Cai Wei-min

Influence of lactic acid on the two-phase anaerobic digestion of kitchen wastes

To evaluate the influence of lactic acid on the methanogenesis, anaerobic digestion of kitchen wastes was firstly conducted in a two-phase anaerobic digestion process, and performance of two digesters fed with lactic acid and glucose was subsequently compared. The results showed that the lactic acid was the main fermentation products of hydrolysis-acidification stage in the two-phase anaerobic digestion process for kitchen wastes. The lactic acid concentration constituted approximately 50% of the chemical oxygen demand (COD) concentration in the hydrolysis-acidification liquid. The maximum organic loading rate was lower in the digester fed with lactic acid than that fed with glucose. Volatile fatty acids (VFAs) and COD removal were deteriorated in the methanogenic reactor fed with lactic acid compared to that fed with glucose. The specific methanogenic activity (SMA) declined to 0.343 g COD/(gVSSxd) when the COD loading were designated as 18.8 g/(Lxd) in the digester fed with lactic acid. The propionic acid accumulation occurred due to the high concentration of lactic acid fed. It could be concluded that avoiding the presence of the lactic acid is necessary in the hydrolysis-acidification process for the improvement of the two-phase anaerobic digestion process of kitchen wastes.

Preparation, characterization and photocatalytic activity of visible light driven chlorine-doped TiO2

A novel chlorine-doped titanium dioxide catalyst with visible light response was prepared by hydrolysis of tetrabutyl titanate in hydrochloric acid. The catalyst samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS). Results showed that the doped element of Cl lowered the temperatures of phase transformation of TiO2 from amorphous to anatase and from anatase to rutile. The absorption edge of chlorine-doped TiO2 calcined at 300°C shifted to visible light region. X-ray photoelectron spectroscopy results proved that chlorine existed in the TiO2 crystal lattice as anion. The photocatalytic degradation of phenol showed that under visible light (λ > 400 nm) irradiation, the chlorine-doped TiO2 calcined at 300°C displayed the best performance, the degradation ratio of phenol was 42.5% after 120 min.

Ozonation of naphthalene sulfonic acids in aqueous solutions: Part II—Relationships of their COD, TOC removal and the frontier orbital energies

This paper evaluated the COD, TOC removal and molecular frontier energies in the ozonation of naphthalene sulfonic acids (NSAs). It was found that both COD and TOC degradation of the 11 compounds followed the pseudo-first-order kinetic and the reaction rate constants with ozone varied widely. A linear relationship between logarithm of global COD degradation rate constant and the energy of the highest occupied molecular orbit, E(homo), was obtained for these NSAs with a regression coefficient of 0.88 and a slope of 0.4672 eV(-1). TOC degradation kinetics also reached similar results with a regression coefficient of 0.90 and a slope of 0.9336 eV(-1). The results of correlation analysis suggested that TOC and COD removal in ozonation of NSAs follow the frontier orbital theory and can be predicted by E(homo), which indicated that electrophilic effect was the main factor in the ozonation of NSAs. Therefore, it is possible to improve the biodegradability of dyestuff wastewater bearing mainly NSAs by ozonation at an accepted cost and evaluate the economy of ozonation process.

Degradation of Methyl Orange in Water by Contact Glow Discharge Electrolysis

The degradation of methyl orange in a neutral phosphate buffer solution was investigated by means of contact glow discharge electrolysis (CGDE). The methyl oranges were degraded and eventually decomposed into inorganic carbon when CGDE was conducted under the applied DC voltage of 480 V and current of ca. 80 mA. As the intermediate products, some phenolic compounds were detected as well as carboxylic acids. Experimental results showed that the oxidation process followed the first-order reaction law. Based on the analysis of the ultraviolet (UV) spectra of the solution and the intermediate products from High Pressure Liquid Chromatography-Mass Spectrum (HPLC-MS), the reaction pathway was proposed. The attack of hydroxyl radicals was considered to be a key step to start the whole oxidation process.

Light scattering of nanocrystalline TiO2 film used in dye-sensitized solar cells

This paper studies the light scattering and adsorption of nanocrystalline TiO2 porous films used in dye-sensitized solar cells composed of anatase and/or rutile particles by using an optical four-flux radiative transfer model. These light properties are difficult to measure directly on the functioning solar cells and they can not be calculated easily from the first-principle computational or quantitative theoretical evaluations. These simulation results indicate that the light scattering of 1–25 nm TiO2 particles is negligible, but it is effective in the range of 80 and 180 nm. A suitable mixture of small particles (10 nm radius), which are resulted in a large effective surface, and of larger particles (150 nm radius), which are effective light scatterers, have the potential to enhance solar absorption significantly. The rutile crystals have a larger refractive index and thus the light harvest of the mixtures of such larger rutile and relatively small anatase particles is improved in comparison with that of pure anatase films. The light absorption of the 10 μm double-layered films is also examined. A maximal light absorption of double-layered film is gotten when the thickness of the first layer of 10 nm-sized anatase particles is comparable to that of the second larger rutile layer.

Anaerobic digestion of kitchen wastes in a single-phased anaerobic sequencing batch reactor (ASBR) with gas-phased absorb of CO2.

The performance of the single-stage anaerobic digestion of kitchen wastes was investigated in an anaerobic sequencing batch reactor(ASBR) with gas-phased absorb of CO2. The ASBR was operated at four chemical oxygen demand(COD) loading rates, 2.8, 5.1, 6.2 and 8.4 g/(L x d) respectively. The COD loading rate was increased with the TS concentration and HRT changing. At maximum COD loading rate of 8.4 g/(L x d), the COD, total solid(TS) removal rate and methane gas yield were 69%, 68% and 2.5 L/(L x d) respectively. The operation of the reactor with gas-phased absorb of CO2 was stable in spite of the low pH (2.6-3.9) and high concentration of TS (142 g/L) of input mixture. The output volatile fatty acid(VFA) concentration was between 2.7-4.7 g/L and had no inhibition on the methanogenic microorganism. The reactor without gas-phased absorb of CO2 became acidified when the total COD loading rate was increased to 5.1 g/(L x d). Stoichiometry of the methanogenesis for kitchen wastes showed a considerable amount of alkaline will be required to keep pH in the appropriate range for the methanogenic microorganism based on theoretical calculation. Gas-phased absorb of CO2 effectively reduced the alkaline consumption, hence avoided excessive cation into the reactor.

Preparation of nanocrystalline anatase TiO2 using basic sol-gel method

Nanocrystalline titanium dioxide particles with anatase structure and high thermal stability have been synthesized using the basic sol-gel method. The particle size and morphology were refined under hydrothermal conditions in the presence of different concentrations of tetramethylammonium hydroxide (TMAH) at 210°C and 230°C. XRD and TEM analysis showed that the TiO2 particles obtained were homogeneous and monodispersive at low contents of TMAH. All intense peaks, clearly observed in the XRD patterns, were assigned to the anatase phase and no rutile phase was observed. At high contents of TMAH, nanoscale small (10–30 nm) and larger (>100 nm) TiO2 particles were one-pot synthesized. The nanocrystalline TiO2 particles synthesized by this method have good thermal stability. With the sintering temperature of up to 650°C, all the XRD peaks maintained good agreement with the anatase reference data.

SO2 REMOVAL WITH FERRIC SULFATE SOLUTION

Abstract The determination of the influence of the concentration of ferric sulfate solution on SO2 absorption was performed in this study. It was found that the SO2 absorption efficiency increased with increasing ferric concentration, and decreased with the acidity of the spraying solution. As the hydrolysis of ferric ions occurs in solution, the SO2 removal efficiency increased slowly with increasing Fe(III) concentration. Taking into account the hydrodynamic and mass transfer characteristics of the packed column, the enhancement factor (E) was found to depend on the concentration of the ferric ions and pH, which indicated that it could be used for the simulation or design of SO2 scrubbers.The determination of the influence of the concentration of ferric sulfate solution on SO2 absorption was performed in this study. It was found that the SO2 absorption efficiency increased with increasing ferric concentration, and decreased with the acidity of the spraying solution. As the hydrolysis of ferric ions occurs in solution, the SO2 removal efficiency increased slowly with increasing Fe(III) concentration. Taking into account the hydrodynamic and mass transfer characteristics of the packed column, the enhancement factor (E) was found to depend on the concentration of the ferric ions and pH, which indicated that it could be used for the simulation or design of SO2 scrubbers.

Preparation, Characterization and Visible Light Photocatalytic Activity of Nitrogen-doped TiO2

The N-doped TiO2 polycrystalline powder was synthesized through calcining the hydrolysis product of tetra-butyl titanate with ammonia. The photocatalytic activity of N-doped TiO2 powder with anatase phase calcined at 400 °C was 2.7 times higher than that of Degussa P25 for phenol decomposition under visible light. All samples had mesoporous structures. X-ray photoelectron spectroscopy confirmed that a trace amount of N atoms remained in the anatase polycrystalline TiO2 powder when calcined at 400 °C as substitutional atoms at the oxygen sites. UV-Vis and EPR analyses indicated that oxygen vacancy states were created during the course of N-doped TiO2 powder formation. It is considered that substitutional N atoms, oxygen vacancy states, large BET surface areas and mesoporous structure are important factors for the N-doped photocatalyst to present a high vis-activity.