Safe utilization of bioresources in gentamicin mycelial residues by thermal treatment: Antibiotic degradation, resistance gene inactivation and available nutrients promotion.

Gentamicin mycelium residues (GMRs) abundant in organic substances were generated during the production of gentamicin. Inappropriate handling techniques not only waste valuable resources, they could also result in residual gentamicin into the natural environment, leading to the generation of antibiotic resistance genes (ARGs), which would cause a significant threat to ecological system and human health. In the present work, the effects of thermal treatment on the removal of residual gentamicin in GMRs, as well as the changes of associated ARGs abundance, antimicrobial activity and bioresources properties were investigated. The results indicated that the hazards of GMRs was significantly reduced through thermal treatment. The degradation rate of residual gentamicin in GMRs reached 100 %, the total abundance of gentamicin resistance genes declined from 8.20 to 1.14 × 10-5 and the antibacterial activity of the decomposition products of GMRs on Vibrio fischeri was markedly reduced at 200 °C for 120 min. Additionally, the thermal treatment remarkably influenced the bioresource properties of GMRs-decomposition products. The release of soluble organic matters including soluble carbohydrates and soluble proteins have been enhanced in GMRs, while excessively high temperatures could lead to a reduction of nutrient substances. Generally, thermal treatment technology was a promising strategy for synergistic reducing hazards and utilizing bioresources of GMRs.

Heat and carbon co-activated persulfate to regenerate gentamicin-laden activated carbon: Performance, mechanism, and safety assessment.

Activated carbon enriched with high concentrations of gentamicin (ACG) was generated in the production process of gentamicin. Inappropriate handling methods for ACG not only squanders carbon resource, but also seriously hinders achieving global carbon neutrality and hazardous to human health. In the present work, thermal and carbon co-activated persulfate method (TC-PS) was developed to regenerate ACG with degrading gentamicin. The results showed that ACG was effectively regenerated by TC-PS, restoring the adsorption performance for gentamicin. When the treatment temperature was 80 °C, the persulfate dosage was 20 mM and the initial pH was 3.0, the degradation efficiency of gentamicin reached 100%. The HO• and SO4•- were the major reactive species for gentamicin degradation. The possible degradation routes of gentamicin were proposed and the safety assessment indicated that the produced intermediates during the regeneration process of ACG by TC-PS have insignificant impact on the biological and ecological environment.

In-situ production and activation of H2O2 over hydroxyapatite modified CuFeO2 for self-sufficient heterogeneous photo-Fenton degradation of doxycycline hydrochloride.

The self-sufficient heterogeneous photo-Fenton (SH-PF) system was constructed for doxycycline hydrochloride (DOH) degradation with hydroxyapatite (Hap) modified CuFeO2 (Hap/CuFeO2) composites through H2O2 in-situ production. The modification of Hap could improve the specific surface area, visible-light response, light conversion efficiency, photoelectron lifetime and oxygen vacancies (OVs) of CuFeO2, which was conducive to H2O2 production and DOH degradation in SH-PF system. Notably, Hap/CuFeO2 fabricated with 0.5 g Hap (Hap/CuFeO2-0.5) displayed more superior performance for DOH degradation compared to other synthesized catalysts. The Hap/CuFeO2-0.5 load and initial solution pH for DOH degradation in SH-PF system were optimized, and the Hap/CuFeO2-0.5 had good reusability and stability. The •OH was the main active species for DOH degradation, and the facilitation effect of •O2- and photoelectrons on DOH degradation was associated with the H2O2 production in the present work. In addition, the capture of photogenerated holes suppressed the recombination of photogenerated carriers, elevating the production of photoelectrons and thereby enhancing H2O2 production and DOH degradation. The degradation pathways for DOH were proposed and the comprehensive toxicities of DOH were relieved after degradation in SH-PF system.

[Adsorption Characteristics of Tetracycline by CuFeO2-modified Biochar].

CuFeO2-modified biochars were prepared through co-precipitation and hydrothermal methods, and the composites had high efficiency removal for tetracycline (TC) from water. The CuFeO2-modified biochar with a 2:1 mass ratio of CuFeO2 to BC450 (CuFeO2/BC450=2:1) demonstrated the best adsorption performance. The kinetic process of TC adsorption by CuFeO2/BC450=2:1 was well fitted with the intraparticle diffusion model, suggesting that the adsorption process was controlled by film and pore diffusion. Under the condition of neutral pH and 298 K, the maximum adsorption capacity of the Langmuir model of CuFeO2/BC450=2:1 was 82.8 mg·g-1, which was much greater than that of BC450 (13.7 mg·g-1) and CuFeO2(14.8 mg·g-1). The thermodynamic data suggested that TC sorption onto CuFeO2/BC450=2:1 was a spontaneous and endothermic process. The removal of TC by CuFeO2/BC450=2:1 increased first and then decreased with increasing pH, and the maximum adsorption occurred under the neutral condition. The strong adsorption of TC by CuFeO2/BC450=2:1 could be attributed to better porosity, larger specific surface area, and more active sites (e.g., functional groups and charged surfaces). This work provided an efficient magnetic adsorbent for removing antibiotics.

Highly efficient nanocomposite of Y2O3@biochar for oxytetracycline removal from solution: Adsorption characteristics and mechanisms.

Nano Y2O3-modified biochar composites (Y2O3@BC600) were fabricated successfully and exhibited great adsorption toward oxytetracycline (OTC). The Langmuir adsorption capacity of Y2O3@BC600-1:4 for OTC reached 223.46 mg/g, 10.52 times greater than that of BC600. The higher dispersion of Y2O3 nanoparticles, increased surface area of 175.65 m2/g and expanded porosity of 0.27 cm3/g accounted for higher OTC adsorption by Y2O3@BC600-1:4. Y2O3@BC600-1:4 could resist the interference of co-existing cations (Na+, K+, Mg2+, Ca2+) and anions (Cl-, NO3-, SO42-) on OTC removal. Y2O3 coating changed surface charge property of BC600, favoring the contribution of electrostatic interaction. Synchrotron radiation-based Fourier transform infrared spectroscopy detected obvious peak shift and intensity change of surface -OH when OTC adsorption occurred. Accordingly, stronger H-bonding (charge-assisted hydrogen bond, OTC-H2N+···HO-Y2O3@BC600-1:4) was proposed for OTC adsorption. Y2O3@BC600 exhibited renewability and stability in the adsorptive removal of OTC. Therefore, Y2O3@BC600 may be a novel and suitable adsorbent for antibiotic removal.

Fenton oxidation treatment of oxytetracycline fermentation residues: Harmless performance and bioresource properties.

The pharmaceutical factories of oxytetracycline (OTC) massively produce OTC fermentation residues (OFRs). The high content of residual OTC and antibiotic resistance genes in OFRs must to be considered and controlled at an acceptable level. This study therefore investigated the applicability of Fenton oxidation in OTC degradation and resistant gene inactivation of OFRs. The results revealed that Fe2+ as catalyzer could very rapidly activate H2O2 to produce HO•, leading to instantaneous degradation of OTC. The optimum conditions for OTC removal were 60 mM H2O2 and 140 mg/L Fe2+ under pH 7. After Fenton oxidation treatment, the release of water-soluble polysaccharides, NO3-N, and PO4-P was enhanced, whereas for proteins and NH3-N were reduced. Three soluble fluorescence components (humic, tryptophan-like, and humic acid-like substances) were identified through fluorescence spectra with parallel factor analysis, and their reduction exceeded 50% after Fenton oxidation. There were twelve intermediates and three degradation pathways of OTC in OFRs during Fenton process. According to toxicity prediction, the comprehensive toxicity of OTC in OFRs was alleviated via Fenton oxidation treatment. In addition, Fenton oxidation showed the ability to reduce antibiotic resistance genes and mobile genetic elements, and even tetO, tetG, intI1, and intI2 were eliminated completely. These results suggested that Fenton oxidation treatment could be an efficient strategy for removing OTC and resistance genes in OFRs.

Enhanced heterogeneous photo-Fenton-like degradation of tetracycline over CuFeO2/biochar catalyst through accelerating electron transfer under visible light.

The visible-light induced heterogeneous photo-Fenton-like (HPF-like) process is regarded as a promising technique for organic pollutants degradation due to its efficient utilization of solar energy and high H2O2 activation activity. This study prepared the CuFeO2/biochar catalysts via hydrothermal technique at no extra reductant and systematically investigated their band structure and photoelectric properties. The dispersed distribution of CuFeO2 particles in CuFeO2/biochar composites narrowed bandgap of CuFeO2 and promoted electron transport of CuFeO2. Compared with CuFeO2, the CuFeO2/biochar containing 1.0 g biochar in the preparation (CuFeO2/biochar-1.0) possessed higher carrier density and longer photoelectron lifetime, which is beneficial to higher catalytic performance. The apparent rate constant for tetracycline as target pollutant degradation by CuFeO2/biochar-1.0 was 2.0 times higher than that by CuFeO2. The acquired optimum conditions for tetracycline degradation were 220 mg L-1 CuFeO2/BC-1.0, 22 mM H2O2 and pH 6.4 using response surface methodology. The quenching experiments and ESR analysis revealed that OH was the predominant active species, and photoelectron and O2- were auxiliary species. The photoelectron could promote in-situ recycling of Cu2+ to Cu+ and Fe3+ to Fe2+, which significantly improved H2O2 activation by CuFeO2. The possible pathway of tetracycline was proposed according to intermediates identified by HPLC/MS. The toxicity analysis demonstrated that the overall toxicity of the identified intermediates was reduced in HPF-like system.

Photoelectrocatalytic degradation of p-chloronitrobenzene by g-C3N4/TiO2 nanotube arrays photoelectrodes under visible light irradiation.

As a typical refractory pollutant, p-chloronitrobenzene (p-CNB) from industrial wastewater poses a serious threat to the aquatic environment safety and human health. The photoelectrocatalytic (PEC) technology is regarded as a promising and cleaner approach for p-CNB removal. Therefore, the graphitic carbon nitride (g-C3N4) modified TiO2 nanotube arrays (g-C3N4/TNAs) were prepared as the photoelectrodes for p-CNB degradation. The PEC degradation efficiency for p-CNB by g-C3N4/TNAs (0.00484 min-1) was much higher than that by bare TNAs (0.00135 min-1) under visible light. The g-C3N4/TNAs photoelectrodes exhibited excellent visible-light response, efficient charges separation and high redox potentials of electron/hole, which was favorable for p-CNB degradation. The radical scavenging experiments indicated that both reductive electrons and oxidized species (holes and ·OH) played crucial roles simultaneously during the dechlorination process, whereas the mineralization of p-CNB mainly depended on the photo-generated holes and ·OH. The degradation pathways of p-CNB were proposed through GC/MS spectra. The acute toxicity, bioaccumulation factor and mutagenicity of identified intermediates were reduced after PEC degradation by g-C3N4/TNAs photoelectrodes. The Z-scheme g-C3N4/TNAs provided an efficient approach for simultaneous dechlorination and mineralization of refractory pollutants.

Effects of feedstock and inherent mineral components on oxidation resistance of biochars.

Chemical stability assessment of biochar has been universally used to indicate its potential of long-term carbon sequestration. The comparative study on oxidation resistance of biochars from diverse series of feedstock is relatively limited, as well as the effects of endogenous minerals on biochar stability. Herein, oxidation resistance of biochars from peanut shell, bamboo, saw dust, reed stalk, furfural residues, seaweed degumming residues and Enteromorpha prolifera at 500 °C (PS500, BB500, SD500, RS500, FR500, SR500 and EP500) was examined by the treatments of H2O2, K2Cr2O7 and thermogravimetric analysis (TGA). Under H2O2 or K2Cr2O7 condition, C loss of algae-derived biochars (SR500 and EP500) was extremely greater than that of other biochars due to higher content of labile carbon components. PS500, BB500, SD500, RS500 and FR500 characterized with similar properties in carbon fraction, but they exhibited different ability to resist oxidation. The mineral fraction of biochars (e.g., content and species) varied with the feedstock, which played complex effects on the oxidation resistance. The mineral decomposition (e.g., CaCO3) in EP500 and SR500 above 500 °C influenced the analysis of biochar stability by TGA. After acid-washing, EP500 and SR500 showed weaker thermal oxidation resistance, agreed with the results of H2O2 and K2Cr2O7 oxidation. The oxidation resistance of biochars was correlated better with O/C ratio, implying that O/C ratio was more robust indicator than other indexes (e.g., H/C ratio and the ratio of D band to G band of Raman). The FTIR, Raman and XPS results further demonstrated the elimination of aliphatics and amorphous aromatics and/or the carboxylation/carbonylation of aromatic structures by H2O2 and K2Cr2O7. These findings are useful for better understanding the impacts of feedstock and inherent minerals on the oxidation resistance of biochars.

The enhanced effect of oxalic acid on the electroreduction of Cr(VI) via formation of intermediate Cr(VI)-oxalate complex.

In this study, the enhanced effect of oxalic acid (Ox) on Cr(VI) electroreduction was evaluated. It was found that for Cr(VI)-contaminated solution ([Cr(VI)]0 = 1.0 mM, pH = 3.0), addition of 5.0 mM Ox can significantly increase Cr(VI) reduction from 0.36 to 1.0 mM within 90 min electrolysis reaction, accompanying with the increase of current efficiency from 19% to 53%. Increasing initial Ox concentration (0-10 mM) and electric current (10-40 mA) facilitated Cr(VI) reduction, whereas it was inhibited with decreasing solution pH value (2.0-3.5) and elevating Cr(VI) concentration (0.1-2.0 mM), respectively. Results show that reactive electron was the primary reductant for the heterogeneous reduction of Cr(VI) on the cathode. In addition, Ox can also serve as an electron donor for the homogeneous reduction of Cr(VI). During this process, the formation of Cr(VI)-oxalate complex is indispensable for the enhanced Cr(VI) reduction. The coordination of Ox with Cr(VI) did not only make the structure of Cr(VI) more distorted but also improved the reactivity of Cr(VI) in Cr(VI)-oxalate complex toward reduction reaction. In general, this study provides an energy-efficient and environmentally benign strategy for the treatment of Ox and Cr(VI) co-contaminated wastewater.

Cost-effective electrogeneration of H2O2 utilizing HNO3 modified graphite/polytetrafluoroethylene cathode with exterior hydrophobic film.

Electrochemical 2-electrons oxygen reduction process has been regarded as the effective strategy for H2O2 generation in wastewater treatment. However, its large-scale application is still limited by the relatively high cost of the carbon materials and short-term stability. In this study, a nitric acid modified graphite/polytetrafluoroethylene (PTFE) composite cathode with exterior hydrophobic film was fabricated for cost-effective electrogeneration of hydrogen peroxide (H2O2). Experimental results show that 2 M HNO3 modification rendered the introduction of much more defect sites and oxygen/nitrogen-containing groups on graphite. As a result, H2O2 electrogeneration was 3.0 times as much as that of virgin graphite counterpart at 3 mA cm-2. Moreover, the additional introduction of exterior hydrophobic film on the as-prepared graphite/PTFE cathode did not only further promote H2O2 electrogeneration, but also endowed the cathode with strong hydrophobic stability. As for the modified cathode with exterior hydrophobic film, the influence of mass graphite/PTFE binder ratio (1:1-4:1) and pH (3.0-9.0) on H2O2 electrogeneration was slight, but the current density (3.0-15 mA cm-2) had evident effect on H2O2 electrogeneration. Generally, owing to its low price and being easily available, the modified graphite would be cost-effectively utilized to prepare the gas diffusion cathode for the large-scale electrogeneration of H2O2 in industry.

The role of thiocyanate in enhancing the process of sulfite reducing Cr(VI) by inhibiting the formation of reactive oxygen species.

The reductive detoxification of Cr(VI) by sulfite is known as the prevailing strategy and can be successfully implemented for the treatment of Cr(VI)-contaminated waters. However, this method inevitably faces the challenges of excessive consumption of sulfite due to the generations of highly oxidative OH and SO4- during the process of sulfite reducing Cr(VI). In this study, we find that a small quantity of thiocyanate (SCN) can catalytically enhance the process efficiency of Cr(VI) reduction by sulfite and effectively prevent the excessive consumption of sulfite. Specifically, when adding 5µM SCN into 100µM Cr(VI) + 600µM sulfite reaction system at pH 3.5, Cr(VI) reduction amount and [sulfite]oxidation/[Cr(VI)]reduction ratio value were approximately 2 and 0.45, respectively, times those in the SCN-free case. The maximum Cr(VI) reduction amount can be achieved at an initial [SCN]/[Cr(VI)] molar ratio of 2.0. Electron spin resonance measurement, combined with the fluorescence spectrum detection, verified that the process of sulfite reducing Cr(VI) mediated by SCN probably proceeds via the non-radical pathway, avoiding the formation of OH and SO4- under aerobic condition.

Evaluation of the photooxidation efficiency of As(III) applying the UVC/oxalate technique.

In this study, the photooxidation capacity of UVC/Oxalate (Ox) was evaluated using As(III) as a typical pollutant. The results show that the direct oxidation amount of As(III) induced by UVC in water was negligible, but the presence of Ox remarkably accelerated the oxidation rate of As(III). Under UVC irradiation, 50 µM As(III) can be completely oxidized to As(V) in the case of Ox concentration above 300 µM within 60 min. As(III) oxidation was found greatly related with the photodecomposition of Ox. Much more Ox can be mineralized in more acidic solution. At the same time, the photooxidation of As(III) was significantly favored at decreased initial pH from 8.0 to 3.0. In this reaction system, the role of oxygen was indispensable for Ox photodecomposition and As(III) photooxidation, which can be ascribed to its special roles as a precursor of reactive superoxide and an electron acceptor. In oxygen-present atmosphere, the in situ production of H2O2 was detected during the photolysis of Ox and its photolysis product, i.e., OH primarily contributed to the oxidation of As(III). However, the photodecomposition of Ox and photooxidation of As(III) were significantly inhibited in the anaerobic environment. In general, the homogeneous photolysis of Ox in many commonly practiced UVC oxidation processes can be also proposed as a supplementary method of generating highly oxiditive species in aerobic condition.