Ammonium Ion Adsorption and Settleability Improvement Achieved in a Synthetic Zeolite-Amended Activated Sludge

Municipal wastewater treatment plants typically exhibit two classic problems： high ammonium concen- tration in water after conventional biological treatment and, in some cases, poor activated sludge sediment ability. Potential solutions to these problems were investigated by adding a synthetic zeolite obtained from coal fly ash to different steps of activated sludge treatment. The experimental results for ammonium removal fit well with the theoretical adsorption isotherms of the Freundlich model with a maximum adsorption capacity of 13.72 mg.g-＇. Utiliza- tion of this kind of zeolite to improve activated sludge sediment ability is studied for the first time in this work. It is found that the addition of the zeolite （1 g. L-1） to an activated sludge with settling problems significantly enhances its sediment ability and comoact ability. This is confirmed by the sludge volume index （SVI）, which was reduced from 163 ml.g-1 to 70 ml.g-r, the V60 value, which was reduced from 894 ml.L-1 to 427 ml.L-1, and the zeta poten- tial （0, which was reduced from -19.81 mV to -14.29 mV. The results indicate that the addition of this synthetic zeolite to activated sludge, as an additional waste management practice, has a positive impact on both ammonium removal and sludge settleability.

Application of zeolite adsorption and biological anaerobic digestion technology on hydrothermal liquefaction wastewater

The post-hydrothermal liquefaction wastewater(PHWW)was obtained from a conversion process of Spirulina sp.to bio-crude oil via hydrothermal liquefaction(HTL)technology that was rich in organic matter and toxicant.In this study,zeolite was applied to overcome the inhibitions and improve anaerobic digestion(AD)efficiency.Three zeolite adding ways were evaluated:PHWW pretreated with zeolite for 5 h with/without solid-liquid separation before AD process and zeolite added to PHWW AD process directly,in order to find the most ideal way to add zeolite.Results indicated that zeolite had a positive effect on the AD process of the PHWW.The gas potential of PHWW after adding zeolite,as well as the chemical oxygen demand(COD)removal rate,was much higher than those of its initial state.Especially when the PHWW was pretreated by zeolite for 5 h without separation,the biogas yield increased by 73.96%(6170μmol/g CODremoved)compared with the initial PHWW(3546.7μmol/g CODremoved).

Molecular Simulation of Adsorption of Quinoline Homologues on FAU Zeolite

The Grand Canonical Monte Carlo(GCMC) simulation method was used to investigate the adsorption properties of quinoline homologues(quinoline, 2-methyl quinoline, and 2,4-dimethyl quinoline) on the FAU zeolite. The adsorption heat, adsorption isotherms, and adsorption sites of them were obtained. At the temperature ranging from 673.15 to 873.15 K, the Henry constant of quinoline homologues calculated on the FAU zeolite was applied to simulate their adsorption heat. And its value was more in accordance with the related data reported in the literature. The results showed that their isosteric heat decreased in the following order: 2,4-dimethyl quinoline(118.63 kJ/mol) > 2-methyl quinoline(110.45 kJ/mol) > quinoline(98 kJ/mol), and complied with the order of their adsorbate basicity. The competitive adsorption of three components of quinoline homologues on the FAU zeolite was calculated numerically at a temperature of 773.15 K and a pressure range of 0.1—100 MPa under the Universal force field. Their adsorption capacity decreased in the following order: quinoline > 2-methyl quinoline > 2,4-dimethyl quinoline. The smaller the molecule size of the adsorbate, the greater the saturated adsorption capacity would be. It was found that the quinoline homologues could be adsorbed in the main channels of 12- membered-ring framework of the zeolite. Simultaneously, the influence of silica/alumina ratio on the adsorption property of quinoline homologues in FAU zeolite was studied. The smaller the silica/alumina ratio, the greater the isosteric heat and adsorption capacity would be.

MCM-36 zeolites tailored with acidic ionic liquid to regulate adsorption properties of isobutane and 1-butene

Adsorption properties of an adsorbent or a catalyst towards adsorbates are crucial in the process of adsorption separation or catalytic reaction. Surface morphology and structure of adsorbents have a significant impact on the adsorption properties. In this study, a novel acidic ionic liquid, 1-butyl-3-(triethoxysilylpropyl)imidazolium hydrogen sulfate(i.e., [BTPIm][HSO_4]), was synthesized and subsequently grafted onto the MCM-36 zeolite for the regulation of its adsorption properties towards isobutane and 1-butene. The resultant [BTPIm][HSO_4]-immobilized MCM-36(i.e., MCM-36-IL) was characterized by FT-IR, XPS, XRD, SEM, TG/DTG and N_2 adsorption–desorption measurement. It was found that the specific surface area, micropore volume and mesopore volume of the MCM-36 support underwent a reduction upon the immobilization of ionic liquid,while the surface density of acid increased from 0.0014 to 0.0035 mmol·m^(-2). The adsorption capacity of isobutane and 1-butene on the MCM-36-IL was determined by a static volumetric method. Results demonstrated that the interaction between isobutane and MCM-36-IL was enhanced and the interaction between 1-butene and MCM-36-IL was reduced. As a result, a tunable adsorption ratio of isobutane/1-butene on MCM-36 was achieved.With the increase in surface density of acid and the tunable adsorption ratio of isobutane and 1-butene on the functionalized MCM-36, the acidic ionic liquid-immobilized zeolites are beneficial to obtain an improved reaction yield and a prolonged catalyst life in the reactions catalyzed by solid acid.

Molecular Simulations of FCC Dry Gas Components Adsorption in Zeolite Y

Adsorption of FCC dry gas components, hydrogen(H_2), nitrogen(N_2), methane(CH_4), ethane(C_2H_6) and ethylene(C_2H_4) in zeolite Y was studied by performing the Grant Canonical Monte Carlo(GCMC) simulations at 298K and 823K and under a pressure range up to 10 MPa. Simulation results were analyzed using the Langmuir model, which presented fitting of dry gas components adsorption to be suggested as the monolayer adsorption. C_2H_4 presented most single adsorption amount, which reached 7.63 mol/kg at 298K under a pressure of 200kPa. Thermodynamic parameters of the Gibbs free energy change, enthalpy change and entropy change were analyzed based on adsorption equilibrium constant obtained from the GCMC simulations. The results suggested that it was more favorable for C_2H_4 to be adsorbed in zeolite Y. Adsorption molecules were in ordered arrangement in the zeolite, and C_2H_4 exhibited a more orderly arrangement than other components. Additionally, a competition in the adsorption of a mixture of dry gas components was found, and supercages were the priority adsorption space. The competition was favorable to CH_4 and C_2H_6, and the competitive power was affected by temperature.

Synthesis of ZSM-5@ Ordered Mesoporous Silica Composites by Dodecylamine Surfactant

The core-shell structures of ZSM-5 coated with mesoporous silica were synthesized by means of dodecylamine（DDA） surfactant. The results show that the mesoporous silica shells are coated on ZSM-5 cores and result in the formation of hierarchical porous structures. The thickness of the coating shell can be controlled by changing the adding amount of TEOS. The core-shell composites with the thickness of 35 nm possess high surface areas（about 528 m2·g-1）, large pores（about 3.5 nm in diameter） on the silica shells. The composite molecular sieves display higher adsorption capacity for benzene（140.2 mg·g-1） and butyraldehyde（213.7 mg·g-1） than that of pristine ZSM-5 for benzene（99.2 mg·g-1） and butyraldehyde（134.7 mg·g-1）. The composite molecular sieves show a wide application foreground for harmful gas adsorbent for environmental protection.

Application of high silica zeolite ZSM-5 in a hybrid treatment process based on sequential adsorption and ozonation for VOCs elimination

In this study,a hydrophobic synthetic zeolite,namely ZSM-5 is chosen as an adsorbent/catalyst for toluene removal.Experimental results showed that toluene adsorption onto ZSM-5 was favourable,following a Langmuir adsorption isotherm model.ZSM-5 zeolite was regenerated using gaseous ozone at low temperature.Adsorbed toluene was oxidised,releasing mainly CO_2 and H_2O.Traces of oxidation by-products such as acetic acid and acetaldehyde were formed and remained adsorbed after the oxidativate regeneration with ozone.After four successive cycles of adsorption/ozonation,the adsorption efficiency was not affected（92%-99%）.These results showed that volatile organic compound（VOC）removal by adsorption onto ZSM-5 zeolite followed by ozone regeneration could be used as a promising hybrid process for the control of VOC emissions in terms of efficiency.

Strong selective adsorption of N-nitrosamines on zeolites

With the functional group of -N-N=O, N-ni-trosamines are well known to constitute a serious health risk[1]. These toxicant chemicals not only give rise to poisoning sometimes[2], but also play an important role in causing cancer in almost all organs of experimental animals and are therefore likely to be related to human beings, since they have the similar metabolism and meta-balin to those animals[3]. Gaseous nitrogen oxides like NO2, N2O3 and N2O4 are reportedly to react with-secondary amines and form N-nitrosamines in environment[4], and some foods, such as beer and salted fish, contain a high concentration of N-nitrosamines and their precursors. However, tobacco and cigarette smoke are believed to be the largest N-nitrosamines pollution for human beings besides the industrial working place. N-nitrosamines are considered important contributors to the total burden of carcinogens resulting from tobacco, especially tobacco smoke, because they can be deposited directly into the blood following inhalation