Nanofiltration for the possible reuse of water and recovery of sodium chloride salt from textile effluent

During the reactive dyeing of cotton, salts such as sodium chloride (NaCl) are placed in a dyebath to aid the exhaustion of various dyes onto the fabric while bases are added to raise the pH from around neutral to pH 11 to achieve fixation. Afterwards, the used dyebath solution, called dyebath spent liquor, is discharged with almost all the salts and bases added as well as unfixed dyes. Consequently, many raw materials are lost in the waste stream ending up in the environment as pollutants. In this study possibilities of reusing the water and salts of dyebaths were investigated using a nanofiltration membrane. When the NaCl concentration in the spent liquor was increased from 10 to 80 g/L, the NaCl rejection by the membrane was found to decrease initially; however, the NaCl rejection increased over time, which was not expected. The aggregation of dye was also studied and found to decrease in the concentrate when the salt concentration was increased. This information is useful for the textile industry in evaluating the treated water quality for the purpose of reuse.     

CaCl_2对葡萄糖纳滤截留率的影响

采用Desal-DK纳滤膜进行中性有机物、CaCl2、葡萄糖/CaCl2混合体系的水溶液纳滤实验与数学模型表征研究。结果表明:CaCl2截留率随本体溶液浓度增大而减小,葡萄糖/CaCl2混合体系中葡萄糖截留率随CaCl2浓度增大而减小。采用道南-立体细孔模型描述CaCl2的截留率变化趋势与实验值吻合良好。实验拟合所得等效孔径、等效膜厚与等效荷电密度随CaCl2浓度增大而增大,表明本体溶液中的CaCl2促使膜孔膨胀。     

纳滤法处理含氟废水工艺条件的研究

采用Dow FilmTec公司的NF-90纳滤膜处理模拟含氟废水,主要考察了压力、pH、流量、温度、氟离子初始浓度等对膜渗透通量和氟离子截留率的影响。结果表明:压力升高,膜渗透通量增大,氟离子截留率先增大后减小;pH对膜渗透通量无明显影响,氟离子截留率随pH的升高而增大;流量升高膜渗透通量和氟离子截留率略有增大;温度升高,膜渗透通量增大,氟离子截留率降低;氟离子初始浓度增大,膜渗透通量减小,氟离子截留率降低。在压力1.0 MPa、pH 10.01、流量30 L/h、温度20℃的条件下NF-90膜截留率可达到95%;当处理氟浓度小于100 mg/L,出水氟浓度可达到国家工业一级排放标准。     

Formation and Characterization of Carboxymethyl Cellulose Sodium (CMC‐Na)/Poly (vinylidene fluoroide) (PVDF) Composite Nanofiltration Membranes

Abstract

A series of carboxymethyl cellulose sodium composite nanofiltration membranes were prepared through the method of coating and cross‐linking. Effects of the preparation techniques and the operating conditions on the rejection performance of the resulting membranes were investigated, respectively. It suggested that the resulting composite NF membrane with excellent rejection performance should be prepared through a certain preparing technology. Attenuated total reflection infrared spectroscopy and atomic force microscopy were employed to characterize the resulting membrane. The rejection of this kind of negatively charged membrane to the electrolyte solutions decreased in the order of Na₂SO₄, NaCl, MgSO₄, and MgCl₂.     

纳滤膜去除水中双酚A的研究

酚类环境激素双酚A(BPA)在各种水体中都有检出,且检出浓度有逐年增大的趋势;酚类有一定的毒性,加之它在水中的溶解度小,常规方法不易去除。本试验研究了NF-270型纳滤膜在不同压强、浓度、温度下对双酚A的去除效果。结果表明:原水中微量双酚A浓度的变化对膜通量基本无影响,截留率会随原水中双酚A浓度的增大而略有增加;随着操作压力的增加,膜通量增加,截留率增大,温度增加,截留率也增大,但超过30℃时,截留率明显下降。     

Tuning of the swelling and dye removal efficacy of poly(acrylamide-AMPS)-based smart hydrogel

Hydrogels responsive to pH change based on poly(acrylamide-co-2-acrylamido-2-methylpropane sulfonic acid) are synthesized. The hydrogels are characterized in terms of FTIR spectroscopy, swelling–deswelling behavior, morphological analysis and dye removal properties. The swelling of the hydrogel is strongly dependent on the copolymer composition, pH and ionic strength of the medium. The dye removal efficiency (DRE) also depends on the copolymer composition, pH and ionic strength. Pseudo-second-order kinetics and Langmuir isotherms model, respectively, are the best-fit models for the present gel. The cellular structures of the hydrogels are clearly revealed by optical microscopic and SEM images.     

一种新型羧甲基甲壳素/聚砜复合纳滤膜的研究

羧甲基甲壳素(CMCH)溶液浇铸在聚砜超滤膜上,并与戊二醛(GA)交联制得一种新型荷负电复合纳滤膜.制备该膜的最佳条件为:CMCH浓度为2.0%,GA浓度为1.5%,50℃下交联2.0 h,然后50℃下热处理15 min.复合膜对中性分子的截留分子量为7.425×10-22 g (450 Da),膜孔径在(6.6～7.6)×10×10 m,静电位为-0.15 mV,电压渗系数为-0.85,离子交换容量为2.2 mmol·cm-2,在18℃,1.3 Mpa压力和流量为38 L·h-1时,对浓度为2000 mg·L-1的Na3PO4,K2SO4,Na2SO4,MgSO4,KCl,NaCl 和 MgCl2 溶液的截盐率分别为 92.10%,90.93%,91.83%,62.51%,30.29%,29.46% 和 10.96%,通量分别为 3.96 L·h-1·m-2,4.81 L·L·h-1·m-2,复合膜对不同盐的截留行为与其它荷负电纳滤膜类似,主要决定于荷电膜与电解质离子之间静电作用力的大小.随着进料液浓度的增加,复合膜的截盐率减小,通量增加;随着操作压力的升高,通量增加,截盐率先增加后保持不变.另外,发现该膜具有较好的抗藻类附着性.该膜可望用于脱除水中NO3-,PO43-,SO42-及阴离子表面活性剂等负电荷离子,在中水、工业水、饮用水处理及加工等方面有广阔的应用前景.     

纳滤海水软化的实验研究

利用小型平板膜测试设备,进行纳滤海水全回流实验研究.考察了操作压力、流量对DL膜通量的影响和膜对海水中主要离子的截留效果,进而研究在7 h的运行过程中DL膜对海水的软化效果,最后采用扫描电镜与X射线能谱分析纳滤海水软化过程中微溶盐的结晶情况及二价阳离子与海水中有机物的络合作用.结果表明,荷负电DL纳滤膜具备良好的渗透性和分离性能,膜通量随压力的升高线性增加,提高流量通量略有增大.在0.8～2.4 Mpa的压力范围内,DL膜对SO42-和Mg2+的截留率分别保持在98%和70%以上,对Ca2+、Na+和Cl-的截留率是随着压力的升高先增大后保持稳定.随着运行时间的延长,膜通量和离子截留率呈现一定下降趋势.在全回流运行方式下,硫酸钙表面结晶是膜通量衰减的主要原因,海水有机物与二价钙镁离子的络合作用甚微.     

纳滤膜去除水中微量邻苯二甲酸酯的研究

邻苯二甲酸酯（PAEs）是一类环境雌激素,对人体健康造成严重危害。本研究运用纳滤膜处理水中微量PAEs,以最常用的邻苯二甲酸二乙酯（DEP）,邻苯二甲酸二丁酯（DBP）,邻苯二甲酸二环己酯（DCHP）,邻苯二甲酸二异辛酯（DEHP）为研究对象,研究压力、原水浓度、离子强度、和pH值等因素对其截留行为的影响。结果表明：纳滤技术是去除水中微量PAEs的有效方法,平均截留率在90%以上;纳滤过程中,截留率随物质分子量的增加而增加;影响膜性能的主要的因素是操作压力、离子强度和pH值,原液浓度对膜性能影响不大;最佳去除条件为：压力0.4MPa,pH=7,电导率为0.2μS/cm。     

Arsenic Separation by a Membrane-Integrated Hybrid Treatment System: Modeling,Simulation, and Techno-Economic Evaluation

A modeling and simulation study along with economic analysis was carried out for arsenic separation by a membrane-integrated hybrid treatment system that consisted of an oxidation unit integrated with a cross flow nanofiltration membrane module. About 96–98% arsenic removal efficiency was achieved in the membrane module after pre-oxidation. When pH was increased from 3 to 10, arsenic rejections reached as high as 98.5%. The dynamic mathematical model developed for the system used Extended Nernst-Plank equation as the basis for the nanofiltration model. A linearized approach in modeling was adopted that reduced the computation time significantly. Model predictions were found to corroborate very well with the experimental findings as indicated in the small relative errors of the order of only 0.003 and Willmott d-index of 0.993 reflecting very good model performance. Thus the developed model is expected to be very useful in scale-up, design and optimization of the membrane-integrated hybrid treatment system for removal of arsenic from contaminated groundwater.     

Influence of dyes, salts and auxiliary chemicals on the nanofiltration of reactive dye baths: experimental observations and model verification

The aim of this study was to investigate the effects of dyes, salts and auxiliary chemicals in reactive dye baths on the separation performance of nanofiltration membranes. A reactive dye bath was simulated for this purpose with auxiliary chemicals. A DS5-type nanofiltration membrane was used in the experimental runs. Performance of the nanofiltration membrane was evaluated by measuring permeate flux, salt and color rejections in five steps. Reactive black 5, reactive orange 16, NaCl, NaOH, Na₂SO₄, acidic acid, mollan and slipper were used to prepare synthetic dye baths. Pressures in the range of 8 to 24 bars were applied, and flow velocity was kept constant at 0.74 m/s. NaCl rejection of 20% and color rejection of more than 95% were achieved throughout the experiments. Permeate quality was satisfactory enough to recycle these effluents in reactive dyeing. Acidification ofthe original synthetic dye bath solution with HCl and H₂S0₄ decreased the membrane fouling and also increased the NaCl recovery and color rejection. Besides, using HCI instead of H₂SO₄ increased these positive effects. The effects of auxiliary chemicals were determined by using salt rejection model parameters of α and k_D in the presence of an organic ion. There was a correlation among the results of experiments and the model. The model parameters (α and k_D were also calculated for all steps.     

Salt rejection in nanofiltration for single and binary salt mixtures in view of sulphate removal

Three commercial membranes (NF70, NF90 and TFC-SR) were firstly characterized in terms of pure water flux and the rejection of uncharged (alcohols and sugars) compounds. Subsequently, the rejection of monovalent (sodium and chloride) and divalent (calcium and sulphate) ions in single (NaCl, CaCl, and Na₂SO₄) and binary (NaCI/Na₂,SO₄ CaCl₂/CaSO₄, NaCI/CaCl₂, and Na₂SO₄/CaSO₄) salt mixtures was studied. According to the pure water permeability the TFC-SR membrane is a loosely packed NF membrane (12.3 L.m ⁻².h⁻¹.bar⁻¹), while both NF70 and NF90 are tightly packed (2.6 and 3.6 Lm⁻².h⁻¹.bar-). According to the uncharged solute rejection, the MWCO_NF70 = 60, MWCO_NF90= 200 and MWCO_TFC-SR > 500. NF70 and NF90 were equally efficient in rejecting 1-2, 1-1 and 2-1 salts (>90%), while TFC-SR showed typical negatively charged surface behaviour, i.e., R (1-2) salt > R (11) salt > R (2-1). Sulphate rejection decreased in the presence of sodium chloride more significantly than in the presence of calcium chloride due to the more efficient retention of the bivalent calcium.     

Comparison study of dyestuff wastewater treatment by the coupled photocatalytic oxidation and biofilm process

Degradation of Rhodamine B (RhB) and COD by means of the coupled photocatalytic oxidation (PCO) and biofilm systems has been studied. The coupled PCO-biofilm systems were divided into two operation systems. The one (R1) consisted of a pre-PCO and a post-biofilm reactor system and the other (R2) was a pre-biofilm and a post-PCO reactor system. In a batch experiment, the order of initial decolorization rate was photocatalytic oxidation > adsorption > photolysis. The color removal rate of RhB was decreased with an increase of the initial COD concentration. In a continuous experimental study, almost all color was removed in the PCO reactor. During 180 days, the color and COD removal efficiencies in the R2 (pre-biofilm + post-PCO) system were higher than those in the R1 (pre-PCO + post-biofilm) system. In our experimental ranges, the PCO process was superior to Fenton oxidation in the color and COD removal.     

Degradation of Alizarin Red by electro-Fenton process using a graphite-felt cathode

The removal of the anthraquinone dye Alizarin Red S (AR) has been investigated by electro-Fenton process using a commercial graphite-felt to electrogenerate in situ hydrogen peroxide and regenerate ferrous ions as catalyst. The effect of operating conditions such as applied current, catalyst concentration, and initial dye content on AR degradation has been studied. AR decay kinetic, the evolution of its oxidation intermediates and the mineralization of the aqueous solutions were monitored during the electrolysis by UV–Vis analysis and TOC measurements. The experimental results showed that AR was completely removed by the reaction with OH radicals generated from electrochemically assisted Fenton's reaction, and the decay kinetic always follows a pseudo-first-order reaction. Applying a current of 300 mA and with catalyst concentration of 0.2 mM Fe²⁺, 95% of the initial TOC was removed in 210 min of electrolysis, meaning the almost complete mineralization of the organic content of the treated solution.     

Significantly enhanced dye removal performance of hollow tin oxide nanoparticles via carbon coating in dark environment and study of its mechanism

Understanding the correlation between physicochemical properties and morphology of nanostructures is a prerequisite for widespread applications of nanomaterials in environmental application areas. Herein, we illustrated that the uniform-sized SnO₂@C hollow nanoparticles were large-scale synthesized by a facile hydrothermal method. The size of the core-shell hollow nanoparticles was about 56 nm, and the shell was composed of a solid carbon layer with a thickness of 2 ~ 3 nm. The resulting products were characterized in terms of morphology, composition, and surface property by various analytical techniques. Moreover, the SnO₂@C hollow nanoparticles are shown to be effective adsorbents for removing four different dyes from aqueous solutions, which is superior to the pure hollow SnO₂ nanoparticles and commercial SnO₂. The enhanced mechanism has also been discussed, which can be attributed to the high specific surface areas after carbon coating.