Facile preparation of magnetic porous biochars from tea waste for the removal of tetracycline from aqueous solutions: Effect of pyrolysis temperature.

Pyrolysis process significantly influences the physicochemical properties and potential application of magnetic porous biochars (MPBCs). However, the effects of pyrolysis temperature on the properties of MPBCs as well as substantial adsorption are still unclear. This study reported a facile method to obtain the MPBC from tea waste via pyrolysis of a mixture of hydrochar, KHCO3, and FeCl3·6H2O under different temperatures (500-800 °C), and explored further the adsorption toward tetracycline (TC). Results showed pyrolysis temperature obviously influenced the physicochemical properties of MPBCs, and MPBC pyrolyzed at 700 °C (MPBC-700) has a highest specific surface area (1066 m2 g-1) and pore volume (2.693 cm3 g-1). However, the adsorption potential increased consistently from 59.35 mg g-1 for MPBC-500 to 333.22 mg g-1 for MPBC-800, suggesting that the surface area and pore volume were not the only factors determining TC adsorption. Further analysis showed that the pore-filling, π-π interaction, complexation, and hydrogen bonding contributed together to TC adsorption. Moreover, all MPBCs possessed a high saturation magnetization, indicating the easy separation by an external magnet. Therefore, MPBCs (especially at 700 °C) can act as the excellent adsorbents for contaminant removal due to their high separation, adsorption, and reuse performance.

Enhanced adsorption capacity of tetracycline on tea waste biochar with KHCO3 activation from aqueous solution.

Activation is an important pathway that can enhance the adsorption capacity of biochar. In this study, a modified tea waste biochar (MTWBC) was prepared via a two-step pyrolysis approach with KHCO3 activation. Pristine tea waste biochar (TWBC) was also produced as control via one-step pyrolysis without activation. Various characterizations were undertaken to investigate the influence of modification on the morphology, composition, carbon structure, surface area, and functional group of biochar, including scanning electron microscope (SEM), surface area and pore analyzer, element analysis, point of zero charge (pHPZC), X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). After KHCO3 activation treatment, the surface area, total pore volume, and micropore volume of MTWBC reached 1981 m2·g-1, 0.8547 cm3·g-1, and 0.6439 cm3·g-1 which were 7.34-fold, 7.27-fold, and 7.30-fold increases, respectively, compared with TWBC. The aromaticity, hydrophilicity, and polarity of the MTWBC increased after modification. More graphitization with less defective structures occurred in MTWBC after modification. The C-, O-, and N-containing groups in MTWBC also changed after the reaction of KHCO3. The pseudo-second-order and Freundlich models best described the adsorption process on biochar. The maximum adsorption capacity of tetracycline (TC) on MTWBC reached 293.46 mg·g-1, which was 15-fold more than that of TWBC (19.68 mg·g-1). An alkaline environment decreased the TC adsorption on biochars. The presence of Na+, K+, Ca2+, and Mg2+ inhibited TC adsorption onto biochars. The influence of Cu2+ on TC adsorption by biochars depends on its initial concentration. The enhanced adsorption capacity of TC on MTWBC was mainly attributable to the large surface area, the improved pore volume, and more aromatic structure. The adsorption mechanism was based on pore filling and π-π EDA interaction. Therefore, KHCO3 activated biochar has the potential to remove TC from aquatic environments.

Effect of carbonization methods on the properties of tea waste biochars and their application in tetracycline removal from aqueous solutions.

The properties of biochars and their adsorption performance are highly dependent on the carbonation methods. In this study, five carbonation methods, namely, hydrothermal treatment (HT), direct carbonization (BC), carbonization of hydrochar (HBC), KHCO3 activation carbonation (KBC), and KHCO3 activation carbonation of hydrochar (KHBC), were adopted to prepare tea waste biochars. Adsorption behaviors and mechanisms toward tetracycline (TC) by biochar in the aquatic environment were investigated. The results showed that carbonation methods significantly influence the morphology, carbon structure, chemical composition, and functional groups of the biochars based on the characterization of surface area and pore volume analysis, Fourier Transform Infrared Spectroscopy, Raman spectrum, Scanning Electron Microscope, Transmission Electron Microscope, X-ray photoelectron spectroscopy, X-Ray Diffraction, and elemental analysis. Combination of hydrothermal treatment with KHCO3 activation can significantly increase the surface area and enlarge the pore structure of biochar (KHBC and KBC). The BET of KHCO3-activated BCs nearly increased 280 times (KHBC: 1350.80 m2 g-1; KBC: 1405.06 m2 g-1). BET, total pore volume and micropores volume of biochar has a positive influence on TC adsorption capacity. In addition, all adsorption processes can be well fitted by Langmuir and pseudo-second-order kinetic models. The maximum adsorption capacity of KHCO3-activated BCs nearly increased approximately 40 times (KHBC: 451.45 mg g-1; KBC: 425.17 mg g-1). The dominant mechanisms of biochar-adsorbed TC were pore-filling effect and π-π interactions, followed by hydrogen bonds and electrostatic interactions. Therefore, KHBC has the potential to act as sorbents for TC removal from aquatic environment.

Dynamic transport of antibiotics and antibiotic resistance genes under different treatment processes in a typical pharmaceutical wastewater treatment plant.

The propagation of antibiotic resistance is a challenge for human health worldwide, which has drawn much attention on the reduction of the resistance genes. To understand their occurrence during different treatment processes, in this study, four classes of antibiotics (tetracyclines, sulfonamides, quinolones, and macrolides), eight antibiotic resistance genes (ARGs) (tetB, tetW, sul1, sul2, gyrA, qepA, ermB, and ermF), and two mobile elements (int1 and int2) were investigated in a typical pharmaceutical plant. The total concentrations of antibiotics were detected in the range of 2.6 × 102 to 2.5 × 103 ng/L in the treatment processes, and the high abundance of ARGs was detected in the biological treatment unit. The dynamic trend analysis showed that antibiotics were partially removed in the anaerobic/aerobic processes, where ARGs were proliferated. The abundance of tetB and gyrA genes was positively correlated with pH and EC (p < 0.05), and the tetW, sul1 and sul2 genes were significantly correlated with TOC, TN, and DO (p < 0.05), indicating the influence of physicochemical properties of the solution on the levels of ARG subtypes. The phylogenetic analysis showed that the tetW clones had high homology with some pathogenic microorganisms, such as Klebsiella pneumonia and Neisseria meningitides, which would threaten human health. Results indicated that the horizontal transfer acted as a major driver in the ARGs evolution.

Removal Behavior of Methylene Blue from Aqueous Solution by Tea Waste: Kinetics, Isotherms and Mechanism.

Tea waste (biosorbent) was characterized by BET, SEM, FTIR, XPS, solid state 13C-NMR and applied to remove methylene blue (MB) from aqueous solution. The effect of different factors on MB removal, kinetics, isotherms and potential mechanism was investigated. The results showed that tea waste contains multiple organic functional groups. The optimum solid-to-liquid ratio for MB adsorption was 4.0 g·L−1 and the initial pH of the MB solution did not need to be adjusted to a certain value. The pseudo-second-order model could well fit the adsorption kinetic process. The adsorption process could be divided into two stages: a fast adsorption stage and a slow adsorption stage. The adsorption isotherm could be well described by Langmuir and Temkin isotherm models. The maximum adsorption amount could reach 113.1461 mg·g−1 based on Langmuir isotherm fitting. Desorption and reusability experiments showed that MB adsorption onto tea waste could be stable and could not cause secondary pollution. The interaction mechanism between tea waste and MB involved electrostatic attraction, hydrogen bond, ion exchange, π-π binding. The organic functional groups of tea waste played an important role during the MB removal process. Therefore, tea waste has the potential to act as an adsorbent to remove MB from aqueous solution.

Phosphorus removal and N2O production in anaerobic/anoxic denitrifying phosphorus removal process: long-term impact of influent phosphorus concentration.

This study was conducted to investigate the long-term impact of influent phosphorus concentration on denitrifying phosphorus removal and N2O production during denitrifying phosphorous removal process. The results showed that, denitrifying phosphate accumulating organisms (DPAOs) could become dominant populations quickly in anaerobic/anoxic SBR by providing optimum cultivating conditions, and the reactor performed well for denitrifying phosphorus removal. The influent phosphorus concentration significantly affected anaerobic poly-ß-hydroxyalkanoates (PHA) synthesis, denitrifying phosphorus removal, and N2O production during the denitrifying phosphorus removal process. As the influent phosphorus concentration was more than 20 mg L(-1), the activity of DPAOs began to be inhibited due to the transformation of the available carbon source type. Meanwhile, N2O production was inhibited with the mitigation of anoxic NO2(-)-N accumulation. Adoption of a modified feeding could enhance denitrifying phosphorus removal and inhibit N2O production during denitrifying phosphorous removal processes.