Feasibility of using nanoscale zero-valent iron and persulfate to degrade sulfamethazine in aqueous solutions

Shaddock peels biochar doping with Fe-Co bimetal for peroxymonosulfate activation on the degradation of tetracycline: The influence of HCO3- and PO43

To reduce the negative impact of antibiotics on the water environment, shaddock peels biochar co-doped with iron and cobalt (Fe-Co@SPC) was employed in the peroxymonosulfate (PMS) system to eliminate tetracycline (TC). The obtained Fe-Co@SPC could efficiently activate PMS and degrade 95.6 % of TC within 1 h at pH 9.06. Notably, the presence of HCO3- promoted PMS activation, which was mainly because the weakly alkaline system inhibited metal ion leaching. PO43- invaded the surface active sites on the Fe-Co@SPC and formed O-P/C-PO3, which inhibited PMS activation. The scavenging and EPR analysis results demonstrated SO4•-, •OH, 1O2 and O2•- were the major ROS. Besides, the C=O functional group and Fe-Co bimetal on Fe-Co@SPC accelerated the electronic transfer. Three reaction pathways were proposed in the Fe-Co@SPC/PMS system and the potential ecotoxicity of the intermediates was significantly declined. Based on the reusability and stability, Fe-Co@SPC could efficiently activate PMS to degrade organic pollutants in water bodies.

Removal of sulfonamides by persulfate-based advanced oxidation: A mini review

Sulfonamides (SAs) are known for their persistence and have become one of the most frequently detected pharmaceuticals and personal care products (PPCPs) in the environments. The widespread presence of SAs in natural waters, wastewater, soil, and sediment has prompted growing concern due to their potential threats to both human health and ecological systems. Persulfate-based advanced oxidation processes (PS-AOPs) have emerged as a promising technology for effectively mitigating the presence of these pollutants in the environment. This review offers a comprehensive overview of the degradation of SAs by PS-AOPs. The various activation methods of persulfate for the purpose of removing SAs are elaborated upon in detail. The factors influencing the removal efficiency of SAs through PS-AOPs is thoroughly discussed. Additionally, the conceivable mechanisms and degradation pathways associated with various types of SAs are discussed. Lastly, existing challenges are identified, and future prospects pertaining to the utilization of PS-AOPs for efficient SA removal are presented.

Enhancement of hydrogenotrophic methanogenesis for methane production by nano zero-valent iron in soils

Nanoscale zero-valent iron (nZVI) is attracting increasing attention as the most commonly used environmental remediation material. However, given the high surface area and strong reducing capabilities of nZVI, there is a lack of understanding regarding its effects on the complex anaerobic methane production process in flooded soils. To elucidate the mechanism of CH4 production in soil exposed to nZVI, paddy soil was collected and subjected to anaerobic culture under continuous flooding conditions, with various dosages of nZVI applied. The results showed that the introduction of nZVI into anaerobic flooded rice paddy systems promoted microbial utilization of acetate and carbon dioxide as carbon sources for methane production, ultimately leading to increased methane production. Following the introduction of nZVI into the soil, there was a rapid increase in hydrogen levels in the headspace, surpassing that of the control group. The hydrogen levels in both the experimental and control groups were depleted by the 29th day of culture. These findings suggest that nZVI exposure facilitates the enrichment of hydrogenotrophic methanogens, providing them with a favorable environment for growth. Additionally, it affected soil physicochemical properties by increasing pH and electrical conductivity. The metagenomic analysis further indicates that under exposure to nZVI, hydrogenotrophic methanogens, particularly Methanobacteriaceae and Methanocellaceae, were enriched. The relative abundance of genes such as mcrA and mcrB associated with methane production was increased. This study provides important theoretical insights into the response of key microbes, functional genes, and methane production pathways to nZVI during anaerobic methane production in rice paddy soils, offering fundamental insights into the long-term fate and risks associated with the introduction of nZVI into soils.

Affecting factors and mechanism of removing antibiotics and antibiotic resistance genes by nano zero-valent iron (nZVI) and modified nZVI: A critical review

Antibiotics and antibiotic resistance genetic pollution have become a global environmental and health concern recently, with frequent detection in various environmental media. Therefore, finding ways to control antibiotics and antibiotic resistance genes (ARGs) is urgently needed. Nano zero-valent iron (nZVI) has shown a positive effect on antibiotics degradation and restraining ARGs, making it a promising solution for controlling antibiotics and ARGs. However, given the current increasingly fragmented research focus and results, a comprehensive review is still lacking. In this work, we first introduce the origin and transmission of antibiotics and ARGs in various environmental media, and then discuss the affecting factors during the degradation of antibiotics and the control of ARGs by nZVI and modified nZVI, including pH, nZVI dose, and oxidant concentration, etc. Then, the mechanisms of antibiotic and ARGs removal promoted by nZVI are also summarized. In general, the mechanism of antibiotic degradation by nZVI mainly includes adsorption and reduction, while promoting the biodegradation of antibiotics by affecting the microbial community. nZVI can also be combined with persulfates to degrade antibiotics through advanced oxidation processes. For the control of ARGs, nZVI not only changes the microbial community structure, but also affects the proliferation of ARGs through affecting the fate of mobile genetic elements (MGEs). Finally, some new ideas on the application of nZVI in the treatment of antibiotic resistance are proposed. This paper provides a reference for research and application in this field.

Role of direct current on thermal activated peroxydisulfate to degrade phenanthrene in soil: Conversion of sulfate radical and hydroxyl radical to singlet oxygen, accelerated degradation rate and reduced efficiency

Electrokinetic (EK) delivery followed by thermal activated peroxydisulfate (PS) has turned out to be a potential in situ chemical oxidation technology for soil remediation, but the activation behavior of PS in an electrical coupled thermal environment and the effect of direct current (DC) intervention on PS in heating soil has not been explored. In this paper, a DC coupled thermal activated PS (DC-heat/PS) system was constructed to degrade Phenanthrene (Phe) in soil. The results indicated that DC could force PS to migrate in soil, changing the degradation rate-limiting step in heat/PS system from PS diffusion to PS decomposition, which greatly accelerated the degradation rate. In DC/PS system, ¹O₂ was the only reactive species directly detected at platinum (Pt)-anode, confirming that S₂O₈^2- could not directly obtain electrons at the Pt-cathode to decompose into SO₄^•-. By comparing DC/PS and DC-heat/PS system, it was found that DC could significantly promote the conversion of SO₄^•- and •OH generated by thermal activation of PS to ¹O₂, which was attributed to the hydrogen evolution caused by DC that destroys the reaction balance in system. It was also the fundamental reason that DC leaded to the reduction of oxidation capacity of DC-heat/PS system. Finally, the possible degradation pathways of phenanthrene were proposed on the basis of seven detected intermediates.

Degradation of rifamycin from mycelial dreg by activated persulfate: Degradation efficiency and reaction kinetics

Rifamycin mycelial dreg (RMD) is a biological waste, and its residual rifamycin (RIF) is potentially harmful to both the environment and human health. In this work, thermally activated persulfate (PDS) oxidative degradation of RIF in RMD was developed for the first time. The effects of reaction temperature, initial PDS concentration, and pH on RIF degradation in RMD were investigated, and the treatment conditions were optimized using response surface methodology (RSM). The results showed that 90 °C, 50 mg/g PDS, and pH = 5.3 were the optimal pretreatment conditions, and 100% degradation efficiency of RIF (734 mg/kg) was achieved. SEM and FTIR analyses confirmed that the RIF was destroyed and decomposed after the oxidation reaction. The possible degradation pathways of RIF in the thermally activated PDS system were discussed through HPLC/MS and ESR analyses. The intermediate product was identified, and the toxicity of the final product was predicted to be low or nontoxic. In this work, a degradation pathway of RMD was proposed by activating persulfate, which facilitates subsequent resource utilization and provides meaningful guidance for the practical treatment of antibiotic mycelium residue (AMR).

Electrochemical-assisted ultraviolet light coupled peroxodisulfate system to degrade ciprofloxacin in water: Kinetics, mechanism and pathways

The persulfate advanced oxidation is an emerging and efficient pollutant treatment method, but usually requires the help of other materials or energy to catalyze and produce highly oxidizing active substances. In this paper, electrochemical-assisted ultraviolet light coupled peroxodisulfate system (E-UV-PDS) was used to degrade ciprofloxacin (CIP), and it was determined that electrolysis and ultraviolet photolysis were synergistic by calculation. The effects of initial pH, voltage, peroxodisulfate dosage, CIP concentration and coexisting anions on the degradation process were explored. The quenching experiments showed that ¹O₂, ⋅OH and SO₄^-⋅ were the main active oxygen species. Under the following conditions, ultraviolet light = 6 W, voltage = 4 V, [peroxodisulfate] = 20 mM, [pH]₀ = 7 and [CIP] = 100 mgL^-1, the degradation rate of CIP reached about 100% after 120 min, and the influence of inorganic anions was also discussed. Several intermediate products were identified by LC-MS, and three degradation pathways were speculated for CIP degradation. Finally, economic evaluation of the E-UV-PDS system was made, and it was useful to construct environmentally friendly and low-cost catalytic processes for the efficient degradation of organic pollutants.

Preparation, characterization, and applications of Fe-based catalysts in advanced oxidation processes for organics removal: A review

Fe-based catalysts as low-cost, high-efficiency, and non-toxic materials display superior catalytic performances in activating hydrogen peroxide, persulfate (PS), peracetic acid (PAA), percarbonate (PC), and ozone to degrade organic contaminants in aqueous solutions. They mainly include ferrous salts, zero-valent iron, iron-metal composites, iron sulfides, iron oxyhydroxides, iron oxides, and supported iron-based catalysts, which have been widely applied in advanced oxidation processes (AOPs). However, there is lack of a comprehensive review systematically reporting their synthesis, characterization, and applications. It is imperative to evaluate the catalytic performances of various Fe-based catalysts in diverse AOPs systems and reveal the activation mechanisms of different oxidants by Fe-based catalysts. This work detailedly summarizes the synthesis methods and characterization technologies of Fe-based catalysts. This paper critically evaluates the catalytic performances of Fe-based catalysts in diverse AOPs systems. The effects of solution pH, reaction temperature, coexisting ions, oxidant concentration, catalyst dosage, and external energy on the degradation of organic contaminants in the Fe-based catalyst/oxidant systems and the stability of Fe-based catalysts are also discussed. The activation mechanisms of various oxidants and the degradation pathways of organic contaminants in the Fe-based catalyst/oxidant systems are revealed by a series of novel detection methods and characterization technologies. Future research prospects on the potential preparation means of Fe-based catalysts, practical applications, assistive technologies, and impact in AOPs are proposed.

Synthetic Fe-rich nontronite as a novel activator of bisulfite for the efficient removal of tetracycline

In this work, the iron-containing smectite nontronite (NNT) was artificially prepared by hydrothermal process and used as a heterogeneous catalyst to activate bisulfite (BS) for degradation of tetracycline (TC). Two NNT samples with different iron content (NNT1 and NNT2) were characterized by XRD, FTIR, XPS and SEM-EDS analysis. Under dark condition, the TC removal rates of NNT1/BS and NNT2/BS reached about 91.7% and 95.5% respectively at 60 min. Due to the heterogeneous catalysis of structural Fe(III), the NNT catalysts showed great catalytic activity and low iron leaching at the pH range 3.0-7.5. In addition, NNT particles were also stable and reusable in activating BS for TC removal. According to the EPR and radical quenching experiments, it could be proved that the precursor radical ^•SO₃- was first generated in NNT/BS system, then ^•SO₄- and ^•OH were the active species that played a role in TC degradation. The synthetic NNT clay is a promising Fe-based catalyst for treatment of TC wastewater thanks to its high activity, good stability and effective reusability.

Encapsulation of iron nanoparticles with magnesium hydroxide shell for remarkable removal of ciprofloxacin from contaminated water

The rapid evolution of antimicrobial resistant genes (AMRs) in water resources is well correlated to the persistent occurrence of ciprofloxacin in water. For the first time, encapsulated nanoscale zerovalent iron (nZVI) with a shell of magnesium hydroxide (Mg/Fe⁰) was used to adsorb ciprofloxacin from water. Optimization of the removal conditions exhibited that 5% was the optimum mass ratio between magnesium hydroxide and nZVI [Mg(OH)₂/nZVI)] as more than 96% of 100 mg L^-1 of ciprofloxacin was removed. In addition, 0.5 g L^-1 of Mg/Fe⁰ showed an extraordinary performance in removing ciprofloxacin over a wide range of pH (3-11) with removal efficiencies exceeded 90%. Kinetic analysis displayed that the kinetic data was well described by both Pseudo first-order and second-order models. Also, the equilibrium data was well fitted by Freundlich isotherm model. In addition, thermodynamic analysis evidenced that the removal of ciprofloxacin by Mg/Fe⁰ was exothermic, and spontaneous. The experiments also revealed that physisorption and chemisorption were the responsible mechanisms for ciprofloxacin removal. The proposed treatment system remediated 10 litters of 100 mg L^-1 of ciprofloxacin solution with 100% overall removal efficiency. This treatment system could be a promising and practical solution to decrease ciprofloxacin concentration in different water bodies.

One-step synthesis of mixed valence FeOX nanoparticles supported on biomass activated carbon for degradation of bisphenol A by activating peroxydisulfate

A novel FeO_X nanoparticles supported biomass activated carbon (BAC/FeO_X) composite was prepared through one-pot calcination method with FeCl₃ and cherry stone powder as precursors. The carbonization of biomass, reduction of Fe³⁺, and FeO_X anchored on carbon substrate could be achieved at the same time. Characterization with transmission electron microscope (TEM) and scanning electron microscope indicated that nanoscale FeO_X distributed uniformly on carbon substrate, and X-ray photoelectron spectroscopy, X-ray diffraction, and high resolution TEM characterization proved that the loaded FeO_X was high crystallinity of Fe₃O₄ and α-Fe⁰. Bisphenol A (BPA) was used to investigate the degradation performance of BAC/FeO_X activating peroxydisulfate (PDS). The ratio of raw materials affected degradation efficiency of BPA intensively through the content, valence state, and dispersibility of FeO_X nanoparticles, and the optimal material could degrade 20 mg/L BPA completely in 5 min at 0.1 g/L in the presence of 1 g/L PDS. Free radical determination and quenching experiments indicated that both SO₄^•- and •OH were involved in BPA degradation. The degradation pathway was proposed based on the identification of degradation intermediates. The facile synthesis method, high activation efficiency, and low-cost and environmental friendly raw materials made the BAC/FeO_X-50 an alternative catalyst for organic pollution water treatment.

Effect of chelated iron activated peroxydisulfate oxidation on perchloroethene-degrading microbial consortium

In this work, the effect of In-Situ Chemical Oxidation (ISCO) using peroxydisulfate (PDS) on chloroethenes-degrading microbial consortium in the presence of perchloroethene (PCE; tetrachloroethene) was investigated. Degradation of PCE was examined using PDS without an activation, activated with iron Fe(II) chelated by citric acid (CA), and microbial consortium derived from chloroethenes-contaminated site in liquid and sand microcosms. Two different molar ratios of PCE/PDS/(Fe(II)+CA) (1/8/1.6 and 1/16/3.2) were tested. The PCE removal efficiency was the highest in the bacteria-free microcosms. An expected increase in the PCE removal efficiency by coupling PDS and microbial consortium was not confirmed. Surprisingly, the reduced capacity of PDS to remove PCE in the systems containing both PDS and microbial consortium was observed indicating that indigenous microbes may reduce the efficiency of PDS during a remediation. High-throughput 16S rRNA gene sequencing analysis revealed negative effect of PDS on organohalide-respiring bacteria (OHRB), which were not detected after 19 days of the experiment, unlike in biotic control. On the other hand, amplicon sequence variants (ASVs) affiliated with genera Brevundimonas and Pseudomonas that have been described for their capability of aerobic cometabolic/metabolic degradation of chloroethenes (CEs) were among the most frequently detected ASVs after the PDS treatment. Results further showed that the sole Fe(II)-CA affected the diversity of the microbial consortium. Overall, results of this study provide new insight into the coupling ISCO using PDS with in situ bioremediation of CEs.

Effects of the formation of reactive chlorine species on oxidation process using persulfate and nano zero-valent iron

The chloride ion (Cl^-) is a matrix ion that plays crucial roles in radical-based oxidation processes used to treat brackish or saline water. Here, the effects of the formation of reactive chlorine species on the performance of and reaction mechanisms involved in persulfate/nano zero-valent iron process were evaluated by investigating the reaction kinetics and performing reactive species scavenging tests. The phenol oxidation rate increased markedly in the early reaction stage in the presence of 25-200 mM of Cl^-. This was because excess sulfate radicals (SO₄^-) reacted with Cl^- to produce short-lived reactive chlorine species such as Cl and Cl₂^- rather than being scavenged by Fe²⁺ or other SO₄^-. The reactive chlorine species caused OH to form through radical propagation reactions. The total numbers of reactive species involved in phenol oxidation were higher at brackish to weakly saline Cl^- concentrations than at lower and higher Cl^- concentrations. At high Cl^- concentrations (>400 mM), the phenol oxidation rate decreased because most of the SO₄^- reacted with Cl^- to give large amounts of weaker oxidants such as Cl₂^- and HOCl. Acceleration of Fe corrosion by Cl^- negligibly affected the persulfate/nano zero-valent iron oxidation process.

Persulfate activation by nano zero-valent iron for the degradation of metoprolol in water: influencing factors, degradation pathways and toxicity analysis

In this study, nano zero-valent iron (nZVI) was utilized to activate persulfate (PS) for the degradation of metoprolol (MTP), a commonly used drug for curing cardiovascular diseases, in water. Quenching tests indicated that both the sulfate radical (SO₄˙⁻) and hydroxyl radical (˙OH) contributed to the degradation of MTP, while SO₄˙⁻ seemed to play a large role under natural pH conditions. Batch tests were conducted to investigate the effects of several influencing factors, such as PS concentration, initial MTP concentration, pH, temperature and common anions, on the degradation performance of MTP. Generally, lower MTP concentration and pH values, and higher PS concentration and temperature favoured MTP degradation. HCO₃⁻, NO₃⁻ and SO₄²⁻ were found to inhibit MTP degradation, while Cl⁻ enhanced MTP degradation. Several corrosion products of nZVI, including Fe₃O₄, Fe₂O₃ and FeSO₄, were formed during the reaction, which was reflected by the combined XRD and XPS analysis. Degradation pathways of MTP were proposed according to the identified transformation products, and the peak areas of the major products along with the time were also monitored. Finally, the toxicity of the reaction solution was assessed by experiments using Aliivibrio fischeri. Overall, it could be concluded that nZVI/PS might be a promising method for the rapid treatment of MTP-caused water pollution.

The influencing factors, mechanism and toxicity of MTP degradation by nZVI activated persulfate were investigated.

New insight into the mechanism of peroxymonosulfate activation by nanoscaled lead-based spinel for organic matters degradation: A singlet oxygen-dominated oxidation process

Crystalline iron-based nanoparticles with spinel structure have received great attention for catalyzing peroxymonosulfate (PMS). This study introduces lead ferrite (PbFe₂O₄) as a novel, simple, and efficient catalyst to activate PMS for the degradation of organic contaminants in aqueous solution. The results indicated that, under pH 9.0, nearly 100% of 10 μM thionine was removed in 20 min. Operation factors, including pH, oxidant concentrations, catalyst dosage, and coexisting ions, were investigated and found to be influential for the thionine removal. PbFe₂O₄ showed higher catalytic activity and lower ions leaching than well-crystallized lead oxide (PbO) and ferric oxide (Fe₂O₃). The results from the characterization of the PbFe₂O₄ with X-ray diffraction (XRD) before and after reaction suggested that the structure and properties of the catalyst kept stable, and the recovered catalyst exhibited good catalytic performance during the recycling batch experiments. Free radical quenching experiments and electron paramagnetic resonance (EPR) spectra revealed that singlet-oxygen (¹O₂) is the dominant active oxygen species rather than sulfate radical for thionine degradation in PbFe₂O₄/PMS system. Meanwhile, the possible pathways of ¹O₂ generation were proposed: the redox reaction between Pb(Ⅳ)/Pb(II) and PMS may play an key role in PMS activation. This study provides an interesting insight in PMS activation by the high-efficient non-radical process, and the PbFe₂O₄ could be as efficient and recyclable heterogeneous catalyst for organic degradation.

Activated persulfate by iron-based materials used for refractory organics degradation: a review

Recently, the advanced oxidation processes (AOPs) based on sulfate radicals (SRs) for organics degradation have become the focus of water treatment research as the oxidation ability of SRs are higher than that of hydroxyl radicals (HRs). Since the AOP-SRs can effectively mineralize organics into carbon dioxide and water under the optimized operating conditions, they are used in the degradation of refractory organics such as dyes, pesticides, pharmaceuticals, and industrial additives. SRs can be produced by activating persulfate (PS) with ultraviolet, heat, ultrasound, microwave, transition metals, and carbon. The activation of PS in iron-based transition metals is widely studied because iron is an environmentally friendly and inexpensive material. This article reviews the mechanism and application of several iron-based materials, including ferrous iron (Fe²⁺), ferric iron (Fe³⁺), zero-valent iron (Fe⁰), nano-sized zero-valent iron (nFe⁰), materials-supported nFe⁰, and iron-containing compounds for PS activation to degrade refractory organics. In addition, the current challenges and perspectives of the practical application of PS activated by iron-based systems in wastewater treatment are analyzed and prospected.

Geoenvironmental characteristics of bisphenol A contaminated soil after persulfate treatment with different activation/enhancement methods

Persulfate (PSF) is a strong oxidant that has been used extensively in the In-Situ Chemical Oxidation (ISCO) technology. The geoenvironmental impact of PSF treatment is barely investigated. This situation should be carefully considered as it may affect the reutilization of contaminated soil as engineering materials. This paper studied the removal of bisphenol A (BPA) by PSF with Nano Zero-Valent Iron (nZVI) and percarbonate (SPC) activated/enhanced and their subsequent impacts on the engineering properties of soil. The physicochemical and geotechnical properties of soils before and after treatment were evaluated using batch experiments. The results indicate that the introduced pristine PSF can be activated by some naturally occurring matters and subsequently lead to the mineralization of BPA. Both non-activated PSF and activated/enhanced PSF treatment led to the soil improvement in the undrained shear strength at different degrees. The primary mechanism of soil improvement is ascribed to the heterogeneous sulfate and/or carbonate precipitation. Meanwhile, Ca²⁺ in the pore fluid played a significant role in the enhancement of the soil strength. A conclusion was drawn that the treatment of both non-activated PSF, nZVI- and SPC-activated PSF treatment can achieve removal of BPA and soil improvement in the short-term simultaneously. This study can improve the PSF-involved remediation of brownfields and dredged sediments for a sustainable and low-carbon society.

Effect of pH on Zero Valent Iron Performance in Heterogeneous Fenton and Fenton-Like Processes: A Review

Heterogeneous Fenton processes with solid catalysts have gained much attention for water and wastewater treatment in recent years. In the field of solid catalysts, zero valent iron (ZVI) is among the most applicable due to its stability, activity, pollutant degradation properties and environmental friendliness. The main limitation in the use of ZVI in heterogeneous Fenton systems is due to its deactivation in neutral and alkaline conditions, and Fenton-like processes have been developed to overcome this difficulty. In this review, the effect of solution pH on the ZVI-Fenton performance is discussed. In addition, the pH trend of ZVI efficiency towards contaminants removal is also considered in oxic solutions (i.e., in the presence of dissolved O₂ but without H₂O₂), as well as in magnetic-field assisted Fenton, sono-Fenton, photo-Fenton and microwave-Fenton processes at different pH values. The comparison of the effect of pH on ZVI performance, taking into account both heterogeneous Fenton and different Fenton-like processes, can guide future studies for developing ZVI applications in water and wastewater treatment.