Chlortetracycline degradation by photocatalytic ozonation in the aqueous phase: mineralization and the effects on biodegradability

Efficient removal of chlortetracycline hydrochloride and doxycycline hydrochloride from aqueous solution by ZIF-67

ZIF-67 nanoparticles were synthesized by a simple method at room temperature and used to remove chlortetracycline hydrochloride (CTC) and doxycycline hydrochloride (DOX) from water. ZIF-67 was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) surface area, X-ray photoelectron spectroscopy (XPS), thermogravimetry (TGA) and zeta potential analyzer. The morphology and chemical composition of the synthesized ZIF-67 were characterized. The effects of key parameters such as pH, dosage, temperature, contact time, different initial concentrations and coexisting ions on the adsorption behavior were systematically studied. The results of batch adsorption experiments indicate that the adsorption process conforms to the pseudo-second-order kinetic model and Sips model. At 303K, the removal rates of CTC and DOX at 150 mg/L reached 99.16 % and 97.61 %, and the maximum adsorption capacity of CTC and DOX reached 1411.68 and 1073.28 mg/g, respectively. At the same time, ZIF-67 has excellent stability and reusability. Most importantly, the possible adsorption mechanism is proposed by exploring the changes of SEM, TEM, BET and FT-IR characterization results before and after the reaction, which mainly includes pore filling, electrostatic interaction and π-π interaction. The prepared ZIF-67 has a large specific surface area (1495.967 m2 g-1), achieves a high removal rate within a short time frame, and maintains a high removal rate across a wide pH range. These characteristics make ZIF-67 a potentially promising adsorbent for removing antibiotics from aqueous solutions.

Activation of persulfate by homogeneous and heterogeneous iron catalyst to degrade chlortetracycline in aqueous solution

This study investigates the removal of chlortetracycline (CTC) antibiotic using sulfate radical-based oxidation process. Sodium persulfate (PS) was used as a source to generate sulfate radicals by homogeneous (Fe²⁺) and heterogeneous (zero valent iron, ZVI) iron as a catalyst. Increased EDTA concentration was used to break the CTC-Fe metal complexes during CTC estimation. The influence of various parameters, such as PS concentration, iron (Fe²⁺ and ZVI) concentration, PS/iron molar ratio, and pH were studied and optimum conditions were reported. CTC removal was increased with increasing concentration of PS and iron at an equal molar ratio of PS/Fe²⁺ and PS/ZVI processes. PS/Fe²⁺ and PS/ZVI oxidation processes at 1:2 (500 μM PS and 1000 μM) molar ratio showed 76% and 94% of 1 μM CTC removal in 2 h. Further increased molar ratio 1:2 onwards, PS/Fe²⁺ process showed a slight increase in CTC degradation whereas in PS/ZVI process showed similar degradation to 1:2 (PS/Fe) ratio at constant PS 500 μM concentration. Slower activation of persulfate which indirectly indicates the slower generation of sulfate radicals in PS/ZVI process showed higher degradation efficiency of CTC. The detected transformation products and their estrogenicity results stated that sulfate radicals seem to be efficient in forming stable and non-toxic end products.

Ozonation of chlortetracycline in the aqueous phase: Degradation intermediates and pathway confirmed by NMR

Chlortetracycline (CTC) degradation mechanism in aqueous phase ozonation was evaluated for degradation mechanism and its correlation with the biodegradability and mineralization. CTC was removed within 8 and 4 min of ozonation at pH 2.2 and 7.0, respectively. At pH 2.2, HPLC-triple quadrupole mass spectrometry (MS) detected 30 products. The structures for some of these products were proposed on the basis of ozonation chemistry, CTC structure and MS data; these structures were then confirmed by nuclear magnetic resonance (NMR) spectra. Double bond cleavages, dimethyl amino group oxidation, opening and removal of the aromatic ring and dechlorination, mostly direct ozonation reactions, gave products with molecular weights (m.w.) 494, 510, 524, 495 and 413, respectively. Subsequent degradations gave products with m.w. 449, 465, 463 and 415. These products were arranged into a degradation pathway. At pH 7.0, the rate of reaction was increased, though the detected products were similar. Direct ozonation at pH 2.2 increased the biodegradability by altering the structures of CTC and its products. Nevertheless, direct ozonation alone remained insufficient for the mineralization, which was efficient at pH 7.0 due to the production of free radicals.

Preparation of Cathode-Anode Integrated Ceramic Filler and Application in a Coupled ME-EGSB-SBR System for Chlortetracycline Industrial Wastewater Systematic Treatment

Chlortetracycline (CTC) contamination of aquatic systems has seriously threatened the environmental and human health throughout the world. Conventional biological treatments could not effectively treat the CTC industrial wastewater and few studies have been focused on the wastewater systematic treatment. Firstly, 40.0 wt% of clay, 30.0 wt% of dewatered sewage sludge (DSS), and 30.0 wt% of scrap iron (SI) were added to sinter the new media (cathode-anode integrated ceramic filler, CAICF). Subsequently, the nontoxic CAICF with rough surface and porous interior packed into ME reactor, severing as a pretreatment step, was effective in removing CTC residue and improving the wastewater biodegradability. Secondly, expanded granular sludge bed (EGSB) and sequencing batch reactor (SBR), serving as the secondary biological treatment, were mainly focusing on chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) removal. The coupled ME-EGSB-SBR system removed about 98.0% of CODcr and 95.0% of NH3-N and the final effluent met the national discharged standard (C standard of CJ 343-2010, China). Therefore, the CTC industrial wastewater could be effectively treated by the coupled ME-EGSB-SBR system, which has significant implications for a cost-efficient system in CTC industrial systematic treatment and solid wastes (DSS and SI) treatment.

Catalysed ozonation for removal of an endocrine-disrupting compound using the O3/Fenton reagents system

Aqueous solutions of diethyl phthalate (DEP) were oxidized by using ozone combined with Fenton reagents. The effects of operating parameters such as initial pH; initial concentration of DEP, H2O2 and Fe2+; [H2O2]0/[Fe2+]0 ratio and O3 dosage on the degradation rates of DEP were investigated. The results showed that DEP degradation is strongly dependant on the pH; initial concentrations of the phthalate, H2O2 and Fe2+; [H2O2]0/[Fe2+]0 ratio and O3 dosage. The addition of H2O2 and Fe2+ ions was effective to achieve almost 98% degradation of 200 mg L(-1) of DEP in about 40 min using a dose of O3=45 g m(-3) NTP; [H2O2]0=2.5×10(-2) mol L(-1) and [Fe(II)]0=5×10(-3) mol L(-1), as compared to over 60 min by using O3 and Fenton processes applied separately. DEP degradation followed apparent pseudo-first-order kinetics under ozonation, Fenton's reagents oxidation and the combined ozonation/Fenton reagents oxidation process. The overall reaction rates were significantly enhanced in the O3/Fe2+/H2O2 oxidation system, and allows achieving 100% degradation of DEP (100 mg L(-1)) in 30 min of reaction time. The notable decrease in DEP removal rate observed in the presence of a radical scavenger indicates that there was an obvious synergetic effect in the combined ozonation/Fenton reagent process most likely because ozonation could accelerate Fenton reagents to generate hydroxyl radical HO•. Thus, the reaction between DEP and HO• proceeds mainly in the bulk of the aqueous phase. Under optimal conditions, the O3/Fe2+/H2O2 system oxidation was the most effective in DEP removal in water.

Removal of oxalic acid, oxamic acid and aniline by a combined photolysis and ozonation process

Aniline (ANL), an aromatic amine, oxalic acid (OXA) and oxamic acid (OMA), short-chain carboxylic acids, were chosen as model organic pollutants for testing the combined effect of neat photolysis and ozonation in the treatment of aqueous effluents. In order to better understand the results, single ozonation and neat photolysis were also carried out. OXA has a high refractory character relatively to single ozonation and neat photolysis only accounted for 26% conversion of OXA after 2 h of reaction. On the other hand, OXA complete degradation was observed in less than an hour when ozone and light were used simultaneously. Despite OMA, a compound never studied before by a combined ozonation and photolysis treatment, being highly refractory to oxidation, more than 50% was removed by photo-ozonation after 3 h of reaction. In the case of ANL, both single ozonation and photo-ozonation resulted in 100% removal in a short reaction period due to the high reactivity of ozone to attack this type of molecules; however, only the combined method leads to efficient mineralization (89%) after 3 h of reaction. A significant synergetic effect was observed in the degradation of the selected contaminants by the simultaneous use of ozone and light, since the mineralization rate of combined method is higher than the sum of the mineralization rates of the individual treatments. The promising results observed in the degradation of the selected contaminants are paving the way to the application of photo-ozonation in the treatment of wastewater containing this type of pollutants.

Organic pollutants removal in wastewater by heterogeneous photocatalytic ozonation

Heterogeneous photocatalysis and ozonation are robust advanced oxidation processes for eliminating organic contaminants in wastewater. The combination of these two methods is carried out in order to enhance the overall mineralization of refractory organics. An apparent synergism between heterogeneous photocatalysis and ozonation has been demonstrated in many literatures, which gives rise to an improvement of total organic carbon removal. The present overview dissects the heterogeneous catalysts and the influences of different operational parameters, followed by the discussion on the kinetics, mechanism, economic feasibility and future trends of this integrated technology. The enhanced oxidation rate mainly results from a large amount of hydroxyl radicals generated from a synergistically induced decomposition of dissolved ozone, besides superoxide ion radicals and the photo-induced holes. Six reaction pathways possibly exist for the generation of hydroxyl radicals in the reaction mechanism of heterogeneous photocatalytic ozonation.