Increasing Feed Concentration Research Articles

Coupling of photovoltaic thermal with hybrid forward osmosis-membrane distillation: Energy and water production dynamic analysis

This study proposes a novel solar photovoltaic thermal (PVT)-driven forward osmosis (FO) and membrane distillation (MD) system for desalinating brackish water, addressing water scarcity issues by combining the advantages of FO's low operating cost with MD's ability to treat hypersaline water. A physics-based dynamic model was developed for the system, and the model equations were discretized and solved using an open-source algebraic modeling language. Model validation involved verifying the consistency of outputs between successive unit operations and conducting sensitivity analysis by varying one operating condition at a time. The analysis considered varying weather conditions while maintaining constant operating conditions. Increasing the flow rate of brackish water (cooling fluid) from 19.79 to 59.38 kg/h improved thermal efficiency by 28.7 %; however, FO and MD water fluxes decreased by 1.12 LMH and 7.77 kg/m2/h, respectively. Peak thermal efficiency (81.2 %) was achieved at the highest flow rate. Incorporating heat transfer analysis into FO models goes beyond the common focus on mass transfer, allowing for a more comprehensive understanding of energy dynamics within the system. Both FO and MD water fluxes improved with irradiance and ambient temperature but decreased with cooling fluid flow rate and wind velocity. Increasing feed concentration to 10,000 mg/l reduced water flux by 0.66 LMH, and for each 0.5 M increase in draw solution concentration, FO water flux increased by >10 LMH. Compared to MD water flux, FO water flux is more sensitive to changes in concentration than to changes in weather conditions.

Development of temperature-controlled batch and 3-column counter-current protein A system for improved therapeutic purification

Maximizing product quality attributes by optimizing process parameters and performance attributes is a crucial aspect of bioprocess chromatography process design. Process parameters include but are not limited to bed height, eluate cut points, and elution pH. An under-characterized chromatography process parameter for protein A chromatography is process temperature. Here, we present a mechanistic understanding of the effects of temperature on the protein A purification of a monoclonal antibody (mAb) using a commercial chromatography resin for batch and continuous counter-current systems. A self-designed 3D-printed heating jacket controlled the 1 mL chromatography process temperature during the loading, wash, elution, and cleaning-in-place (CIP) steps. Batch loading experiments at 10, 20, and 30 °C demonstrated increased dynamic binding capacity (DBC) with temperature. The experimental data were fit to mechanistic and correlation-based models that predicted the optimal operating conditions over a range of temperatures. These model-based predictions optimized the development of a 3-column temperature-controlled periodic counter-current chromatography (TCPCC) and were validated experimentally. Operating a 3-column TCPCC at 30 °C led to a 47% increase in DBC relative to 20 °C batch chromatography. The DBC increase resulted in a two-fold increase in productivity relative to 20 °C batch. Increasing the number of columns to the TCPCC to optimize for increasing feed concentration resulted in further improvements to productivity. The feed-optimized TCPCC showed a respective two, three, and four-fold increase in productivity at feed concentrations of 1, 5, and 15 mg/mL mAb, respectively. The derived and experimentally validated temperature-dependent models offer a valuable tool for optimizing both batch and continuous chromatography systems under various operating conditions.

Numerical simulation and optimization of Pervaporation process based on Heat-Mass-Flow coupling

Pervaporation (PV) has the advantages of low energy consumption and high separation efficiency, but the trade-off effect between flux and separation factor restricts its large-scale application. Based on the conservation equations of mass, momentum and heat, a transient model of the whole PV process coupled with heat-mass-flow was established in this paper. The effects of feed temperature, feed concentration and feed flow rate on heat and mass transfer in PV process were analyzed. TEOS crosslinked PDMS/PTFE-PVDF membrane was prepared by scraping coating method. The reliability of the model was verified by taking n-butanol/water separation system as an example. The concentration polarization and temperature boundary layer under different operating conditions are discussed. The effect of operating conditions on the separation performance was evaluated by response surface method, and the optimal operating conditions are obtained. The results show that the concentration polarization of the membrane surface becomes more obvious with the increase of feed concentration. The temperature boundary layer decreases with the increase of feed flow rate. Surprisedly, there is a significant temperature gradient in the membrane, and the maximum temperature difference between the two sides of the membrane is as high as 1.02 K. Diffusion in the membrane is the rate controlling factor of PV process. The contribution of operating conditions to the separation performance is in the order of feed temperature > feed concentration > feed flow rate. The best operating conditions are: feed temperature 350.2 K, feed concentration 3.8 wt% n-butanol/water and feed flow rate 23.6 L/h. This work provides a theoretical basis for the design of PV membrane materials and the optimization of PV operating conditions.

Experimental investigation on the hybrid system of mechanical vapor recompression and hollow fiber vacuum membrane distillation applied for wastewater treatment

In order to achieve zero discharge and resource utilization of industrial high salt wastewater, a hybrid system of mechanical vapor recompression (MVR) and hollow fiber vacuum membrane distillation (HFVMD) was constructed, and several experiments of air tightness, single working condition and multiple working conditions were carried out with ammonium chloride solution as feed, then thermal economic performance were evaluated via a single factor analysis method. The obtained results showed that the system had excellent airtightness to ensure normal evaporation experiment, and high separation efficiency of 99.9% and lower evaporation energy consumption to achieve high efficient separation by combining the advantages of the hydrophobic membrane evaporation and latent heat recovery in view of MVR and HFVMD technologies. Furthermore, increasing feed temperature and feed flow rate increased evaporation rate and decreased evaporation energy consumption, while increasing feed concentration decreased evaporation rate and increased evaporation energy consumption. Finally, the single factor analysis indicated that total investment cost, annual operation cost and annual evaporation capacity were the main factors while environmental cost and equipment service life were the secondary factors which affected the specific evaporation cost. The above research provides theoretical and experimental bases for the development of the proposed system in the future.

Study on the Classification Performance of a Novel Wide-Neck Classifier.

A novelty-designed wide-neck classifier (WNC) was proposed to enhance the passing ability and classification efficiency of fine particles. Using computational fluid dynamics (CFD), we studied the flow field and velocity distribution in the newly designed WNC. The velocity of the fluid gradually decreased from the wall to the center and from the cylinder to the cone, which facilitates particle classification and thickening. The Reynolds number (Re) and turbulent intensity (I) inside the WNC were discussed. The turbulent intensity increased with increasing feed velocity and overflow outlet diameter and decreased with increasing feed concentration and spigot diameter. The classification of coal slurry was performed to analyze the performance of WNC. The classification efficiency increased with increasing feed velocity but decreased as the feed concentration, spigot diameter, and overflow outlet diameter increased. The predictive models for classification efficiency influenced by the operational and structural parameters were constructed at high correlation coefficients, and the average error of these models was analyzed at 0.28%. Our results can provide valuable insights into the development of mineral classification.

Research of phosphate removal from water on reverse osmotic filters

Eutrophication of natural water bodies caused by an excess of biogenic substances is one of the global environmental problems of modern times. Usually, phosphorus is a limiting biogenic element, the concentration of which determines the intensity of eutrophication processes in water bodies. Therefore, it is important to develop methods aimed at preventing excessive amounts of phosphates from entering the environment. To remove phosphates from water, typically used biological degradation technologies, which usually proceed very slowly and depend on the conditions under which the process takes place. Also, Biogenic elements can be removed by using ion exchange, reverse osmosis, and chemical methods. However, the disposal of concentrated solutions becomes an issue with these methods. Baromembrane purification methods, particularly reverse osmosis, are becoming increasingly important in the field of water treatment and purification and are essential in creating efficient and low-waste complex technologies for water purification from biogenic compounds. The study investigated the processes of removing orthophosphates from distilled and artesian water using a low-pressure reverse osmosis membrane Filmtec TW30-1812-50. The dependence of membrane productivity and selectivity on the concentration of phosphates and the degree of permeate rejection was determined. Was found that residual concentrations of phosphates in the permeate increase with the increase in the degree of permeate rejection. The lowest residual concentrations of phosphates were observed at the initial concentration of up to 10 mg/dm3. The highest residual phosphate concentrations were observed at initial concentrations above 900 mg/dm3. At the same time, the membrane productivity constantly decreased with increasing feed concentration and degree of permeate recovery due to the increased osmotic pressure on the membrane. The selectivity of the membrane was highest at an initial concentration of up to 10 mg/dm3 and slightly decreased at a rejection rate of 20-50% for initial phosphate concentrations of 100-900 mg/dm3. At the maximum degree of permeate rejection (90%), the selectivity of the membrane reached 97-99 % and decreased with an increase in phosphate concentrations, which is due to a change in the pH of the medium, hydrolysis of phosphates, hydration of ions, and concentration polarization. The membrane selectivity for phosphates in solutions in artesian water was slightly lower (95-99 %), which was due to the competing influence of chlorides, sulfates, and bicarbonates, as well as a decrease in the pH of the solution to 7.52-7.67, which promotes the hydrolysis of o-phosphates.

Prediction of sulfuric acid solution in the vacuum membrane distillation process using Artificial Neural Network

This paper presented an effective approach utilizing Artificial Neural Network (ANN) to predict the vacuum membrane distillation (VMD) process of sulfuric acid solution. Firstly, mathematical models have been developed and the influence mechanisms of critical parameters on the transfer resistance in the VMD process were explored via a simulation process. Furthermore, an ANN model from the experimental data under actual working conditions, was developed and applied to simulate the effects of critical parameters on the VMD process performance including membrane flux and gained output ratio (GOR). The simulation results revealed that decreasing feed concentration or vacuum side pressure and increasing feed temperature or feed velocity would contribute to the reduction of total transfer resistance. Then, the operation data at multiple working conditions using actual sulfuric acid solution was divided into three sets (training, validation and test) to develop the ANN model. The trained ANN model was subsequently observed to have good agreement between the predicted and experimental data. From the subsequent simulations with various variable controls, increasing feed concentration or vacuum side pressure led to the declines of membrane flux and GOR, while increasing feed temperature or feed flow rate were helpful to improve membrane flux and GOR. Obviously, the developed ANN model performed well to predict the VMD process performance with minimum error, which could be effectively utilized to predict and optimize the VMD system for industrial wastewater treatment without performing a complicated, expensive and dangerous experimental test.

Study on the separation mechanism of coal and gangue particles during coal slime classification in a hydrocyclone

The precise classification of coal slime containing lots of ultrafine particles provides appropriate size range of feed for subsequent sorting. In this study, experiments are performed to investigate the classification performance of coal slime. Both high-density gangue and low-density coal are considered in simulating the multi-component system of coal slime. The misplacement of fine particles in the underflow is mainly caused by −0.045 mm fine gangue component. The enrichment ratio of −0.045 mm gangue is much larger than that of −0.045 mm coal in the underflow due to its higher density. The adverse effect of particle density on classification can be reduced by increasing feed concentration appropriately. Multiphase flow pattern, theoretical force analysis, and particle trajectory are applied to reveal the migration mechanism of the coal and gangue components. This work will give insights into the migration mechanism of multi-component particles during the classification of coal slime.

Energy and exergy assessments of supercritical water oxidation of wet organic wastes under hydrothermal flames with a Y-shape reactor for power generation

A novel Y-shape reactor combined the concepts of transpiring wall reactor (TWR) and hydrothermal flame was proposed for supercritical water oxidation (SCWO) of wet organic wastes. Hydrothermal flames can enhance feed degradation, and the Y-shaped structure enables the efficient gas–solid separation and allows extracting a part of uncooled supercritical fluids for power generation. The proposed reactor and corresponding system were simulated using Aspen Plus 8.2, and simulation results agree well with experimental flame temperatures and reaction products. Exergy analysis results indicate the reactor, heat exchanger 7, heat exchanger 1, and turbine contribute to the main destruction of the system, with exergy distribution coefficients of 18.65%, 17.75%, 11.95%, and 7.64%, respectively. The exergy destruction coefficient for the reactor has been greatly reduced compared with previous TWR-SCWO systems, indicating great improvement in exergy efficiency with the Y-shape reactor. The exergy efficiency can be increased from 24.83% to 40.50% when hot water output is replaced with steam production because of the great reduction in exergy destruction. Lower ratios of fuel flow to feed flow contribute to higher exergy efficiencies on the premise of the safety and economy of the system. The increases of separation efficiency and split coefficient are helpful for increasing system efficiency for more supercritical fluids can be converted into high-grade energy. The increase of feed concentration is beneficial for the increase of system economy even though at a relative low exergy efficiency.

Dietary uptake of geosmin in rainbow trout (Oncorhynchus mykiss)

Geosmin is a primary source of muddy/earthy ‘off-flavors’ in farmed fish, which may render their organoleptic quality unacceptable to consumers. Model systems of geosmin uptake typically comprise exposure to waterborne geosmin that is absorbed via the gills. The present research demonstrates dietary exposure as an alternative route of geosmin uptake in Rainbow Trout (Oncorhynchus mykiss) fillets. Trout (average initial weight of 355 g) were stocked in quadruplicate compartmentalized raceways (N = 4 compartments per treatment, n = 50 fish per compartment) supplied with first-use, flow-through water (4.5 complete turnovers per hour). Fish were fed diets containing 0 (control dose), 0.005 (low dose), 0.05 (medium dose), or 0.5 (high dose) mg geosmin/kg feed at 1% body weight/day for four weeks. Fillets (12 fillets/diet/week plus 12 pre-trial fillet samples) and weekly feed and water samples were analyzed via GC–MS to determine geosmin concentrations. Feeding behavior was documented daily according to a four-point scale. ANOVA with post-hoc Tukey tests and polynomial contrast, regression, correlation, and chi-squared statistical analyses were applied to data (α = 0.05 significance level). Palatability of feed did not hinder consumption of the geosmin-spiked feeds: although fish responded positively to all feeds, the most aggressive feeding behavior was observed among those fed medium and high dose feed. Geosmin was effectively imparted into fillets after one week, and no significant temporal effect was found after four weeks. Mean geosmin concentrations significantly increased in fillets from low (mean of 26 ng/kg geosmin) to medium (202 ng/kg) to high (441 ng/kg) dose feed groups during the trial. Polynomial contrasts and regression modeling validated this significant positive effect of dose on geosmin uptake, with an estimated 166 ng/kg rise in fillet-geosmin for every log10 increase in feed concentration. Waterborne geosmin levels immediately post-feeding were conditionally independent of concentrations in feed and fillets, therefore dietary uptake was affirmed as the predominant mechanism of absorption in the present experimental system. Based on these findings, geosmin-spiked feeds may be used to induce predictable, repeatable levels of this off-flavor compound in fillets and serve as a model system for further investigation of sensory quality and off-flavor mitigation strategies for farm-raised fish.

Separation of TiO2 particles from suspension using indigenous low-cost ceramic microfiltration membrane

The increased use of TiO2 nanoparticles in manufacturing and commercial products has led to environmental contamination and health issues. This study aimed to apply tubular ceramic membrane fabricated using low-cost clays (kaolin, quartz) along with hydroxypropyl methylcellulose binder for the separation of TiO2 nanoparticles from water. The prepared tubular ceramic membrane exhibited excellent water permeability (1.4945 × 10−7 m3/m2s kPa) with an average pore size of 0.178 μm and porosity of 40 %. Cross flow microfiltration experiments using TiO2 nanoparticles suspension were performed by varying the applied pressure (138–414 kPa), cross flow velocity (2.41 × 10−3 - 5.63 × 10−3 m/s), pH (4–11) and feed concentration (0.05–1 wt%). The permeate flux increased linearly with an increase in the pressure as well as cross flow velocity with a maximum permeate flux of 4.24 × 10−5 m3/m2s at 414 kPa, whereas a reduction in permeate flux was observed with increasing feed concentration of TiO2. The membrane displayed 100 % separation efficiency at all the investigated pressures. Furthermore, the membrane fouling mechanism during the microfiltration process was analyzed using resistance-in-series model. Results demonstrated that filtration resistance (Rf) and total resistance (Rt) decreased with increasing cross flow velocity from 2.41 × 10−3 m/s to 5.63 × 10−3 m/s, whereas filtration resistance remained constant at high pressures. The estimated membrane cost is 253 USD/m2 based on raw materials, energy consumption, manpower and equipment cost. These promising results elucidated the suitability of tubular ceramic membrane towards the removal of TiO2 from wastewater.

Tailor‐made iron‐organic molecular cage embedded polydimethylsiloxane membranes via emulsion casting technique for efficient VOCs removal

AbstractUrgent needs for the removal of volatile organic compounds (VOCs) from gas streams has stimulated a vigorous research for high‐performance separation membranes. Herein, porous iron‐organic molecular cage (Fe‐cage) embedded polydimethylsiloxane (PDMS) mixed miatrix membranes (MMMs) were fabricated through emulsion casting method for efficient VOCs removal. The membrane separation performance was systematically investigated by separating VOC/N2 gas mixtures under various operating conditions (e.g., feed concentration, operating temperature) using n‐hexane, n‐heptane, and cyclohexane as model organic vapors. It was found that the resultant membranes demonstrated homogeneous Fe‐cage dispersion and intimate interfacial adhesion. With the increase of the Fe‐cage loading, the MMMs demonstrated obviously improved permselectivity for the separation of n‐hexane/N2 and n‐heptane/N2. The MMM containing 4 wt% Fe‐cage showed a n‐heptane permeability of 1657 × 10−8 mol μm m−2 s−1 Pa−1 and a n‐heptane/N2 selectivity of 145 at 25°C when the feed concentration is 4.3 mol%. These values were 231% and 158% of those for the pristine PDMS membrane, respectively. Furthermore, the VOC permeability and VOC/N2 selectivity of the membranes increased with decreasing operating temperature or increasing feed concentration. Because of its excellent mixed‐gas VOC/N2 permselectivity, the Fe‐cage embedded PDMS membrane could find use in petrochemical applications such as gasoline vapor recovery.

Transmission of sodium chloride in PDMS membrane during Pervaporation based on polymer relaxation

Polydimethylsiloxane (PDMS) composite membrane is used for treating pharmaceutical wastewater containing NaCl and solvent. In this study, the influence of feed concentrations of NaCl and isobutanol, process temperature and membrane microstructures on salt rejection are evaluated. Microstructures of PDMS membrane before and after separation are characterized by nuclear magnetic resonance (NMR), energy dispersive X-ray spectroscopy (EDS), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Positron annihilation life-time spectroscopy (PALS). The PV results show that NaCl will not spontaneously enter PDMS membrane without isobutanol. However, while NaCl feed concentration is 13 wt%, salt rejection of PDMS membrane drops from 100% to 99.09% with increasing feed concentration of isobutanol (up to 7 wt%). On the contrary, a higher temperature increases salt rejection of PDMS membrane and NaCl permeation through PDMS membrane is not through a vapor permeate process. Due to the relaxation of PDMS polymer chain, when PDMS cross-linking ratio is 0.1, the salt rejection increases from 99.87% to 100% with its thickness increasing from 10 μm to 17.5 μm. While the cross-linking ratio rises to 0.2, the salt rejection is 100% with the PDMS layer thickness of 10 μm. The relationship between relaxation of polymer chains and transport of NaCl in PDMS membrane is an excellent guidance and will be beneficial for the treatment of saline organic wastewater.

Enriching volatile aromatic compounds of lavender hydrolats by PDMS/ceramic composite membranes

Lavender hydrolats are of low value due to its low aromatic compound concentration. This work applied polydimethylsiloxane (PDMS) /ceramic composite membranes to enrich volatile aromatic compounds (linalool, terpinen-4-ol, α-terpineol, and camphor) of lavender hydrolats for improving antioxygenic property. The effect of operating conditions on the enrichment was systematically studied. The results showed that the fluxes of the four aromatic compounds increased with the increase of feed concentration in the binary simulation system. The enrichment factor of camphor increased more significantly than other components with the increase of flow velocity and the total flux was basically unchanged in pervaporation. The flux of lavender hydrolats was 254.84 g·m-2·h-1, the enrichment factors of linalool, terpinen-4-ol, α-terpineol, and camphor were found to be 5.64, 4.56, 2.59 and 15.31 at 40 °C, respectively. The free radical scavenging rate of enriched lavender hydrolats was significantly improved. This work provides a basis for the recovery of aromatic compounds from lavender hydrates by using PDMS/ceramic composite membranes.

Crystallization Process as a Final Part of Zero Liquid Discharge System for Treatment of East Baghdad Oilfield Produced Water

This study investigated the application of the crystallization process for oilfield produced water from the East Baghdad oilfield affiliated to the Midland Oil Company (Iraq). Zero liquid discharge system (ZLD) consists of several parts such as oil skimming, coagulation/flocculation, forward osmosis, and crystallization, the crystallization process is a final part of a zero liquid discharge system. The laboratory-scale simple evaporation system was used to evaluate the performance of the crystallization process. In this work, sodium chloride solution and East Baghdad oilfield produced water were used as a feed solution with a concentration of 177 and 220 g/l. The impact of temperature (70, 80, and 90 °C), mixing speed (300, 400, and 500 rpm), feed concentration (177 and 220 g/l), and time (0.5-9.5 h) on the crystallization performance for oilfield produced water treatment were investigated on evaporation rate and recovery. The recovery increased with increasing temperature and mixing speed while decreasing with an increase in feed concentration. Pure water and salts were recovered from the concentrated produced water, the recovery of pure water at 80 °C, 400 rpm, and 220 g/l feed concentration was 82.22 and 81.35% after 5.5 h for NaCl solution (i.e., simulated oilfield produced water) and oilfield produced water, respectively.

Hydrophobic silica sand ceramic hollow fiber membrane for desalination via direct contact membrane distillation

A porous hollow fibre ceramic membrane derived from a low-cost natural material (silica sand) and fabricated by combine phase inversion and sintering technique followed by fluoroalkylsilane (FAS17) grafting to improve its hydrophobicity is reported in this study. Prior to the subjection of the silica sand ceramic hollow fibre membrane (SSCHFM) to a desalination performance test via direct contact membrane distillation (DCMD), characterization studies were performed on the SSCHFM before and after grafting using different characterization techniques, such as scanning electron microscopy (SEM), atomic force microscopy (AFM), 3-points bending, water liquid entry pressure (LEPw), and water contact angle measurement. Mercury porosimetry analysis (MIP) was also used to determine the pore size distribution and porosity of the SSCHFM. The grafting process caused an increasing of the contact angle from 0° to 142.5° ± 2.0, and LEPw value of (2.6 ± 0.4 bar) was achieved. AFM images showed an increment in the surface roughness of the grafted SSCHFM from 0.305 µm to 0.375 μm, with a slight decrease in the average pore size and porosity from 0.17 µm and 17% to 0.12 µm and 14.7% respectively. After the grafting process, the performance of the membrane in DCMD was evaluated on a salt solution for 32 h at different NaCl concentrations (8,16, 24, 32 and 40) g/L, feed flow rates and feed temperatures. The results showed a decrease in the permeate flux at increasing feed concentration, but the reverse was at higher feed flow rates and feed temperatures. The surface-modified membrane recorded a water flux value of 35 kg/m2.h and 100% salt rejection. The results indicate that the hydrophobic hollow fibre ceramic membranes derived from silica sand have significant potential to be developed for membrane distillation application in water purification and reclamation.

Concentrating Fish Farm Effluent for its Nutrient Recovery via Nanofiltration

Excessive nutrients in aquaculture effluent have become an alarming environmental issue. However, current treatment methods for recovering nutrients are ineffective since the effluent contains trace amounts of nutrients. Pressure-driven nanofiltration (NF) is a potential solution to the problem of low concentration gradient. In this work, NF was applied to concentrate and recover the nutrients (ammonium (NH4+), phosphate, (PO43-), and nitrate ions (NO3-)) from the synthetic and real fish farm effluents. The experiments were first carried out to study the effect of membrane type, feed concentrations, and operating pressures on membrane performance. It is found that NF 90 membrane was able to retain more nutrient ions but compromise with a lower flux compared to NF 270. This study also revealed that an increase in feed concentration enhanced the concentrating ability for both PO43- and NO3- ions but reduced the concentrating factor of NH4+ ions. Moreover, both NF flux and concentrating factor increased with pressure. NF on actual fish farm effluents were investigated under optimal conditions (NF 90, 5 bar). Surprisingly, prefiltered effluent was found to have lower flux than raw effluent due to the presence of denser cake layer. NF could concentrate more nutrients from prefiltered fish farm effluent with concentrating factor up to 6.17 for PO43- ions and 1.55 for NH4+ions, claiming that NF was a promising approach for concentrating nutrients. These nutrients concentrate has an opportunity to be reapplied as fertilizer as a part of sustainable resource management.

Assessment of Graphical Methods for Determination of the Limiting Current Density in Complex Electrodialysis-Feed Solutions.

Electrodialysis (ED) is a promising technology suitable for nutrient recovery from a wide variety of liquid waste streams. For optimal operating conditions, the limiting current density (LCD) has to be determined separately for each treated feed and ED equipment. LCD is most frequently assessed in the NaCl solutions. In this paper, five graphical methods available in literature were reviewed for LCD determination in a series of five feed solutions with different levels of complexity in ion and matrix composition. Wastewater from microbial fermentation was included among the feed solutions, containing charged and uncharged particles. The experiments, running in the batch ED with an online conductivity, temperature, and pH monitoring, were conducted to obtain data for the comparison of various LCD determination methods. The results revealed complements and divergences between the applied LCD methods with increasing feed concentrations and composition complexity. The Cowan and Brown method had the most consistent results for all of the feed solutions. Online conductivity monitoring was linearly correlated with the decreasing ion concentration in the feed solution and corresponding LCD. Therefore, the results obtained in this study can be applied as a base for the automatized dynamic control of the operating current density–voltage in the batch ED. Conductivity alone should not be used for the ED control since LCD depends on the ion exchange membranes, feed flow, temperature and concentration, ionic species, their concentration ratios, and uncharged particles of the feed solution.

Optimization of methionine in inhalable High-dose Spray-dried amorphous composite particles using response surface Method, infrared and low frequency Raman spectroscopy

The influence of amino acids, other than leucine, in improving aerosolization of inhalable powders has not been widely explored. This detailed study focused on the use of methionine, another promising endogenous amino acid, in high dose spray-dried co-amorphous powders by investigating the influence of methionine proportion (0 – 20% w/w), and feed concentration (0.2 – 0.8% w/v) on aerosolization of kanamycin, a model drug, using a design of experiment approach. Low frequency Raman spectroscopy was used to assess the stability of the powders stored at 25 °C/53% relative humidity over 28 days. An increase in concentration of methionine was associated with an increase in fine particle fraction (FPF), with the highest FPF of 84% being achieved at 20% w/w and 0.2% w/v feed concentration. With an increase in feed concentration, both yield and particle size increased for all formulations; the FPF did not change except for kanamycin only formulation in which it decreased. During storage at high humidity, similar aerosolization stabilities were offered by different proportions of methionine although methionine crystallized out in all formulations. Furthermore, the crystallization was accompanied by surface enrichment of methionine on the particles. This study suggests that there is a direct relationship between methionine content and aerosolization for kanamycin-methionine amorphous matrices but feed concentration has little effect. In addition, methionine proportion has no effect on physical stability of such matrices at high humidity.

Effective fluoride removal from brackish groundwaters by flow-electrode capacitive deionization (FCDI) under a continuous-flow mode

Herein, we demonstrated the suitability and effectiveness of utilizing flow-electrode capacitive deionization (FCDI) for treatment of fluoride-contaminated brackish groundwater. By comparing operational modes of short-circuited closed-cycle (SCC), isolated closed-cycle (ICC) and single cycle (SC), it was found that SCC mode was the most advantageous. In SCC configuration, the effects of different parameters on the removal of F− and Cl− were investigated including current density, hydraulic residence time (HRT), activated carbon (AC) loading and feed concentration of coexisting NaCl. Results indicated that the steady-state effluent Cl− concentration dropped with elevated applied current, and the decreasing rate got faster with the increase of HRT or AC loading. However, for the steady-state effluent F− concentration, it dropped to a value under a small applied current and maintained stable in spite of the increase in applied current, and both HRT and AC loading had insignificant effects on the steady-state effluent F− concentration. F− was preferentially removed from the treated water compared with Cl−, and a higher ion selectivity could be obtained at lower applied current and smaller HRT with the trade-off being that operation under these circumstances would generate outlet water with little change in conductivity compared to the influent. The removal efficiencies of F− and Cl− both decreased with increasing feed concentration of coexisting NaCl. This study should be of value in establishing FCDI as a viable technology for treatment of fluoride-contaminated brackish groundwater.