Use of reverse osmosis membranes to remove perfluorooctane sulfonate (PFOS) from semiconductor wastewater

Perfluorooctane sulfonate (PFOS) and related substances are persistent, bioaccumulative, and toxic, and thus of substantial environmental concern. PFOS is an essential photolithographic chemical in the semiconductor industry with no substitutes yet identified. The industry seeks effective treatment technologies. The feasibility of using reverse osmosis (RO) membranes for treating semiconductor wastewater containing PFOS has been investigated. Commercial RO membranes were characterized in terms of permeability, salt rejection, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and membrane surface zeta potential (streaming potential measurements). Filtration tests were performed to determine the membrane flux and PFOS rejection. Over a wide range of feed concentrations (0.5 - 1500 ppm), the RO membranes generally rejected 99% or more of the PFOS. Rejection was better for tighter membranes, but was not affected by membrane zeta potential. Flux decreased with increasing PFOS concentration. While the flux reduction was severe for a loose RO membrane probably due to its higher initial flux, very stable flux was maintained for tighter membranes. At a very high feed concentration (about 500 ppm), all the membranes exhibited an identical stable flux. Isopropyl alcohol, present in some semiconductor wastewaters, had a detrimental effect on membrane flux. Where present it needs to be removed from the wastewater prior to using RO membranes.     

Cake-enhanced concentration polarization: a new fouling mechanism for salt-rejecting membranes

Results from well-controlled colloidal fouling experiments with reverse osmosis (RO) and nanofiltration (NF) membranes suggest the existence of a new source of flux decline for salt-rejecting membranes-cake-enhanced osmotic pressure. The physical mechanisms leading to this enhanced osmotic pressure are a combination of hindered back-diffusion of salt ions and altered cross-flow hydrodynamics within colloidal deposit layers, which lead to an enhanced salt concentration polarization layer. A model that accounts for both hindered diffusion of salt ions and altered hydrodynamics within colloidal deposit ("cake") layers is presented. The model successfully links permeate flux and salt rejection to cake-enhanced concentration polarization and provides new insight into the mechanisms through which salt-rejecting membranes foul. Experimental data support the model calculations and highlight the role of enhanced concentration polarization phenomena in the performance (i.e., water flux and salt rejection) of polymeric thin-film composite RO/NF membranes in environmental applications.     

Ultrafiltration and Reverse Osmosis of the Waste Water from Sweet Potato Starch Process

The primary waste water discharged from pilot plant scale sweet potato starch manufacturing was processed by ultrafiltration (UF). The UF permeate was then concentrated by reverse osmosis (RO). Growth of microorganisms in waste water would reduce the flux of UF. When the feed velocity of UF was higher than 2.5 m/sec, its positive effect on permeation rate was no longer existent. Relationships between transmembrane pressure and permeate flux were linear at all tested concentrations. UF filtered protein and calcium reduced two-thirds of the biochemical oxygen demand (BOD) and half the chemical oxygen demand (COD) at weight concentration ratio (WCR) of 5. With RO the rest of the components were recovered and BOD and COD were reduced more than 99% and 98%, respectively, at a WCR of 6.     

Concentration of Skim Milk by a Cascade Comprised of Ultrafiltration and Nanofiltration: Investigation of the Nanofiltration of Skim Milk Ultrafiltration Permeate

In order to reach a high volume reduction ratio (VRR) prior to drying of skim milk, a membrane cascade comprising of an ultrafiltration (UF) coupled with a nanofiltration (NF) can be applied. The present study investigated the impact of processing (filtration temperature, transmembrane pressure (TMP)) and product (feed pH) parameters on the NF of skim milk UF permeate. It could be shown that a low filtration temperature of 10 °C is more advantageous in terms of flux stability and rejection of the solute fraction as compared to higher filtration temperatures up to 45 °C. The solution pH did not affect permeate flux and lactose retention. However, in order to avoid calcium losses, it is more favorable to conduct the concentration at a pH of 6.8 instead of at a lower pH of 5. The application of a higher TMP (up to 4 MPa) enhances permeate flux and VRR as well as solute rejection during concentration of UF permeate. It was also shown that the retention of solutes decreases towards the end of the concentration process. As a consequence, the achievement of high final VRR must be weighed against increased product losses at the end.     

Fouling of nanofiltration, reverse osmosis, and ultrafiltration membranes by protein mixtures: the role of inter-foulant-species interaction

Protein fouling of nanofiltration (NF), reverse osmosis (RO), and ultrafiltration (UF) membranes by bovine serum albumin (BSA), lysozyme (LYS), and their mixture was investigated under cross-flow conditions. The effect of solution chemistry, membrane properties, and permeate flux level was systematically studied. When the solution pH was within the isoelectric points (IEPs) of the two proteins (i.e., pH 4.7-10.4), the mixed protein system experienced more severe flux decline compared to the respective single protein systems, which may be attributed to the electrostatic attraction between the negatively charged BSA and positively charged LYS molecules. Unlike a typical single protein system, membrane fouling by BSA-LYS mixture was only weakly dependent on solution pH within this pH range, and increased ionic strength was found to enhance the membrane flux as a result of the suppressed BSA-LYS electrostatic attraction. Membrane fouling was likely controlled by foulant-fouled-membrane interaction under severe fouling conditions (elevated flux level and unfavorable solution chemistry that promotes fouling), whereas it was likely dominated by foulant-clean-membrane interaction under mild fouling conditions. Compared to nonporous NF and RO membranes, the porous UF membrane was more susceptible to dramatic flux decline due to the increased risk of membrane pore plugging. This study reveals that membrane fouling by mixed macromolecules may behave very differently from that by typical single foulant system, especially when the inter-foulant-species interaction dominates over the intra-species interaction in the mixed foulant system.     

Role of soluble microbial products (SMP) in membrane fouling and flux decline

Soluble microbial products (SMP), a significant component of effluent organic matter (EfOM), play an important role in membrane fouling and flux decline in wastewater reclamation/reuse applications. The SMP compounds of a microbial origin are derived during biological processes of wastewater treatment. They exhibit the characteristics of hydrophilic organic colloids and macromolecules. These high molecular weight compounds play an important role in creating high resistance of the membrane, leading to a reduction of permeate flux. The SMP fouling of RO, NF, and tight UF membranes is associated with formation of a cake/gel layer due to size (steric) exclusion. FTIR spectra of SMP- and EfOM-fouled membranes exhibited foulants' composition, consisting of polysaccharides, proteins, and/or aminosugar-like compounds. This finding reveals the important role of the SMP components as factors in membrane fouling and flux decline associated with EfOM source waters. Solids retention time (SRT) affects the characteristics and amounts of SMP, however, SRT did not affect flux decline trends of RO and NF membranes.     

Decolorization of vegetable oils by membrane processing

Membrane decolorization studies of chlorophyll added sunflower oil and crude soybean oil were conducted in a batch membrane cell using two polymeric composite membranes (NTGS-2100 and NTGS-1100), and one polyethylene microfiltration membrane (PE-30). NTGS-2100 membrane could remove up to 96% and 72% chlorophyll from the undiluted and oil-hexane (50 wt%) solutions, respectively. Permeate oil flux was very low when undiluted oil was used as feed, but improved many fold by diluting with hexane. NTGS-1100 membrane gave higher permeate flux compared to NTGS-2100, but showed reduced rejection. Absorbance spectra of crude soybean oil and the permeate in the 350-550 nm range showed a greater degree of decolorization by polymeric composite membranes. PE-30 membrane showed insignificant rejection of color compounds. The permeate of conventionally bleached soybean oil showed a reduction in extinction coefficients at 232 and 270 nm, indicating possible rejection of dienes and trienes by the composite polymeric membranes. The membrane process was effective in reducing the color compounds in crude vegetable oils besides offering many advantages over the conventional process.     

Ultrafiltration and reverse osmosis for clarification and concentration of fruit juices at pilot plant scale

The process of ultrafiltration of raw juices (peach, pear, apple and mandarin) through tubular polysulphone membranes (8 kDa) and finally concentrated by reverse osmosis membranes of tubular composite polyamide film (99 g/100 g NaCl rejection) with filtration area of 0.9 m² was studied. Furthermore, in order to obtain a higher permeate flow, the fluids were previously treated with commercial pectinolytic enzyme.The following parameters were analyzed: permeate flow, soluble solids, viscosity, density, pH, acidity, formol index, starch, pulp content, color and presence of pectin. The use of a pectinolytic enzyme provides increased permeate flux of approximately 40%, retaining the juice properties. The highest total soluble solids content was clarified peach juice from 12.2 °Brix concentrated up to 30.5 and 21.52 °Brix by using RO with transmembranes pressures of 4 and 2 MPa respectively.The results show a cross-flow velocity (1.8 m/s) which corresponds with Reynolds number that is on the lower border of a laminar flow and above of transition rate (2090 < Re < 2900). Also the (VCF) for mandarin (1.49), pear (1.53), apple (1.56) and peach (1.58) was obtained for RO process. The membranes used were characterized morphologically using scanning electron microscopy.     

膜分离技术及其在果汁加工中的应用

介绍了应用于果汁加工中的膜分离过程(微滤、超滤、纳滤、反渗透、电渗析、膜蒸馏)及其分离性能。由渗透通量和截留率表征,在果汁加工中,膜分离技术可用于果汁的澄清、浓缩、脱气、脱苦、脱酸、脱色等。     

Separation of Sucrose and Reducing Sugar in Cane Molasses by Nanofiltration

Recovery of sugars from cane molasses is a promising approach to increase the added value of molasses and reduce its environmental pollution. In this work, for the first time, nanofiltration (NF) was used for the separation of sucrose and reducing sugar in cane molasses by a cascade diafiltration-concentration process. The retention difference between sucrose and reducing sugar by all the tested NF membranes was not distinct at 25 °C, while due to the thermal-induced pore size change and enhanced solute diffusivity, the NF retention behavior changed significantly at 60 °C, and the DL membrane with a sucrose retention of 96% and a reducing sugar retention 5% was selected for the process optimization and modeling. High temperature (55–60 °C), low permeate flux (below 15 Lm^?2 h^?1), and high sugar concentration resulted in a low retention of reducing sugar due to the dominant diffusive mass transfer, which was desirable for the molasses separation by NF. Mathematical modeling could well predict the diafiltration and concentration processes if using right sugar retention data. The deviations between prediction lines and experimental data in the cross-flow filtration of real solution were mainly caused by the permeate flux variation rather than membrane fouling. After diafiltration, the ratio of sucrose in total molasses sugar increased from 76.1 to 87.9%, while in the permeate of the second concentration step, the ratio of sucrose was only 2.4%. Thus, the retentate of diafiltration could be directly used for sucrose crystallization to avoid the accumulation of reducing sugar and salts, and the permeate of the second concentration step could be concentrated by NF270 at room temperature to produce syrup drinking.     

Evaluation of membrane fouling for in-line filtration of oil sands process-affected water: the effects of pretreatment conditions

Membrane filtration is an effective reclamation option for oil sands process-affected water (OSPW). However, fresh OSPWs contain suspended solids and inorganic constituents in suspended and dissolved forms that can severely foul membranes. Pretreatment of OSPW with coagulation-flocculation (CF) was investigated to determine the effects of different coagulant aids (anionic, cationic, and nonionic polymers) on membrane surface properties and fouling. Our results showed that CF pretreatment effectively enhanced nanofiltration (NF) and reverse osmosis (RO) membrane permeate flux and salt rejection ratio through reducing membrane fouling. It was shown that coagulants and coagulant aids applied to OSPW feedwater can affect membrane physicochemical properties (surface hydrophilicity, zeta potential, and morphology), membrane performance, and the fouling indexes. Membrane rejection of ionic species increased significantly with the inclusion of an anionic coagulant aid and slightly with a cationic coagulant aid. Among three coagulant aids tested, anionic coagulant aids led to the most enhanced membrane performance through increasing membrane surface negativity and decreasing the formation of a fouling layer. Conversely, although cationic coagulant aids were the most effective in reducing OSPW turbidity, the application of cationic coagulant aids promoted the adsorption of foulants on membrane surfaces.     

Rejection efficiency of water quality parameters by reverse osmosis and nanofiltration membranes

The objective of this study was to evaluate the effectiveness of reserve osmosis (RO) and nanofiltration (NF) membranes, under various solution chemistries, on water quality. The effects of organic carbon, divalent and monovalent cations, bacteria, and permeate drag on the rejection efficiencies of three different membranes were investigated through a series of laboratory bench-scale experiments. Quantitative models were successfully developed to predict the rejection of turbidity, divalent and monovalent cations, ultraviolet absorbance at 253.7 nm (UV254), and dissolved organic carbon (DOC) by membrane filtration. It was found that mechanical sieving (measured as molecular weight cutoff, MWCO) and electrostatic interactions were the most significant parameters since they were found to be important in nearly all models developed. For negatively charged membranes, under high ionic strength solution environments that repress electrostatic interaction between charged compounds and membranes, passage of compounds was mainly a function of size exclusion (i.e. MWCO). Further, of the feedwater parameters tested, bacteria concentration was observed to be the most significant influence on UV254, divalent cation and monovalent cation rejections. The developed models revealed that interactions between feedwater composition and membrane properties impacted the rejection efficiency of membranes as significantly as water composition and membrane properties individually.     

聚偏氟乙烯光致热纳米纤维膜的制备及其性能

为解决减压膜蒸馏过程中温度极化现象造成膜渗透通量下降的问题,以聚偏氟乙烯(PVDF)为成膜聚合物,引入具有红外致热效应的功能性纳米掺锑二氧化锡(ATO),采用静电纺丝技术制备了PVDF/ATO纳米纤维膜,并对其进行热压处理优化纤维结构和孔径,然后探讨ATO质量分数、热压温度对纤维膜结构和性能的影响,并测试了红外辐照下纤维膜的致热效果和膜蒸馏性能。结果表明:PVDF/ATO纳米纤维膜经170 ℃热压处理后,具有更优异的综合性能;当ATO质量分数为3%时,PVDF/ATO纳米纤维膜经120 s红外辐照后,表面温度升高了40 ℃以上,其膜蒸馏渗透通量相对于原膜从12 L/(m ²·h)提高到22 L/(m ²·h),并且在5 h运行时间内,截盐率保持在99%以上。     

Desalination of mixed tannery effluent with membrane bioreactor and reverse osmosis treatment

A limiting factor for the reuse and recycling of treated tannery wastewater for irrigation and other uses is the high salt content, which persists even after conventional treatment. Reverse osmosis (RO) membrane treatment has been shown to significantly reduce the salt contents of tannery effluents. However, the high organic content of tannery effluent leads to rapid scaling and biofouling of RO membranes with a consequent reduction in flux rates and performance. Membrane bioreactors (MBR) have been shown to be highly effective in the removal of organic pollutants and suspended solids from tannery effluent. This research investigated the use of a combined MBR and RO treatment process to treat tannery effluents to an acceptable level for irrigation purposes. The MBR was operated at 17-20 h retention time, at a F/M ratio of 0.52 kg COD x kg SS(-1) x day(-1) and a volumetric loading rate of 3.28 kg COD x m(-3) x day(-1). This treatment reduced the COD, BOD, and ammonia concentrations of the effluent by 90-100%. The MBR was shown to be an excellent pretreatment prior to RO technology, due to the high removal efficiency of organic compounds and suspended solids, with average concentrations of 344 mg x L(-1) COD and 20 mg x L(-1) BOD achieved in the permeate. RO treatment reduced the salt content of the MBR permeate by up to 97.1%. The results of the research demonstrated that the MBR system developed was appropriate for the treatment of tannery effluents and, in combination with the RO treatment, reduced the salt content to acceptable levels for irrigation. The MBR pretreatment reduced bio-fouling and scaling of subsequent RO treatment and improved the overall performance of the RO unit. It is believed that this is the first investigation of a combined MBR and RO treatment for tannery effluents. This research provided data for an outline design of a full-scale MBR and RO plant with a treatment capacity of 5000 m3 per day for mixed tannery effluents.     

Deacidification of Coconut Oil by Membrane Filtration

Ultrafiltration (UF) of coconut oil was carried out using a Millipore membrane cell at different pressures (0.1–0.4 MPa) and with different molecular weight cutoff membranes, that is,YM-1 (1 kDa), YM-3 (3 kDa), YM-10 (10 kDa), YM-30 (30 kDa), and PLTK-30 (30 kDa). Reduction of free fatty acids (FFAs) was 93.6%, 92.7%, 83.5%, 82.6%, and 81.6% with ethanol, methanol, acetone, n-propanol, and isopropyl alcohol, respectively, in three-stage filtration. The effects of temperature and applied pressure on the permeate flux and oil rejection were also studied with membranes using multistage filtration. As pressure increased from 0.1 to 0.4 MPa, the permeate flux and oil rejection increased linearly. A significant reduction of FFA was observed, which is in proportional with the amount of solvent in the feed used. The oil loss was less at lower temperature (25 °C) and pressure (0.2 MPa). Using PLTK 30 membrane with three-stage filtration, reduction of FFA was achieved up to 93% and 94% with methanol and ethanol solvents, respectively.     

Ultrafiltration and Reverse Osmosis Recovery of Limonene from Citrus Processing Waste Streams

Commercial ultrafiltration (UF) and reverse osmosis (RO) membranes were used to concentrate the terpene, limonene, present in cold pressed oil centrifuge effluent and molasses evaporator condensate. UF membrane rejections were 78–97% for mixtures with initial limonene concentrations from 0.04–0.6%v/v. RO membrane rejection of limonene ranged from 87–99% for feed streams containing 0.06–0.23% limonene. Initial membrane flux rates for centrifuge effluents were in the range 10–100 kg/m²/hr. Evaporator condensate fluxes were higher, 25–400, while pure water rates ranged from 25 (RO) to 1000 kg/m²/hr (UF). Contact with limonene adversely affected membrane flux rates in decreasing order of severity: polysulfone > cellulose acetate > teflon-type.     

Comprehensive bench- and pilot-scale investigation of trace organic compounds rejection by forward osmosis

Forward osmosis (FO) is a membrane separation technology that has been studied in recent years for application in water treatment and desalination. It can best be utilized as an advanced pretreatment for desalination processes such as reverse osmosis (RO) and nanofiltration (NF) to protect the membranes from scaling and fouling. In the current study the rejection of trace organic compounds (TOrCs) such as pharmaceuticals, personal care products, plasticizers, and flame-retardants by FO and a hybrid FO-RO system was investigated at both the bench- and pilot-scales. More than 30 compounds were analyzed, of which 23 nonionic and ionic TOrCs were identified and quantified in the studied wastewater effluent. Results revealed that almost all TOrCs were highly rejected by the FO membrane at the pilot scale while rejection at the bench scale was generally lower. Membrane fouling, especially under field conditions when wastewater effluent is the FO feed solution, plays a substantial role in increasing the rejection of TOrCs in FO. The hybrid FO-RO process demonstrated that the dual barrier treatment of impaired water could lead to more than 99% rejection of almost all TOrCs that were identified in reclaimed water.     

REVERSE OSMOSIS CONCENTRATION of APPLE JUICE: FLUX and FLAVOR RETENTION BY CELLULOSE ACETATE and POLYAMIDE MEMBRANES

Apple juice was concentrated in a pilot scale reverse osmosis unit using two commercial spiral wound cellulose acetate membranes with 97% (CA-97) and 99% (CA-99) NaCl rejection ratings and an experimental polyamide (PA-99) membrane with 99% salt rejection rating. Flux and concentration rates were higher for the PA-99 membrane than for the CA membranes. Gas chromatographic analysis of feed, permeate, and concentrate samples was undertaken and a mass balance of odor-active volatiles was performed. the PA-99 membrane retained 45% of the total odor-active volatiles while the CA-99 retained 23 %. Acetates were not found to increase when apple juice was concentrated with the cellulose acetate membrane. Retention of individual aroma compounds for the CA-99 and PA-99 membrane was rationalized using polar, nonpolar, and steric parameters.     

Chemical characterization by gas chromatography-mass spectrometry and inductively coupled plasma-optical emission spectroscopy of membrane permeates from an industrial dairy ingredient production used as process water

Reusing reverse osmosis (RO) membrane permeate instead of potable water in the dairy industry is a very appealing tactic. However, to ensure safe use, the quality of reclaimed water must be guaranteed. To do this, qualitative and quantitative information about which compounds permeate the membranes must be established. In the present study, we provide a detailed characterization of ultrafiltration, RO, and RO polisher (ROP) permeate with regard to organic and inorganic compounds. Results indicate that smaller molecules and elements (such as phosphate, but mainly urea and boron) pass the membrane, and a small set of larger molecules (long-chain fatty acids, glycerol-phosphate, and glutamic acid) are found as well, though in minute concentrations (<0.2 µM). Growth experiments with 2 urease-positive microorganisms, isolated from RO permeate, showed that the nutrient content in the ROP permeate supports limited growth of 1 of the 2 isolates, indicating that the ROP permeate may not be guaranteed to be stable during protracted storage.     

Buffering curves of ideal whey fractions obtained from a cascade membrane separation process

Skimmed milk was fractionated via a cascade system: Graphic plotting of microfiltration (MF); ultrafiltration (UF); nanofiltration (NF); and reverse osmosis (RO). The buffering curves of each fraction were studied over the pH range 4–7. Depending on their composition, the individual permeate streams showed different buffering capacity values and pH ranges where the buffering occurred. The concentration of active buffering substances in the permeates decreased (in mmol/L) from ~26.6 (MF) to ~17.4 (UF) to 1.39 (NF) to 0.07 (RO). Contributions to the total buffering capacity for MF permeate, which represents the serum phase of milk, were ~37% from whey proteins and ~63% from milk salts (especially citrates, phosphates and carbonates) including lactose and water.