Ya-nan Wang

Removal of humic substances from reverse osmosis (RO) and nanofiltration (NF) concentrated leachate using continuously ozone generation-reaction treatment equipment

Concentrated leachate from membrane treatment process, which contains large amount of difficult-to-degrade humic substances, can induce potential hazards to ecological environment. In this study, the concentrated leachates from reverse osmosis (RO) and nanofiltration (NF) were treated by continuous ozone generating-reaction integrated equipment, and the removal characteristics of humic substances were analyzed using gel filtration chromatography (GFC), excitation-emission matrix fluorescence spectroscopy (EEM), XAD-8 resin fractionation, and Fourier transform infrared spectroscopy (FTIR). The results of XRD-8 fractionation and SUVA254 showed that the humic substances including humic acid (HA) and fulvic acid (FA), were effectively removed along with the breakdown of aromatic hydrocarbons and decrease in the degree of humification during the ozonation process. After 110min of reaction, HA in both concentrated leachates was completely removed. GFC analysis indicated that both concentrated leachates had much broader distribution after the degradation. The high molecular weight (MW) organic matter was transformed into low molecular weight of <10kDa. The majority of high MW organics in NF concentrate were converted to low MW molecules of 10kDa-1kDa, while those in RO concentrate were decomposed to small MW molecules of <1kDa. The results of EEM analysis implied that the degradation of HA and FA led to a significant decrease in the fluorescence intensity. Though the effluent of two concentrated leachate did not meet the maximum allowable criterion for leachate direct or indirect discharge standard in China, the composition and properties of organic matters in concentrated leachate were changed significantly after entire ozonation reaction, which would be conducive to the further biological treatment or other advanced treatment.

Seed-induced synthesis of hierarchical ZSM-5 nanosheets in the presence of hexadecyl trimethyl ammonium bromide

Hierarchical ZSM-5 nanosheets with intracrystal mesopores and honeycomb morphology have been synthesised by seed-inducing via a hydrothermal route in the presence of hexadecyl trimethyl ammonium bromide (CTAB) as the second template.

Preparation of Cs–La–Sb/SiO2 catalyst and its performance for the synthesis of methyl acrylate by aldol condensation

A variety of cesium supported catalysts with amorphous SiO2 as a carrier were prepared by vacuum impregnation and ultrasonic impregnation methods, which were used for the synthesis of methyl acrylate by aldol condensation of methyl acetate and formaldehyde. The as-prepared catalysts were characterized by XRD, N2 adsorption–desorption, NH3-TPD, CO2-TPD, XPS, ICP and TG. The results indicated that the bifunctional Cs–La–Sb/SiO2 showed a high conversion of methyl acetate as well as a high yield of methyl acrylate, which was attributed to the weak acid–base sites and the formation of basic Cs–O–Si species with the addition of antimony and lanthanum, respectively. Furthermore, Cs–La–Sb/SiO2-(V) prepared by vacuum impregnation showed a high initial catalytic activity, but its activity sharply decreased due to the loss of active species. Comparatively, Cs–La–Sb/SiO2-(U) prepared by ultrasonic impregnation showed a good stability owing to the cavitation effect of ultrasonic waves. The conversion of methyl acetate and yield of methyl acrylate remained above 20% and 9.0% (based on methyl acetate) for 100 h without obvious deactivation. Moreover, carbon deposition was the main factor for the deactivation of Cs–La–Sb/SiO2-(U), and the coked catalyst could be regenerated by calcination in air.

N2O emission from a combined ex-situ nitrification and in-situ denitrification bioreactor landfill

A combined process comprised of ex-situ nitrification in an aged refuse bioreactor (designated as A bioreactor) and in-situ denitrification in a fresh refuse bioreactor (designated as F bioreactor) was constructed for investigating N2O emission during the stabilization of municipal solid waste (MSW). The results showed that N2O concentration in the F bioreactor varied from undetectable to about 130 ppm, while it was much higher in the A bioreactor with the concentration varying from undetectable to about 900 ppm. The greatly differences of continuous monitoring of N2O emission after leachate cross recirculation in each period were primarily attributed to the stabilization degree of MSW. Moreover, the variation of N2O concentration was closely related to the leachate quality in both bioreactors and it was mainly affected by the COD and COD/TN ratio of leachate from the F bioreactor, as well as the DO, ORP, and NO3(-)-N of leachate from the A bioreactor.

Effect of external surface of HZSM-5 zeolite on product distribution in the conversion of methanol to hydrocarbons

Abstract The external surface of HZSM-5 zeolite was passivated by liquid siliceous deposition and by acidic sites poisoning with lepidine, respectively. Then methanol-to-hydrocarbons (MTH) reaction was investigated over the above as-prepared catalysts and the dissoluble coke on these used catalysts was analyzed by GC-MS, to study the role of the external surface of HZSM-5 in the catalytic reaction. Comparison with the experimental results based on parent ZSM-5 showed that the product distribution of MTH reaction was obviously influenced by the external surface. Evidences were listed as follows: (1) the final product on parent HZSM-5 showed higher aromatic selectivity, lower olefin selectivity, lower ratio of C2/C3+ aliphatics and higher ratio of C3/C4+ aliphatics than the reaction mixture produced by the sole catalysis of acidic sites in HZSM-5 channel; (2) a little of pentamethylbenzene and hexamethylbenzene in the product on parent HZSM-5, was produced via multi-methylation of methylbenzene on the external surface. The above conclusion may also be suitable for MTH reaction over other zeolites with 10-ring channel.

Response of cbb gene transcription levels of four typical sulfur-oxidizing bacteria to the CO2 concentration and its effect on their carbon fixation efficiency during sulfur oxidation

The variability in carbon fixation capability of four sulfur-oxidizing bacteria (Thiobacillus thioparus DSM 505, Halothiobacillus neapolitanus DSM 15147, Starkeya novella DSM 506, and Thiomonas intermedia DSM 18155) during sulfur oxidation was studied at low and high concentrations of CO2. The mechanism underlying the variability in carbon fixation was clarified by analyzing the transcription of the cbb gene, which encodes the key enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase. DSM 15147 and DSM 505 fixed carbon more efficiently during sulfur oxidation than DSM 506 and DSM 18155 at 0.5% and 10% CO2, which was mainly because their cbb gene transcription levels were much higher than those of DSM 506 and DSM 18155. A high CO2 concentration significantly stimulated the carbon fixation efficiency of DSM 505 by greatly increasing the cbb gene transcription efficiency. Moreover, the influence of the CO2 concentration on the carbon fixation efficiency of the four strains differed greatly during sulfur oxidation.

Characterization of a designed synthetic autotrophic–heterotrophic consortia for fixing CO2 without light

Microbial interactions are important for metabolism, and they improve metabolic substrate types and metabolic efficiency. To discover microbial combinations with high CO2 fixation efficiencies, a series of synergistic microbial consortia of increasing diversity and complexity were devised using chemoautotrophic strains, including Ochrobactrum, Stenotrophomonas, Castellaniella, and Sinomicrobium strains, which were isolated from a non-photosynthetic microbial community (NPMC) with CO2 fixation capacity. Addition of a small inocula of NPMC universally improved the CO2 fixation efficiencies of the consortia by up to 10-fold, while the CO2 fixation efficiencies of most multimember consortia were similar to those of single strains. An analysis of the microbial community structure revealed that both autotrophic–autotrophic microbial interactions and autotrophic–heterotrophic microbial interactions occurred in the synthetic microbial consortia. Ochrobactrum and Castellaniella strains were crucial for autotrophic metabolism, while Lysinibacillus and Pseudomonas strains were crucial for heterotrophic metabolism. These devised microbial consortia have potential applications in addressing environmental issues.

Catalytic Properties of Hierarchical Mordenite Nanosheets Synthesized by Self-Assembly Between Subnanocrystals and Organic Templates

An effective and rapid procedure to synthesize hierarchical MOR (Hi-MOR) nanosheets by self-assembly between subnanocrystals and organic templates was reported. The hierarchical pore systems provided a large quantity of Brønsted acid sites. Compared with conventional mordenite, Hi-MOR showed higher activity, xylene selectivity and longer catalytic life in the reaction of toluene disproportionation, thanks to its excellent diffusion from hierarchical structure.Graphical AbstractHierarchical morednite (Hi-MOR) nanosheets were synthesized by self-assembly between subnanocrystals and organic templates.

A microscopic and spectroscopic study of rapid antimonite sequestration by a poorly crystalline phyllomanganate: differences from passivated arsenite oxidation

During the reaction of arsenite (As(III)) with δ-MnO2 (a typically poorly crystalline phyllomanganate), a significant decrease in the oxidation rate is frequently observed, which is mainly attributed to the surface passivation of δ-MnO2. However, whether surface passivation also occurs during the antimonite (Sb(III)) oxidation process is unclear. In this study, the behavior and mechanisms of Sb(III) oxidation were compared with those of As(III) during their reactions with δ-MnO2. The experimental kinetics results indicated that the oxidation rate of Sb(III) was 6.14–44.71 times faster than that of As(III) with initial concentrations ranging from 100 to 1000 μM. The macroscopic and spectroscopic results suggested that surface passivation during the adsorption of Mn(II) and the formation of Mn(III) were the predominant causes for the decrease in the As(III) oxidation rate, whereas surface passivation may not have been the limiting factor during Sb(III) oxidation. Compared to As(III) oxidation, the rapid oxidation of Sb(III) by δ-MnO2 led to significant changes in the structure and properties of δ-MnO2, and contributed to the precipitation of Mn(II) antimonate (MnSb2O6). The results of this study facilitate a better understanding of the environmental behavior of Sb and As on metal-oxide surfaces in aquatic environments.

Bifunctional Organic Polymeric Catalysts with a Tunable Acid-Base Distance and Framework Flexibility

Acid-base bifunctional organic polymeric catalysts were synthesized with tunable structures. we demonstrated two synthesis approaches for structural fine-tune. In the first case, the framework flexibility was tuned by changing the ratio of rigid blocks to flexible blocks within the polymer framework. In the second case, we precisely adjusted the acid-base distance by distributing basic monomers to be adjacent to acidic monomers, and by changing the chain length of acidic monomers. In a standard test reaction for the aldol condensation of 4-nitrobenzaldehyde with acetone, the catalysts showed good reusability upon recycling and maintained relatively high conversion percentage.