Many chemical and biocatalytic reactions are consuming gaseous species like oxygen, provided by the mass transfer across interfaces of multiphase contact apparatuses. For biocatalytic reactions a macroscopic aeration can lead to reduced enzyme activity by foaming and shear forces and for fast chemical reactions in multiphase flows, the mass transfer limitation is often the bottleneck for a process optimization. The present study investigates the use of bubbles with diameters less than 100 µm for aeration of a 3 L lab scale stirred tank reactor. For demineralized water and a solution of glucose and bovine serum albumin (BSA) as biocatalytic model protein solution, two different membrane spargers with a mean pore size of 1 µm and 2 µm are investigated. Determining the influence of the energy input on the hydrodynamics of the system, endoscopic measurements of bubble size distributions are carried out. The mass transfer performance of the two spargers is analyzed by measurements of the oxygen kla value for varying gas flow rates. As a result microbubble aeration shows a significant higher mass transfer performance compared to an open tube aeration saving 60% of the gaseous phase by reaching the same kla values. Besides high specific interfacial areas and long residance times, the Laplace pressure inside the bubble is identified as an enhancing force for mass transfer at microscale.
In the process of desalination and salt production from seawater, a lot of bittern arises as by-products. The bittern contains various resources and is mostly unutilized. We focus on the syntheses of layered double hydroxides (LDH) from components of the bittern for economical use. The LDH is a clay mineral and has an anion exchange ability. In this study, syntheses of LDHs from the bittern and the anion exchange property are investigated in comparison with that from reagents of stoichiometric concentrations of LDHs. The simulated bittern was adjusted based on the actual composition of the bittern and was mixed with Al solutions. The precipitate of LDH obtained by adding drop-wise into sodium hydroxide solution by co-precipitation method in a high pH region and the powder sample was obtained by filtration from the slurry. The structure, ion concentration and anion exchange property of the LDHs, were analyzed by SEM, XRD and ICP. The precipitated LDH from the bittern was preferentially Mg-type hydrotalcite according to the results of the XRD measurements. The synthesis of Ca-type hydrocalumite can be also synthesized from the solution excluding the hydrotalcite at another higher pH region. In the syntheses, all LDHs had chloride ions as charged intercalants for keeping charge neutrality in the layer structures. The anion exchange property was investigated between Cl− and HPO42−. The exchange structures were checked by interlayer distance variation before and after the exchange operation. The anion exchange capacity of the hydrotalcite and hydrocalumite from the bittern was lower than that from the reagents prepared in stoichiometric concentrations. A recovery process of Mg and Ca ions from the bittern is proposed in this paper.
In the present study, a novel combined flocculant comprising starch-capped Na2SiO3·9H2O and Al2(SO4)3·18H2O was successfully synthesized by a process of polymerization and coating. The novel flocculant exhibited high efficiency and eco-friendliness. Experiments on the flocculation of simulated water showed that the flocculant prepared from starch-capped poly-aluminum silicate exhibited excellent performance. The product was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction to analyze its structure and performance. A comparison of its coagulation efficiency in terms of the removal of turbidity and chroma was conducted in experiments. The results show that the flocculant exhibited the highest coagulation efficiency when the aluminum/silicon molar ratio was 1, the starch/Si mass ratio was 1.5, the pH was 1.5, the reaction temperature was 35°C, and the reaction time was 120 min. The rates of removal of turbidity and chroma exceeded 99% and 98%, respectively, under the optimal conditions.
Cr(VI) has been confirmed as a toxic carcinogenic contaminant; consequently, it must be removed from wastewater pipes prior to discharge. In the present work, the reductive adsorption of Cr(VI) was investigated using coal-based activated carbon. Batchwise reductive adsorption and chromatography study of Cr(VI) were carried out, with varying parameters, such as pH, time, initial concentration, and temperature. The Cr(VI) species adsorbed on the activated carbon were immediately reduced to Cr(III), such that only Cr(III) was observed. The reductive adsorption followed the Langmuir adsorption model, and the highest adsorption capacity of 3.43 mmol g−1 was obtained at an equilibrium pH of 2.04. Thermodynamic studies indicated that the adsorption process was endothermic. The reductive adsorption kinetics were controlled by the adsorption step and expressed by the pseudo-second-order kinetic model. The chromatographic recovery of Cr(VI) using the activated carbon was achieved at a feed pH of 3.0 until a bed volume of 500 was achieved, although the elution of the loaded Cr was difficult.
The sorption of various antibiotics, pharmaceuticals, and personal care products in water onto didodecyldimethylammonium bromide (DDAB)-modified montmorillonite organoclay was studied. The extent of their sorption onto the organoclay was largely dependent on the DDAB content; the effect of DDAB modification on the sorption was also influenced by the hydrophobicity and/or net charge of the pharmaceutical. The binding constants of β-lactam antibiotics were determined from their interaction with the DDAB molecules on the organoclay and were correlated with their aqueous–octanol distribution coefficients. Additionally, they were influenced by the net charge of the antibiotic. A wide range of β-lactam antibiotics, including penicillin- and cephalosporin-type antibiotics, were sorbed on the organoclay and rapidly degraded under mild conditions (pH 7, 25°C). The continuous sorption and degradation of penicillin G in a buffer solution and in synthesized hospital wastewater using an organoclay-packed column were demonstrated. The resulting effluent was free of penicillin, and contained only penicillin degradation products, suggesting the usefulness of DDAB-MT organoclay as a barrier material for controlling the diffusion of antibiotics.
The present study examines zeolitic imidazolate framework-8 (ZIF-8) membranes for propylene/propane separation prepared via direct growth on a zinc oxide (ZnO)-modified support, and their permeation properties. ZnO acts as a secondary zinc source and induces crystallization of the ZIF-8 selective layer, thereby actualizing a simple and more versatile preparation method. The ZnO layer was prepared by dip-coating the porous support in an aqueous solution of zinc nitrate and subsequent calcination in air at 200°C. ZIF-8 membranes with well-intergrown crystalline layers were obtained via direct growth on the modified support without activation with 2-methyimidazole. The ZIF-8 membranes prepared from the support modified by a 0.1-M aqueous solution of zinc nitrate demonstrated the highest performance with an average propylene permeance of (1.8±0.29)×10−8 mol·m−2·s−1·Pa−1 and a mean propylene/propane selectivity of 25±1.8, using an equimolar feed of propylene and propane at 25°C. The intermittent, long-term propylene/propane separation measurements across the ZIF-8 membranes showed an approximately constant performance up to 20 d, thus demonstrating the effectiveness of our proposed method. A molecular sieve was identified as the dominant permeation mechanism; however, selectivity was lower than that presented in previous reports. To estimate the influence of defects in the selective layer, the sum of parallel micropores and Knudsen and viscous flows were fitted to experimental data. Viscous flow was quantitatively estimated to be the main cause for the decrease in selectivity.
A fixed-bed dehumidifying adsorption process with a phase-change material (PCM)-containing mesoporous silica SBA-15 was simulated, and various key parameters were varied to identify the optimal conditions for adsorption. The effectiveness of the PCM-containing SBA-15 adsorbent was evaluated based on the performance of the fixed-bed dehumidifying adsorption process, i.e. the amount of water adsorbed per unit time. To this end, the enthalpy of fusion and amount of the inserted PCM, along with the fluid temperature at the inlet of the adsorbent bed, were investigated as the key parameters governing the adsorption performance. Upon increasing both the enthalpy of fusion and the amount of the inserted PCM, the latent heat storage efficiency increased and the adsorption performance improved. Upon increasing the fluid temperature at the inlet, the adsorption performance increased drastically. On modeling the PCM-containing SBA-15 using the optimized conditions, the amount of adsorbed water was four times larger than that for the experimentally prepared PCM-containing SBA-15 in the initial stages of the process.
The flexible operations of gas turbine combined cycle power plants, especially with reduction of start-up time, are important. In this paper, the modeless start-up method without determination of the start-up curves corresponding to the start-up modes (e.g., hot start, warm start, and cold start) were developed. This method generates the start-up curves in which the start-up time is minimized against the initial steam turbine metal temperature by optimizing the start-up parameters. Based on the candidates of these start-up parameter values obtained during the optimization process, the look-up tables corresponding to the initial metal temperature for the parameters are estimated. The start-up time of the start-up curves generated by referring to the look-up tables continuously vary against the initial metal temperature without exceeding the thermal stress limit of the steam turbine rotor. The results obtained by the developed method show that modeless start-up curves for gas turbine combined cycle power plants can be generated. In addition, by visualizing the relationship of the start-up time and the initial metal temperature, the start-up curves can be interactively selected to facilitate planning of the plant start-up schedules.
Magnesium hydroxide Sulfate hydrate (MHSH) whiskers are synthetic inorganic functional materials with certain aspect ratio. The formula is xMgSO4·yMg(OH)2·zH2O. In the NH4+–NH3 buffer system, MgSO4·5Mg(OH)2·3H2O with a length of 10–30 µm, a diameter of 0.05–0.3 µm and an aspect ratio of 30–150 are prepared by one step at atmospheric pressure for a short time. The products are characterized by XRD, SEM, TG, TEM, etc. The influence factors such as reaction concentration, reaction temperature, reaction time and aging time are studied by combining the characterization results. First-principles analysis of the growth mechanism of MHSH whiskers show that growth habits accord with the dislocation spiral growth mechanism. The buffer system stabilizes the acidity and basicity of the solution, reduces the non-ideality of the solution, and enables the crystals to grow directionally under non-forced conditions, which provides an important reference for further industrial application and low-energy consumption production of MHSH whiskers.
The pulp and paper industry employs processes that produce a large amount of wastewater, resulting in pollution of the environment. In the present study, deinking wastewater was treated using an integrated process of combined coagulation/flocculation, activated sludge process, and Fenton reaction system. The deinking wastewater produced from a large-scale papermaking company was treated. Results indicated that the sedimentation with coagulation and flocculation, used as a pretreatment process, was a preferred option for SS removal. The semi-extended aeration system for COD and BOD5 removal delivered excellent performance. The residual and barely biodegradable pollutants in the wastewater could be efficiently removed by Fenton reactions. The COD, BOD5, and SS total removal efficiencies achieved were 94%, 90%, and 99%, respectively. Measures for control proposed in the present study can efficiently resolve the problems encountered in the operation and can maintain a stable process. The integrated process combining coagulation/flocculation, activated sludge process, and the Fenton reaction system is a favorable option for the long-term operation of the treatment of deinking wastewater. Fenton reactions as a tertiary process applied in deinking wastewater treatment can remove efficiently recalcitrant pollutants and show reliable performance for effluent.
In this study, we compared the photodegradation behavior of pentachlorophenol (PCP) and 2,3,4,6-tetrachlorophenol (TeCP) sorbed on polyethylene (PE), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) to investigate the plastic effect. PE accelerated photodegradation of PCP and TeCP, and the photodegradation rate constants on the PE surface were approximately 1.50 times higher than that on a glass surface. In contrast, photodegradation of these organochlorine pollutants on PET was slower than on the glass surface. Furthermore, photodegradation of PCP on the PVC surface was suspended after approximately 60 min of ultraviolet irradiation. These results confirmed that plastics affected the photodegradation behavior of organochlorine pollutants. Lower chlorinated phenols were detected as degradation products, such as di-, tri- and tetra-chlorophenols, thereby confirming occurrence of dechlorination. Fourier transform infrared analysis showed that C=C bonds were produced on PE after UV irradiation, suggesting that PE might act as a hydrogen donor to accelerate photodegradation of PCP and TeCP. For PVC, an increase of the absorbance of the C–Cl bond after photodegradation indicated occurrence of chlorine migration, resulting in rechlorination of the intermediate chlorophenols. This study suggests that the characteristics of plastics should be considered for assessment of the fate of organic pollutants sorbed on plastics through phototransformation.
To utilize chicken manure as a source of phosphorus, we employed dissolution–precipitation treatment to recover phosphorus from the incineration ash of chicken manure (IACM), which was used as fuel to power a boiler. To recover useful phosphorus-containing solids from IACM, the ash was dissolved in aqueous solutions of either nitric acid, hydrochloric acid, or sulfuric acid to elute phosphorus together with various component elements, followed adding aqueous NH3 to yield a precipitate containing phosphorus. Using nitric acid and hydrochloric acid, calcium phosphate species such as calcium hydroxyapatite (Ca10(PO4)6(OH)2) and monetite (CaHPO4) were obtained following the precipitation treatment. By contrast, sulfuric acid resulted in the precipitation of magnesium ammonium phosphate (MAP) species, such as struvite (MgNH4PO4∙6H2O) and dittmarite (MgNH4PO4∙H2O). Both the calcium phosphate and MAP species could be used as a slow-acting fertilizer containing phosphorus, while the MAP species could be simultaneously used as a slow-acting fertilizer containing nitrogen. Notably, the calcium phosphate species obtained in the present study were equivalent to those found on a phosphate rock, which is widely used as a raw material in phosphorus-based industries, and the natural sources of this material could be depleted in the near future. Though IACM has not been used effectively thus far, it shows promise as viable alternative to the dwindling natural sources of phosphorus.