The aqueous degradation of bisphenol A and steroid estrogens by ferrate

Overlooked interaction between redox-mediator and bisphenol-A in permanganate oxidation

Research efforts on permanganate (Mn(VII)) combined with redox-mediator (RM), have received increasing attention due to their significant performance for bisphenol-A (BPA) removal. However, the mechanisms underpinning BPA degradation remain underexplored. Here we show the overlooked interactions between RM and BPA during permanganate oxidation by introducing an RM-N-hydroxyphthalimide (NHPI). We discovered that the concurrent generation of MnO2 and phthalimide-N-oxyl (PINO) radical significantly enhances BPA oxidation within the pH range of 5.0-6.0. The detection of radical cross-coupling products between PINO radicals and BPA or its derivatives corroborates the pivotal role of radical cross-coupling in BPA oxidation. Intriguingly, we observed the formation of an NHPI-BPA complex, which undergoes preferential oxidation by Mn(VII), marked by the emergence of an electron-rich domain in NHPI. These findings unveil the underlying mechanisms in the Mn(VII)/RM system and bridge the knowledge gap concerning BPA transformation via complexation. This research paves the way for further exploration into optimizing complexation sites and RM dosage, significantly enhancing the system's efficiency in water treatment applications.

Unlocking the potential of ferrate(VI) in water treatment: Toward one-step multifunctional solutions

Ferrate(VI), though well-acknowledged for its multiple treatment functions, has traditionally found application in an auxiliary treatment of conventional water treatment trains, primarily targeting specific contaminants. However, the reactor configurations and system operations developed from this traditional approach are not optimally suited for harnessing its full multifunctionality. In contrast, an alternative process integration approach, such as process intensification, can allow for the tailored development of modular, multifunctional ferrate(VI) reactors capable of achieving various treatment objectives within a single unit. This perspective article critically analyzes and compares the two distinct development approaches for ferrate(VI) technology in water treatment. We argue that the process integration pathway represents a promising approach, given that it facilitates the reactor design to accommodate different ferrate(VI)-driven treatment processes and their interactions, while potentially accomplishing enhanced treatment efficiency, reduced costs and energy consumption, and a smaller physical footprint. The resulting system intensification and adaptability have the potential to drive technological innovation and revolution in water treatment for achieving water security.

A two-stage Fe(VI) oxidation process enhances the removal of bisphenol A for potential application

Ferrate (Fe(VI)) has been extensively studied as a green oxidant to treat wastewater. But Fe(VI) oxidation still faces several challenges for application, such as the sensitivity of Fe(VI) to pH and the restrictions on the Fe(VI) utilization efficiency for pollutant elimination at low concentration levels. This study proposed a two-stage Fe(VI) oxidation process to enhance the bisphenol A (BPA) removal for potential applicability, consisting of the adsorption by CNTs of stage I and the degradation by Fe(VI) of stage II. The Fe(VI) utilization efficiency in the two-stage process (0.848) was higher than that in one-stage processes (0.727) and Fe(VI) alone system (0.504) at pH 9. In stage I, the adsorption process had good compliance with the Langmuir isotherm model and pseudo-second-order kinetic model. In stage II, the effective utilization of low-concentration Fe(VI) was 2.45 times more than Fe(VI) alone, and the reduction of reaction volume was beneficial to further enhance utilization. The probe experiments (sulfoxide) and the degradation experiments of other electron-donating/withdrawing pollutants (e.g., atrazine, benzoic acid) demonstrated that Fe(IV) and Fe(V) were major oxidizing species in the two-stage process. The regeneration experiments showed that CNTs still had acceptable adsorption and catalytic capabilities after five cycles. Finally, the intermediate products in the two-stage process were detected and four possible degradation pathways of BPA were proposed. These findings were meaningful for the practical application of Fe(VI) oxidation to overcome the conditional limitation and improve the utilization.

Research Progress of Methods for Degradation of Bisphenol A

Bisphenol A (BPA), an endocrine disruptor widely used in industrial production, is found in various environmental sources. Despite numerous reports on BPA degradation and removal, the details remain unclear. This paper aims to address this gap by providing a comprehensive review of BPA degradation methods, focusing on biological, physical, and chemical treatments and the factors that affect the degradation of BPA. Firstly, the paper uses VOSviewer software (version 1.6.15) to map out the literature on BPA degradation published in the past 20 years, which reveals the trends and research focus in this field. Next, the advantages and limitations of different BPA degradation methods are discussed. Overall, this review highlights the importance of BPA degradation to protect the environment and human health. The paper provides significant insights for researchers and policymakers to develop better approaches for BPA degradation and removal.

Enhanced biodegradation of endocrine disruptor bisphenol A by food waste composting without bioaugmentation: Analysis of bacterial communities and their relative abundances

Composting with food waste was assessed for its efficacy in decontaminating Bisphenol A (BPA). In a BPA-treated compost pile, the initial concentration of BPA 847 mg kg-1 fell to 6.3 mg kg-1 (99% reduction) over a 45-day composting period. The biodegradation rate was at its highest when bacterial activity peaked in the mesophilic and thermophilic phases. The average rate of total biodegradation was 18.68 mg kg-1 day-1. Standard methods were used to assess physicochemical parameters of the compost matrix and gas chromatography combined with mass spectrometry (GC/MS) was used to identify BPA intermediates. Next-generation sequencing (NGS) was used to detect BPA degraders and the diverse bacterial communities involved in BPA decomposition. These communities were found consist of 12 phyla and 21 genera during the composting process and were most diversified during the maturation phase. Three dominant phyla, Firmicutes, Pseudomonadota, and Bacteroidetes, along with Lactobacillus, Proteus, Bacillus, and Pseudomonas were found to be the most responsible for BPA degradation. Different bacterial communities were found to be involved in the food waste compost biodegradation of BPA at different stages of the composting process. In conclusion, food waste composting can effectively remove BPA, resulting in a safe product. These findings might be used to expand bioremediation technologies to apply to a wide range of pollutants.

Photocatalytic degradation of bisphenol-A (BPA) over titanium dioxide, and determination of its by-products by HF-LPME/GC-MS

In this work, analytical strategies were developed based on the technique of hollow fiber liquid-phase microextraction and chromatographic methods (LC-UV and GC/MS). These methods allowed the identification of the main Bisphenol-A by-products applying heterogeneous photocatalysis in water samples. BPA degradation in this study was in the order of 90%, and the conditions used in the HF-LPME were optimized through 2³ factorial design (6 cm fiber length, stirring speed of 750 rpm, and an extraction time of 30 min). Using a HF-LPME/GC-MS analytical strategy, it was possible to identify six by-products of BPA photodegradation, two of which have not been reported in the literature so far. This knowledge was quite important since the degradation can lead to the formation of more toxic and persistent by-products than the BPA. With the Toxtree software, three degradation products were found to be persistent to the environment, in addition to BPA; however, in 360 minutes of reaction, chromatographic peaks of the precursors were not identified, suggesting that there may have been a total degradation of these compounds. The results showed a great application potential of a miniaturized extraction technique to extract and pre-concentrate the degradation products of emerging contaminants.

Facile Synthesis of Diatomite/β-Cyclodextrin Composite and Application for the Adsorption of Diphenolic Acid from Wastewater

Diphenolic acid (DPA) is a kind of endocrine-disrupting compound, which brings serious health problems to humans and animals. An eco-friendly and cost-effective adsorbent was prepared through a simple method, in which the β-Cyclodextrin(β-CD) was crosslinked onto the surface of diatomite (DA), the as-prepared DA/β-CD composite showed higher adsorption efficiency for DPA than DA as the host–guest interaction between DPA and β-CD. DA is a kind of biosilica with a hierarchical pore structure that provides enough surface area for the DA/β-CD. The surface area and pore size of DA/β-CD were investigated by nitrogen adsorption and desorption. The DA/β-CD composite illustrated a good adsorption capability, and was used for removing DPA from wastewater. The adsorption ratio of DPA could achieve 38% with an adsorption amount of 9.6 mg g−1 under room temperature at pH = 6. The adsorption isotherm curves followed the Langmuir (R2 = 0.9867) and Freundlich (R2 = 0.9748) models. In addition, the regeneration rate of the DA/β-CD was nearly at 80.32% after three cycles of regeneration. These results indicated that the DA/β-CD has the potential for practical removal of the EDC contaminants from wastewater.

Oxidative degradation of sulfamethoxazole from secondary treated effluent by ferrate(VI): kinetics, by-products, degradation pathway and toxicity assessment

Sulfamethoxazole (SMX) is a typical antibiotic in the world, which is frequently detected in the aquatic environment. The current study was aimed to investigate the SMX degradation in secondary treated wastewater using potassium Ferrate [Fe(VI)]. The effects of various experimental conditions, EDTA and phosphate as chelating agents, and toxicity assessment were also considered. Secondary treated effluent was spiked with predefined SMX concentrations, and after desired reaction time with Fe(VI), residual SMX was measured using HPLC. Results indicated that SMX degradation by Fe(VI) was favored under acidic condition, where 90% of SMX degradation was achieved after 120 min. Fe(VI) and SMX reaction obeyed first-order kinetic; meantime, the SMX degradation rate under pH 3 was 7.6 times higher than pH 7. The presence of phosphate (Na₂HPO₄) and EDTA declined SMX degradation, while Fe (III) effect was contradictory. In addition to promising demolition, 10% TOC removal was achieved. Eighteen major intermediates were identified using LC-MS/MS and the degradation pathways were suggested. Transformation products (TPs) were formed due to hydroxylation, bond cleavage, transformation after bond cleavage, and oxidation reactions. The ECOSAR analysis showed that some of the SMX oxidation products were toxic to aquatic organisms (fish, daphnia and green algae).

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40201-021-00769-9.

Evaluation of Fe(VI)/Fe(II) combined with sludge adsorbents in secondary effluent organic matter removal

Wastewater reclamation and reuse are important methods that help to achieve an equilibrium within demand and offer, and also one of the important ways to reduce carbon emission. The existence of secondary effluent organic matter (EfOM) will bring potential threat to the environment in reuse process. Therefore, it is important to develop reclaimed water reuse technology that effectively remove EfOM. In this study, the removal of EfOM performance of ferrates enhanced by FeCl₂ (Fe(VI)/Fe(II)) combined with sludge adsorbents (SAs) was evaluated by using the continuous-flow process (FeSDF), which was composed of Fe(VI)/Fe(II), SAs, densadeg and filtration. The results showed that when the inflow rate was 1 L/h, the optimal operating conditions of FeSDF including 5 mg/L of Fe(VI), 1 mg/L of Fe(II), 1 g/L of SA and 50% of the reflux ratio. Bulk organic indicators, including chemical oxygen demand, dissolved organic carbon, ammonia, total nitrogen, total phosphorus, turbidity, and ultraviolet absorbance at 254 nm in the effluent met the water quality standard for scenic environment use (GB/T 18921-2019 in China). The addition of Fe(II) makes the coagulation process by Fe(VI) produce more Fe(III) and produce more quality of sedimentary flocs and improve the removal efficiency of EfOM. The removal of organic micro-pollutants (OMPs) was mainly due to ferrate oxidation and SA adsorption in FeSDF, and the removal of most of the OMPs was more than 90%. The total fluorescence intensity removal efficiency in FeSDF was 63.8%. Moreover, the genotoxicity of the FeSDF effluent decreased to 0.73 μg 4-nitroquiniline-N-oxide/L, and the reduction efficiency reached 97.6%. The actual efficiency of most of the indicators is greater than the expected efficiency, indicating that there is a synergistic comprehensive effect during the whole process operation of FeSDF.

Ferrate(VI) oxidation of bisphenol E-Kinetics, removal performance, and dihydroxylation mechanism

Bisphenol E (bis (4-hydroxyphenyl) ethane, BPE), as a typical endocrine disrupting chemical, is commonly detected in source water and drinking water, which poses potential risks to human health and ecological environment. This paper investigated the removal of BPE by ferrate(VI) (Fe^VIO₄^2-, Fe(VI)) in water. Under the optimal condition of [Fe(VI)]₀:[BPE]₀ = 10:1 and pH = 8.0, a removal efficiency of 99% was achived in 180 s. Sixteen intermediates of BPE were detected, and four possible reaction pathways were proposed, which mainly involved the reaction modes of double-oxygen and single-oxygen transfer, bond breaking, carboxylation and polymerization. The double-oxygen transfer mechanism, different from traditional mechanisms, was newly proposed to illustrate the direct generation of di-hydroxylated products from parent BPE, which was demonstrated by theoretical calculations for its rationality. Significantly, NO₂^-, HCO₃^-, Cu²⁺, and humic acid, constituents of water promoted the removal of BPE. Additionally, samples from river, tap water, synthetic wastewater, and secondary effluent were tested to explore the feasibility of Fe(VI) oxidation for treating BPE in water. It was found that 99% of BPE was degraded within 300 s in these waters except for synthetic wastewater. The toxicity of BPE and its intermediates was evaluated by ECOSAR program, and the results showed that Fe(VI) oxidation decreased the toxicity of reaction solutions. These findings demonstrated that the Fe(VI) oxidation process was an efficient and green method for the treatment of BPE, and the new insights into the double-oxygen transfer mechanism aid to understand the reaction mechanisms of organic pollutants oxidized by Fe(VI).

Reactive High-Valent Iron Intermediates in Enhancing Treatment of Water by Ferrate

Efforts are being made to tune the reactivity of the tetraoxy anion of iron in the +6 oxidation state (Fe^VIO₄^2-), commonly called ferrate, to further enhance its applications in various environmental fields. This review critically examines the strategies to generate highly reactive high-valent iron intermediates, Fe^VO₄^3- (Fe^V) and Fe^IVO₄^4- or Fe^IVO₃^2- (Fe^IV) species, from Fe^VIO₄^2-, for the treatment of polluted water with greater efficiency. Approaches to produce Fe^V and Fe^IV species from Fe^VIO₄^2- include additions of acid (e.g., HCl), metal ions (e.g., Fe(III)), and reductants (R). Details on applying various inorganic reductants (R) to generate Fe^V and Fe^IV from Fe^VIO₄^2- via initial single electron-transfer (SET) and oxygen-atom transfer (OAT) to oxidize recalcitrant pollutants are presented. The common constituents of urine (e.g., carbonate, ammonia, and creatinine) and different solids (e.g., silica and hydrochar) were found to accelerate the oxidation of pharmaceuticals by Fe^VIO₄^2-, with potential mechanisms provided. The challenges of providing direct evidence of the formation of Fe^V/Fe^IV species are discussed. Kinetic modeling and density functional theory (DFT) calculations provide opportunities to distinguish between the two intermediates (i.e., Fe^IV and Fe^V) in order to enhance oxidation reactions utilizing Fe^VIO₄^2-. Further mechanistic elucidation of activated ferrate systems is vital to achieve high efficiency in oxidizing emerging pollutants in various aqueous streams.

Sustainable ferrate oxidation: Reaction chemistry, mechanisms and removal of pollutants in wastewater

This review is intended to evaluate the use of ferrate (Fe(VI)), being a green coagulant, sustainable and reactive oxidant, to remove micro pollutants especially pharmaceutical pollutants in contaminated water. After a brief description of advanced oxidation processes, fundamental dimensions regarding the nature, reactivity, and chemistry of this oxidant are summarized. The degradation of contaminants by Fe(VI) involves several mechanisms and reactive agents which are critically evaluated. The efficiency and chemistry of Fe(VI) oxidation differs according to the reaction conditions and activation agent, such as soluble Fe(VI) processes, which involve Fe(VI), UV light, and electro-Fe(VI) oxidation. Fe(VI) application methods (including single dose, multiple doses, chitosan coating etc), and Fe(VI) with activating agents (including sulfite, thiosulfate, and UV) are also described to degrade the micro pollutants. Besides, application of Fe(VI) to remove pharmaceuticals in wastewater are intensely studied. Electrochemical prepared Fe(VI) has more wide application than wet oxidation method. Meanwhile, we elaborated Fe(VI) performance, limitations, and proposed innovative aspects to improve its stability, such as the generation of Fe(III), synergetic effects, nanopores entrapment, and nanopores capsules. This study provides conclusive direction for synergetic oxidative technique to degrade the micro pollutants.

Powdered activated carbon-catalyzed chlorine oxidation of bisphenol-A and methylene blue: Identification of the free radical and effect of the carbon surface functional group

The effect of powdered activated carbon (PAC) on chlorine oxidation is not well understood, therefore this study was designed to further investigate the chlorine oxidation mechanism with the presence of PAC. The oxidation processes of two model organic pollutants (bisphenol-A and methylene blue) with chlorine were compared in the absence and presence of PAC. The results showed a significant increase in reaction rates with the addition of PAC. Electron spin resonance indicated that the PAC catalyzed the oxidation of chlorine to generate more Cl and O₂^-. Additionally, the analysis of the surface characteristics of thermally modified PACs under N₂ and their corresponding reaction rates revealed that there existed a significant correlation between the CO groups and the catalytic effect. PAC exhibited a much lower reaction rate under H₂ modification, which indicated that the π electrons of the basal plane might be involved in the catalysis. Density functional theory calculations confirmed that the various oxygen groups on PAC reduced the activation barrier for HOCl dissociation, particularly the carboxyl group. This investigation provides a better understanding of the interactions between chlorine and activated carbon materials, which could be useful for selecting suitable water treatment agents.

Antibiotic resistant bacteria and genes in shrimp aquaculture water: Identification and removal by ferrate(VI)

Enclosed shrimp culturing ponds are breeding environments for the spread of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in the aquatic environment. This paper surveyed the presence of antibiotics, ARB, and ARGs in aquaculture waters and demonstrated their removal by ferrate (Fe(VI), FeO₄^2-). Tetracyclines were the most prevalent antibiotics, followed by quinolones and β-lactam. The bacterial resistance rates to three antibiotics were ordered as follows: amoxicillin (AMX) > oxytetracycline (OTC) > enrofloxacin (ENR). Proteobacteria, Verrucomicrobia, and Bacteroidetes were the predominant phyla, while sul1 and sul2 were the predominant ARGs. sul2 was positively correlated with Proteobacteria. Water quality parameters significantly influenced the dissemination of tetracycline resistance genes in aquacultures due to high organic waste accumulation. The removal efficiency of antibiotics by Fe(VI) depended on the structural moieties of antibiotics, with phenol-containing antibiotics more thoroughly oxidized (i.e., OTC) than amine-containing (ENR and AMX) antibiotics. Greater removal of antibiotics in aquaculture waters suggested that the constituents of farming water enhances the efficacy of antibiotics removal by Fe(VI). An acidic pH environment enhanced Fe(VI) inactivation of ARB over the circumneutral pH. The presented results are intended to improve aquaculture managing practices to minimize the antibiotic proliferation in aquaculture waters and the environment.

Three Kinetic Patterns for the Oxidation of Emerging Organic Contaminants by Fe(VI): The Critical Roles of Fe(V) and Fe(IV)

For the first time, this study showed that the apparent second-order rate constants (kapp) of six selected emerging organic contaminants (EOCs) oxidation by Fe(VI) increased, remained constant, or declined with time, depending on [EOC]0/[Fe(VI)]0, pH, and EOCs species. Employing excess caffeine as the quenching reagent for Fe(V) and Fe(IV), it was found that Fe(V)/Fe(IV) contributed to 20-30% of phenol and bisphenol F degradation by Fe(VI), and the contributions of Fe(V)/Fe(IV) remained nearly constant with time under all the tested conditions. However, the contributions of Fe(V)/Fe(IV) accounted for over 50% during the oxidation of sulfamethoxazole, bisphenol S, and iohexol by Fe(VI), and the variation trends of kapp of their degradation by Fe(VI) with time displayed three different patterns, which coincided with those of the contributions of Fe(V)/Fe(IV) to their decomposition with time. Results of the quenching experiments were validated by simulating the oxidation kinetic data of methyl phenyl sulfoxide by Fe(VI), which revealed that the variation trends of kapp with time were significantly determined by the change in the molar ratio of Fe(V) to Fe(VI) with time, highlighting the key role of Fe(V) in the oxidative process. This study provides comprehensive and insightful information on the roles of Fe(V)/Fe(IV) during EOC oxidation by Fe(VI).

Role of TEMPO in Enhancing Permanganate Oxidation toward Organic Contaminants

Permanganate (Mn(VII)) has been widely applied as an oxidant in water treatment plants. However, compared with ozone, Fenton, and other advanced oxidation processes, the reaction rates of some trace organic contaminants (TrOCs) with Mn(VII) are relatively low. Therefore, further studies on the strategies for enhancing the oxidation of organic contaminants by Mn(VII) are valuable. In this work, 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), as an electron shuttle, enhanced Mn(VII) oxidation toward various TrOCs (i.e., bisphenol A (BPA), phenol, estrone, sulfisoxazole, etc.). TEMPO sped up the oxidative kinetics of BPA by Mn(VII) greatly, and this enhancement was observed at a wide pH range of 4.0-11.0. The exact mechanism of TEMPO in Mn(VII) oxidation was described briefly as follows: (i) TEMPO was oxidized by Mn(VII) to its oxoammonium cation (TEMPO⁺) by electron transfer, which was the reactive species responsible for the accelerated degradation of TrOCs and (ii) TEMPO⁺ could decompose TrOCs rapidly with itself back to TEMPO or TEMPOH (TEMPO hydroxylamine). To further illustrate the interaction between TEMPO and target TrOCs, we explored the transformation pathways of BPA in Mn(VII)/TEMPO oxidation. Compared to Mn(VII) alone, adding TEMPO into the Mn(VII) solution significantly suppressed BPA's self-coupling and promoted hydroxylation, ring-opening, and decarboxylation. Moreover, the Mn(VII)/TEMPO system was promising for the abatement of TrOCs in real waters for humic acid, and ubiquitous cations/anions had no adverse or even beneficial impact on the Mn(VII)/TEMPO system.

New insights of metal free 2D graphitic carbon nitride for photocatalytic degradation of bisphenol A

Polymeric oxygen rich exfoliated graphitic carbon nitride (exfoliated GCN, EGCN) was synthesized by the acid treatment of bulk GCN. The photocatalyst was characterized using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and point of zero charge. EGCN shows high valance band hole transfer under short-time visible light (λ > 420 nm) exposure for photocatalytic mineralization of bisphenol A (BPA). Enhanced BPA removal was achieved by EGCN (99 %) due to formation of OH^● radicals (H₂O/h_VB⁺ →OH^●/H⁺). Major factors affecting BPA degradation including catalyst dose, wide pH range, and pollutant concentration were optimized. Repeated cycles of BPA degradation were performed with negligible rate decreased from 0.045 to 0.029 min^-1. The degradation profile and plausible reaction mechanism of BPA was established and well justified by the byproducts identified by mass analysis HR-ESI-MS. Therefore, the as-synthesized metal free EGCN, active under visible light, offers a new platform for complete mineralization of byproducts of halogenated organic contaminants.

Efficiency of pre-oxidation of natural organic matter for the mitigation of disinfection byproducts: Electron donating capacity and UV absorbance as surrogate parameters

Pre-oxidation is often used before disinfection with chlorine to decrease the reactivity of the water matrix and mitigate the formation of regulated disinfection byproducts (DBPs). This study provides insights on the impact of oxidative pre-treatment with chlorine dioxide (ClO₂), ozone (O₃), ferrate (Fe(VI)) and permanganate (Mn(VII)) on Suwannee River Natural Organic Matter (SRNOM) properties characterized by the UV absorbance at 254 nm (UV₂₅₄) and the electron donating capacity (EDC). Changes in NOM reactivity and abatement of DBP precursors are also assessed. The impact of pre-oxidants (based on molar concentration) on UV₂₅₄ abatement ranked in the order O₃ > Mn(VII) > Fe(VI)/ClO₂, while the efficiency of pre-oxidation on EDC abatement followed the order Mn(VII) > ClO₂ > Fe(VI) > O₃ and two phases were observed. At low specific ClO₂, Fe(VI) and Mn(VII) doses corresponding to < 50% EDC abatement, a limited relative abatement of UV₂₅₄ compared to the EDC was observed (~ 8% EDC abatement per 1% UV₂₅₄ abatement). This suggests the oxidation of phenolic-type moieties to quinone-type moieties which absorb UV₂₅₄ and don't contribute to EDC. At higher oxidant doses (> 50% EDC abatement), a similar abatement of EDC and UV₂₅₄ (~ 0.9-1.2% EDC abatement per 1% UV₂₅₄ abatement) suggested aromatic ring cleavage. In comparison to the other oxidants, O₃ abated the relative UV₂₅₄ more effectively, due to a more efficient cleavage of aromatic rings. For a pre-oxidation with Mn(VII), ClO₂ and Fe(VI), similar correlations between the EDC abatement and the chlorine demand or the adsorbable organic halide (AOX) formation were obtained. In contrast, O₃ pre-treatment led to a lower chlorine demand and AOX formation for equivalent EDC abatement. For all oxidants_, trihalomethane formation was poorly correlated with both EDC and UV_254. The EDC abatement was found to be a pre-oxidant-independent surrogate for haloacetonitrile formation. These results emphasize the benefits of combining EDC and UV₂₅₄ measurement to understand and monitor oxidant-induced changes of NOM and assessing DBP formation.

Study on the Release Potential of BPA and Steroid Estrogens in the Sediments of Erhai Lake, a Typical Plateau Lake of China

On-site sampling analysis and laboratory-scale experiments were conducted to study the pollution status and release potential of EDCs in Erhai Lake. We found that nitrogen and phosphorus pollution in Erhai Lake sediment were both at a high level, as well as EDCs pollution. The concentrations of BPA, E2α, E1, E2β, EE2, and E3 were 36.84 ng/g(DW), 13.04 ng/g(DW), 128.97 ng/g(DW), 52.57 ng/g(DW), 18.48 ng/g(DW) and 5.36 ng/g(DW), respectively. The concentrations of E2α, E1, E2β and EE2 in the bottom water were higher than the surface water due to the impact of sediment release. The results of the 20 days release test indicated that BPA release from the sediment had a greater correlation with the original concentration and the particle size of sediment, while the steroid EDCs had no obvious correlation with these two factors, probably due to the difference in hydrophobicity between them. Under hydraulic disturbance and aerobic conditions, the release process of EDCs was accompanied by a large amount of microbial degradation, and degradation amount > released amount. BPA was released quickly, 9.56% was released in 20 days, but only 3.37% of steroid EDCs released. In comparison, the release process of steroids was longer and posed a greater threat to aquatic ecology.

Galvanic oxidation processes (GOPs): An effective direct electron transfer approach for organic contaminant oxidation

The activation of peroxymonosulfate (PMS) for organic contaminant oxidation usually relies on the formation of reactive oxygen species (ROSs). However, the ubiquitous anions and natural organic matter can easily scavenge ROSs and/or PMS, resulting in lower efficiencies and/or the formation of toxic byproducts. Relying on the unique long-distance electron transfer property, the recently developed Galvanic Oxidation Process (GOP) successfully achieved bisphenol A (BPA) degradation when BPA and PMS were physically separated in two reactors. In this study, we systematically investigated the performance of GOP at different PMS or BPA concentrations, pH, and ionic strength (IS) in both PMS and BPA solutions. The kinetic modeling employing the Langmuir-Hinshelwood model at different BPA concentrations suggested that although BPA and PMS were physically separated, the oxidation of the adsorbed BPA and reduction of the adsorbed PMS still followed a similar mechanism to that in traditional heterogeneous catalytic processes. The anions in the target water showed little impact on BPA degradation; higher IS enhanced the solution conductivity but inhibited BPA and electrode interactions, resulting in increased and then decrease BPA degradation rate. The electrodes presented high stability with a rate increase of 12% after 13 times of uses, and their hydration significantly facilitated BPA degradation but reduced the current by decreasing the potential difference between the anode and cathode. The graphite sheet itself without catalyst coating was also capable of shuttling electrons, while the use of a graphite fiber anode increased the BPA degradation by near 100% because of the larger surface area. The developed continuous stirred-tank reactor coupled with GOP (CSTR-GOP) achieved stable BPA degradation in less than 35 min and its scaling up is promising for future applications.

Overlooked Role of Fe(IV) and Fe(V) in Organic Contaminant Oxidation by Fe(VI)

Fe(VI) has received increasing attention since it can decompose a wide range of trace organic contaminants (TrOCs) in water treatment. However, the role of short-lived Fe(IV) and Fe(V) in TrOC decomposition by Fe(VI) has been overlooked. Using methyl phenyl sulfoxide (PMSO), carbamazepine, and caffeine as probe TrOCs, we observed that the apparent second-order rate constants (k_app) between TrOCs and Fe(VI) determined with the initial kinetics data were strongly dependent on the initial molar ratios of TrOCs to Fe(VI). Furthermore, the k_app value increases gradually as the reaction proceeds. Several lines of evidence suggested that these phenomena were ascribed to the accumulation of Fe(IV) and Fe(V) arising from Fe(VI) decay. Kinetic models were built and employed to simulate the kinetics of Fe(VI) self-decay and the kinetics of PMSO degradation by Fe(VI). The modeling results revealed that PMSO was mainly degraded by Fe(IV) and Fe(V) rather than by Fe(VI) per se and Fe(V) played a dominant role, which was also supported by the density functional theory calculation results. Given that Fe(IV) and Fe(V) have much greater oxidizing reactivity than Fe(VI), this work urges the development of Fe(V)/Fe(IV)-based oxidation technology for efficient degradation of TrOCs.

A novel hollow-sphere cyclodextrin nanoreactor for the enhanced removal of bisphenol A under visible irradiation

A novel hybrid nanoreactor with spatially separated co-catalysts (SH-CD-Au@CdS@MnO_x) was successfully synthesised to remove bisphenol-A (BPA) from water by visible light. The photooxidation intermediates, degradation pathway of BPA and the enhancement mechanism were investigated in particular. Gold (Au) nanoparticles modified with SH-β-cyclodextrin and MnO_x nanoparticles were selectively decorated on the interior and exterior surface of hollow CdS nanoreactors, respectively. The directed migration of photogenerated electrons and holes induced by spatially separated co-catalysts lead to high utilization of light, and SH-β-cyclodextrin modification makes catalytic active sites more accessible for oxidation intermediates. Compared with pristine CdS, the hybrid nanoreactor increased the BPA photooxidation reaction rate and the TOC removal efficiency by 5.6-fold and 3.6-fold, respectively. Moreover, the toxic intermediates, such as phenol, were further degraded by visible light. Molecular orbital calculation predicted that the sites on BPA molecule values of (FED²_HOMO + FED²_LUMO) can be easier attacked by the radical, whereas atoms with higher values of 2FED²_HOMO can easily be extracted into electrons. Thus, SH-CD-Au@CdS@MnO_x can provide a new strategy for the high-efficiency photodegradation of endocrine disrupter compounds in advanced water treatments.

Ferrate Oxidation of Phenolic Compounds in Iodine-Containing Water: Control of Iodinated Aromatic Products

Highly toxic iodinated products would form in oxidation and disinfection of iodine-containing water. Variation of iodinated aromatic products in ferrate [Fe(VI)] oxidation of phenolic compounds (phenol, bisphenol A (BPA), and p-hydroxybenzoic acid (p-HBA)) in iodine-containing water was investigated. At pH 5.0, oxidation of phenolic compounds was inhibited by competitive reaction of ferrate with I^-, and no formation of iodinated aromatic products was detected. Almost all I^- was converted into nontoxic IO₃^-. At pH 7.0, 8.0, and 9.0, HOI formed in ferrate oxidation of I^- and further reacted with phenols, with the formation of iodinated aromatic products. Mass spectrometry analysis showed that both kinds and contents of iodinated aromatic products were raised with the increase in solution pH and the content of I^-, and these iodinated aromatic products were further oxidized by ferrate. Ferrate deprived iodine from iodinated aromatic products and transferred highly toxic organic iodine into nontoxic IO₃^-. An electron-donating substituent (alkyl) increased the reactivity of phenol with ferrate and HOI and facilitated ferrate oxidation of iodinated phenols. An electron-drawing substituent (carboxyl) decreased the reactivity of phenol with ferrate and HOI and hindered the further oxidation of iodinated aromatic products. A kinetic model about the variation of phenol, BPA, and p-HBA in reaction with ferrate in iodine-containing water was developed, and the oxidation profile of phenolic compounds could be satisfactorily predicted at various iodide concentrations.

Catalytic degradation of organic pollutants in Fe(III)/peroxymonosulfate (PMS) system: performance, influencing factors, and pathway

This study demonstrated, for the first time, Fe(III)/peroximonosulphate (PMS) could be an efficient advanced oxidation process (AOP) for wastewater treatment. Bisphenol A (BPA) was chosen as a model pollutant in the present study. Fe(III)-activated PMS system proved very effective to eliminate 92.18% of BPA (20 mg/L) for 30-min reaction time at 0.50 mM PMS, 1.5 g/L Fe(III), pH 7.0. The maximum degradation of BPA occurred at neutral pH, while it was suppressed at both strongly acidic and alkaline conditions. Organic and inorganic ions can interfere with system efficiency either positively or negatively, so their interaction was thoroughly investigated. Furthermore, the presence of organic acids also affected BPA degradation rate, especially the addition of 10 mM citric acid decreased the degradation rate from 92.18 to 66.08%. Radical scavenging experiments showed that SO₄^•- was the dominant reactive species in Fe(III)/PMS system. A total of 5 BPA intermediates were found by using LC/MS. A possible degradation pathway was proposed which underwent through bridge cleavage and hydroxylation processes. Acute toxicity of the BPA degradation products was assessed using Escherichia coli growth inhibition test. These findings proved to be promising and economical to deal with wastewater using iron mineral for the elimination of organic pollutants. Graphical abstract.

Degradation of dye in wastewater by Homogeneous Fe(VI)/NaHSO3 system

The homogeneous Fe(VI)/Na₂SO₃ system has been proposed for highly efficient degradation of recalcitrant contaminants, in which sulfite could significantly enhance the transformation of organic substrate by Fe(VI). Also, the Fe(VI)/NaHSO₃ system could show high efficiency across a wide range of pH conditions. The degradation rates reached up to 80% within 2 min and 70% within 5 min in strongly acidic and alkaline conditions, respectively. Unexpectedly, a faster removal rate was obtained in Fe(VI)/NaHSO₃ system than that in Fe(VI)/Na₂SO₃ system for the degradation of methylene blue (MB). A reasonable dye degradation mechanism was proposed and verified by a series of experiments. The high oxidation potential of Fe(VI) and other species such as sulfate and hydroxyl radicals were responsible for the outstanding capabilities of Fe(VI)/NaHSO₃ system, which could significantly improve the treatment of organics in wastewater under a very wide range of pH conditions.

Activation of ferrate by carbon nanotube for enhanced degradation of bromophenols: Kinetics, products, and involvement of Fe(V)/Fe(IV)

Very recently, several studies have found that homogeneous reducing agents (e.g., sodium thiosulfate (Na₂S₂O₃), and sodium sulfite (Na₂SO₃)) can activate ferrate to enhance the degradation of selected contaminants. In this work, it was found that heterogeneous carbon nanotube (CNT) could accelerate ferrate (Fe(VI)) for the degradation of bromophenols (BrPs) of environmental concerns and alleviate the appearance of undesired by-products in effluent. Fe(VI) could react with BrPs over a wide pH range of 6-10 with apparent second-order rate constants of 1.8-1850 M^-1 s^-1. Electrospray ionization-triple quadrupole mass spectrometry (ESI-QqQMS) analysis showed that dibrominated dihydroxylated biphenyls and dibrominated phenoxyphenols were possibly formed via coupling reaction of BrPs radicals generated from Fe(VI) oxidation through one-electron transfer. The presence of CNT could remarkably accelerate the degradation rates of BrPs by Fe(VI) in a wide pH range from 7 to 10. Moreover, the formed undesired polybrominated products during Fe(VI)/CNT oxidation were absorbed on CNT surface and thus removed from treated water. The Fe(VI)/CNT system was capable of selectively oxidizing electron-rich pollutants (e.g., BrPs, and sulfamethoxazole (SMX)), but reluctant to iopamidol (IPM) and nitrobenzene (NB). High-valent metal-oxo intermediates Fe(V)/Fe(IV) formed in situ from the reaction of CNT with Fe(VI) were likely responsible for this activation effect of CNT, which was further confirmed via using methyl phenyl sulfoxide (PMSO) as a probe compound. Comparatively, homogeneous reducing agent Na₂S₂O₃ could enhance Fe(VI) degradation of BrPs at pH 7 and 8, while undesired polybrominated products were detected in effluent from Fe(VI)/Na₂S₂O₃ system. These findings have crucial implications for the development of a promising oxidation process by combination of Fe(VI) and CNT for water and wastewater treatment.

Removal of sulfapyridine by ferrate(VI): efficiency, influencing factors and oxidation pathway

The removal of sulfapyridine (SPY) by ferrate(VI) in aqueous solutions under a broad range of reaction conditions, including ferrate(VI) dosage, solution pH, natural organic matter and coexisting inorganic ions, was systematically investigated and the oxidation pathway of SPY by ferrate(VI) was deeply explored. Results showed that 500 µg/L of SPY was efficiently decomposed (86%) within 1 min by 5 mg/L ferrate(VI) at pH 5.6. The increment in ferrate(VI) dosage was surely favorable for SPY removal. The best SPY degradation was achieved at pH 5.6, under or above which the removal decreased. The introduction of inorganic ions in solutions retarded SPY removal. Ten oxidation intermediates were identified and the cleavages of C-S and S-N bonds might be the primary ways of SPY oxidation by ferrate(VI).

Reusable magnetic Ag/Fe, N-TiO2/Fe3O4@SiO2 composite for simultaneous photocatalytic disinfection of E. coli and degradation of bisphenol A in sewage under visible light

A visible-light-driven and magnetic photocatalyst Ag/Fe,N-TiO₂/Fe₃O₄@SiO₂ (AgFeNTFS) was synthesized through a multi-step method. AgFeNTFS was tested for the photocatalytic disinfection of Escherichia coli (E. coli) and degradation of bisphenol A (BPA) under visible light irradiation, separately and simultaneously. The results showed that a 6.3-log reduction in cell density of E. coli was achieved and BPA (2 mg/L) was completely removed by AgFeNTFS in the separated photocatalytic processes within 120 min. In the simultaneous process, the photocatalytic disinfection of E. coli was not influenced in the presence of BPA, but the efficiency of BPA degradation was dropped by 10%. This was likely due to the competition for the same dominant reactive species of O₂^- and H₂O₂ between E. coli and BPA in the simultaneous process, as evidenced by the scavenger study and the interactions between the pollutants and AgFeNTFS. Moreover, the simultaneous photocatalytic activity of E. coli disinfection and BPA degradation by AgFeNTFS was investigated in the sewage obtained from a local wastewater treatment plant. The photocatalysis treated sewage could meet with the local disinfection discharge standard with a 3-log reduction of E. coli after 90 min, and a complete removal of BPA was achieved simultaneously after 360 min. Moreover, AgFeNTFS showed high magnetic separation efficiency and had a good reusability over three cycles for the simultaneous photocatalytic disinfection and degradation of BPA in both synthetic water and sewage. This study provides insights on the application of a reusable magnetic photocatalyst for simultaneous disinfection and degradation of BPA in sewage.

Enhanced Removal of Chlorophene and 17β-estradiol by Mn(III) in a Mixture Solution with Humic Acid: Investigation of Reaction Kinetics and Formation of Co-oligomerization Products

Reaction with soluble Mn(II) has been considered as a main decay pathway for superoxide in natural waters, accompanied by an important Mn redox cycling. In this study, the interaction of Mn(II) and humic acid (HA) was investigated in visible light irradiated water. Our results indicate that HA may play a dual role to act as a photosensitizer to produce superoxide anions (O₂^-) and as a strong ligand to stabilize the Mn(III), forming soluble Mn(III)_L species for substrate transformation. Furthermore, the reaction kinetics, products, and mechanisms of chlorophene (CP) and estradiol (E2) mixture in the Mn(II)/HA/visible light reaction systems were assessed. The removal of CP and E2 was enhanced by 24.3% and 13.2%, respectively, in mixture solution at initial concentration of 1.0 μM for each target contaminant, as compared to the case of single-compound degradation. Product identification and density functional theory calculations indicated that cross-coupling reaction of CP and E2 radicals was more likely to occur than the self-coupling reaction in mixture solution. In addition, estrogenic activities of initial reaction solution were also effectively decreased during the transformation process. These findings provide new insights into Mn(III)-mediated reactions to better understand the environmental fate of organic contaminant mixture in waters.

Photodegradation of 17β-estradiol on silica gel and natural soil by UV treatment

This paper evaluates the UV photodegradation of 17β-estradiol (E2) on silica gel and in natural soil with different soil components. Silica gel was chosen as a stable and pure support to simulate the photochemical behavior of E2 on the surface of natural soil. Ultraviolet light, rather than visible light, was confirmed to play a decisive role in the photodegradation of E2 on silica gel. The effect of three soil components, including humic acid (HA), inorganic salts, and relative humidity (RH), on the photochemical behavior of E2 on silica gel or soil under UV irradiation was then evaluated. Two HA concentrations (10 and 20 mg g^-1) and three salts (ferric sulfate, copper sulfate and sodium carbonate) were observed to obviously inhibit the degradation of E2 on silica gel. Interestingly, nitrate was found to obviously improve the removal efficiency of E2. Both too-dry and too-wet conditions obviously reduced the removal rate of E2, and the optimum relative humidity (RH) value was found to be approximately about 35% (30 °C). Furthermore, twenty intermediate products and two major pathways were proposed to describe the transformation processes of E2 treated by UV irradiation, among which oligomers were found to be the major intermediate products before complete mineralization. The efficient UV removal of E2 on silica gel and natural soil suggested a feasible strategy to remediate E2 contaminated soil.

Facile preparation of microscale hydrogel particles for high efficiency adsorption of bisphenol A from aqueous solution

Hydrogel microparticles (HMPs) were synthesized via reverse emulsion/UV light polymerization and employed as adsorbents for removing bisphenol A (BPA) from aqueous solution. Results demonstrated the smooth surface of HMPs, with particle size ranging from 137 to 535 μm. Functional groups, including -OH, C-O, C=O, and C-H, are all involved in BPA adsorption confirmed by FTIR. Effect of solution pH, contact time, and initial BPA concentration on adsorption process was examined. The adsorption capacity was found pH independent below pH 8.0 and decreased when pH values greater than 8.0. The maximum adsorption capacity of the HMPs for BPA was 174.77 mg/g. The adsorption process achieved an equilibrium state within 30 min by the pseudo-second-order kinetic rather than the other kinetic models and was fitted well with the Freundlich linear isotherm model. Also, the obtained isotherms reflected the formation of S-type isotherm curve according to Giles's classification. The BPA loaded on the HMPs could be totally regenerated by methanol/dimethylsulfoxide and can be used for five cycles maintaining 100% of adsorption capacity. When the HMPs were applied for the treatment of spiked real surface water, excellent results were also achieved indicating the high efficiency and potential of the adsorbent.

Enhancement of the sludge disintegration and nutrients release by a treatment with potassium ferrate combined with an ultrasonic process

Sludge disintegration by ultrasound is a promising sludge treatment method. In order to enhance the efficiency of the sludge reduction and hydrolysis, potassium ferrate (K₂FeO₄) (PF) was used. A novel method was developed to improve the sludge disintegration-sludge pretreatment by using PF in combination with an ultrasonic treatment (PF + ULT). After a short-term PF + ULT treatment, 17.23% of the volatile suspended solids (VSS) were reduced after a 900-min reaction time, which is 61.3% higher than the VSS reduction for the raw sludge. The supernatant soluble chemical oxygen demand (SCOD), total nitrogen (TN), volatile fatty acids (VFAs), soluble protein and polysaccharides increased by 522.5%, 1029.4%, 878.4%, 2996.6% and 801.9%, respectively. The constituent parts of the dissolved organic matter of the sludge products were released efficiently, which demonstrated the positive effect caused by the PF + ULT. The enhanced sludge disintegration process further alleviates environmental risk and offers a more efficient and convenient method for utilizing sludge.

Degradation of bisphenol A through transition metals activating persulfate process

In this study, the process of transition metals (Fe²⁺, Fe⁰, Ni₂O₃) activating persulfate was attempted to degrade aqueous bisphonel A (BPA). Compared with thermal activation mode, significant degradation can be achieved at normal atmospheric temperature in transition metal activation mode. BPA removal in the transition metal-PS system can be divided into rapid phase (0-5 min) and slow phase (5-60 min). In rapid phase, 87.71% and 90.60% removal efficiencies were obtained in the Fe²⁺-PS and Ni₂O₃-PS systems, and the contaminant was almost completely oxidized after 60 min. There are many similarities between the Fe²⁺-PS and Fe⁰-PS systems, in particular the optimal removal efficiencies were achieved at n₀(Fe²⁺):n₀(PS) = 1:2 and n₀(Fe⁰):n₀(PS) = 1:2 rather than with maximum metal dosage. The Ni₂O₃ dosage had positive correlation with BPA removal rate while the degradation efficiency of the Fe²⁺-PS system could be promoted by keeping n₀(sodium citrate):n₀(Fe²⁺) below 1:1. Intermediate products of the Fe²⁺-PS system were analyzed by LC-MS and were predominantly phenol, p-hydroxyacetophenone, benzoquinone and propanedioic acid, therefore a possible oxidation degradation pathway was speculated.

Stabilisation and dewatering of primary sludge using ferrate(VI) pre-treatment followed by freeze-thaw in simulated drainage beds

This study evaluated the ability of potassium ferrate(VI) and freeze-thaw to stabilise and dewater primary sludge. Potassium ferrate(VI) additions of 0.5 and 5.0 g/L were used as a pre-treatment prior to freeze-thaw. Samples were frozen at -10, -20 and -30 °C, and were kept frozen for 1, 8 and 15 days. The samples were subsequently thawed at room temperature in a setup which allowed meltwater to be separated from the sludge cake via gravity drainage. The meltwater was characterised in terms of fecal coliform, soluble chemical oxygen demand (COD), soluble proteins, soluble carbohydrates, pH and turbidity. The sludge cake was characterised in terms of fecal coliform, total solids (TS) and volatile solids (VS). Freeze-thaw with gravity meltwater drainage reduced the sludge volume by up to 79%. After being frozen for only 1 day, the concentrations of fecal coliform in many of the primary sludge samples were reduced to <1000 MPN/g dry solids (DS), representing >3-log inactivation in some cases. However, pre-treatment of the primary sludge with ≤5.0 g/L potassium ferrate(VI) resulted in significant increases in soluble proteins, soluble carbohydrates, and sCOD, and reduced the effectiveness of stand-alone freeze-thaw. Follow-up experiments using higher doses ranging from 5.1 to 24.9 g/L of potassium ferrate(VI) demonstrated that >5-log inactivation of fecal coliform in raw primary sludge can be achieved within 15 min using 15 g/L of potassium ferrate(VI), and the resulting concentration of fecal coliform in the sludge was 1023 MPN/g DS. Pre-treatment with 22.0 g/L of potassium ferrate(VI), followed by freeze-thaw, with only 3 days frozen, reduced the concentration of fecal coliform to below the detection limit in the meltwater and the sludge cake. This demonstrates that potassium ferrate(VI) and freeze-thaw offers the flexibility to adjust the ferrate(VI) dose to meet treatment requirements for land application, and can be used as a stand-alone sludge treatment technology for primary sludge that achieves both treatment and dewatering.

A critical review of ferrate(VI)-based remediation of soil and groundwater

Over the past few decades, diverse chemicals and materials such as mono- and bimetallic nanoparticles, metal oxides, and zeolites have been used for soil and groundwater remediation. Ferrate (Fe^VIO₄^2-) has been widely employed due to its high-valent iron (VI) oxo compound with high oxidation/reduction potentials. Ferrate has received attention for wide environmental applications including water purification and sewage sludge treatment. Ferrate provides great potential for diverse environmental applications without any environmental problems. Therefore, this paper provides comprehensive information on the recent progress on the use of (Fe^VIO₄^2-) as a green material for use in sustainable treatment processes, especially for soil and water remediation. We reviewed diverse synthesis recipes for ferrates (Fe^VIO₄^2-) and their associated physicochemical properties as oxidants, coagulants, and disinfectants for the elimination of a diverse range of chemical and biological species from water/wastewater samples. A summary of the eco-sustainable performance of ferrate(VI) in water remediation is also provided and the future of ferrate(VI) is discussed in this review.

Kinetics and mechanism of 17β-estradiol chlorination in a pilot-scale water distribution systems

The kinetics and mechanisms of 17β-estradiol (E2) chlorination in water distribution systems (WDS) were studied. We examined the impacts of different factors, including pH, temperature, humic acid concentration and type, and flow velocity. The experimental results showed that the rate constants in beaker tests and WDS were described by a pseudo-first-order model. pH had the greatest impact on E2 chlorination in the beaker tests. However, temperature had the greatest impact on E2 chlorination in WDS. Mechanistic analysis of E2 chlorination showed that chlorine attacked E2 in three stages: 1) halogenation of the aromatic ring, 2) cleavage of the benzene moiety and chlorine or bromine substitution formation, and 3) formation of trihalomethanes (THMs) and halogenated acetic acids (HAAs) from phenolic intermediates through benzene ring opening with chlorine and/or bromine substitution of hydrogen on the carbon atoms. In the third stage, the concentrations of THMs and HAAs increased rapidly.

Ferrrate(VI) and freeze-thaw treatment for oxidation of hormones and inactivation of fecal coliforms in sludge

This study examined the individual and combined effects of potassium ferrate(VI) additions and freeze-thaw conditioning for the treatment and dewatering of wastewater sludge in cold climates, with particular focus on the inactivation of fecal coliforms and oxidation of estrogens, androgens, and progestogens. The first phase of the study evaluated the effects of potassium ferrate(VI) pre-treatment followed by freeze-thaw at -20 °C using a low (0.5 g/L) and high (5.0 g/L) dose of potassium ferrate(VI). The results showed that pre-treatment of anaerobically digested sludge with 5 g/L of potassium ferrate(VI) reduced the concentration of fecal coliforms in the sludge cake to below 100 MPN/g DS. The second phase evaluated the ability of ferrate(VI) to oxidise selected hormones in sludge. Anaerobically digested sludge samples were spiked with 10 different hormones: estrone (E1), 17α-estradiol, 17β-estradiol (E2), estriol (E3), 17α-ethinylestradiol (EE2), equilin, mestranol, testosterone, norethindrone and norgestrel in two groups of low (3-75 ng/mL) and high (12-300 ng/L) concentration ranges of hormones. The samples were treated with either 0.5 or 1.0 g/L of potassium ferrate(VI), and hormone concentrations were measured again after treatment. Potassium ferrate(VI) additions as low as 1.0 g/L reduced the concentration of estrogens in sludge. Potassium ferrate(VI) additions of 0.5 and 1.0 g/L were less effective at reducing the concentrations of androgens and progestogens. Increasing ferrate(VI) dose would likely result in more substantial decreases in the concentrations of fecal coliforms and hormones. The results of this study indicate that the combined use of freeze-thaw and ferrate(VI) has the potential to provide a complete sludge treatment solution in cold regions.

Oxidation of indometacin by ferrate (VI): kinetics, degradation pathways, and toxicity assessment

The oxidation of indometacin (IDM) by ferrate(VI) (Fe(VI)) was investigated to determine the reaction kinetics, transformation products, and changes in toxicity. The reaction between IDM and Fe(VI) followed first-order kinetics with respect to each reactant. The apparent second-order rate constants (k _app) decreased from 9.35 to 6.52 M^-1 s^-1, as the pH of the solution increased from 7.0 to 10.0. The pH dependence of k _app might be well explained by considering the species-specific rate constants of the reactions of IDM with Fe(VI). Detailed product studies using liquid chromatography-tandem mass spectrometry (LC-MS/MS) indicated that the oxidation products were primarily derived from the hydrolysis of amide linkages, the addition of hydroxyl groups, and electrophilic oxidation. The toxicity of the oxidation products was evaluated using the Microtox test, which indicated that transformation products exhibited less toxicity to the Vibrio fischeri bacteria. Quantitative structure-activity relationship (QSAR) analysis calculated by the ecological structure activity relationship (ECOSAR) revealed that all of the identified products exhibited lower acute and chronic toxicity than the parent pharmaceutical for fish, daphnid, and green algae. Furthermore, Fe(VI) was effective in the degradation IDM in water containing carbonate ions or fulvic acid (FA), and in lake water samples; however, higher Fe(VI) dosages would be required to completely remove IDM in lake water in contrast to deionized water.

On-line batch production of ferrate with an chemical method and its potential application for greywater recycling with Al(III) salt

Ferrate(VI) salt is an oxidant and coagulant for water and wastewater treatment. It is considered as a possible alternative method in greywater treatment. However, challenges have existed in putting ferrate(VI) technology into full-scale practice in water and wastewater treatment due to the instability of ferrate solution and high production cost of solid ferrate products. This study demonstrated a new approach of greywater treatment with on-line batch production of Fe(VI) to which Fe(III) salt was oxidized at a weak acidity solution. A series of experiments were conducted to investigate the effect of Fe(VI) on light greywater (total organic carbon (TOC)=19.5mg/L) and dark greywater (TOC=55mg/L) treatment under different conditions with varying pH and Fe(VI) doses. In addition, the combination use of Fe(VI) and Al(III) salts was proved to be more efficient than using the Fe(VI) salts alone at greywater recycling. The optimum dosage of Fe(VI)/Al(III) salts was 25/25mg/L for light greywater, 90/60mg/L for dark greywater, respectively. The TOC values of both light greywater and dark greywater were reduced to less than 3mg/L with the dosages. The cost for treating greywater was 0.06-0.2$/ton at ferrate(VI) dosage of 25-90mg/L and 0.008-0.024$/ton at AlCl₃ dosage of 25-60mg/L. The full operating cost needs further assessment before the Fe(VI)/Al(III) technology could be implemented in greywater treatment.

Catalyst support materials for prominent mineralization of bisphenol A in catalytic ozonation process

Degradation of aqueous solution of bisphenol A (BPA) has been investigated through non-catalytic and catalytic ozonation treatments conducted in a semi-batch reactor. Non-catalytic ozonation resulted in complete degradation of aqueous BPA in less than 3 min but did not completely convert the reaction intermediates of BPA ozonation into CO2 and H2O. The main goal of this study was to find an effective heterogeneous catalyst to increase the extent of BPA mineralization at different pH conditions. In this way, the most promising catalyst carrier was γ-Al2O3; at pH = 8.0, 68 % of total organic carbon (TOC) was removed in the period of 75 min, out of which 42 % was attributed to mineralization. Finally, 3.0 wt.% Ru/γ-Al2O3 catalyst exhibited over 82 % of TOC removal after 240 min of ozonation at pH = 5.9, of which 56 % was mineralized.

Mechanistic study of photo-oxidation of Bisphenol-A (BPA) with hydrogen peroxide (H2O2) and sodium persulfate (SPS)

The removal of Bisphenol-A (BPA) from contaminated water using advanced oxidation methods such as UV-C assisted oxidation by hydrogen peroxide (H2O2) and sodium persulfate (SPS) has been reported by the authors earlier (Sharma et al., 2015a). In the present study, the authors report the removal of BPA from aqueous solution by the above two methods and its degradation mechanism. UV-C light (254 nm wavelength, 40 W power) was applied to BPA contaminated water at natural pH (pHN) under room temperature conditions. Experiments were carried out with the initial BPA concentration in the range of 0.04 mM-0.31 mM and the oxidant/BPA molar ratio in the range of 294:1-38:1 for UV-C/H2O2 and 31.5-4.06:1 for UV-C/SPS systems. The removal of BPA enhanced with decreasing BPA concentration. The total organic carbon also decreased with the UV-C irradiation time under optimum conditions ([H2O2]0 = 11.76 mM; [SPS]0 = 1.26 mM; temperature (29 ± 3 °C). Competition of BPA for reaction with HO or [Formula: see text] radicals at its higher concentrations results in a decrease in the removal of BPA. The intermediates with smaller and higher molecular weights than that of BPA were found in the treated water. Based on GC-MS and FTIR spectra of the reaction mixture, the formation of hydroxylated by-products testified the HO mediated oxidation pathway in the BPA degradation, while the formation of quinones and phenoxy phenols pointed to the [Formula: see text] dominating pathway through the formation of hydroxycyclohexadienyl (HCHD) and BPA phenoxyl radicals. The main route of BPA degradation is the hydroxylation followed by dehydration, coupling and ring opening reactions.