Removal of Ni(II) ions from wastewater by micellar enhanced ultrafiltration using mixed surfactants

Ni(II) ions were removed from aqueous waste using micellar enhanced ultrafiltration (MEUF) with a mixture of surfactants. The surfactant mixture was the nonionic surfactant Tween 80 (TW80) mixed with the anionic surfactant sodium dodecyl sulfate (SDS) in different molar ratios ranging from 0.1–1.5. The operational variables of the MEUF process such as pH, applied pressure, surfactant to metal ion ratio and nonionic to ionic surfactant molar ratio (α) were evaluated. Rejection of Ni and TW80 was 99% and 98% respectively whereas that for SDS was 65%. The flux and all resistances (fouling resistance, resistance due to concentration polarization) were measured and calculated for entire range of α respectively. A calculated flux was found to be declined with time, which was mainly attributed to concentration polarization rather than resistance from membrane fouling.     

利用低浓度表面活性剂胶团强化超滤处理含锌废水

利用低浓度的阴离子表面活性剂十二烷基硫酸钠（SDS）,对含Zn^2＋废水进行了胶团强化超滤（MEUF）研究．结果表明：进料液的静置时间为3h时,Zn^2＋在SDS胶团上的吸附达到平衡状态。当Zn^2＋的浓度一定时,由于发生在膜表面的浓差极化现象的影响,在进料液中投加浓度低于1倍临界胶束浓度（CMC）的SDS,不但在很大程度上降低了SDS的用量,而且亦可获得较高的Zn^2＋截留率和渗透通量,Zn^2＋的截留率主要受膜表面SDS浓度的影响。随着进料液中SDS浓度的升高,渗透通量逐渐降低,而渗透液中SDS的浓度随之不断增大,但无论进料液中SDS浓度有多大,渗透液中SDS的浓度都不会高于1倍CMC（2．25g／L）,所以渗透液中的SDS的损失相对较小。Zn^2＋截留率随进料液中Zn^2＋浓度逐步增大而逐渐减小,基于低浓度表面活性剂的胶团强化超滤技术适宜处理低浓度含Zn^2＋废水．     

Membrane fouling and chemical cleaning in water recycling applications

Fouling and subsequent chemical cleaning are two important issues for sustainable operation of nanofiltration (NF) membranes in water treatment and reuse applications. Fouling strongly depends on the feed water quality, especially the nature of the foulants and ionic composition of the feed water. Consequently, appropriate selection of the chemical cleaning solutions can be seen as a critical factor for effective fouling control. In this study, membrane fouling and chemical cleaning under condition typical to that in water recycling applications were investigated. Fouling conditions were achieved over approximately 18 h with foulant cocktails containing five model foulants namely humic acids, bovine serum albumin, sodium alginate, and two silica colloids in a background electrolyte solution. These model foulants were selected to represent four distinctive modes of fouling: humic acid, protein, polysaccharide, and colloidal fouling. Three chemical cleaning solutions (alkaline solution at pH 11, sodium dodecyl sulphate (SDS), and a combination of both) were evaluated for permeate flux recovery efficiency. The results indicated that with the same mass of foulant, organic fouling was considerably more severe as compared to colloidal fouling. While organic fouling caused a considerable increase in the membrane surface hydrophobicity as indicated by contact angle measurement, hydrophobicity of silica colloidal fouled membrane remained almost the same. Furthermore, a mechanistic correlation amongst cleaning efficiency, characteristics of the model foulants, and the cleaning reagents could be established. Chemical cleaning of all organically fouled membranes by a 10 mM SDS solution particularly at pH 11 resulted in good flux recovery. However, notable flux decline after SDS cleaning of organically fouled membranes was observed indicating that SDS was effective at breaking the organic foulant—Ca²⁺ complex but was not able to effectively dissolve and completely remove these organic foulants. Although a lower permeate flux recovery was obtained with a caustic solution (pH 11) in the absence of SDS, the permeate flux after cleaning was stable. In contrast, the chemical cleaning solutions used in this study showed low effectiveness against colloidal fouling. It is also interesting to note that membrane fouling and chemical cleaning could permanently alter the hydrophobicity of the membrane surface.     

Chromate removal from wastewater using micellar enhanced crossflow filtration: Effect of transmembrane pressure and crossflow velocity

Removal of chromate from wastewater was investigated using Micellar Enhanced Crossflow Microfiltration Technique (MEMF) with cationic surfactant, cetyltrimetylammoniumbromide (CTAB). The variation of chromate, surfactant rejections and permeate flux with time were measured at two different CTAB concentrations as a function of transmembrane pressure drop (ΔP) and crossflow velocity, while CTAB/chromate, membrane pore size, temperature and pH of the feed solution was kept constant. For low CTAB concentration, it was observed that the efficiencies of chromate and surfactant removal increased with increasing ΔP, but decreased with increasing crossflow velocities. It was also observed that the effects of crossflow velocities and ΔPs on the rejections decreased for high CTAB concentration. It was found that fouling of the membrane by surfactant is very rapid at low crossflow velocity and high ΔPs at low CTAB concentration. As a result of this case, both transient permeate flux (J) and steady state permeate flux (J^?) decreased with decreasing crossflow velocity and increasing ΔP for both CTAB concentration. Unlike, modified fouling index (MFI) values increase with decreasing crossflow velocity and increasing ΔP. It was also observed that the effect of surfactant concentration in the 150, 200, and 250 kPa pressure and 3, 4, and 5 m/s crossflow velocity intervals dominates at high surfactant concentration.     

Optimization of hollow fiber membrane cleaning process for microalgae harvest

Biodiesel made from microalgae could be a possible replacement for fossil fuel. The separation of microalgae from their culture medium is a critical process in biotechnology. Membrane techniques seem to be effective, reliable, and safe, despite some limitations such as the progressive fouling and the associated decline in flux. Microalgae harvested from membranes have less chemical contamination and therefore membrane systems are more environmentally friendly than other harvesting techniques. We used a microfiltration (MF) system to concentrate the microalgae Tetraselmis sp. KCTC12236BP. Two cleaning processes, forward flushing and backwashing, were assessed to minimize the fouling required to concentrate the microalgae Tetraselmis sp. KCTC12236BP. It was concluded that backwashing was a more effective method than forward flushing. Furthermore, higher frequencies of backwashing greatly improved the membrane flux. However, even though the optimum cleaning frequency for maintaining high flux was every 5 min, from the perspective of microalgae concentrate and energy consumption, better results were obtained when backwashing was applied every 10 min. Under these conditions the microalgae culture reached 90% concentration in 60 min.     

Pilot plant study of an ultrafiltration membrane system fordrinking water treatment operated in the feed-and-bleed mode

A pilot plant study of a polysulfone ultrafiltration (MWCO of 30 kD) tubular membrane process was conducted for the treatment of reservoir water. The membrane separation system was operated in the cross-flow filtration mode at 4.7 m/s and the feed-and-bleed mode for a long term of 4000 h without chemical cleaning and backwashing. The results showed that the behavior of permeate flux of the membrane system operated in the feed-and-bleed mode was similar to that of membrane systems with a periodic backwashing. At the beginning of filtration, bleeding of highly concentrated retentate caused a significant increase in permeate flux by 20%. However, as filtration progressed over time, the permeate flux of the fouled membrane was almost independent of the change in concentration of retained materials by bleeding the retentate. Three distinct stages in permeate flux decline were observed as follows: (1) sharp decrease from 120 to 30 1/m²/h in 1250 h due to a rapid build-up of a fouling layer, (2) gradual decrease to 15 1/m²/h in 2800 h due to the role of tangential shear induced by cross-flow velocity, and (3) stable permeate flux until 4000 h due to the establishment of a pseudo-steady-state condition. Permeate quality was stable, regardless of concentrating and diluting retentate in each cycle and fouling for a long duration of filtration. Rejection efficiencies for ultraviolet absorbance at 260 nm (UV₂₆₀) and dissolved organic carbon (DOC) were around 58% and 49%, respectively. The measured turbidity and concentration of suspended solids in bleed water agreed with calculated values from a simple mass valance, while the measured DOC and UV₂₆₀ of bleed water were much lower than calculated values.     

Cleaning of fouled ultrafiltration (UF) membrane by algae during reservoir water treatment

Ultrafiltration (UF) membrane fouling is often encountered in water treatment. Algae could be removed by UF membrane for its nominal pore size, and the algae cells deposited on the surface of UF membrane. The cells attach to the membrane, they start to release secretion and produce extracellular polymetric substances (EPS), which accumulate on the surface and cause the flux decline. This study examined the effects of hydraulic and chemical cleaning on fouled membrane by algae-rich reservoir water. Four kinds of hydraulic cleaning method were investigated, including forward flushing, backwashing, forward flushing followed by backwashing and backwashing followed by forward flushing. Backwashing followed by forward flushing was more effective for flux recovery, and 20 min duration were enough for the cleaning. To maximize flux recovery for the algae-fouled membrane, chemical cleaning was applied as enhanced cleaning strategies. NaOH, NaOCl, and citric acid were used for cleaning agents. The cleaning with the combination of NaOH (0.02 N) and NaOCl (100 mg/L) was effective than separate uses. And the cleaning duration was determined as 4 h.     

Micellar enhanced ultrafiltration and activated carbon fibre hybrid processes for copper removal from wastewater

Several series of experiments were conducted to investigate copper removal from artificial suspension in micellar enhanced ultrafiltration (MEUF) and activated carbon fibre (ACF) hybrid processes. Sodium dodecyl sulphate (SDS) was used as a surfactant. Copper removal increased with the increase of molar ratio of copper to SDS, operating retentate pressure and initial permeate flux. Permeate flux decreased with the increase of molar ratio of copper to SDS. Specific and relative fluxes declined, respectively, with the increase of retentate pressure and initial permeate flux. Based on removal efficiency and permeate flux, initial permeate flux of 1.05 m³/m²/day, copper to SDS molar ratio of 1:30 (9.44 mM of SDS), and operating retentate pressure of 1.4 bar were found to be the optimum operating parameters for 0.5 mM or less initial copper concentration. Average copper removal at the optimised condition was 98% and the corresponding permeate copper concentration was less than 1 mg/L. Adsorptive capacity of activated carbon fibre (ACF) for SDS was 170 mg/g. Langmuir isotherm equation gives a better fit with the experimental results compared to the Freundlich isotherm equation. Overall SDS removal efficiency of two sets of ACF unit in series was 85%.     

Treatment of oily wastewater using low cost ceramic membrane: Comparative assessment of pore blocking and artificial neural network models

This work addresses the performance and modeling of the separation of oil-in-water (o/w) emulsions using low cost ceramic membrane that was prepared from inorganic precursors such as kaolin, quartz, feldspar, sodium carbonate, boric acid and sodium metasilicate. Synthetic o/w emulsions constituting 125 and 250 mg/L oil concentrations were subjected to microfiltration (MF) using this membrane in batch mode of operation with varying trans-membrane pressure differentials (ΔP) ranging from 68.95 to 275.8 kPa. The membrane exhibited 98.8% oil rejection efficiency and 5.36 × 10⁻⁶ m³/m² s permeate flux after 60 min of experimental run at 68.95 kPa trans-membrane pressure and 250 mg/L initial oil concentration. These experimental investigations confirmed the applicability of the prepared membrane in the treatment of o/w emulsions to yield permeate streams that can meet stricter environmental legislations (<10 mg/L). Subsequently, the experimental flux data has been subjected to modeling study using both conventional pore blocking models as well as back propagation-based multi-layer feed forward artificial neural network (ANN) model. Amongst several pore blocking models, the cake filtration model has been evaluated to be the best to represent the fouling phenomena. ANN has been found to perform better than the cake filtration model for the permeate flux prediction with marginally lower error values.     

微纳米气泡对超滤膜过滤腐植酸污染影响研究

为有效解决超滤过程中因有机物堵塞膜孔导致的膜污染和渗透通量下降问题，提出在对腐植酸（HA）溶液超滤传输及反洗过程中引入微纳米气泡水处理工艺，以强化超滤过程，实验研究了微纳米气泡对超滤膜渗透通量和截留效率的影响以及膜污染去除效果。结果表明在纯水和HA溶液中鼓入微纳米气泡后其归一化通量增大到1.1~1.3，截留效率提高了2.5%~22.0%，微纳米气泡水清洗和反洗后膜通量恢复分别高于纯水21%和25%。     

A new enhancement technique on air gap membrane distillation

The most serious concern in the application of air gap membrane distillation (AGMD) configuration is the low permeate flux caused by an additional transport resistance owing to the air gap, by the temperature and concentration polarization and by the surface fouling. This paper presents an innovative design of a low-cost and high efficient membrane module with an advanced enhancement technique in an AGMD configuration, which not only yields a much improved permeate flux but also requires no additional facility for the enhancement. The new module design includes a tangent directional and rotational inlet turbulent flow of hot feed and a partial contact between the membrane and the cooling plate in a small air gap. The concrete structure of the module is introduced in detail in the paper. Using this new module the permeate flux can be obtained up to 119 kg/m²h for tap water when the temperature of the hot and cold water is 77 °C and 12 °C respectively, which is about a 2.5-fold improvement over the traditional AGMD technique at the almost the same conditions. Within the range of our experimental study, the optimum partial contact area ratio is about 75–80%. Mechanistically, the tangent and rotational inlet turbulent flow can accelerate the diffusive process of mass and heat, reduce the boundary layer thickness of temperature and concentration and wash the membrane surface so as to improve the temperature and concentration polarization near the membrane surface and to raise the efficiencies of mass and heat transfer. Because of the partial contact between the membrane and the cooling plate with a large area, the main heat transfer and permeate condensation in the gap both are carried out on the contact area, which is very different from either the common AGMD or DCMD (direct contact membrane distillation) so as to reduce the transport resistance in the gap and thus to raise the permeate flux significantly. The new enhancement technique is also applied for the desalination of 15 wt.% salt water, which shows the similar improvement in permeate flux.     

Effect of different operating parameters on the recovery of proteins from casein whey using a rotating disc membrane ultrafiltration cell

In this study, effects of different operating parameters in ultrafiltration (UF) of casein whey in rotating disk ultrafiltration module, fitted with a 30 kD followed by a 5 kD molecular weight cut-off (MWCO) membrane have been analyzed and the benefits of membrane rotation with respect to stationary membrane module are highlighted. Prior to UF, centrifugation and microfiltration (MF) were carried out with the raw casein whey with an aim to remove the major membrane foulants like colloidal matters, suspended casein particles and lipid. The effects of pH, membrane rotation and transmembrane pressure (TMP) on UF flux and rejection were studied thoroughly, giving an emphasis on the effect of operating conditions in pressure and mass transfer controlled region as well. It was observed that solution pH was having a strong effect on UF flux and rejection for treating casein whey, which was explained in terms of prevailing monomer-dimer equilibrium of β-lactoglobulin, a major constituent of casein whey, as well as due to conformational changes of protein molecules with respect to isoelectric point. It was observed that for the 30 kD membrane, after 20 min of operation, 28.5% higher flux was obtained at pH 2.8 compared to pH 5.5 at a pressure of 490 kPa for stationary membrane, whereas the same figure for rotating membrane was 49.5%. Further, 38.7% higher UF flux at 300 rpm membrane speed compared to stationary membrane in 20 min of operation at pH 2.8 and TMP 490 kPa suggests the importance of shear across the membrane in minimizing the effects of concentration polarization. In the 5 kD membrane α-lactalbumin, which was mainly in the permeate stream from the 30 kD membrane, was separated from the other low molecular weight component of whey, such as lactose.     

Mathematical Modelling for Removal of Mixture of Heavy Metal Ions from Waste-Water Using Micellar Enhanced Ultrafiltration (MEUF) Process

The micellar enhanced ultrafiltration (MEUF) was studied for the removal of heavy metals using a mixture of non-ionic surfactant TWEEN-80 and anionic surfactant sodium dodecyl sulphate (SDS). The gel polarization model and resistance-in-series model were used to estimate the mass transfer coefficient (3 x 10-6 m/s) and the permeate flux. The total metal ion concentration was varied from 1 mM-4 mM and the corresponding effect of the trans-membrane pressure and limiting fluxes were studied. The modified resistance-in-series model was applied to these experimental data to correlate the flux with the feed concentration and applied pressure.     

Treatment of Oily Wastewaters Using the Microfiltration Process: Effect of Operating Parameters and Membrane Fouling Study

This work focuses on the treatment of oily wastewater using the cross-flow microfiltration (MF) process to determine the effect of different operating parameters such as transmembrane pressure (TMP) and cross-flow velocity on the separation performance and to study the mechanism of membrane fouling during microfiltration of oil in water emulsions. In this regard, the permeation flux and oil rejection of a polyvinylidene fluoride (PVDF) membrane in a flat-frame MF module for separation of 3000 ppm oil/water emulsions were measured. The results indicated that the permeate flux increased by an enhancement in both TMP and cross-flow velocity, while the oil rejection decreased. The analysis of variance (ANOVA) showed that the individual effect of TMP and cross-flow velocity is more important than the interactional effect of these operating parameters on the permeate flux and oil rejection. The results of fouling modeling revealed that the membrane fouling mechanism was affected by the applied TMP. The cake filtration model dominates the fouling mechanism at lower operating pressures. The fouling mechanism was changed from the cake formation to intermediate pore blocking and then to standard pore blocking as the TMP varied from 1 to 3 bar. Finally, a five-step procedure was used for cleaning the oil/water fouled membranes.     

An experimental study of UF membrane fouling by humic acid and sodium alginate solutions: the effect of backwashing on flux recovery

One of the critical issues for the successful application of ultrafitration in water treatment is membrane fouling due to dissolved organic matter, which negatively affects productivity, product quality and process cost. The aim of the present study is to contribute to the understanding of fouling phenomena by organic matter and the efficiency of the backwashing technique, which is applied in practice to restore membrane flux. In this experimental study commercial humic acid and sodium alginate have been used as model substances representative of natural organic matter and extracellular organic matter, respectively. All fouling experiments were carried out in a special single fiber apparatus. An important parameter considered in the study of both model substances is the concentration of calcium ions, which promote their aggregation and influence the rate of flux decline, the reversibility of fouling and rejection. Membrane fouling by humic acid appears to be the outcome of simultaneous action of several fouling mechanisms. Initially, a relatively rapid irreversible fouling takes place due to internal pore adsorption; however, progressively pore blocking becomes important and a fouling layer develops on the membrane. Sodium alginate fouling on the other hand is apparently due to two consecutive mechanisms; i.e. a rapid irreversible fouling due to internal pore constriction, followed by cake development on the membrane surface which becomes the dominant mechanism. Comparing fouling in both cases it can be inferred that even though sodium alginate fouling is more severe than the one caused by humic acids, it is to a large extent reversible by backwashing. On the contrary, fouling caused by humic acid is characterized by greater and increasing with calcium addition irreversibility, which is not remedied by the periodic backwashing. The different fouling propensity of the two types of macromolecules is apparently due to differences of their physical–chemical characteristics.     

往复旋转管式陶瓷膜超滤脱脂奶水溶液的研究

往复旋转管式陶瓷膜过滤系统通过膜组件往复旋转在膜表面反复产生高剪切率,达到减缓膜污染的效果。在相同操作条件下,与单向旋转过滤和死端过滤相比较,往复旋转过滤具有更好的减缓膜污染的作用。本实验利用往复旋转膜过滤装置超滤脱脂奶水溶液,考察了各种参数对该膜系统过滤特性的影响。实验结果表明,料液浓度增大,膜通量减小;过高的操作压差将会抑制膜通量增加;旋转速度增大,膜表面剪切强化作用增强,膜通量相应增大;膜稳态通量随往复旋转周期增大呈现先增大后减小的趋势。当料液速度达到膜组件转速时,瞬时反方向旋转膜组件,膜表面产生最大的剪切率,膜稳态通量也达到最大值。能耗分析表明,往复旋转过滤较单向旋转过滤单位通量能耗低。     

Application of micellar enhanced ultrafiltration and activated carbon fiber hybrid processes for lead removal from an aqueous solution

Micellar enhanced ultrafiltration (MEUF) and activated carbon fiber (ACF) hybrid processes were used to investigate the removal condition of lead ions and surfactant sodium dodecyl sulfate (SDS) from an aqueous solution. Lead removal efficiency increased with the increase of initial surfactant concentration. Molar ratio of lead to SDS up to 1: 5 has shown over 90% removal efficiency of lead, and the optimum molar ratio of lead to SDS was found to be 1: 5. Lead removal efficiency increased with the increase of pH, while it was maintained below 30% without surfactant. Lead removal was mainly due to the adsorption mechanism and no secondary layer was formed to reduce the flux. Lower molecular weight cut-off (MWCO) membrane has shown higher removal efficiency than higher MWCO one. Permeate flux decreased with the increase of molar ratio of lead to SDS. Flux decline was mainly due to the accumulation of micelles on the membrane surface. The presence of copper as a co-existing heavy metal highly affected the lead removal while nickel did not. Two sets of ACF unit in series were able to remove SDS surfactant effectively from the effluents of MEUF process.     

The effect of transmembrane pressure and pH on treatment of paper machine process waters by using a two-step nanofiltration process: Flux decline analysis

In this work, the treatment of paper machine whitewater obtained from paper production by using loose and tight Nanofiltration (NF) membranes in a lab-scale plant with a plate and frame module was investigated. The NF membranes were evaluated for fouling, flux decline due to concentration polarization and their suitability for removing of components present in wastewater. The loose NF membrane was used for the first step under different transmembrane pressure (8 to 32 bars) and pH (3, 5.6 and 10) values. The best filtration performances were provided under a pressure of 32 bar and a pH of 5.6. The fouling mechanism at different transmembrane pressures and pH values was investigated by “Hermia's model”. Also, fouling on pores and on the surface of NF membranes was characterized by Scanning electron microscopy (SEM) and contact angle measurements, respectively. For the advanced treatment of permeate obtained from the loose NF membrane that provided the lowest fouling and flux decline, a tight NF membrane was used in the second step. Even better retentions were achieved from experiments with this NF membrane. Results obtained in this study showed that the combination loose and tight NF membranes achieved reuse of paper machine white water for use as shower water of paper machine.     

Tannin and polyacrylic acid polarity and structure influence on the performance of polyvinylchloride ultrafiltration membrane

Tannin and polyacrylic acid were selected to represent the hydrophobic and hydrophilic compounds with similar molecular weights to investigate their fouling characteristics on a polyvinylchloride ultrafiltration membrane and the cleaning efficiencies of the two compounds fouled membranes by three kinds of cleaning methods, i.e., backwashing, flushing&backwashing and 0.5% NaOH solution. The results obtained showed that their configuration optimized by PM3 method of quantum chemistry was significantly different, i.e., tannin was sphere-like, and polyacrylic acid was cylinder-like, though they had similar MW. The hydrophobic tannin, showed higher rejection and rapid permeate flux decline because it was prone to adsorption on membrane pore, resulting in partial flux recovery by hydraulic cleaning and complete recovery by NaOH cleaning. The hydrophilic polyacrylic acid rejection was lower, resulting from its penetrating through membrane pore, cylinder-like-configuration polyacrylic acid can twist in membrane pore passage so that the flux was not recovered by backwashing.     

Solubilization and micellarenhanced ultrafiltration ofo-cresol by Sodium Dodecyl Sulfate Micelles

The solubilization and the micellar-enhanced ultrafiltration (MEUF) of o-cresol were investigated by using an anionic surfactant, sodium dodecyl sulfate (SDS). In order to study the solubilization behaviour of the solute, the semiequilibrium dialysis (SED) method was employed and stirred-cell ultrafiltration experiments were performed for the test of MEUF. The analysis of the results supported that approximately two surfactant molecules provide a location for the solubilized solute within micelle. In the removal of o-cresol by MEUF, as long as high SDS concentrations in the retentate (>0.2 M) are avoided, relatively good rejection of o-cresol (85 %) could be obtained under the conditions used (initial concentration ratio:[o-cresol]/[SDS]=0.2 and 0.6). Furthermore, the ultrafiltration processes were nearly at equilibrium, so that the permeate concentrations of o-cresol could be predicted from the SED results. The separation efficiency was greater at lower o-cresol concentrations when the SDS concentrations were fixed in the feed, while the rejection increased with increasing the SDS concentrations at constant intramicellar mole fraction of the solute Xc. In addition, as the o-cresol loading of retentate increased, the less SDS in the retentate permeated through ultrafiltration membranes. On the other hand, the higher o-cresol loadings reduced the fluxes of MEUF runs.