Mechanistic study on the combination of ultrasound and peroxymonosulfate for the decomposition of endocrine disrupting compounds

Ultrasonic treatment of endocrine disrupting compounds, pharmaceuticals, and personal care products in water: An updated review

Pharmaceuticals, personal care products (PPCPs), and endocrine-disrupting compounds (EDCs) have seen a recent sustained increase in usage, leading to increasing discharge and accumulation in wastewater. Conventional water treatment and disinfection processes are somewhat limited in effectively addressing this micropollutant issue. Ultrasonication (US), which serves as an advanced oxidation process, is based on the principle of ultrasound irradiation, exposing water to high-frequency waves, inducing thermal decomposition of H2O while using the produced radicals to oxidize and break down dissolved contaminants. This review evaluates research over the past five years on US-based technologies for the effective degradation of EDCs and PPCPs in water and assesses various factors that can influence the removal rate: solution pH, temperature of water, presence of background common ions, natural organic matter, species that serve as promoters and scavengers, and variations in US conditions (e.g., frequency, power density, and reaction type). This review also discusses various types of carbon/non-carbon catalysts, O3 and ultraviolet processes that can further enhance the degradation efficiency of EDCs and PPCPs in combination with US processes. Furthermore, numerous types of EDCs and PPCPs and recent research trends for these organic contaminants are considered.

Tetracycline degradation by dual-frequency ultrasound combined with peroxymonosulfate

Tetracycline has received a great deal of interest for the harmful effects of substance abuse on ecosystems and humanity. The effects of different processes on the degradation of tetracycline were compared, with dual-frequency ultrasound (DFUS) in combination with peroxymonosulfate (PMS) being the most effective for the tetracycline degradation. Free radical scavenging experiments showed that O2∙-,SO4∙- and •OH were the main reactive radicals in the degradation of tetracycline. According to the major intermediates of tetracycline degradation identified, three possible degradation pathways were proposed, which are of significance for translational studies of tetracycline degradation. Notably, these intermediates were found to be significantly less toxicity. The number of active bubbles in the degradation vessel was calculated using a semi-empirical formula, and a higher value of 1.44 × 108 L-1s-1 of bubbles was obtained when using dual-frequency ultrasound at 20 kHz (210 W/L) and 80 kHz (85.4 W/L). Therefore, compared to 20 kHz, although the yield of strong oxidizing substances from individual active bubbles decreased slightly, a significant increment of the number of active bubbles still resulted in a higher synergistic effect, and the combination of DFUS and PMS should be effective in promoting the generation of reactive free radicals and mass transfer processes within the degradation vessel, which provides a method for efficient removal of tetracycline from wastewater.

The effect of dual-frequency ultrasound on synergistic Sonochemical oxidation to degrade aflatoxin B1

This study investigated the degradation of aflatoxin B1 (AFB1) in food by using dual-frequency ultrasound (DFUS) and the effects of sonochemical oxidation on the efficacy. It was found that the degradation of AFB1 by bath ultrasound (BU), probe ultrasound (PU), and DFUS were all consistent with first-order kinetics. The use of DFUS significantly increased the AFB1 degradation to 91.3%, and compared with BU and PU, it increased by about 177.0% and 61.5% after 30 min treatment. DFUS could generate a synergistic effect to accelerate the generation of free radicals, which promoted sonochemical oxidation to degrade AFB1. It could be speculated that hydroxyl radical (·OH) probably acted a dominant part in the AFB1 degradation by DFUS, and the hydrogen atoms (·H) might also are contributed. These results indicated that DFUS was an effective method of AFB1 degradation.

Advanced degradation of organic pollutants using sonophotocatalytic peroxymonosulfate activation with CoFe2O4/Cu- and Ce-doped SnO2 composites

The rampant upsurge of organic pollutants in aqueous media has become one of the major concerns nowadays. Finding non-specific catalysts that can target a wide range of organic pollutants is a key challenge. Eco-friendly oxidative radicals, such as promoted by peroxymonosulfate (PMS), are necessary for efficient water decontamination. We propose a multicomponent composite catalyst for activating PMS using a dual strategy of sonophotocatalysis. The composite integrates cobalt ferrite and Cu- or Ce-doped SnO2, with the at. % of doping metal and the mixture ratio carefully balanced. The top-performing architectures were able to decompose rhodamine B (20 ppm), a representative pollutant, in under 3 min and achieve over 70% mineralization in just 5 min. The synthesized nanocomposites demonstrated exceptional sonophotocatalytic performance, even when treating complex and diverse multipollutant solutions (80 ppm), achieving over 75% mineralization after 150 min. Considering their high stability and reusability, the proposed CoFe2O4/Cu- and Ce-doped SnO2 materials are among the state-of-the-art heterogeneous catalysts for mineralizing organic pollutants through PMS activation.

Systematic study of the synergistic and kinetics effects on the removal of contaminants of emerging concern from water by ultrasound in the presence of diverse oxidants

The enhancement of the ultrasound system by adding diverse oxidants to remove a model contaminant (acetaminophen, ACE) in water was investigated. Different parameters were evaluated to study their effect on both the degradation kinetics and the synergy of the combination. The variables studied were the ultrasonic frequency (575, 858, and 1135 kHz), type of oxidant (hydrogen peroxide, sodium peroxydisulfate (or persulfate, PDS), and potassium peroxymonosulfate (PMS)), ACE concentration (4, 8, and 40 µM), and oxidant concentration (0.01, 0.1, 1, and 5 mM). Particular interest was placed on synergistic effects, implying that one process (or both) is activated by the other to lead to greater efficiency. Interestingly, the parameters that led to the higher synergistic effects did not always lead to the most favorable degradation kinetics. An increase in ACE removal of 20% was obtained using the highest frequency studied (1135 kHz), PMS 0.1 mM, and the highest concentration of ACE (40 µM). The intensification of degradation was mainly due to the ability of ultrasound to activate oxidants and produce extra hydroxyl radicals (HO•) or sulfate radicals (SO4•-). Under these conditions, treatment of ACE spiked into seawater, hospital wastewater, and urine was performed. The hospital wastewater matrix inhibited ACE degradation slightly, while the urine components inhibited the pollutant degradation completely. The inhibition was mainly attributed to the competing organic matter in the effluents for the sono-generated radical species. On the contrary, the removal of ACE in seawater was significantly intensified due to "salting out" effects and the production of the strong oxidant HOCl from the reaction of chloride ions with PMS.

Structure of a novel Co-based heterogeneous catalyst via Mn3(PO4)2 as a carrier to efficiently activate peroxymonosulfate for improving degradation of sulfonamides

Effective degradation of sulfonamides (SAs) in water is of global importance for decreasing its pathogenicity and bioaccumulation. In this study, Mn₃(PO₄)₂ was used as a carrier to fabricate a novel and high-efficient catalyst with Co₃O₄ anchored (Co₃O₄@Mn₃(PO₄)₂) for the activation of peroxymonosulfate (PMS) to degrade SAs. Surprisingly, the catalyst exhibited superior performance, and nearly 100% of SAs (10 mg L^-1) including sulfamethazine (SMZ), sulfadimethoxine (SDM), sulfamethoxazole (SMX), and sulfisoxazole (SIZ) was degraded by Co₃O₄@Mn₃(PO₄)₂-activated PMS within 10 min. A series of characterization of the Co₃O₄@Mn₃(PO₄)₂ composite were conducted and the main operational parameters of SMZ degradation were investigated. SO₄^•-, •OH, and ¹O₂ were determined to be the dominating reactive oxygen species (ROS) responsible for the degradation of SMZ. Co₃O₄@Mn₃(PO₄)₂ also exhibited excellent stability and the removal rate of SMZ still maintained over 99% even in the fifth cycle. The plausible pathways and mechanisms of SMZ degradation in the system of Co₃O₄@Mn₃(PO₄)₂/PMS were deduced on the basis of the analyses of LCMS/MS and XPS. This is the first report on high-efficient heterogeneous activating PMS by mooring Co₃O₄ on Mn₃(PO₄)₂ to degrade SAs, which provides us with a strategy to structure novel bimetallic catalysts for PMS activation.

Highly Active Manganese Oxide from Electrolytic Manganese Anode Slime for Efficient Removal of Antibiotics Induced by Dissociation of Peroxymonosulfate

In this paper, high-activity manganese oxide was prepared from electrolytic manganese anode slime to realize the efficient removal of antibiotics. The effects of sulfuric acid concentration, ethanol dosage, liquid-solid ratio, leaching temperature and leaching time on the leaching of manganese from electrolytic manganese anode slime were systematically studied. Under the optimal conditions, the leaching rate of manganese reached 88.74%. In addition, a Mn₃O₄ catalyst was synthesized and used to activate hydrogen persulfate (PMS) to degrade tetracycline hydrochloride (TCH). The synthesized Mn₃O₄ was characterized by XRD, XPS, Raman, SEM and HRTEM. As a result, the prepared Mn₃O₄ is spherical, with high purity and crystallinity. The catalytic activity of Mn₃O₄ for PMS to degrade TCH was increased to 82.11%. In addition, after four cycles, the performance remained at 78.5%, showing excellent stability and recyclability. In addition, O₂^- and ¹O₂ are the main active species in the degradation reaction. The activity of Mn₃O₄ is attributed to it containing Mn(II) and Mn(III) at the same time, which can quickly realize the transformation of high-valence and low-valence manganese, promote the transfer of electrons and realize the degradation of organic pollutants.

Emerging environmental contaminants: A global perspective on policies and regulations

Emerging contaminants include many synthetic or natural substances, such as pharmaceuticals and personal care products, hormones, and flame retardants that are not often controlled or monitored in the environment. The consumption or use of these substances is on an ever-rising trend, which dangerously increases their prevalence in practically all environmental matrices. These contaminants are present in low environmental concentrations and cause severe effects on human health and the biota. The present review analyzed 2012-2022 years papers via PubChem, science direct, National Center for Biotechnology Information, web of science on the legislations and policies of emerging contaminants globally. A state-of-the-art review of several studies in the literature focus on examining and evaluating the emerging contaminants and the frameworks adopted by developed and developing countries to combat the release of emerging contaminants and form footprints towards water sustainability which includes water availability, usage patterns, generation and pollution management, the health of aquatic systems, and societal vulnerability. The paper aims to provide a comprehensive view of current global policies and framework regarding evaluating and assessing the chemicals, in light of being a threat to the environment and biota. The review also highlights the future global prospects, including current governmental activities and emerging contaminant policy measures. The review concludes with suggestions and way forward to control the inventory and disposal of emerging contaminants in the environment.

Co/N co-doped porous carbon as a catalyst for the degradation of RhB by efficient activation of peroxymonosulfate

We report on the preparation of Co/N-NPC_x/y with porous structure and excellent activation properties. The synthesis involves the preparation of Zn/Co-ZIF_x and the carbonization of Zn/Co-ZIF_x at a high temperature in an inert atmosphere. The volatilization of zinc during carbonization results in a porous structure, which is beneficial to the migration of pollutants. The sizes, specific surface areas, and pore size distribution of Co/N-NPC_x/y can be achieved by tuning Zn/Co ratio. The calcination temperatures mainly affect the crystalline phase, crystallinity, and magnetic properties of the as-prepared materials. The effects of the as-prepared materials properties and activation conditions on the Rhodamine B (RhB) degradation by PMS activation were investigated. Overall, it exhibited superior catalytic activity in PMS activation, as evidenced by almost complete removal of RhB (0.020 mM, 100 mL) by using 5 mg/L Co/N-NPC_0.5/900 and 1.250 mM PMS within 30 min. Furthermore, it confirmed the participation of SO₄^•-, •OH, and ¹O₂ in the catalytic reaction, and both SO₄^•- and ¹O₂ were the main reactive oxygen species that play a major role.

Preparation of VCo-MOF@MXene composite catalyst and study on its removal of ciprofloxacin by catalytically activating peroxymonosulfate: Construction of ternary system and superoxide radical pathway

The synergistic effect between transition metal active centers and the generation of multiple removal pathways has a significant impact on the catalytic activation efficiency of peroxymonosulfate. In this work, a kind of composite catalyst was prepared by growing VCo-metal-organic frameworks (VCo-MOF) in-situ on the surface of Ti3C2Tx by a solvothermal method. The morphology and structure are characterized by Transmission Electron Microscope (TEM), Energy Dispersion Spectrum (EDS), Atomic Force Microscope (AFM), etc. Response surface methodology was used to optimize the experimental conditions. Only 5 mg catalyst can be used to effectively activate PMS and remove 96.14 % ciprofloxacin (CIP, 20 mg/L) within 30 min. The removal effect of catalyst on CIP in different actual water environment was explored. In addition, the fluorescence spectrum test also verified the effective removal of ciprofloxacin. V-Co-Ti ternary system provides a wealth of active sites for CIP removal. Cyclic voltammetry (CV) and lear sweep voltammetry (LSV) tests showed the existence of the electron transfer pathway. The results of density functional theory (DFT) calculation show that VCo-MOF@Ti3C2Tx has excellent adsorption and activation ability for PMS. At the same time, the hydrophilicity of the catalyst makes PMS more inclined to react with water molecules, which promotes the formation of a unique superoxide radical path.

Promising Low-Cost Adsorbent from Waste Green Tea Leaves for Phenol Removal in Aqueous Solution

Phenol is the most common organic pollutant in many industrial wastewaters that may pose a health risk to humans due to its widespread application as industrial ingredients and additives. In this study, waste green tea leaves (WGTLs) were modified through chemical activation/carbonization and used as an adsorbent in the presence of ultrasound (cavitation) to eliminate phenol in the aqueous solution. Different treatments, such as cavitation, adsorption, and sono-adsorption were investigated to remove the phenol. The scanning electron microscope (SEM) morphology of the adsorbent revealed that the structure of WGTLs was porous before phenol was adsorbed. A Fourier Transform Infrared (FTIR) analysis showed an open chain of carboxylic acids after the sono-adsorption process. The results revealed that the sono-adsorption process is more efficient with enhanced removal percentages than individual processes. A maximum phenol removal of 92% was obtained using the sono-adsorption process under an optimal set of operating parameters, such as pH 3.5, 25 mg L⁻¹ phenol concentration, 800 mg L⁻¹ adsorbent dosage, 60 min time interval, 30 ± 2 °C temperature, and 80 W cavitation power. Removal of chemical oxygen demand (COD) and total organic carbon (TOC) reached 85% and 53%. The Freundlich isotherm model with a larger correlation coefficient (R², 0.972) was better fitted for nonlinear regression than the Langmuir model, and the sono-adsorption process confirmed the pseudo-second-order reaction kinetics. The findings indicated that WGTLs in the presence of a cavitation effect prove to be a promising candidate for reducing phenol from the aqueous environment.

Atmospheric plasma-based approaches for the degradation of dimethyl phthalate (DMP) in water

Cold plasma based treatment of contaminated water is becoming a promising novel green remediation option. This study assessed the performance of two different cold plasma reactors, using, respectively, a self-pulsing discharge (SPD) and a multipin corona discharge (MCD), in the degradation of dimethyl phthalate (DMP), a persistent and ubiquitous pollutant of the aquatic environment. The process kinetics and energy efficiency, as well as the main plasma generated reactive species were determined under various operating conditions concerning the plasma feed gas and flowrate, the voltage polarity, the input power, the DMP initial concentration, the liquid conductivity, and the aqueous matrix used to prepare DMP solutions for these experiments. The MCD reactor, operated with air as plasma feed gas and negative voltage polarity, gave the best results in terms of rate and energy efficiency. Moreover, variations in plasma input power and in the liquid conductivity have limited effect on DMP degradation rate, making this reactor suitable for treating liquids with a range of initial conductivities The effects of DMP initial concentration on its rate of degradation and on the process energy efficiency were also investigated. Differences in the efficiency of production and distribution of plasma generated reactive species, notably ^•OH and H₂O₂, observed for the two tested reactors are discussed in terms of different extension of the plasma/liquid interface and diffusion into the bulk solution. It is proposed that among the reactive species, ^•OH foremost, and O₃ to a lesser extent, play a pivotal role in DMP degradation, while the contribution of H₂O₂ appears to be limited. The rate of DMP degradation was not drastically different in Milli-Q water and in tap water, a positive outcome in view of practical applications of the technology. The lower rate observed in tap than in Milli-Q water is attributed to the presence of bicarbonate and carbonate, which are known scavengers of hydroxyl radicals.

Peracids - New oxidants in advanced oxidation processes: The use of peracetic acid, peroxymonosulfate, and persulfate salts in the removal of organic micropollutants of emerging concern - A review

In recent years, there has been increasing interest in using of advanced oxidation processes in water and wastewater decontamination. As a new oxidants peracids, mainly peracetic acid (PAA) and peracid salts, i.e. peroxymonosulfate (PMS) and persulfate (PS) are used. The degradation process of organic compounds takes place with the participation of radicals, including hydroxyl (^•OH) and sulfate (SO₄^•-) radicals derived from the peracids activation processes. Peracids can be activated in homogeneous systems (UV radiation, d-electron metal ions, e.g. Fe²⁺, Co²⁺, Mn²⁺, base, ozonolysis, thermolysis, radiolysis), or using heterogeneous activation (metals with zero oxidation state, metal oxides, quinones, activated carbon, semiconductors). As a result of oxidation, products of a lower mass than the parent compounds, less toxic, and more susceptible to biodegradation are formed. An important task is to investigate the effect of the peracid activation method and matrix composition on the efficiency of contamination removal. The article presents the latest information about the application of peracids in the removal of organic micropollutants of emerging concern (mainly focuses on endocrine disrupted compounds). The most important information on peracetic acid, peroxymonosulfate and persulfate salts, and methods of their activation are presented. Current uses of these oxidants in organic micropollutants removal are also described. Information was collected on the factors influencing the oxidation process and the effectiveness of pollutant removal. This paper compares PAA, PMS and PS-based processes for the first time in terms of kinetics and efficiency.

Enhanced degradation of bisphenol A by mixed ZIF derived CoZn oxide encapsulated N-doped carbon via peroxymonosulfate activation: The importance of N doping amount

In this study, mixed metal cobalt zinc oxide embedded nitrogen enriched porous carbon composites (CoZnO-PC) were prepared via pyrolyzing polyvinylpyrrolidone (PVP) encapsulated Co, Zn-bimetal centered zeolitic imidazolate frameworks (ZIF). The prepared composites were then used to activate peroxymonosulfate (PMS) for bisphenol A (BPA) removal in water. When mole ratio of Co/Zn was 2/1, the resulted Co₂Zn₁O-PC possessed spinel structure with prominent degradation capability, in which the introduction of Zn accelerated the PMS activation performance of Co through establishing bimetal synergistic interactions. Both radical and non-radical activation pathways were existed in the Co₂Zn₁O-PC/PMS system, in which Co₂Zn₁O dominated the radical pathway whereas PC dominated the non-radical way. Since PVP contained abundant nitrogen atoms and could form strong coordination interactions with the ZIF precursor, the introduction of PVP in the ZIF precursor prevented pore collapsing during pyrolysis process, as well as enhancing the nitrogen content in the pyrolzed composites, which significantly promoted the generation of singlet oxygen. With combined pathways, the Co₂Zn₁O-PC/PMS system showed a wide pH application range with promising mineralization rate. Meanwhile, the spinel-structured Co₂Zn₁O-PC was magnetically separable with desirable recyclability. This study presents a novel composite with remarkable performance for the removal of refractory organic pollutants in municipal wastewater.

A review on efficient removal of phthalic acid esters via biochars and transition metals-activated persulfate systems

As emerging contaminants, PAEs (Phthalic Acid Esters or Phthalate Esters) have been extensively utilized in industrial production to soften the rigid plastics (plasticizers), and their related products are widely distributed in our daily life. The PAEs can readily transfer from the products to the surrounding environment due to not being chemically bound to the products. In this study, we analyzed the PAEs' properties, usage, and consumption in the world, as well as toxicity to human beings. As endocrine-disrupting chemicals (EDCs), PAEs can disturb the normal hormones reactions, resulting in developmental and reproductive problems. Thus, we have to concern the removal strategies of PAEs. We summarized two novel approaches, including biochars and persulfate (PS) oxidation for effectively removing PAEs in the literature. Their characteristics, removal mechanisms, and the main impact factors on the removal of PAEs were highlighted. Moreover, transition metal-activated PS showed good performance on PAEs degradation. Furthermore, the synergy of biochars and transition metals-PS can overcome the disadvantages of a single approach, and show better performance on the removal of PAEs. Finally, we put forward vital strategies to update two approaches (including the combined) for enhancing the removal of PAEs. It is expected that the researchers or scientists can get a hint on effectively remediating PAEs-contaminated sites via the biochars' sorption/transition metals-PS or the combined two from this review paper.

Fe3C-porous carbon derived from Fe2O3 loaded MOF-74(Zn) for the removal of high concentration BPA: The integrations of adsorptive/catalytic synergies and radical/non-radical mechanisms

In this study, novel Fe₃C-porous carbon composites (Fe₃C-C) were prepared via the pyrolysis of Fe₂O₃ loaded MOF-74(Zn), which could integrate both strong adsorption properties and excellent peroxymonosulfate (PMS) activating performance for the removal of bisphenol A (BPA) in water. Results indicated that the composite obtained at 1000 °C (Fe₃C-C1000) exhibited optimal catalytic capability. Specifically, 0.1 mM BPA could be completely removed by 0.1 g/L Fe₃C-C1000 within 10 min after the adsorption enrichment. Afterwards, the mechanism of Fe₃C-C/PMS system was unveiled based on quenching tests, electron spin resonance analysis, electrochemical analysis, PMS consumption detection and solvent exchange (H₂O to D₂O) test. The BPA degradation pathways were also analyzed through identifying its decomposition intermediates. Results showed that the Fe₃C and porous carbon constituents could activate PMS via radical and non-radical mechanisms respectively, and BPA was readily degraded through both pathways. Additionally, it was found that the Fe₃C-C1000/PMS system could maintain conspicuous catalytic performance in a variety of complicated water matrices with wide pH application range and long-time use stability. This study suggests a new insight for the design and development of novel catalyst which can be used for the removal of refractory organic contaminants with high concentrations in water media.

Electron paramagnetic resonance of sonicated powder suspensions in organic solvents

The chemical effects of the acoustic cavitation generated by ultrasound translates into the production of highly reactive radicals. Acoustic cavitation is widely explored in aqueous solutions but it remains poorly studied in organic liquids and in particular in liquid/solid media. However, several heterogeneous catalysis reactions take place in organic solvents. Thus, we sonicated trimethylene glycol and propylene glycol in the presence of silica particles (SiO₂) of different sizes (5-15 nm, 0.2-0.3 µm, 12-26 µm) and amounts (0.5 wt% and 3 wt%) at an ultrasound frequency of 20 kHz to quantify the radicals generated. The spin trap 5,5-dimethyl-1-pyrrolin-N-oxide (DMPO) was used to trap the generated radicals for study by electron paramagnetic resonance (EPR) spectroscopy. We identified the trapped radical as the hydroxyalkyl radical adduct of DMPO, and we quantified it using stable radical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as a quantitation standard. The concentration of DMPO spin adducts in solutions containing silica size 12-26 µm was higher than the solution without particles. The presence of these particles increased the concentration of the acoustically generated radicals by a factor of 1.5 (29 µM for 0.5 wt% of SiO₂ size 12-26 µm vs 19 µM for 0 wt%, after 60 min of sonication). Ultrasound produced fewest radicals in solutions with the smallest particles; the concentration of radical adducts was highest for SiO₂ particle size 12-26 µm at 0.5 wt% loading, reaching 29 µM after 60 min sonication. Ultrasound power of 50.6 W produced more radicals than 24.7 W (23 µM and 18 µM, respectively, at 30 min sonication). Increased temperature during sonication generated more radical adducts in the medium (26 µM at 75 °C and 18 µM at 61 °C after 30 min sonication). Acoustic cavitation, in the presence of silica, increased the production of radical species in the studied organic medium.

A Review on Additives-assisted Ultrasound for Organic Pollutants Degradation

In the past 2 decades, considerable attentions have been paid to the sonochemical advanced oxidation processes (SAOPs) in the fields of pollutants removal. SAOPs are powerful methods for refractory pollutants degradation due to the free radicals (e.g., •OH and •H) generated by water pyrolysis and extremely high temperature and pressure in and around cavitation bubbles. Reports on various additives for the improvement of sonochemical pollutants degradation including oxidants, inorganic anions, etc. have been made. This paper presents a comprehensive review on the ultrasound (US) alone and sono-hybrid systems for various pollutants degradation. In this paper, the degradation efficiency of various pollutants in sono-hybrid systems are elucidated in detail, and particular emphasis is placed on the reaction mechanism of additives in US for the enhancement of pollutants degradation. The problems on the applications of the current sono-hybrid systems are identified and discussed, and the outlooks for further in-depth studies on the challenges and some research needs for the applications of SAOPs for the removal of organic pollutants from aquatic systems are made at the end.

Efficient removal of bisphenol A with activation of peroxydisulfate via electrochemically assisted Fe(III)-nitrilotriacetic acid system under neutral condition

In this work, an innovative electrochemically assisted Fe(III)-nitrilotriacetic acid system for the activation of peroxydisulfate (electro/Fe(III)-NTA/PDS) was proposed for the removal of bisphenol A (BPA) at neutral pH with commercial graphite electrodes. The efficient BPA decay was mainly originated from the continuous activation of PDS by Fe(II) reduced from Fe(III)-NTA complexes at the cathode. Scavenger experiments and electron paramagnetic resonance (EPR) measurements confirmed that the removal of BPA occurred through graphite adsorption, direct electron transfer (DET) and radical oxidation. Sulfate and hydroxyl radicals were primarily responsible for the oxidation of BPA while graphite adsorption and DET played a minor role in BPA removal. The influence of Fe(III) concentration, PDS dosage, input current, NTA to Fe(III) molar ratio as well as coexisting inorganic anions (Cl^-, NO₃^-, H₂PO₄^- and HCO₃^-) on BPA elimination was explored. The BPA removal efficiency reached 93.5 % after 60 min reaction in the electro/Fe(III)-NTA/PDS system under the conditions of initial pH 7.0, 0.30 mM Fe(III), 0.15 mM NTA, 5 mM PDS and 5 mA constant current. Overall, this research provided a novel perspective and potential for remediation of organic wastewater using NTA in combination with electrochemistry in the homogeneous Fe(III)/persulfate system.

Yeast biomass-induced Co2P/biochar composite for sulfonamide antibiotics degradation through peroxymonosulfate activation

Advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS) activation have attracted increasing attention in recent years for organic pollutants removal. Herein, we put forward a facile method to form cobalt phosphide/carbon composite for PMS activation. Combining impregnation approach with pyrolysis treatment enabled the formation of Co₂P/biochar composites using baker's yeast and Co²⁺ as precursors. The as-synthesized products exhibited excellent catalytic activity for sulfamethoxazole (SMX) degradation over the pH range 3.0-9.0 b y activating PMS. For example, 100% of SMX (20 mg L^-1) removal was achieved in 20 min with catalyst dosage of 0.4 g L^-1 and PMS loading of 0.4 g L^-1. Near zero Co²⁺ leaching was observed during catalytic reaction, which remarkably lowered the toxic risk of transition metal ion in water. Meanwhile, the reusability of catalyst could be attained by thermal treatment. SMX degradation intermediates were identified by liquid chromatography-mass spectrometry (LC-MS), which facilitated the proposal of possible SMX degradation pathways. Ecological Structure Activity Relationships (ECOSAR) analysis indicated that SMX degradation intermediates may not pose ecological toxicity to the environment. Further investigation verified that Co₂P/biochar composites could set off PMS activation not only for the degradation of SMX but also for other sulfonamides. In this study, we not only developed a facile method of utilizing environmental-benign biomass for transition metal phosphide/carbon composite formation, but also achieved highly efficient antibiotic elimination by PMS-based AOP.

Catalytic degradation of mefenamic acid by peroxymonosulfate activated with MWCNTs-CoFe2O4: influencing factors, degradation pathway, and comparison of activation processes

The cobalt ferrite loaded on multi-walled carbon nanotubes (MWCNTs-CoFe₂O₄) was synthesized and used as a novel catalyst for the degradation of mefenamic acid (MFA) in the presence of peroxymonosulfate (PMS). The results showed that MWCNTs-CoFe₂O₄ has higher catalytic performance in the activation of PMS and degradation of MFA compared with MWCNTs, Co²⁺, Fe²⁺, and CoFe₂O₄. The highest kinetic constant rate (0.0198 min^-1) and MFA degradation (97.63%) were obtained at pH = 7, PMS = 4 mM, catalyst = 500 mg/L, MFA = 10 mg/L, and time = 150 min. MFA degradation accelerated with increasing PMS and catalyst dosage but decreased by initial pH. The influence of different anions and water matrix on the catalytic system was investigated, and the results explained a decrease in the MFA rate in the presence of the interfering substances. Scavenging experiments showed that both sulfate radical anion (SO₄^•-) and hydroxyl radical (^•OH) were effective on MFA degradation, but SO₄^•- had a greater effect on the degradation of MFA. In addition, the stability and recyclability of MWCNTs-CoFe₂O₄ were evaluated in the consecutive reaction cycle; the MFA degradation rate reached 89.75% after 4 cycles of reaction. The MFA degradation products were identified by gas chromatography-mass spectrometry (GC-MS) and their degradation pathway was suggested. Finally, a comparison was conducted among the methods used for PMS activation, and the results showed that the cobalt ferrite-based catalyst has high degradation efficiency. However, ultrasound, heat, and ultraviolet (UV) processes can be used to improve the degradation rate of the MWCNTs-CoFe₂O₄/PMS system at different reaction times.

Efficient degradation of bisphenol A in water by heterogeneous activation of peroxymonosulfate using highly active cobalt ferrite nanoparticles

Cobalt ferrite CoFe₂O₄ catalyst was fabricated and systematically investigated as an efficient peroxymonosulfate (PMS, HSO₅^-) activator for the degradation of recalcitrant organic contaminants (ROCs) in water treatment. Both SO₄^- and OH on the surface of catalyst were unveiled to be primarily responsible for bisphenol A (BPA) degradation by a comprehensive study using electron paramagnetic resonance (EPR), radical scavengers and quantification of SO₄^-, and the negligible contribution of singlet oxygen (¹O₂) was also observed. BPA degradation was accelerated in the presence of humic acid, and it increased first but then decreased with the further addition of fulvic acid. Moreover, the presence of chloride and bicarbonate ions can enhance both BPA and TOC removal. The toxicity of the target aqueous solution ascended slowly at the early stage but then declined dramatically and almost vanished as the reaction proceeded. The removal efficiencies of other typical ROCs (clofibric acid, 2,4-dichlorophenol, etc.) and the decontamination of natural surface water spiked with BPA were also evaluated. This CoFe₂O₄/PMS process could be well applied as a safe, efficient, and sustainable approach for ROCs remediation in complex wastewater matrix.

Influence of co-existing cations and anions on removal of direct red 89 dye from synthetic wastewater by hydrodynamic cavitation process: An empirical modeling

In the present study the evaluation of Direct Red 89 (DR89) dye removal from synthetic wastewater by a lab-scale hydrodynamic cavitation (HC) process has been investigated under different operational conditions; the influence of co-existing cations and anions was applied using synthetic wastewater to assess whether the DR89 removal was enhanced. To study the effect of operational parameters, an empirical approach was adopted for the modeling of the HC process. The results showed that the DR89 degradation rate was strongly influenced by solution pH, reaction time and initial DR89 concentration. The removal efficiencies of DR89 were enhanced remarkably with the reaction time increment. When the initial concentration of DR89 increased from 30 to 90 mg/L, the DR89 removal efficiency decreased from 36.3 ± 3.8% to 17.5 ± 2.5%. In addition, the highest DR89 removal efficiency (75.4 ± 3.4%) was observed at a solution pH of 3. At a solution pH of 8, the DR89 removal efficiency was 18.4 ± 1.1%. An initial DR89 concentration of 80 mg/L was 75.4 ± 5.1% degraded after 130 min at a solution pH of 3. The results indicated that a synergistic effect occurred due to the added ions except for HCO₃^-. The removal of DR89 by the HC process was extremely enhanced with NO₃‾ ions with synergetic index higher than 2.5. Kinetic studies revealed that the decolorization of DR89 by HC followed a first order kinetic mechanism. The comparison between the predicted results of the empirical model and experimental data was also conducted. The empirical model described the DR89 removal efficiency under different conditions (R²: 0.93) and the results showed the HC reaction to be a useful technology for the treatment of dye in the textile wastewater.

Activation of peroxymonosulfate using drinking water treatment residuals modified by hydrothermal treatment for imidacloprid degradation

In this study, water treatment residuals (WTRs), a safe and valuable by-product containing iron, was used as a precursor for preparing effective activator (HWTRs) of peroxymonosulfate (PMS) for imidacloprid (IMD) degradation by hydrothermal treatment. Several affecting parameters on IMD degradation including PMS concentration, HWTRs dosage, initial pH and water matrix were discussed. The results of degradation experiments demonstrated that within the reaction time of 4 h, 97.64% of IMD could be removed with 0.5 g L^-1 HWTRs and 1.5 mM PMS, and the acidic conditions were favorable for IMD degradation. Both sulfate radicals (SO₄^•-) and hydroxyl radicals (·OH) were generated to attack the target pollutant IMD, and ·OH was the dominating radical in the HWTRs/PMS system, which was confirmed by the results of radicals scavenging experiments, electron spin-resonance spectroscopy (ESR) tests and quantitative analysis. What's more, X-ray photoelectron (XPS) spectroscopy was used to further verify the activation mechanism. Consequently, the activation by Fe(II) on the surface of HWTRs might dominate the reaction was confirmed. In addition, the possible degradation pathways of IMD were proposed on the basis of the degradation intermediates identified by LC-MS. This study offers an innovative idea for modifying raw WTRs to prepare efficient catalysts to activate PMS under relatively mild conditions.

Degradation of emerging contaminants by sono-Fenton process with in situ generated H2O2 and the improvement by P25-mediated visible light irradiation

Developing advanced treatment methods to minimize the release of emerging contaminants to natural water has become a matter of considerable interest. Sono-Fenton process was investigated to degrade bisphenol A (BPA) and sulfadiazine (SDZ). The H₂O₂ generated in situ was used as the exclusive source. Results showed that, the 400 kHz ultrasound is more efficient in creating homogeneous sono-Fenton than the 20 kHz apparatus due to the higher production of OH. Influence of Fe²⁺ was more remarkable on the degradation of hydrophilic SDZ, and its degradation kinetics was well fitted by two-stage kinetic model. However, the Fe²⁺ and H₂O₂ were unproductively wasted, which could not be improved by changing the dosing modes of Fe²⁺. The presence of P25 under visible light irradiation could significantly accelerate SDZ degradation at small amount of iron precursors, mainly via promoting the Fe²⁺/Fe³⁺ cycling by the photoelectrons. Moreover, SDZ degradation in sono-Fenton process was significantly inhibited at pH > 7, but the inhibition was very weak in P25-assisted sono-Fenton process. The presence of P25 also improved the mineralization. Three primary degradation pathways of SDZ degradation were proposed, including the attacking of the benzene ring, the oxidation of the amino group and the extrusion of SO₂.

Cooperation of Fe(II) and peroxymonosulfate for enhancement of sulfamethoxazole photodegradation: mechanism study and toxicity elimination

This study aims at systematically examining the potential of removing the emerging pollutant sulfamethoxazole (SMX) from aqueous solution under photo-assisted peroxymonosulfate (PMS) activation by Fe(ii). The residual SMX was determined by HPLC analysis. The concentration of Fe(ii) ([Fe(ii)]) was monitored during SMX degradation. Fe(ii) and PMS cooperated with each other for faster SMX photodegradation; a relatively lower or higher molar ratio between Fe(ii) and PMS led to lower SMX removal efficiency due to the insufficient radicals or scavenging effect. A fixed reaction ratio of [Fe(ii)]_Δ : [PMS]₀ with 1.6 : 1 at the first 5 min was detected for reactions with [Fe(ii)]₀ ≥ 0.5 mM or [PMS]₀ ≤ 0.25 mM. The pH level of around 6.0 was recommended for optimal SMX removal under the treatment process UVA + Fe(ii) + PMS. Six transformation products were detected through UPLC/ESI-MS analysis, and four of the proposed intermediates were newly reported. Concentrations of the intermediates were proposed based on the isoxazole-ring balance and the Beer–Lambert law. Total Organic Carbon (TOC) reduction was mainly attributed to the loss of benzene ring, N–S cleavage, and isoxazole ring opening during SMX degradation. The contributions of reactive species OH˙ and SO₄˙⁻ were determined based on quench tests. The acute toxicity of SMX to the rotifers was eliminated after the proposed treatment, demonstrating that the process was effective for SMX treatment and safe to the environment.

For the first time, this study systematically revealed the potential, the mechanism and the risk of removing sulfamethoxazole by UV/Fe(II)/peroxymonosulfate.