Remediation of sulfathiazole contaminated soil by peroxymonosulfate: Performance, mechanism and phytotoxicity

New insights into soil active substances enhance the biochar/periodate process for remediation of sulfadiazine: The changes of soil properties and toxicity

In recent years, periodate (SPI)-based advanced oxidation processes have been successfully applied in wastewater treatment. However, their application in soil pollution remediation remains limited. To our knowledge, this study represents the first attempt to utilize SPI catalyzed by the Eichhornia crassipes biochar (EBC) system for the remediation of sulfadiazine (SD)-contaminated soil. In the EBC/SPI system, the degradation performance of SD-spiked soils was significantly improved, achieving complete degradation within 60 min, which indicates a clear synergistic effect between SPI and EBC. Notably, our findings highlighted that active soil constituents play crucial roles in SPI activation. Specifically, free Fe-oxides in soil were essential for SPI activation to form reactive species (RS) compared to amorphous Fe-oxides and dissolved Fe, leading to superior SD degradation. Soil organic matter (SOM) also contributed to RS formation and conversion. Adding Fe3+, Cl-, and humic acid accelerated SD elimination, whereas Mn2+ and HCO3- inhibited it. Quenching experiments and electron paramagnetic resonance spectroscopy confirmed the formation of singlet oxygen, superoxide radicals, and iodate radicals, which actively degraded SD. Analysis of soil properties, including SOM content, total phosphorus, functional groups, crystal structure, and pH value, showed negligible changes after EBC/SPI treatment. Additionally, potential decomposition pathways of SD were proposed based on identified SD intermediates. Ecotoxicity analyses and phytotoxicity tests indicated a marked reduction in the toxicity of these intermediates compared to SD. These findings provide an efficient strategy for soil remediation and offer new insights into the role of inherent substances in the field of contaminated soil remediation.

Efficient simultaneous degradation of multiple sulfonamide antibiotics in soil using biocarbon-based nanomaterials as catalysts for persulfate activation

There is an urgent need to develop effective and sustainable methods to decrease sulfonamide (SA) contamination of soil. Herein, a non-homogeneous system of zero-valent metal-biochar-based composites was proposed and tested for persulfate (PS) activation. This system employed zero-valent iron (Fe0) as an electron donor to catalyze the cleavage of the OO bond in PS, thereby generating reactive oxygen species (ROS) that degrade SAs. Notably, the incorporation of elemental sulfur (S) significantly mitigated the passivation of Fe0, leading to an enhanced degradation capability of the system. The system decomposes 84-97 % of SAs at their concentration in soil suspension 10 mg/kg in 3 h. Among the coexistence of several SAs, the system showed the fastest degradation rate of sulfisoxazole with a kobs of 0.0305 min-1, nearing complete removal within 3 h. The system is resistant to the impact of organic matter in soil. It allows to decrease concentration of sulfadiazine in actual contaminated soil on 73 % in 2 h. The system remains effective with decreasing concentrations of PS from 20 mM to 2.5 mM, which lowered the operating cost. T.E.S.T software evaluation showed a significant reduction in the bioaccumulation toxicity and developmental toxicity of the degradation products, suggesting that the system is environmentally friendly. The high efficiency of the catalytic system, the simplicity and economy of the manufacturing process, the resistance to interference in real soil, and the environmental friendliness make this technology promising for mitigating the problem of the environment contamination by SAs.

Activation of persulfate by a layered double oxide supported sulfidated nano zero-valent iron for efficient degradation of 2,2',4,4'-tetrabromodiphenyl ether in soil

The nano zero-valent iron (nZVI) activated persulfate (PS) is recognized as a promising approach to degrade 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), which is ubiquitous in the soil at electronic waste sites. However, all the reported studies were performed in liquids, gaps in the real behaviour and microbial contribution to the degradation of BDE-47 in soil media need to be urgently filled. The removal efficiency of BDE-47 is low using traditional nZVI as activator because of its aggregation and corrosion. Herein, we designed a novel layered double oxide supported sulfidated nano zero-valent iron (S-nZVI@LDO) composite and explored the performance of S-nZVI@LDO/PS to remediate BDE-47 contaminated soil. The results showed that S-nZVI@LDO has excellent stability and superior reduction capability. It could couple PS to achieve a rapid and efficient degradation of BDE-47, and the removal efficiency reached 92.31 % (5 mg/kg) within 6 h, which was much higher than that of n-ZVI/PS (53.38 %) or S-nZVI/PS (75.69 %). The kinetic constant of BDE-47 degradation by S-nZVI@LDO/PS was 23.6 and 3.7 times higher than that by single S-nZVI@LDO and nZVI/PS, respectively. It is attributable to the efficient production of SO4•-, •OH, O2•-, and 1O2 in the system, in which SO4•- and •OH dominated. The bioinformatic analysis demonstrate that soil remediation by S-nZVI@LDO/PS significantly enriched aromatic compounds-degrading bacteria and increased the abundance of hydrocarbon degradation functions. Microbial degradation may play important roles in the BDE-47 degradation and soil quality recovery. The identification of degradation pathways suggests that BDE-47 was degraded to very low-toxic products based on GHS toxicity prediction through a series process of debromination, hydroxylation, cleavage central oxygen, and ring opening, or even completely mineralized. The findings may provide significant implications for the in-situ clean-up of brominated flame retardants in contaminated soil using S-nZVI@LDO/PS Fenton-like system.

A review of pathogen removal from municipal wastewater using advanced oxidation processes: Agricultural application, regrowth risks, and new perspectives

Pathogen removal in wastewater offers a chance to recover water and nutrients for crop production, reducing environmental contamination and public health risks. However, the risk of pathogens regrowing in treated effluents can endanger public health if reused in agriculture, attracting stringent reuse standards. While advanced oxidation processes (AOPs) promise to reduce pathogens, eliminating regrowth potential in AOP-treated effluents requires further scrutiny. This review aimed to summarize the available evidence on understanding pathogen reduction and regrowth potential in AOP-treated effluents, following best practices for scoping reviews like the preferred reporting items for systematic reviews and meta-analysis (PRISMA). It covers recent pathogen studies under AOPs, current AOP investigations, the impact of AOP dosage and retention time on pathogen control, and challenges in reusing AOP-treated effluents for crop production. Additionally, it identifies areas needing improvement or complementary treatments for pathogen-free effluents with no regrowth potential. The review concludes by summarizing key findings and suggesting research areas for further exploration.

Mechanical insights into desulfurization by peroxymonosulfate oxidation via a non-reactive oxygen species pathway

Air pollution by sulfur dioxide (SO2) remains a pressing concern for both the environment and human health. Desulfurization enhanced by persulfate based advanced oxidation processes (PS-AOPs) has been proven to be a feasible method. However, the inherent contradiction between the rapid diffusion mass transfer of SO2 in the "gas-liquid-gas" phase and the limited lifespan of reactive oxygen species (ROS) can not be ignored. Excessive investment in PS is required to sustainably generate ROS to achieve continuous desulfurization performance, which may lead to excessive PS consumption. To address this issue, whether PS can achieve the oxidation absorption of SO2 via a non-reactive oxygen species pathway was investigated. Experimental and computational results demonstrated that peroxymonosulfate (PMS) instead of peroxydisulfate (PDS) had a great SO2 removal performance, the utilization of PS could be effectively achieved by maintaining a 1:1 molar ratio of PMS and removed SO2. The presence of HOO bonds in the PMS introduced a partial positive charge to the oxygen atom, making the PMS polar and more susceptible to be attacked by the nucleophile HSO3-. So SO2 underwent a series of processes including dissolution, dissociation, one-oxygen atom transfer, and ionization before ultimately being converted into SO42- ions, effectively achieving its removal from flue gas. This study may presents a novel approach for achieving high-efficiency flue gas desulfurization.

Mechanism and ecological environmental risk assessment of peroxymonosulfate for the treatment of heavy metals in soil

Oxidation technologies based on peroxymonosulfate (PMS) have been effectively used for the remediation of soil organic pollutants due to their high efficiency. However, the effects of advanced PMS-based oxidation technologies on other soil pollutants, such as heavy metals, remain unknown. In this study, changes in the form of heavy metals in soil after using PMS and the risk of pollution to the ecological environment were investigated. Furthermore, two risk assessment methods, the mung bean germination toxicity test and groundwater leaching soil column test, were employed to evaluate the soil before and after PMS treatment. The results showed that PMS has a strong ability to degrade complex compounds, enabling the transformation of heavy metals, such as Cd, Pb, and Zn, from stable to active states in the soil. The risk assessments showed that PMS treatment activated heavy metals in the soil, which delayed the growth of plants, increased heavy metal content in plant tissues and the risk of groundwater pollution. These findings provide a new perspective for understanding the effects of PMS on soil, thus facilitating the sustained and reliable development of future research in the field of advanced oxidation applied to soil treatment.

Activation of peroxymonosulfate with natural pyrite-biochar composite for sulfamethoxazole degradation in soil: Organic matter effects and free radical conversion

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) represent an effective method for the remediation of antibiotic-contaminated soils. In this study, a natural pyrite-biochar composite material (FBCx) was developed, demonstrating superior activation performance and achieving a 76% removal rate of SMX from soil within 120 min. There existed different degradation mechanisms for SMX in aqueous and soil solutions, respectively. The production of 1O2 and inherent active species produced by soil slurry played an important role in the degradation process. The combination of electron paramagnetic resonance (EPR) and free radical probe experiments confirmed the presence of free radical transformation processes in soil. Wherein, the·OH and SO4·- generated in soil slurry did not directly involve in the degradation process, but rather preferentially reacted with soil organic matter (SOM) to form alkyl-like radicals (R·), thereby maintaining a high concentration of reactive species in the system. Furthermore, germination and growth promotion of mung bean seeds observed in the toxicity test indicated the environmental compatibility of this remediation method. This study revealed the influence mechanism of SOM in the remediation process of contaminated soil comprehensively, which possessed enormous potential for application in practical environments.

Alkali-thermal activated persulfate treatment of tetrabromobisphenol A in soil: Parameter optimization, mechanism, degradation pathway and toxicity evaluation

The continued accumulation of halogenated organic pollutants in soil posed a potential threat to ecosystems and human health. In this study, tetrabromobisphenol A (TBBPA) was used as a typical representative of halogenated organic pollutants in soil, for alkali-thermal activated persulfate (PS) treatment. The results of response surface methodology (RSM) showed a optimal debromination efficiency of TBBPA was 88.99 % under the optimum reaction conditions. Quenching experiments and electron paramagnetic resonance (EPR) confirmed that SO4-•, HO•, O2-• and 1O2 existed simultaneously in the oxidation process. SO4-• played a major role in the initial stage of the reaction, and O2-• played a major role in the the last stage. Based on density functional theory (DFT) and intermediate products, two degradation pathways were proposed, including debromination reaction and β bond scission. Moreover, the basic physical and chemical properties of the soil were affected to a certain extent, while the soil surface structure, elements and functional group composition rarely changed. In addition, the T.E.S.T. analysis and biotoxicity tests proved that alkali-thermal activated PS can effectively reduce the toxicity of TBBPA-contaminated soil, which is conducive to the subsequent safe secondary utilization of soil.

Dual Activation of Peroxymonosulfate Using MnFe2O4/g-C3N4 and Visible Light for the Efficient Degradation of Steroid Hormones: Performance, Mechanisms, and Environmental Impacts

Single activation of peroxymonosulfate (PMS) in a homogeneous system is sometimes insufficient for producing reactive oxygen species (ROS) for water treatment applications. In this work, manganese spinel ferrite and graphitic carbon nitride (MnFe2O4/g-C3N4; MnF) were successfully used as an activator for PMS under visible light irradiation to remove the four-most-detected-hormone-contaminated water under different environmental conditions. The incorporation of g-C3N4 in the nanocomposites led to material enhancements, including increased crystallinity, reduced particle agglomeration, amplified magnetism, improved recyclability, and increased active surface area, thereby facilitating the PMS activation and electron transfer processes. The dominant active radical species included singlet oxygen (1O2) and superoxide anions (O2•-), which were more susceptible to the estrogen molecular structure than testosterone due to the higher electron-rich moieties. The self-scavenging effect occurred at high PMS concentrations, whereas elevated constituent ion concentrations can be both inhibitors and promoters due to the generation of secondary radicals. The MnF/PMS/vis system degradation byproducts and possible pathways of 17β-estradiol and 17α-methyltestosterone were identified. The impact of hormone-treated water on Oryza sativa L. seed germination, shoot length, and root length was found to be lower than that of untreated water. However, the viability of both ELT3 and Sertoli TM4 cells was affected only at higher water compositions. Our results confirmed that MnF and visible light could be potential PMS activators due to their superior degradation performance and ability to produce safer treated water.

Alkali-catalyzed hydrothermal oxidation treatment of triclosan in soil: Mechanism, degradation pathway and toxicity evaluation

The continuous accumulation of chlorinated organic pollutants in soil poses a potential threat to ecosystems and human health alike. Alkali-catalyzed hydrothermal oxidation (HTO) can successfully remove chlorinated organic pollutants from water, but it is rarely applied to soil remediation. In this work, we assessed this technique to degrade and detoxify triclosan (TCS) in soil and we determined the underlying mechanisms. The results showed a dechlorination efficiency of TCS (100 mg per kg soil) of 49.03 % after 120 min reaction (H₂O₂/soil ratio 25 mL·g^-1, reaction temperature 180 °C in presence of 1 g·L^-1 NaOH). It was found that soil organic constituents (humic acid, HA) and inorganic minerals (SiO₂, Al₂O₃, and CaCO₃) suppressed the dechlorination degradation of TCS, with HA having the strongest inhibitory effect. During alkali-catalyzed HTO, the TCS molecules were effectively destroyed and humic acid-like or fulvic acid-like organics with oxygen functional groups were generated. Fluorescence spectroscopy analysis showed that hydroxyl radicals (OH) were the dominant reactive species of TCS degradation in soil. On the basis of the Fukui function and the degradation intermediates, two degradation pathways were proposed. One started with cleavage of the ether bond between the benzene rings of TCS, followed by dechlorination and the opening of benzene via oxidation. The other pathway started with direct hydroxylation of the benzene rings of TCS, after which they were opened and dechlorinated through oxidation. Analysis of the soil structure before and after treatment revealed that the soil surface changed from rough to smooth without affecting soil surface elements. Finally, biotoxicity tests proved that alkali-catalyzed HTO effectively reduced the toxicity of TCS-contaminated soil. This study suggests that alkali-catalyzed hydrothermal oxidation provides an environmentally friendly approach for the treatment of soil contaminated with chlorinated organics such as TCS.

Hydrogen sulfite promoted the activation of persulfate by μM Fe2+ for bisphenol A degradation

This study evaluated the improvement of bisphenol A (BPA) elimination through hydrogen sulfite (HS) coupling with persulfate (PS) activated by low amounts of Fe²⁺. Under the optimum condition (10 μM Fe²⁺, 0.6 mM HS, 0.8 mM PS, pH = 4.0), 100% BPA (5 μM) was removed within 15 min. Sulfate radical (SO₄^•-) and singlet oxygen (¹O₂) were confirmed as the primary active species for BPA degradation in the Fe²⁺/HS/PS system, and the steady-state concentration of SO₄^•- and ¹O₂ was 2.43 × 10^-9 M and 1.67 × 10^-9 M, respectively. Besides, FeHSO₃⁺ and FeOHSO₃H⁺ were the main iron species in the Fe²⁺/HS/PS system. The removal potency of BPA depended on the operation parameters, such as chemical reagent dosages, reaction temperature, and the solution initial pH. The impact of NO₃^-, SO₄^2-, and humic acid (HA) on BPA removal was negligible, whereas Cl^-, HCO₃^-, and HPO₄^2- restrained BPA decomposition. Two injections of HS could improve the limitation of BPA degradation efficiency due to the rapid consumption of HS in the reaction process. The lower removal efficiency of BPA was observed in real water matrices than that in ultrapure water. Whatever, up to 58.1%, 66.3%, 68.1%, and 88.1% of BPA were removed from domestic wastewater, lake water, river water, and tap water within 10 min, respectively. In addition, the BPA degradation process was characterized by the 3D fluorescence spectra technique, which indicated the BPA oxidation intermediates also have fluorescence characteristics. Moreover, 6 intermediate products were identified, and the possible degradation pathways of BPA were proposed. Additionally, the Fe²⁺/HS/PS system also exerted an excellent performance for the removal of other representative organic contaminants including enrofloxacin, acid orange 7, acetaminophen, and phenol. All results indicated that the Fe²⁺/HS/PS system could be a promising method for organic pollutant removal.

Metal-free single heteroatom (N, O, and B)-doped coconut-shell biochar for enhancing the degradation of sulfathiazole antibiotics by peroxymonosulfate and its effects on bacterial community dynamics

Metal-free single heteroatom (N, O, and B)-doped coconut-shell biochar (denoted as N-CSBC, O-CSBC, and B-CSBC, respectively) were fabricated in a one-step pyrolysis process to promote peroxymonosulfate (PMS) activation for the elimination of sulfathiazole (STZ) from aquaculture water. B-CSBC exhibited remarkably high catalytic activity with 92% of STZ degradation in 30 min attributed to the presence of meso-/micro-pores and B-containing functional groups (including B-N, B-C, and B₂O₃ species). Radical quenching tests revealed SO₄^•-, HO•, and ¹O₂ being the major electron acceptors contributing to STZ removal by PMS over B-CSBC catalyst. The B-CSBC catalyst has demonstrated high sustainability in multiple consecutive treatment cycles. High salinity and the presence of inorganic ions such as chloride, enhanced the performance of the sulfate radical-carbon-driven advanced oxidation processes (SR-CAOPs) as pretreatment strategy that significantly facilitated the removal of STZ from aquaculture water. Furthermore, a potential sulfonamide-degrading microorganism, Cylindrospermum_stagnale, belonging to the phylum Cyanobacteria, was the dominant functional bacteria according to the results of high-throughput 16S rRNA gene sequencing conducted after the B-CSBC/PMS treatment. This study provides new insights into the SR-CAOP combined with bioprocesses for removing STZ from aqueous environments.