查看更多>>摘要：Leakage currents existing in a bipolar membrane electrodialysis (EDBM) stack caused loss of coulombic efficiency, ranged from approximately 0.9% to 12%, and created undesirable heat that impaired its operation. A mathematical model for electrical analog of a cell pair, predicting leakage currents and Joule heating effect of the external circuits in a EDBM stack was developed by considering the electrochemical process as an electrical analog circuit. Current and potential balance equations was used to define the equivalent network, and differential calculus was applied to solve these equations. Leakage current model was validated with experimental and simulated results. On this basis, leakage currents and Joule heating effect in a pilot-scale EDBM stack were analyzed. The results revealed that leakage currents in external circuits were distributed symmetrically around the membrane stack and were significantly affected by the number of cell pairs, current density, and element resistivity. Moreover, Joule heating effect in the external circuit in the stack was quantitatively analyzed and the temperature effect was dominated by the slot closed to the electrode cell in the acid compartment. This was most pronounced (raised by 12.18 °C in 0.3 s) during the termination stage. Using these findings, EDBM stacks can be improved and the optimal spacers and a more reasonable process can be designed, which could boost the development of EDBMs.
查看更多>>摘要：A dynamic pore network modelling (DPNM) framework is used to evaluate pressure drop and residual saturation in oleo-phobic nonwoven media in mist filters. The advanced fully-resolved VOF simulations along with μ-CT measurements are also carried out to substantiate the validity of the DPNM simulations. The results of the study show that PNM could be a beneficial and reliable tool for predicting oil saturation and pressure drop during early-stage design of oleo-phobic filters with nonwoven media. Given the considerably higher efficiency of PNM models compared to CFD-based techniques, some parametric studies were also conducted. Our findings suggest that, for a given set of operating conditions, efficiency/performance can be improved by appropriate choice of filters with optimized properties (fibre diameter, packing density, contact angle, etc.) for which the overall oil saturation and pressure drop in the filter attain minimum, may offer a self-cleaning mist filter. Finally, a correlation was developed for evaluating the performance of oleo-phobic media using the filter specifications and the data of steady state saturation and pressure drop found in open literature. The obtained correlation shows a good conformity with the experimental measurements with an average of 12.1% error for about 93% of data out of 68 data sets collected with a correlation coefficient of (R~2) of 0.934.
查看更多>>摘要：Pre-coagulation is an excellent method for alleviating membrane fouling in aerobic granular sludge (AGS) membrane systems (AGSMSs) for wastewater reuse. However, little attention has been paid to modified microbial flocculants (MMFs) for membrane fouling mitigation. Herein, an MMF was prepared, and the effect of its dosage (5-30 mg/L) on membrane fouling mitigation was investigated. MMF pre-coagulation could effectively alleviate membrane fouling by utilizing electrical neutralization and adsorption bridging. When the MMF dosage was 10 mg/L, the membrane flux was increased by 79.4% and the total fouling resistance was reduced by 90.3%. The MMF dosage of 10 mg/L greatly inhibited the adhesion and accumulation of foulants, thereby forming a loose and porous cake layer on the membrane surface. Moreover, the extended Derjaguin-Landau-Verwey-Overbeek theory further clarified that the greatest energy barriers existed throughout the filtration process with an MMF dosage of 10 mg/L. Correlation analysis showed that the occurrence of membrane fouling was mainly related to total phosphorus, chemical oxygen demand, and polysaccharides in the raw wastewater. This study reveals the effects of different MMF dosages on membrane fouling and provides a novel approach for MMF pre-coagulation to mitigate membrane fouling.
查看更多>>摘要：In this work, pervaporation (PV) was employed to desalinate seawater reverse osmosis (SWRO) brine. Synthetic brines were used to examine the influence of operating conditions (e.g., feed salt content, temperature, permeate pressure and feed pH) on the PV performance. A flux of 6.6 kg/(m~2 h) with a salt rejection of 99.9% was achieved for a feed salt content of 50 g/L at a temperature of 50 °C and permeate pressure of 0.5 kPa. Water flux was increased with an increase in temperature and/or a decrease in permeate pressure, whereas the feed pH had little impact. The fouling behavior of the PV membrane was examined using a real SWRO brine at different volume concentration factors (VCFs). When the VCF increased from 1.0 to 3.0, the corresponding TDS in the feed solution increased from 55 to 165 g/L, and the water flux decreased from 6.2 to 3.0 kg/(m~2 h). The PV and membrane distillation (MD) processes were compared under the same operating conditions. After 110 h, the water fluxes of the PV and MD membranes were reduced by 21.8% and 52.1%, respectively. The MD membrane suffered more severe fouling than the PV membrane, and the fouled PV membrane could be cleaned more easily with a simple water rinse. These results demonstrated that PV is advantageous over MD in terms of fouling resistance, membrane cleaning and flux recovery.
Danilo Alexander Figueroa ParedesRamiro Julian SanchezMicaela Magarino
13页
查看更多>>摘要：The study carried out in the present work focused on the conceptual design of the aroma recovery stage of from a lager beer by pervaporation with a PDMS membrane taking into account the condensation step. First, using laboratory-scale experiments, the performance of the Pervatech PDMS membrane was measured in terms of aroma recovery, ratio of higher alcohols to esters (A/E ratio), ethanol flux and overall flux for different operating conditions. In addition, model was obtained that adequately characterized the fluxes through the membrane as a function of temperature and permeate pressure. This model allowed estimating the membrane area requirements for different operating conditions. Secondly, the possibility of using two partial condensers in the condensation stage to approximate the A/E ratio of a lager beer was explored through simulations. Influence of operating conditions and presence of CO2 and air on values for the A/E ratio, the overall fractional recovery of aroma compounds and the economics of the process were modeled. Both the case of mixing condensates obtained from the two condensers and that of an optimal combination of condensates were taken into account in order to approximate the A/E ratio of the lager beer. The best alternative for this variant was the one corresponding to the operating conditions of 30 °C temperature and a pressure of 2.13 kPa for the pervaporation stage, with two partial condensers in series operating at -5 °C and -46 °C, respectively. In this way, two condensates would be obtained which, when combined in a 0.43/1 ratio for subsequent reincorporation into the dealcoholized beer, would result in a product maintaining the (A/E) ratio of the original beer. Under these conditions, a recovery of 14.1% of aromas would be achieved with a total cost of 0.1070 USD/L. Finally, the state-of-the-art alternative consisting of two total condensers condensers in parallel working out of phase was also considered. Results indicate that, if properly designed, the A/E ratio obtained at lab scale level would coincide with that achieved after total condensation and thus, the adjustability of the ratio of higher alcohols to esters would decrease with respect to that achieved when partial condensers are used. Although the use of a total condenser results in more expensive designs, this alternative is very advantageous in terms of overall aroma recovery and process feasibility. From the results obtained, the importance of developing conceptual models that make use of both experimental runs of the aroma recovery process at laboratory scale and simulations of the condensation process from parameters corresponding to the vapour-liquid equilibrium of the multi-component system can be deduced.
查看更多>>摘要：Carbon nanospheres are attractive materials with great potentials in many applications. Herein, we presented the synthesis and CO2 capture of N-doped monodisperse carbon nanospheres with high surface area. Spherical 3-aminophenol-formaldehyde resin with uniform size and shape was used as the precursor, which was then converted into carbon nanospheres through KHCO3 activation. KHCO3 activation was the key to the synthesis of carbon spheres, because it led to the formation of highly porous structure with surface area up to 3096 m~2/g, and perfectly preserved the spherical shape at the same time. In contrast, the spherical structure was completely destroyed during KOH activation. The carbon nanospheres also showed high nitrogen content of 2.54-8.54 wt%. CO2 adsorption performances of the carbon nanospheres were studied with pressure up to 20 bar. The carbons showed impressively high uptakes of 31.42/21.55 mmol/g at 0/25 °C and 20 bar, which outperformed many reported results under the same conditions. The correlation between CO2 adsorption performances and physicochemical properties at different pressures were studied and revealed.
查看更多>>摘要：Under the great challenge brought by global warming, nuclear power gains sustained attention as an important low-carbon base load power source. Removal of trace amounts of strontium ion (~(90)Sr~(2+)) from highly Na~+-rich liquid wastes generated from the process of nuclear fuel cycle can make nuclear power more economical and environmentally-friendly. The efficient and low-cost method is urgent but still absent. In this study, sodium manganese silicate (SMSO) is prepared via one-pot hydrothermal method. The as-prepared material with high specific surface area (～559.86 m~2 g~(-1)) shows high adsorption of 249.0 mg g~(-1) for Sr~(2+) ions. The removal rate of Sr~(2+) by material always keeps a high adsorption capacity (above 98%) in the wide pH range of 3-12. Besides, the removal effect can maintain at a high level in the presence of a variety of competitive ions. Owing the combination of the high performance and low cost, the title SMSO becomes a promising Sr~(2+) adsorbent for the nuclear wastewater treatment.
查看更多>>摘要：The development of environmentally friendly and highly efficient adsorbent materials is an important issue under study all the time all over the world. Herein, a robust 3D scaffold of sodium alginate/graphene oxide/nanocrystalline cellulose (SA/GO/NC) was fabricated for the potential adsorption of methylene blue (MB) dye. First, NC was extracted from palm sheath fibers and graphene oxide was synthesized from graphite. Then the scaffold was fabricated from a lyophilized SA/GO/NC bio-nanocomposite via cross-linking treatment. The impact of NC content (10,15, and 20%) on the chemical, physical, thermal, and mechanical properties of fabricated scaffolds was studied too. The physical properties, chemical structure, and surface morphology of SA/GO/NCs scaffolds were investigated by Brunauer-Emmett-Teller (BET), Attenuated total reflection infrared spectroscopy (ATR-FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA) instruments. The effect of pH, adsorbent dose, contact time, pseudo-first-order models, pseudo-second-order models, and thermodynamics on MB uptake was also studied. The obtained thermodynamic values (△H°, △S°, and △G°) indicate that the process is exothermic and spontaneous with physisorption mechanism directly dependent on the amount of NC used.
查看更多>>摘要：Herein, chloramphenicol (CAP) antibiotic was degraded by water falling film dielectric barrier discharge (WFFDBD) and FeO catalyst. The treatment performance and catalytic mechanisms were studied by experiments and density functional theory (DFT) simulations. The results show that 69.5% of CAP was degraded by WFFDBD at 8 min, and the degradation efficiency increased to 97.7% by WFFDBD/FeO at the same treatment time. The formation of "OH caused by the catalytic reactions was mainly responsible for the catalytic effect. The electron transfer from FeO to the antibonding orbits of O3, H2O2 and dissolved oxygen was the key for the catalytic reactions, which promoted their decomposition and transformation. Dissolved oxygen was converted to O2~(·-) that adsorbed on FeO by the electron transfer, which played an important role for the catalytic process. Oxygen vacancies raised the charge density of Fe and accelerated the electron transfer. Fe near the oxygen vacancies achieved the dissociated adsorption of H2O2 and O3, and transformed dissolved oxygen to O2 due to the enhancement of the electron transfer.
查看更多>>摘要：The radioactive pollution caused by uranium-containing effluents brings serious detriments to environmental safety and human health. Herein the chitosan/graphene oxide (CS/GO) electrodes were nano-fabricated for the effective electro sorption of U(VI) from aqueous solution. The cyclic voltammetry measurements were conducted to determine the specific capacitance of the CS/GO materials. The U(VI) electrosorption was performed on capacitive deionization (CDI) system. The results showed that CS/GO-4 presented best electrosorption performance for U(VI) among various CS/GO materials, which is associated with a well-balanced meso-/micro- porous structure for promoting ion transfer and superior conductivity for ion trapping through electrical double-layer (EDL) interaction. The isotherms could be described by Langmuir model, whereas the kinetics could be fitted by Langmuir model. The maximum removal capacity for U(VI) electrosorption by CS/GO-4 reached 271.2 mg/g at 0.9 V, which was almost double that achieved at 0.0 V. The electrosorption mechanism may involve in the formation of electrical double-layer (EDL) and the coordination of U(VI) by the amine and carboxyl groups of CS/GO materials. The electrosorption-desorption cycles further demonstrated that the potential application of CS/GO electrode materials for the electrosorptive removal of U(VI) from radioactive wastewater.
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