Deterioration of denitrification by oxygen and cost evaluation of electron donor in an uncovered pre-denitrification process

Specific nitrate uptake rates (SNURs) under two test conditions were measured to evaluate effects of oxygen inhibition on denitrification. A test condition was that activated sludge was completely prevented from contacting of oxygen (SNUR _closed ), the other was that activated sludge was contacted to free air (SNUR _open ). Municipal wastewater and acetate were used as electron donors. SNUR _closed was 2.42 mg NO₃-N/g VSS-hr and SNUR _open was 1.09 mg NO₃-N/g VSS-hr when municipal wastewater was used as electron donor. Meanwhile, when acetate was used as electron donor, SNUR _closed was 24.65 mg NO₃-N/g VSS-hr and SNUR _open was 18.00 mg NO₃-N/g VSS-hr. The operating costs for electron donors were calculated based on the unit price of acetate to remove nitrate. When municipal wastewater was used as electron donor the ratio of cost _open to cost _closed was 0.45. Cost evaluation showed the adverse impacts on denitrification and explained why an anoxic reactor should be sequestered from oxygen.     

Antibacterial Effects of Bicarbonate in Media Modified to Mimic Cystic Fibrosis Sputum

Cystic fibrosis (CF) is a hereditary disease caused by mutations in the gene encoding an epithelial anion channel. In CF, Cl⁻ and HCO₃⁻ hyposecretion, together with mucin hypersecretion, leads to airway dehydration and production of viscous mucus. This habitat is ideal for colonization by pathogenic bacteria. We have recently demonstrated that HCO₃⁻ inhibits the growth and biofilm formation of Pseudomonas aeruginosa and Staphylococcus aureus when tested in laboratory culture media. Using the same bacteria our aim was to investigate the effects of HCO₃⁻ in artificial sputum medium (ASM), whose composition resembles CF mucus. Control ASM containing no NaHCO₃ was incubated in ambient air (pH 7.4 or 8.0). ASM containing NaHCO₃ (25 and 100 mM) was incubated in 5% CO₂ (pH 7.4 and 8.0, respectively). Viable P. aeruginosa and S. aureus cells were counted by colony-forming unit assay and flow cytometry after 6 h and 17 h of incubation. Biofilm formation was assessed after 48 h. The data show that HCO₃⁻ significantly decreased viable cell counts and biofilm formation in a concentration-dependent manner. These effects were due neither to extracellular alkalinization nor to altered osmolarity. These results show that HCO₃⁻ exerts direct antibacterial and antibiofilm effects on prevalent CF bacteria.     

Processing Low‐Oxide ZrB2 Ceramics with High Strength Using Boron Carbide and Spark Plasma Sintering

A phase diagram‐assisted powder processing approach is shown to produce low‐oxygen (0.06 wt%O) ZrB₂ ceramics using minimal B₄C additions (0.25 wt%) and spark plasma sintering. Scanning electron microscopy and scanning transmission electron microscopy with elemental spectroscopy are used to identify “trash collector” oxides. These “trash collector” oxides are composed of manufacturer metal powder impurities that form discreet oxide particles due to the absence of standard Zr–B oxides found in high oxygen samples. A preliminary Zr–B–C–O quaternary thermodynamic database developed as a part of this work was used to calculate the ZrO₂–B₄C pseudobinary phase diagram and ZrB₂–ZrO₂–B₄C pseudoternary phase diagrams. We use the calculated equilibrium phase diagrams to characterize the oxide impurities and show the direct reaction path that allows for the formation of ZrB₂ with an oxygen content of 0.06 wt%, fine grains (3.3 μm) and superior mechanical properties (flexural strength of 660 MPa).     

Oxidation of butenes to maleic anhydride on MnMoO4 based catalyst

The oxidation of n-butene-1 was carried out in a stirred tank reactor and in a pulse reactor using MnMoO₄ as a catalyst. This catalyst exhibits a fairly good selectivity to maleic anhydride. MnMoO₄ shows a polyfunctional nature; it is possible to distinguish the properties of isomerization, dehydrogenation, oxidation with oxygen insertion, and complete oxidation by varying parameters such as temperature, oxygen concentration and contact time.The compositions of the products in the oxidation of n-butene-1 carried out in a pulse reactor are completely different in the presence and in the absence of oxygen, respectively. In the absence of oxygen, MnMoO₄ is a very selective catalyst in the dehydrogenation of n-butene-1 to butadiene. In the presence of oxygen, CO and CO₂ are the main products together with small amounts of maleic anhydride.The selectivity of MnMoO₄ to butadiene formation has been attributed to the presence of MoO bonds which are responsible for dehydrogenation reactions.A monocenter oxidation mechanism, accounting for the formation of CO, CO₂, and maleic anhydride, has been proposed in which the gaseous oxygen is considered to be adsorbed on the same center of the hydrocarbon.     

Oxygen evolution reaction on transition metal borides

The oxygen evolution reaction on the transition metal borides (mainly Co_xB and Ni_xB) was investigated with various composition ratio of BMetal and sintering temperature. The activity of oxygen evolution reaction became maximum at the composition range of BCo =$\text{1}\text{3}$ and BNi ? $\text{1}\text{3}$, respectively. The sintering temperature also affected largely the activity of oxygen evolution reaction and the metal borides with the composition ratio BMetal = $\text{1}\text{3}$ gave the highest activity at the sintering temperature lower than 300°C for nickel borides and 400 ～ 500°C for cobalt borides. The oxygen evolution reaction on iron boride and lanthanum hexaboride was also briefly discussed, and the order of the activity of oxygen evolution reaction was as follows:

The Tafel slope of oxygen evolution reaction on metal borides was varied from ca. 40 mV for Ni (ca 70 mV for Co) to ca. 120 mV with the increase in the activity of oxygen evolution reaction. The oxide formation became easier with the increase in the activity of oxygen evolution reaction and the differential capacity of the oxide formation in the range more cathodic than the oxygen evolution increased with the decrease in the apparent activation energy of oxygen evolution reaction at 0.60 V (HgHgO).     

Comparative study of the structure and microstructure of PAN-based nano- and micro-carbon fibers

The work presents results on the manufacture and comparative assessment of the structure and microstructure parameters of polyacrylonitrile polymer (PAN)-based carbon nano- and micro-fibers. Using the same polymer solution, PAN nano- and microfibers were obtained. The PAN nanofibers were obtained by electrospinning, and microfibers were spun using the conventional solution-spinning method. The PAN-based fiber precursors were annealed to 1000 °C, 2000 °C and to 2800 °C. Using X-ray diffraction and Raman spectroscopy, the structural and microstructural parameters of both types of carbon fibers were examined. The morphology of PAN nanofibers and carbon nanofibers (CNF) were studied by SEM. Both types of ex-PAN carbon fibers (nano and micro) have similar the c-axis spacing (d₀₀₂) values and crystallite sizes after heat treatment to 2000 °C presenting turbostratic structure. HR-TEM images of low temperature CNF show uniform microstructure with the misoriented small carbon crystallites along the fiber axis. The ratio of the integrated intensities of the D and G peaks for carbon nanofibers after heat treatment at 2000 °C was distinctly higher in comparison to carbon microfibers (CF). After additional annealing the fibers to 2800 °C a better structural ordering show CNF. The crystallite sizes (L_c, L_a) in CNF were distinctly higher in comparison to the crystallites in CF. CF consist of two carbon components, whereas CNF contain three carbon components varying in structural and microstructural parameters. One of carbon phases in CNF was found to have the interlayer spacing close to graphite, i.e. d₀₀₂=0.335 nm.     

Adhesion of copper to poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) surfaces modified by vacuum UV photo-oxidation downstream from Ar microwave plasma

Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) surfaces were exposed to vacuum UV (VUV) photo-oxidation downstream from Ar microwave plasma. The modified surfaces showed the following: (1) an improvement in wettability as observed by water contact angle measurements; (2) surface roughening; (3) defluorination of the surface; and (4) incorporation of oxygen as CF—O—CF₂, CF₂—O—CF₂ and CF—O—CF₃ moieties. With long treatment times, a cohesive failure of copper sputter-coated onto the modified surface occurred within the modified FEP and not at the Cu–FEP interface.     

In-situ segregation of A-site defect (La0.6Sr0.4)0.90Co0.2Fe0.8O3-δ to form a high-performance solid oxide fuel cell cathode material with heterostructure

As a potential cathode material for solid oxide fuel cells, the commercial application of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) has to face the challenges in insufficient oxygen reduction reaction (ORR) activity, segregation of Sr element, and CO₂ poisoning. Therefore, the effect of A-site non-stoichiometry on the electrochemical performance of (LS)_1-xCFs (x = ?0.05, 0, 0.05, 0.10, 0.15) from the aspect of microstructure/elemental surface chemical environment evolution is investigated in this paper. The results show that (LS)_0.90CF has the best ORR activity and the highest electrochemical performance. The excellent electrochemical performance is attributed to the (LS)_0.90CF/Co₂FeO₄/CoFe₂O₄-type heterostructure, formed by in-situ segregation induced by A-site defects, which improves the surface oxygen diffusion coefficient and chemical bulk diffusion coefficient of the cathode. At the same time, the A-site defect can effectively inhibit the segregation of Sr element in (LS)_0.90CF, thereby improving the tolerance of CO₂. At 800 °C, the area-specific resistance (ASR) of (LS)_0.90CF (0.023 Ω cm²) is 66.7% lower than that of LSCF (0.069 Ω cm²), and the peak power density (1.57 Wcm^?2) is 1.8 times higher than that of LSCF (0.87 Wcm^?2). Therefore, perovskite A-site defect-induced B-site segregation to form heterostructures provides an effective strategy for the preparation of high-performance cathode materials.     

Fabrication of multilayer porous structured TiO2–ZrTiO4–SiO2 heterostructure towards enhanced photo-degradation activities

Multilayer porous structured TiO₂–ZrTiO₄–SiO₂ photocatalyst with built-in TiO₂/ZrTiO₄ heterojunction and oxygen vacancies was synthesized by sol-gel method combined with template method using colloidal polystyrene spheres as templates. Results show that the multilayer porous structure can be fabricated by controlling the calcination system and the amount of template, and the fabrication of which can also contribute to the generation of oxygen vacancies by creating an anoxic environment. During the photodegradation process, high efficiency of visible light utilization can be achieved due to the slow photon effect of the multilayer porous structure, which can also increase the probability of the contact between Rhodamine B (RhB) with the active sites of the catalyst. Also, the synergistic effect of the generated TiO₂/ZrTiO₄ heterojunction and built-in oxygen vacancy defects jointly promoted the separation of photogenerated carriers. Thus excellent adsorption rate (75.6%, 60 min) and photodegradation rate (95%, 90 min) of the catalyst were obtained. Furthermore, the up-shifted conduction band and valence band maximum positions are beneficial for the mobility of photogenerated holes and inhibit their reaction with H₂O to generate ·OH, while the photogenerated electrons can react with O₂ to form ·O₂⁻, resulting that the holes and ·O₂⁻ participated in the photodegradation of RhB over the as-prepared catalyst.     

Modeling biological nutrient removal in a liquid–solid circulating fluidized bed bioreactor

BACKGROUND: Both laboratory‐scale and pilot‐scale liquid–solid circulating fluidized bed (LSCFB) bioreactors have demonstrated excellent biological nutrient removal (BNR) from municipal wastewater. In this study, a model for the LSCFB for biological nutrient removal has been developed, calibrated, and validated using pilot‐scale experimental results. RESULTS: An efficient reactor arrangement predicted anoxic–anaerobic and aerobic biofilm thicknesses of 150–400 and 70–175 µm in the riser and downer, respectively. Furthermore, distribution of chemical oxygen demand (COD), NH₄‐N, NO_X‐N, and dissolved oxygen in the biofilm, as well as nutrients removed in the aerobic and anoxic zones, reflect nitrification, denitrification and enhanced biological phosphorus removal in the LSCFB. The model predicted both anoxic effluent and final effluent COD, SCOD, SBOD, NH₄‐N, NO₃‐N, TKN, TN, PO₄‐P, and TP were within the 95% confidence intervals of the experimental data. Model‐predicted simultaneous nitrification/denitrification occurring in the aerobic downer. CONCLUSION: This model developed for LSCFB using the AQUIFAS biofilm diffusion model successfully evaluated the process performance. It is an efficient tool for further research, design, and optimization of the fixed film bioreactor. Copyright © 2010 Society of Chemical Industry     

Improvements in interfacial and heat-resistant properties of carbon fiber/methylphenylsilicone resins composites by incorporating silica-coated multi-walled carbon nanotubes

The multi-scale reinforcement and interfacial strengthening on carbon fiber (CF)-reinforced methylphenylsilicone resin (MPSR) composites by adding silica-coated multi-walled carbon nanotubes (SiO₂-CNTs) were investigated. SiO₂-CNT has been successfully prepared via the hydrolysis of tetraethoxysilane in the presence of acid-oxidized multi-walled carbon nanotubes. Transmission electron microscopy, X-ray diffraction, and Fourier Transform infrared spectroscopy were carried out to examine the functional groups and structures of CNTs. Then, SiO₂-CNT was incorporated into MPSR matrix to prepare CF/MPSR-based composites by the compression molding method. The effects of the introduced SiO₂-CNT on the interfacial, impact, and heat-resistant properties of CF/MPSR composites were evaluated by short-beam bend method, impact test, and thermal oxygen aging experiments, respectively. Experimental results revealed that the CF/MPSR composites reinforced with 0.5 wt% SiO₂-CNT showed a significant increase 34.53% in the interlaminar shear strength (ILSS) and 20.10% in impact properties. Moreover, the heat-resistant properties of composites were enhanced significantly by adding SiO₂-CNT hybrid nanoparticles. These enhancements are mainly attributed to the improved matrix performance resulted from the molecular-level dispersion of SiO₂-CNT in MPSR matrix and the strong interfacial adhesion between SiO₂-CNT and matrix resin, which are beneficial to improve the mechanical stress transfer from MPSR matrix to CFs reinforcement and alleviate stress concentrations.     

Characterization of the oxygen scavenging capacity and kinetics of SBS films

Butadiene-containing polymers such as styrene-butadiene-styrene (SBS) block copolymers are of a potential use as oxygen scavenging polymers (OSP) in barrier applications. To evaluate their use in such applications, oxygen uptake was measured for films made of an SBS copolymer and four cobalt catalyst loadings with various thicknesses. The oxygen uptake was found to be kinetically limited for thin films while diffusion controls the uptake at long times for thick films. The thickness of the oxidized region at long oxidation times is termed the critical thickness L_c and was quantified by various analyses. Thin films (i.e.,L ≤ 2L_c) oxidize fully and homogeneously, whereas heterogeneous oxidation typically occurs in thicker films (i.e., L > 2L_c). A thin film model was used to extract the reaction rate parameters and a stoichiometric oxidation coefficient that describe oxygen uptake in the absence of diffusion limitation. An approximate moving-boundary model was developed to describe thick film oxidation behavior at long times and was found to be in semi-quantitation agreement with the measured uptake.     

Direct conversion mechanism of fluorine-GIC into poly(carbon monofluoride), (CF)n

The reaction mechanisms of a stage-1 fluorine-graphite intercalation compound (GIC), C_2.5F, with 0.10 MPa of fluorine gas have been studied at 573-773 K. The original stage-1 structure of C_2.5F with semi-ionic C-F bonds and planar sp² carbon sheets is maintained in most part of the compound after the reaction at 573 K, although a large number of covalent C-F bonds are formed on the surface. This compound is partially or completely converted to poly(carbon monofluoride), (CF)_n, with covalent C-F bonds and puckered sp³ carbon sheets at 673 or 773 K, respectively. Single-phase (CF)_n obtained at 773 K possesses remarkably small BET specific surface area, 61 m²/g carbon, almost unchanged from the value of the precursor C_2.5F (69 m²/g carbon). In this reaction, the accommodation of fluorine atoms supplied from the atmosphere into the galleries of C_2.5F is facilitated by the rearrangement of originally intercalated fluorine atoms in the GIC, forming (CF)_n with fewer defects compared to those by the conventional direct fluorination of graphite.     

Treatment of textile dye effluents using coagulation–flocculation coupled with membrane processes or adsorption on powdered activated carbon

This study describes the treatment of textile wastewater by various combinations of physicochemical and membrane processes. The basic physicochemical treatment consists in coagulation/flocculation (CF) with different coagulant and flocculant concentrations. The parameters analyzed prior and after treatment are turbidity, chemical oxygen demand (COD) and absorbance (Abs). The optimal process parameters for CF are 5 for pH, 100 mg/l for coagulant (Al₂(SO₄) ₃) of 100 mg/l and 4 mg/l for flocculant. This simple treatment by CF was inefficient concerning COD reduction and dyes deterioration. It was therefore combined with microfiltration (MF) or ultrafiltration (UF) on one hand and adsorption on powdered activated carbon (PAC) on the other. The CF/MF, CF/UF and CF/PAC combinations ensure a COD removal of 37%, 42% and more than 80% respectively and a color reduction of 65%, 74% and 50% respectively.     

Performance assessment of a UASB–anoxic–oxic system for the treatment of tomato‐processing wastes

An upflow anaerobic sludge blanket (UASB)–anoxic–oxic system was used to achieve biochemical oxygen demand, NH₄ and total suspended solids (TSS) criteria of 15, 1 and 15 mg dm^?3 at 1.17 days of system hydraulic retention time during treatment of tomato‐processing waste. The incorporation of an anoxic tank was found to affect the improvement in sludge‐settling characteristics, as reflected by about 25–33% reduction in the sludge volume index, along with final effluent TSS and soluble biochemical oxygen demand concentrations of 13 and 9 mg dm^?3, respectively, which met the discharge criteria. Despite incomplete denitrification, sludge settleability was very good (sludge volume index < 60 cm³ g^?1) owing to reduction in volatile suspended solids/TSS ratio from 0.75 to 0.6 as a result of higher alkalinity in the UASB effluent. Also in this study, phosphorus release was observed in the anoxic tank, predominantly due to abundance of acetic acid in the UASB effluent. A phosphate release of 5.4 mg P dm^?3 was observed in the anoxic tank with subsequent P uptake in the following aerobic stage. Copyright © 2006 Society of Chemical Industry     

Wet chemical route synthesis of Cr doped CoFe2O4 @rGO nanocomposite for photodegradation of organic effluents present in drinking water

The current work comprises of the fabrication of spinel cobalt ferrite (CF1), and chromium doped cobalt ferrite (CF2) by wet chemical method (co-precipitation). Moreover, the nanocomposite of Cr-doped cobalt ferrite with reduced graphene oxide (CF3) was fabricated by an ultra-sonication method. The structural, functional, morphological, and optical or photocatalytic properties of prepared photocatalysts i.e. CF1, CF2, CF3 were determined by XRD, FT-IR, SEM, and UV–Visible spectroscopy techniques respectively. The present work deals with the removal of an organic dye (Rhodamine B), and a colorless compound (Benzoic acid) from waste water using photocatalysts CF1, CF2, and CF3. Using CF3 (Cr-CoFe₂O₄@rGO) as photocatalytic material, 81% degradation of rhodamine B, and 67% of benzoic acid was observed. CF3 exhibited remarkable photocatalytic degradation activity than CF1 (43%) and CF2 (53%) against rhodamine B. Moreover, CF3 also showed outstanding degradation efficiency (67%) against benzoic acid than pure cobalt ferrite i.e. CF1 (46%). The outstanding removal efficacy of CF3 nanocomposite was due to the 2D structure, high/massive surface area and increased capacity to transport electrons of reduced graphene oxide (rGO).     

Stable oxygen-selective sorbents for air separation

Commercial sorption-based air separation is usually done using nitrogen selective zeolites in pressure swing adsorption (PSA) systems. Separation of air by adsorption of less abundant oxygen is more desirable. In this study we have developed some stable oxygen selective sorbents with silver and cerium salts. AgCl, AgBr, AgI and CeCl₃ all showed stable adsorption characteristics with pure component selectivity of O₂/N₂∼2.0-3.0 at 1 atm. For these salts heat of adsorption of oxygen was found to be slightly higher than that of nitrogen, which was also predicted by ab initio molecular orbital calculations by Chen and Yang (Ind. Eng. Chem. Res. 35 (1996) 4020). The adsorption capacity of these salts was increased by thermal dispersion on high surface area SiO₂ support. AgBr thermally spread on SiO₂ is the best sorbent obtained in this study. AgBr/SiO₂ (1.0 g/g) showed a pure component oxygen selectivity of ∼3 at 1 atm and ∼5 at 7 atm. PSA simulations were used to show the feasibility of nitrogen production using AgBr/SiO₂.     

Development of new nickel based catalyst for biomass tar steam reforming producing H2-rich syngas

Mayenite (Ca₁₂Al₁₄O₃₃ or 12CaO.7Al₂O₃) was previously developed and applied as Ni support for biomass tar steam reforming in the absence and presence of H₂S by our group because of its high oxygen restoring property in the structure [C. Li et al., Appl. Catal., B. 2008]. In this study, catalyst Ni/mayenite (mayenite as support) was prepared by impregnation method with nickel nitrate hexahydrate. Experiments were tested in a fixed-bed reactor, toluene as a tar model compound. The influence of the catalyst preparation and operating parameters (reaction temperature, steam to carbon ratio and space time) on catalyst activity and products selectivity were studied, and a long-time evaluation (more than 76 h) also exhibited excellent resistance to coking. These results were compared to these obtained by commercial-like catalysts: Ni/CaO_x/MgO_1−x and our previous NiO/mayenite, showing that Ni/mayenite exhibited excellent property for biomass tar reforming, with higher H₂ yield than that of Ni/CaO_x/MgO_1−x, and higher CO selectivity than that of NiO/mayenite. For kinetic model, the first order reaction used for toluene with activation energy of 80.24 kJ.mol^− 1 was coincident with literature data.     

Discharge characteristics of graphite fluorides prepared via graphite intercalation compounds in nonaqueous lithium cells

Two types of graphite fluorides (C₂F)_n and (CF)_n were prepared by refluorination of thermally decomposed ionic graphite intercalation compounds of fluorine. Discharge behavior and effect of the heat treatment of graphite fluoride were investigated. This method drastically decreased the reaction time compared with the direct fluorination of graphite. OCV of (C₂F)_n was higher by 0.3 V than that of the conventionally prepared one, however, overpotential was the same at the constant current density of 0.5 mA cm⁻². On the other hand, the same OCV and less overpotential by 0.3 V were observed for (CF)_n. The heat treatment of these samples in fluorine atmosphere at higher temperatures increased the discharge capacity and provided a more flat discharge potential.