would decrease the content of ·OH thus diminishing PHE removal. Stepwise linear regression and sensitivity analysis indicated that the key influential factors in the PHE degradation rate were the residual PHE content after oxidation (60.12%) and hydrolase nitrogen content (30.97%). High-throughput sequencing results showed the bacterial diversity and richness in four soils decreased after combined remediation compared to pristine soil. Redundancy analyses revealed that the fluorescein diacetate (FDA) hydrolase enzyme was the key factor effect of soil bacterial community development in SS; and electrical conductivity and FDA hydrolase enzyme were the key factors in RS, CS, and PAS. This study may provide technical support for optimizing chemical conditions for PS-microbial remediation.

Ciprofloxacin degradation over Co3O4 catalysts by the microwave-assisted persulfate oxidation: a critical role of coordination composition

The combination of catalysts and microwave (MW) effects presents an emerging approach for persulfate (PS) activation, while the effect of active sites of catalysts on the synergistic reaction remains poorly understood. Here, we regulated the coordination composition of Co3O4 by strategically controlling the oxygen atmosphere during fabrication. We found that Co3+ and Co2+ acted as reactive centers for microwave absorption and catalytic activation of persulfate, respectively. By altering the ratio between Co3+ and Co2+, we explored the Co3O4 (2.23)-550 catalysts with significantly improved synergistic activity for degrading ciprofloxacin (CIP), which was 33.0 and 26.8 times higher than PS- Co3O4 (2.23)-550 (without microwave) and MW- Co3O4 (2.23)-550 (without persulfate), respectively. Meanwhile, Co3O4 (2.23)-550 catalyst (0.5mgL-1) showed the highest degradation rate of CIP 92.6% (0.5mgL-1) within 10min under microwave. According to the radical identification and intermediate analysis, the efficient degradation of CIP was ascribed to both free radical and non-free radical pathways. Thus, this work raises new insights into the structure-activity relationship of catalysts, and provides an efficient way to eliminate antibiotics via synergistic catalysis.

Sustainable humification of food waste slurry through thermally activated persulfate oxidation

This study introduces a thermoanalytical approach utilizing sodium persulfate (PS) to expedite the humification of food waste (FW) through advanced oxidation processes (AOPs). The method harnesses heat-induced free radicals to break down complex organic compounds into simpler forms, leading to the formation of humic substances. We conducted an analysis of changes in soluble chemical oxygen demand (SCOD), dissolved organic carbon (DOC), ammonia nitrogen, soluble proteins, and sugars, employing advanced techniques such as three-dimensional fluorescence spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM). The findings indicate that the activation of PS at 70°C effectively increases SCOD and DOC levels, converts proteins into soluble forms, and enhances NH4+-N content. This study, which focuses on the utilization of thermal methods, affirms that the thermal activation of persulfate (PS) significantly boosts the humification of food waste (FW), presenting a sustainable approach for waste management and resource recovery.

Pomelo peel biochar supported nZVI@Bi0 as a persulfate activator for the degradation of acetaminophen: Enhanced performance and degradation mechanism

Due to the contradiction between superior reaction kinetics and imperfect reproducibility of nanoscale zero-valent iron (nZVI) in persulfate oxidation systems, how to improve the reusability of nZVI while highly guaranteeing efficiency is an important but challenging matter. Hence, we took a hydrothermal-assisted carbon reduction to synthesize nZVI encapsulated with Bi being loaded on pomelo peel biochar (nZVI@Bi0/PPBC), and the results indicated that the presence of Bi could improve the reproducibility of nZVI and facilitate the removal of acetaminophen (ACE) in the persulfate (PDS) system. The degradation rate constant of the nZVI@Bi0/PPBC800 composite for ACE was approximately 1.5 times higher than that of the nZVI/PPBC800. nZVI exhibited synergistic effects with Bi on PDS activation through electron transfer. Interestingly, the Bi(0) became increasingly pure as the pyrolysis temperature increased, and the catalytic performance of ZVI@Bi0/PPBC became better. In addition,electron spin resonance and quenching experiments revealed that 1O2 and O2·− were the predominant reactive oxygen species in nZVI@Bi0/PPBC/PDS system.The nZVI@Bi0/PPBC/PDS system showed excellent oxidation ability across a broad pH range (3.0–9.0) and resisted interference from certain anions. This work reveals the possible role of Bi(0) in nZVI based PDS system, and provides an idea for the protection of nZVI.

A self-contained catalytic sponge for point-of-use solar driven persulfate oxidation and photothermal evaporation

A self-contained catalytic sponge for point-of-use solar driven persulfate oxidation and photothermal evaporation

Enhanced gaseous benzene degradation by bimetallic MIL-101(Fe, Cu) activated persulfate system: Efficiency and mechanism

Persulfate oxidation is a promising technology for air pollution control but still suffers from degrading refractory volatile organic compounds (VOCs) under mild conditions. Metal-doped metal-organic frameworks (MOFs) offer a novel strategy to enhance persulfate activation and VOCs degradation. Herein, a novel bimetallic MIL-101 (Fe, Cu) is prepared for more effective degradation of gaseous benzene via persulfate activation. Under optimal conditions (Fe/Cu ratio of 1:4, persulfate concentration of 7 mM/L, pH of 5, and reaction temperature of 70 °C), the MIL-101(Fe1, Cu4) activated persulfate system achieves a benzene degradation efficiency of 79.1 %, a value significantly higher than that of MIL-101(Fe) (20.1 %). The enhanced performance can be attributed to the synergistic effect of Fe²⁺/Fe³⁺ and Cu²⁺/Cu⁺ redox interactions facilitating the activation of persulfate and generation of radical species. Density functional theory (DFT) calculations indicate an increase in the adsorption energy of MIL-101(Fe) in the presence of Cu doping from −3.46 eV to −5.92 eV along with a rise in the Fermi energy level from 0.5 eV to 1.33 eV, enhancing the electron density and mobility. A reaction energy diagram is provided to illustrate the reaction pathways and transition states involved in the degradation of benzene. Overall, the incorporation of Cu in MOFs significantly enhances the efficiency of persulfate-based oxidation systems toward VOCs degradation.

Advancements and Challenges in Nanoscale Zero-Valent Iron-Activated Persulfate Technology for the Removal of Endocrine-Disrupting Chemicals.

Endocrine-disrupting chemicals are a new class of pollutants that can affect hormonal metabolic processes in animals and humans. They can enter the aquatic environment through various pathways and gradually become enriched, thus posing a serious threat to the endocrine and physiological systems of both animals and humans. Nano zero-valent iron has promising applications in endocrine disruptor removal due to its excellent reducing properties and high specific surface area. However, given the dispersed focus and fragmented results of current studies, a comprehensive review is still lacking. In this paper, it was analyzed that the types of endocrine disruptors and their emission pathways reveal the sources of these compounds. Then, the main technologies currently used for endocrine disruptor treatment are introduced, covering physical, chemical, and biological treatment methods, with a special focus on persulfate oxidation among advanced oxidation technologies. Also, the paper summarizes the various activation methods of persulfate oxidation technology and proposes the nZVI-activated persulfate technology as the most promising means of treatment. In addition, this paper reviews the research progress of different modification methods of nZVI in activating persulfate for the removal of EDCs. Finally, the discussion includes recycling studies of nZVI/PS technology and emphasizes the urgency and importance of endocrine disruptor treatment. The review of this paper provides further scientific basis and technical support for nZVI/PS technology in the field of endocrine disruptor management.

Persulfate oxidation of plant-based indigo wastewater enhanced by Aspergillus niger

Due to a lack of effective treatments and processes, the substantial amount of wastewater generated during plant indigo production causes environmental issues, impacting the production's sustainability. This study found that the constituents of plant indigo wastewater influence using activated carbon on persulfate. After the activated carbon treatment, the wastewater contained 78.87% sugar and 28.09% saponins. Aspergillus niger (A. niger) exhibited a high degradation performance against sugars and saponins, owing to the activities of cellulase, β-glucosidase, and β-glucuronidase. The degradation improved the activation ability of activated carbon for persulfate, with the removal rates of 46.87% and 31.62% for chemical oxygen demand (COD) and total organic carbon (TOC), respectively. Further analyses indicated that the A. niger treatment significantly increased the level of reactive oxygen species in the oxidation system and improved the microstructure, porosity, and adsorption capacity of activated carbon. Through the synergy of response surface analysis, prediction, and validation, we significantly reduced COD and TOC concentrations to 225.8 and 185.6mg/L (removal rates of 96.7% and 94.1%), respectively. These findings are essential for promoting the sustainable development of plant indigo production.

Performance of Dye-Containing Wastewater Treatment Using MnxOy-Catalyzed Persulfate Oxidation

Dye wastewater is characterized by high salinity, intense coloration, difficulty in degradation, and complex organic compositions, posing significant environmental risks. Manganese oxide (MnxOy)-based materials have been widely used for the removal of recalcitrant organic pollutants in water environments. In this study, various MnxOy polymorphs were prepared, and their catalytic activities for persulfate (PS) activation were evaluated using Orange II (AO7) as a model molecule. After 50 min treatment, the degradation efficiency of AO7 ranked as α-MnO2/PS > γ-MnO2/PS > β-MnO2/PS > Mn2O3/PS, with α-MnO2/PS achieving the highest efficiency of 98.6%. XPS, XRD, and electrochemical analyses indicated that α-MnO2 exhibited an exceptional crystal structure and performance. The α-MnO2/PS system exhibited a strong pH adaptability across a wide pH range of 3.0–9.0. The presence of coexisting anions at 0.1 mM, including Cl−, NO3−, CO32−, and SO42−, slightly reduced the degradation rate of AO7. The reactive oxygen species, mainly SO4•− and 1O2, predominantly destroyed the naphthalene ring structure of AO7. Furthermore, α-MnO2 exhibited an excellent stability, allowing for multiple reuse cycles without interference from common anions in water, highlighting its strong potential for practical applications. These results provided insights into the environmental fates of AO7 in the α-MnO2/PS system.

Snowflake-like In2S3/Cu2S heterojunction for simultaneous photocatalytic persulfate oxidation of tetracycline hydrochloride and CO2 photoreduction

To achieve tetracycline hydrochloride (TCH) elimination and CO2 photoconversion to CH4 and CO, snowflake-like In2S3/Cu2S heterojunctions were fabricated through the hydrothermal approach. Z-scheme junction generated between In2S3 and Cu2S was likely to separate and migrate the photoactivated e-/h+ pairs, boosting the photocatalytic-persulfate (photo-PS) activity and CO2 photoconversion capacity. The single photo-PS oxidation of TCH and CO2 photoreduction as well as their simultaneous photocatalytic behaviors over snowflake-like In2S3/Cu2S composites were comparatively investigated. For optimal 3-In2S3/Cu2S with a nominal In2S3 content of 5.0 wt%, the removal efficiency of unary photo-PS oxidation system was 99.90 %, CH4 and CO yield rates of single CO2 photoreduction process were respectively 177.67 and 94.42 μmol g-1h−1. In dual photo-PS oxidation and CO2 photoreduction system, the addition of CO2 leaded to the lower photo-PS activity, while the higher CH4 and CO yield rates of 3-In2S3/Cu2S. When added CO2 to dual photocatalytic system, the removal efficiency of TCH, CH4 and CO yield rates reached to 78.38 %, 106.80, and 73.84μmol g-1h−1, which were 0.94, 1.34, and 1.39 folds than those without CO2. This work provided the possibility of simultaneous photo-PS oxidation of pollutants and CO2 photoconversion to C1 compounds.

Efficient extraction of refractory Cr from stainless steel dust by sodium persulfate oxidation roasting

Stainless steel dust (SSD) contains a high content of Cr and is listed as hazardous solid waste. However, SSD is mainly stockpiled in legacy waste sites due to its complexity and lack of investigation. Herein we comprehensively investigates the microscopic interaction between heavy metals and coexisting phases of SSD from the electric arc furnace (EAF). Furthermore, a new approach for extracting Cr from SSD was developed for the first time. It was found that SSD is enriched with Cr, Ni, Mn, and Zn. Most of these heavy metals are bound to stable spinel (e.g., FeCr2O4) and encapsulated by silicate. Using Na2S2O8 as the flux (1–24 mmol), under roasting at 350–750 °C in the air for 0.25–6 h, efficient heavy metal extraction can be achieved (Cr-80 %, Ni-86 %, Mn-93 %, Zn-94 %) at 650 °C for 1h. During the roasting processes, the silicate shell was broken, which facilitated the mass transfer of the oxidant. Fe(II) was oxidized to Fe(III) and collapsed the spinel structure, releasing the heavy metals during the following acid leaching. The total mass of SSD is reduced by 90–95 %, and detoxification of SSD is achieved after processing. In conclusion, efficient extraction refractory metals in SSD by Na2S2O8 roasting and the mechanism was elucidated for the first time. This method might also be applied for the treatment of other slags/ash waste that have a stable spinel structure and are encapsulated by silicate.

Application of electro-activated persulfate oxidation enhanced with an ultraviolet process in a multi-stage flow-through filtration system for antibiotics abatement

The treatment of antibiotic wastewater from various water matrices remains challenging because of some complex pollutants in nature. Single treatment methods are often inadequate for eliminating these contaminants. The integrated technology is brilliantly effective over an individual process alone. The electro-activated persulfate oxidation enhanced with an ultraviolet process (EO/PS/UV) was established as a novel technology in antibiotic wastewater treatment. It exhibited to be highly effective with much more efficiency in degrading amoxicillin (AMX) (97.10 %) than the two couple and individual processes in a multi-stage flow-through reactor. The Box-Behnken design’s quadratic model using the response surface methodology (RSM) revealed a reasonable prediction with a suggestive correlation of R2 = 0.9986. This study shows that the AMX degradation mechanism in the EO/PS/UV process involves coordinating of SO4·-, and OH, with OH playing a more significant role. It could effectively treat the tetracycline and sulfamethoxazole within 40 min in both simulated wastewater and secondary effluent, except for tetracycline, which took only 30 min in simulated wastewater. However, AMX did not undergo sufficient removal within 100 min and required a higher EE/O compared to other pollutants. Lastly, the integrated technology has proven to be an efficient and energy-saving method for eliminating antibiotics with promising standpoints for various wastewater treatments.

Influence of Terrigenious Inorganic Nitrogen on Marine Nitrogen Cycle Reconstruction Inferred from Sedimentary Bulk Nitrogen Isotope

This study reevaluates the application of sedimentary bulk nitrogen isotopes (δ15NTN) as proxies for reconstructing past marine nitrogen dynamics, traditionally assumed to reflect organic nitrogen (δ15NON) derived from marine productivity. Employing a novel method that utilizes persulfate oxidation to convert organic nitrogen (ON) and ammonium into nitrate, followed by nitrate reduction to nitrous oxide via denitrifying bacteria, we quantified and characterized both ON and inorganic nitrogen (IN) across diverse environments, including soils, rivers, lakes, and marine sediments. We found that IN, primarily sourced from clay-fixed ammonium via riverine and dust inputs, constitutes 30 % to 50 % of total nitrogen (TN) in marine sediments. Our findings reveal that δ15N values of IN are typically 2 ‰ to 5 ‰ lower than those of δ15NON, resulting in a − 0.5 ‰ to −2 ‰ negative shift in marine δ15NTN. This significant isotopic deviation necessitates a reevaluation of nitrogen cycle interpretations inferred from δ15NTN, especially regarding the potential underestimation of nitrate utilization in nitrate-rich regions and the overestimation of nitrogen fixation in oligotrophic oceans.

Balanced adsorption and oxidation in a porous P, N-doped carbon prepared by melt-salt-mediated strategy for enhanced fenton-like reaction

The activation of persulfate oxidation processes using carbon-based catalysts is attractive for eliminating persistent aromatic organic pollutants in wastewater treatment. Herein, N and P co-doped carbonaceous (NPC) catalysts with an ultrahigh surface area were synthesized using a melt-salt-mediated strategy, employing Zeolitic Imidazolate Framework-8 as a self-sacrificing template. The NPC(1:1) carbon, prepared under optimized conditions, exhibited the highest surface area of 2001.5 m2/g, characterized by the highest number of defects and a high dispersion of N (1.89 %) and P (0.30 %) atoms on the carbon. This carbon catalyst exhibited a high capacity for adsorption and potential for activating persulfates in the removal of p-Nitrophenol (p-NP). Experimental data indicate a balance between adsorption and oxidation in the NPC(1:1)/PDS/p-NP system, with the highest catalytic removal rate achieved through moderate pre-adsorption of p-NP. Evidence from quenching, electron paramagnetic resonance (EPR), and amperometric i-t experiments suggests that the NPC(1:1)/PDS system primarily degrades p-NP through an electron transfer pathway. Defects in carbon and graphitic N were identified as catalytic sites. These defects resulted in an electron-deficient state, which leads to the activation of PDS and graphitic N was more reactive than both pyridinic and pyrrolic N in the adsorption of PDS molecules. Additionally, P-containing groups such as C-P-O, C-O-P, and C3-P were pinpointed as active sites on the carbons through DFT calculations. The intermediates during p-NP degradation were identified, and possible degradation pathways were proposed. A toxicity analysis indicated a significant reduction in overall toxicity following the oxidation treatment. This study provides innovative insights into the balance between adsorption and catalytic activity in porous carbon-activated persulfate oxidation reactions, thereby aiding in the development of enhanced oxidation catalysts for environmental remediation.

Treatment of high-concentration semi-coke wastewater by phenolic condensation and persulfate oxidation

In this study, the combined process of phenolic condensation-persulfate(PS) advanced oxidation was adopted to treat semi-coking wastewater. Using the phenolic condensation method as a pretreatment unit to remove phenolic substances for the preparation of phenol-formaldehyde resins, and using an aerated/PS/pyrite oxidation system as a deep treatment unit to remove chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) from the wastewater. Analysis and characterization of phenol-formaldehyde resin, organic compounds in wastewater, and pyrite using FT-IR, TG-DTG, GC-MS, and XPS techniques. The results showed that under the conditions of adding 1.8vt % formaldehyde, pH 10.5, reaction temperature 95 ℃ and reaction time 3 h, the removal rates of volatile phenol, COD and NH3-N in semi-coke wastewater were 97.54 %, 41.14 % and 56.50 %, and the yield of phenolic resin was 6.62 g/L. Subsequently, treated with an aerated/PS/pyrite system, the PS concentration 0.4 mol/L, the pyrite dosage 15 g/L, the pH 3, the temperature 65 ℃, and the aeration 3 h, the removal rates of COD and NH3-N are 99.20 % and 86.80 %. In the phenolic condensation process, phenolic substances in semi-coke wastewater generate phenoxy anions under the influence of OH-, which undergo addition reactions with formaldehyde to produce hydroxymethyl phenol. Hydroxymethyl phenol further undergoes condensation reactions with other phenolic substances and itself to form phenolic resin, while amide compounds are generated through reactions between ammonia nitrogen and carboxylic acid substances. In the aeration/PS/pyrite system, Fe2+ released from pyrite oxidation activates PS to produce SO4•− and O2•−. The contribution of free radical oxidation and decomposition of pollutants such as phenols, amides, and NH3-N in wastewater is 84.60 %. Specifically, SO4•− oxidation contributes 61.54 %, while O2•− accounts for 22.21 %. Amide compounds and phenolic substances in the wastewater are oxidized, leading to ring opening and chain scission, resulting in the formation of alkane compounds.

Unveiling electron transfer and radical transformation pathways in coupled electrocatalysis and persulfate oxidation reactions for complex pollutant removal

The degradation of multiple organic pollutants in wastewater via advanced oxidation processes might involve different radicals, of which the types and concentrations vary upon interacting with different pollutants. In this study, electrochemical activation of peroxymonosulfate (E/PMS) using advanced activated carbon cloth (ACC) as electrode was applied for simultaneous degradation of mixed pollutants, e.g., metronidazole (MNZ) and p-chloroaniline (PCA). 92.5 % of MNZ and 91.4 % of PCA can be degraded at the cathode and anode at a low current density and PMS concentration, respectively. The rate constants for the simultaneous removal of MNZ and PCA in the E/PMS/MNZ(PCA) system were 118 times and 6 times higher than those in the sole PMS system, and 2.5 times and 1.6 times higher than those in the E/Na2SO4/MNZ(PCA) system, respectively. Different electrochemical characteristics, EPR spectra and radical quenching tests verified that the degradation of MNZ and PCA in the optimal system proceeded primarily through non-radical-dominated oxidation, involving electron transfer and 1O2 effect. The system also exhibited low energy consumption (0.215 kWh/m−3·order−1), broad operational pH range, excellent removal efficiency for water matrix, and low by-products toxicity, indicating its strong potential for practical applications. The ACC, with its super stable, low cost, and electrochemical activity, make it as a promising materials applicable in the E/PMS system for degradation of multiple pollutants. The study further elucidated the mechanism of pollutant interaction with electrode materials in terms of radical and non-radical transformation, providing fundamental insight into the application of this system for treatment of complex wastewater.

Application of composite persulfate oxidation to remediate weathered lubricating oil-contaminated soils: Batch and pilot-scale studies

In this study, two novel composite persulfate (PS) oxidants [base pulverized NaOH composite persulfate (BPS) and metal (iron and manganese) composite persulfate (MPS)] were developed. The feasibility, mechanisms, and optimal conditions for remediating weathered lubricating oil (WLO)-contaminated soils using composite PS oxidants were evaluated. BPS was prepared by blending PS and NaOH powders (molar ratio = 1:0.3), while MPS was prepared by mixing PS, FeCl2, and KMnO4 at a molar ratio of 1:0.3:0.05 for PS:Fe:Mn. The oxidation of rhodamine B (RhB) dye using BPS and MPS followed second-order kinetics. MPS process was more effective in organic oxidation, likely due to its electron transfer mechanism. The generation of •SO4- in the BPS process required activation by •OH, potentially leading to more efficient and stable •SO4- generation and subsequent organic chemical oxidation. Radical analyses revealed that •SO4- was present in the pH range of 3–12, with the strongest •OH signal at pH 7–9. Employing hybrid BPS and MPS for WLO-contaminated soil remediation could achieve optimal TPH removal efficiency due to the combined generation of •OH (high reactivity) and •SO4- (stable characteristics). The addition of BPS helped neutralize acidified soils and maintained a higher soil pH (around 6.1). The multi-stage oxidation using the hybrid composite PS oxidants (MPS + BPS) at a 1:1 ratio (w/w) achieved 84 % TPH removal (initial TPH = 7721 mg/kg) after three oxidation stages (5 % w/w oxidant dosage). The composite oxidation process offers a more reactive oxidation potential with an extended oxidant life without causing a substantial pH drop.

Scaling-up the use of macroscopic photo-CWPO La1-xTixFeO3/SiC alveolar foam catalyst for solar water treatment against micropollutants

Current wastewater treatment plants are not prepared for the removal of micropollutants like phenol, pharmaceuticals and pesticides in water. As their release into the environment has adverse consequences towards the living organisms of ecosystems, the engineering of novel sustainable processes able to ultimately remove the emerging organic contaminants is an objective of paramount importance. Hereby we report for the first time on the successful scale-up of a macroscopic photo-CWPO La1-xTixFeO3/SiC alveolar foam catalyst used at the pilot-plant scale inside a Compound Parabolic Collectors based photoreactor. The removal of a span of organic micropollutants in water matrices of different complexity was efficiently realized under natural solar radiation using H2O2 or persulfates as oxidizing agent. The water matrix composition affected the efficiency of the degradation process. Using H2O2, for a collected energy of ca. 27 KJ/mol, the rate of micropollutant removal ranged from 53 % to 95 % in distilled water depending on the micropollutant in a cocktail configuration. It was lowered to the 17–66 % range in tap water, and to the 8–42 % range in simulated urban wastewater. The results demonstrated the promise of using sodium persulfate as oxidant instead of H2O2, with a better efficiency towards the removal of most of the micropollutants tested. The use of the sodium persulfate oxidant allows for overcoming the drawbacks associated to the treatment of real water matrices observed using H2O2, as better performances were reached when increasing the water matrix complexity. Complete removal of carbamazepine and diclofenac micropollutants was reached in tap water and simulated urban wastewater for ca. 27 KJ/mol of collected energy. The degradation performances combined to the catalyst robustness make this water treatment technology promising for operating in a continuous way under natural solar light.