Organic Contaminants In Water Research Articles

Accelerated removal of organic pollutants by biochar-based iron carbon granule-activated periodate in chloride-containing water: The role of active chlorine

Ubiquitous in water environments, the chloride ion (Cl−) can impact the decontamination capacity of an oxidation system. However, minimal studies are available on its effects in periodate (PI)-based advanced oxidation processes. In this study, a novel biochar-based iron-carbon (FeBC) granule was synthesized to activate PI and remove organic pollutants from water containing Cl−. The FeBC/PI/Cl− system (FeBC: 0.5 g/L; PI: 0.5 mM; AO7: 20 mg/L; NaCl: 50 mM) exhibited excellent performance on various organic pollutants, with ˃ 85 % of Acid Orange (AO7) removal over a pH range of 3–10. Within 20 min after the tenth run, approximately 80 % of AO7 was removed. Inorganic ions and natural organic matter had a negligible effect on AO7 removal. Characterization results confirmed that the presence of Cl− enhanced Fe corrosion, thereby improving PI activation efficiency for removing AO7. Electron paramagnetic resonance spectroscopy and active species trapping experiments verified that radicals (•OH and O2•−) and nonradical (1O2, Fe(IV), and electron transfer) oxidation processes participated in the FeBC/PI system. Moreover, the presence of Cl− accelerated •OH, O2•−, 1O2, and Fe(IV) formation and generated active chlorine, such as HOCl. The main pathways involved in the generation of multiple reactive species were evaluated. AO7 degradation pathways were proposed, and numerous intermediates exhibited decreased toxicity. These findings provide new insights for the decontamination of organic contaminants in water containing Cl−.

A non-targeted analysis workflow for the identification of organic contaminants in a sludge water based on fragmentation matching score and metadata

ABSTRACT Non-targeted analysis (NTA) methods have been increasingly used to discover organic contaminants in environmental samples. The identification efficiency of conventional NTA workflow is often very low due to many factors such as low fragmentation score between experimental MS2 data and reference MS2 data/in-silico MS2 data. Additionally, the prioritisation of possible candidates is also challenging due to the large number of candidates obtained from MS acquisitions. In this study, a multiplatform data processing workflow applicable to non-targeted LC-MS data is proposed to improve the identification accuracy of organic contaminants in water. This workflow consists of (1) scanning quadrupole data-independent acquisition (SONAR) to acquire relatively clean MS1 and MS2 data, (2) data deconvolution using Progenesis QI Software to filter/select the appropriate ions (MS1 data), (3) the selected MS1 data matching against U.S. EPA Chemistry Dashboard to get a list of the environmentally related candidates with metadata (e.g., data sources, toxicity, and exposure), (4) experimental MS2 data matching against in-silico fragmentation data of the obtained candidate by MetFrag to obtain a fragmentation score, (5) compound identification through ranking the candidates by MetFrag based on fragmentation score and metadata. The identification efficiency of the metadata-based NTA workflow was evaluated using a 33-component mixture of chemicals in a complex sludge water. Out of 33 spiked compounds, 26 compounds had been identified using the defined NTA workflow. Most of the 26 identified compounds were recognized as 1st hit of the candidates obtained from the library searching. Overall, the incorporation of fragmentation score and metadata to rank the candidates has significantly improved the accuracy of the organic contaminant identification in the sludge water, compared to the conventional NTA workflow based solely on the fragmentation score.

Preparation of Cobalt-Nitrogen Co-Doped Carbon Nanotubes for Activated Peroxymonosulfate Degradation of Carbamazepine.

Cobalt-nitrogen co-doped carbon nanotubes (Co3@NCNT-800) were synthesized via a facile and economical approach to investigate the efficient degradation of organic pollutants in aqueous environments. This material demonstrated high catalytic efficiency in the degradation of carbamazepine (CBZ) in the presence of peroxymonosulfate (PMS). The experimental data revealed that at a neutral pH of 7 and an initial CBZ concentration of 20 mg/L, the application of Co3@NCNT-800 at 0.2 g/L facilitated a degradation rate of 64.7% within 60 min. Mechanistic investigations indicated that the presence of pyridinic nitrogen and cobalt species enhanced the generation of reactive oxygen species. Radical scavenging assays and electron spin resonance spectroscopy confirmed that radical and nonradical pathways contributed to CBZ degradation, with the nonradical mechanism being predominant. This research presents the development of a novel PMS catalyst, synthesized through an efficient and stable method, which provides a cost-effective solution for the remediation of organic contaminants in water.

Trace organic contaminants in lake waters: Occurrence and environmental risk assessment at the national scale in Canada

Numerous contaminants are produced and used daily, a significant fraction ultimately finding their way into natural waters. However, data on their distribution in lakes is lacking. To address this gap, the presence of 54 trace organic contaminants (TrOCs), representative of various human activities, was investigated in the surface water of 290 lakes across Canada. These lakes ranged from remote to highly impacted by human activities. In 88% of the sampled lakes, contaminants were detected, with up to 28 detections in a single lake. The compounds most frequently encountered were atrazine, cotinine, and deethylatrazine, each of which was present in more than a third of the lakes. The range of detected concentrations was from 0.23 ng/L to about 2200 ng/L for individual compounds, while the maximum cumulative concentration exceeded 8100 ng/L in a single lake. A risk assessment based on effect concentrations for three aquatic species (Pimephales promelas, Daphnia magna, and Tetrahymena pyriformis) was conducted, revealing that 6% of lakes exhibited a high potential risk for at least one species. In 59% of lakes, some contaminants with potential sub-lethal effects were detected, with the detection of up to 17 TrOCs with potential impacts. The results of this work provide the first reference point for monitoring the evolution of contamination in Canadian lakes by TrOCs. They demonstrate that a high proportion of the sampled lakes bear an environmentally relevant anthropogenic chemical footprint.

Effective activation of peroxymonosulfate by CoCr-LDH for removing organic contaminants in water: from lab-scale to practical applications.

In this study, CoCr layered double hydroxide material (CoCr-LDH) was prepared and used as an effective catalyst for peroxymonosulfate (PMS) activation to degrade organics in water. The prepared CoCr-LDH material had a crystalline structure and relatively porous structure, as determined by various surface analyses. In Rhodamine B (RhB) removal, the most outstanding PMS activation ability belongs to the material with a Co:Cr molar ratio of 2:1. The removal of RhB follows pseudo-first-order kinetics (R2 > 0.99) with an activation energy of 38.23 kJ/mol and efficiency of 98% after 7 min of treatment, and the total organic carbon of the solution reduced 47.2% after 10 min. The activation and oxidation mechanisms were proposed and the RhB degradation pathways were suggested with the key contribution of O2•- and 1O2. Notably, CoCr-LDH can activate PMS over a wide pH range of 4 - 9, and apply to a wide range of organic pollutants and aqueous environments. The material has high stability and good recovery, which can be reused for 5 cycles with a stable efficiency of above 88%, suggesting a high potential for practical recalcitrant water treatment via PMS activation by heterogeneous catalysts.

Enhancing hexachlorocyclohexane solubility with surfactants and ionic liquids

Surfactant-enhanced remediation of soil can increase the solubility of hydrophobic organic contaminants in water and improve their removal. In this study, the effect of 24 traditional surfactants and surface-active ionic liquids (SAILs) on the solubility of hexachlorocyclohexane isomers (α-, β-, γ-, δ-HCH) was evaluated in batch-type experiments. The combination of two different proportions of a cationic SAIL and an anionic surfactant was also assessed. The solubilisation capacity of the surfactant varied depending on its concentration and structure, but also the HCH isomer considered. In general, the anionic surfactants yielded the best results, increasing solubilisation of HCH up to 2.4 times compared to the control (pure water). α-HCH and γ-HCH isomers were more easily solubilised than β-HCH and δ-HCH regardless of the surfactant’s type. The main advantage of ionic liquids being their tunability, some clues are given for formulating surfactants to enhance the solubilisation of HCH. The combination of a traditional surfactant and a SAIL influenced the critical micelle concentration, but not the solubilisation of the contaminant. Further studies on the use of blends for this application are required. The increase of solubility achieved with the studied surfactants encourages their application in washing HCH-contaminated soils through solubility enhancement.

Source Apportionment and Health Risk of Some Organic Contaminants in Water and Suspended Particulate Matter from Imo River, Nigeria

The objective of this study was to provide the source identification and assessment of potential health associated with some organic contaminant detected in water and suspended particle matter (SPM) from the Imo River, Nigeria using gas chromatography with a flame ionization detector (GC/FID) after 1:1 ratio solvent mixture (n-hexane and dichloromethane) extraction. The findings on SPM revealed the values; pH (5.42±0.097-5.567±0.057), conductivity (74.58±5.390-87.6±0.9 uS/cm), and total organic carbon (TOC) (3.626±0.366-6.143±0.176), and surface water; pH (6.077±0.049-6.46±0.52), conductivity (49.03±1.430- 58.12±0.553 uS/cm). The total concentrations of both low and high molecular PAHs in SPM recorded at stations1-3 were 4.384 mg/kg, 16.87 mg/kg, and (22.69 mg/kg); surface water 2.329 mg/L, 7.428 mg/L and 6.657 mg/L. The source apportionment of PAHs in SPM and surface water via molecular diagnostic ratios identified both petrogenic source (crude oil, petroleum spillages, and seepages) and pyrogenic sources (combustion of grass, wood, coal, and gas flaring). A further analysis with Principal Component Analysis (PCA) revealed two principal components, with 65.568% for component 1 and 34.432% for component 2 for SPM, and 62.80% for principal components and 37.2% for principal component 2 for surface water. The correlation analysis of PAHs affirmed common sources such as petrogenic and pyrogenic origins. The toxic equivalent factor of total benzo(a)pyrene for 6 ∑PAHs in SPM was recorded as 3.693 mg/kg, 1.605 mg/kg, and 0.453 mg/kg; surface water was recorded as 0.823 mg/L, 1.858 mg/L, and 0.353 mg/L, while the mutagenic equivalency quantities of SPM were recorded as 3.693mg/kg, 1.146 mg/kg, and 0.316 mg/kg; surface water 0.739 mg/L, 0.938, and 0.577 for stations 1-3. The effect of carcinogenic PAHs in SPM was higher in adults than in children, with regards to ILCR analysis. Users of Imo Rivers should be guided on the exposure of SPM and surface water since the toxic, mutagenic, and cancer risk levels of the river are above the permissible limit in some stations.

Highly Efficient Solar-Light-Driven Photodegradation of Metronidazole by Nickel Hexacyanoferrate Nanocubes Showing Enhanced Catalytic Performances.

Environmental pollution is a complex problem that threatens the health and life of animal and plant ecosystems on the planet. In this respect, the scientific community faces increasingly challenging tasks in designing novel materials with beneficial properties to address this issue. This study describes a simple yet effective synthetic protocol to obtain nickel hexacyanoferrate (Ni-HCF) nanocubes as a suitable photocatalyst, which can enable an efficient photodegradation of hazardous anthropogenic organic contaminants in water, such as antibiotics. Ni-HCF nanocubes are fully characterized and their optical and electrochemical properties are investigated. Preliminary tests are also carried out to photocatalytically remove metronidazole (MDZ), an antibiotic that is difficult to degrade and has become a common contaminant as it is widely used to treat infections caused by anaerobic microorganisms. Under simulated solar light, Ni-HCF displays substantial photocatalytic activity, degrading 94.3% of MDZ in 6h. The remarkable performance of Ni-HCF nanocubes is attributeto a higher ability to separate charge carriers and to a lower resistance toward charge transfer, as confirmed by the electrochemical characterization. These achievements highlight the possibility of combining the performance of earth-abundant catalysts with a renewable energy source for environmental remediation, thus meeting the requirements for sustainable development.

High performance of reduced graphene oxide and g-C3N4 co-doped CuFe2O4 for peroxymonosulfate activation under visible light: Degradation process of sulfamethazine via a singlet oxygen dominated pathway

Peroxymonosulfate (PMS) activation by heterogeneous metal-based catalysts has been extensively applied for the degradation of organic pollutants in water. However, the catalysts suffer from the low oxidant utilization efficiency, pH limitations and severe matrix interference. Here, a reduced graphene oxide and g-C3N4 co-doped copper ferrite (rGO-CNCF) was synthesized and its performance for PMS activation under visible light was evaluated for removal of sulfamethazine. In the condition of rGO-CNCF (0.2 g/L) and PMS (0.1 g/L), the vis/rGO-CNCF/PMS system could degrade 99.9 % of sulfamethazine (SMT, 10 mg/L) within 30 min at pH 7.0, and the system also showed high degrading abilty of SMT over a wide pH range (0–14), along with a good adaptability to common coexisting ions in water solution. The introduction of rGO not only enhanced the stability of rGO-CNCF but also changed the binding sites between PMS and rGO-CNCF which reduced the adsorption energy. Singlet oxygen (1O2) was unveiled to be the major reactive oxygen species (ROS), which was produced by the transformation between negatively charged PMS (HSO5−) and water,along with the self-degradation of PMS. SMT was decomposed through four degradation pathways in this system, and quantitative structure–activity relationship (QSAR) predictions indicated a significant decrease in its toxicity. Results of this study indicated that the material can efficiently activate persulfate for the removal of organic pollutants from water under visible light conditions and it provided a novel catalytic system for removal of organic contaminants in water.

Recent advances in degradation of N,N-diethyl-3-toluamide (DEET)-an emerging environmental contaminant: a review.

N,N-Diethyl-3-toluamide (DEET) is a commonly used insect repellent, which acts as an organic chemical contaminant in water and considered as an emerging contaminant which has been observed worldwide. It gets discharged into the environment through sewage waste. The various methods have been used to degrade DEET, such as UV based, ozonation, photocatalytic degradation, and biodegradation (based on the metabolic activity of fungi and bacteria). However, less research has been done on the degradation of DEET by deploying nanoparticles. Therefore, biodegradation and nanotechnology-based methods can be the potential solution to remediate DEET from the environment. This review is an attempt to analyze the routes of entry of DEET into the atmosphere and its environmental health consequences and to explore physical, chemical, and biological methods of degradation. Furthermore, it focuses on the various methods used for the biodegradation of the DEET, including their environmental consequences. Future research is needed with the application of biological methods for the degradation of DEET. Metabolic pathway for biodegradation was explored for the new potent microbial strains by the application of physical, chemical, and microbial genomics; molecular biology; genetic engineering; and genome sequencing methods.

Occurrence and path pollution of emerging organic contaminants in mineral water of Hranice hypogenic Karst

The Hranice hypogenic karst region includes urban, spa and agricultural areas and industry complexes that affect water quality in the region. Emerging organic contaminants (EOCs), especially pesticides and pharmaceuticals, are released into the complex aquatic system. These substances and their metabolites can affect aquatic and human life, as well as the regional development of the wider area traditionally associated with the spa. In this study, we conducted preliminary screening for pesticides and pharmaceuticals at 33 sampling sites and across different location types, including surface water, drainage water, a shallow well, groundwater and thermal karst water. Sampling occurred between February 2022 and June 2023. The results generally confirm that current land use is causing pollution in the karst system. The monitored substances were present in all water types, and in most cases the concentrations of pesticides were lower than those of their metabolites. Chloridazon desphenyl (DESPH) is the most widespread pesticide in surface, ground and hypogenic waters. Its concentrations in surface waters were 5.7 ng·L−1–2,230 ng·L−1, in groundwaters were 11.3 ng·L−1–1,490 ng·L−1 and in karst hypogenic waters 5.4 ng·L−1–378 ng·L−1. Diclofenac was the most widespread substance from the pharmaceutical group. Its concentrations ranged from 5.6 ng·L−1–549 ng·L−1 in surface waters, 8.4 ng·L−1–112 ng·L−1 in groundwaters and 5.1 ng·L−1–47.4 ng·L−1 in karst hypogenic waters. Directly in the karst hypogenic waters, the following EOCs were repeatedly detected: atrazine and its metabolites, simazin, metazachlor ethane sulfonic acid (ESA), metolachlor ESA, alachlor ESA, chloridazon DESPH, diclofenac, ibuprofen, azithromycin, bisphenol A and diethyltoluamide (DEET). The initial research hypothesis is that hydrothermal karst waters are of sub-recent age and deep circulation and, unlike surface and groundwaters, are not contaminated by recent pollutants. A certain component of these waters is therefore a shallow and shorter circulation.

Mn3O4/Vulcan XC-72R composites: preparation, physicochemical characterization and electrochemical study for purification of organic contaminants

The microwave-assisted technique was applied to the preparation of composites from manganese(II) acetate and Carbon-supported (Vulcan XC-72R). Composites were prepared by chemical deposition of manganese(II) acetate nanoparticles onto Vulcan XC-72R carbon black (catalytic mass) using microwave irradiation. The new composites were physicochemically characterized by Energy-dispersive X-ray spectroscopy (EDX) with scanning electron microscopy (SEM), BET surface area, pore size distribution and X-ray diffraction (XRD). BET analysis of Mn3O4/Vulcan XC-72R composites obtained by alkali method has shown specific surface area of 1135 m2/g. Novel composites were electrochemically studied as catalysts for the remediation of organic contaminants in industrial waters. From novel catalytic mass, double-sided coated electrodes on a Nickel mesh conductor were made by pressing and heating at 250 °C. The prepared electrodes have geometric area of 2.5 cm2. The electrodes were fabricated and studied regarding the amount of catalyst and 35 % Teflonized Vulcan XC-72R. Electrochemical studies were carried out for phenol oxidation in an aqueous solution in model electrolyte: phenol solution 200 mg.L-1 and supporting electrolyte: 18 g.L-1 NaCl and 2.6 mg.L-1 Na2SO4.

Directional growth of Bi2WO6 with highly exposed facets on 2D‐Co3O4 for different properties under two light sources

AbstractA composite of two or more materials usually results in enhanced specific properties. In this paper, a kind of composite material composed of Bi2WO6 with highly exposed {010} facets and 2D‐Co3O4 was prepared by a one‐pot reaction and then applied to decontaminate hydrocortisone in wastewater. The Bi2WO6/Co3O4 composite possessed a rose‐like surface microtopography self‐assembled from Bi2WO6 and Co3O4 nanosheets. The micro‐interface analysis showed that {110} facets of Co3O4 and {010} facets of Bi2WO6 were glued in situ and formed heterojunction. Additionally, the removal ability of hydrocortisone through Bi2WO6/Co3O4 varied under different light sources, which was 85.0 % under ultraviolet light and 97.3 % under visible light within 60 min. It was considered that Bi2WO6/Co3O4 was similar to a traditional heterojunction and the major reactive species was H2O2 under ultraviolet light, while it played a role as a Z‐scheme photocatalyst and the major reactive species was ⋅OH under visible light. Finally, product analysis of hydrocortisone demonstrated that the dexter chain broke whatever under ultraviolet or visible light, but the breakage of parent nucleus appeared only under visible light. This research revealed the enhanced catalytic properties of p‐n heterojunction catalysts and indicated the specifically exposed facets are promising for organic contaminants in water.

Predicting the concentration range of trace organic contaminants in recycled water using supervised classification

Trace Organic Contaminants (TrOCs) have evidence for many health and environmental issues. Frequent monitoring of TrOC concentration is a time-consuming and costly process, which cannot be achieved easily. Identifying surrogate markers for these contaminants is a practical solution to monitor and ensure water quality. However, this topic is seldom explored in previous literature. This study aimed to find surrogate markers to predict concentration class (i.e., three classes: low concentration, medium concentration, high concentration) for a set of widely used pharmaceutical and personal care product TrOCs (e.g., Fluoxetine, Primidone, Saccharin, Sucralose to name a few) in recycled water from Melbourne Eastern Treatment Plant (ETP), Melbourne, Australia. For this purpose, three popular supervised learning classification algorithms namely Naïve Bayes, Random Forest and Support Vector Machines were utilized. Physicochemical parameters colour, Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) were found to be the top three predictive features for the majority of the investigated TrOCs. UV Transmittance (UVT) and the total amount of suspended solids (TSS) were the next frequent features. The Random Forest model resulted in the highest classification accuracy (≥73 %) for the majority of compounds. This paper presents evidence that with the acquired intelligence of supervised machine learning, the concentration range of hard to measure TrOCs in water can be predicted from a handful of low-cost and easy-to-measure physicochemical parameters.

True Order Determination of Sonochemical Degradation Kinetics of Organic Contaminants in Water Using the Half-lives Method

In the literature, the modeling of the sonolytic decomposition kinetics of organic contaminants in water has been carried out using the pseudo-first and pseudo-second order equations. The results obtained with this method are totally biased because it requires the assumption of the order of the degradation reaction, which is a real limitation, and the sonochemical oxidation mechanism is a very complex phenomenon that cannot be described by such simple models. In this paper, for the first time, the true order of the sonochemical degradation kinetics of organic pollutants in aqueous solutions at various initial substrate concentrations was determined using the half-lives method combined with the general rate law model, i.e., the pseudo-nth order equation. Linear and nonlinear regression techniques were used to determine the order of the sonolytic destruction reaction. The half-life technique for the general rate law model can adequately describe the experimental results of the sono-destruction of the investigated pollutants. For rhodamine B and naphthol blue black, the sono-destruction mechanism for both contaminants does not change as the initial contaminant concentration varies over the range examined, while for 4-isopropylphenol and furosemide, the sono-destruction mechanism changes as the initial substrate concentration varies. A fractional order of the sonolytic destruction reaction was determined for all the pollutants tested. These fractional orders of sono-destruction reactions indicate the complex nature and behavior of the reactions, often involving multiple steps or mechanisms. They also reveal a more complex interaction between pollutant concentration and sonolytic destruction rate. In a word, the method developed in this paper should be used to determine the real order of the sono-oxidation reaction of nonvolatile organic pollutants in aqueous phase.

Lab-scale engineered hydrochar production and techno-economic scaling-up analysis

Despite the extensive use of engineered hydrochar (EHC) for contaminants adsorption in water, little is known about the scaling-up of EHC production which has kept the technology at a low readiness level (TRL). Full-scale EHC production was simulated to help bridge this knowledge gap. A systematic analysis was performed where EHC was produced from rice straw using hydrothermal carbonization (HTC) at 200 °C with iron addition. A techno-economic evaluation model was employed to simulate the production process and to estimate energy requirements, configuration, and cost scenarios for the HTC process. The minimum selling price (MSP) analysis of the engineered hydrochar was found to be almost half compared to the market price for other similar sorbents ($ 76/t vs. $136/t) suggesting that EHC production is feasible for scaling up. Finally, as a trial, the resulting material was tested for its efficacy in the adsorption of an anionic organic contaminant (e.g., Congo Red, C32H22N6Na2O6S2) in water to identify its potential for water treatment. Experimental results showed that EHC adsorbed > 95% CR suggesting significant adsorption capability and feasibility for production scale-up.

Recent Progress in Applications of Atmospheric Pressure Plasma for Water Organic Contaminants’ Degradation

Recent Progress in Applications of Atmospheric Pressure Plasma for Water Organic Contaminants’ Degradation

Development and testing of a mechanistic model for wetland treatment of neutral and polar organic contaminants in oil sands process-affected water

A mechanistic model of the fate of neutral and polar organic contaminants in a free water surface flow wetland was developed to assess the removal efficiency of polycyclic aromatic hydrocarbons (PAHs) and naphthenic acids (O2-NAs), which are chemicals primarily responsible for oil sands process-affected water (OSPW) toxicity. The model simulates wetland mechanisms of chemical removal based on physicochemical properties, environmental conditions, and wetland design and operation. Good agreement between model estimated and observed concentrations of PAHs and O2-NAs in OSPW in the Kearl Treatment Wetland (Alberta, Canada) was observed over time. Model simulations indicate that the removal of PAHs and O2-NAs from OSPW is highly sensitive to biotransformation rates and that sustained wetland treatment is feasible with robust PAH and NA degrading microbial communities in the wetland. Wetland treatment efficiency is greatest for substances with a log KOW or log D between 3.0 and 5.5 whereas substances with a log KOW or log D >6.0 are not suitable for wetland treatment, even if they can be biodegraded. The log KOW of PAHs and log D for O2-NAs range from 0.7 to 6.7 suggesting most organic contaminants in OSPW are suitable for wetland treatment. Chemical removal via evapotranspiration is not significant pathway of chemical removal from wetlands for PAHs and O2-NAs due to their very low log KAW (less than −1.6). The treatment wetland model presented is the first model to evaluate the fate of both neutral and polar organic contaminants in a flow-through treatment wetland operation, making it a helpful tool to assess the feasibility of these treatment systems for the oil sands industry. The model is particularly useful in evaluating chemical removal efficiency of OSPW contaminants, whether specific water quality objectives can be achieved after treatment, and to assess trade-offs in wetland design and operation to balance treatment performance with design and operational features.

Colloid-bound radicals formed in NOM-enhanced Fe(III)/peroxymonosulfate process accelerate the degradation of trace organic contaminants in water

The omnipresence of natural organic matter (NOM) in water bodies traditionally hinders the degradation of trace organic contaminants (TrOCs) in peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs). This study elucidates the positive role of NOM in enhancing the degradation of TrOCs through the Fe(III)/PMS process. During this process, NOM reduces Fe(III), yielding semiquinone-like radical (NOM•) and concurrently forming NOM-Fe(III) colloids. In addition to the Fe(II)-mediated activation pathway, Fe(III) sites on NOM-Fe(III) colloids effectively transfer electrons from NOM• or some redox-active moieties to PMS, resulting in the generation of long-lived colloid-bound SO4•−, which can readily undergo hydrolysis to produce HO•. The stabilization of SO4•− and HO• by NOM-Fe(III) colloids, combined with their moderate adsorption of TrOCs, results in surface-confined reactions that significantly enhance TrOC removal, despite the presence of concurrent quenching reactions between radicals and NOM. Further, the significant positive correlation between the phenolic contents of eight NOM types and TrOC degradation kinetics suggests phenolic moieties as the primary electron source for PMS activation. By in-situ utilizing NOM in raw water, a PMS-amended iron coagulation process with 0.2 mM Fe(III) and PMS effectively removes 90–100 % of six coexisting TrOCs. This study unveils the previously unrecognized role of colloid-bound radicals in decontamination processes, offering valuable insights into harnessing NOM's influence in advanced oxidation water treatment processes.

Oxidation of organic pollutants over MnO2 in cold water assisted by peroxydisulfate

MnO2 can be used in advanced oxidation processes to activate peroxydisulfate (PS) and generate reactive species such as sulfate radicals (SO4•-), hydroxyl radicals (•OH) and singlet oxygen (1O2) for the abatement of organic water contaminants. Alternatively, one can use MnO2 as particulate oxidant which, in contrast to PS, is active already at low temperatures. This low-temperature activity is particularly attractive for in situ groundwater treatment. The roles of PS and MnO2 as oxidant and catalyst, respectively, may invert: MnO2 functions as primary oxidant and PS works as re-oxidant of reduced Mn-oxides. In this way, the limited oxidation capacity of particulate MnO2 can be overcome. So far, such reaction systems have not been extensively explored.In the present study, the degradation of 4-hydroxybenzoic acid (HBA) by PS + MnO2 was studied under various experimental conditions, by varying reaction temperature (15–45 °C), reagent concentrations, and water matrix. Both PS and MnO2 alone have the ability to effect the oxidation of HBA. In the co-presence of PS and MnO2, a fast removal of HBA from water was achieved even at low temperatures (half-life of HBA about 0.5 h with 2.4 g L-1 MnO2 at 25 °C), owing to a synergic effect between the two components.Quenching experiments indicate that the primary HBA oxidation step is a heterogeneous reaction on the MnO2 surface rather than a homogeneous reaction driven by SO4•- or 1O2, as frequently reported in literature. This is in line with results from the PS driven oxidation of perfluorooctanoic acid which is not significantly enhanced in the presence of MnO2.