Abiotic transformation and ecotoxicity change of sulfonamide antibiotics in environmental and water treatment processes: A critical review

Enhanced removal of antibiotics and antibiotic resistance genes in a soil microbial fuel cell via in situ remediation of agricultural soils with multiple antibiotics

Soil microbial fuel cells (MFCs) have been applied for the in situ remediation of soils polluted by single antibiotics. However, the investigation of only single antibiotic pollution has hindered MFC application in real-world soil remediation, where the effects of multiple antibiotics with similar chemical structures on the fate of antibiotics and their corresponding antibiotic resistance genes (ARGs) remain unknown. In this study, antibiotic removal rates, microbial community compositions, metabolite compositions, and ARG abundances were investigated in soil MFCs by adding two commonly used antibiotics (sulfadiazine, SDZ, and sulfamethoxazole, SMX), and comparing them with the addition of only a single antibiotic (SDZ). The antibiotic removal rate was higher in the soil MFC with addition of mixed antibiotics compared to the single antibiotic due to enhanced biodegradation efficiency in both the upper (57.24% of the initial antibiotic concentration) and lower layers (57.07% of the initial concentration) of the antibiotic-polluted soils. Bacterial community diversity in the mixed antibiotic conditions increased, and this likely resulted from the decreased toxicity of intermediates produced during antibiotic biodegradation. Moreover, the addition of mixed antibiotics led to lower risks of ARG release into soil environments, as reflected by higher abundances of host bacteria in the single antibiotic treatment. These results encourage the further development of soil MFC technology for in situ remediation of antibiotic-polluted soils.

Enhanced ferrate oxidation of organic pollutants in the presence of Cu(II) Ion

In this study, we found that the introduction of Cu(II) (several μM, close to the concentration level of some real water/wastewater) in ferrate (Fe(VI)) oxidation can remarkably accelerate the abatement of various organic pollutants under slightly alkaline conditions. The results show that 5 μM sulfamethoxazole (SMX) can be completely degraded by Fe(VI) (50 μM) in the presence of 20 μM Cu(II) within 10 min at pH 8.0, which was 1.65 times higher than that by Fe(VI) alone. High-valent iron intermediates (i.e. Fe(V), Fe(IV)) and Cu(III) were generated as reactive species in the Cu(II)/Fe(VI) system, all of which contributed to the enhanced oxidation of SMX. Common water components, except for HCO₃^- and humic acid, exhibited no influence on SMX removal. Additionally, the enhanced removal of SMX by Cu(II)/Fe(VI) was also observed in real water with the benefit of total removal of Cu(II) by the ferrate resultant particles. Due to the presence of highly reactive and selective oxidant, the Cu(II)/Fe(VI) system could react readily with organic pollutants containing electron-rich moieties, such as phenol, olefin or amino groups. This study provided a simple, selective, and practical strategy for the abatement of organic pollutants and a simultaneous removal of Cu(II).

Combining Ultraviolet Photolysis with In-Situ Electrochemical Oxidation for Degrading Sulfonamides in Wastewater

Ultraviolet photolysis (UVC, 254 nm) was coupled with an electrochemical oxidation process to degrade three kinds of veterinary sulfonamide (sulfamethazine [SMZ] tablets, sulfamonomethoxine [SMM] tablets, and compound sulfamethoxazole [SMX] tablets). The treatment was applied using a flat ceramic microfiltration membrane to study the effects of photocatalysts. The effectiveness of degradation of the three sulfonamides was evaluated under different conditions. Dissolved oxygen was provided via aeration, but this resulted in a large decrease in the degradation effectiveness due to the inhibition of free chlorine electrogeneration. The photocatalysts had no promotional effect on sulfonamide removal from wastewater due to reduced UV penetration. Because of the different distribution coefficients of sulfonamides, UV irradiation had different effects on different sulfonamide species. For SMZ and SMM, anionic species exhibited a higher degradation rate, whereas for SMX, degradation was most effective for neutral species. In addition, the free chlorine yield increased as the pH increased. Free chlorine conversion reactions occurred under UV irradiation, with the reactions possibly restrained by sulfonamides. Reactive chlorine species promoted SMM degradation. Compared to UV irradiation or electrochemical oxidation alone, the UV/in-situ electrochemical oxidation process was more effective and is suitable for treating real wastewater under various environmental pH levels.

Formation of stable imine intermediates in the coexistence of sulfamethoxazole and humic acid by electrochemical oxidation

The electrochemical degradation performance of sulfamethoxazole (SMX) was studied in the presence of humic acid (HA) by using a Ti/Ti₄O₇/β-PbO₂ anode. The electrochemical degradation efficiency of SMX decreased from 93.4% to 45.8% in 50 min after the addition of 25 mg L^-1 HA. The pseudo-first-order kinetic rate constant decreased by 71.4%, and the E_EO value increased from 63.8 Wh L^-1 to 90.9 Wh L^-1. HA and its degradation intermediates could compete for free radicals, especially for ·OH, with SMX. The analytical results obtained using UPLC-ESI-Q-TOF-MS showed that 18 degradation intermediates were identified in the coexistence of SMX and HA. Four imine intermediates were formed through the reactions between the aniline moieties of SMX and quinone groups in the HA structure through covalent bonds. Furthermore, the relative abundances of the intermediates demonstrated that the imine intermediates were complex and stable during electrochemical degradation.

Tailoring a novel hierarchical cheese-like porous biochar from algae residue to boost sulfathiazole removal

Aquatic pollution caused by antibiotics poses a significant threat to human health and the ecosystem. Inspired from "Emmental Cheese" that owns lots of natural pores, we here fabricated a hierarchical cheese-like porous Spirulina residue biochar (KSBC) activated by KHCO₃ for efficiently boosting the removal of sulfathiazole (STZ). Through learning form nature that the CO₂ produced by bacteria can serve as the natural pore maker (like cheese-making), KHCO₃ was thus selected as the gas generating agent in this study. The effect of adding KHCO₃ on the surface properties of KSBC was comprehensively investigated. Benefiting from the activation, the KSBC with the mass ratio of 2:1 (2K-SBC) possessed the largest specific surface areas (1100 m² g^-1), which was approximately 81 times that of the original (not activated) Spirulina residue biochar (SBC) (13.56 m² g^-1). Moreover, 2K-SBC exhibited the maximum adsorption capacity for STZ (218.4 mg g^-1), dramatically higher than the SBC (25.78 mg g^-1). The adsorption kinetics and adsorption isotherms exhibited that the adsorption behavior of 2K-SBC for STZ was consistent with the pseudo-second-order and Langmuir models. Additionally, the adsorption thermodynamics revealed that the adsorption of STZ on 2K-SBC was spontaneous and exothermic. The pore-filling and electrostatic interaction were considered the main mechanism for the adsorption of STZ on 2K-SBC, whereas the π-π electron donor-acceptor (EDA) interaction and hydrogen bond would also partially contribute to the adsorption process.

Comparison of chemical and biological degradation of sulfonamides: Solving the mystery of sulfonamide transformation

Sulfonamides (SAs) are widespread in aquatic environments and pose serious environmental risks. The removal efficiencies and degradation mechanisms of SAs in both chemical and biological degradation systems were comprehensively reviewed. Density functional theory (DFT) was utilized to decipher the reaction types and reactive sites of both degradation mechanisms at the electron level. In chemical degradation, the rate of the reactive oxidants to degrade SAs follows the order SO₄•^- ≈ •OH > O₃ > ¹O₂ > ClO₂ ≈ Fe(VI) ≈ HOCl > peroxymonosulfate. pH affects the oxidation-reduction potentials of oxidants, the reactivity of SAs, and the intermolecular force between oxidants and SAs, thereby affecting the chemical degradation efficiencies and mechanisms. In biological degradation, oxidoreductase produced by bacteria, fungi, algae, and plants can degrade SAs. The catalytic activity of the enzyme is affected by the enzyme system, reaction conditions, and type of SAs. Despite the different reaction modes and removal efficiencies of SAs in chemical degradation and biological degradation, the transformation pathways and products show commonalities. Modification of the amino (N¹H₂-) moiety and destruction of sulfonamide bridge (-SO₂-N¹¹H-) moiety are the main pathways for both chemical and biological degradation of SAs. Most oxidants or enzymes can react with the N¹H₂- moiety. Reactions of the -SO₂-N¹¹H- moiety are mainly initiated by the cleavage of S-N bonds for five-membered heterocyclic ring-substituted SAs, and by SO₂ extrusion for six-membered heterocyclic ring-substituted SAs. Chlorine substitution and coupling on the N¹H₂- moiety, hydroxylation of the benzene moiety, oxidation of methyl, and isomerization of the R substituents are the transformation pathways unique to chemical degradation. Formylation/acetylation, glycosylation, pterin conjugation, and deamination of the N¹H₂- moiety are the transformation pathways unique to biological degradation. DFT studies revealed the same reaction types and the same reactive sites of SAs in chemical and biological degradation. Electrophiles are mostly prone to attack the N¹ atom on the amino moiety of neutral SAs and the N¹¹ atom on the sulfonamide bridge moiety of anionic SAs, leading to nitration or electrophilic substitution of the amino moiety and the cleavage of S-N bonds or SO₂ extrusion of the sulfonamide bridge moiety. Reactions on the -SO₂-N¹¹H- moiety eliminate antibacterial activity in the SA degradation process. This review elucidated SA transformation by comparing the chemical and biological degradation of SAs. This could provide theoretical guidance for the development of more efficient and economical treatment technologies for SAs.

Carbonaceous composite membranes for peroxydisulfate activation to remove sulfamethoxazole in a real water matrix

In this study, we fabricated carbonaceous composite membranes by loading integrated mats of nitrogen-doped graphene, reduced graphene oxide, and carbon nanotubes (NG/rGO/CNTs) on a nylon microfiltration substrate and employed it for in-situ catalytic oxidation by activating peroxydisulfate (PDS) for the removal of sulfamethoxazole (SMX) in a real water matrix. The impact of coexisting organics on the performance of carbonaceous catalysis was investigated in the continuous filtration mode. Reusability testing and radical quenching experiments revealed that the non-radical pathways of surface-activated persulfate mainly contributed to SMX degradation. A stable SMX removal flux (r_SMX) of 22.15 mg m^-2·h^-1 was obtained in 24 h when tap water was filtered continuously under a low pressure of 1.78 bar and in a short contact time of 1.4 s, which was slightly lower than the r_SMX of 23.03 mg m^-2·h^-1 performed with deionized water as the control group. In addition, higher contents of protein-, fulvic acid-, and humic acid-like organics resulted in membrane fouling and significantly suppressed SMX removal during long-term filtration. Changes in the production of sulfate ions and the Raman spectra of carbon mats indicated that organics prevent the structural defects of the carbon matrix from participating in PDS activation. Moreover, NG/rGO/CNTs composite membranes coupled with activated persulfate oxidation exhibited good self-cleaning ability, because membrane fouling could be partly reversed by restoring filtration pressure during operation. This study provides a novel and effective oxidation strategy for efficient SMX removal in water purification, allowing the application of carbonaceous catalysis for the selective degradation of emerging contaminants.

Insights into the degradation of emerging organic pollutants by peroxydisulfate activated with Co3O4@NiO: role of each component and catalytic mechanism

A novel Co3O4@NiO as a high-efficiency catalyst was employed to activate peroxydisulfate for degrading antibiotics, and the catalytic mechanism was investigated.