Enhancement of Fenton and photo-Fenton processes at initial circumneutral pH for the degradation of the β-blocker metoprolol

Transformation of metoprolol in UV/PDS process: Role and mechanisms of degradation and polymerization

Advanced oxidation processes for the treatment of organic pollutants in wastewater suffer from difficulties in mineralization, potential risks of dissolved residues, and high oxidant consumption. In this study, radical-initiated polymerization is dominated in an UV/peroxydisulfate (PDS) process to eliminate organic pollutant of pharmaceutical metoprolol (MTP). Compared with an ideal degradation-based UV/PDS process, the present process can save four fifths of PDS consumption at the same dissolved organic carbon removal of 47.3%. Simultaneously, organic carbon can be recovered from aqueous solution by separating solid polymers at a ratio of 50% of the initial chemical oxygen demand. The chemical structure of products was analyzed to infer the transformation pathways of MTP. Unlike previous studies on simple organic pollutants that the polymerization can occur independently, the polymerization of MTP is dependent on the partial degradation of MTP, and the main monomer in polymerization is a dominant degradation product (4-(2-methoxyethyl)-phenol, denoted as DP151). The separated solid polymers are formed by repeated oxidation and coupling of DP151 or its derivatives through a series of intermediate oligomers. This proof-of-concept study demonstrates the advantage of polymerization-dominated mechanism on dealing with large organic molecules with complex structures, as well as the potential of UV/PDS process for simultaneous organic pollution reduction and organic carbon recovery from aqueous solution.

Advancements of the Fluidized Bed Fenton (FBF) Technology for wastewater treatment: Mechanism, mass and heat transfer

Fluidized Bed Fenton (FBF) technology, a fusion of the Fenton method and fluidized bed reactor, has emerged as a superior alternative to conventional Fenton technology for treating organic industrial wastewater. This innovative approach has garnered significant attention from researchers in recent years. While earlier studies primarily focused on pollutant degradation in simulated wastewater and catalyst development, there has been a growing interest in examining the alterations in mass or heat transfer performance attributed to fluidized beds. This paper explores the factors that contribute to the effectiveness of Fluidized Bed Fenton technology in efficiently degrading various challenging organic pollutants, while also reducing iron sludge production and expanding the applicable pH range, through an analysis of reaction kinetics. Meanwhile, combined with the related work of fluid dynamics, the research related to mass and heat transfer inside the reactor of Fluidized Bed Fenton technology is summarized, and it is proposed that the use of computers to establish a suitable model of Fluidized Bed Fenton and solve it with the assistance of computational fluid dynamics (CFD) and other software will help to further explore the process of mass and heat transfer inside the fluidized bed, which will provide the basis for the future of the Fluidized Bed Fenton from the laboratory to the actual industrial application.

Photodegradation performance and mechanism of sulfadiazine in Fe(III)-EDDS-activated persulfate system

In order to overcome the shortcomings in the traditional Fenton process, Fe(III)-EDDS-activated persulfate advanced oxidation process under irradiation is carried out as a promising technology. The photodegradation of sulfadiazine (SD) in Fe(III)-EDDS-activated persulfate system was investigated in this paper. The results showed that SD could be effectively degraded in Fe(III)-EDDS/S 2 O 8 2 - /hv system. The effects of Fe(III):EDDS molar ratio, the concentration of Fe(III)-EDDS, and the concentration of S 2 O 8 2 - on SD degradation were explored. At neutral pH, when Fe(III):EDDS = 1:1, Fe(III)-EDDS = 0.1 mM, S 2 O 8 2 -  = 1.5 mM, the best SD degradation was achieved. The experiment of external influence factors showed that the degradation of SD could be obviously inhibited by the presence of C O 3 2 - , S O 4 2 - , whereas the degradation of SD was almost unaffected by the addition ofCl-. The degradation of SD could be slightly inhibited by the presence of humic acid and NO3-. The effect of pH on SD degradation was investigated, and SD could be degraded effectively in the pH range of 3-9. ESR proved that 1O2, ·OH, S O 4 - , and O2- were produced in the process. S O 4 - and ·OH were identified as the main radicals while O2·- also played non-ignorable role. Eleven intermediate products of SD were analysed. The C = N, S-N, and S-C bonds of SD were attacked by radicals firstly, leading to a series of reactions that eventually resulted in the destruction of SD molecules and the formation of small organic molecules.

Deep dewatering of refinery oily sludge by Fenton oxidation and its potential influence on the upgrading of oil phase

Highly efficient dewatering is essential to the reduction and reclamation disposal of oily sludge, which is a waste from the extraction, transportation, and refining of crude oil. How to effectively break the water/oil emulsion is a paramount challenge for dewatering of oily sludge. In this work, a Fenton oxidation approach was adopted for the dewatering of oily sludge. The results show that the oxidizing free radicals originated from Fenton agent effectively tailored the native petroleum hydrocarbon compounds into smaller organic molecules, hence destructing the colloidal structure of oily sludge and decreasing the viscosity as well. Meanwhile, the zeta potential of oily sludge was increased, implying the decrease of repulsive electrostatic force to realize easy coalescence of water droplets. Thus, the steric and electrostatic barriers which restrained the coalescence of dispersed water droplets in water/oil emulsion were removed. With these advantages, the Fenton oxidation approach derived the significant decrease of water content, in which 0.294 kg water was removed from per kilogram oily sludge under the optimal operation condition (i.e., pH value of 3, solid-liquid ratio of 1:10, Fe²⁺ concentration of 0.4 g/L and H₂O₂/Fe²⁺ ratio of 10:1, and reaction temperature of 50 °C). In addition, the quality of oil phase was upgraded after Fenton oxidation treatment accompanying with the degradation of native organic substances in oily sludge, and the heating value of oily sludge was increased from 8680 to 9260 kJ·kg^-1, which would facilitate to the subsequent thermal conversion like pyrolysis or incineration. Such results demonstrate that the Fenton oxidation approach is efficient for the dewatering as well as the upgrading of oily sludge.

Fenton Reaction–Unique but Still Mysterious

This study is devoted to the Fenton reaction, which, despite hundreds of reports in a number of scientific journals, provides opportunities for further investigation of its use as a method of advanced oxidation of organic macro- and micropollutants in its diverse variations and hybrid systems. It transpires that, for example, the choice of the concentrations and ratios of basic chemical substances, i.e., hydrogen peroxide and catalysts based on the Fe2+ ion or other transition metals in homogeneous and heterogeneous arrangements for reactions with various pollutants, is for now the result of the experimental determination of rather randomly selected quantities, requiring further optimizations. The research to date also shows the indispensability of the Fenton reaction related to environmental issues, as it represents the pillar of all advanced oxidation processes, regarding the idea of oxidative hydroxide radicals. This study tries to summarize not only the current knowledge of the Fenton process and identify its advantages, but also the problems that need to be solved. Based on these findings, we identified the necessary steps affecting its further development that need to be resolved and should be the focus of further research related to the Fenton process.

Color removal from secondary treated pulp & paper industry effluent using waste driven Fe-TiO2 composite

In the present study, the concurrent fixed-bed dual technology (photocatalysis and photo-Fenton) was performed as a polishing step for the color removal of tertiary treated agro-based paper & pulp industry effluent. For this purpose, the cheap and visibly dynamic Fe-TiO₂ composite was prepared using industrial waste materials which also promoted the idea of the circular economy. The effectiveness of the prepared composite and the dual process was evaluated in terms of color removal efficiency and rate constant along with optimizing the process factors. Various kinetic models namely Log-linear, Weibull, and Biphasic with shoulder were used for the comparative study of three different processes i.e. photocatalysis, photo-Fenton, and dual process. Several parameters such as pH (4.5), % surface area covered (100%), and H₂O₂ dose (525 mgL^-1) were optimized which gave the best output using dual-process i.e. 91.6% of color reduction along with good R² values i.e. 0.874, 0.981 and, 0.998 for Log-linear, Weibull and, Biphasic with Shoulder model respectively. The proposed composite was durable enough to retain its dual catalytic ability with minor activity reduction of 5-10% even after 50 recycles. Thus, this innovative technology with the dual effect of photocatalysis and photo-Fenton can be a potential bet as a tertiary treatment option in the existing industrial wastewater treatment system for removing color from the final treated effluent.

A thorough observation of an ozonation catalyst under long-term practical operation: Deactivation mechanism and regeneration

Heterogeneous catalytic oxidation, as an efficient advanced treatment technology, has been gradually applied in industrial wastewater treatment. The fixed bed technique is one of the most popular catalytic ozonation methods. However, few studies have concentrated on the long-term operation effects on catalysts. In this study, we conducted long-term (~5 years) observations of the operation of the largest petrochemical wastewater treatment plant (treatment capacity 120,000 m³/d) with catalytic ozonation technology in China. A commercial catalyst, which uses Al₂O₃ pellets supporting copper oxide was applied in this plant. The results showed that the catalytic efficiency gradually decreased from 60.65% to 25.98% since 2018, and the ozone dosage to COD removal ratio (ozone/COD) also increased from 0.82 to 1.93 mg/mg as the running time continued. By means of the comparison and characterization of fresh catalyst and used catalyst, a "mucus layer" was formed by the adsorption of negatively charged extracellular polymeric substances on the positively charged catalyst surface and the interception of the catalyst layer. The mucus layer significantly reduced the catalytic efficiency by isolating ozone with catalytic active sites and releasing extra organic contaminants during the catalytic process resulting in 53.97% TOC increase in the batch test. Meanwhile, regeneration experiments revealed that the TOC removal efficiency was 4.76% and 43.48% in presence of washed catalysts and calcinated catalysts, respectively. Compared with the fresh catalyst, 73% of the catalytic activity was recovered for calcinated catalyst. Consequently, this study provides much practical information, showing positive effects on the promotion of catalytic ozonation application in actual wastewater treatment.

Decontamination of real urban sewage-comparison between Fenton and electrochemical oxidation

Advanced oxidation processes have been used for wastewater treatment due to their capacity to reduce the organic loading and for their fast reactions. In this paper, we explore the viability of isolated and sequential use of electrochemical oxidation and Fenton processes into treatment of real raw urban sewage. The electrochemical process was carried out using DSA®-Cl₂ electrodes and factorial planning in order to investigate the influence of pH, current density, and electrolyte. Fenton reaction was also used and H₂O₂ and Fe²⁺ concentration effects were investigated. The efficiency was estimated by chemical oxygen demand (COD) removal and in the optimized conditions the effluent was characterized by turbidity, suspended/dissolved/total solids, ammonia, chloride ions, free chlorine, nitrite, and potassium analysis and bioassays with Artemia ssp. and Lactuca sativa. The study demonstrated that the use of electrochemical technique followed by Fenton allowed an improvement in the degradation of organic matter and reduction of turbidity and solid content, reaching reductions of 86.8, 96.4, 99.4, 56.1, and 66.7% for COD, turbidity, SS, DS, and TS, respectively. The associated treatment also contributed to the reduction of energy consumption by 74.9%, from the 23.9 kWh m^-3 observed during the electrochemical treatment isolated to the 6 kWh m^-3 during the associated process. All the treatments presented toxicity reduction, with the electrochemical process achieving the best results.

Taping into the super power and magic appeal of ultrasound coupled with EDTA on degradation of 2,4,6-TCP by Fe0 based advanced oxidation processes

Chlorophenol is a widely used organic compound, and the environmental and health problems caused by it have being worsened in recent years. This study used 2,4,6-trichlorophenol (2,4,6-TCP) as the target pollutant, and employed ultrasound (US) enhanced zero-valent iron (Fe⁰)/EDTA/air system (FEA), namely US/FEA, to remove 2,4,6-TCP. The influence of single factor experimental conditions such as EDTA concentration, Fe⁰ dosage, US power, pH and pollutant concentration on the removal efficiency of 2,4,6-TCP was investigated, and the optimal reaction conditions were determined. The mechanism of reactive oxygen species (ROS) produced by US/FEA was explored. The degradation process and removal mechanism of 2,4,6-TCP in the US/FEA were discussed through the determination and analysis of intermediate products. The results showed that US could continuously activate and renew the Fe⁰ surface, accelerate its oxidation and corrosion process, and then continuously and stably produce sufficient amounts of Fe²⁺ and Fe³⁺. Ultrasonic cavitation effect could reduce the difficulty of O₂ activation reaction, and promote the production of sufficient H₂O₂. The addition of EDTA made the system have a wide range of pH applications, and its performance under neutral and alkaline conditions was also superior. The ROS of US/FEA included ·OH, O₂^·- and Fe(IV), where Fe(IV) was the main contributor to the removal of 2,4,6-TCP. In addition, the degradation of 2,4,6-TCP had two processes including dechlorination and benzene ring opening. First, 2,4,6-TCP was dechlorinated and degraded into phenol. And then, phenol was degraded into small molecular acids by ring-opening, and finally it was mineralized into CO₂ and H₂O completely. US/FEA is a promising technology for high-efficiency degradation of organic matter and deep environmental purification.

Evaluation of advanced oxidation processes for β-blockers degradation: a review

This study summarizes the results of scientific investigations on the removal of the three most often used β-blockers (atenolol, metoprolol and propranolol) by various advanced oxidation processes (AOP). The free radical chemistry, rate constants, degradation mechanism and elimination effectiveness of these compounds are discussed together with the technical details of experiments. In most AOP the degradation is predominantly initiated by hydroxyl radicals. In sulfate radical anion-based oxidation processes (SROP) both hydroxyl radicals and sulfate radical anions greatly contribute to the degradation. The rate constants of reactions with these two radicals are in the 10⁹-10¹⁰ M^-1 s^-1 range. The degradation products reflect ipso attack, hydroxylation on the aromatic ring and/or the amino moiety and cleavage of the side chain. Among AOP, photocatalysis and SROP are the most effective for degradation of the three β-blockers. The operating parameters have to be optimized to the most suitable effectiveness.

Activation of organic chloramine by UV photolysis: A non-negligible oxidant for micro-pollutant abatement and disinfection by-product formation

Due to the wide-presence of organic amines in natural waters, organic chloramines are commonly formed during (pre-)chlorination. With the increasing application of UV disinfection in water treatment, both the activation mechanism of organic chloramine by UV photolysis and its subsequent impact on water quality are not clear. Using sarcosine (Sar) as an amine group-containing compound, it was found that organic chloramines (i.e., Cl-Sar) would be firstly formed during chlorination even in the presence of natural organic matter. Compared with self-decay of Cl-Sar, UV photolysis accelerated Cl-Sar decomposition and induced NCl bond cleavage. Using metoprolol (MTP) as a model micro-pollutant, UV-activated Cl-Sar (UV/Cl-Sar) can accelerate micro-pollutant degradation, attributed to reactive radicals formation. HO^• and Cl^• were important contributors, with a total contribution of 45%‒64%. Moreover, the degradation rate of MTP by UV/Cl-Sar was pH-dependent, which monotonically increased from 0.044 to 0.065 min^‒1 under pHs 5.5‒8.5. Although the activation of organic chloramine by UV could accelerate micro-pollutant degradation, UV/Cl-Sar treatment could also enhance disinfection by-products formation. Trichloromethane (TCM) formation was observed during MTP degradation by UV/Cl-Sar. After post-chlorination, TCM, 1,1-dichloropropanone, 1,1,1-trichloropropanone, and dichloroacetonitrile were detected. Their individual and total concentrations were all positively proportional to UV/Cl-Sar treatment time. The total concentration with 30 min treatment (66.93 μg L^‒1) was about 2.3 times that with 1 min treatment (28.76 μg L^‒1). Finally, the accelerated effect was verified with Cl-glycine and Cl-alanine. It is expected to unravel the non-negligible role of organic chloramine on water quality during UV disinfection.

Magnetically modified in-situ N-doped Enteromorpha prolifera derived biochar for peroxydisulfate activation: Electron transfer induced singlet oxygen non-radical pathway

Herein, in-situ N-doped Enteromorpha prolifera derived magnetic biochar (MBC) was prepared by loading Fe₃O₄. It can effectively activate peroxodisulfate (PDS) to degrade tetracycline (TC) and easy recycling. The removal rate of TC reached 87.2%, and its possible degradation pathway was revealed through a liquid chromatography-mass spectrometer. This work first proposes the mechanism of in-situ N-doping and Fe synergistic effect on PDS activation. Unlike the well-reported role of N doping in activating PDS, except for the edge pyridine N plays a significant role in the activation of PDS. After the load of Fe, the synergistic effect of Fe and graphite N induces a non-radical path dominated by singlet oxygen (¹O₂) due to the excellent electron transfer function. Through chemical quenching experiment, electron spin detection, and electrochemical analysis, the mechanism of PDS activation by MBC was thoroughly investigate. This research will deepen the understanding of the mechanism of transition metals and carbon materials in synergistically driving PDS activation, and guide biochar-mediated PDS activation in environmental remediation.

Modeling degradation kinetics of gemfibrozil and naproxen in the UV/chlorine system: Roles of reactive species and effects of water matrix

The UV/chlorine system has been regarded as an efficient oxidation technology for the removal of aqueous micropollutants. However, the roles of the possible radical species for this system on the elimination under environmentally relevant conditions/real waters were still largely unknown. Herein, the specific roles of radical species in the UV/chlorine oxidation degradation of gemfibrozil and naproxen as representative micropollutants were quantified by a steady-state kinetic prediction model considering the effects of water matrices. Overall, the model predicted results are consistent with the experimental data well. •OH and reactive chlorine species (RCS, such as Cl•, ClO•, and Cl₂•^-) contributions to gemfibrozil and naproxen degradation were water matrix specific. In pure water, both primary reactive species (i.e., •OH and Cl•) and secondary species ClO• dominated gemfibrozil and naproxen degradation, and their individual and the sum of the contributions to degradation rates reduced with pH increase of from 5 to 9. In the presence of Cl^-, we found that Cl₂•^- and in particular ClO• were responsible for the enhanced degradation with increasing Cl^- concentrations due to the considerable ClO• reactivity of gemfibrozil (1.93 × 10⁹ M^-1 s^-1) and naproxen (9.24 × 10⁹ M^-1 s^-1) and the rapid transformation of Cl₂•^- to ClO•. The presence of HCO₃^- notably facilitated the degradation in the UV/chlorine process because of the generation of CO₃•^-. CO₃•^- showed high reactivity with gemfibrozil and naproxen corresponding to respective second-order reaction rate constants of 2.45 × 10⁷ and 3.50 × 10⁷ M^-1 s^-1. Dissolved organic matter induced obvious scavenging for •OH, Cl•, and ClO• and greatly retarded the degradation. The constructed model considering the effects of above water matrix has successfully predicted the oxidation degradation kinetics in real waters, and both •OH and CO₃•^- are the predominant reactive species in the degradation. This study is helpful for comprehensive understanding the roles of possible radical species in micropollutant removal by UV/chlorine oxidation under real water matrix.

Comparative overview of advanced oxidation processes and biological approaches for the removal pharmaceuticals

Nowadays, pharmaceuticals are the center of significant environmental research due to their complex and highly stable bioactivity, increasing concentration in the water streams and high persistence in aquatic environments. Conventional wastewater treatment techniques are generally inadequate to remove these pollutants. Aiming to tackle this issue effectively, various methods have been developed and investigated on the light of chemical, physical and biological procedures. Increasing attention has recently been paid to the advanced oxidation processes (AOPs) as efficient methods for the complete mineralization of pharmaceuticals. Their high operating costs compared to other processes, however, remain a challenge. Hence, this review summarizes the current and state of art related to AOPs, biological treatment and their effective exploitation for the degradation of various pharmaceuticals and other emerging molecules present in wastewater. The review covers the last decade with a particular focus on the previous five years. It is further envisioned that this review of advanced oxidation methods and biological treatments, discussed herein, will help readers to better understand the mechanisms and limitations of these methods for the removal of pharmaceuticals from the environment. In addition, we compared AOPs and biological treatments for the disposal of pharmaceuticals from the point of view of cost, effectiveness, and popularity of their use. The exploitation of coupling AOPs and biological procedures for the degradation of pharmaceuticals in wastewater was also presented. It is worthy of note that an integrated AOPs/biological system is essential to reach the complete degradation of pharmaceuticals; other advantages of this hybrid technique involve low energy cost, an efficient degradation process and generation of non-toxic by-products.

Manufacturing and Application of 3D Printed Photo Fenton Reactors for Wastewater Treatment

Additive manufacturing (AM) or 3D printing offers a new paradigm for designing and developing chemical reactors, in particular, prototypes. The use of 3D printers has been increasing, their performance has been improving, and their price has been reducing. While the general trend is clear, particular applications need to be assessed for their practicality. This study develops and follows a systematic approach to the prototyping of Advanced Oxidation Processes (AOP) reactors. Specifically, this work evaluates and discusses different printable materials in terms of mechanical and chemical resistance to photo-Fenton reactants. Metallic and ceramic materials are shown to be impracticable due to their high printing cost. Polymeric and composite materials are sieved according to criteria such as biodegradability, chemical, thermal, and mechanical resistance. Finally, 3D-printed prototypes are produced and tested in terms of leakage and resistance to the photo-Fenton reacting environment. Polylactic acid (PLA) and wood-PLA composite (Timberfill^®) were selected, and lab-scale raceway pond reactors (RPR) were printed accordingly. They were next exposed to H2O2/Fe(II) solutions at pH = 3 ± 0.2 and UV radiation. After 48 h reaction tests, results revealed that the Timberfill^® reactor produced higher Total Organic Carbon (TOC) concentrations (9.6 mg·L^-1) than that obtained for the PLA reactor (5.5 mg·L^-1) and Pyrex^® reactor (5.2 mg·L^-1), which suggests the interference of Timberfill^® with the reaction. The work also considers and discusses further chemical and mechanical criteria that also favor PLA for 3D-printing Fenton and photo-Fenton reactors. Finally, the work also provides a detailed explanation of the printing parameters used and guidelines for preparing prototypes.

Comparative evaluation of metoprolol degradation by UV/chlorine and UV/H2O2 processes

The degradation of metoprolol (MTP), a β-blocker commonly used for cardiovascular diseases, by UV/chlorine and UV/H₂O₂ processes was comparatively evaluated. MTP direct photolysis at 254 nm could be neglected, but remarkable MTP degradation was observed in both the UV/chlorine and UV/H₂O₂ systems. Compared with UV/H₂O₂, UV/chlorine has a more pronounced MTP degradation efficiency. In addition to primary radicals (OH and Cl), secondary radicals (ClO and Cl₂^-) played a pivotal role in degrading MTP by UV/chlorine process. The relative contributions of hydroxyl radicals (OH) and reactive chlorine species (RCS) in the UV/chlorine system varied at different solution pH values (i.e., the contribution of RCS increased from 57.7% to 75.1% as the pH increased from 6 to 8). The degradation rate rose as the oxidant dosage increased in the UV/chlorine and UV/H₂O₂ processes. The presence of Cl^- slightly affected MTP degradation in both processes, while the existence of HCO₃^- and HA inhibited MTP degradation to different extents in both processes. In terms of the overall cost of electrical energy, UV/chlorine is more cost efficient than UV/H₂O₂. The degradation products during the two processes were identified and compared, and the degradation pathways were proposed accordingly. Compared with the direct chlorination of MTP, pre-oxidation with UV/chlorine and UV/H₂O₂ significantly enhanced the formation of commonly known DBPs. Therefore, when using UV/chlorine and UV/H₂O₂ in real waters to remove organic pollutants, the possible risk of enhanced DBP formation resulting from the degradation of certain pollutants during post-chlorination should be carefully considered.

Biogas and phosphorus recovery from waste activated sludge with protocatechuic acid enhanced Fenton pretreatment, anaerobic digestion and microbial electrolysis cell

Biogas and phosphorus recovery from waste activated sludge (WAS) with sequential homogeneous protocatechuic acid (PCA) enhanced Fenton pretreatment, anaerobic digestion (AD) and microbial electrolysis cell (MEC) were investigated. The cumulation of biogas production of WAS-Fenton-AD was 330.4 mL/g VS, which was 2.05-fold of the control without pretreatment (WAS-AD) during anaerobic digestion. Biogas production of 178 mL/L/d from WAS-Fenton-AD-MEC was achieved, which was 5.23-fold of the WAS-MEC, 2.28-fold of WAS-Fenton-MEC and 1.46-fold of WAS-AD-MEC, respectively. Enhanced phosphorus recovery in form of struvite reached 1.72 g/g TS (18.03% of total P) with a purity of 74.4%. Microbial community richness and diversity analysis revealed that the pretreatment process under circumneutral condition improved the diversity of microbial community, which was consisted of Bacteroidetes (33.90%), Proteobacteria (33.14%), and Chloroflexi (10.14%), compared to a majority of Firmicutes (70.81%) in WAS-AD. This study provides a feasible strategy for the recovery of biogas combined with phosphorus from WAS.

Photo-Fenton process at natural conditions of pH, iron, ions, and humic acids for degradation of diuron and amoxicillin

Effect of ferric ions at concentrations typically found in natural waters (0.05 to 1.06 mg L^-1) and low H₂O₂ concentrations (between 0.5 and 17.9 mg L^-1) on simulated sunlight-induced (300 W m^-2) photo-Fenton degradation at initial neutral pH (7.0) of amoxicillin and diuron in Milli-Q water was studied using an rotatable central composite experimental design 2² with a central and two axial points. H₂O₂ concentration was the parameter playing the key role on the degradation of both pollutants. Despite that initial pH was 7.0 in Milli-Q water, this latter decreased rapidly in the first minutes, reaching values of 3.5 and 5.0 for diuron and amoxicillin respectively after 15 min of simulated sunlight irradiation. In contrast, in presence of bicarbonate/carbonate (HCO₃^-/CO₃⁼), fluoride (F^-), and humic acids (HAs) at concentrations found often in surface and well waters with ferric ion and H₂O₂ concentrations of 0.3 and 9.7 and 15.2 mg L^-1 respectively, both pollutants exhibited a strong degradation keeping the circumneutral pH. Amoxicillin and diuron degradation byproducts found by HPLC/MS were compatible with HO^• and/or CO₃^-• radical attack. Several photo-induced processes such as photo-Fenton (by dissolved ferric-HA complexes), heterogeneous photocatalysis (by colloidal iron), UV-B H₂O₂ photolysis, irradiated-dissolved organic matter, and their reactions with pollutants would be the main oxidative route responsible of degradations. These findings demonstrated that it could be possible using iron concentrations often found in natural waters to oxidize via photo-Fenton processes among other events, organic pollutants at natural pH conditions.

Enhancement of iron-mediated activation of persulfate using catechin: From generation of reactive species to atenolol degradation in water

Persulfate (PS) activation reaction, which forms sulfate radical (SO₄^-), can be used to degrade organic pollutants in water. However, a drawback of this reaction is that the regeneration of ferrous ions requires a high concentration of hydrogen peroxide (Fenton-like reaction) or use of UV radiation. Catechin (CAT), a non-toxic antioxidant of natural origin from tea, is used in this work to improve the sulfate radical-mediated degradation of atenolol (ATL, a model pollutant) in water using relatively low concentrations of reactive chemical species (less than 100 μM). To the best of the author's knowledge, the direct effect of CAT on the oxidation state of iron, which is promoted by the reduction of ferric into ferrous ions with the enhancement of SO₄^- formation in the presence of PS, is demonstrated for the first time. The enhancement versus inhibition effect of CAT and the chemical mechanism of the iron-based activation process are explained. Results show that UVA radiation, which is representative of solar light, accelerates the initial degradation of ATL by more than 30% through ferric iron photolysis. Finally, a reaction mechanism leading to the formation of hydroxyl radicals (HO) and SO₄^- is proposed considering the implication of different activation/reaction chemical steps.

Metoprolol and metoprolol acid degradation in UV/H2O2 treated wastewaters: An integrated screening approach for the identification of hazardous transformation products

Advancements on analytical strategies to determine the chemicals present in treated wastewater are necessary to clearly link their occurrence with the ecotoxicity of such effluents. This study describes the development of an integrated screening approach to determine the highest number of pharmaceutical transformation products (TPs) in a single run. The identification of TPs was based on the comparison of detected features with literature sources, compound prediction tools, in-house libraries and reference standards using high-resolution mass spectrometry (HRMS). This integrated approach allowed a better estimation (in silico) of the ecotoxicological contribution of the individual TPs identified. As a proof of concept, this methodology was applied for identification of the TPs generated from metoprolol and its main human metabolite (metoprolol acid) in pure water, hospital wastewater and industrial wastewater treated by UV/H₂O₂. Twenty-four TPs with potential ecotoxicological implications were identified and their presence was pinpointed as a function of the treated wastewater. An integrated screening approach has been developed using four different screening methodologies in the same run. Additionally, the metabolite MTPA has been considered as a target pollutant in UV/H₂O₂ experiments.

Complete degradation of ciprofloxacin over g-C3N4-iron oxide composite via heterogeneous dark Fenton reaction

Graphitic carbon nitride (g-C₃N₄) supported iron oxide (CN@IO) composite was first fabricated via synthesizing g-C₃N₄ in-situ onto iron oxide. The fabricated CN@IO composite was characterized by several techniques including XRD, XPS, TEM and nitrogen adsorption-desorption analysis. This composite was then used as a catalyst for the dark Fenton oxidative degradation of ciprofloxacin (CIP). Results demonstrated that the incorporation of g-C₃N₄ profoundly changed the structure and chemical properties of iron oxide, endowing CN@IO composites with high-efficient catalytic activity in dark Fenton system. In the synthesis process of CN@IO composites, iron oxide nanoparticles were successfully intercalated into the layers of g-C₃N₄, enlarging the surface area and thus providing more active sites for the reactions. Meanwhile, the existence of g-C₃N₄ can accelerate the Fe³⁺/Fe²⁺ redox cycle during the Fenton reaction, which further facilitated CIP degradation. In addition, the effects of reaction parameters, including pH, catalyst dosage, initial concentration of CIP and H₂O₂, on CIP degradation were investigated. Without any assistance of light irradiation, complete degradation and 48.5% mineralization of CIP were achieved under the best conditions of pH 3.0, 1 g/L CN@IO-2, 20 mg/L CIP and 0.0056 M H₂O₂. The trapping of iron oxide between g-C₃N₄ layers helped to stabilize iron oxide so the metal leaching problem that usually occurred in acidic media (pH = 3) can be effectively overcome. This work provides a new thought to develop environmental-friendly and high-efficient catalysts for the degradation of refractory pollutants in dark Fenton system, which is much easier to scale up for industrial application comparing with the photo-Fenton reaction.

Fungal treatment of metoprolol and its recalcitrant metabolite metoprolol acid in hospital wastewater: Biotransformation, sorption and ecotoxicological impact

Hospital wastewater (HWW) effluents represent an important source of contaminants such as pharmaceutical compounds and their human metabolites. To better evaluate dedicated treatment of hospital effluents for pollutant mitigation, not only the parent compounds should be considered but also the intermediates generated during treatment. The metabolite metoprolol acid (MTPA) has been found in urban wastewaters at higher concentration than its parent compound metoprolol (MTP), being more recalcitrant to biodegradation. The aim of this study was to investigate degradation, transformation and sorption of the β-blocker MTP, and its recalcitrant metabolite MTPA, during water treatment based on the fungi Ganoderma lucidum, Trametes versicolor and Pleurotus ostreatus. Fourteen intermediates were identified in MTP biotransformation while five of them also attributed to MTPA biodegradation and two to MTPA only. Their identification allowed their correlation in separate biotransformation pathways suggested. The highest degradation rate of metoprolol (up to 51%) and metoprolol acid (almost 77%) was found after 15-days treatment with Ganoderma lucidum, with an increase in toxicity up to 29% and 4%, respectively. This fungus was further selected for treating real HWW in a batch fluidized bed bioreactor (FBB). Treated wastewater and fungal biomass samples were used to evaluate the distribution of the target compounds and the intermediates identified between solid and liquid phases. While similar elimination capabilities were observed for the removal of metoprolol, and even higher for its persistent metabolite metoprolol acid, the extent on compound transformation diminished considerably compared with the study treating purified water: a high level of the persistent α-HMTP and TP240 were still present in effluent samples (15% and 6%, respectively), being both TPs present at high proportion (up to 28%) in fungal biomass. This is the first time that pharmaceutical TPs have been investigated in the fungal biomass.

Environmental assessment of solar photo-Fenton processes in combination with nanofiltration for the removal of micro-contaminants from real wastewaters

Scarcity of water and concerns about the ecotoxicity of micro-contaminants are driving an interest in the use of advanced tertiary processes in wastewater treatment plants. However, the life cycle environmental implications of these treatments remain uncertain. To address this knowledge gap, this study evaluates through life cycle assessment the following four advanced process options for removal of micro-contaminants from real effluents: i) solar photo-Fenton (SPF) operating at acidic pH; ii) acidic SPF coupled with nanofiltration (NF); iii) SPF operating at neutral pH; and iv) neutral SPF coupled with NF. The results show that acidic SPF coupled with NF is the best option for all 15 impacts considered. For example, its climate change potential is almost three times lower than that of the neutral SPF process (311 vs 928 kg CO₂ eq./1000 m³ of treated effluent). The latter is the worst option for 12 impact categories. For the remaining three impacts (acidification, depletion of metals and particulate matter formation), acidic SPF without NF is least sustainable; it is also the second worst option for seven other impacts. Neutral SPF with NF is the second worst technology for climate change, ozone and fossil fuel depletion as well as marine eutrophication. In summary, both types of SPF perform better environmentally with than without NF and the acidic SPF treatment is more sustainable than the neutral version. Thus, the results of this work suggest that ongoing efforts on developing neutral SPF should instead be focused on further improvements of its acidic equivalent coupled with NF. These results can also be used to inform future development of policy related to the removal of micro-contaminants from wastewater.

Identification of intermediates, acute toxicity removal, and kinetics investigation to the Ametryn treatment by direct photolysis (UV254), UV254/H2O2, Fenton, and photo-Fenton processes

This paper reports the degradation of 10 mg L^-1 Ametryn solution with different advanced oxidation processes and by ultraviolet (UV₂₅₄) irradiation alone with the main objective of reducing acute toxicity and increase biodegradability. The investigated factors included Fe²⁺ and H₂O₂ concentrations. The effectiveness of the UV₂₅₄ and UV₂₅₄/H₂O₂ processes were investigated using a low-pressure mercury UV lamp (254 nm). Photo-Fenton process was explored using a blacklight blue lamp (BLB, λ = 365 nm). The UV₂₅₄ irradiation process achieved complete degradation of Ametryn solution after 60 min. The degradation time of Ametryn was greatly improved by the addition of H₂O₂. It is worth pointing out that a high rate of Ametryn removal was attained even at low concentrations of H₂O₂. The kinetic constant of the reaction between Ametryn and HO^● for UV₂₅₄/H₂O₂ was 3.53 × 10⁸ L mol^-1 s^-1. The complete Ametryn degradation by the Fenton and photo-Fenton processes was observed following 10 min of reaction for various combinations of Fe²⁺ and H₂O₂ under investigation. Working with the highest concentration (150 mg L^-1 H₂O₂ and 10 mg L^-1 Fe²⁺), around 30 and 70% of TOC removal were reached within 120 min of treatment by Fenton and photo-Fenton processes, respectively. Although it did not obtain complete mineralization, the intermediates formed in the degradation processes were hydroxylated and did not promote acute toxicity of Vibrio fischeri. Furthermore, a substantial improvement of biodegradability was obtained for all studied processes.

Kinetics and efficiency of ozone for treatment of landfill leachate including the effect of previous microbiological treatment

The application of conventional physicochemical and microbiological techniques for the removal of organic pollutants has limitations for its utilization on wastewaters as landfill leachates because of their high concentration of not easily biodegradable organic compounds. The use of ozone-based technologies is an alternative and complementary treatment for this type of wastewaters. This paper reports the study of the degradation of landfill leachates from different stages of a treatment plant using ozone and ozone + UV. The experimental work included the determination of the temporal evolution of COD, TOC, UV254, and color. Along the experimental runs, the instantaneous off-gas ozone concentration was measured. The reaction kinetics follows a global second order expression with respect to COD and ozone concentrations. A kinetic model which takes into account the gas liquid mass transfer coupled with the chemical reaction was developed, and the corresponding parameters of the reacting system were determined. The mathematical model is able to appropriately simulate COD and ozone concentrations but exhibiting limitations when varying the leachate type. The potential application of ozone was verified, although the estimated efficiencies for COD removal and ozone consumption as well as the effect of UV radiation show variations on their trends. In this sense, it is interesting to note that the relative ozone yield has significant oscillations as the reaction proceeds. Finally, the set of experimental results demonstrates the crucial importance of the selection of process conditions to improve ozone efficiencies. This approach should consider variations in the ozone supply in order to minimize losses as well as the design of exhaustion methods as multiple stage reactors using chemical engineering design tools.

Redox mediators and irradiation improve fenton degradation of acesulfame

Widely recognized as a promising approach to degrading recalcitrant pollutants, Advanced Oxidation Processes (AOPs) have drawn much attention for their effectiveness and efficiency. Among all the AOPs, the Fenton system has been widely applied for oxidation and mineralization of micropollutants due to its ease of implementation and high catalytic efficiency. However, the necessity of preceding acidification, together with rapid consumption and slow regeneration of Fe(II) resulting in deterioration of reactivity, has reduced its competitiveness as a practical option for water treatment. Acknowledging the above drawbacks, this study investigates the potential viable option to enhance the Fenton system. Acesulfame was chosen as the model compound due to its ubiquitous occurrence and persistence in the environment. UV-assisted photo-Fenton treatment was found to remove the parent compound effectively; the transformation profile of acesulfame was identified and elucidated with the ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry. Prolonged UV photo-Fenton treatment was effective for mineralization of the majority of the transformation products, without increasing the overall toxicity as indicated by Vibrio fischeri bioluminescence assay. The positive effects of the addition of redox mediators to Fenton systems at neutral pH were confirmed in this study. The results could be the basis for further development of homogeneous catalytic degradation techniques for the oxidation of environmental contaminants at circumneutral pHs to neutral pHs.

Highly efficient treatment of real benzene dye intermediate wastewater by simple limestone and lime neutralization-coagulation with improved Fenton oxidation

Multistage Fenton oxidation is a favored method for the treatment of benzene dye intermediate (BDI) wastewater, but the pH adjustments required after each stage of the Fenton process with a simple way is still a challenge. Limestone pretreatment and lime neutralization-coagulation were used to solve the problem in multistage Fenton process. First, we determined the optimal conditions of Fenton oxidation using the Box-Behnken response surface method. Limestone pretreatment before the multistage Fenton process allowed for simultaneous pH adjustment and 14.15% COD removal. Most notably, the lime cream neutralization-coagulation process effectively adjusted the pH after each stage of the Fenton process. The optimum CaO particle size, lime mass fraction, mixing time, and stirring speed were determined by orthogonal tests. COD removal (89.23%) was obtained when lime cream neutralization-coagulation was applied to the three-staged Fenton process, while only 58.57% COD removal was obtained by the unadjusted single-staged Fenton process. The COD and wastewater color were reduced from 10,600 mg/L and 12,200 multiples to 495 mg/L and 20 multiples, respectively, using the adjusted process. This improved method provides a promising cost-effective way to efficiently treat real BDI wastewater.

Utilizing recycled LiFePO4 from batteries in combination with B@C3N4 and CuFe2O4 as sustainable nano-junctions for high performance degradation of atenolol

In this report recycled LiFePO₄ (LFP) from exhaust batteries was utilized to form B@C₃N₄/LiFePO₄/CuFe₂O₄ (BLC) nano-junction as a visible active photocatalyst. The junction synthesized by two routes: Using as extracted LFP and forming LFP by extracted FePO₄ and Li₂CO₃ via in-situ deposition method. The two ternary junctions BLC and BLC (E) (utilizing as extracted LFP) were utilized for visible and solar powered degradation of beta-blocker drug Atenolol (ATL). Varying the loading of CuFe₂O₄ (CF) which possesses lowest band gap, BLC (10%), BLC-3 (30%), BLC-5 (50%) and BLC-E (30% CF and as extracted LFP) were produced with BLC-3 exhibiting remarkable activity. The optical band gaps of BLC-3 (2.40 eV) and BLC (E) (2.46 eV) and photocurrent responses reveal high visible absorption and highly diminished recombination. 99.5% and 85.3% of ATL (20 mg L^-1) could be degraded by BLC-3 and BLC (E) (0.3 g L^-1) respectively in 60 min of exposure to Xe lamp and retaining of high activity in natural sunlight. Band-junction analysis, effect of scavengers and effect on teraphthalic acid and nitroblue tetrazolium reveal O₂^- and OH radicals as active species and mineralization was confirmed by liquid chromatography-mass spectrometer (LC-MS). Cyto-toxicity studies on human peripheral blood cells and effect on growth of Pseudomonas aeruginosa confirm the complete mineralization. The BLC photocatalyst is a promising multi-functional catalyst utilizing LFP (rarely used as photocatalyst) for treatment of pharmaceutical waste water and other environmental applications.

Disilicate-Assisted Iron Electrolysis for Sequential Fenton-Oxidation and Coagulation of Aqueous Contaminants

Sodium disilicate (SD), an inorganic and environmentally friendly ligand, is introduced into the conventional iron electrolysis system to achieve an oxidizing Fenton process to degrade organic pollutants. Electrolytic ferrous ions, which are complexed by the disilicate ions, can chemically reduce dioxygen molecules via consecutive reduction steps, producing H₂O₂ for the Fenton-oxidation of organics. At the near-neutral pH (from 6 to 8), the disilicate-Fe(II) complexes possess strong reducing capabilities; therefore, a near-neutral pH rather than an acid condition is preferable for the disilicate-assisted iron electrolysis (DAIE) process. Following the DAIE process, the different complexing capacities of disilicate for ferrous/ferric ions and calcium ions can be used to break the disilicate-iron complexes. The addition of CaO or CaCl₂ can precipitate ferrous/ferric ions, disilicates and possibly heavy metals in the wastewater. Compared to previously reported organic and phosphorus ligands, SD is a low-cost inorganic agent that does not lead to secondary pollution, and would not compete with the target organic pollutants for •OH; therefore, it would greatly expand the application fields of the O₂ activation process. The combination of DAIE and CaO treatments is envisioned to be a versatile and affordable method for treating wastewater with complicated pollutants (e.g., mixtures of biorefractory organics and heavy metals).

Removal of pharmaceuticals from water by homo/heterogonous Fenton-type processes - A review

The presence of emerging contaminants such as pharmaceuticals in natural waters has raised increasing concern due to their frequent appearance and persistence in the aquatic ecosystem and the threat to health and safety of aquatic life, even at trace concentrations. Conventional water treatment processes are known to be generally inadequate for the elimination of these persistent contaminants. Therefore, the use of advanced oxidation processes (AOPs) which are able to efficiently oxidize organic pollutants has attracted a great amount of attention. The main limitation of AOPs lies in their high operating costs associated with the consumption of energy and chemicals. Fenton-based processes, which utilize nontoxic and common reagents and potentially can exploit solar energy, will considerably reduce the removal cost of recalcitrant contaminants. The disadvantages of homogeneous Fenton processes, such as the generation of high amounts of iron-containing sludge and limited operational range of pH, have prompted much attention to the use of heterogeneous Fenton processes. In this review, the impacts of some controlling parameters including the H₂O₂ and catalyst dosage, solution pH, initial contaminants concentrations, temperature, type of catalyst, intensity of irradiation, reaction time and feeding mode on the removal efficiencies of hetero/homogeneous Fenton processes are discussed. In addition, the combination of Fenton-type processes with biological systems as the pre/post treatment stages in pilot-scale operations is considered. The reported experimental results obtained by using Fenton and photo-Fenton processes for the elimination of pharmaceutical contaminants are also compiled and evaluated.

Introducing saccharic acid as an efficient iron chelate to enhance photo-Fenton degradation of organic contaminants

The identification of iron chelates that can enhance photo-Fenton degradation is of great interest in the field of advanced oxidation process. Saccharic acid (SA) is a polyhydroxy carboxylic acid and completely non-toxic. Importantly, it can effectively bind Fe(III) as well as induce photoreduction of Fe(III). Despite having these interesting properties, the effect of SA on photo-Fenton degradation has not been studied. Herein, we demonstrate the first assessment of SA as an iron chelate in photo-Fenton process using methylene blue (MB) as a model organic contaminant. Our results demonstrate that SA has the ability to (i) enhance the photo-Fenton degradation of MB by about 11 times at pH 4.5 (ii) intensify photochemical reduction of Fe(III) to Fe(II) by about 17 times and (iii) accelerate the rate of consumption of H₂O₂ in photo-Fenton process by about 5 times (iv) increase the TOC reduction by about 2 times and (v) improve the photo-Fenton degradation of MB in the presence of a variety of common inorganic ions and organic matter. The influential properties of SA on photo-Fenton degradation is attributed to the efficient photochemical reduction of Fe(III) via LMCT (ligand to metal charge transfer reaction) to Fe(II), which then activated H₂O₂ to generate OH and accelerated photo-Fenton degradation efficiency. Moreover, the effect of operational parameters such as oxidant: contaminant (H₂O₂: MB) ratio, catalyst: contaminant (Fe(III)SA: MB) ratio, Fe(III): SA stoichiometry and pH on the degradation of MB by photo-Fenton in the presence of SA is demonstrated. Importantly, SA assisted photo-Fenton caused effective degradation of MB and 4-Chlorophenol under natural sunlight irradiation in natural water matrix. The findings strongly support SA as a deserving iron chelate to enhance photo-Fenton degradation.

Phenol degradation by Fenton-like process

The main objective of this study was to investigate the optimum conditions for the Fenton-like process on phenol degradation, using Mn(2+) as a supporting catalyst in the Fenton reaction. The effect of the independent factors [H2O2], [Fe(2+)], [Mn(2+)] and t (reaction time) was evaluated on the efficiency of phenol degradation at two pHs (3 and 5). The experimental arrangement adopted was the Box-Behnken delineation, with the phenol concentration after the treatments suggested as response variable. At less acidic pH (5), regardless of [Mn(2+)], it was observed that the conventional Fenton process was the most efficient alternative, considering the optimum condition: 2.65 mmol L(-1) for [H2O2], 0.36 mmol L(-1) for [Fe(2+)], and 90 min for t. It was observed that the addition of Mn(2+) helped the phenol degradation at more acidic pH (3), obtaining the optimum condition: 6.17 mmol L(-1) for [H2O2], 0.36 mmol L(-1) for [Fe(2+)], 1.09 mmol L(-1) for [Mn(2+)], and 90 min for t.

Enhancing enzymolysis and fermentation efficiency of sugarcane bagasse by synergistic pretreatment of Fenton reaction and sodium hydroxide extraction

A study on the synergistic pretreatment of sugarcane bagasse (SCB) using Fenton reaction and NaOH extraction was conducted. The optimized process conditions for Fenton pretreatment were 10% (w/w) of H2O2, 20mM of Fe(2+), pH 2.5, pretreatment time 6h, and pretreatment temperature 55°C. Sequential pretreatments were performed in combination with NaOH extraction (NaOH 1% (w/w), 80°C, 5% of solid loading, 1h). Among all the pretreatments, Fenton pretreatment followed by NaOH extraction had the highest efficiency of 64.7% and 108.3% for enzymolysis and simultaneous saccharification fermentation (SSF) with an ethanol concentration of 17.44g/L. The analyses by the scanning electron microscopy, X-ray diffraction and confocal laser scanning microscopy revealed that Fenton pretreatment disrupts the structure of SCB to facilitate the degradation of lignin by NaOH. The overall data suggest that this combinatorial strategy is a promising process for SCB pretreatment.