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Fan H.,Beijing University of Technology | Peng Y.,Beijing University of Technology | Li Z.,Changchun Gold Research Institute | Chen P.,North China Pharmaceutical Group Corporation | And 2 more authors.
Journal of Polymer Research | Year: 2013

Hydrophobic symmetric flat-sheet membranes of polyvinylidene fluoride (PVDF) for use in vacuum membrane distillation (VMD) were successfully fabricated by the vapor-induced phase separation (VIPS) method using the double-layer casting process. To avoid the delamination that often occurs in double-layered membranes, the same PVDF polymer was employed in both the upper layer and support layer casting solutions. Solutions with low and high PVDF contents were co-cast as the upper layer and support layer of the membrane that was formed. In the VIPS process, the low PVDF content solution favored the formation of a layer with a porous and hydrophobic surface, whereas the solution with a high PVDF concentration favored the formation of a layer with high mechanical strength. The effect of the vapor-induced time on the morphological properties of the membranes was studied. As the vapor-induced time was increased, the cross-section of the membrane changed from an asymmetrical finger-like structure to a symmetrical sponge-like structure, and the surface of the membrane became rough and porous. The membrane subjected to the longer vapor-induced time also exhibited a higher permeating flux during the VMD process. The best PVDF membrane fabricated in this study had a mean radial pore size of 0.49 μm, and the rough upper surface produced a static contact angle of 145 with water. During the VMD process with a 3.5 wt.% sodium chloride (NaCl) aqueous solution, the best membrane that was fabricated produced a permeating flux of 22.4 kg m-2 h-1 and an NaCl rejection rate of 99.9 % at a feed temperature of 73 C and a downstream pressure of 31.5 kPa. This performance is comparable to or superior to the performances of most of the flat-sheet PVDF membranes reported in the literature and a polytetrafluoroethylene membrane used in this study. © 2013 Springer Science+Business Media Dordrecht. Source

Song Y.,Nanjing Agricultural University | Li Y.,National Major Science and Technology Program Management Office for Water Pollution Control and Treatment | Liu Y.,Taiyuan University of Technology | He W.,Nanjing Agricultural University
Huanjing Kexue Xuebao/Acta Scientiae Circumstantiae | Year: 2013

Acinetobacter sp. Y1, a high effective heterotrophic nitrification bacterium, was isolated from the activated sludge of a coking wastewater treatment facility. The characteristics of nitrogen removal by strain Y1 at different carbon sources, C/N ratios, nitrogen sources and substrate concentrations were investigated. The result shows that Acinetobacter sp. Y1 can remove different forms of nitrogen sources. The most efficient ammonium removal and growth rate for Y1 was occurred at C/N=15 when sodium citrate was supplemented as the carbon source, ammonium removal rate reached 99% and OD600max was 1.432. High concentration of ammonium ranging from 400 mg·L-1 to 1600 mg·L-1 could be degraded well by strain Y1. The most efficient nitrogen removal was occurred at C/N=20 when nitrite or nitrate was treated as a sole nitrogen source. Source

Li Z.,Changchun Gold Research Institute | Peng Y.,Beijing University of Chemical Technology | Dong Y.,Beijing University of Chemical Technology | Fan H.,Beijing University of Chemical Technology | And 3 more authors.
Applied Surface Science | Year: 2014

The effects of the membrane characteristics and operational conditions on the vapor flux and thermal efficiency in a direct contact membrane distillation (DCMD) process were studied with a mathematical simulation. The membrane temperature, driving force of vapor transfer, membrane distillation coefficient, etc. were used to analyze the effects. The operating conditions that increased the vapor flux improved the thermal efficiency. The membrane characteristics of four microporous membranes and their performances in DCMD were compared. A polysulfone (PSf) membrane prepared via vapor-induced phase separation exhibited the lowest thermal conductivity. The PSf and polyvinylidene difluoride (PVDF) membranes were modified using SiO2 aerogel blending and coating to reduce the thermal conductivity of the membrane. The coating process was more effective than the blending process toward this end. The changes in the structure of the modified membrane were observed with a scanning electron microscope. Si was found on the modified membrane surface with an energy spectrometer. The PVDF composite and support membranes were tested during the DCMD process; the composite membrane had a higher vapor flux and a better thermal efficiency than the support. A new method based on a 3ω technique was used to measure the thermal conductivity of the membranes. © 2014 Elsevier B.V. All rights reserved. Source

Liu Y.,Taiyuan University of Technology | Wang Y.,Taiyuan University of Technology | Li Y.,National Major Science and Technology Program Management Office for Water Pollution Control and Treatment | An H.,Taiyuan University of Technology | Lv Y.,Taiyuan University of Technology
Chinese Journal of Chemical Engineering | Year: 2015

Alcaligenes faecalis C16 was found to have the ability to heterotrophically nitrify and aerobically denitrify. In order to further understand its nitrogen removal ability and mechanism, the growth and ammonium removal response were investigated at different C/N ratios and ammonium concentrations in the medium with citrate and acetate as carbon source separately. Furthermore, experiments of nitrogen sources, production of nitrogen gas and enzyme assay were conducted. Results show that the bacterium converts NH4+-N and produces NH2OH during the growing phase and nitrite accumulation is its distinct metabolic feature. A. faecalis C16 is able to tolerate not only high ammonium concentration but also high C/N ratio, and the ammonium tolerance is associated with carbon source and C/N ratio. The nitrogen balance under different conditions shows that approximately 28%-45% of the initial ammonium is assimilated into the cells, 44%-60% is denitrified and several percent is converted to nitrification products. A. faecalis C16 cannot utilize hydroxylamine, nitrite or nitrate as the sole nitrogen source for growth. However, nitrate can be used when ammonium is simultaneously present in the medium. A possible pathway for nitrogen removal by C16 is suggested. The preliminary enzyme assay provides more evidence for this nitrogen removal pathway. © 2014 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved. Source

Geng H.,Shanxi University | Li Y.,National Major Science and Technology Program Management Office for Water Pollution Control and Treatment | Zhang Z.-M.,Shanxi University | Ro C.-U.,Inha University
Zhongguo Huanjing Kexue/China Environmental Science | Year: 2012

A quantitative single particle analytical technique, low-Z particle electron probe X-ray microanalysis (EPMA) was used to characterize 2821 individual particles in 16 sets of aerosol samples collected on July 25~31, 2007 at Ny-Alesund, Svalbard (78̈55̀N, 11̈56̀E) and 1460 individual particles in 5 sets of aerosol samples collected on March 12~16, 2009 at King George Island (62̈13̀S, 58̈47̀W). There was great difference in chemical compositions between the atmospheric particles of the two sites. For the Arctic samples, aged sea salt, fresh (or genuine) sea salt, and mineral dust particles accounted for 44%, 9%, and 27%, respectively, in the examined particles (their aerodynamic diameters were in the range of 0.5~8μm). Whereas for the Antarctic samples, fresh sea salt particles accounted for 74% and aged sea salt particles containing sulfate accounted for 19% in the examined particles (their aerodynamic diameters were in the range of 1~10μm). The majority of aged sea salt particles at Ny-Alesund contained nitrate, indicating that the atmosphere was disturbed by anthropogenic air pollutants. On the contrary, all of the aged sea salt particles contained sulfate in the samples at King George Island, none of them containing nitrate. It was likely that the oxidation of dimethylsulfide (DMS) emitted from phytoplanktons in the ocean rather than anthropogenic sulfur emission was responsible for the formation of sulfate-containing aged sea salt particles, implying that the air in the Antarctic area was relatively clean, without being polluted by anthropogenic pollutants. Source

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