Influence of light and Fe(III) ions on tetracycline degradation

Interaction and band structure-determined inhibition of negative Cr (VI) and positive Fe (III) for antibiotic photodegradation by nitrogen-doped dissolved black carbon

The influences of the positive Fe3+ and the negative Cr2O72- on the tetracycline (TC) photodegradation by N-doped dissolved black carbon (NDBC) have been investigated in this work. A series of samples (NDBC300, NDBC400 and NDBC500) have been extracted from the corresponding biochar. NDBC400 has the best photodegradation performance (79%) for TC under visible light irradiation. Adding Cr2O72- and Fe3+ can reduces TC photodegradation efficiency into 37% and 53%, respectively. This maybe from that Cr2O72- has stronger interaction with NDBC400 than Fe3+ since it can quench more fluorescence intensity of NDBC400 than Fe3+. Furthermore, Cr2O72- can reduce the steady-state concentration of 3NDBC400*, 1O2 and •OH, whereas Fe3+can just reduce the steady-state concentration of 3NDBC400* and increase the concentration of •OH. This may explain why Cr2O72- has stronger inhibit performance of TC photodegradation by NDBC400 than Fe3+. The band structures of NDBC400, NDBC400-Fe3+ and NDBC400-Cr2O72- are constructed. And the VB of NDBC400-Fe3+ has a stronger ability to produce •OH than NDBC400. In summary, coupling interaction and band structure characterization of NDBC400, NDBC400-Fe3+ and NDBC400-Cr2O72- can explain well why Cr2O72 has stronger inhibition effect than Fe3+ and Fe3+ can increase the concentration of •OH. This work provides a deep insight for the photochemical behavior of dissolved black carbon and the transformation behavior of the co-existed metal ions and antibiotics.

Floc aging: Crystallization and improving low molecular weight organic removal in re-coagulation

Iron coagulants have been used extensively in drinking water treatment. This typically produces substantial quantities of insoluble iron hydrolysis products which interact with natural and anthropogenic organic substances during the coagulation process. Previous studies have shown that the removal of low molecular weight (MW) organics is relatively poor by coagulation, which leads to their presence during disinfection, with the formation of halogenated byproducts, and in treated water supplies as potentially biodegradable material. Currently, there is little knowledge about the changes that occur in the nature of coagulant flocs as they age with time and how such changes affect interactions with organic matter, especially low MW organics. To improve this deficiency, this study has investigated the variation of aged flocs obtained from two commonly used iron salts and their impact on representative organic contaminants, natural organic matter (NOM) and tetracycline antibiotic (TC), in a real surface water. It was found that aging resulted in increasing crystallization of the flocs, which can play a beneficial role in activating persulfate oxidant to remove the representative organics. Furthermore, acidification was also found to further improve the removal of low MW natural organics and tetracycline. In addition, the results showed that the low MW fractions of NOM (<1 K Dalton) were substantially removed by the aging flocs. These results are in marked contrast to the poor removal of low MW organic substances by conventional coagulation, with or without added oxidants, and show that aged flocs have a high potential of reuse for re-coagulation and activation of oxidants to reduce low MW organics, and enhance drinking water quality.

Studies on the Efficiency of Iron Release from Fe(III)-EDTA and Fe(III)-Cit and the Suitability of These Compounds for Tetracycline Degradation

Iron ions can be used to degrade tetracycline dispersed in nature. Studies of absorption and fluorescence spectra and quantum chemistry calculations showed that iron is more readily released from Fe(III)-citrate than from Fe(III)-EDTA, so Fe(III)-citrate (Fe(III)-Cit) is more suitable for tetracycline (TC) degradation. At 30 °C, a severe degradation of TC by Fe(III)-Cit occurred as early as after 3 days of incubation in the light, and after 5 days in the dark. In contrast, the degradation of TC by Fe(III)-EDTA proceeded very slowly in the dark. By the fifth day of incubation of TC with Fe(III)-Cit in darkness, the concentrations of the former compound dropped by 55% and 75%, at 20 °C and 30 °C, respectively. The decrease in tetracycline concentrations caused by Fe(III)-EDTA in darkness at the same temperatures was only 2% and 6%, respectively. Light increased the degradation rates of TC by Fe(III)-EDTA to 20% and 56% at 20 °C and 30 °C, respectively. The key role of the light in the degradation of tetracycline by Fe(III)-EDTA was thus demonstrated. The TC degradation reaction showed a second-order kinetics. The rate constants of Fe(III)-Cit-induced TC degradation at 20 °C and 30 °C in darkness were k = 4238 M^-1day^-1 and k = 11,330 M^-1day^-1, respectively, while for Fe(III)-EDTA were 55 M^-1day^-1 and 226 M^-1day^-1. In light, these constants were k = 15,440 M^-1day^-1 and k = 40,270 M^-1day^-1 for Fe(III)-Cit and k = 1012 M^-1day^-1 and 2050 M^-1day^-1 at 20 °C and 30 °C; respectively. A possible reason for the higher TC degradation rate caused by Fe(III)-Cit can be the result of its lower thermodynamical stability compared with Fe(III)-EDTA, which we confirmed with our quantum chemistry calculations. Two quantum chemistry calculations showed that the iron complex with EDTA is more stable (the free energy of the ensemble is 15.8 kcal/mol lower) than the iron complex with Cit; hence, Fe release from Fe(III)-EDTA is less effective.

Study on the degradation of tetracycline in wastewater by micro-nano bubbles activated hydrogen peroxide

Recently, the micro-nano bubble (MB) technology has attracted people's attention due to its special advantages. Here, we carried out the technology of combining MB and hydrogen peroxide (MB/H₂O₂) to achieve efficient degradation of tetracycline wastewater. The effect of MB/H₂O₂ technology on the degradation efficiency of tetracycline was deeply analysed by investigating the reaction time, H₂O₂ dosage, pH and MB inlet flow. The results showed that the degradation rate of tetracycline hydrochloride by MB/H₂O₂ technology can reach 92.43%, which is 9.44 and 3.94 times that of MB and H₂O₂ alone. Through electron spin resonance (ESR) analysis and free radical quenching experiments, a possible mechanism for MB/H₂O₂ technology to efficiently degrade TC was proposed. In the MB/H₂O₂ system, the high temperature and high pressure environment generated when MB ruptures can activate H₂O₂ to obtain a higher number of active oxygen species. •OH is the main reactive oxygen radical in the process of MB/H₂O₂ degradation of TC, followed by HO₂•/•O₂-. In addition, the possible intermediate products of the oxidation TC process were identified by HPLC-MS technology. Under the action of •OH and HO₂•/•O₂- free radicals, TC molecules undergo demethylation and hydroxylation, ring-opening reactions, isomerization, deethylation, deacylation, deamination and dehydration reactions to generate intermediate products and finally convert them into CO₂ and H₂O. The development of MB/H₂O₂ technology can potentially be used to efficiently remove TC substances in the water environment and provide a new method for water purification.

Effect of Packaging Materials and the Leached Iron on the Stability of Butorphanol Tartrate Injection

The aim of this study was to investigate the effect of various parameters on the stability of butorphanol tartrate injection and to screen the optimal packaging material. The effect of the headspace oxygen levels, ampoule color, manufacturer, and size on the stability of butorphanol tartrate formulation were evaluated. The headspace oxygen levels controlled by nitrogen purging were found to be particularly effective in improving stability of the butorphanol formulation, especially below 2%. Although it is a photolabile drug, butorphanol tartrate was getting degraded at much higher extent in amber color ampoules in comparison to clear ampoules. The degradation by oxidation was found to be a free radical-mediated process catalyzed by the presence of iron ions leached from the amber ampoules. The ampoule manufacturers also had a significant effect on the stability of butorphanol. Two-milliliter ampoules provided a better stability of the butorphanol tartrate injection than 1mL ampoules as 2-mL ampoules had the lower headspace oxygen level at the same level of oxygen content. The oxidation mechanism of the butorphanol tartrate injection was investigated under various conditions, which include iron powder spiking, removal of excipients, exposure to oxygen/nitrogen, exposure to stainless steel and at different pH. Iron powder spiking, presence of citric acid, exposure to oxygen, exposure to stainless steel, and high pH accelerated the oxidative degradation. The effect of oxygen, iron ion and citric acid is in agreement with a metal-catalyzed oxidation mechanism called Udenfriend reaction. Based on the formulation test results, limiting headspace oxygen level, ampoule color, manufacturer, size, controlling iron ion contamination, and pH are recommended for formulation development. In conclusion, it can be suggested that this study can lead to a better understanding of the degradation mechanism of butorphanol tartrate; hence, it would contribute to the development of butorphanol tartrate injection with improved stability. Virous packaging materials have different effects on the stability of butorphanol tartrate injection, and the leached iron of packaging ampoules and stainless steel can trigger Udenfriend reaction with butorphanol tartrate and citric acid (CA), which lead to the oxydative degradation of butorphanol tartrate injection.

Application of Biochar Derived From Pyrolysis of Waste Fiberboard on Tetracycline Adsorption in Aqueous Solution

In this study, biochars derived from waste fiberboard biomass were applied in tetracycline (TC) removal in aqueous solution. Biochar samples were prepared by slow pyrolysis at 300, 500, and 800°C, and were characterized by ultimate analysis, Fourier transform infrared (FTIR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET), etc. The effects of ionic strength (0–1.0 mol/L of NaCl), initial TC concentration (2.5–60 ppm), biochar dosage (1.5–2.5 g/L), and initial pH (2–10) were systemically determined. The results present that biochar prepared at 800°C (BC800) generally possesses the highest aromatization degree and surface area with abundant pyridinic N (N-6) and accordingly shows a better removal efficiency (68.6%) than the other two biochar samples. Adsorption isotherm data were better fitted by the Freundlich model (R² is 0.94) than the Langmuir model (R² is 0.85). Thermodynamic study showed that the adsorption process is endothermic and mainly physical in nature with the values of ΔH⁰ being 48.0 kJ/mol, ΔS⁰ being 157.1 J/mol/K, and ΔG⁰ varying from 1.02 to −2.14 kJ/mol. The graphite-like structure in biochar enables the π-π interactions with a ring structure in the TC molecule, which, together with the N-6 acting as electron donor, is the main driving force of the adsorption process.