Adsorption mechanisms and the effect of oxytetracycline on activated sludge

Co-metabolism of microorganisms: A study revealing the mechanism of antibiotic removal, progress of biodegradation transformation pathways

The widespread use of antibiotics has resulted in large quantities of antibiotic residues entering aquatic environments, which can lead to the development of antibiotic-resistant bacteria and antibiotic-resistant genes, posing a potential environmental risk and jeopardizing human health. Constructing a microbial co-metabolism system has become an effective measure to improve the removal efficiency of antibiotics by microorganisms. This paper reviews the four main mechanisms involved in microbial removal of antibiotics: bioaccumulation, biosorption, biodegradation and co-metabolism. The promotion of extracellular polymeric substances for biosorption and extracellular degradation and the regulation mechanism of enzymes in biodegradation by microorganisms processes are detailed therein. Transformation pathways for microbial removal of antibiotics are discussed. Bacteria, microalgae, and microbial consortia's roles in antibiotic removal are outlined. The factors influencing the removal of antibiotics by microbial co-metabolism are also discussed. Overall, this review summarizes the current understanding of microbial co-metabolism for antibiotic removal and outlines future research directions.

Treatment performance of different units in the anaerobic-anoxic-aerobic process of landfill leachate under antibiotic exposure

The effectiveness of three different treatment units (anaerobic, anoxic, and aerobic) in A/A/O reactors when treating landfill leachate that contained varying concentrations of tetracycline (TC) was evaluated. The effluent quality, sludge performance, and removal rates of COD, TN, TP, and NH3-N of the reactors were investigated. The results showed that in the three treatment units (anaerobic, anoxic, and aerobic), when the TC dosage was 10 mg/L, the removal rates of NH3-N continued to decrease to 6.9%, 16.3%, and 32.8%, and the removal rates of COD, TN, and TP in the three treatment units reached their maximum values, which were 37.5%, 57.4%, and 69.6%; 21.1%, 37.1%, and 41.0%; 13.0%, 16.2%, and 27.4%, respectively. During the reactor's operation, the heavy metal content in the treatment units initially increased followed by a decrease, especially for Mn and Zn. This was due to the production of more EPS by microorganisms, resulting in more active sites for heavy metal adsorption. In addition, with the increase of TC concentration, TC removal rate was always positively correlated with PN, COD, TN and heavy metals removal rates, and negatively correlated with NH3-N, TP, pH, and PS. Further analysis revealed that TC was toxic to microorganisms, leading to a decrease in biodiversity and microbial community diversity among the three treatment units in the reactor. This article analyzed the treatment effects of different treatment units in leachate under antibiotic exposure conditions, to explore better external conditions for sewage biological treatment facilities.

Green synthesis of diatom-allophane bio-nanocomposites for highly efficient oxytetracycline adsorption

The extensive use of the antibiotic oxytetracycline (OTC) has led to considerable environmental contamination and other negative impacts, prompting an urgent need for a green, effective, and innovative OTC adsorption material. In this study, diatom-allophane bio-nanocomposites were synthesized using a simple and eco-friendly method, yielding a homogeneous coating of allophane nanoparticles on diatom surfaces. The resultant bio-nanocomposites were found to have hierarchically porous structures and abundant active sites derived from successful allophane loading and dispersion on diatom surfaces. The OTC adsorption capacity of this novel adsorbent is remarkable (219.112 mg·g-1), surpassing the capacities of raw allophane and diatoms by >5 and 10 times, respectively. Mechanistically, OTC adsorption by the bio-nanocomposites was found to be driven primarily by chemisorption through a process involving complexation between the amide and amino groups on OTC and the aluminum hydroxyl and carboxyl groups on the adsorbent surface. Electrostatic interactions and hydrogen bonding also contribute significantly to OTC capture. Furthermore, the diatom-allophane bio-nanocomposites exhibit excellent performance over a wide pH range (4-7), in the presence of various cations (Na+, K+, Ca2+, Mg2+) and anions (Cl-, NO3-, SO42-), and in real water bodies. These findings demonstrate the potential of the diatom-allophane bio-nanocomposite as a green, efficient, and promising biological-mineral adsorbent for environmental remediation, leveraging the combined utilization of biological and mineral resources.

Optimizing oxytetracycline removal from aqueous solutions using activated carbon from barley lignocellulosic wastes with isotherms and thermodynamic studies

The excessive presence of antibiotics such as Oxytetracycline (OTC) in the wastewater has increased health problems due to their toxic impact on the aquatic ecosystem. Therefore, their removal has become an important topic. This study aims to produce high surface area-activated carbon derived from low-cost and environmentally friendly barley lignocellulosic wastes to remove OTC from aqueous solutions. The synthesized barley wastes-activated carbon (BW-AC) was characterized using Fourier-Transform Infrared spectroscopy, Thermal Gravimetric Analysis, X-ray diffraction analysis, N2 adsorption/desorption isotherms, and Scanning Electron Microscopy. A Central Composite Design under the Response Surface Methodology (CCD-RSM) was applied to optimize the operational parameters (adsorbent dosage, pH, OTC initial concentration, and contact time) affecting the adsorption capacity as the response factor. The optimum condition of OTC adsorption by BW-AC was the adsorbent dosage of 16.25 mg, pH of 8.25, initial concentration of 62.50 mg/L, and contact time of 23.46 min. An analysis of variance (ANOVA) was performed to investigate the significance of the designed quadratic model and evaluate the parameters interactions. The linear regression coefficient (R2) of 0.975 shows a good correlation between predicted and actual results. The adsorption isotherms were used to determine the contaminant distribution over the adsorbent surface, and the equilibrium data was best described by the Freundlich isotherm due to the R2 value of 0.99 compared to other isotherms and β parameter of 0.23 in Redlich-Peterson equation. Moreover, the n value of 1.25 in Freundlich equation and E value of 0.31 in Dubinin-Radushkevich equation indicates a physical nature of adsorption process. According to the equations results, the maximum adsorption capacity of BW-AC for OTC removal was 500 mg/g, based on the Langmuir isotherm equation. In addition, the thermodynamic studies indicated an endothermic process based on the 0.31 value of ΔH° and spontaneous nature due to the negative amount of ΔG° within the temperature range of 288-318 K. Consequently, the prepared BW-AC can be deemed as a highly effective adsorbent with a large surface area, resulting in significant capacity for removing OTC. This synthesized BW-AC can serve as an environmentally friendly adsorbent for affordable wastewater treatment and is poised to make valuable contributions to future research in this field.

Adsorptive removal of oxytetracycline hydrochloride using bagasse-based biochar powder and beads

Oxytetracycline Hydrochloride (OTC), a common antibiotic used to treat specific illnesses in humans and animals, is characterized by poor absorption into cells, low volatility, and high hydrophilicity. It is a potent contaminant that poses a serious threat to the ecosystem, particularly the aquatic sources. Adsorption onto natural adsorbents is one of the most successful, economical, and ecologically friendly ways to remove antibiotics from waste water. The present work focuses on the adsorption of OTC utilizing alginate biochar beads (AlBCB) and biochar powder (BC) derived from bagasse. The influence of several factors were studies and optimized through batch studies employing BC and AlBCB. After 50 min BC displayed a removal of 97%, at an initial concentration of 10 ppm. The experimental data was discovered to follow PFO kinetics and fit with the Freundlich isotherm adsorption model. AlBCB, after a contact time of 40 min, indicated a maximum percentage removal of 86% for initial concentration of 10 ppm OTC. Al-biochar beads showed the maximum percentage removal at pH 10. 0.5 g of adsorbent was used to carry out all batch experiments at room temperature. The adsorption fitted Freundlich adsorption isotherm and intraparticle diffusion kinetics.

Biogas slurry-derived dissolved organic matter inhibited oxytetracycline adsorption by tropical agricultural soils

The increasing presence of oxytetracycline (OTC) in agricultural soils has raised global environmental concerns. We investigated the environmental behavior and fate of OTC in two types of tropical agricultural soils, focusing on the impact of dissolved organic matter (DOM) from biogas slurry. Techniques such as three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM), Fourier Transform Infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and Ultraviolet-visible spectrophotometer (UV-vis) were used to explore the adsorption mechanisms. Our findings revealed that biogas slurry-derived DOM decreased the OTC adsorption on soils and extended the time to reach adsorption equilibrium. Specifically, the equilibrium adsorption of OTC by the two soils decreased by 19.41 and 15.32 %, respectively. These adsorption processes were effectively modelled by Elovich, intraparticle diffusion, linear, and Freundlich thermodynamic models. Thermodynamic parameters suggested that OTC adsorption onto soils was spontaneous and endothermic, with competitive interactions between biogas slurry-derived DOM and OTC molecules intensifying at higher DOM concentrations. The adsorption mechanisms were governed by both physical and chemical processes. Furthermore, the presence of Ca2+ and Na+ ions significantly inhibited OTC adsorption. These insights advanced our understanding of the fate and risk of OTC in soil environments influenced by DOM, contributing to more informed agricultural and environmental management practices.

Exploring the environmental pathways and challenges of fluoroquinolone antibiotics: A state-of-the-art review

Fluoroquinolone (FQ) antibiotics have become a subject of growing concern due to their increasing presence in the environment, particularly in the soil and groundwater. This review provides a comprehensive examination of the attributes, prevalence, ecotoxicity, and remediation approaches associated with FQs in environmental matrices. The paper discusses the physicochemical properties that influence the fate and transport of FQs in soil and groundwater, exploring the factors contributing to their prevalence in these environments. Furthermore, the ecotoxicological implications of FQ contamination in soil and aquatic ecosystems are reviewed, shedding light on the potential risks to environmental and human health. The latter part of the review is dedicated to an extensive analysis of remediation approaches, encompassing both in-situ and ex-situ methods employed to mitigate FQ contamination. The critical evaluation of these remediation strategies provides insights into their efficacy, limitations, and environmental implications. In this investigation, a correlation between FQ antibiotics and climate change is established, underlining its significance in addressing the Sustainable Development Goals (SDGs). The study further identifies and delineates multiple research gaps, proposing them as key areas for future investigational directions. Overall, this review aims to consolidate current knowledge on FQs in soil and groundwater, offering a valuable resource for researchers, policymakers, and practitioners engaged in environmental management and public health.

Study on mechanism of removal of sudden Tetracycline by compound modified biological sand filtration process

The removal of tetracycline from the sewage plant effluents through advanced treatment methods is key to controlling tetracycline levels in the water environment. In this study, modified quartz sands (QS) were used in a biological sand filter to remove tetracycline. The modified QS, with different surface characteristics, were prepared using glass etching technology combined with subsequent chemical modification methods, including hydroxylation treatment, metal ion modification, and amino modification. The adsorption efficiency of hydroxylated QS was higher than that of metal ion modified and amino modified QS, with adsorption efficiencies of 20.4331 mg/kg, 12.8736 mg/kg, and 10.1737 mg/kg, respectively. Results indicated that QS primarily reduce tetracycline through adsorption. Adsorption on ordinary QS fit the pseudo-first-order kinetic model, while adsorption on other modified QS and biofilm-coated QS fit the pseudo-second-order kinetics model. Biodegradation was identified as another mechanism for tetracycline reduction, which fit the zero-order kinetic model. Pseudomonas alcaligenes and unclassified Pseudomonas accounted for 96.6% of the total tetracycline-degrading bacteria. This study elucidates the effectiveness and mechanisms of five types of QS in treating tetracycline from sewage plant effluents. It provides a novel method for tetracycline reduction in real-world wastewater scenarios.

Enhanced adsorption performance of oxytetracycline in aqueous solutions by Mg-Fe modified suaeda-based magnetic biochar

Oxytetracycline (OTC) in the waste water can be removed by biochar adsorption. How to separate the biochar adsorbed antibiotics from the wastewater was also a problem. The nontoxic magnetic biochar was prepared from Suaeda biochar (800SBC) by mafic bimetal modification, and used for the removal of OTC. The results of XRD and VSM indicated that the main composition of biochar was ferrite. Then through batch adsorption experiments, the adsorption kinetics, isothermal adsorption, thermodynamics, and coexisting ion and adsorbent regeneration experiments were studied. Through the fitting of the adsorption model, it was found that Mg-Fe@800SBC(1:1) and 800SBC belonged to chemisorption. 800SBC was consistent with the Langmuir model, mainly monolayer adsorption, and Mg-Fe@800SBC(1:1) was consistent with the Freundlich model, mainly multilayer adsorption. The adsorption processes of the two materials were spontaneous, endothermic and entropic decreasing processes. The maximum adsorption capacity of the Mg-Fe@800SBC(1:1) for OTC from the Sips L-F model was 82.83 mg/g. Through various characterizations of magnetic biochar, it was found that the adsorption mechanism of the modified biochar included the hydrogen bonds between the oxygen-containing functional group of biochar and the -NH2 group of OTC, π-π EDA interaction, electrostatic attraction and complexation. Coexistence anions (CO32- and PO43-) have a negative effect on the adsorption process.

One-step synthesis of chiral molecularly imprinted polymer TiO2 nanoparticles for enantioseparation of phenylalanine in coated capillary electrochromatography

A novel chiral molecularly imprinted polymer TiO₂ nanoparticle was synthesized in one step for the enantioseparation of phenylalanine in coated capillary electrochromatography. To the author's knowledge, the chiral molecularly imprinted nanomaterials have still not been reported, to date. Chiral molecularly imprinted TiO₂ nanomaterials (L-PHE@MIP(APTES-TEOS)@TiO₂) were used as a chiral stationary phase to separate the phenylalanine enantiomers in coated capillary electrochromatography (CEC). The imprinted coating was prepared from L-phenylalanine (L-PHE) as the template, TiO₂ nanoparticles (NPs) as the support substrate, 3-aminopropyltriethoxysilane (APTES) as the functional monomer, and tetraethyl silicate (TEOS) as the cross-linker. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used for the characterization of the L-PHE@MIP(APTES-TEOS)@TiO₂@capillary. Fourier transform infrared spectra (FT-IR), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA) were employed for the characterization of the L-PHE@MIP(APTES-TEOS)@TiO₂. The effects of the applied voltage, pH value, buffer concentration, and acetonitrile content were investigated  experimentally to determine the optimum conditions for CEC. The best resolution for  phenylalanine enantiomers by CEC reached a value of 3.48. In addition, the specific recognition effect of L-PHE@MIP(APTES-TEOS)@TiO₂ on PHE enantiomers was studied by selective experiment. Finally, adsorption kinetic research, adsorption equilibrium isotherm study, and adsorption thermodynamic experiment were carried out to investigate the separation mechanism of PHE enantiomers with the L-PHE@MIP (APTES-TEOS)@TiO₂@capillary, and the results were consistent with those of CEC experiments.

Achieving tetracycline removal enhancement with granules in marine matrices: Performance, adaptation, and mechanism studies

Using the aerobic granular sludge (AGS) to improve tetracycline (TET) removal in the treatment of mariculture wastewater was investigated in the present study. The AGS rapidly adapted to and was sustained in seawater matrices with a robust granule strength (k = 0.0014) and a more stable sludge yield than the activated sludge (AS) (0.14 vs 0.11 g-VSS/g-COD_rem). The compact structure provided the AGS with an anoxic environment, which favored the growth of N (37.3 %) and P removal bacteria (30.4 %) and the expression of functional genes (nos, nor, and nar), resulting in more than 62 % TN and TP removals, respectively. Similar abundances of aromatic compound-degrading bacteria (∼34 %) in both reactors (AGS and AS) led to comparable TET biodegradation efficiencies (∼0.045 mg/g-VSS). The greater size and surface area of the AGS expanded the boundary layer diffusion region, leading to 16 % increases in the granule's TET adsorption capacity.

Extracellular polymeric substances-antibiotics interaction in activated sludge: A review

Antibiotics, the most frequently prescribed drugs, have been widely applied to prevent or cure human and veterinary diseases and have undoubtedly led to massive releases into sewer networks and wastewater treatment systems, a hotspot where the occurrence and transformation of antibiotic resistance take place. Extracellular polymeric substances (EPS), biopolymers secreted via microbial activity, play an important role in cell adhesion, nutrient retention, and toxicity resistance. However, the potential roles of sludge EPS related to the resistance and removal of antibiotics are still unclear. This work summarizes the composition and physicochemical characteristics of state-of-the-art microbial EPS, highlights the critical role of EPS in antibiotics removal, evaluates their defense performances under different antibiotics exposures, and analyzes the typical factors that could affect the sorption and biotransformation behavior of antibiotics. Next, interactions between microbial EPS and antibiotic resistance genes are analyzed. Future perspectives, especially the engineering application of microbial EPS for antibiotics toxicity detection and defense, are also emphatically stressed.

The effect of nitrification inhibitors on the aerobic biodegradation of tetracycline antibiotics in swine wastewater

The aerobic biotreatment process for the dual goals of antibiotic removal and ammonia retainment for the field-return-based treatment of swine wastewater was optimized by adding 2-chloro-6-trichloromethylpyridine (TCMP), commonly used as a nitrogen fertilizer synergist. The results show that the dosage of 5-10 mg/L TCMP daily effectively inhibited nitrification. The COD and tetracycline antibiotics (TCs) in the absence of TCMP was removed by 91% and 76%, and became 87% and 78% with 5 mg/L TCMP and 83% and 70% with 10 mg/L TCMP, respectively. The removal efficiency of four TCs generally followed a decreasing trend of chlortetracycline (CTC) > doxycycline (DC) > tetracycline (TC) > oxytetracycline (OTC). A dosage of 5 mg/L TCMP daily inhibited ammonia nitrification effectively and only slightly affected the removal of conventional organic pollutants and TCs. The contribution of volatilization and hydrolysis to the removal of TCs was negligible. The overall removal efficiency of four TCs in removal pathway experiments was 98%, 94%, 97%, and 96% for OTC, CTC, DC, and TC, of which 69%, 41%, 56%, and 62% was contributed by absorption, and 29%, 53%, 41%, and 34% was contributed by biodegradation, respectively. This study may have significant implications for the proper management of livestock wastewater intended to be used as fertilizers, which aims to reduce the exposure risk of antibiotics and preserve its nutrient value.

A critical review on retaining antibiotics in liquid digestate: Potential risk and removal technologies

Substantial levels of antibiotics remain in liquid digestate, posing a significant threat to human safety and the environment. A comprehensive assessment of residual antibiotics in liquid digestate and related removal technologies is required. To this end, this review first evaluates the potential risks of the residual antibiotics in liquid digestate by describing various anaerobic digestion processes and their half-lives in the environment. Next, emerging technologies for removing antibiotics in liquid digestate are summarized and discussed, including membrane separation, adsorption, and advanced oxidation processes. Finally, this study comprehensively and critically discusses these emerging technologies' prospects and challenges, including techno-economic feasibility and environmental impacts.

Transport of oxytetracycline through saturated porous media: role of surface chemical heterogeneity

The current state of knowledge on the transport behaviors of oxytetracycline (OTC, a typical tetracycline antibiotic) in porous media with heterogeneous chemical surfaces is inadequate. In this work, the mobility properties of OTC through saturated porous media with different chemical heterogeneities (i.e., quartz sand, montmorillonite (MMT)-, humic acid (HA)-, and goethite (Goe)-coated sands) were investigated. In comparison with the mobility of OTC in the quartz sand, HA and goethite coatings inhibited the mobility of OTC, whereas montmorillonite coating enhanced OTC mobility. HA coating inhibited the transport of OTC that stemmed from the strong interactions between HA and OTC via complexation, π-π stacking, hydrogen bonding, and hydrophobic interaction. The positively charged iron oxide coating on Goe-coated sand provided favorable sites for OTC deposition through complexation and electrostatic attraction. The enhanced transport of OTC through MMT-coated sand was mainly due to the strong electrostatic repulsion between the anionic OTC species (i.e., OTC^-) and negatively charged porous media. Solution pH (5.0-9.0) posed a negligible effect on the trend of OTC mobility in different porous media. Furthermore, Ca²⁺ inhibited the transport of OTC mobility through various porous media via cation-bridging. The findings of this work contribute significantly to our understanding of the influence of aquifer surface chemical heterogeneities on OTC mobility behaviors in the subsurface environment.

Sustainable adsorbents for the removal of pharmaceuticals from wastewater: A review

Over the previous three decades, the worldwide use of pharmaceuticals has surged by more than 2.5 times. Although being considered essential to save many lives, pharmaceuticals have also emerged as a large source of complex environmental contaminants in recent decades. Consequently, the pharmaceuticals and their breakdown products are ending up into the water bodies thus progressively contaminating them and the surrounding environments. Based on recent studies concentrations in water sources are typically >0.1 μg/l and the concentration in treated water is typically >0.05 μg/l. These pharma drugs are removed from aquatic systems by processes such as oxidation, Ultraviolet degradation, reverse osmosis and nano-filtration. However, hazardous sludge creation, incomplete removal, expensive capital and operating costs, and the need for professional operating and maintenance personnel have all limited the economic sustainability of these systems. As a result, the presence of pharmaceuticals in water necessitates even more advanced technologies of purification to harvest clean water, yet present approaches are constrained by their high costs, low reusability, and disposal issues. Here, we review sustainable adsorbents for the removal of pharmaceuticals from wastewater. In this comprehensive review, an evaluation of water contamination caused by pharmaceutical compounds is discussed. An overview of current research on the employment of sustainable adsorbents for the removal of the major pharmaceuticals prevalent in water sources. Numerous aspects of high adsorption efficiencies of these pharmaceutical compounds with such sustainable adsorbents were observed; however, other factors, such as adsorbent regeneration and cost evaluation, must be taken into account in order to assess the true applicability of adsorbents.

Removal of tetracycline by aerobic granular sludge from marine aquaculture wastewater: A molecular dynamics investigation

Although biological treatment of marine aquaculture wastewater is promising, the fundamental principles driving the adsorption of tetracycline to microbial cell membrane are not well understood. Using a combination of experiments and molecular dynamics (MD) simulations, the mechanism underlying the biological removal of tetracycline from seawater was investigated. More than 90% tetracycline removal was achieved in an aerobic granular sludge system, with degradation accounting for 30% of total removal. A model of the tetracycline-dipalmitoylphosphatidylcholine lipid bilayers was established to elucidate the transport mechanism of tetracycline from bulk solution to microorganisms' cell membrane. 62% of the driving force for tetracycline adsorption on the cell membrane originated from electrostatic attraction. The electrophilic groups on tetracycline (amino and aromatic groups) were attracted to the phosphate groups in the cell membrane. Sodium ions, which are abundant in seawater, decreased the interaction energy between tetracycline and the cell membrane.

Effects of different oxygen conditions on pollutants removal and the abundances of tetracycline resistance genes in activated sludge systems

The individual and combined effects of tetracycline (TC) and divalent copper (Cu²⁺) on the performance of activated sludge systems and the abundances of tetracycline resistance genes (TRGs) in activated sludge, under both aerobic and anaerobic conditions, were studied. Activated sludge systems received TC (0.2 mg L^-1) and Cu²⁺ (5 mg L^-1) separately or jointly under either aerobic or anaerobic conditions. The addition of TC did not affect the performance of activated sludge systems and the addition of Cu²⁺ and mixed TC/Cu²⁺ inhibited biological phosphorus removal. The TC removal efficiencies in systems under aerobic and anaerobic conditions were 98.4%-99.7% and 96.8%-99.9%, respectively, and Cu²⁺ promoted TC removal in activated sludge systems. The TC degradation product was 4-epitetracycline (ETC) in activated sludge systems under both aerobic and anaerobic conditions. The total relative abundances of TRGs (tetA, tetC, tetE, tetM, tetO, tetW, tetX and tetB(P)) in activated sludge showed opposite development trends under the two oxygen conditions and aerobic condition was beneficial to the attenuation of high-risk TRGs. The results of this study might improve evaluation of the combined effects of antibiotics and heavy metals on wastewater biological treatment systems.

The sorption of Tebuconazole and Linuron from an Aqueous Environment with a Modified Sludge-Based Biochar: Effect, Mechanisms, and Its Persistent Free Radicals Study

In this study, the sludge-based biochar was prepared and utilized as an adsorbent for the removal of two commonly used pesticides in agriculture, namely tebuconazole (Teb) and linuron (Lin) in an aqueous solution. The main contributing factors such as biochar preparation conditions, persistent free radicals as well as contact time, agitation speed, biochar dose, temperature, and pH were investigated. The physicochemical properties were characterized by SEM + EDS, FTIR, BET, EPR, etc. The results showed that the maximum adsorption capacities based on the Langmuir model was 7.8650 mg g−1 for tebuconazole and that based on Freundlich model was 9.0645 mg·g-1 for linuron at 25°C. The pseudo-second-order kinetic equations were all fitted well to the kinetic process of the adsorption of the two pesticides with all R2 ≥ 0.915. The maximum values of tebuconazole adsorption capacity occur at pH = 3. Meanwhile, linuron was not affected by pH. Both Cr6+ (r = −0.793∗∗/ −0.943∗∗) and humic acid (r = −0.798∗∗/ −0.947∗∗) significantly inhibited the adsorption amount of tebuconazole and linuron onto the biochar. Electron spin resonance signals (ESR) indicated that environmentally persistent radicals (EPFRs) are preferentially formed at lower pyrolysis temperatures and lower transition metal concentrations. The g-factors for BC400, BC600, BCF400, and BCF600 were 2.0036, 2.0035, 2.0034, and 2.0033, respectively, indicating that the EPFRs mainly have a carbon-centered structure with adjacent oxygen atoms. In addition, to close to the actual situation, natural water (from YanTai) was collected to simulate pesticide contamination. This study demonstrates that sludge-based biochar can achieve efficient removal of tebuconazole and linuron in aqueous environment in a short period of time with no secondary environmental risk especially on the waste activated sludge.

Optimization of synergistic biosorption of oxytetracycline and cadmium from binary mixtures on reed-based beads: modeling study using Brouers-Sotolongo models

The first aim of this study was to synthesize and characterize reed-based-beads (BBR), an enhanced adsorbent from Tunisian reed. The second purpose was to evaluate and optimize the BBR efficiency for the simultaneous removal of oxytetracycline (OTC) and cadmium (Cd(II)), using central composite design under response surface methodology. The third goal was to elucidate the biosorption mechanisms taking place. It was shown that under optimum conditions (4.19 g L^-1 of BBR, 165.54 μmol L^-1 of OTC, 362.16 μmol L^-1 of Cd(II), pH of 6, and 25.14-h contact time) the highest adsorption percentages (63.66% for OTC and 99.99% for Cd(II)) were obtained. It was revealed that OTC adsorption mechanism was better described by Brouers-Sotolongo fractal equation, with regression coefficient (R²) of 0.99876, and a Person's chi-square (χ²) of 0.01132. The Weibull kinetic equation better explained Cd(II) biosorption (R² = 0.99959 and χ² = 0.00194). FTIR and isotherm studies confirmed that the BBR surface was heterogeneous, and that adsorption mechanisms were better described by the Freundlich/Jovanovich equation (R² = 0.99276 and χ² = 0.04864) for OTC adsorption, and by the Brouers-Sotolongo model (R² = 0.9851 and χ² = 0.77547) for Cd(II) biosorption. Overall results indicate that, at last, the BBR lignocellulosic biocomposite beads could be considered as cost-effective and efficient adsorbent, which could be of socioeconomic and environmental relevance. Graphical abstract.

Insight into the adsorption mechanisms of ionizable imidazolinone herbicides in sediments: Kinetics, adsorption model, and influencing factors

To reveal the adsorption mechanisms of imazamox, imazapic, and imazethapyr on sediment and batch experiments were carried out in this study. The adsorption kinetics of three imidazolinone herbicides on sediment were accurately described by the pseudo-second-order kinetic model(R² > 0.9004). The values of adsorption capacity (Q_e.cal) were ranged from 0.0183 to 0.0859 mg kg^-1 for three herbicides. Adsorption equilibrium was reached within 24 h for three herbicides on sediment, and well fitted by the Freundlich model(R² > 0.9561). The K_F of values for adsorption obtained sediment samples were ranged from 0.2501 to 1.322 L^1/n mg^1-1/n kg^-1for three herbicides. These results indicated that intraparticle diffusion and external mass transport were the main rate controlling steps of the adsorption of herbicides on sediment and that the chemical adsorption was dominant during the adsorption processes. The calculated hysteresis coefficient H were 0.9422,0.7877 and 0.744 for imazmox, imazapic and imazethapyr in raw sediment, respectively, indicating that there is a hysteresis in desorption. The influences of solution pH and sediment organic carbon content on the imidazolinone herbicide adsorption behaviors were also examined. Which shown that the adsorption process for herbicides was highly pH-dependent and adsorption efficiency was closely related to the organic matter content of the sediment, suggesting that electrostatic interactions played crucial roles in the adsorption behavior between sediment and imidazolinone herbicides, and the herbicides were mostly absorbed by the amorphous materials of sediment. These research findings are important for assessing the fate and transport of imidazolinone herbicides in water-sediment systems.

Antibiotics in wastewater: From its occurrence to the biological removal by environmentally conscious technologies

In this critical review, we explored the most recent advances about the fate of antibiotics on biological wastewater treatment plants (WWTP). Although the occurrence of these pollutants in wastewater and natural streams has been investigated previously, some recent publications still expose the need to improve the detection strategies and the lack of information about their transformation products. The role of the antibiotic properties and the process operating conditions were also analyzed. The pieces of evidence in the literature associate several molecular properties to the antibiotic removal pathway, like hydrophobicity, chemical structure, and electrostatic interactions. Nonetheless, the influence of operating conditions is still unclear, and solid retention time stands out as a key factor. Additionally, the efficiencies and pathways of antibiotic removals on conventional (activated sludge, membrane bioreactor, anaerobic digestion, and nitrogen removal) and emerging bioprocesses (bioelectrochemical systems, fungi, and enzymes) were assessed, and our concern about potential research gaps was raised. The combination of different bioprocess can efficiently mitigate the impacts generated by these pollutants. Thus, to plan and design a process to remove and mineralize antibiotics from wastewater, all aspects must be addressed, the pollutant and process characteristics and how it is the best way to operate it to reduce the impact of antibiotics in the environment.

Synthesis and Characterization of Novel Hybridized CeO2@SiO2 Nanoparticles Based on Rice Husk and Their Application in Antibiotic Removal

This work aims to synthesize a core-shell material of CeO₂@SiO₂ based on rice husk as a novel hybridized adsorbent for antibiotic removal. The phase structures of CeO₂@SiO₂ and CeO₂ nanoparticles that were fabricated by a simple procedure were examined by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared (FT-IR) spectroscopy, while their interfacial characterizations were performed by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), the Brunauer-Emmett-Teller (BET) method, and ζ-potential measurements. The removal efficiency of the antibiotic amoxicillin (AMX) using CeO₂@SiO₂ nanoparticles was much greater than that using SiO₂ and CeO₂ materials in solutions of different pH values. The optimum conditions for AMX removal using CeO₂@SiO₂ including contact time and adsorbent dosage were 120 min and 5 mg/mL, respectively. The maximum AMX removal using CeO₂@SiO₂ reached 100% and the adsorption capacity was 12.5 mg/g. Adsorption isotherms of AMX onto CeO₂@SiO₂ were fitted by Langmuir, Freundlich, and two-step adsorption models, while the adsorption kinetics of AMX achieved a better fit by the pseudo-second-order model than the pseudo-first-order model. The electrostatic and nonelectrostatic interactions between the zwitterionic form of AMX and the positively charged CeO₂@SiO₂ surface were controlled by adsorption. The effects of different organics such as humic acid, ionic surfactants, and pharmaceutical substances on AMX removal using CeO₂@SiO₂ were also thoroughly investigated. The high AMX removal efficiencies of about 75% after four regenerations and about 70% from an actual water sample demonstrate that CeO₂@SiO₂-based rice husk is a hybrid nanomaterial for antibiotic removal from water environments.

Interaction between tetracycline and microorganisms during wastewater treatment: A review

Tetracycline (TC) is a commonly used human and veterinary antibiotic that is mostly discharged into wastewater in the form of the parent compounds. At present, wastewater treatment plants (WWTPs) use activated sludge processes that are not specifically designed to remove such pollutants. Considering the biological toxicity of TC in aquatic environment, the migration and fate of TC in the process of wastewater treatment deserve attention. This paper reviews the influence of TC on the functional bacteria in the sludge matrix and the development of tetracycline-resistant genes, and also discusses their adsorption removal rates, their adsorption kinetics and adsorption isotherm models, and infers their adsorption mechanism. In addition, the biodegradation of TC in the process of biological treatment is reviewed. Co-metabolism and the role of dominant bacteria in the degradation process are described, along with the formation of degradation byproducts and their toxicity. Furthermore, the current popular integrated coupling-system for TC degradation is also introduced. This paper systematically introduces the interaction between TC and activated sludge in WWTPs. The review concludes by providing directions to address research and knowledge gaps in TC removal from wastewater.

Fabrication of the magnetic mesoporous silica Fe-MCM-41-A as efficient adsorbent: performance, kinetics and mechanism

Antibiotics are emerging pollutants and increasingly present in aquaculture and industrial wastewater. Due to their impact on the environment and health, their removal has recently become a significant concern. In this investigation, we synthesized nano zero-valent iron-loaded magnetic mesoporous silica (Fe-MCM-41-A) via precipitation and applied the adsorption of oxytetracycline (OTC) from an aqueous solution. The effects of competing ions such as Na⁺, Ca²⁺ and Cu²⁺ on the adsorption process under different pH conditions were studied in depth to providing a theoretical basis for the application of nanomaterials. The characterization of the obtained material through transmission electron microscopy demonstrates that the adsorbent possesses hexagonal channels, which facilitate mass transfer during adsorption. The loaded zero-valent iron made the magnetic, and was thus separated under an applied magnetic field. The adsorption of OTC onto Fe-MCM-41-A is rapid and obeys the pseudo-second-order kinetic model, and the maximum adsorption capacity of OTC is 625.90 mg g^-1. The reaction between OTC and Fe-MCM-41-A was inner complexation and was less affected by the Na⁺. The effect of Ca²⁺ on the adsorption was small under acidic and neutral conditions. However, the promotion effect of Ca²⁺ increased by the increase of pH. Cu²⁺ decreased the removal efficiencies continuously and the inhibitory effects decrease varied with the increase of pH. We propose that surface complexing, ion-exchange, cationic π-bonding, hydrogen bonding, and hydrophobicity are responsible for the adsorption of OTC onto Fe-MCM-41-A.

Multiple roles of Ca2+ in the interaction of ciprofloxacin with activated sludge: Spectroscopic investigations of extracellular polymeric substances

Calcium ion is an important cation influencing the binding of recalcitrant organic contaminants with activated sludge during wastewater treatment process, but there is still unknown about its role in amphoteric fluoroquinolones binding. Binding experiments show that Ca²⁺ markedly inhibited binding of ciprofloxacin (CIP) onto sludge, causing 7-203 times of CIP release. Multi-spectroscopic examinations indicate that tryptophan-like and tyrosine-like proteins in extracellular polymeric substances (EPS) were dominant components for CIP binding by static quenching and forming CIP-proteins complexes. Addition of Ca²⁺ into EPS and CIP binding systems induced increase of association constants (from 0.024-0.064 to 0.027-0.084 L/μmol) and binding constants (from 0.002-0.039 to 0.012-0.107) and decrease of binding sites number (from 0.893-2.007 to 0.721-1.386). Functional groups of EPS and secondary structure of proteins were remarkably changed upon reactions with CIP and Ca²⁺. Calcium ion interacted with EPS and CIP binding system in two distinct ways: Ca²⁺ shielded CO in amide I in EPS for CIP binding, whereas strengthened binding between CIP and functional groups including CO in carboxyl groups in extra-microcolony polymers and OH in extra-cellular polymers by forming ternary complexes. Cation competition for CO in amide I is responsible for Ca²⁺ induced CIP release from the sludge. Results suggest the highly potential release of CIP from high saline wastewater and cation-conditioned sludge which needs further monitoring and evaluation.

Effect of sulfamethoxazole and oxytetracycline on enhanced biological phosphorus removal and bacterial community structure

The individual and combined effects of sulfamethoxazole (SMX) and oxytetracycline (OTC) on an enhanced biological phosphorus removal (EBPR) system was investigated. OTC at 5 mg/L resulted in filamentous bulking with a collapse of EBPR system. P removal decreased to 44.8% and COD was mostly removed during the aerobic phase. SMX and OTC had antagonistic effects in EBPR system. The inhibitory effect of SMX and SMX + OTC on P removal, COD removal, glycogen transformation and extracellular polymeric substances content was reversible with prolonged operation, accompanied with increase of polyphosphate accumulating organisms. The presence of nitrification inhibitor allylthiourea, high pH and low tetX abundance limited the removal of SMX and OTC. The bacterial community structure, antibiotic resistance genes abundances and genes functions were also investigated by metagenomic analysis. The results of this study offer insights into the individual and combined environmental risks of SMX and OTC, and their impact on EBPR.

Interrelationships between tetracyclines and nitrogen cycling processes mediated by microorganisms: A review

Due to their broad-spectrum antibacterial activity and low cost, tetracyclines (TCs) are a class of antibiotics widely used for human and veterinary medical purposes and as a growth-promoting agent for aquaculture. Interrelationships between TCs and nitrogen cycling have attracted scientific attention due to the complicated processes mediated by microorganisms. TCs negatively impact the nitrogen cycling; however, simultaneous degradation of TCs during nitrogen cycling mediated by microorganisms can be achieved. This review encapsulates the background and distribution of TCs in the environment. Additionally, the main nitrogen cycling process mediated by microorganisms were retrospectively examined. Furthermore, effects of TCs on the nitrogen cycling processes, namely nitrification, denitrification, and anammox, have been summarized. Finally, the pathway and microbial mechanism of degradation of TCs accompanied by nitrogen cycling processes were reviewed, along with the scope for prospective studies.

Removal of Tetracycline from Aqueous Solution Using Nanocomposite Based on Polyanion-Modified Laterite Material

This work investigated the removal of antibiotic tetracycline (TC) from wastewater using nanocomposite material based on laterite modified with polyanion, polystyrene sulfonate (PSS). The effective factors influenced on the TC removal using nanocomposite PSS-modified laterite (NCPML) were optimized and found to be pH 4, solid-liquid ratio 5 mg/mL, and contact time 180 min. The highest removal of TC reached about 88% under the optimum adsorption conditions. The adsorption isotherm and kinetics of TC adsorption onto NCPML were in good agreement with the Langmuir and pseudo-second-order models, respectively. The characteristics of the NCPML material before and after TC adsorption were examined by zeta (ζ) potential measurements, Brunauer-Emmett-Teller (BET) method, and Fourier transform infrared spectroscopy (FT-IR). The TC adsorption onto NCPML was induced by electrostatic interaction, hydrogen bonding, and diffusion interaction. The TC removal from wastewater was approximately 94% while efficiency still reached 66% after five regenerations. Our research reveals that NCPML is a high-performance adsorbent for TC removal from wastewater.

Facile Fabrication of Flocculent Magnesium Silicate for the Adsorption of Oxytetracycline

The discharge of antibiotics and the potential threat to organisms posed by this have received increasing attention. In this work, flocculent magnesium silicate (FMS) was fabricated by a facile hydrothermal and freeze-drying process, and its adsorption behavior for antibiotic oxytetracycline (OTC) was investigated. FMS presented a sepiolite-type structure and the alkaline solution promoted its hydroxylation. A hierarchical pore structure ranging from micropores to macropores and a high specific surface area of 660 m2/g were exhibited. FMS exhibited a higher adsorption amount in neutral solution than in acidic or alkaline conditions as the physicochemical properties of FMS and OTC were significantly affected by the pH. Adsorption isotherm could be well-described by the Langmuir model, and the calculated saturated adsorption capacity was as high as 265 mg/g. Adsorption kinetics followed the pseudo-second-order kinetic model, and the adsorption rate-controlling step was intraparticle diffusion. Thermodynamic parameters indicated that the adsorption was a spontaneous physicochemical reaction. After five cycles, around 91% of the adsorption performance was still maintained, demonstrating the excellent reusability of FMS. The sepiolite-type FMS fabricated in this work could be applied to remove OTC from wastewater.

Upcycling of Fe-bearing sludge: preparation of erdite-bearing particles for treating pharmaceutical manufacture wastewater

Groundwater treatment sludge is a type of solid waste with 9.0-28.9% wt.% Fe content and is precipitated in large quantity from backwash wastewater in groundwater treatment. The sludge is mainly composed of fine particles containing Fe, Si and Al oxides, such as ferrihydrite, quartz and boehmite. The Fe oxides mostly originate from the oxidation of ferrous Fe in groundwater, whilst the silicate/aluminium compounds mainly originate from the broken quartz sand filter in the backwash step. In general, the sludge is firstly coagulated, dewatered by filter pressing and finally undergoes harmless solidification before it is sent to landfills. However, this process is costly (approximately US$66.1/t) and complicated. In this study, groundwater treatment sludge was effectively recycled to prepare novel erdite-bearing particles via a one-step hydrothermal method by adding only Na2S·9H2O. After hydrothermal treatment, the quartz and boehmite of the sludge were dissolved and recrystallised to sodalite, whilst ferrihydrite was converted to an erdite nanorod at 160 °C and a hematite at 240 °C. SP160 was prepared as fine nanorod particles with 200 nm diameter and 2-5 μm length at a hydrothermal temperature of 160 °C. Nearly 100% OTC and its derivatives in pharmaceutical manufacture wastewater were removed by adding 0.1 g SP160. The major mechanism for the removal was the spontaneous hydrolysis of erdite in SP160 to generate Fe oxyhydroxide and use many hydroxyl groups for coordinating OTC and its derivatives. This study presents a novel method for the resource reutilisation of waste groundwater treatment sludge and reports efficient erdite-bearing particles for pharmaceutical manufacture wastewater treatment.

Preparation of pyramidal SnO/CeO2 nano-heterojunctions with enhanced photocatalytic activity for degradation of tetracycline

Pyramidal SnO/CeO₂ nano-heterojunction photocatalysts were successfully synthesized via a facile hydrothermal method. The structural characterization was investigated by using common characterization tools. The content of SnO affected the morphology and photocatalytic performance of the SnO/CeO₂ nano-heterojunctions. With the increase of the SnO content, the morphology of the samples changed from a spherical structure to a pyramidal structure. The photocurrent of the SnO/CeO₂ (1:6) sample was about 36 times that of pure CeO₂. With SnO/CeO₂ (1:6) as the photocatalyst, the degradation rate of tetracycline (TC) was 99% within 140 min under visible light and after five cyclic tests the photocatalytic efficiency of TC remained at 98%, which suggests that the SnO/CeO₂ (1:6) nano-heterojunction had a high photocatalytic efficiency and stable photocatalytic performance. These results indicate that SnO/CeO₂ (1:6) nano-heterojunction possesses broad prospects for industrial application.

Toxicity of tetracycline and its transformation products to a phosphorus removing Shewanella strain

Tetracycline (TC) as an emerging contaminant has raised serious concerns about its toxicity and removal in wastewater treatment processes. The more toxic transformation products of TC, 4-epitetracycline (ETC), anhydrotetracycline (ATC) and 4-epianhydrotetracycline (EATC) are also widely detected. This study investigated the antibacterial and bactericidal activity of TC, ETC, ATC, EATC against Shewanella sp, using Escherichia coli and Pseudomonas aeruginosa strains as quality controls. Further, batch assays were conducted to investigate the inhibition of these antibiotics on the phosphorus removal of the Shewanella strain, and removal mechanisms of TC and its transformation products (TCs). The inhibition on phosphorus removal by the Shewanella strain at 20 mg L^-1 was in the order of ATC > EATC > TC > ETC. COD removal, poly-P accumulation and glycogen synthesis by the Shewanella strain were also inhibited. Biodegradation was the main removal mechanism of TC and ETC, while adsorption was the main one of ATC and EATC. This study helps to further understand the structure-activity relationship of TC.

The removal of tetracycline, oxytetracycline, and chlortetracycline by manganese oxide-doped copper oxide: the behaviors and insights of Cu-Mn combination for enhancing antibiotics removal

Adsorption process is suitable to the advanced treatment of tetracycline antibiotics (TCs; including tetracycline (TTC), oxytetracycline (OTC), and chlortetracycline (CTC)) in poultry wastewater. In this research, Mn oxide-doped Cu oxide (MODCO) was synthesized and used for the removal of TTC, OTC, and CTC. According to the XRD and SEM analysis results, MODCO has an amorphous crystal structure and is formed by the aggregation of nano-sized particles with a uniform distribution of Cu and Mn elements. In addition, MODCO has a BET surface area of 67.7 m²/g and a pH_IEP value of 7.8. The results of batch experiments illustrated that the reaction rates for the removal of three TCs were in the order of OTC > CTC > TTC. In addition, the theoretical maximum amounts of TTC, OTC, and CTC adsorbed on MODCO were determined to be 2.90 mmol/g, 4.15 mmol/g, and 2.20 mmol/g via the Langmuir model, respectively. The optimal removal performances of TCs were achieved in the pH range of 6~9, and the coexistence of anions posed an unnoticeable effect on the removal efficiencies. The spectroscopic analysis results demonstrated that the removal mechanism of TCs was mainly attributed to surface complexation. Furthermore, a part of TCs may be decomposed by Mn oxides during the removal process according to the UV spectrogram results. Overall, MODCO has exhibited a great potential for the removal of TCs from aqueous solution.

Micro-interfacial mechanisms on sludge dewaterability enhancement using cerium chloride for preparation of carbon-based functional material

In this work, sludge conditioning efficiency of cerium chloride (CeCl₃) in combination with organic polymers was evaluated, the floc microstructure and extracellular polymeric substances (EPS) properties under flocculation conditioning were analyzed. The interaction mechanisms between EPS and Ce(III) were systematically investigated through two-dimension correlation spectroscopy, X-ray photoelectron spectroscopy, and confocal laser scanning microscopy. In addition, the adsorption and catalytic abilities of Ce-sludge based carbon (SBC) in tetracycline (TC) removal were evaluated. The results showed that CeCl₃ conditioning performed well in improving sludge dewaterability, and CeCl₃ and cationic polyacrylamide showed a synergistic effect in sludge conditioning. Contents of EPS decreased as the dosage of CeCl₃ increased because of charge neutralization and complexation reactions. 2D-UV-FTIR heterospectral correlation spectroscopy analysis suggested the reaction activity of EPS to Ce(III) followed the order of humic acid > protein > polysaccharide. The decrease of α-helix content improved the hydrophobicity of proteins in EPS, which was responsible for sludge dewaterability improvement in CeCl₃ conditioning. Besides, the SBC was prepared with CeCl₃ conditioned sludge for treating water containing TC. Ce-SBC had a dual function of adsorption and Fenton-like activity. This work provides a sludge recycling process that coupled chemical conditioning to pyrolysis carbonization to prepare functional carbon-based materials.

Amino-functionalized mesoporous silica-magnetic graphene oxide nanocomposites as water-dispersible adsorbents for the removal of the oxytetracycline antibiotic from aqueous solutions: adsorption performance, effects of coexisting ions, and natural organic matter

The amino-functionalized mesoporous silica-magnetic graphene oxide nanocomposite (A-mGO-Si) was synthesized and used for oxytetracycline (OTC) removal from water. Various factors like the effects of initial concentration, contact time, and influence of pH were investigated. Selective adsorption experiments in connection with coexisting ions and dissolved organic matter (DOM) were also investigated. In this study, humic acid (HA) and tannic acid (TA) were representative of both hydrophobic and hydrophilic DOM, respectively. Results indicated that A-mGO-Si had an adsorption ability for OTC that was relatively greater than that of virgin magnetic graphene oxide (mGO), graphene oxide (GO), Fe₃O₄ particles, and SBA-15 mesoporous silica and also showed a better uptake removal capacity for OTC at low initial concentration in comparison with the other adsorbents. The adsorption behavior of OTC onto A-mGO-Si could be described by the pseudo-second-order kinetic model and the Freundlich isotherm model. The electrostatic interaction has no influence on the OTC absorbed when the OTC is in an aqueous medium in its zwitterion form (3.22 < pH < 7.46). At high pH, the weak π-π EDA interactions and hydrogen bonding may manifest themselves, hence causing a lower adsorption capacity. The main adsorption mechanisms were plausibly activated by H-bonding, and π-π EDA interactions, while the electrostatic interaction (cation-π interaction) might be the minor adsorption mechanism. Addition of individually exogenous ions (Na⁺, Mg²⁺, NO^-, and CO₃^2-) resulted in a decrease of OTC adsorption due to the emergence of a competitive effect. Considering the presence of HA and TA in mixed solute systems, the DOM was likely to form a stronger interaction system with mGO-Si, thereby resulting in an adsorption level which was more competitive in the process at low aqueous phase concentration of OTC. In contrast to the high aqueous phase, the coexistence of DOM could promote OTC adsorption. The phenomenon may reflect the result that a surface complexation mechanism could achieve in adsorptions.

Preparation of polyglycerol mediated superparamagnetic graphene oxide nanocomposite and evaluation of its adsorption properties on tetracycline

In this paper, we synthesized a polyglycerol(PG)-mediated superparamagnetic graphene oxide nanocomposite called MGON, consisting of PG-modified superparamagnetic iron oxide nanoparticles (SPION) covalently bonded to PG-functionalized graphene oxide (GO). MGON exhibits better dispersibility and colloidal stability in aqueous solution than the magnetic graphene oxide reported in the literature. The physicochemical properties of MGON were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and UV-vis spectroscopy. Applied to the adsorption of tetracycline (TC) in aqueous solution as an adsorbent, the MGON showed excellent adsorption performance with the maximum adsorption capacity of 684.93 mg/g at 298 K. Adsorption kinetics and isotherm results indicate that the adsorption process conforms to the pseudo-second-order kinetics and Langmuir isotherm models. Adsorption thermodynamics has confirmed that the adsorption process of TC on MGON is spontaneous and endothermic. With the increase of temperature, the adsorption capacity of MGON increases continuously, and the adsorption capacity of MGON is the largest when the pH value is 7. Furthermore, the π-π and cation-π interaction, amidation reaction, and hydrogen bonding can be used to explain the adsorption mechanism of TC on MGON. Desorption and regeneration experiments showed that MGON still had 67.65% regenerative performance after five cycles. Hence, MGON is a promising adsorbent in the removal of tetracycline from wastewater.

Mechanism of oxytetracycline removal by aerobic granular sludge in SBR

In this study, oxytetracycline (OTC) as a target pollutant in swine wastewater was removed by aerobic granular sludge (AGS). The removal rate of 300 μg/L OTC in aerobic granular sludge sequencing batch reactor (AGSBR) increased to 88.00% in 33 days and maintained stable. The chemical oxygen demand (COD), ammonium nitrogen (NH₄⁺-N) and total phosphorus (TP) in wastewater were also efficiently removed. The removal of OTC mainly depended on the adsorption and biodegradation of AGS, and the biodegradation was increased obviously after AGS adaptation to OTC. The degradation products of OTC were analyzed by mass spectrometry. The analysis of metagenome sequencing revealed that the enzymes, such as glycosyl transferases (GTs), polysaccharide lyases (PLs) and auxiliary activities (AAs), may play an important role in the removal of OTC. The Lefse analysis showed that the Flavobacteriia, Flavobacteriales, Cryomorphaceae and Fluviicola were four kinds of microbes with significant difference in OTC feed reactor, which are considered to be drug-resistant bacteria in AGSBR. Furthermore, the dynamics of microbial community changed significantly at three levels, including the enrichment of drug-resistant microorganisms and the microorganisms that gradually reduced or even disappeared under the pressure of OTC.

Insights into the Fate and Removal of Antibiotics in Engineered Biological Treatment Systems: A Critical Review

Antibiotics, the most frequently prescribed drugs of modern medicine, are extensively used for both human and veterinary applications. Antibiotics from different wastewater sources (e.g., municipal, hospitals, animal production, and pharmaceutical industries) ultimately are discharged into wastewater treatment plants. Sorption and biodegradation are the two major removal pathways of antibiotics during biological wastewater treatment processes. This review provides the fundamental insights into sorption mechanisms and biodegradation pathways of different classes of antibiotics with diverse physical-chemical attributes. Important factors affecting sorption and biodegradation behavior of antibiotics are also highlighted. Furthermore, this review also sheds light on the critical role of extracellular polymeric substances on antibiotics adsorption and their removal in engineered biological wastewater treatment systems. Despite major advancements, engineered biological wastewater treatment systems are only moderately effective (48-77%) in the removal of antibiotics. In this review, we systematically summarize the behavior and removal of different antibiotics in various biological treatment systems with discussion on their removal efficiency, removal mechanisms, critical bioreactor operating conditions affecting antibiotics removal, and recent innovative advancements. Besides, relevant background information including antibiotics classification, physical-chemical properties, and their occurrence in the environment from different sources is also briefly covered. This review aims to advance our understanding of the fate of various classes of antibiotics in engineered biological wastewater treatment systems and outlines future research directions.

Treatment of a simulated sludge by ultrasonic zero-valent iron/EDTA/Air process: Interferences of inorganic salts in polyaromatic hydrocarbon removal

Understanding the occurrence states of persistent organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) in textile dyeing sludge is the key to their further treatment and disposal. Here, the effects of inorganic salts (silicate, sulfate, phosphate, hydroxide, and iron salts) that were typically rich in textile dyeing sludge on PAH adsorption by sludge and PAH degradation by an ultrasound (US) combined zero-valent iron/EDTA/Air (ZEA) system were studied in a simulated sludge system. The results showed that the simulated sludge containing inorganic salts had a larger specific surface area, which was beneficial for the adsorption of PAHs. More low-ring PAHs were adsorbed on the surface of the particles in the simulated sludge because of the inorganic salts, which was conducive to low-ring PAHs degradation by US/ZEA. The PAH removal rates were increased by 15.37% and 11.19%, respectively, in the presence of SiO₃^2- and HPO₄^2-. The yield of hydroxyl radicals (OH) was increased by 42.39% and 66.25% by SiO₃^2- and HPO₄^2-, respectively. The reason was that the oxidation of the ligand ([Fe^Ⅱ(EDTA)]) formed by ethylenediaminetetraacetic acid (EDTA) and divalent iron was promoted by SiO₃^2- and HPO₄^2-. The formation of OH in the US/ZEA system was inhibited by the corrosion inhibition of SO₄^2- on zero-valent iron (ZVI), the reaction of ferric salt with EDTA, and the reaction of Mg(OH)₂ with the ligand ([Fe^III(EDTA)]). This work provides an essential theoretical insight into the role of the inorganic components of sludge in the removal of PAHs by advanced oxidation processes.

Phosphate affects adsorption and desorption of oxytetracycline in the seawater-sediment systems

The fate and transport of antibiotics in the aquatic environment are usually influenced by the combined effects of environmental factors. In this study, batch-type experiments were conducted to investigate the combined effects of phosphate and salinity on oxytetracycline (OTC) adsorption on, and desorption from, two marine sediments. Pseudo-second-order kinetic model fitted the kinetic data better than pseudo-first-order model. The pseudo-second-order kinetic rate (k₂) of OTC increased significantly with increasing phosphate concentrations. Sorption isotherms of OTC can be well described by both the Langmuir and Freundlich models. Compared with the control experiments (without phosphate addition), Freundlich distribution coefficients (K_F) after addition of 50 mg L^-1 phosphate decreased from 24.9 to 17.9 L kg^-1 on sediments collected from Laizhou Bay, and from 52.2 to 31.3 L kg^-1 on sediments collected from Bohai Bay, which indicated that phosphate could inhibit adsorption of OTC on marine sediments. Furthermore, phosphate had a stronger inhibitory effect on OTC adsorption at low salinity level than at high salinity level. The effects of phosphate on OTC adsorption can be explained by ion exchange, change of sediment surface charge, and electrostatic repulsion mechanisms. Desorption experiments showed that phosphate can enhance the total desorption percentage of OTC from marine sediments. Overall, the presence of phosphate in marine system may enhance OTC's long-term transport.

The Presence of Cu Facilitates Adsorption of Tetracycline (TC) onto Water Hyacinth Roots

Batch experiments were conducted to investigate the adsorption characteristics of tetracycline (TC), and the interactive effects of copper (Cu) on the adsorption of TC onto water hyacinth roots. TC removal efficiency by water hyacinth roots was ranging from 58.9% to 84.6%, for virgin TC, 1:1 TC-Cu and 1:2 TC-Cu. The Freundlich isotherm model and the pseudo-second-order kinetic model fitted the adsorption data well. Thermodynamics parameters ΔG⁰ for TC were more negative in the TC plus Cu than the TC-only treatments, indicating the spontaneity of TC adsorption increased with increasing of Cu concentrations. An elevated temperature was associated with increasing adsorption of TC by water hyacinth roots. The additions of Cu(II) significantly increased TC adsorption onto water hyacinth roots within the pH range 4 to 6, because copper formed a strong metal bridge between root surface and TC molecule, facilitating the adsorption of TC by roots. However, Cu(II) hindered TC adsorption onto water hyacinth roots on the whole at pH range from 6⁻10, since the stronger electrostatic repulsion and formation of CuOH⁺ and Cu(OH)₂. Therefore, the interaction between Cu(II) and TC under different environmental conditions should be taken into account to understand the environmental behavior, fate, and ecotoxicity of TC.