Fouling control in sugarcane juice ultrafiltration with surface modified polysulfone and polyethersulfone membranes

Commercial 50 and 100 kD polyethersulfone (PES) and polysulfone (PS) ultrafiltration membranes were surface modified by UV photografting of poly(ethylene glycol) methacrylate (PEGMA) monomer. The modified membranes were characterized by the degree of grafting, water flux and molecular weight cutoff (MWCO) rating. The flux and fouling of the modified and unmodified membranes were examined with sugarcane juice and its polysaccharide fraction. Under the conditions of this study, the modified membranes displayed a low degree of grafting (26-36 μg/cm²), which was independent of the UV exposure duration; however, both membrane water flux and MWCO rating were affected by the irradiation time. In the best case, the modified membranes exhibited lower fouling with sugarcane juice; furthermore, the propensity to foul also decreased. More significantly, juice flux recovery was almost complete for successive UF-cleaning cycles.     

Selective swelling of polysulfone/poly(ethylene glycol) block copolymer towards fouling-resistant ultrafiltration membranes

Fouling resistance of ultrafiltration (UF) membranes is critical for their long-term usages in terms of stable performance, so convenient approaches to prepare fouling-resistant membranes are always anticipated. Herein, we demonstrate the facile fabrication of antifouling polysulfone-block-poly(ethylene glycol) (PSF-b-PEG, SFEG) composite membranes. SFEG layer was coated onto macroporous supports and cavitated by immerging them in acetone/n-propanol following the mechanism of selective swelling induced pore generation. Thus-produced SFEG membranes possessed high permeance and excellent mechanical strength. Meanwhile, the structures and separation performances of the SFEG layers can be continuously tuned through simply changing swelling durations. More importantly, the hydrophilic PEG chains were spontaneously enriched onto the pore walls through swelling treatment, endowing intrinsic antifouling property to the SFEG membranes. Bovine serum albumin (BSA)/humic acid (HA) fouling tests proved the prominent fouling resistance of SFEG membranes, and the fouling resistance is expected to be long-standing because of the firm connection between PEG chains and PSF matrix by covalent bonding.     

聚砜超滤膜表面辐照改性研究

以聚砜为膜材料,聚乙二醇(PEG)为添加剂,采用浸入沉淀相转化法制备聚砜平板超滤膜,然后对实验制备的聚砜膜进行紫外辐照改性,考察了辐照对聚砜膜结构和性能的影响,研究了膜辐照前后断裂强度的变化,通过表面接触角测定仪、红外分析仪(FTIR)、扫描电镜(SEM)、改性膜的纯水通量和截留性能等方法来表征膜辐照前后的结构和性能变化.研究表明:聚砜膜断裂强度经辐照后变小,但降低幅度不大;在乙醇溶液中紫外辐照后,开始纯水通量提高而截留率降低,但降低幅度不大,时间增加到一定时通量又降低,截留率变化也不大;表面接触角随辐照时间的增长而减小,表明改性后膜表面的亲水性得到明显改善;通过FTIR分析证实在聚砜膜表面产生了新的官能团;SEM实验证实反应只发生在聚砜膜的表面而非膜内部.聚砜超滤膜经紫外辐照改性取得了良好的效果.     

Fouling of nanofiltration and ultrafiltration membranes applied for wastewater regeneration in the textile industry

Textile effluents usually contain high concentrations of inorganics as well as organics, and the therefore difficult to treat. Membrane processes can be used for many of these wastewaters in the textile industry. Two typical examples are discussed: (1) the use of nanofiltration for the treatment of exhausted dye baths, in view of water recycling, and (2) the use of ultrafiltration for the removal of spin finish from waste water resulting from rinsing of textile fibres. Both applications are in principle feasible, but in practice the process is negatively influenced by membrane fouling. In the first application, fouling is assumed to be caused by (ad)sorption of organic compounds, which has a large influence because of the high concentrations used in textile dyeing. Furthermore, the high salt concentrations result in a decrease of the effective driving force because of the high osmotic pressures obtained for typical dye baths. Experimental results are discussed, and the applicability of nanofiltration is related to the characteristics of the dye baths for different dyeing methods. In the second application, the concentration of organic compounds is relatively low, but because of the hydrophobic nature of the spin finish compounds, a significant effect of membrane fouling is expected. An improvement is suggested by using nanofiltration membranes instead of ultrafiltration membranes.     

Feasibility investigation of refinery wastewater treatment by combination of PACs and coagulant with ultrafiltration

This laboratory scale study investigated the effectiveness of ultrafiltration (UF) technology for treatment of refinery wastewater using powdered activated carbons (PACs) and coagulant. Flux decline, removal rates of total organic compounds (TOCs) and the possibilities of membrane cleaning during intermittent backwashing were studied. Addition of two kinds of typical PACs, PACs-1 and PACs-2, showed that the UF unit performance by adding PACs-2 was better than that of PACs-1. Suitable amounts were 20 mg.L⁻¹. When different kinds of coagulant, HYM, HY-3, HYC-601 and HCA, were added into the wastewater samples, respectively, it indicated that the HCA system was well resistant to membrane fouling. Investigation also showed that the UF unit performance could be significantly improved by simultaneously adding 15 mg.L⁻¹ of PACs-2 and 0.8 ml.L⁻¹ of HCA into the system. The removal rates of TOCs in the wastewater were over 99%.     

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.     

Lab and pilot scale investigations on membrane fouling during the ultrafiltration of surface water

In the combined laboratory and pilot plant investigation powder activated carbon dosing and inline coagulation were investigated for surface water from river Spree. The aim was to understand the fouling behaviour of this raw water and to understand and to identify strategies to minimize the irreversible fouling in this application. Trials with activated carbon showed significant differences in the adsorption of biopolymers on different types of carbon. Whereas the TOC removal was in the same range for both types the coarse carbon type showed very small removal of biopolymers. The effect of different types of coagulants, dosage and pH was investigated in a laboratory filtration set up. Samples were investigated by LC-OCD measurements for fractionation of DOC for raw water, flocculated water and permeate. The removal of biopolymers was possible with iron and alumina salts, however the alumina salts tend to remove humic acids as well and this results in a higher overall DOC removal. In the pilot plant the inline coagulation was investigated under actual site conditions. Whereas the results for the effect of coagulation and DOC removal were confirmed it turned out that aluminium coagulants give a significantly higher increase in differential pressure. The use of ferric coagulants at slightly acidic pH was thus identified as a robust method to achieve a stable performance of the ultrafiltration system at this site.     

A statistical method for quantifying the different fouling effects of three combined water sources on an ultrafiltration membrane

A simple statistical model has been developed to explain the fouling of an ultrafiltration (UF) membrane treating three mixed feedwater matrices. A tubular UF membrane operating under dead-end conditions, based at the Millennium Dome Water Recycling Plant, was used for this study. The feedwaters comprised surface water, greywater and groundwater, all having distinct quality differences. The analysis utilises the least-squares fit regression technique. Fouling, as manifested in the diurnal change in trans-membrane pressure (TMP), is related numerically to the volumes of the feedwaters, the mean TMP and the cross product of mean TMP with water volume. It was found that the impact of the recovered greywater on TMP was not statistically significant only due to the low daily volumes of this matrix generated, compared with those of the other sources. The model that best described the data was chosen on the basis of highest R² and lowest residual mean square, and demonstrated the surface water to be more fouling than the ground water by a factor, which is a function of the mean TMP.     

Direct drinking water treatment by spiral-wound ultrafiltration membranes

This paper presents the results of a research on direct drinking water treatment through an ultrafiltration pilot plant unit using spiral-wound membranes (3500 MWCO). The source of water is the Guarapiranga Reservoir, an eutrophicated water body located in the metropolitan region of São Paulo, Brazil. The data were collected during a period of almost 3400 h, from August 2005 to January 2006. The main objective of the study was to evaluate the membrane production capacity and contaminant removal efficiency. It was verified that the system was able to produce a high quality permeate with a flow close to the specified by the membrane manufacturer. The average permeate flow was 19.7 L.h⁻¹.m⁻², at 467 kPa and 25°C, with a global water recovery of almost 85%. The removal efficiencies for TOC, UV light absorption, and turbidity were 85%, 56%, and 95%, respectively. The results provide substantial evidence of the technical feasibility of spiral-wound UF membranes for direct drinking water treatment from euthrophicated sources, as an alternative for conventional drinking water treatment systems.     

Charged modified tight ceramic ultrafiltration membranes for treatment of cationic dye wastewater

Tight ceramic uitrafiltration membranes have been proven to exhibit good rejection performance for reactive dye wastewater at high temperatures because of their high thermal and chemical resistance.However,the application of ceramic membranes for the treatment of cationic dye wastewater is chal-lenging because of their surface charge.In this study,a ceramic membrane is modified by grafting aminosilane (KH-551) to enhance the positive charge of the membrane surface.The rejection perfor-mance of the charged modified ceramic membrane toward the methylene blue solution is significantly improved.The modification substance is bonded to the ceramic membrane surface via covalent bonding,which imparts good thermal stability.The modified ceramic membrane exhibits stable separation perfor-mance toward the methylene blue solution.Overall,this study provides valuable guidance for the adjust-ment of the ceramic membrane surface charge for treating industrial cationic dye wastewater.     

Surface modification of poly(vinylidene fluoride) film by remote Ar, H2, and O2 plasmas

The surface modification of poly(vinylidene fluoride) (PVDF) film induced by remote Ar, H₂, and O₂ plasmas have been investigated using contact angle measurement, X-ray photoelectron spectroscopy, and scanning probe microscope. The contact angle of water shows an improvement in the PVDF surface wettability during short plasma exposure time. Three remote plasmas treated PVDF sheet surfaces occurred dehydrofluorination and oxidation reactions simultaneously. Remote hydrogen plasma was the most effective in defluorination reactions and remote oxygen plasma was unfavorable to abstract fluorine atoms.     

Regeneration of Pd/TiO2 catalyst deactivated in reductive CCl4 transformations by the treatment with supercritical CO2, ozone in supercritical CO2 or oxygen plasma

Carbonaceous deposits formation was established as the primary reason of Pd/TiO₂ catalyst deactivation during reductive processing of CCl₄ to form hydrodechlorination and oligomerization products. Three methods of carbonaceous deposits elimination were tested: (1) extraction by supercritical CO₂, (2) oxidation by ozone in supercritical CO₂, and (3) low-temperature glow-discharge oxygen plasma treatment. Synchronic thermal analysis confirms effective carbonaceous deposits removal during regeneration by ozone or low temperature glow-discharge oxygen plasma; by XPS deep oxidation of surface Pd after oxidative treatment (by ozone or oxygen plasma) was found. Thus H₂ reduction was proposed as the second step making possible full regeneration of initial catalytic activity of Pd/TiO₂.     

Customization of ZrO2 loose/tight bilayer ultrafiltration membranes by reverse micelles-mediated aqueous sol-gel process for wastewater treatment

Two types of spherical zirconyl oxalate aqueous sols were successfully customized by a reverse micelles-mediated aqueous sol-gel process, and the sols were sequentially spin-coated on porous supports to prepare ZrO₂ loose/tight bilayer ultrafiltration membranes. After three times of spin-coating process, a defect-free ZrO₂ loose ultrafiltration membrane with pure water permeability of 110.5 ± 2.25 L m^?2 h^-1 bar^-1, molecular weight cut-off (MWCO) of 16.5 kDa and excellent rejection of up to 97.5 % for bovine serum albumin was fabricated. Then, the loose ultrafiltration membrane was used as a substrate to prepare ZrO₂ tight ultrafiltration membrane. Performances of tight ultrafiltration membrane regarding to permeability, retention of polyethylene glycol and treatment of dyes wastewater were evaluated. The tight ultrafiltration membrane with a thickness of 200 nm exhibited a pure water permeability of 22.5 ± 0.3 L m^-2 h^-1 bar^-1 and MWCO of 1150 Da. Additionally, the rejections of methyl red and methyl orange by the tight ultrafiltration membrane were both <65 %, while of alizarin red, direct red, bromocresol green and methyl blue achieved maximum values of 98.5 %, 99.2 %, 99.5 % and 99.6 %, respectively. The fouled membranes could restore the virgin performance for reuse by cleaning and low-temperature calcination.     

Properties of polyethersulfone ultrafiltration membranes modified by polyelectrolytes

This study reports on the surface modification of ultrafiltration membranes using the layer-by-layer (LbL) technique. The novelty of this work resides in the LbL assembly of charged polyelectrolytes by electrostatic adsorption directly onto the ultrafiltration membranes without any prior treatment of the surface. Polyethersulfone ultrafiltration membranes have been employed for the deposition of branched poly(ethyleneimine) and poly(sodium 4-styrene sulfonate) to create a thin polyelectrolyte film on their surface. The modified membranes are characterized by their permeability and molecular weight cut-off (MWCO) value. Experiments show that the deposited polyelectrolyte layer causes a decrease in the permeability due to the additional resistance of the layers. However, the MWCO value is shifted meaning a better rejection of the dextran solution is achieved. Thus, the LbL assembly of polyelectrolyte multilayers on the surface of the membrane makes it possible to convert a membrane with open structure to a membrane with denser active layer.     

CO2压缩机密封气的回收改造

通过增设一台水环式压缩机将放空的密封CO2气回收,解决氨富余的问题,增加装置负荷.     

CO2—21世纪的新碳源

本文对21世纪的一种新碳源CO     

Formation of unzipped carbon nanotubes by CF4 plasma treatment

In this paper the evidence of the formation of short and unzipped single-walled carbon nanotube (SWCNTs) through a facile and scalable plasma method is reported. The approach consists of a CF₄ RF plasma treatment of SWCNTs; transmission electron microscopy as well as atomic force microscopy showed the evidence of the attainment of unzipped SWCNTs chemical microanalysis has been used to demonstrate the fluorination of such nanostructures. The production of such nanostructured architectures may allow for their large scale integration into polymer based nanocomposites.     

Spray coating of polysulfone/poly(ethylene glycol) block polymer on macroporous substrates followed by selective swelling for composite ultrafiltration membranes

Polysulfone(PSF) is extensively used for the production of ultrafiltration(UF) membranes thanks to its high strength,chemical stability,and good processibility.However,PSF is intrinsically hydrophobic,and hydrophilic modification is always required to PSF-based membranes if they are intended to be used in aqueous systems.Facile strategies to prepare hydrophilic PSF membranes are thus highly demanded.Herein we spray coat a PSF-based amphiphilic block polymer onto macroporous substrates followed by selective swelling to prepare flat-sheet PSF UF membranes.The polymer is a triblock polymer containing PSF as the majority middle block tethered with shorter block of polyethylene glycol(PEG) on both ends,that is,PEG-b-PSF-b-PEG.We use the technique of spray coa ting to homogeneously dispense diluted triblock polymer solutions on the top of macroporous supports,instantly resulting in uniform,defect-free polymer coating layers with the thickness down to ～1.2 μm.The bi-layered composite structures are then immerged in ethanol/acetone mixture to generate mesoscale pores in the coating layers following the mechanism of selective swelling-induced pore generation,thus producing composite membranes with the mesoporous triblock polymer coating as the selective layers.This facile strategy is free from additional hydrophilic modification and much smaller dosages of polymers are used compared to conventional casting methods.The pore sizes,porositie s,hydrophilicity,and consequently the separation properties of the membranes can be flexibly tuned by changing the swelling duration and the composition of the swelling bath.This strategy combining spray coating and selective swelling is upscalable for the production of highperformance PSF UF membranes.     

Morphological and separation performance study of polysulfone/titanium dioxide (PSF/TiO2) ultrafiltration membranes for humic acid removal

In this study, polysulfone (PSF) hollow fiber membranes with enhanced performance for humic acid removal were prepared from a dope solution containing PSF/DMAc/PVP/TiO₂. The main reason for adding titanium oxide during dope solution preparation was to enhance the antifouling properties of membranes prepared. In the spinning process, air gap distance was varied in order to produce different properties of the hollow fiber membranes. Characterizations were conducted to determine membrane properties such as pure water flux, molecular weight cut off (MWCO), humic acid (HA) rejection and resistance to fouling tendency. The results indicated that the pure water flux and MWCO of membranes increased with an increase in air gap distance while HA retention decreased significantly with increasing air gap. Due to this, it is found that the PSF/TiO₂ membrane spun at zero air gap was the best amongst the membranes produced and demonstrated > 90% HA rejection. Analytical results from FESEM and AFM also provided supporting evidence to the experimental results obtained. Based on the anti-fouling performance investigation, it was found that membranes with the addition of TiO₂ were excellent in mitigating fouling particularly in reducing the fouling resistances due to concentration polarization, cake layer formation and absorption.     

Influence of Ca and Na ions in backwash water on ultrafiltration fouling control

The effect of calcium and sodium in backwash water on the fouling control of ultrafiltration is investigated on a bench scale. Besides permeate of ultrafiltration and demineralized water, solutions with different calcium or sodium concentrations were used for backwash. The results show that backwashing with demineralized water is better than with permeate of ultrafiltration. The backwash efficiency decreases when calcium and sodium are added in demineralized water for backwash. That is probably because the presence of calcium and sodium in backwash water increases the Ca-bridging effect between the negatively charged membrane and the negatively charged NOM, and compresses the double layer of the membrane and the NOM, leading to a strong adhesion force on the membrane.