Influence of feed concentration and transmembrane pressure on membrane fouling and effect of hydraulic flushing on the performance of ultrafiltration

Micellar-enhanced ultrafiltration (MEUF) is a promising technology developed for treating the wastewater containing metal ions or organic pollutants. One of the greatest problems in MEUF is membrane fouling which is mainly caused by concentration polarization, gel layer or cake formation caused by the deposition of surfactant micelles on the membrane surface and surfactant adsorption in the membrane interior. In this study, surfactant sodium dodecyl sulfate (SDS), which was used in membrane separation as colloidal particles, caused the flux decline. The transmembrane pressure (TMP) and feed concentration of SDS had significant influences on the flux. This paper presented that the lower TMP had a smaller effect on membrane fouling, and when SDS concentration was around the critical micelle concentration (CMC), lower permeate flux and higher additional membrane fouling resistance were obtained. The effects of three kinds of hydraulic flushing methods on membrane permeate flux were investigated, including periodic forward flushing, periodic backwashing and forward flushing followed by backwashing. It was found that when the periodic combined flushing interval was 10 min, forward flushing and backwashing phase times were 150 s and 90 s, respectively, and that combined flushing was more conductive to permeate flux recovery in this study.     

Influence of Nonionic Surfactant on Hydrolysis of Vinyl Sulfone Reactive Dye

Nonionic surfactants are widely used in reactive dyeing processes, and the interaction between surfactants and reactive dyes affect the hydrolytic property of reactive dyes. In this study, reactive brilliant blue KN‐R (C.I. reactive blue 19) was employed as a model dye, and fatty alcohol polyoxyethylene ether (AEO‐9) was selected as a model nonionic surfactant. The interaction was first investigated in aqueous solutions by a UV‐spectrophotometry method, then the effect of surfactant concentration on the hydrolytic behavior of KN‐R was studied using high performance liquid chromatography method. Below the critical micelle concentration, the surfactant served as dispersant; the hydrolysis of reactive dye was accelerated. However, when the concentration of surfactant was above its critical micelle concentration, the dye was solubilized into the micellar phase, which was revealed from the changes in absorbance intensity and wavelength of the maximum absorbance. This led to slowed hydrolysis of reactive dye. These findings are useful in understanding the effect of concentration of nonionic surfactant on the hydrolysis of vinyl sulfone reactive dyes.     

Interaction of Azo Dye with Cationic Surfactant Under Different pH Conditions

The aggregation induced by Alizarin Yellow R (AYR) in the cationic surfactant, cetyltrimethylammonium bromide (CTAB), was investigated by measuring their UV–visible absorption spectra. Conductance measurements as a function of surfactant concentration below and above the critical micelle concentration (CMC) were studied. CTAB aggregation takes place at the concentration far below its normal CMC in the presence of AYR. Both hydrophobic and electrostatic interactions affect the aggregation process in aqueous solution. The dye effect on the CMC of CTAB was noted by a specific conductivity method as well. AYR–CTAB binding constant (K_s) and water–micelle partition co-efficient (K_x) were quantified with the help of mathematical models employed to determine the partitioning of organic additives in the micellar phase. The number of dye molecules per micelle was estimated at particular CTAB concentrations above CMC, during this study.     

Fluorescence technique for the determination of low critical micelle concentrations

A technique for determining low critical micelle concentrations (CMC) by means of a hydrophobic fluorescence probe has been developed. The amount of the fluorescent probe at the CMC is so small that the effect of the probe on micelle formation is negligible. The fluorescence intensity was measured at fixed dye/surfactant ratios, and it decreased with concentration. A quantity proportional to fluorescent quantum yield was calculated and found to be high for concentrations of surfactant above the CMC and almost zero below the CMC, giving a distinct break in the quantum yield vs. the concentration curve.     

Determination of critical micelle concentration of surfactant by ultraviolet absorption spectra

A method was investigated for determining the critical micelle concentration (CMC) by the shift of absorption maxima when an organic compound (I) with ultraviolet absorption was added to an aqueous solution of a surfactant. When I was added to the surfactant solution at higher concentrations (above the CMC), λ_max of I approached the value inn-octane, since I was solubilized in the hydrocarbon atmosphere of the inner part of the surfactant micelle. At lower concentrations (below the CMC), however, I was present in the water phase and λ_max approached the value in water. The curve of λ_max vs. surfactant concentration declined from the high concentration values as the CMC was approached and at the CMC, the curve broke upward sharply. Then, it rose for some time and approached the value in water. N,N′-diethylaniline was used because it exhibited larger shifts of λ_max. The standard amount used was 0.002 ml/3–10 ml of aqueous solution of the surfactant. The CMC values obtained agreed with those obtained by the electric conductivity method, dye adsorption method and light scattering method, for surfactants such as tetradecyldimethylbenzylammonium chloride, sodium dodecyl sulfate and polyoxyethylene cetyl ether.     

十二烷基硫酸钠的临界胶束浓度的测定及影响分析

临界胶束浓度(CMC)是表面活性剂活性的度量。采用电导法测定表面活性剂十二烷基硫酸钠的临界胶束浓度,并探讨了温度、NaCl或乙醇等对临界胶束浓度的影响。随着温度的升高,CMC增大;NaCl的加入量增大时,CMC在较低浓度下增大,在0.2~0.8 mmol/L范围内CMC随NaCl的量增大而降低;乙醇的加入量随体积比从0%~2.5%增大时,CMC增大,并分析了SDS的CMC发生变化的原因。     

Different fouling modes of submerged hollow-fiber and flat-sheet membranes induced by high strength wastewater with concurrent biofouling

Exploration of two major commercialized flat-sheet and hollow-fiber membranes in a submerged membrane fungi reactor fed with a synthetic textile wastewater revealed striking differences in the extent and mechanism of fouling between the two types, indicating a case-specific scope of choice between the two for industrial wastewater treatment. The hollow-fiber membrane exhibited fouling with a cake layer composed of fungi and starch, intensity being proportional to the operating flux (0.05–0.3 m/d). Conversely, the flat-sheet membrane suffered from immediate internal pore blocking beyond a critical flux of 0.2 m/d. During the experiment with major constituents of the synthetic wastewater separately, while media containing only starch and only dye induced negligible fouling, flux-dependent pore blocking was evident for both the hollow-fiber (0.288 m/d) and flat-sheet membranes (1.3 m/d) for the mixture of starch and dye. Despite a remarkable 99% color and 97% TOC removal achieved by both membranes, fouling with different modes and intensity for the two types under similar conditions and for the same type of membrane under different exposure conditions warrants development of suitable modules for such recalcitrant wastewater.     

The study of Sunset Yellow anionic dye interaction with gemini and conventional cationic surfactants in aqueous solution

In the present study, the interaction of an anionic azo dye, Sunset Yellow, with two cationic gemini surfactants with different spacer lengths (s = 3, 6 methylene groups) and their monomeric counterpart, dodecyl trimethyl ammonium bromide (DTAB), was investigated by surface tension, UV–Vis spectroscopy, and zeta potential measurements. The critical micelle concentration (CMC) was determined from plots of the surface tension (γ) as a function of the logarithm of total surfactant concentration. Moreover, the values of binding constants (K_b) of dye-surfactant complexes were calculated by UV–Vis spectroscopy. The UV–Vis spectra showed that the dye–surfactant interaction occurred in the solution at concentrations far below the CMC of each surfactant. The gemini surfactant with a shorter spacer showed stronger interaction with dye in comparison to DTAB and the gemini with longer spacer. The effect of surfactant chemical structure on solubilization of dye-surfactant aggregates at surfactant concentration above CMC was investigated by zeta potential.     

Fouling of reverse osmosis membranes by hydrophilic organic matter: implications for water reuse

Effluent organic matter (EfOM) is suspected as a major cause of fouling of reverse osmosis (RO) membranes in advanced wastewater reclamation. Among the main constituents in EfOM, polysaccharides are the most ubiquitous. The influence of solution chemistry and hydrodynamics on RO membrane fouling with alginate — a model for polysaccharides in secondary wastewater effluent — was systematically investigated. Results of fouling runs with alginate demonstrate that RO membrane fouling increases with decreasing pH, increasing ionic strength, and addition of calcium ions. At fixed solution ionic strength and pH, the presence of divalent calcium ions, at concentrations typical of those found in secondary wastewater effluent, had a dramatic effect on membrane fouling. However, for similar concentrations of divalent magnesium ions, fouling was negligible. The severe fouling in the presence of calcium is attributed to the formation of a thick, dense alginate gel layer on the membrane surface via calcium-alginate complexation and crosslinking (bridging) of alginate macromolecules by calcium. In addition to solution chemistry, hydrodynamic operating conditions — initial permeate flux and crossflow velocity — were also shown to influence RO membrane fouling with alginate.     

Solubilisation study of water‐insoluble dye in cationic single/dimeric surfactant micelles: effect of headgroup,non‐polar tail,and spacer chain in aqueous and salt solution

The solubilisation of hydrophobic azo dye Orange OT in aqueous/salt solution in several cationic surfactant micelles was studied using UV‐vis spectroscopy. An attempt was made to correlate dye solubilising strength with adsorption/micellar characteristics. In our experiments we determined the change in solubilisation of hydrophobic dye when added to an aqueous solution of oppositely charged quaternary‐salt‐based cationic surfactants (conventional and gemini) and remarked on the probable location of the solubilised dye in the surfactant micelle. Results highlight the onset of dye solubilisation around the critical micelle concentration of each surfactant, which is influenced by the non‐polar tail, spacer, and polar headgroup, while no dye could be solubilised at concentrations below the critical micelle concentration. Orange OT solubilised almost linearly with increase in surfactant concentration at and above the critical micelle concentration. The change in colour intensity of the dye (darker below the critical micelle concentration, lighter at and above the critical micelle concentration) could be attributed to dye–surfactant interactions. Further dye solubilisation was observed in the presence of salt.     

膜分离技术在染料行业中的应用研究进展

介绍了粗制染料的脱盐与浓缩纯化生产的研究进展。膜分离作为一种清洁生产工艺技术,使合成染料的脱盐和浓缩同时进行,从而成功地得到高浓度、低盐的染料产品如活性染料、荧光增白剂和酸性染料等。在膜法治理染料废水方面,介绍了膜分离、预处理/膜分离组合和膜分离/氧化组合等3种工艺及其应用实例,并简要介绍了新型膜材料和膜过程的发展状况。     

聚砜超滤膜与低分子有机物交互作用的研究

选取聚砜平板超滤膜,采用间歇错流循环方式对离子型表面活性剂与低分子有机物的混合料液进行分离,考察了表面活性剂的浓度、操作压力等因素对超滤过程的影响,研究料液与膜之间的交互作用。结果表明,有机物与表面活性剂的混合料液的通量均高于自来水的通量;表面活性剂的浓度低于临界胶束浓度(CMC)时,膜通量随其浓度的增加而增加,而高于CMC时通量略有下降;改变操作压力,混合溶液的通量随压力的降低而减小,其中苯酚的通量变化不大,但均保持较高的渗透通量。     

Grey water treatment and simultaneous surfactant recovery using UF and RO process

The membrane-based grey water treatment for grey water reuse and surfactant recovery is presented in this research paper. Grey water from washing machine discharges having turbidity and used surfactant was processed through the polymeric ultrafiltration (UF) membrane to remove the turbidity. The UF treated grey water is further purified by reverse osmosis (RO) membrane for surfactant recovery and water reuse. The surfactant trapped inside the RO spiral wound membrane module is recovered through various membrane physical regeneration techniques such as backwashing, simultaneous backwash–back-flush and ozone back-flush. Among this, backwash–back-flush is found to be effective process for surfactant recovery. The methodology for optimising surfactant recovery is captured by studying effect of various operating parameters such as feed detergent concentration, backwash pressure, backwash temperature and back-flush flow rate. By implementing optimal process conditions, the integrated UF and RO membrane process is able to produce 300 L of reusable pure water and 80 L of concentrated detergent solution and 20 L of turbid water while treating 400 L of grey water discharges. Maximum surfactant recovery of 82% is obtained while treating grey water which consists of 720 ppm of total dissolved solids (detergent) and 45 ppm of surfactant. The extent of UF and RO membrane fouling is determined by measuring the pure water flux before and after the grey water treatment. The membrane performance is found to be stable when membrane is regenerated by backwash–back-flush technique for RO and gravity backwash for UF membrane.     

Nanofiltration of textile wastewater for water reuse

The textile industry produces a large amount of wastewater that is highly coloured with high loading of inorganic salt. Crossflow nanofiltration using thin film composite polysulfone membrane was used to recover the electrolyte solution and reject the colour. Using a synthetic textile effluent of reactive dye and NaCl solution, the study focused on the mechanism controlling flux and rejection by varying four main parameter; crossflow velocity, initial dye concentration, feed pressure, and electrolyte concentration. Results show that flux was dominated by the osmotic pressure created from the presence of NaCl, and that dye concentration did not significantly effect the flux or rejection. Working at low pressures of up to 500 kPa, relatively high fluxes were obtained, with an average dye rejection of 98% and NaCl rejections of less than 14%. Thus, a high quality of reuse water could be recovered. Even after a number of cycles, the membrane did not foul irreversibly, with an overall mean waterflux recovery of 99%.     

Green and feasible fabrication of loose nanofiltration membrane with high efficiency for fractionation of dye/NaCl mixture by taking advantage of membrane fouling

Loose nanofiltration membrane emerges as required recently, since it is hard for conventional nanofiltration membrane to fractionate mixture of dyes and salts in textile wastewater treatment. However, the polymeric membranes unavoidably suffer from membrane fouling, which was caused by the adsorption of organic pollutants (like dyes). Normally, the dye fouling layer will shrink membrane pore size, thus resulting in flux decline and rejection increase. It is thought that membrane fouling may be a double-edged sword and can be an advantage if properly utilized. Thereby, loose nanofiltration membranes were constructed here by a green yet effective method to fractionate dyes/salt mixture by taking advantage of membrane fouling without using poisonous ingredients. A commercially available polyacrylonitrile (PAN) ultrafiltration membrane with high permeability was chosen as the substrate, and dyes were used to contaminate PAN substrate and formed a stable barrier layer when adsorption of dyes reached dynamic equilibrium. The resultant PAN-direct red 80 (DR80) composite membranes displayed superior permeability (~128.4 L m⁻² h⁻¹) and high rejection (~99.9%) to DR80 solutions at 0.4 MPa. Moreover, PAN-DR80 membranes allowed fast fractionation of dyes/sodium chloride (NaCl) mixture, which maintained a negligible dye loss and a low NaCl rejection (~12.4%) with high flux of 113.6 L m⁻² h⁻¹ at 0.4 MPa. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47438.     

On the measurement of critical micelle concentrations of pure and technical-grade nonionic surfactants

The critical micelle concentrations (CMC) of nine commercial nonionic surfactants (Tween 20, 22, 40, 60, and 80; Triton X-100; Brij 35, 58, and 78) and two pure nonionics [C₁₂(EO)₅ and C₁₂(EO)₈] were determined by surface tension and dye micellization methods. Commercially available nonionic surfactants (technical grade) usually contain impurities and have a broad molecular weight distribution owing to the degree of ethoxylation. It was shown that the surface tension method (Wilhelmy plate) is very sensitive to the presence of impurities. Much lower CMC values were obtained with the surface tension method than with the dye micellization method (up to 6.5 times for Tween 22). In the presence of highly surfaceactive impurities, the air/liquid interface is already saturated at concentrations well below the true CMC, leading to a wrong interpretation of the break in the curve of surface tension (γ) vs. concentration of nonionic surfactant (log C). The actual onset of micellization happens at higher concentrations, as measured by the dye micellization method. Furthermore, it was shown that when a commercial surfactant sample (Tween 20) is subjected to foam fractionation, thereby removing species with higher surface activity, the sample yields almost the same CMC values as measured by surface tension and dye micellization methods. It was found that for monodisperse pure nonionic surfactants, both CMC determination methods yield the same results. Therefore, this study indicates that precaution should be taken when determining the CMC of commercial nonionic surfactants by the surface tension method, as it indicates the surface concentration of all surface-active species at the surface only, whereas the dye method indicates the presence of micelles in the bulk solution.     

Nanofiltration and reverse osmosis thin film composite membrane module for the removal of dye and salts from the simulated mixtures

Nanofiltration (NF) and reverse osmosis (RO) thin film composite polyamide membrane modules were used to remove the color from the contaminated solution mixture. The feasibility of membrane processes for treating simulated mixture by varying the feed pressures (100-400 psi) and feed concentrations was studied to assess the separation performance of both NF and RO membranes. It was found that the efficiency of NF and RO membranes used in the treatment of colored water effluents was greatly affected by the presence of salts and dyes in the mixture. Color removal by NF with a high rejection of 99.80% and total dissolved solids (TDS) of 99.99% was achieved from RO by retaining significant flux rate compared to pure water flux, which suggested that membranes were not affected by fouling during the simulated wastewater process operation. The effect of varying concentrations of Na₂SO₄ salt and methyl orange (MO) dye on the performance of spiral wound membranes was determined. Increasing the dye concentration from 500 to 1000 mg/L resulted in a decrease of salt rejection at all operating pressures and for both concentrations of 5000 and 10,000 mg/L as the feed TDS. Increasing the salt concentration from 5000 to 10,000 mg/L resulted in a slight decrease in dye removal.     

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．     

利用Gemini联接链上生色基团测定临界胶团浓度

利用Gemini表面活性剂分子聚集使联接链上生色基团吸光截面积增大的原理,发展了自吸收光谱测定水溶液中临界胶团浓度(CMC)的方法。实验测得C11pPHCNa水溶液(pH=12)的CMC值0．0891 mmol／L,与表面张力法测定的结果(CMC=0．0925 mmol／L)吻合。当这些分子聚集形成较完整胶团后造成联接链上生色基团的荧光猝灭,由此可测定形成较完整胶团的临界点(≈0．451 mmol／L)。     

膜分离技术在染料工业清洁生产中的应用

介绍了近年来膜分离技术在染料行业中的应用现状。膜技术的应用包括染料的脱盐、浓缩、生产,印染废水的处理、回用等方面。同时介绍了膜的污染及其防治等相关方面的内容。