Simulation of ammonia removal from industrial wastewater streams by means of a hollow-fiber membrane contactor

The performance of a hollow-fiber membrane contactor in removing ammonia from aqueous solution was simulated. An unsteady state 2D mathematical model was developed to study the ammonia stripping in the hollow-fiber membrane contactor. Two sets of equations were considered for the membrane contactor and the feed tank. CFD technique was applied to solve the model equations in which concentration distribution was determined using continuity equation. Velocity field is also determined using Navier–Stokes equations for the contactor. The model was implemented in linked MATLAB–COMSOL Multiphysics. COMSOL software was applied to solve the model equations for the contactor while MATLAB software was employed to consider changes in the concentration of the feed tank. Predictions of the model were then validated against experimental data which were found to be in good agreement. The assumption of Knudsen diffusion for the transport of ammonia molecules through the membrane pores increased the accuracy of the model. The effect of different parameters including feed velocity, feed concentration and pH on the removal of ammonia was investigated. The results of simulation revealed that the developed model can be used to evaluate the effective parameters which involve in the ammonia removal by means of membrane contactors.     

Evaluation of recovery characteristic of acidic and alkaline solutions from NaNO3 using conventional electrodialysis and electrodialysis with bipolar membranes

We compared the electrodialysis performance for HNO₃ and NaOH recovery from NaNO₃ solution by conventional electrodialysis (ED) and electrodialysis with bipolar membranes (EDBM) at constant current and constant voltage. The individual resistances of the components of the electrodialysis systems were also evaluated. The electrodialysis extent for HNO₃ and NaOH recovery from NaNO₃ solution was almost proportional to the total amount of electricity supplied to the system, regardless of the operation mode and the electrodialysis systems. For the same volume of feed solution, the energy consumption and current efficiency differed depending on the operation mode and the electrodialysis system. In both the ED and EDBM systems, the conductivity of the feed solution strongly affected the overall cell resistance after approximately 50% of the ions in the feed solution had migrated.     

Response Surface Modelling and Optimization of Mercury Extraction through Emulsion Liquid Membrane

Mercury(II) is a very harmful metal, highly toxic, and carcinogenic in nature. Experiments were carried out using the emulsion liquid membrane (ELM) technique in order to evaluate the maximum extraction of mercury(II) from aqueous solutions of mercuric chloride using 3³ factorial design. The ELM consisted of di-2-ethylhexylphosphoric acid as a carrier, toluene as an organic solvent, span 80 as a surfactant, and sulphuric acid with thiourea solution as stripping phase. The three factors for the factorial design were mercury(II) concentration in the aqueous solution, that is, feed phase concentration, carrier concentration in the membrane phase, and sulphuric acid concentration in the stripping phase. The study has also highlighted the effects of various other parameters, such as pH of the feed phase and thiourea concentration on mercury(II) extraction. The optimization of the factors to obtain maximum extraction were carried out by incorporating main effect plots, interaction plots, analysis of variance (ANOVA), normal probability plots, residual plots, surface plots, and contour plots. A reduced model developed by regression analysis was suggested in which the experimental data were fitted very well. The results showed that it is possible to extract mercury(II) up to 98% from aqueous solutions at the optimum conditions.     

Swollen-Dry-Layer Model for the Pervaporation of Ethanol-Water Solution through Hydrophilic Membranes

Abstract

A swollen-dry-layer model is presented for the pervaporation of ethanol-water solution through hydrophilic polymer membranes: poly(vinyl alcohol) and carboxymethyl cellulose. Independent measurements were conducted of the sorption equilibrium, the hydraulic permeation rates through the swollen membranes, and the permeabilities of ethanol and water vapors. The hydraulic permeabilities were estimated from the mutual diffusion coefficients of solution in the swollen membrane. Sorption behavior and hydraulic permeabilities showed a dependence on feed concentration. Vapor permeabilities of water and ethanol through dry membranes differ by a factor of about 20. Comparisons between the experimental data from the pervaporation run and the results calculated from the model were made. The model offers a quantitative explanation for the dependency of selectivity and flux on feed concentration. The model explained that the flux dependency caused by a change in the swollen-dry-layer ratio, and that the selectivity is governed by vapor permeabilities through the dry layer.     

Treatment of sea water using electrodialysis: Current efficiency evaluation

In this paper, desalination of seawater using a laboratory scale electrodialysis (ED) cell was investigated. At steady state operation of ED, the outlet concentration of dilute stream was measured at different voltages (2−6 V), flow rates (0.1−5.0 mL/s) and feed concentrations (5000−30,000 ppm). The electrical resistance of sea water solution in the dilute compartment was initially calculated using basic electrochemistry rules and average concentration of feed and dilute streams. Then, current intensity in each run was evaluated using Ohm's law. Finally, current efficiency (CE) which is an important parameter in determining the optimum range of applicability of an ED cell was calculated. It was found out that, at flow rates larger than 1.5 mL/s, higher feed concentrations lead to larger values of CE. However, exactly opposite behavior was observed at lower flow rates. Increasing the feed flow rate increases CE to a maximum value then decreases it down to zero for all cell voltages and feed concentrations. In the case of higher feed concentrations, maximum values of CE are obtained at higher flow rates. As expected, in almost all experiments, CE increases by intensifying cell voltage. CE values of up to 48 indicate effective ion transfer across the ion exchange membranes in spite of low separation performance of the ED cell.     

Effect of Process Parameters on Separation Performance of Nitrate by Electrodialysis

Abstract

The electrodialytic separation of nitrate from water was investigated as a function of feed characteristics such as applied voltage, feed flow rate, and nitrate concentration in the solution. The separation performance was evaluated in terms of percent removal of nitrate, process time, and energy consumptions. TS‐1‐10 electrodialysis equipment (Tokuyama) was used in experimental studies. During the unsteady state run of the ED system, both inlet and outlet concentrations of nitrate and conductivities of streams were measured at certain time intervals until the current drops to 0.01 A. It was obtained that the percent removal of nitrate from the solution increased when the concentration of nitrate in the feed solution increased. The operation time became shorter when a high potential was applied.     

On the control of an unstable periodic state in the repeated fed‐batch operation of a biochemical system

In this paper we discuss the proportional feedback control of a repeated fed‐batch reactor around a desired but unstable periodic state. The flow rate in each cycle is assumed to be a constant. The unstable periodic state is determined using a shooting method technique and its stability is found using the Floquet theory. The control action is based on the performance, i.e., biomass concentration, at the end of the cycle. Two choices of the manipulated variable are investigated, i.e., the cycle time and the flow rate. The concentration of the substrate in the feed is assumed to be a constant.     

Extractive distillation: Advances in conceptual design,solvent selection,and separation strategies

Extractive distillation(ED) is one of the most promising approaches for the separation of the azeotropic or closeboiling mixtures in the chemical industry. The purpose of this paper is to provide a broad overview of the recent development of key aspects in the ED process involving conceptual design, solvent selection, and separation strategies. To obtain the minimum entrainer feed flow rate and reflux ratio for the ED process, the conceptual design of azeotropic mixture separation based on a topological analysis via thermodynamic feasibility insights involving residue curve maps, univolatility lines, and unidistribution curves is presented. The method is applicable to arbitrary multicomponent mixtures and allows direct screening of design alternatives. The determination of a suitable solvent is one of the key steps to ensure an effective and economical ED process. Candidate entrainers can be obtained from heuristics or literature studies while computer aided molecular design(CAMD) has superiority in efficiency and reliability. To achieve optimized extractive distillation systems, a brief review of evaluation method for both entrainer design and selection through CAMD is presented. Extractive distillation can be operated either in continuous extractive distillation(CED) or batch extractive distillation(BED), and both modes have been well-studied depending on the advantages in flexibility and low capital costs. To improve the energy efficiency, several configurations and technological alternatives can be used for both CED and BED depending on strategies and main azeotropic feeds. The challenge and chance of the further ED development involving screening the best potential solvents and exploring the energy-intensive separation strategies are discussed aiming at promoting the industrial application of this environmentally friendly separation technique.     

Photocatalytic decolorization of Basic Blue 41 using TiO2-Fe3O4-bentonite coating applied to ceramic in continuous system

Abstract

Photocatalytic degradation/decolorization of Basic Blue 41 dye assisted by UV radiation has been studied over TiO₂-Fe₃O₄ supported by bentonite. In this experiment, photocatalytic decolorization process was performed continuously; where dye feed solution was supplied to a coated-ceramic vessel. The influence of the initial concentration, pH, and flow rate of the dye feed solution on the degradation efficiency process was examined in this study. The results showed that the increase in the dye concentration and flow rate reduces decolorization efficiency. The highest decolorization efficiency was at pH of 5.5. The kinetic study of this photo-decolorization indicated that under the experimental condition, the photocatalytic kinetic process followed first-order kinetics on the basis of Langmuir–Hinshelwood heterogeneous reaction mechanism, where the reaction rate constant, namely k_r, is 0.7707 and the adsorption rate constant, namely K, is 0.01298.     

Chromate Removal from Water Using Surfactant-Enhanced Crossflow Filtration

Abstract

Removal of chromate from water was investigated using the surfactant enhanced crossflow filtration technique in which the cationic surfactant, cetyl trimethylammonium bromide (CTAB), was the carrier for the metal ions. The variation of chromate and surfactant rejections, and permeate flux with time were measured as a function of CTAB/chromate concentration ratio, while maintaining a constant transmembrane pressure drop, membrane pore size, and pH of the feed solution. The method was found to be effective in removing chromate from water. It was observed that the efficiency of chromate removal increased with increasing CTAB/ chromate ratio. It was also found that the chromate concentration had a significant effect on the CTAB concentration in the permeate and on the time taken to establish the secondary membrane which consists of a highly viscous surfactant phase in the hexagonal state in the absence of chromate. In the presence of chromate, permeate flux increased at the same CTAB concentration although the surfactant and chromate rejections decreased, indicating lowering of the secondary membrane resistance to permeate flow. These conclusions were confirmed by deadend filtration experiments which showed that the fouling index decreased by the addition of chromate while the opposite was valid when sodium chloride was present in the surfactant/water/electrolyte ternary system.     

Selective transport of cobalt (II) from ammoniacal solutions containing cobalt (II) and nickel (II) by emulsion liquid membranes using 8-hydroxyquinoline

The selective transport of cobalt (II) from ammoniacal solutions containing nickel (II) and cobalt (II) by emulsion liquid membranes (ELMs) using 8-hydroxyquinoline (8-HQ) as extractant has been presented. Membrane solution consists of a diluent (kerosene), a surfactant (ECA 4360J), and an extractant (8-HQ). Very dilute sulphuric solution buffered at pH 5.0 has been used as a stripping solution. The ammoniacal feed solution pH was adjusted to 9.0 with hydrochloric acid. The important variables governing the permeation of cobalt (II) have been studied. These variables are membrane composition, pH of the feed solution, cobalt (II) and nickel (II) concentrations of the feed solution, stirring speed, surfactant concentration, extractant concentration, complexing agent concentration and pH of the stripping solution, and phase ratio. After the optimum conditions had been determined, it was possible to selectively transport 95.0% of cobalt (II) from ammoniacal feed solution containing Co²⁺ and Ni²⁺ ions. The separation factors of cobalt (II) with respect to nickel (II), based on initial feed concentration, have experimentally found to be of as high as 31 for equimolar Co(II)–Ni(II) feed solution.     

Study of Phenol Removal from Aqueous Solutions by a Double Emulsion (W/O/W) System Stabilized with Polymer

Polybutadiene rubber was used for stabilization of the emulsion for removal of phenol from aqueous solution via emulsion liquid membrane technique. The results showed that the addition of the polymer increased the stability of the emulsion, considerably. The effect of various parameters such as polymer concentration, temperature, mixing intensity, internal phase concentration, phases ratio, and pH of feed phase was studied. It was found that by increasing the volume ratio of emulsion to feed, internal phase concentration, and decreasing pH, the extraction efficiency was increased. Under optimum conditions, an extraction efficiency of 92% was obtained within only 35 minutes.     

Economical treatment of reverse osmosis reject of textile industry effluent by electrodialysis–evaporation integrated process

Membrane separation methods such as electrodialysis (ED) can reduce the volume load on evaporators by facilitating further concentration of rejects from reverse osmosis (RO) plants. ED studies were carried out on a bench-scale system using five membrane cell pairs to obtain a textile effluent concentrate containing approximately 6 times the quantity of salts present in the RO reject. The limiting current densities were determined to be in the range 2.15–3.35 amp/m² for feed flow rates varying from 18 to 108 L/h. Apart from feed rate, the influence of volume of concentrate and current on membrane performance was evaluated to optimize current utilization. An estimation of energy requirement of an integrated process constituting ED and evaporation for concentration of inorganics present in textile effluent from 4.35% to 24% was made and found to be approximately one eighth of the operating cost incurred by evaporation alone. Detailed design of a commercial ED system revealed that a membrane area of 13.1 m² was required to treat a feed rate of 1500 L/h. The payback period to recover capital investment was found to be 110 days.     

Extraction of Hexavalent Chromium from Aqueous Stream by Emulsion Liquid Membrane (ELM)

Emulsion Liquid Membrane (ELM) separation technique is an effective procedure for the removal of Chromium (VI) ions from the wastewater stream. In the present study, the effect of changes of different parameters such as the pH of feed solution, the stirring speed, and the emulsification time, carrier concentration, surfactant concentration, the effect on the presence of other metal ions, are systematically investigated. The membrane phase consists of kerosene with hexane as diluant, Aliquat 336 as extractant, sorbitan mono-oleate (span 80) as surfactant. 1 (N) Sodium hydroxide is the stripping solution. Results show that by the ELM process, 90% Cr(VI) can remove successfully in optimum condition from feed.     

Enantiomeric Separation of Tryptophan by Ultrafiltration Using the BSA Solution System

Abstract

The optical resolution of racemic tryptophan was performed by ultrafiltration using the BSA solution system. The pH of the feed solution had a strong influence on the complexation constants between BSA and tryptophan, especially for L-tryptophan. The complexation constant for L-tryptophan reached a maximum value at pH 9 (K _L = 110,000), varying by 2 orders of magnitude in the range from pH 6 (K _L = 1000) to pH 11 (K _L = 21,000). Smaller variations of the complexation constant of D-tryptophan were observed. Based on these data, the recovery and the purity of the permeate were optimized by a proper control of the physicochemical parameters of the feed solution (essentially pH and initial concentrations). In one stage, 91% purity with a 89% recovery of D-tryptophan has been easily obtained with a high permeation rate (6.3 × 10^?4 mol·m^?2s^?1 at 1.5 bar).     

改性沸石除氟的动态实验研究

为将阴离子型改性沸石应用于实际,通过动态吸附实验,对用改性沸石除氟技术的可行性进行了研究。实验对影响除氟的pH、水力停留时间、溶液中可能共存的阴离子竞争影响、前水的氟浓度的几个主要的因素水平进行了实验分析。得出在原水pH为7.7、水力停留时间为80 min、氟离子浓度为5 mg/L时改性沸石除氟动态平衡吸附量最佳。溶液中的阴离子SO42-对除氟效果影响较大     

PTFE中空纤维膜萃取烟酸工艺研究

以氢氧化钠溶液为萃取剂,采用PTFE中空纤维膜萃取料液中的烟酸,考察了料液相烟酸的初始浓度、料液相初始pH值、料液相与萃取相流量比、萃取剂的初始浓度对烟酸萃取率(η)的影响。结果表明,随着料液初始浓度增大,η增大,当烟酸浓度0.9 g/L时,η减小,但膜通量基本不变,即存在一个最大膜通量,此时烟酸浓度变化对传质无影响;烟酸料液存在一个最佳pH值为4~5;萃取相氢氧化钠浓度增大,η增大;存在一个最佳相流量比(Q料/Q萃)为2.1;温度升高有利于膜萃取。     

Boron removal from seawater using high rejection SWRO membranes — impact of pH, feed concentration, pressure, and cross-flow velocity

The main objective of this work was to investigate boron removal from seawater using two commercial high rejection SWRO membranes. The impact of solution pH, feed concentration, pressure, and cross-flow velocity on boron rejection and permeate flux was determined. The membranes used were the Toray™ UTC-80-AB and Filmtec™ SW30HR. A lab-scale cross-flow flat-sheet configuration test unit was used for all RO experiments. Seawater sample was collected from the Mediterranean Sea, Alanya-Kızılot shores, south Turkey. For all experiments, mass balances were between 91% and 107%, suggesting relatively low loss of boron on membrane surfaces during 14 h of operation. Operation modes did not have any impact on boron rejection, indicating that boron rejection were independent of feedwater boron concentrations up to 6.6 mg/L. For both membranes, much higher boron rejection were obtained at pH of 10.5 (>98%) than those at original seawater pH of 8.2 (about 85–90%). Permeate boron concentrations less than 0.1 mg/L were easily achieved at pH 10.5 by both membranes. The dissociated boron species are dominant at this pH, thus both electrostatic repulsion and size exclusion mechanisms are responsible for the higher boron rejection. The rejection of salts in seawater did not correlate with boron rejection at constant conditions. For each membrane type, permeate fluxes at constant pressure were generally lower at pH of 10.5, which may be partially explained by membrane fouling and enhanced scale formation by Mg and Ca compounds from concentration polarization effect at higher pH values. While somewhat higher boron rejection was found for one membrane type as the pressure was increased from 600 to 800 psi, increasing pressure did not affect boron rejection for the other membrane. Feed flowrate thus the cross-flow velocity (0.5–1.0 m/s) did not exert any significant impact on boron rejection at constant conditions.     

Investigation of combined fouling behavior in nano-filtration process under various feed conditions

Despite the great advance in nano-filtration (NF) process development in various applications, its performance in water treatment is still impeded by the undesired fouling phenomenon, which is not yet fully understood nowadays. In this study, a comprehensive investigation on the fouling behavior, more specifically the combined fouling behavior with the presence of more than one type of foulant was carried out under various solution chemistries and feed hydraulic pressures. The interaction between the model organic foulant (alginate) and inorganic foulant (silica colloid) was systematically studied with nano-filtration membranes, with a more severe fouling observed in the combined fouling than individual foulants. However, the results also revealed that the commonly observed synergistic effect of combined fouling in the forward osmosis process was not present in the nano-filtration process. In addition, the solution chemistries (pH and calcium ions) and feed hydraulic pressure were also found to have certain influence on the combined fouling, especially the feed hydraulic pressure which exhibited a more pronounced impact on the flux decline than the other factors, thus in turn, affecting more on the reversibility of the membrane fouling.     

Mixing and Crystallization Kinetics in Gas‐liquid Reactive Crystallization

A study of gas‐liquid reactive crystallization for CO₂‐BaCl₂‐H₂O system was performed in a continuous flow crystallizer. The influences of mixing on the crystallization kinetics of barium carbonate crystals were investigated. The mixing parameters are stirrer speed, feed concentration, gas‐flow rate, pH of solution, addition rate of NaOH solution, and mean residence time. Under pH‐stat operation, the crystallization mechanism can be assessed by the addition rate of NaOH solution, which acts as an indicator for the absorption rate of carbon dioxide. Assuming a size‐independent agglomeration mechanism, the nucleation rate, growth rate and agglomeration kernel can be obtained, simultaneously, at steady state, by the method of moments. Evidence shows that feed concentration, feed rate, gas‐flow rate, and stirrer speed have a significant influence on the nucleation rates and mean particle sizes. This shows the effect of micromixing. The crystallization mechanism tends to be reaction limited when the feed concentration of barium chloride solution is higher than 5 mM, while at lower stirrer speeds and feed concentrations, the mechanism tends to be both mixing and reaction controlled. The growth rate depends on the mean supersaturation value and the pH of the solution and the mass‐transfer resistance cannot be completely eliminated in this work. For a monodispersal collision model, in the viscous sub‐range of turbulence, the agglomeration kernel can be expressed as β ∝ d^{3 –1/4}, showing a low efficiency of collision. The result is also demonstrated by the agglomeration kernel expression. Comparison with a liquid‐liquid‐mixing reactive crystallization system is also discussed.