Yaobin Zhang

Enhanced anaerobic digestion of waste activated sludge digestion by the addition of zero valent iron

Anaerobic digestion is promising technology to recover energy from waste activated sludge. However, the sludge digestion is limited by its low efficiency of hydrolysis-acidification. Zero valent iron (ZVI) as a reducing material is expected to enhance anaerobic process including the hydrolysis-acidification process. Considering that, ZVI was added into an anaerobic sludge digestion system to accelerate the sludge digestion in this study. The results indicated that ZVI effectively enhanced the decomposition of protein and cellulose, the two main components of the sludge. Compared to the control test without ZVI, the degradation of protein increased 21.9% and the volatile fatty acids production increased 37.3% with adding ZVI. More acetate and less propionate are found during the hydrolysis-acidification with ZVI. The activities of several key enzymes in the hydrolysis and acidification increased 0.6-1 time. ZVI made the methane production raise 43.5% and sludge reduction ratio increase 12.2 percent points. Fluorescence in situ hybridization analysis showed that the abundances of hydrogen-consuming microorganisms including homoacetogens and hydrogenotrophic methanogens with ZVI were higher than the control, which reduced the H2 accumulation to create a beneficial condition for the sludge digestion in thermodynamics.

Photocatalytic Oxidation of Aqueous Ammonia Using Atomic Single Layer Graphitic-C3N4

Direct utilization of solar energy for photocatalytic removal of ammonia from water is a topic of strong interest. However, most of the photocatalysts with effective performance are solely metal-based semiconductors. Here, we report for the first time that a new type of atomic single layer graphitic-C(3)N(4) (SL g-C(3)N(4)), a metal-free photocatalyst, has an excellent photocatalytic activity for total ammonia nitrogen (TAN) removal from water. The results demonstrated that over 80% of TAN (initial concentration 1.50 mg · L(-1)) could be removed in 6 h under Xe lamp irradiation (195 mW · cm(-2)). Furthermore, the SL g-C(3)N(4) exhibited a higher photocatalytic activity in alkaline solution than that in neutral or acidic solutions. The investigation suggested that both photogenerated holes and hydroxyl radicals were involved the TAN photocatalytic oxidation process and that the major oxidation product was NO3(-)-N. In addition, SL g-C(3)N(4) exhibited good photocatalytic stability in aqueous solution. This work highlights the appealing application of an inexpensive metal-free photocatalyst in aqueous ammonia treatment.

Adsorption of ionizable organic contaminants on multi-walled carbon nanotubes with different oxygen contents.

Multi-walled carbon nanotubes (MWNTs), which are considered to be promising candidates for the adsorption of toxic organics, are released into aqueous environment with their increasing production and application. In this study, the adsorption behaviors of five structurally related ionizable organic contaminants namely perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorooctanesulfonamide (PFOSA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-n-nonylphenol (4-NP) onto MWNTs with different oxygen contents (3.84-22.85%) were investigated. The adsorption kinetics was investigated and simulated with pseudo-second-order model. The adsorption isotherms were found to be fitted with Freundlich model and influenced by both the properties of organic chemicals and the oxygen contents of MWNTs. As adsorption capacity decreases dramatically with the increasing of oxygen contents, the MWNTs with the lowest oxygen contents possess the highest adsorption capacity among four MWNTs. For the MWNTs with the oxygen contents of 3.84%, the adsorption affinity related with hydrophobic interaction and π-electron polarizability decreased in the order of 4-NP>PFOSA>PFOS>2,4-D>PFOA. Furthermore, the adsorption characters of five contaminants were affected by solution pH and solute pK(a) considering electrostatic repulse force and hydrogen bonding, which showed the adsorption of MWNTs with lower oxygen content is much sensitive to solution chemistry.

Photonic Crystal Coupled TiO2/Polymer Hybrid for Efficient Photocatalysis under Visible Light Irradiation

Inverse TiO(2) opal photonic crystal coupled TiO(2)/poly(3-hexylthiophene) (bilayer TiO(2)/P3HT) was structured on FTO substrate for efficient photocatalysis under visible light irradiation (lambda > 400 nm). We expected that the photocatalytic capability of this hybrid photocatalyst could be enhanced by the efficient visible light absorption owing to the photonic crystal structure and effective charge separation owing to the unique heterojunction built between TiO(2) and P3HT. The bilayer TiO(2)/P3HT photocatalyst was prepared first by depositing inverse TiO(2) opal on FTO substrate via replicating polystyrene opal, followed by spin coating a layer of TiO(2) nanoparticles on the inverse TiO(2) opal. The as prepared bilayer TiO(2) was modified by P3HT via dipping method. Environmental scanning electron microscopy (ESEM) images demonstrated that the as prepared photocatalyst was composed of inverse TiO(2) opal layer and TiO(2) nanoparticles layer. The UV-vis diffuse reflectance spectra showed that the optical absorption for bilayer TiO(2)/P3HT was more intensive than for pristine TiO(2) nanoparticle/P3HT (NP-TiO(2)/P3HT) in the range of 400-650 nm. The enhanced generation of photocurrent under visible light irradiation (lambda > 400 nm) was observed using the bilayer TiO(2)/P3HT. The results of photocatalytic experiments under visible light irradiation revealed that the pseudofirst-order kinetic constant of photocatalytic degradation of methylene blue using the bilayer TiO(2)/P3HT was 2.08 times as great as that using NP-TiO(2)/P3HT, showing the advantage of the unique structure in the bilayer TiO(2)/P3HT for efficient photocatalysis.

Preparation of Ag doped BiVO4 film and its enhanced photoelectrocatalytic (PEC) ability of phenol degradation under visible light

Ag particles were doped on BiVO(4) film by photoreduction technique. XRD analysis indicated that the chemical state of the Ag particles was metallic Ag. TEM observation confirmed that the sizes of the Ag particles were 10-20nm. The investigation of the phenol degradation demonstrated that the photocatalytic (PC) degradation rate of the phenol on the Ag doped BiVO(4) film was enhanced by 1.61 times in PC process and by 42.7 times in photoelectrocatalytic (PEC) process compared with that of the BiVO(4) film. The transportation of the electrons from the BiVO(4) to Ag driven by the schottky barrier formed between Ag and BiVO(4) can increase the charge carrier separation, and consequently enhance the PC performance. The enhancement of the PC ability in PEC process could be attributed to the simultaneous movements of the photogenerated electrons to external circuit and the photogenerated holes to the Ag particles deposited on the BiVO(4) film. In 4h, the elimination efficiency and the TOC removal efficiency of phenol on the Ag doped BiVO(4) film in PEC process were 94.1% and 61.0%, respectively.

Osmotic Dehydration Pretreatment in Drying of Fruits and Vegetables

Abstract Several vegetables and fruits, apple, ginger, carrot, and pumpkin were dehydrated under various osmotic conditions using sucrose and salt as the permeating agents. The dehydrated materials were then dried. The influence of solute concentration, process temperature and the type of solute on osmotic dehydration and further thermal drying were investigated. The nutrition loss during the osmotic process was measured using carotene as the nutrition index. The effect of calcium chloride present in osmotic solution on the product quality was also studied. A first order kinetic model was chosen to describe the mass transfer phenomena of the osmotic process. The equilibrium value of water loss, solute gained, kinetic constants K WL and K SG under various conditions are successfully predicted by the model. The relationship between the equilibrium value and four major factors that influence osmotic process of carrot was obtained based on the experimental data. The relations between the loss constant of carotene and the solute concentration in carrot and pumpkin were obtained based on the experimental data. The qualities of dried products are better for the osmotic dehydration pretreated samples than those dried directly.

Applying an electric field in a built-in zero valent iron--anaerobic reactor for enhancement of sludge granulation.

A zero valent iron (ZVI) bed with a pair of electrodes was installed in an upflow anaerobic sludge blanket (UASB) reactor to create an enhanced condition to increase the rate of anaerobic granulation. The effects of an electric field and ZVI on granulation were investigated in three UASB reactors operated in parallel: an electric field enhanced ZVI-UASB reactor (reactor R1), a ZVI-UASB reactor (reactor R2) and a common UASB reactor (reactor R3). When a voltage of 1.4 V was supplied to reactor R1, COD removal dramatically increased from 60.3% to 90.7% over the following four days, while the mean granule size rapidly grew from 151.4 μm to 695.1 μm over the following 38 days. Comparatively, COD removal was lower and the increase in granule size was slower in the other two reactors (in the order: R1 > R2 > R3). The electric field caused the ZVI to more effectively buffer acidity and maintain a relatively low oxidation-reduction potential in the reactor. In addition, the electric field resulted in a significant increase in ferrous ion leaching and extracellular polymeric substances (EPS) production. These changes benefited methanogenesis and granulation. Scanning electron microscopy (SEM) images showed that different microorganisms were dominant in the external and internal layers of the reactor R1 granules. Additionally, fluorescence in situ hybridization (FISH) analysis indicated that the relative abundance of methanogens in reactor R1 was significantly greater than in the other two reactors. Taken together, these results suggested that the use of ZVI combined with an electric field in an UASB reactor could effectively enhance the sludge granulation.

Electrochemically Assisted Photocatalytic Inactivation of Escherichia coli under Visible Light Using a ZnIn2S4 Film Electrode

ZnIn2S4 film was fabricated on Ti substrate by a two-step approach including electrodeposition and annealing. The film obtained after electrodeposition was composed of Zn, In, and S. Then this precursor film was gradually converted to hexagonal phase ZnIn2S4 during the process of annealing in a nitrogen flow. The crystallographic structures and photoresponse ability of the film could be affected significantly by the annealing temperature. From diffuse reflection spectra, ZnIn2S4 film annealed at 500 degrees C exhibited the highest absorption intensity in visible light region among all the samples, resulting in a high photoresponse in the electrochemical measurement. The microstructures of ZnIn2S4 were characterized by transmission electron microscopy, and the results indicated that the interlayer distance was 0.295 nm, corresponding to d(104) space of hexagonal ZnIn2S4. Energy-dispersive X-ray spectra showed that the atomic ratio of Zn:In:S was 9.3:20.3:39.5, which was close to the stoichiometry ZnIn2S4. The photocatalytic ability of ZnIn2S4 was investigated by photoelectrocatalytic inactivation of Escherichia coli ( E. coli) with the initial concentration of approximately 3 x 10(8) colony forming units per milliliter. More than 3 logs of E. coli were killed within 60 min with the ZnIn2S4 film under visible light, and when the photocatalytic process was assisted by a 0.6 V positive potential, no surviving bacteria were detected after 60 min of inactivation.

Enhanced adsorption of PFOA and PFOS on multiwalled carbon nanotubes under electrochemical assistance.

Removal of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) from aqueous solution has attracted wide attention in light of their environmental persistence, bioaccumulation, and potential toxicity. Although various destructive technologies were developed, removal of PFOX (X = A and S) under mild conditions are still desirable. In this work, multiwalled carbon nanotubes (MWNTs) were applied to remove PFOX in electrochemically assistant adsorption. Electrosorption kinetics and isotherms were investigated relative to open circuit (OC) adsorption and adsorption on powder MWNTs. Compared with powder MWNTs adsorption, the initial adsorption rate (υ(0)) of 100 μg/L PFOX at 0.6 V increased 60-fold (PFOA) and 41-fold (PFOS) according to pseudosecond-order kinetics model and the maximum electrosorption capacity (q(m)) of PFOX (50 μg/L to 10 mg/L) increased 150-fold (PFOA) and 94-fold (PFOS) simulated with Langmuir model. These significant improvements were assumed to benefit from enhanced electrostatic attraction under electrochemical assistance. Furthermore, the used MWNTs were found to be regenerative and reusable. This work provides not only a new approach to effective removal of perfluorochemicals from aqueous solution but also a low energy-consumption and environmentally-friendly strategy for application of carbon nanotubes in water treatment.

A structured macroporous silicon/graphene heterojunction for efficient photoconversion.

Improvement of conversion efficiency of solar energy to electricity or chemical energy has attracted extensive attention due to the increasing need for clean and renewable energy. Silicon has successfully been applied in photoelectric conversion, but it is difficult to employ Si in converting solar energy to chemical energy due to rapid formation of an insulating oxide layer. This problem could be overcome by coating the surface of Si with a transparent charge collector serving as a protective layer. Noble metals, wide-gap semiconductors, and polymer films were commonly employed as protective layers. The high price (noble metal), relatively low conductivity (wide-gap semiconductor), and limited thermal and chemical stability (polymer) restricted practical application of these materials in conversion of solar to chemical energy. Graphene (Gr), discovered in 2004, is a promising protective material due to its good stability, extremely high electron mobility, and excellent optical transparency. Moreover, Gr is an ideal two-dimensional ultrathin material with comparatively fewer defects than film constructed from nanoparticles. Thus, it is a favorable material for charge transfer. In fact, Gr has found applications as the electron acceptor in dye-sensitized solar cells and polymer solar cells. However, no work has been reported Gr protective layers. We have now built a macroporous Si (MPSi)/Gr heterojunction by depositing Gr on the surface of MPSi and demonstrated that Gr can be used as protective layer for MPSi to improve its ability to convert solar to chemical energy. Macroporous Si was selected as the substrate because it can offer higher surface area and lower reflection than planar Si wafer. The MPSi was fabricated by chemically etching p-type Si wafer ((100) orientation, 3–4 Wcm resistivity). The etching electrolyte was composed of 5m NH4F and 0.02m AgNO3. Graphene was obtained in two steps: fabricating graphite oxides by the Hummer method, and then reducing them to Gr by pyrolysis at 1050 8C. To deposit Gr on the surface of MPSi, an MPSi cathode was immersed in a Gr suspension, and electrophoresis was performed. The stable Gr suspension was composed of 0.01 g of Gr, 100 mL of isopropyl alcohol, and 0.005 g of Mg(NO3)2·6H2O, [13] and the applied voltage and deposition duration of electrophoresis were 160 V and 10 s, respectively. After electrophoresis, annealing was carried out to improve the adhesion between the Gr layer and MPSi. As shown in Figure 1 a, the longest part of the as-prepared Gr sheets is shorter than 2 mm, and ripples can be observed. The typical thicknesses of the ripples were measured from different sections marked by the rectangular frames in Figure 1b. According to their line profiles, the average thickness of the ripples is 2.35 nm, which indicates that the sample as prepared is few-layer Gr (4–6 layers). According to Liu et al. , few-layer Gr is less reactive but more stable than monolayer Gr in aqueous solution. Therefore, few-layer Gr is a suitable choice as protective layer.