Removal of tetracycline from an aqueous solution using manganese dioxide modified biochar derived from Chinese herbal medicine residues

Unlocking the potential of Chinese herbal medicine residue-derived biochar as an efficient adsorbent for high-performance tetracycline removal

This study employed hydrothermal carbonization (HTC) in conjunction with ZnCl2 activation and pyrolysis to produce biochar from one traditional Chinese medicine astragali radix (AR) residue. The resultant biochar was evaluated as a sustainable adsorbent for tetracycline (TC) elimination from water. The adsorption performance of TC on two micropore-rich AR biochars, AR@ZnCl2 (1370 m2 g-1) and HAR@ZnCl2 (1896 m2 g-1), was comprehensively evaluated using adsorption isotherms, kinetics, and thermodynamics. By virtue of pore diffusion, π-π interaction, electrostatic attraction, and hydrogen bonding, the prepared AR biochar showed exceptional adsorption properties for TC. Notably, the maximum adsorption capacity (930.3 mg g-1) of TC on HAR@ZnCl2 can be achieved when the adsorbent dosage is 0.5 g L-1 and C0 is 500 mg L-1 at 323 K. The TC adsorption on HAR@ZnCl2 took place spontaneously. Furthermore, the impact of competitive ions behavior is insignificant when coexisting ion concentrations fall within the 10-100 mg L-1 range. Additionally, the produced biochar illustrated good economic benefits, with a payback of 701 $ t-1. More importantly, even after ten cycles, HAR@ZnCl2 still presented great TC removal efficiency (above 77%), suggesting a good application prosperity. In summary, the effectiveness and sustainability of AR biochar, a biowaste-derived product, were demonstrated in its ability to remove antibiotics from water, showing great potential in wastewater treatment application.

Insights into levofloxacin adsorption with machine learning models using nano-composite hydrochars

Hydrothermal carbonization was applied to taro peel wastes to produce hydrochars using a facile and environmentally friendly process. Four different entities were prepared: hydrochar (TPh), phosphoric-activated hydrochar (P-TPh), and silver@hydrochars (Ag@TPh, Ag@P-TPh). The elemental compositions of the single and composite hydrochars were confirmed by EDX. Among the produced hydrochars, the morphology of the Ag@hydrochar composites demonstrated more wrinkled structure, and Ag nanoparticles decorated the surface. The optimal experimental conditions for levofloxacin adsorption were determined to be a contact time of 45 min, hydrochar dose of 0.15 g L-1, and pH of 7. The best adsorption performances were assigned to Ag@hydrochars. Two machine learning models were applied to predict the levofloxacin adsorption efficiency of the Ag@hydrochars. A central composite design (CCD) and a 3-10-1 artificial neural network (ANN) model were developed to estimate the removal performance of levofloxacin using Levenberg-Marquardt backpropagation algorithm based on correlation and error analysis of the adopted training functions. Furthermore, the ANN sensitivity analysis revealed the order of the relative importance variable as initial concentration> hydrochar dose> pH. The predicted values of the CCD and ANN models fitted the experimental results with R2> 0.989. Therefore, the applied models were effective in predicting levofloxacin removal under different operating conditions. This work provides an open option for the sustainable management of food industry wastes and the possibility of waste valorization to effective hydrochar composites to be applied in water treatment processes.

Investigating the different transformations of tetracycline using birnessite under different reaction conditions and various humic acids

Prior studies have successfully used manganese oxides to facilitate the transformation of tetracycline in aqueous solution. To further understand the kinetic and the transformation pathway of tetracycline via birnessite (δ-MnO2) under different conditions, experiments were conducted at pH levels of 3, 6, and 9 in the presence or absence of Aldrich humic acid (ADHA). Tetracycline removal followed the pseudo-second-order reaction model in all investigated cases, and the removal efficiency (g mg-1 h -1) followed the following trend: pH 3 (0.45/0.27) > pH 6 (0.036/0.087) > pH 9 (0.036/0.103) in the absence/presence of ADHA. Liquid chromatography-mass spectrometry/mass spectrometry results identified five main transformation products at m/z 495, 477, 493, 459, and 415, produced by the transformation reactions, including hydration, oxidation, desaturation, and oxy reduction. Notably, in the presence of ADHA at pH 3, products with higher toxicity secondary (m/z 477 and 495) were reduced, while less toxicity products (m/z 459 and 415) were enhanced. The experiments utilizing tetracycline and δ-MnO2 with varied humic acids (HA) revealed that HA with high polar organic carbon groups, such as O-alkyl, exhibited higher removal efficiency at pH 6. This research offers the first comprehensive insights into the pathway transformations of tetracycline via δ-MnO2 under different pH conditions and HA types. For further understanding, future work should investigate the binding of HA, TTC, and/or Mn2+ and the oxidation capacity of MnO2 after the reaction to clarify Mn2+ elution mechanisms.

Manganese oxide-loaded activated carbon for ammonium removal from wastewater: the roles of adsorption and oxidation

The urgent need to address the severe issue of nitrogen pollution has prompted the search for a functional and easy recycling material. In this study, manganese oxides (MnOx) were loaded on activated carbon (AC), resulting in a composite known as AC-MnOx, for efficient ammonium removal from aqueous solutions. The results indicated a remarkable 15.6-fold increase in ammonium removal efficiency and a fivefold enhancement in removal capacity for AC-MnOx (3.20 mg/g) compared to AC. Under specific conditions (initial NH4+-N concentration of 15 mg/L, adsorbent dose of 2.5 g, pH of 6.5, and temperature of 35 ℃), the highest achieved ammonium removal efficiency reached 94.6%. Furthermore, the study distinguishes the contributions of catalytic oxidation and adsorption in the removal process. The adsorption process was effectively modeled using pseudo-second-order kinetics and Langmuir isotherm models. Interestingly, the amount of oxidation conversion (Ntur) exhibited a linear relationship with the dosage when the initial ammonium concentration was sufficiently high, while the relationship between initial ammonium concentration and the ratio of Ntur to adsorption capacity (Nsur) followed a negative exponential trend. The removal mechanisms involved electrostatic interaction between ammonium and the negatively charged dehydrogenated hydroxyl groups (- OHsur) or cation tunnel in crystal structures of MnOx, ion exchange adsorption, and the oxidation impact of MnOx. This research provides valuable insights into the application of immobilized MnOx media for ammonium removal. Moreover, filling AC-MnOx into constructed wetlands (CW) proved to be an effective method for reducing ammonium pollution, demonstrating its potential in the field of engineering wastewater treatment.

Enhanced adsorption of Congo red from urea/calcium chloride co-modified biochar: Performance, mechanisms and toxicity assessment

Adsorbents with excellent physicochemical properties and green synthetic routes are desired for efficient removal of Congo red (CR) wastewater. Hence, a novel approach was proposed within this work. Biochar NCBC obtained from Medulla Tetrapanacis was synthesized through co-modification with urea/calcium chloride. NCBC exhibited an enormous surface area (750.09 m2/g) and a micro-mesoporous composite structure. Higher nitrogen content was detected on the surface of NCBC (8.17%) compared to that of urea directly modified biochar (4.63%). Nitrogen observed on the surface of NCBC was presented as graphitic N, pyrrolic N, amine N as well as pyridinic N. Kinetic and isothermal investigations revealed the active sites on NCBC to be homogeneous and bind to CR mainly by chemisorption. Calculated maximum sorption of CR on NCBC was 2512.82 mg/g basing on Langmuir model. Moreover, the practicality of NCBC was further proved by the cultivation of Nelumbo nucifera Gaertn. and Penicillium.

Mn-modified biochars for efficient adsorption and degradation of cephalexin: Insight into the enhanced redox reactivity

Mn-modified biochars (BCs) were developed by pre-treatment of feedstock (MBCs) or post-modification of biochar (BCM), for simultaneous adsorption and degradation of a model pollutant, cephalexin. The apparent removal rates of cephalexin in the presence of MBCs (2.49 - 6.39 × 10-2 h-1) and BCM (13.3 × 10-3 h-1) were significantly higher than that in the presence of biochar prepared under similar conditions (4.2 × 10-3 h-1). While the •OH generated from the activation of dissolved O2 by the persistent free radicals (PFRs) and phenolic -OH on BC could cause degradation of cephalexin, its removal was drastically enhanced through direct oxidation by the MnOx and related Mn species on Mn-modified BCs. The removal of cephalexin by MBCs decreased as the solution pH was raised from 5.0 to 9.0, which supports the critical role played by Mn3O4 in its oxidation. Removal of cephalexin in the presence of MBCs and Mn3O4 was enhanced with the introduction of Mn(II) ions, suggesting that the Mn3O4 present on MBCs facilitates the re-oxidation of Mn(II) to highly reactive Mn(III). While MnO2 anchored on BCM also enhanced the cephalexin oxidation, the active sites of BC and MnO2 were partially destroyed during post-modification of BC, compromising the redox cycling of Mn(II)/Mn(III) and the generation of •OH. As a result, the performance of BCM in oxidizing cephalexin was inferior to that of MBCs. These findings shed new light on the development of environmentally benign sorbents capable of simultaneously adsorbing and oxidizing organic pollutants.

Antimony(III) removal by biogenic manganese oxides formed by Pseudomonas aeruginosa PA-1: kinetics and mechanisms

In this study, Pseudomonas aeruginosa PA-1, a manganese-oxidizing bacterium screened from the soil at a manganese mining area, was found to be tolerated to Sb(III) stress during the Mn(II) oxidation, and the generated biological manganese oxide (BMO) outperformed the identical type of Abiotic-MnOX in terms of oxidation and adsorption of Sb(III). Adsorption kinetics and isotherm experiments indicated that Sb(III) was primarily adsorbed through chemisorption and multilayer adsorption on BMO; the maximum adsorption capacity of BMO was 143.15 mg·g-1. Removal kinetic studies showed that the Sb(III) removal efficiency by BMO was 72.38-95.71% after 15 min, and it could be up to 96.32-98.31% after 480 min. The removal procedure could be divided into two stages, fast (within 15 min) and slow (15 ~ 480 min), both of which exhibited first-order kinetic behavior. Dynamic fitting in two steps revealed that the removal speed correlated to the level of dissolved Sb(III) with low Sb(III) concentrations, but with the initial concentration being high, the removal speed rate was independent of dissolved Sb(III). During the whole process, the Sb(III) removal speed by BMO was also higher than that by the Abiotic-MnOX. Combining multiple spectroscopic techniques revealed that Sb(V) was generated through the Sb(III) oxidation by BMO and replacing surface metal hydroxyl groups to form the complex internal Mn-O(H)-Sb(V) or generating stable Mn(II)-antimonate precipitates on the surface. In addition, microbial metabolites, including tryptophan and humus, in BMO may be complex with Sb(III) and Sb(V) to achieve the treatment of Sb(III). This research investigates the factors and mechanisms influencing the adsorption and removal of Sb(III) by BMO, which could aid in its future engineering applications for the BMO.

Unveiling the drives behind tetracycline adsorption capacity with biochar through machine learning

This study aimed to develop a robust predictive model for tetracycline (TC) adsorption onto biochar (BC) by employing machine learning techniques to investigate the underlying driving factors. Four machine learning algorithms, namely Random Forest (RF), Gradient Boosting Decision Tree (GBDT), eXtreme Gradient Boosting (XGBoost) and Artificial Neural Networks (ANN), were used to model the adsorption of TC on BC using the data from 295 adsorption experiments. The analysis revealed that the RF model had the highest predictive accuracy (R² = 0.9625) compared to ANN (R² = 0.9410), GBDT (R² = 0.9152), and XGBoost (R² = 0.9592) models. This study revealed that BC with a specific surface area (S (BET)) exceeding 380 cm³·g^-1 and particle sizes ranging between 2.5 and 14.0 nm displayed the greatest efficiency in TC adsorption. The TC-to-BC ratio was identified as the most influential factor affecting adsorption efficiency, with a weight of 0.595. The concentration gradient between the adsorbate and adsorbent was demonstrated to be the principal driving force behind TC adsorption by BC. A predictive model was successfully developed to estimate the sorption performance of various types of BC for TC based on their properties, thereby facilitating the selection of appropriate BC for TC wastewater treatment.

Degradation of tetracycline by activated peroxodisulfate using a sulfur-modified iron-based material

The activation of persulfate by an iron-based catalyst presents a promising approach for the degradation of antibiotics; however, the activation efficiency remains a challenge. Herein, a sulfur-modified iron-based catalyst (S-Fe) by co-precipitation of sodium thiosulfate and ferrous sulfate in a molar ratio of 1:2 was prepared and the efficacy of the S-Fe/PDS system for the removal of tetracycline (TCH) was studied, where a higher removal efficiency was observed compared to the Fe/PDS system. Moreover, the effects of TCH concentration, PDS concentration, initial pH, and catalyst dosage on TCH removal were evaluated, and the highest efficiency was about 92.6% within a 30 min reaction time using a catalyst dosage of 1.0 g/L, a PDS dosage of 2.0 g/L, and a solution pH value of 7. The products and degradation pathways of TCH were analyzed by LC-MS. The free-radical-quenching experiments revealed that both SO₄^- • and •OH radicals contributed to the degradation of TCH in the S-Fe/PDS system, with the former playing a more significant role. The S-Fe catalyst also showed good stability and reusability for the removal of organic pollutants. Our findings suggest that the modification of an iron-based catalyst offers an effective approach to activate persulfate for removal of tetracycline antibiotics.

Removal Performance of KOH-Modified Biochar from Tropical Biomass on Tetracycline and Cr(VI)

Biochar can be used to address the excessive use of tetracycline and micronutrient chromium (Cr) in wastewater that potentially threatens human health. However, there is little information about how the biochar, made from different tropical biomass, facilitates tetracycline and hexavalent chromium (Cr(VI)) removal from aqueous solution. In this study, biochar was prepared from cassava stalk, rubber wood and sugarcane bagasse, then further modified with KOH to remove tetracycline and Cr(VI). Results showed that pore characteristics and redox capacity of biochar were improved after modification. KOH-modified rubber wood biochar had the highest removal of tetracycline and Cr(VI), 1.85 times and 6 times higher than unmodified biochar. Tetracycline and Cr(VI) can be removed by electrostatic adsorption, reduction reaction, π-π stacking interaction, hydrogen bonding, pore filling effect and surface complexation. These observations will improve the understanding of the simultaneous removal of tetracycline and anionic heavy metals from wastewater.

Novel ZIF-67-derived Co@CNTs nanocomposites as effective adsorbents for removal of tetracycline and sulfadiazine antibiotics

Tetracycline (TCC) and sulfadiazine (SDZ) are two of the most consumed antibiotics for human therapies and bacterial infection treatments in aquafarming fields, but their accumulative residues can result in negative effects on water and aquatic microorganisms. Removal techniques are therefore required to purify water before use. Herein, we concentrate on adsorptive removal of TCC and SDZ using cobalt@carbon nanotubes (Co@CNTs) derived from Co-ZIF-67. The presence of CNTs on the edge of nanocomposites was observed. Taguchi orthogonal array was designed with four variables including initial concentration (5-20 mg L^-1), dosage (0.05-0.2 g L^-1), time (60-240 min), and pH (2-10). Concentration and pH were found to be main contributors to adsorption of tetracycline and sulfadiazine, respectively. The optimum condition was found at concentration 5 mg L^-1, dosage 0.2 g L^-1, contact time 240 min, and pH 7 for both TCC and SDZ removals. Confirmation tests showed that Co@CNTs-700 removed 99.6% of TCC and 97.3% of SDZ with small errors (3-5.5%). Moreover, the kinetic and isotherm were studied, which kinetic and isotherm data were best fitted with pseudo second-order model and Langmuir. Maximum adsorption capacity values for TCC and SDZ were determined at 118.4-174.1 mg g^-1 for 180 min. We also proposed the main role of interactions such as hydrogen bonding, π-π stacking, and electrostatic attraction in the adsorption of antibiotics. With high adsorption performance, Co@CNTs-700 is expected to remove antibiotics efficiently from wastewater.

Effects of functional group loss on biochar activated persulfate in-situ remediation of phenol pollution in groundwater and its countermeasures

Biochar is considered a good activator for use in advanced oxidation technology. However, dissolved solids (DS) released from biochar cause unstable activation efficiency. Biochar prepared from saccharification residue of barley straw (BC-SR) had less DS than that prepared directly from barley straw (BC-O). Moreover, BC-SR had a higher C content, degree of aromatization, and electrical conductivity than BC-O. Although the effects of BC-O and BC-SR on activation of Persulfate (PS) to remove phenol were similar, the activation effect of DS from BC-O was 73% higher than that of DS from BC-SR. Moreover, the activation effect of DS was shown to originate from its functional groups. Importantly, BC-SR had higher activation stability than BC-O owing to the stable graphitized carbon structure of BC-SR. Identification of reactive oxygen species showed that SO₄•^-, •OH, and ¹O₂ were all effective in degradation by BC-SR/PS and BC-O/PS systems, but their relative contributions differed. Furthermore, BC-SR as an activator showed high anti-interference ability in the complex groundwater matrix, indicating it has practical application value. Overall, this study provides novel insight that can facilitate the design and optimization of a green, economical, stable, and efficient biochar-activated PS for groundwater organic pollution remediation.

Adsorption of antibiotics on different microplastics (MPs): Behavior and mechanism

MPs can adsorb antibiotics to coexist and accumulate in the aquatic environment in the form of complexes, resulting in unforeseeable adverse consequences. The adsorption behavior and mechanism of three antibiotics amoxicillin (AMX), ciprofloxacin (CIP), and tetracycline (TC) by four MPs Polyvinyl chloride (PVC), polystyrene (PS), polypropylene (PP), and polyethylene (PE) were studied. Results showed that the adsorption of antibiotics onto MPs follows the pseudo-second-order kinetic and the Freundlich isotherm model, indicating a multilayer chemical adsorption. Combined with FTIR, XRD, and SEM analyses, the adsorption behavior was simultaneously governed by physical processes. Additionally, the equilibrium adsorption capacity was inhibited in the research concentration range of NaCl from 10 mg/L to 10 g/L. The higher the salt concentration, the more pronounced the inhibition phenomenon was. The high (9) and low (3) pH also inhibited the adsorption of antibiotics to MPs. The humic acid (HA) concentration in the range of 0-20 mg/L generally inhibited the MPs-antibiotics adsorption, but the higher HA concentration showed less inhabitation than the lower one. The adsorption inhibition of TC on the four MPs by SA also followed the above rule. However, the adsorption inhibition of sodium alginate (SA) on AMX and CIP on the four MPs was enhanced with its concentration (0-50 mg/L).

A review of antibiotics and antibiotic resistance genes (ARGs) adsorption by biochar and modified biochar in water

Antibiotics have been used in massive quantities for human and animal medical treatment, and antibiotic resistance genes (ARGs) are of great concern worldwide. Antibiotics and ARGs are exposed to the natural environment through the discharge of medical wastewater, causing great harm to the environment and human health. Biochar has been widely used as a green and efficient adsorbent to remove pollutants. However, pristine and unmodified biochars are not considered sufficient and efficient to cope with the current serious water pollution. Therefore, researchers have chosen to improve the adsorption capacity of biochar through different modification methods. To have a better understanding of the application of modified biochar, this review summarizes the biochar modification methods and their performance, particularly, molecular imprinting and biochar aging are outlined as new modification methods, influencing factors of biochar and modified biochar in adsorption of antibiotics and ARGs and adsorption mechanisms, wherein adsorption mechanism of ARGs on biochar is found to be different than that of antibiotics. After that, the directions of biochar and modified biochar worthy of research and the issues that need attention are proposed. It can be noted that under the current dual carbon policy, biochar may have wider application prospects in future.

Biochar for the Removal of Emerging Pollutants from Aquatic Systems: A Review

Water contaminated with emerging pollutants has become a serious environmental issue globally. Biochar is a porous and carbon-rich material produced from biomass pyrolysis and has the potential to be used as an integrated adsorptive material. Many studies have shown that biochar is capable to adsorb emerging pollutants from aquatic systems and could be used to solve the water pollution problem. Here, we provided a dual perspective on removing emerging pollutants from aquatic systems using biochar and analyzed the emerging pollutant removal efficiency from the aspects of biochar types, pollutant types and coexistence with heavy metals, as well as the associated mechanisms. The potential risks and future research directions of biochar utilization are also presented. This review aims to assist researchers interested in using biochar for emerging pollutants remediation in aquatic systems and facilitate research on emerging pollutants removal, thereby reducing their environmental risk.

Selective adsorption of antibiotics on manganese oxide-loaded biochar and mechanism based on quantitative structure-property relationship model

In this study, MnCl₂-impregnated biomass was oxygen-limited pyrolyzed to produce manganese oxide-loaded biochar (MBC), its adsorption behaviors and influencing factors on tetracycline (TTC), norfloxacin (NOR), and sulfamethoxazole (SMX) were systematically investigated. Three antibiotics exhibited enhanced adsorption behavior on MBC, with maximum adsorption capacity as accurately described by Sips isotherm: TTC (534 mg/g) > NOR (67 mg/g) > SMX (28 mg/g). Hydrogen bonding, n/π-π interactions, electrostatic interaction, surface coordination, and hydrophobic interaction are the major mechanisms for the improved adsorption. Manganese oxide particles on MBC promoted surface coordination and hydrogen bonding. Antibiotic molecules with more hydroxyl oxygen-containing functional groups are more susceptible to migrate to biochar surfaces and to be adhered. Moreover, the quantitative structure-property relationship (QSPR) model was constructed and revealed that hydrogen bonding and π-π interactions were crucial for tetracycline antibiotics selective adsorption. Hence, MBC was a prospective adsorbent with promising applications for antibiotic removal in sewage processing.

Adsorptive removal of tetracycline from aqueous solutions using magnetic Fe2O3 / activated carbon prepared from Cynometra ramiflora fruit waste

Herein, the sustainable fabrication of magnetic iron oxide nanoadsorbent prepared with activated carbon of inedible Cynometra ramiflora fruit has been investigated. Activated carbon was obtained from phosphoric acid-treated C. ramiflora fruit, which was then utilized for the synthesis of magnetic nanocomposite (CRAC@Fe₂O₃). The formed nanocomposite was a porous irregular dense matrix of amorphous evenly sized spherical nanoparticles, as visualized by FESEM, and also contained carbon, oxygen, iron, and phosphorous in its elemental composition. FT-IR spectrum depicted characteristic bands attributing to Fe-O, C-OH, C-N, CC, and -OH bonds. VSM and XRD results proved that CRAC@Fe₂O₃ was superparamagnetic with a moderate degree of crystallinity and high saturation magnetization value (1.66 emu/g). Superior surface area, pore size, and pore volume of 766.75 m²/g, 2.11 nm, and 0.4050 cm³/g respectively were measured on BET analysis of CRAC@Fe₂O₃ nanocomposite, indicating their suitability for use as an adsorbent. On application of this nanocomposite for adsorption of tetracycline, maximum removal of 95.78% of 50 ppm TC at pH 4, CRAC@Fe₂O₃ 0.4 g/L in 240 min. The adsorption of TC by CRAC@Fe₂O₃ was confirmed as monolayer sorption by ionic interaction (R² = 0.9999) as it followed pseudo-second-order kinetics and Langmuir isotherm (R² = 0.9801). CRAC@Fe₂O₃ showed a maximum adsorption capacity of 312.5 mg/g towards TC antibiotics indicating its potential for the treatment of antibiotic-contaminated samples. Since negative ΔG^o and positive ΔH^o and ΔS^o values were obtained at all tested temperatures during the thermodynamic studies, the adsorption was confirmed to be endothermic, spontaneous, and feasible with an enhanced degree of randomness.

Reed Rhizome Residue-Based Activated Carbon Adsorption Ultrafiltration Membranes for Enhanced MB Removal

Novel adsorption ultrafiltration (ADUF) membrane was designed for the removal of methylene blue (MB) by introducing Chinese herbal waste-based activated carbon (AC) into the ultrafiltration membrane. We prepared AC particles from Chinese herbal medicine waste residue (reed rhizome residue) as a raw material by ZnCl₂ activation and introduced them into the ultrafiltration membrane by phase inversion to prepare a reed rhizome residue-based activated carbon adsorption ultrafiltration (RAC-ADUF) membrane. The RAC-ADUF-0.1 membrane was characterized by a series of physical structures and chemical properties, which showed that the prepared membrane has a more hydrophilic surface and high porosity. The RAC-ADUF-0.1 membrane showed an excellent pure water flux of 255.77 L·m^-2·h^-1 and a high bovine serum albumin rejection of 99.3%. The RAC-ADUF membranes also possessed excellent antifouling performance. Notably, the RAC-ADUF-0.1 membrane provides excellent removal of MB (99% retention) compared to conventional ultrafiltration membranes. The static adsorption capacity was up to 238.48 mg/g. The significant increase in dynamic adsorption capacity on the RAC-ADUF membrane is due to the three-dimensional distribution of RAC particles on the PSF membrane cross section, which provides more active sites and increases the contact time between RAC and MB. By fitting the adsorption kinetics and isothermal adsorption curves, the results showed that the pseudo-second-order kinetic model and the Langmuir isothermal model were more accurate in explaining the adsorption process. Further kinetic analysis showed that the adsorption process of MB molecules on RAC-ADUF membranes is controlled by both external mass transfer and intraparticle diffusion, with intraparticle diffusion playing a dominant role. In addition, the RAC-ADUF membrane exhibited outstanding adsorption and regeneration abilities, and the MB removal rate stayed at about 95% after 8 adsorption regeneration experiments. In conclusion, this study provides a new idea for the preparation strategy of an adsorption ultrafiltration membrane with high rejection and high permeability and the reuse of Chinese herbal medicine waste residue.

Machine learning-assisted evaluation of potential biochars for pharmaceutical removal from water

A popular approach to select optimal adsorbents is to perform parallel experiments on adsorbents based on an initially decided goal such as specified product purity, efficiency, or binding capacity. To screen optimal adsorbents, we focused on the max adsorption capacity of the candidates at equilibrium in this work because the adsorption capacity of each adsorbent is strongly dependent on certain conditions. A data-driven machine learning tool for predicting the max adsorption capacity (Q_m) of 19 pharmaceutical compounds on 88 biochars was developed. The range of values of Q_m (mean 48.29 mg/g) was remarkably large, with a high number of outliers and large variability. Modified biochars enhanced the Q_m and surface area values compared with the original biochar, with a statistically significant difference (Chi-square value = 7.21-18.25, P < 0.005). K- nearest neighbors (KNN) was found to be the most optimal algorithm with a root mean square error (RMSE) of 23.48 followed by random forest and Cubist with RMSE of 26.91 and 29.56, respectively, whereas linear regression and regularization were the worst algorithms. KNN model achieved R² of 0.92 and RMSE of 16.62 for the testing data. A web app was developed to facilitate the use of the KNN model, providing a reliable solution for saving time and money in unnecessary lab-scale adsorption experiments while selecting appropriate biochars for pharmaceutical adsorption.

Excess sludge biochar facilitates persulfate activation for highly efficient tetracycline removal

This study proposed a novel advanced oxidation system to treat metal and antibiotic pollution in water simultaneously. Meanwhile, the enhancement effect of absorbed metal pollution on the activation of persulfate in the system was also investigated. As the most widely used and polluting material, tetracycline (TC) and metal Fe were used as the pollutant models. In this study, a carbonaceous material (BC) was prepared from excess sludge and then combined with the persulfate system (Fe/BC/PS). It was found that the best biochar was obtained when the pyrolysis temperature reached 500 °C (BC500), with the specific surface area of 39.712 m²/g. Combining it with 300 mg/L PS, the removal rate of 120 mg/L TC reached 70.6%. Moreover, the sludge biochar itself possessed numerous reaction sites and good defective structure, which provided a perfect reaction site for the variable metals absorbed by BC. They accelerated electron conduction greatly, which led to the activation of PS very active and generating far more active radicals than normal. In addition, it also proposed the rational pathway and potential mechanism of TC degradation based on the degradation intermediates. This study has a high reference value for resource utilization of sewage sludge and antibiotics removal from water.

Improved Adsorption of Tetracycline in Water by a Modified Caulis spatholobi Residue Biochar

A potassium modified biochar (KBC) using Caulis spatholobi residue as the raw material was prepared by adopting a two-step method of pyrolysis followed by high-temperature potassium hydroxide activation, and its properties were characterized. Activation using potassium hydroxide under high temperature induced the loss of CaCO₃ and partial C on biochar, which created a high specific surface area (1336.31 m²/g) together with a developed pore structure. pH displayed a slight influence on tetracycline adsorption, which signified the slight influence of the existence of tetracycline and the charge potential of biochar. Besides, pore filling, hydrogen bonding and π-π EDA stacking interactions possibly resulted in tetracycline adsorption on biochar. Tetracycline adsorption was fast in the original period, followed by a slower rate of adsorption until equilibrium was reached. Adsorption kinetics of tetracycline could be described using secondary and Elovich kinetic models. Adsorption isotherms for tetracycline were well fitted to the Langmuir isotherm model, and the maximum adsorption capacity of KBC was 830.78 mg/g at 318 K. According to a study of the thermodynamics, the adsorption of tetracycline on KBC was an endothermic reaction process. Corresponding results in the present study demonstrated that high-temperature potassium hydroxide activation enabled biochar to effectively eliminate tetracycline from water and wastewater.

Remediation of Soil Mercury by Modified Vermiculite-Montmorillonite and Its Effect on the Growth of Brassica chinensis L

In this study, the surface of vermiculite-montmorillonite was modified by MnO₂ loading. The modified vermiculite-montmorillonite was added to remediate the potentially toxic trace element (PTE) Hg present in soil containing coal gangue. Pot experiments were conducted to analyze and compare the pH values, Hg contents and Hg species present in coal gangue-containing soil, with and without the modified materials added, to determine whether the addition of modified materials had an effect on the growth of Brassica chinensis L. Results showed that with the addition of 35 g·kg^-1 modified vermiculite-montmorillonite, the pH of soil increased by a value of 0.79, compared with that in the control group. When 15 g·kg^-1 was added, the concentration of Hg in soil decreased by 98.2%. The addition of modified materials promoted the transformation of Hg in soil from a bioavailable form to an unavailable form; that is, the content of the residual form increased. The plant height and biomass of Brassica chinensis L. also increased, which indicated that the addition of modifiers can increase soil productivity, reduce the effects of PTEs on organisms in soil, and promote plant growth. Therefore, the addition of modified vermiculite-montmorillonite can achieve remediation of coal gangue-containing soil.

Recyclable aminophenylboronic acid modified bacterial cellulose microspheres for tetracycline removal: Kinetic, equilibrium and adsorption performance studies for hoggery sewer

Significant concerns have been raised regarding to the pollution of antibiotics in recent years due to the abuse of antibiotics and their high detection rate in water. Herein, a novel super adsorbent, boronic acid-modified bacterial cellulose microspheres with a size of 415 μm in diameter was prepared through a facile water-in-oil emulsion method. The adsorbent was characterized by atomic force microscopy, scanning electron microscopy, and fourier transform infrared spectroscopy analyses to confirm its properties. The microspheres were applied as packing materials for the adsorption of tetracycline (TC) from an aqueous solution and hoggery sewer via the reversible covalent interaction between cis-diol groups in TC molecules and the boronic acid ligand. TC adsorption performance had been systemically investigated under various conditions, including the pH, temperature, TC concentration, contact time, and ionic strength. Results showed that the adsorption met pseudo-second-order, Elovich kinetic model and Sips, Redlich-Peterson isothermal models. And the adsorption process was spontaneous and endothermic, with the maximum TC adsorption capacity of 614.2 mg/g. After 18 adsorption-desorption cycles, the adsorption capacity remained as high as 84.5% compared with their original adsorption capacity. Compared with other reported adsorption materials, the microspheres had high adsorption capacity, a simple preparation process, and excellent recovery performance, demonstrating great potential in application on TC removal for water purification and providing new insights into the antibiotic's adsorption behavior of bacterial cellulose-based microspheres.

Effect of Biochar Modification by Vitamin C, Hydrogen Peroxide or Silver Nanoparticles on Its Physicochemistry and Tetracycline Removal

Chemical modification of biochars can improve their adsorption capacity relative to antibiotics, posing a serious threat to the environment. Therefore, this research is aimed at the treatment of sunflower husk biochar (BC) by vitamin C, hydrogen peroxide or silver nanoparticles and the impact of this procedure on the biochar porosity, surface chemistry, and ability to remove tetracycline (TC). During the study, BC was produced by pyrolysis of sunflower husks at 650 °C. All solids were characterized using potentiometric titration, nitrogen adsorption/desorption, Fourier transform infrared spectroscopy, etc. The experimental adsorption data was described by kinetics equations: pseudo-first order, pseudo-second order, and particle internal diffusion (IPD) models as well as by isotherms of Langmuir, Langmuir-Freundlich, and Redlich-Peterson. The obtained results indicated that the biochar upgraded by vitamin C (BCV) had the highest ability to attract antibiotic molecules and, as a result, the TC adsorption on its surface was the largest. Furthermore, the TC desorption from this material was minimal. The measured TC adsorbed amounts for the modified BCs were as follows: 47.75% (7.47 mg/g) for BCV, 37.35% (8.41 mg/g)-for biochar treated by hydrogen peroxide (BCH), and 42.04% (9.55 mg/g) for biochar modified by silver nanoparticles (BCA). The lowest adsorption level was noted for non-modified biochar, i.e., 34.17% (6.83 mg/g). Based on the presented results it can be stated that the upgraded biochars had a good potential to improve the tetracycline removal from aqueous media, e.g., groundwater.

Tetracycline removal enhancement with Fe-saturated nanoporous montmorillonite in a tripartite adsorption/desorption/photo-Fenton degradation process

The adsorption and photo-Fenton degradation of tetracycline (TC) over Fe-saturated nanoporous montmorillonite was analyzed. The synthesized samples were characterized using XRD, FTIR, SEM, and XRF analysis, and the adsorption and desorption of TC onto these samples, as well as the antimicrobial activity of TC during these processes, were analyzed at different pH. Initially, a set of adsorption/desorption experiments was conducted, and surprisingly, up to 50% of TC adsorbed was released from Mt structure. Moreover, the desorbed TC had strong antibacterial activity. Then, an acid treatment (for the creation of nanoporous layers) and Fe saturation of the montmorillonite were applied to improve its adsorption and photocatalytic degradation properties over TC. Surprisingly, the desorption of TC from modified montmorillonite was still high up to 40% of adsorbed TC. However, simultaneous adsorption and photodegradation of TC were detected and almost no antimicrobial activity was detected after 180 min of visible light irradiation, which could be due to the photo-Fenton degradation of TC on the modified montmorillonite surface. In the porous structures of modified montmorillonite high, ˙OH radicals were created in the photo-Fenton reaction and were measured using the Coumarin technique. The ˙OH radicals help the degradation of TC as proposed in an oxidation process. Surprisingly, more than 90% of antimicrobial activity of the TC decreased under visible light (after 180 min) when desorbed from nanoporous Fe-saturated montmorillonite compared to natural montmorillonite. To the best of our knowledge, this is the first time that such a high TC desorption rate from an adsorbent with the least residual antimicrobial activity is reported which makes nanoporous Fe-saturated montmorillonite a perfect separation substance of TC from the environment.

Efficient removal of antibiotics from water resources is a public health priority: a critical assessment of the efficacy of some remediation strategies for antibiotics in water

This review discusses the fundamental principles and mechanism of antibiotic removal from water of some commonly applied treatment techniques including chlorination, ozonation, UV-irradiation, Fenton processes, photocatalysis, electrochemical-oxidation, plasma, biochar, anaerobicdigestion, activated carbon and nanomaterials. Some experimental shortfalls identified by researchers such as certain characteristics of degradation agent applied and the strategies explored to override the identified limitations are briefly discussed. Depending on interactions of a range of factors including the type of antibiotic compound, operational parameters applied such as pH, temperature and treatment time, among other factors, all reviewed techniques can eliminate or reduce the levels of antibiotic compounds in water to varying extents. Some of the reviewed techniques such as anaerobic digestion generally require longer treatment times (up to 360, 193 and 170 days, according to some studies), while others such as photocatalysis achieved degradation within short contact time (within a minimum of 30, but up to 60, 240, 300 and 1880 minutes, in some cases). For some treatment techniques such as ozonation and Fenton, it is apparent that subjecting compounds to longer treatment times may improve elimination efficiency, whereas for some other techniques such as nanotechnology, application of longer treatment time generally meant comparatively minimal elimination efficiency. Based on the findings of experimental studies summarized, it is apparent that operational parameters such as pH and treatment time, while critical, do not exert sole or primary influence on the elimination percentage(s) achieved. Elimination efficiency achieved rather seems to be due more to the force of a combination of several factors.

Manganese oxide-modified biochar derived from discarded mushroom-stick for the removal of Sb(III) from aqueous solution

In this study, discarded mushroom-stick, which is widely available, was selected as a precursor to prepare MnO₂-modified biochar (MBC) for Sb(III) removal. Several characterisation methods (SEM, BET, XPS, FT-IR, and XRD) were used to explore the mechanisms of antimony adsorption onto MBC. The results showed that MBC is a mesoporous material with a fluffy structure and a higher specific surface area (23.56 and 32.09 m²·g^-1) than PBC600 (13.62 m²·g^-1), exhibiting superior and stable adsorption capacities for Sb(III) (50.30 mg·g^-1 for 1/30MBC600 and 64·12 mg·g^-1 for 1/20MBC600) across a wide pH range (pH 4-8). X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy analyses indicated that the main oxides and functional groups involved in the adsorption were manganese oxides and hydroxyl groups. Forty-four per cent of the adsorbed Sb(III) was oxidised to Sb(V) by manganese oxides or hydroxyl groups both on the surface of biochar and in solution. According to adsorption kinetics and isotherms, the adsorption process of Sb(III) is chemisorption, which includes monolayer and multilayer heterogeneous chemisorption processes. To sum up, MBC is an excellent adsorbent for the capture of Sb(III) from contaminated water with strong potential for future application.

Preparation of spiramycin fermentation residue derived biochar for effective adsorption of spiramycin from wastewater

Spiramycin (SPI) fermentation residue (SFR) is classified as hazardous waste in China because of the residual antibiotics in it. SFR disposal in the traditional way is costly and wasteful of resources. In this study, pyrolysis method was adopted to covert SFR to biochar for SPI removal from wastewater, and the SPI adsorption performance was investigated. The results showed that the optimal pyrolysis temperature was 700 °C as the prepared biochar BC700 exhibited the highest SPI removal efficiency. The specific surface area of BC700 was 451.68 m²/g, and the maximum adsorption capacity was 147.28 mg/g. The adsorption mechanism involved electrostatic interaction, pore filling, π-π interaction, hydrogen bonding, and the participation of C-C and O-CO functional groups in the adsorption. No residual SPI was detected in BC700 indicating the detoxification of SFR was achieved. Moreover, after recycling for 5 times, the SPI removal efficiency was still higher than 80.0%. Therefore, this study could provide a promising method for SFR disposal.

A study of the effect of reactive oxygen species induced by violet and blue light from oxytetracycline on the deactivation of Escherichia coli

Oxytetracycline (OTC), a tetracycline antibiotic, is a broad-spectrum antibacterial agent. In this investigation, liquid chromatography-mass spectrometry (LC-MS) is utilized to determine the effects of blue light (λ = 448 nm) illumination (BLIA) and violet light (λ = 403 nm) illumination (VLIA) on conformational changes in OTC at pH 7.8. The photochemical effect of OTC that is exposed to BLIA and VLIA on the deactivation of Escherichia coli (E. coli) is studied. The deactivation of E. coli has an insignificant effect on treatment with OTC alone. OTC is relatively unstable under BLIA and VLIA illumination in an alkaline solution, and OTC has been shown to inactivate E. coli by generating reactive oxygen species (ROS). Less anionic superoxide radicals (O₂^•-) are generated from OTC that is treated with BLIA than that from VLIA treatment, so OTC is more efficient in inactivating E. coli under VLIA. Inactivation of reduction rates of 0.51 and 3.65 logs in E. coli are achieved using 0.1 mM OTC under BLIA for 120 min and VLIA for 30 min, respectively, under the same illumination intensity (20 W/m²). Two photolytic products of OTC (PPOs) are produced when OTC is exposed to BLIA and VLIA, with molecular ions at m/z 447 and 431, molecular formulae C₂₁H₂₂N₂O₉ and C₂₁H₂₂N₂O₈, and masses of 446.44 and 430.44 g/mol, respectively. The results show that when exposed to VLIA, OTC exhibits enhanced inactivation of E. coli, suggesting that the photochemical treatment of OTC is a potential supplement in a hygienic process.

HKUST-1 derived carbon adsorbents for tetracycline removal with excellent adsorption performance

As the abuse of antibiotics has led to increasingly serious environmental pollution problems, studies have found that the adsorption method can be used to efficiently and quickly remove residual antibiotics in water with low cost and high efficiency. Metal-organic frameworks and their derived porous carbons have received widespread attention as a new type of adsorption material. In this study, HKUST-1 was synthesized by a hydrothermal method and carbonized to HDC-350 at 350 °C under an oxygen-free atmosphere. Through adsorption experiments, HDC-350 is found to show a superior adsorption effect for tetracycline (TC), with an adsorption capacity that reaches 136.88 mg g^-1. The TC adsorption mechanism was studied through characterization and analysis of HDC-350. The adsorption of TC by HDC-350 mainly relies on electrostatic attraction, hydrogen bonding, metal-organic complexation, and intermolecular interactions. This study shows that HKUST-1-derived porous carbon can be used to improve the water stability of HKUST-1, and, at the same time, can effectively adsorb TC in solution, which provides good conditions for practical research applications in the future.

Enhanced nitrate, manganese, and phenol removal by polyvinyl alcohol/sodium alginate with biochar gel beads immobilized bioreactor: Performance, mechanism, and bacterial diversity

Water pollutants, such as nitrate, heavy metals, and organics have attracted attention due to their harms to environmental and biological health. A novel polyvinyl alcohol/sodium alginate with biochar (PVA/SA@biochar) gel beads immobilized bioreactor was established to remove nitrate, manganese, and phenol. The optimum conditions for preparing gel beads were studied by response surface methodology (RSM). Notably, the removal efficiencies of nitrate, Mn(II), and phenol were 94.64, 72.74, and 93.97% at C/N of 2.0; the concentrations of Mn(II) and phenol were 20 and 1 mg L^-1, respectively. Moreover, addition of different concentrations of phenol significantly affected the components of dissolved organic matter, bacterial activity, and bioreactor performance. The biological manganese oxide (BMO) with three-dimensional petal-type structure produced during Mn(II) oxidation showed excellent adsorption capacity. The removal of phenol relied on a combination of biological action and adsorption processes. High-throughput analysis showed that Zoogloea sp. was the predominant bacterial group.

Magnetic alginate/glycodendrimer beads for efficient removal of tetracycline and amoxicillin from aqueous solutions

The release of antibiotic drugs into aquatic environments is a serious environmental and health problem in recent years. Therefore, the development of potential adsorbents for the effective removal of tetracycline (TC) and amoxicillin (AMX) of aqueous media is of great importance. In this study, new alginate beads were successfully prepared by encapsulation of Fe₃O₄@maltose-functionalized triazine dendrimer in alginate (Alg/Fe₃O₄@C@TD) for the first time. The obtained beads were utilized as a well adsorbent for the removal of TC and AMX antibiotics from aqueous solutions by batch adsorption procedure. The characteristics of the synthesized beads were investigated using FT-IR, Zeta potential, SEM, XRD, EDX, VSM, and BET. The effects of various operation factors such as adsorbent dose, pH of the solution, contact time, antibiotic initial concentration, temperature, and ionic strength on the removal of antibiotics were studied. Moreover, Langmuir and Freundlich adsorption isotherm results showed that the Langmuir model fitted well for the adsorption of both antibiotics onto Alg/Fe₃O₄@C@TD beads. Based on the Langmuir model, the maximum adsorption capacity of TC and AMX onto Alg/Fe₃O₄@C@TD beads at 25 °C was 454.54 and 400 mg/g, respectively. Kinetic and thermodynamic studies also indicated that the TC and AMX adsorption were found to be well fitted with a pseudo-second-order kinetic model, feasible, endothermic, and spontaneous in nature. In addition, the Alg/Fe₃O₄@C@TD beads showed excellent reusability for removal from both antibiotics after six adsorption cycles. Overall, the obtained results suggest that Alg/Fe₃O₄@C@TD beads could be considered as a low-cost and eco-friendly adsorbent for antibiotic contaminants removal from aquatic media.

Reutilization of manganese enriched biochar derived from Phytolacca acinosa Roxb. residue after phytoremediation for lead and tetracycline removal

This study aimed to evaluate the chemical form variation of Mn in Phytolacca acinosa Roxb. residue under different pyrolysis temperatures and its contribution to decontamination efficacy of lead (Pb(II)) and tetracycline (TC). The results illuminated that pyrolysis temperature is a crucial factor of fraction and bioavailability of Mn and other heavy metals in the resultant biochar and pyrolysis temperature under 450 °C may be most suitable for reutilization without potential risk. The Mn-enriched phytolaccaceae biochar (PSB450) exhibited more preferential sorption toward Pb(II) (279.33 mg/g) and TC (47.51 mg/g) than pristine phytolaccaceae biochar in the single system, mainly due to the formation of MnO_x and Mn minerals via pyrolysis. Binary adsorption showed that Pb(II) would serve as a bridge between PSB450 and TC by complexation within a limited concentration range, thus facilitating their joint decontamination. This study provided an efficient alternative approach for reutilization of Mn-contaminated biomass.

Manganese oxide-modified biochar: production, characterization and applications for the removal of pollutants from aqueous environments - a review

The development of manganese (Mn) oxides (MnOx) modified biochar (MnOBC) for the removal of pollutants from water has received significant attention. However, a comprehensive review focusing on the use of MnOBC for the removal of organic and inorganic pollutants from water is missing. Therefore, the preparation and characterization of MnOBC, and its capacity for the removal of inorganic (e.g., toxic elements) and organic (e.g., antibiotics and dyes) from water have been discussed in relation to feedstock properties, pyrolysis temperature, modification ratio, and environmental conditions here. The removal mechanisms of pollutants by MnOBC and the fate of the sorbed pollutants onto MnOBC have been reviewed. The impregnation of biochar with MnOx improved its surface morphology, functional group modification, and elemental composition, and thus increased its sorption capacity. This review establishes a comprehensive understanding of synthesizing and using MnOBC as an effective biosorbent for remediation of contaminated aqueous environments.

High-performance biochar derived from the residue of Chaga mushroom (Inonotus obliquus) for pollutants removal

A high-performance biochar derived from the residue of Chaga mushroom (Inonotus obliquus) was reported in this study. Inonotus obliquus residues were used to prepare biochar, and the optimal synthesis conditions were obtained by response surface methodology. The specific surface area, pore volume, and average pore size of the optimal biochar (Zn-IORBC) was 1676.78 m²/g, 1.87 cm³/g, and 3.88 nm, respectively. Methylene blue (MB) and tetracycline (TC) were selected to estimate the adsorption performance of Zn-IORBC. The adsorption process was suitable for the pseudo-second-order model and Langmuir model. Zn-IORBC could maintained a large amount of TC adsorption (the lowest value was 686.20 mg/g in mountain spring water) in different natural water. The maximum adsorption capacity of TC and MB was 947.42 and 1033.66 mg/g. The adsorption mechanism was contributed to the electrostatic attraction, hydrogen bonding, π-π interactions, and pore-filling. Zn-IORBC is an effective adsorbent for high-performance pollutants removal.

Treatment and bioresources utilization of traditional Chinese medicinal herb residues: Recent technological advances and industrial prospect

Traditional Chinese medicine (TCM) has wide application and important functions in curing many diseases, but a great number of herb residues are usually generated after its manufacture and usage. Without proper and timely treatment, these traditional Chinese medicinal herb (TCMH) residues will cause some environmental pollution. In addition to treatment, bioresources utilization of TCMH residues is also important for its great potential as a suitable feedstock for the production of energy, materials, and chemicals. In this situation, advanced and well-designed solid waste management is important to make the TCM industry environmentally friendly and economically attractive. In this review article, the recent progress focusing on various methods for TCMH residues treatment and bioresources utilization are introduced in detail. In particular, the technologies for thermochemical conversion and biochemical conversion of TCMH residues are mainly focused on in order to show how to fulfill effective and efficient bioresources utilization. Besides, some other technologies which are suitable for the treatment and bioresources utilization of TCMH residues are presented as well. Finally, some industrial prospects are given from the economic, operational, and environmental aspects for the further development of treatment and bioresources utilization of TCMH residues. Overall, this work can provide some systematical and comprehensive information for the development of technologies that help sustainably manage the herb residues generated in the TCM industry.

Transformation of Tetracycline by Manganese Peroxidase from Phanerochaete chrysosporium

The negative impacts on the ecosystem of antibiotic residues in the environment have become a global concern. However, little is known about the transformation mechanism of antibiotics by manganese peroxidase (MnP) from microorganisms. This work investigated the transformation characteristics, the antibacterial activity of byproducts, and the degradation mechanism of tetracycline (TC) by purified MnP from Phanerochaete chrysosporium. The results show that nitrogen-limited and high level of Mn²⁺ medium could obtain favorable MnP activity and inhibit the expression of lignin peroxidase by Phanerochaete chrysosporium. The purified MnP could transform 80% tetracycline in 3 h, and the threshold of reaction activator (H₂O₂) was about 0.045 mmol L^-1. After the 3rd cyclic run, the transformation rate was almost identical at the low initial concentration of TC (77.05-88.47%), while it decreased when the initial concentration was higher (49.36-60.00%). The antimicrobial potency of the TC transformation products by MnP decreased throughout reaction time. We identified seven possible degradation products and then proposed a potential TC transformation pathway, which included demethylation, oxidation of the dimethyl amino, decarbonylation, hydroxylation, and oxidative dehydrogenation. These findings provide a novel comprehension of the role of MnP on the fate of antibiotics in nature and may develop a potential technology for tetracycline removal.

Simultaneous removal of nitrate, manganese, and tetracycline by Zoogloea sp. MFQ7: Adsorption mechanism of tetracycline by biological precipitation

A Mn(II) oxidizing-denitrifying and tetracycline (TC) removal bacterium Zoogloea sp. MFQ7 was isolated in this study. Nitrogen removal was 83.49% by nitrogen balance experiment. The maximum removal efficiencies of nitrate, Mn(II), and TC by strain MFQ7 within 96 h was 100.00, 74.56, and 63.59% at C/N of 2.0, pH of 7.0, Mn(II) of 20 mg L^-1, temperature of 30.0 °C, and TC of 0.2 mg L^-1. SEM illustrated that biogenic manganese oxides (BMO) was petal-like, XRD and XPS analyses confirmed that MnO₂ was the main component of BMO. Besides, the maximum adsorption capacity of BMO for TC was 52.21 mg g^-1. FTIR detected the changes in TC adsorption by BMO. Pseudo-second-order model (R² = 0.994) explained the adsorption kinetics of TC on BMO and Langmuir isotherm model (R² = 0.983) suggested that it was homogeneous adsorption, thermodynamics data (ΔG < 0, ΔH = 18.31 kJ mol^-1, ΔS = 72.8 J (mol*K)^-1) confirmed that adsorption was endothermic and spontaneous.

Enhanced removal of oxytetracycline antibiotics from water using manganese dioxide impregnated hydrogel composite: Adsorption behavior and oxidative degradation pathways

The present work provides the first attempt of using manganese dioxide loaded poly(sodium acrylate) hydrogel (MnO₂@PSA) to address potential threats posed by oxytetracycline (OTC) antibiotics in aqueous environment. The MnO₂@PSA was prepared via a facile approach and demonstrated enhanced removal performance even under extremely high concentrations of OTC. The outstanding performance exhibited by MnO₂@PSA was attributed to synergetic effects of adsorption oxidative degradation. The synthesized composite was characterized evaluated under varying conditions. The adsorption pH was optimized at pH 5, at which the removal efficiency OTC was reached 91.46%. According to the kinetics study, the pseudo-second-order kinetic model was the best to explain the adsorption data, implying the interaction mechanisms were dominated by chemisorption. The Langmuir isotherm model was the best to explain the isotherm data, and the corresponding maximum adsorbed amount of OTC was 1150.4 mg g^-1. The MnO₂@PSA was highly selective for OTC adsorption and degradation under the presence of natural organic matter and common environmental metal ions. The oxidative degradation study indicated that OTC molecules were structurally degraded into 15 intermediate products via six reaction pathways. Both the theoretical models and spectroscopic methods demonstrated the removal mechanism of OTC onto MnO₂@PSA was governed by ion exchange, cation-π bonding, hydrogen-bonding, and π-π electron donor-acceptor. Overall, MnO₂@PSA is an excellent and environmentally sustainable material to remove OTC from water and wastewater via the combined effects of adsorption and oxidative degradation.

A Review of Caffeine Adsorption Studies onto Various Types of Adsorbents

A systematic literature review of publications from 2000 to 2020 was carried out to identify research trends on adsorbent materials for the removal of caffeine from aqueous solutions. Publications were retrieved from three databases (Scopus, Web of Science, and Google Scholar). Words "adsorption AND caffeine" were examined into titles, abstracts, and keywords. A brief bibliometric analysis was performed with emphasis on the type of publication and of most cited articles. Materials for the removal of caffeine were classified according to the type of material into three main groups: organic, inorganic, and composites, each of them subdivided into different subgroups consistent with their origin or production. Tables resume for each subgroup of adsorbents the key information: specific surface area, dose, pH, maximum adsorption capacity, and isotherm models for the removal of caffeine. The highest adsorption capacities were achieved by organic adsorbents, specifically those with granular activated carbon (1961.3 mg/g) and grape stalk activated carbon (916.7 mg/g). Phenyl-phosphate-based porous organic polymer (301 mg/g), natural sandy loam sediment (221.2 mg/g), composites of MCM-48 encapsulated graphene oxide (153.8 mg/g), and organically modified clay (143.7 mg/g) showed adsorption capacities lower than those of activated carbons. In some activated carbons, a relation between the specific surface area (SSA) and the maximum adsorption capacity (Q max) was found.

Tetracyclines in the environment: An overview on the occurrence, fate, toxicity, detection, removal methods, and sludge management

Tetracyclines (TCs) are a group of broad-spectrum antibiotics having vast human, veterinary, and aquaculture applications. The continuous release of TCs residues into the environment and the inadequate removal through the conventional treatment systems result in its prevalent occurrence in soil, surface water, groundwater, and even in drinking water. As aqueous TCs contamination is the tip of the iceberg, and TCs possess good sorption capacity towards soil, sediments, sludge, and manure, it is insufficient to rely on the sorptive removal in the conventional water treatment plants. The severity of the TCs contamination is evident from the emergence of TCs resistance in a wide variety of microorganisms. This paper reviews the recent research on the TCs occurrence in the environmental matrices, fate in natural systems, toxic effects, and the removal methods. The high performance liquid chromatography (HPLC) determination of TCs in environmental samples and the associated technology developments are analyzed. The benefits and limitations of biochemical and physicochemical removal processes are also discussed. This work draws attention to the inevitability of proper TC sludge management. This paper also gives insight into the limitations of TCs related research and the future scope of research in environmental contamination by TCs residues.

Formation and mechanisms of nano-metal oxide-biochar composites for pollutants removal: A review

Biochar, a carbon-rich material, has been widely used to adsorb a range of pollutants because of its low cost, large specific surface area (SSA), and high ion exchange capacity. The adsorption capacity of biochar, however, is limited by its small porosity and low content of surface functional groups. Nano-metal oxides have a large SSA and high surface energy but tend to aggregate and passivate because of their fine-grained nature. In combining the positive qualities of both biochar and nano-metal oxides, nano-metal oxide-biochar composites (NMOBCs) have emerged as a group of effective and novel adsorbents. NMOBCs improve the dispersity and stability of nano-metal oxides, rich in adsorption sites and surface functional groups, maximize the adsorption capacity of biochar and nano-metal oxides respectively. Since the adsorption capacity and mechanisms of NMOBCs vary greatly amongst different preparations and application conditions, there is a need for a review of NMOBCs. Herein we firstly summarize the recent methods of preparing NMOBCs, the factors influencing their efficacy in the removal of several pollutants, mechanisms underlying the adsorption of different pollutants, and their potential applications for pollution control. Recommendations and suggestions for future studies on NMOBCs are also proposed.