High Feed Concentration Research Articles

Potential of Nanofiltration Membrane in Groundwater Treatment for Drinking Water Resources

Groundwater in Malaysia has become an alternative water resouces for daily needs. However, the presence of iron and manganese has been the major problem that caused the water unsuitable for drinking due to reddish colour and bad taste. Therefore, groundwater should be well treated from any hazardous metal before consumption. A dead-end stirred cell was used to investigate the ability of commercial NF membrane in removal of Fe to acceptable level for drinking water. Removal up to 99% for 10 mg/L iron solution at pH9.4 with low pressure of 2 bar was achieved. Further investigation for higher feed concentration is suggested in order to achieve permeate concentration below than 0.3 mg Fe/L. All findings indicated that nanofiltration is a promising technology for groundwater treatment.

Energy consumption analysis of a supercritical water oxidation pilot plant with a transpiring wall reactor based on energy recovery

Supercritical water oxidation (SCWO) is a new and promising technology for treating organic waste and recovering energy. High energy consumption is a major problem preventing its commercial application. Energy recovery is the most effective method for reducing energy consumption of an SCWO system. To maximize the energy recovery of the SCWO pilot plant with a transpiring wall reactor, the reactor effluent is used to preheat both feed and transpiring water and produce hot water. An experimental study was conducted to investigate the influence of the operating parameters on energy consumption per unit total organic carbon (TOC) removal (ECPT) for saving the energy of the system. Results show that the effect of feed concentration on ECPT is the most significant and that of high feed concentrations, result in lower ECPT. Lower ECPT is also present at high feed flow rates, but at the expense of the decrease of TOC removal efficiency when the feed flow rate exceeds 14 kg/h.

Draw solute recovery by metathesis precipitation in forward osmosis desalination

ABSTRACT Forward osmosis (FO) is a natural osmosis process that is under investigation as a potential means of desalination, wastewater treatment, and energy production. This article presents forward osmosis desalination study on a commercial cellulose acetate membrane. The membrane was tested for high feed concentrations ranging from typical brackish water concentration to seawater concentration. For energy-efficient recovery of product water, a 240,000 ppm of MgSO4 draw solution was used. The membrane achieved an average water flux of 4.06 and 0.60 L/m2 h in case of brackish and seawater, respectively. Pure product water with a salt content of 350 ppm was recovered from the diluted MgSO4 draw solution by reaction with stoichiometric amount of barium hydroxide to remove the soluble draw solute as magnesium hydroxide and barium sulfate precipitates.

Development of immobilized cellulase through functionalized gold nano-particles for glucose production by continuous hydrolysis of waste bamboo chopsticks

Cellulase immobilized on silica through the assistance of l-cysteine functionalized gold nano-particle was applied for the continuous hydrolysis of waste bamboo chopsticks powder to produce glucose. The optimal conditions for the continuous hydrolysis were pH 8.0, 50°C. A 4-day reaction with an initial 0.3gL−1 waste bamboo chopsticks powder, a feed containing 0.2gL−1 waste bamboo chopsticks powder at a continuous feed and draw rate of 0.5mLmin−1, and an enzyme loading of 40mgcellulase(gsilica)−1, has 72.0–76.6% conversion rates of repeated hydrolyses that correspond to a total production of 630.5–671.2mg glucose and are much better than batch hydrolyses. At higher enzyme loading (117mgcellulase(gsilica)−1), higher initial concentration (0.5gL−1), and higher feed concentration (0.42gL−1) the conversion rate increases to 82.9% and a total amount of 1418mgglucose. The immobilized cellulase can be recovered easily by filtration and used repeatedly at least 6 times over a period more than 90 days with a recovered activity approximately the same as or better than previous reactions. Thus the process is promising for scaling up.

Optimization of operating conditions for a continuous membrane distillation crystallization process with zero salty water discharge

The concentrated salt solution from reverse osmosis (RO) or other desalination plants is a critical environmental problem that can impact water quality and thereby have economic and social consequences. An integration of a membrane distillation (MD) with a crystallization unit could serve as a potential way to mitigate this problem by having an almost complete water recovery and eliminating the secondary disposal problem. Hence, the continuous membrane distillation crystallization (CMDC) process was studied for a high concentration (close to saturation) feed solution. In addition, the operating conditions were optimized using an orthogonal fractional factorial (OFF) experiment design in order to realize a near zero discharge by varying the flow rates and operating temperatures on both the feed and permeate sides.The results from an L9(34) OFF experiment design indicated that the flow rates on the feed and permeate sides are the principal factors controlling CMDC performance, whereas the temperatures either on the feed or permeate sides are not main factors. The optimal operating parameter values based on four factors and three levels are a flow rate and temperature on the feed side of 0.64Lmin−1 and 338K, respectively, and on the permeate side of 0.35Lmin−1 and 303K, respectively. These operating conditions not only affect the pure water and NaCl solid production, but also the quality of the crystals obtained from the crystallizer.Factors affecting the crystal size distribution were investigated and indicated that the sodium chloride crystals had a narrow size distribution. The feed flow rate and inlet temperature had more influence on the mean crystal size and crystal size distribution, whereas the permeate flow rate and inlet temperature had relatively less effect. Therefore, CMDC operation was found not only to produce a high quality water product but also sodium chloride crystals with a relatively narrow size distribution. These results are beneficial to a better understanding of the CMDC process and improving its performance to realize zero salty water discharge to the environment.

Processing of glycerol under sub and supercritical water conditions

Converting glycerol, a by-product from biodiesel production into useful products and energy could contribute to a positive life cycle for the biodiesel process. One kg of glycerol is produced for every 10 kg of biodiesel and has the potential to be used as a source of H2, syngas or CH4 by an appropriate conversion process. Catalytic Supercritical Water Gasification (CSCWG) processing of crude glycerol solutions is one such viable option. Above its critical point [>221 barg, >374 °C], the properties of water, such as the low relative permittivity and high ionic product make it capable of dissolving non-polar organic compounds, allowing for high reactivity, and the ability to act as an acid/base catalyst. In this work, the degradation of glycerol by CSCWG at temperatures [400–550 °C] and pressures [170–270 barg] was investigated using a packed bed reactor (PBR) containing a Fe2O3 + Cr2O3 catalyst. Glycerol feed concentrations were between 2 and 30 wt% at flow rates from [10–65 ml/min], which gave weight hourly space velocities (WHSV) of [38–125 h−1]. The results indicated that high temperature and low feed concentration tended to increase the gas yield and selectivity toward H2 production with some char (<2.7 wt%). Syngas of up to 64 mole% was obtained with minimum 4:1 mole ratio of H2:CO. High yields of volatile hydrocarbons were also obtained: 14 and 69 mole % for methane and ethylene, respectively, which could be used for energy generation in SOFCs or turbines, reformed to syngas or converted to chemicals by an appropriate route. Pressure had little effect on the gas yields in the subcritical water region, but had a positive effect on H2 and CO2 in the supercritical region where char formation also was increased resulting in loss of catalyst activity. Complete conversion of glycerol was achieved at high temperature (550 °C). A maximum of 11 wt% liquid products were obtained at 400 °C (mainly allyl alcohol, methanol and formaldehyde). Catalyst stability was also evaluated, which was found to reach relative stability in the supercritical water environment for up to 9 h of operation.

Comparison of nonhomogeneous and homogeneous mass transfer in reverse osmosis membrane processes

Reverse osmosis (RO) membranes are pressure driven, diffusion controlled processes. Current diffusion controlled solute mass transfer models assume a homogeneous membrane surface. This study evaluated mass transfer processes assuming mass transport is not a homogeneous process, which is dependent on the thickness variation of the membrane’s active layer. Three-dimensional ridge and valley active layer morphologies were created numerically using Gaussian random vectors. A nonhomogeneous solution diffusion model (NHDM) was then developed to account for surface variation through the active layer. NHDM was further modified by incorporating concentration polarization (CP) effects. A comparison of the NHDM and the NHDMCP with the commonly accepted homogeneous solution diffusion model (HSDM) using pilot-scale brackish water RO operating data indicated that the NHDM is more accurate, when the solute concentration in the feed stream is low, while NHDMCP appears to predict better with a high solute feed concentration.

Comparison of activity behaviors of particle based and monolithic immobilized enzyme reactors operated in semi-micro-liquid chromatography system

The activity behaviors of particle based and monolithic immobilized enzyme reactors (IMERs) developed for proteomics applications in semi-micro-liquid chromatography were comparatively investigated. For monolithic IMER, the plain monolith was synthesized by in situ thermal copolymerization of glycidyl methacrylate (GMA) and ethylene dimethacrylate (EDM) in fused silica capillary. For particle based IMER, monodisperse-porous poly(GMA-co-EDM) beads 6.8μm in size were synthesized by staged-shape template polymerization and used as support in a stainless steel microbore column. α-Chymotrypsin (CT) was covalently attached onto the particle based and monolithic supports via amination and glutaraldehyde coupling stages. In the case of monolithic IMER, higher final substrate conversions were achieved particularly with high substrate feed rates with respect to particle based IMER probably due to the convective diffusion in the macropores of continuous monolithic block. The final substrate conversion increased with increasing substrate feed concentration for monolithic IMER while a decrease was observed for particle based IMER. Hence monolithic IMER was superior when high substrate feed concentration was used with sufficiently high substrate feed flow rates.

Experimental study of the supercritical water reforming of glycerol without the addition of a catalyst

Hydrogen production from the supercritical water reforming of glycerol was studied in a tubular reactor without adding a catalyst. Experiments were carried out at a pressure of 240bar, temperatures of 750–850°C, and glycerol feed concentrations of 5–30wt.%. Likewise, the residence time was changed from 12 to 160s, by handling the feed flow-rate. The dry gas is mainly consisted of H2, CO2, CO, CH4. In addition, small concentrations of glycerol were measured in the liquid phase analysis, but barely traces of others like glycolaldehyde, glyceraldehyde, dihydroxyacetone and lactic acid were detected. Thus, two probable reaction pathways are discussed, which makes it possible to explain the experimental results by using a method applicable to other similar processes. The results showed that the glycerol conversion was almost complete, except at the highest glycerol feed concentration, in which the conversion was of 88%. Hydrogen yields from 2 to 4molH2/molglycerol were obtained at high and low glycerol feed concentrations, respectively, when operating at high temperature and residence time. Besides, it was verified the catalytic effect of the reactor material (Inconel 625) from the trend of the gas product yields with time and the structured carbon nanotubes encountered. The catalytic activity of the reactor material was decreasing to reach a steady state after a few tens of operating hours. This study illustrates that the reforming of glycerol using supercritical water without added catalyst is feasible to achieve a high-yield hydrogen production, and it encourages to continue the research line, to obtain a process economically interesting.

Effect of variation of hydrophobicity of anode diffusion media along the through-plane direction in direct methanol fuel cells

Reducing methanol crossover from the anode to cathode in direct methanol fuel cells (DMFCs) is critical for attaining high cell performance and fuel utilization, particularly when highly concentrated methanol fuel is fed into DMFCs. In this study, we present a novel design of anode diffusion media (DM) wherein spatial variation of hydrophobicity along the through-plane direction is realized by special polytetrafluoroethylene (PTFE) coating procedure. According to the capillary transport theory for porous media, the anode DM design can significantly affect both methanol and water transport processes in DMFCs. To examine its influence, three different membrane-electrode assemblies are fabricated and tested for various methanol feed concentrations. Polarization curves show that cell performance at high methanol feed concentration conditions is greatly improved with the anode DM design with increasing hydrophobicity toward the anode catalyst layer. In addition, we investigate the influence of the wettability of the anode microporous layer (MPL) on cell performance and show that for DMFC operation at high methanol feed concentration, the hydrophilic anode MPL fabricated with an ionomer binder is more beneficial than conventional hydrophobic MPLs fabricated with PTFE. This paper highlights that controlling wetting characteristics of the anode DM and MPL is of paramount importance for mitigating methanol crossover in DMFCs.

Ultrafiltration of humic acid and surface water with tubular ceramic membrane

In recent years, the ceramic membrane filtration has become increasingly attractive for drinking water production. The flux evolution and retention performance of a tubular ceramic membrane with nominal pore size of 0.01μm was systematically investigated. Filtration experiments were carried out on a pilot-scale crossflow unit using humic acid (HA) solution and surface water as feed by varying transmembrane pressure (TMP). Measurements such as total organic carbon (TOC), ultraviolet absorbance at 254nm (UV254), fluorescence excitation emission matrices (EEMs), pH, and conductivity were made on both raw water and the permeate. During filtration, flux declined drastically in the beginning stage due to fouling and proceeded to a pseudostable flux. In the low HA concentration, the flux decreased in the first 30 min for about 36, 48, 50 and 51% with the TMP of 0.5, 0.8, 1.0, and 1.2 bar, respectively, while it came to 47, 52, 57, and 65%, respectively for relatively high concentrations; the steady flux increased with increasing TMP from 0.5 to 1.2 bar at the specific concentration of feed water studied. Finally, the effectiveness of the membrane treatment was determined by evaluating the removal efficiency of TOC, UV254, and EEM. The rejection efficiency decreased with increasing TMP in low organic concentration of feed water, while increased in relatively high feed concentration. In addition, filtration in HA and surface water showed a different retention performance, rejection efficiency for HA (>50%) was higher than that for surface water (<20%), which may have a relevance to nature organic matter molecular weight distribution.

Kinetic and equilibrium modeling for adsorption of textile dyes in aqueous solutions by carboxymethyl cellulose/poly(acrylamide‐co‐hydroxyethyl methacrylate) semi‐interpenetrating network hydrogel

Semi‐interpenetrating network (IPN) hydrogels were synthesized by free radical copolymerization of acrylamide (AM) and hydroxyethyl methacrylate (HEMA) in aqueous solution of sodium carboxy methyl cellulose (CMC). The hydrogels were crosslinked with N,N′‐methylene bisacrylamide (NMBA). Hydrogel was also synthesized from copolymerisation of AM and HEMA. This was designated as PAMHEMA. All of these hydrogels were characterized by Fourier transforms infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), X‐ray diffraction (XRD), mechanical properties, and equilibrium swelling in deionized water. These hydrogels were used for adsorption of two important textile dyes, i.e., basic fuchsin and methyl violet from water at different experimental conditions. These hydrogels were found to show high removal% and adsorption of these two dyes from water for both low and high feed concentration range. Experimental dye adsorption data were fitted to five kinetic and seven adsorption model equations with non‐linear fittings. The experimental data were observed to fit well to most of these model equations because of non‐linear fitting. POLYM. ENG. SCI., 53:2439–2453, 2013. ©2013 Society of Plastics Engineers

Potential of nanofiltration and low pressure reverse osmosis in the removal of phosphorus for aquaculture

Aquaculture activities in developing countries have raised deep concern about nutrient pollution, especially excess phosphorus in wastewater, which leads to eutrophication. NF, NF90, NF450 and XLE membranes were studied to forecast the potential of nanofiltration and low pressure reverse osmosis in the removal of phosphorus from aquaculture wastewater. Cross-sectional morphology, water contact angle, water permeability and zeta potential of these membranes were first examined. Membrane with higher porosity and greater hydrophilicity showed better permeability. Membrane samples also commonly exhibited high zeta potential value in the polyphosphate-rich solution. All the selected membranes removed more than 90% of polyphosphate from the concentrated feed (75 mg/L) at 12 bar. The separation performance of XLE membrane was well maintained at 94.6% even at low pressure. At low feed concentration, more than 70.0% of phosphorus rejection was achieved using XLE membrane. The formation of intermolecular bonds between polyphosphate and the acquired membranes probably had improved the removal of polyphosphate at high feed concentration. XLE membrane was further tested and its rejection of polyphosphate reduced with the decline of pH and the addition of ammonium nitrate.

Extraction Behavior of Fission Products with Tri-n-butyl Phosphate by Countercurrent Multistage Extraction in a Uranium, Plutonium, and Neptunium Co-recovery System

In an attempt to develop a simplified solvent extraction process for U, Pu, and Np co-recovery, three countercurrent experiments were carried out to evaluate the effect of the scrubbing solution on the decontamination of fission products (FPs) using a dissolver solution derived from the irradiated core fuel of fast reactor “JOYO”. In all the runs, Np was co-extracted with U and Pu using tri-n-butyl phosphate (TBP) at the extraction section by using high HNO3 concentration feed solution. Of all the FPs, the decontamination behavior of Zr and Tc varied with the HNO3 concentration of the scrubbing solutions. Zirconium and Tc were not decontaminated with a single scrub flow sheet, which caused the accumulation of Zr at the co-decontamination section. The decontamination factors (DFs) of Zr and Tc were 2.62 × 101 and 1.07 × 100 with flow sheet using 9 and 1 mol/dm3 HNO3 scrubbing solutions, respectively. On the other hand, their DFs increased to >7.68 × 101 and >7.52 × 100 with 2 and 10 mol/dm3 HNO3 scrubbing solutions, respectively. The experimental results indicate that it is necessary to first remove Zr from the loaded solvent with a low HNO3 concentration scrubbing solution and then decontaminate Tc using a high HNO3 concentration solution. Other FPs, such as Cs, were effectively decontaminated with DFs in the range of 105.

Experimental and CFD Studies on the Performance of Microfiltration Enhanced by a Turbulence Promoter

This paper reports experimental and computational fluid dynamics (CFD) studies on the performance of microfiltration enhanced by a helical screw insert. The experimental results show that the use of turbulence promoter can improve the permeate flux of membrane in the crossflow microfiltration of calcium carbonate suspension, and flux improvement efficiency is strongly influenced by operation conditions. The energy consumption analysis indicates that the enhanced membrane system is more energy saving at higher feed concentrations. To explore the intrinsic mechanism of flux enhancement by a helical screw insert, three-dimensional CFD simulation of fluid flow was implemented. It reveals that hydrodynamic characteristics of fluid flow inside the channel are entirely changed by the turbulence promoter. The rotational flow pattern increases the scouring effect on the tube wall, reducing the particle deposition on the membrane surface. The absence of stagnant regions and high wall shear stress are responsible for the enhanced filtration performance. No secondary flow is generated in the channel, owing to the streamline shape of helical screw insert, so that the enhanced performance is achieved at relatively low energy consumption.

Separation of CO2 from the CO2/N2 mixed gas through ionic liquid membranes at the high feed concentration

Separation of CO2 from the CO2/N2 mixtures through ionic liquid membrane was carried out in this study. The CO2 volume fractions (XCO2) at feed side were 0.3–0.5. The microporous polyvinylidine fluoride (PVDF) membrane and two species of ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]), were used as the material for supported membrane and room temperature ionic liquids, respectively. The PVDF membranes were impregnated with the ionic liquids. The total pressures at the feed side were varied from 1.05 to 1.21atm. The experiment was performed under constant temperature at 40°C. The gas flow rates of CO2/N2 mixed gas at feed side were varied in range of 100–300mlmin−1. The effects of total pressure difference, the total flow rate at the feed side and the CO2 concentration were investigated. It was found that the higher permeability of CO2 was obtained from the lower total pressure differential conditions. The feed flow rates do not have the significant effect on permeability of N2. The [bmim][PF6] and [bmim][Tf2N] liquid membrane are given the equivalent CO2/N2 selectivity for XCO2=0.5 even though the feed gas flow rate was adjusted. The carrier saturation inside the ionic liquid membrane at high CO2 concentration and high pressure difference constrain the permeation of CO2. The highest selectivity was obtained in the case of XCO2=0.3 at constant total pressure difference and feed gas flow rate.

Investigation of Pd membrane reactors for one-step hydroxylation of benzene to phenol

Pd membrane reactor for one-step hydroxylation of benzene to phenol was investigated in an effort to reconcile the contradicting reports in the literature. A systematic study of the membrane, reactor and feed mode was conducted. Reactions carried out on Pd-TS-1 and Pd capillary membranes support Niwa's postulate of in situ hydrogen peroxide formation, but at the same time indicate that reactive species generated by reactions between permeated hydride ions and activated oxygen also participate in the reaction. The former reaction is important at low benzene feed concentrations and for reactors with small membrane area-to-reactor volume ratios. TS-1 catalyst in Pd-TS-1 membrane can significantly improve the yield and selectivity to phenol. High benzene feed concentrations and faster mass transfer gives the reactive species greater opportunity to react directly with benzene resulting in high benzene conversion but poor selectivity.

Multiple Feeding Strategy for Phase Transformation of GMP in Continuous Couette–Taylor Crystallizer

A continuous Couette–Taylor (CT) crystallizer with a multiple feed mode was developed to promote the phase transformation of guanosine 5-monophosphate (GMP). In drowning-out crystallization, amorphous GMP is initially precipitated and then transformed into hydrate GMP crystals via the spontaneous nucleation of hydrate crystals and consecutive dissolution of the amorphous GMP and growth of hydrate GMP crystals. Importantly, the multiple feeding strategy had a significant accelerating effect on the phase transformation process, resulting in the complete conversion of the amorphous GMP into hydrate crystals within an overall mean residence time of 2.5 min, even with a high GMP feed concentration of 152.8 g/L and low rotation speed of 300 rpm. Thus, the phase transformation in the continuous CT crystallizer with the multiple feed mode (feeding mode IV) was at least 2 times faster than the phase transformation with the conventional feeding mode (feeding mode I), and 10 times faster when compared to the phase t...

Experimental study on the effects of operating parameters on the performance of a transpiring-wall supercritical water oxidation reactor

An experimental study on the effect of process parameters on the performance of a transpiring wall reactor was conducted in a supercritical water oxidation pilot plant. The optimized process parameters were obtained based on temperature profiles and gas–liquid products. Higher feed concentrations are favorable for feed degradation because of the higher reaction temperatures. The useful residence time (URT) declines from 17.2s to 10.0s when the feed flow increases from 8kg/h to 17kg/h. Thus, higher feed flows result in incomplete feed degradation because of shorter URT. The appropriate feed flow for the pilot reactor is lower than 14kg/h. A total organic carbon (TOC) removal above 99% is achieved even at a feed temperature of 369°C. The transpiration intensity (0.04 to 0.08) has minor effect on the temperature profiles and feed degradation, showing that the mixing and cooling effect of transpiring water can be offset within the transpiration intensity range of 0.04 to 0.08. Increasing of the inlet temperature of the upper branch of transpiring water improves TOC removal. In addition, TOC removal exceeds 99% when the temperature of the middle branch of transpiring water is above 285°C.

Two-Stage VPSA Process for CO2 Capture from Flue Gas Using Activated Carbon Beads

Carbon dioxide removal from flue gas with a two-stage vacuum pressure swing adsorption (VPSA) process, which uses activated carbon (AC) beads as the adsorbent, was investigated both theoretically and experimentally. First, single-column VPSA experiments were studied for CO2/N2 separation with high CO2 feed concentration. Then, a two-stage VPSA process composed two columns for each stage was designed, and the effects of different parameters were investigated. The first-stage VPSA unit operates with a four-step Skarstrom cycle, which includes feed pressurization, adsorption, blowdown, and counter-current purge with N2. For the second-stage VPSA process, a cycle with feed pressurization, adsorption, pressure equalization, blowdown and pressure equalization was employed. With the proposed two-stage VPSA process, a CO2 purity of 95.3% was obtained with 74.4% recovery. The total specific power consumption of the two-stage VPSA process is 723.6 kJ/kg-CO2, while the unit productivity is 0.85 mol-CO2/kg·h.