Abstract

The primary aerobic and anaerobic biodegradability at intermediate concentrations (50–5000 μg/l) of the antibiotics olaquindox (OLA), metronidazole (MET), tylosin (TYL) and oxytetracycline (OTC) was studied in a simple shake flask system simulating the conditions in surface waters. The purpose of the study was to provide rate data for primary biodegradation in the scenario where antibiotics pollute surface waters as a result of run-off from arable land. The source of antibiotics may be application of manure as fertilizer or excreta of grazing animals. Assuming first-order degradation kinetics, ranges of half-lifes for aerobic degradation of the four antibiotics studied were 4–8 days (OLA), 9.5–40 days (TYL), 14–104 days (MET) and 42–46 days (OTC). OLA and OTC were degraded with no initial lag phase whereas lag phases from 2 to 34 days (MET) and 31 to 40 days (TYL) were observed for other substances. The biodegradation behaviour was influenced by neither the concentrations of antibiotics nor the time of the year and location for sampling of surface water. Addition of 1 g/l of sediment or 3 mg/l of activated sludge from wastewater treatment increased the biodegradation potential which is believed to be the result of increased bacterial concentration in the test solution. Biodegradation was significantly slower in tests conducted in absence of oxygen. Assessments of the toxic properties of antibiotics by studying the influence on the biodegradation rates of ¹⁴C-aniline at different concentrations of antibiotics showed that no tests were conducted at toxic concentrations.

The adsorption kinetics of four nitroimidazoles, Dimetridazole (DMZ), Metronidazole (MNZ), Ronidazole (RNZ) and Tinidazole (TNZ), were studied on three activated carbons: two commercial carbons from Sorbo-Norit (S) and Merck (M) and a third prepared by chemical activation of petroleum coke (C). Experimental data of the corresponding adsorption kinetics were analyzed by applying pseudo-first and pseudo-second-order models and a general diffusion model. Application of pseudo-first and pseudo-second-order kinetic models verified the following: (i) The kinetic model used that better predicts the adsorption rates depends of both the adsorbent and adsorbate studied. (ii) Nitroimidazole adsorption rate decreases in the order MNZ>DMZ>RNZ>TNZ; therefore, in the case of MNZ, molecular size does not appear to be a determining factor in the process. (iii) Nitroimidazole adsorption rate on carbons increases in the order C

The objective of the present study was to analyse the behaviour of activated carbon with different chemical and textural properties in nitroimidazole adsorption, also assessing the combined use of microorganisms and activated carbon in the removal of these compounds from waters and the influence of the chemical nature of the solution (pH and ionic strength) on the adsorption process. Results indicate that the adsorption of nitroimidazoles is largely determined by activated carbon chemical properties. Application of the Langmuir equation to the adsorption isotherms showed an elevated adsorption capacity (X(m)=1.04-2.04 mmol/g) for all contaminants studied. Solution pH and electrolyte concentration did not have a major effect on the adsorption of these compounds on activated carbon, confirming that the principal interactions involved in the adsorption of these compounds are non-electrostatic. Nitroimidazoles are not degraded by microorganisms used in the biological stage of a wastewater treatment plant. However, the presence of microorganisms during nitroimidazole adsorption increased their adsorption on the activated carbon, although it weakened interactions between the adsorbate and carbon surface. In dynamic regime, the adsorptive capacity of activated carbon was markedly higher in surface water and groundwater than in urban wastewaters.

A simple classification scheme is suggested to characterize the biological degradation of micropollutants such as pharmaceuticals, musk fragrances and estrogens during wastewater treatment. The scheme should be a basis for the discussion about potential removal efficiencies. Hence, the biological degradation of 25 pharmaceuticals, hormones and fragrances was studied in batch experiments at typical concentration levels using activated sewage sludge originating from nutrient-eliminating municipal wastewater treatment plants. Since pseudo first-order degradation kinetics was observed for all compounds down to ng L(-1) levels, the removal rates can be predicted for various reactor configurations. Therefore dilution of wastewater (e.g. by extraneous water) is expected to reduce the degree of biological removal. Wastewater segregation and treatment at the source are therefore to be favoured for elimination of persistent micropollutants over centralized end-of-pipe treatment. For reactor configurations typical for nutrient removal in municipal wastewater, the derived formula for predicting removal allows the identification of three groups of micropollutants according to their degradation constant k(biol): compounds with k(biol)<0.1 L g(SS)(-1)d(-1) are not removed to a significant extent (<20%), compounds with k(biol)>10 L g(SS)(-1)d(-1) transformed by >90% and in-between moderate removal is expected. Based on the degradation of a heterogeneous group of 35 compounds (including literature data), state of the art biological treatment schemes for municipal wastewater are not efficient in degrading pharmaceuticals: only 4 out of 35 compounds are degraded by more than 90% while 17 compounds are removed by less than 50%.

Abstract

The behaviour of 13 pharmaceutical and personal care products (PPCPs) has been studied during anaerobic digestion of sewage sludge: two musks (Galaxolide and Tonalide), one tranquilliser (Diazepam), one anti-epileptic (Carbamazepine), three anti-phlogistics (Ibuprofen, Naproxen and Diclofenac), two antibiotics (Sulfamethoxazole and Roxithromycin), one X-ray contrast medium (Iopromide) and three oestrogens (Estrone, 17β-oestradiol and 17α-ethinyloestradiol). Two parallel processes have been carried out, one in mesophilic range (37 °C) and the other in thermophilic range (55 °C). The influence of temperature and sludge retention time (SRT) has been analysed. Among the substances considered, the higher removal efficiencies were achieved for the antibiotics, natural oestrogens, musks and Naproxen. For the other compounds, the values ranged between 20% and 60%, except for Carbamazepine, which showed no elimination. The removal of oestrogens, Diazepam and Diclofenac occurred after sludge adaptation. In general, no influence of SRT and temperature on PPCPs removal was observed.

Considering the difficulty of obtaining reliable PPCPs concentrations, especially those corresponding to the fractions sorbed onto sludge, a methodology to validate the experimental data has been developed and successfully applied.

Abstract

Degradation rates and removal efficiencies of Metronidazole using UV, UV/H₂O₂, H₂O₂/Fe²⁺, and UV/H₂O₂/Fe²⁺ were studied in de-ionized water. The four different oxidation processes were compared for the removal kinetics of the antimicrobial pharmaceutical Metronidazole. It was found that the degradation of Metronidazole by UV and UV/H₂O₂ exhibited pseudo-first order reaction kinetics. By applying H₂O₂/Fe²⁺, and UV/H₂O₂/Fe²⁺ the degradation kinetics followed a second order behavior. The quantum yields for direct photolysis, measured at 254 nm and 200–400 nm, were 0.0033 and 0.0080 mol E⁻¹, respectively. Increasing the concentrations of hydrogen peroxide promoted the oxidation rate by UV/ H₂O₂. Adding more ferrous ions enhanced the oxidation rate for the H₂O₂/Fe²⁺ and UV/H₂O₂/Fe²⁺ processes. The major advantages and disadvantages of each process and the complexity of comparing the various advanced oxidation processes on an equal basis are discussed.

Newly designed magnetic g-C3N4/MnFe2O4/graphene (C3N4@MnFe2O4-G) composites with enhanced photocatalytic activity were successfully synthesized. The photocatalytic behavior of C3N4@MnFe2O4-G was assessed in photo Fenton-like degradation of antibiotic pollutants, including metronidazole, amoxicillin, tetracycline and ciprofloxacin, using persulfate (S2O8(2-)) as an oxidant under visible light illumination. The C3N4@MnFe2O4-G composites show a superior catalytic activity with 94.5% removal of metronidazole that was almost 3.5 times as high as that of the pure g-C3N4, which could be attributed to the synergistic promoting effect of the favorable adsorptivity, enhanced light absorption intensity, high migration efficiency of charge carriers and longer lifetime of separated electron-hole pairs derived from the formation of the heterojunction between the g-C3N4 and MnFe2O4. Moreover, the self-redox properties of iron and manganese atoms in MnFe2O4 induced by S2O8(2-) were particularly beneficial for the generation of SO4(-). The quenching tests and electron spin resonance (ESR) display that h(+), O2(-), SO4(-) and OH are responsible for the antibiotics decomposition. The heterogeneous photocatalyst could be easily recovered by an extra magnetic field and reused several times without any obvious deterioration in catalytic activity. According to the investigation of active species and identified intermediates, the possible photocatalytic mechanism and reaction pathways have been proposed.

A high-performance broad band UV/visible photodetector has been successfully fabricated on a fully wide bandgap ZnO/ZnS type-II heterojunction core/shell nanowire array. The device can detect photons with energies significantly smaller (2.2 eV) than the band gap of ZnO (3.2 eV) and ZnS (3.7 eV), which is mainly attributed to spatially indirect type-II transition facilitated by the abrupt interface between the ZnO core and ZnS shell. The performance of the device was further enhanced through the piezo-phototronic effect induced lowering of the barrier height to allow charge carrier transport across the ZnO/ZnS interface, resulting in three orders of relative responsivity change measured at three different excitation wavelengths (385, 465, and 520 nm). This work demonstrates a prototype UV/visible photodetector based on the truly wide band gap semiconducting 3D core/shell nanowire array with enhanced performance through the piezo-phototronic effect.

Among all the functional materials, ZnO plays an outstanding role in terms of chemical and physical properties, but also in terms of morphological variety and the number of reported synthesis approaches. Complex shapes and hierarchical architectures make ZnO a perfect example to study chemical and crystallization mechanisms. In this review article, we will discuss the nucleation and growth of ZnO nanostructures in liquid media by classical and non-classical (i.e., particle-based) crystallization pathways. We elaborate the chemical conditions and parameters that are responsible for the occurrence of one or the other pathway.

A series of Bi₂WO₆/ZnO heterojunction photocatalysts with different Bi₂WO₆ concentrations (1wt%, 2wt%, 4wt%, 8wt%) were prepared by hydrothermal method at different temperatures(120℃-220℃). The prepared pure ZnO, Bi₂WO₆ and Bi2WO6/ZnO heterojunction photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscope (FT-IR), UV-Vis diffuse reflectance spectra, and photoluminescence (PL) spectroscope, respectively. The photocatalytic activity of the prepared catalysts was evaluated by photocatalytic degradation of acid orange II under UV light (λ=365nm) irradiation. Results show that the photocatalytic activity of Bi₂WO₆/ZnO heterojunction photocatalysts is superior to that of pure ZnO and Bi₂WO₆. The optimal concentration of Bi₂WO₆ is 4wt% and the best hydrothermal temperature is 150℃. Under the above conditions, the prepared composite catalyst shows about 2.4 times in activity of the pure ZnO. The formation of Bi₂WO₆/ZnO heterojunction could effectively suppress the recombination of the photo generated electron and hole pairs and result in an increase in photocatalytic activity. Moreover, more surface OH groups over the Bi₂WO₆/ZnO heterojunction photocatalysts will further benefit the improvement of photocatalytic activity.

In this study, heterogeneous Fenton-like degradation of reactive azo dye Rhodamine 6G in water was investigated over a CuFeZSM-5 zeolite catalyst prepared by hydrothermal synthesis. At initial pH of 3.4, a color removal of 100% was achieved after a reaction time of 45 min. TOC elimination was measured to be 51.8% after 2 h of oxidation. Initial decolorization rate was described by an equation of -r(A0) = 4.56 x 10(2) e(-24.83/RT)C(R6G,0)C(0.35)(H2O2,0) where R is in kJ/mol. The leaching of iron and copper cations from zeolite structure into the solution during oxidation was dependent on pH strongly. The regulation of pH from 6.5 (dye solution pH) to 3.4, increased leaching for iron from 0.7 to 0.8 mg/dm3 and for copper from 1.4 to 2.1 mg/dm3. The copper was totally leached from the catalyst during the process at pH 3.4.