Separate and Concentrate Lactic Acid Using Combination of Nanofiltration and Reverse Osmosis Membranes

The processes of lactic acid production include two key stages, which are (a) fermentation and (b) product recovery. In this study, free cell of Bifidobacterium longum was used to produce lactic acid from cheese whey. The produced lactic acid was then separated and purified from the fermentation broth using combination of nanofiltration and reverse osmosis membranes. Nanofiltration membrane with a molecular weight cutoff of 100–400 Da was used to separate lactic acid from lactose and cells in the cheese whey fermentation broth in the first step. The obtained permeate from the above nanofiltration is mainly composed of lactic acid and water, which was then concentrated with a reverse osmosis membrane in the second step. Among the tested nanofiltration membranes, HL membrane from GE Osmonics has the highest lactose retention (97 ± 1%). In the reverse osmosis process, the ADF membrane could retain 100% of lactic acid to obtain permeate with water only. The effect of membrane and pressure on permeate flux and retention of lactose/lactic acid was also reported in this paper.     

Membrane processes used for separation of effluents from wire productions

Metal wires are produced from different metals using drawing methods. The metal used influences both the technology applied and the composition of effluents generated during wires production. Ultrafiltration and nanofiltration are used for the separation of waste emulsions from cable factories. Membrane distillation was proposed for the treatment of acidic saline wastewater generated during steel wire manufacturing (etching). The possibility of the previously mentioned processes application for water reuse is presented. The application of poly(vinylidene fluoride) (PVDF) membranes (FP 100) with the molecular weight cut-off (MWCO) of 100 kDa in the ultrafiltration process resulted in the reduction of 99 % of oil and lubricants in the treated emulsions and allowed complete removal of suspended solids and colloidal substances. Such pre-treated emulsion was subsequently purified by nanofiltration (NF-90-2540) and a 98 % rejection of copper ions was achieved, resulting in a decrease of the permeate electrical conductivity from 3200 μS cm⁻¹ to 260 μS cm⁻¹. The obtained permeate was suitable for preparation of fresh oil emulsion utilized for lubrication in the wire drawing process. The spent etching baths (from steel wire production), which mainly contained FeSO₄ and about 1 mass % of sulfuric acid, were separated by membrane distillation. The obtained permeates were: clean water with electrical conductivity at a level of 3–5 μS cm⁻¹. Concentrates (190–200 g of Fe per L) from the MD process were cooled to 295 K, which enabled the FeSO₄ crystallization. Application of the above-mentioned membrane processes allows producing high quality product water, over 90 % of water was recovered from the treated wastewaters. Presented at the 35th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 26–30 May 2008.     

A critical flux to avoid biofouling of spiral wound nanofiltration and reverse osmosis membranes: Fact or fiction?

The relation between biofouling and membrane flux in spiral wound nanofiltration and reverse osmosis membranes in drinking water stations with extensive pretreatment such as ultrafiltration has been studied. The flux – water volume flowing through the membrane per unit area and time – is not influencing the development of membrane biofouling. Irrespective whether a flux was applied or not, the feed spacer channel pressure drop and biofilm concentration increased in reverse osmosis and nanofiltration membranes in a monitor, test rigs, a pilot scale and a full-scale installation. Identical behavior with respect to biofouling and feed channel pressure drop development was observed in membrane elements in the same position in a nanofiltration installation operated with and without flux. Calculation of the ratio of diffusive and convective flux showed that the diffusive flux is considerably larger than the convective flux, supporting the observations that the convective flux due to permeate production is playing an insignificant role in biofouling. Since fouling occurred irrespective of the actual flux, the critical flux concept stating that “below a critical flux no fouling occurs” is not a suitable approach to control biofouling of spiral wound reverse osmosis and nanofiltration membranes.     

Electrochemical technologies combined with membrane filtration

The aim of this article is to review the recent progress in the coupling of membrane separation and electrochemical technologies for water treatment. Process integration strategies have been classified in three groups. The first group deals with electrocoagulation and electrooxidation as pretreatment of membrane separation, in most cases aimed at reducing membrane fouling and decay of permeate flux of porous ultrafiltration membranes. The second group is dedicated to electrooxidation as remediation treatment for nanofiltration and reverse osmosis concentrates, which accumulate priority pollutants and emerging contaminants. Finally, the article evaluates the optimal integration of technologies using process systems engineering tools, for producing a single purified water stream, considering not only the minimization of the energy consumption but also of the total costs. Overall, it is concluded that the preconcentration strategy provides a remarkable enhancement of electrooxidation performance to degrade persistent pollutants.     

A study of selected phytoestrogens retention by reverse osmosis and nanofiltration membranes - the role of fouling and scaling

Fouling and scaling are common phenomena that accompany membrane filtration and are caused by the presence of organic and inorganic matter in water, which may affect the removal of low-molecular mass organic micropollutants. Comparative filtration of deionized water containing selected phytoestrogens (biochanin A, daidzein, genistein, and coumestrol) was carried out using one new membrane and one contaminated with organic or inorganic matter. Two commercial Osmonics DS membranes were selected for the research, reverse osmosis DS3SE and nanofiltration DS5DK. Filtration was carried out in the dead-end mode. Higher removal of phytoestrogens was caused by reverse osmosis and retention depended on the molar mass of the compound. The decrease in membrane efficiency associated with fouling or scaling brings about an increase in the retention coefficient of phytoestrogens during both reverse osmosis and nanofiltration. The highest increase in phytoestrogen retention was found for the nanofiltraton membrane which was more susceptible to fouling than the osmotic one. This confirms the effect of membrane porosity on the phenomenon studied. The increase in micropollutants removal observed after fouling or scaling was caused by the modification of the membrane surface, hindered diffusion of the compound, and intensified or limited adsorption of micropollutants on the membrane surface.     

The separation potential of pervaporation : Part 2. Process design and economics

Pervaporation is a relatively complex process compared to other membrane processes like reverse osmosis for two reasons:— the process is sensitive to pressure losses at the permeate side— the evaporation enthalpy has to be transferred to the membrane surface (permeate side).Selectivity and flux can decrease markedly in case of hindered permeate flow. This is demonstrated by numerical design calculations of hollow-fiber modules. The calculations indicate that optimal fiber dimensions of hollow-fiber pervaporation modules should be much larger than those employed in RO and gas permeation modules.In principle, several alternatives exist for the supply of the evaporation enthalpy. The most economical solution seems to be to draw this energy from the liquid and to maintain the operating temperature level by a combination of modules and heat-exchangers in series. An alternative is the sweeping of the permeate by a partially condensing, and with respect to the permeate immiscible, carrier vapor. Since the latent heat of the carrier vapor can be utilized only partially, this concept will not be economically competitive.Pervaporation has a wide range of possible applicatio for this reasons it is impossible to discuss the economics of pervaporation in general. In this paper the separation of benzene/cyclohexane, an azeotropic system with similar vapor pressures of the components, has been chosen as an example. But even such a limited discussion reveals tendencies which seem to be generally valid:1.Pervaporation processes consisting of several stages (cascade) cannot compete with conventional separation processes like extractive distillation.2. Hybrid processes like a combination of extractive distillation, pervaporation are very promising, especially in cases where high product purities required     

Ultrafiltration of stable oil-in-water emulsion by polysulfone membrane

This paper focuses on treatment of oily wastewater coming out from the post-treatment unit of petroleum industries where finely divided oil droplets are uniformly dispersed in large volumes of water. Polysulfone (PSf) membranes which had been modified for higher porosity and hydrophilicity through the use of additives such as polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) were used for removal of oil from the oily wastewater. The performances of different PSf membranes were evaluated by treating with pure water as well as with laboratory made oil-in-water (o/w) emulsion. Experiments were carried out with 12 such membranes in a semi-batch filtration cell made of Teflon and the influence of operating conditions such as transmembrane pressure and feed properties such as initial oil concentration and pH of feed solution on membrane performance were investigated. Results show that all the parameters play a key role in permeate flux as well as percent oil separation. Also change in morphological properties of membranes due to addition of different molecular weight PVP and PEG are found to have a significant influence on the permeate flow rate and hence subsequent oil removal. The experimental results showed that oil retentions of almost all the membranes were over 90% and oil concentration in the permeate was below 10 mg/L, which met the requirement for discharge. It was concluded that the ultrafiltration (UF) membranes developed in the study were reasonably resistant to fouling and hence the developed PSf membranes may be considered feasible in treating oily wastewater.     

Biofouling in spiral wound membrane systems: Three-dimensional CFD model based evaluation of experimental data

A three-dimensional (3D) computational model describing fluid dynamics and biofouling of feed channels of spiral wound reverse osmosis and nanofiltration membrane systems was developed based on results from practice and experimental studies. In the model simulations the same feed spacer geometry as applied in practice and the experimental studies was used. The 3D mathematical model showed the same trends for (i) feed channel pressure drop, (ii) biomass accumulation, (iii) velocity distribution profile, resulting in regions of low and high liquid flow velocity also named channeling. The numerical model predicted a dominant biomass growth on the feed spacer, consistent with direct in situ observations on biofouling of spiral wound membrane modules and monitors using Magnetic Resonance Imaging (MRI). The model confirms experimental results that feed spacer fouling is more important than membrane fouling. The paper shows that mathematical modeling techniques have evolved to a stage that they can be used hand-in-hand with experiments to understand the processes involved in membrane fouling.     

Comparison of membrane processes with distillation for alcohol/water separation

The overall objectives of this study were to summarize and evaluate the performance of currently available membranes for purification of fermentation alcohol and to compare the economics of membrane processes with a modern-day energy-efficient distillation scheme.Literature survey showed that very little work had been done on the development of membrane processes for alcohol concentration.Based on laboratory work, it was found that the present-day thin-film composite desalination membranes can be used for partial concentration of beer solution to about 20 to 30% alcohol concentration. The water permeation coefficient for these membranes in reverse osmosis with 7.6% alcohol feed at 60 atm was about 10 kg/m²-day-atm (2 lb/ft²-day-atm).Due to the high osmotic pressures of ethanol/water mixtures, reverse osmosis can be used only for the initial concentration of beer solution and for the final dehydration of 95% alcohol to produce 199 proof alcohol. Thus, a distillation unit would have to be used for the intermediate concentration of alcohol solution. Membrane concentration schemes using distillation for intermediate concentration were prepared for comparison with a conventional distillation process. Based on preliminary analysis it was concluded that while the capital cost of the membrane-augmented distillation schemes can be significantly than that of the conventional system, the annualized cost of these schemes will be approximately equal to that for distillation. The capital and the annualized costs of the membrane process for the final dehydration of alcohol can be significantly lower than those for the conventional dehydration still.     

Experimental study of desalination using direct contact membrane distillation: a new approach to flux enhancement

New membrane distillation configurations and a new membrane module were investigated to improve water desalination. The performances of three hydrophobic microporous membranes were evaluated under vacuum enhanced direct contact membrane distillation (DCMD) with a turbulent flow regime and with a feed water temperature of only 40 °C. The new configurations provide reduced temperature polarization effects due to better mixing and increased mass transport of water due to higher permeability through the membrane and due to a total pressure gradient across the membrane. Comparison with previously reported results in the literature reveals that mass transport of water vapors is substantially improved with the new approach. The performance of the new configuration was investigated with both NaCl and synthetic sea salt feed solutions. Salt rejection was greater than 99.9% in almost all cases. Salt concentrations in the feed stream had only a minor effect on water flux. The economic aspects of the enhanced DCMD process are briefly discussed and comparisons are made with the reverse osmosis (RO) process for desalination.     

Polybenzimidazole (PBI) nanofiltration hollow fiber membranes applied in forward osmosis process

For the first time, the potential of polybenzimidazole (PBI) nanofiltration membrane as a forward osmosis membrane has been investigated. PBI was chosen mainly because of its unique nanofiltration characteristics, robust mechanical strength and excellent chemical stability. The MgCl₂ solutions with different concentrations and other different salt solutions were employed as draw solutions to test the water permeation flux through the PBI membrane during forward osmosis. High water permeation flux and excellent salt selectivity were achieved by using the PBI nanofiltration membrane which has a narrow pore size distribution. Effects of membrane morphology, operation conditions and flowing patterns of two feed streams within the membrane module on water transport performance have been investigated. It may conclude that PBI nanofiltration membrane is a promising candidate as a forward osmosis (FO) membrane.     

Produced water treatment by nanofiltration and reverse osmosis membranes

Produced water, water that is co-produced during oil and gas manufacturing, represents the largest source of oily wastewaters. Given high oil and gas prices, oil and gas production from non-conventional sources such as tar sands, oil shale and coal bed methane will continue to expand resulting in large quantities of impaired produced water. Treatment of this produced water could improve the economic viability of these oil and gas fields and lead to a new source of water for beneficial use.Two nanofiltration and one low-pressure reverse osmosis membrane have been tested using three produced waters from Colorado, USA. The membranes were analyzed before and after produced water filtration using field emission scanning electron microscopy (FESEM), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). In addition, membrane–water contact angles have been measured. XPS data indicate adsorption of organic and inorganic species during filtration. FESEM and ATR-FTIR data support theses findings. Water contact angles indicate the effect of membrane hydrophilicity on fouling. Our results highlight the value of using multiple surface characterization methods with different depths of penetration in order to determine membrane fouling. Depending on the quality of the produced water and the water quality requirements for the beneficial uses being considered, nanofiltration may be a viable process for produced water treatment.     

Improved MEUF removal of naphthenic acids from produced water

Naphthenic acids are naturally occurring organics in produced waters from oil recovery operations. In principle, these contaminants can be removed using micellar-enhanced ultrafiltration (MEUF), which is an effective technique for the removal of organic contaminants from water streams. In this work, we show that the amphiphilic nature of the naphthenic acids contributed to decreasing the critical micelle concentration (CMC) of cetylpyridinium chloride (CPC), a widely used surfactant in MEUF. This reduction in CMC allowed a decrease in the CPC dosage required to attain certain removal of the organics, and hence, improved the performance of traditional MEUF as a result of reducing back contamination and potential fouling of the membrane. The effect of CPC feed concentration, and the concentration and carbon number of the naphthenic acids on permeate flux, recovery ratio and percent rejection of CPC and naphthenic acids were explored over a range of trans-membrane pressure. The MEUF setup employed hydrophilic polyacrylonitrile (PAN) hollow fiber membrane with 13 kDa MWCO, since it allowed for high permeate flux and contaminant rejection.     

The application of ultrafiltration for treatment of ships generated oily wastewater

The wastewaters collected from ships were preliminary separated in harbour installation into an oil fraction (slop oil) and the aqueous phase. The oil phase was then separated from slop oil, and the resulting water phase was subjected to the treatment in a coagulation/flotation process. The effluent (oil content 7–13 ppm) from these processes was further purified in biological wastewater treatment plant. A composition of bilge water is variable what affects the efficiency of coagulation/flotation process and the effluents may contain a significant amount of oil residues. The purification of effluents from coagulation/flotation process was performed in this work with ultrafiltration (UF), using FP100 membranes. The turbidity of obtained UF permeate was varied in the range of 0.08–0.26 NTU and the oil content was at a level of 0.9–1.1 ppm. Such purified water can be utilized for rinsing the oil–water separation devices located in the wastewater treatment plant, instead of tap water used so far. The obtained UF retentate contained 30 ppm of oil can be recycled to the coagulation/flotation process. Fouling of UF membranes was observed during the separation process, however, the FP100 membranes were effective cleaned with alkaline cleaning agents P3 Ultrasil 11.     

Power generation with pressure retarded osmosis: An experimental and theoretical investigation

Pressure retarded osmosis (PRO) was investigated as a viable source of renewable energy. In PRO, water from a low salinity feed solution permeates through a membrane into a pressurized, high salinity draw solution; power is obtained by depressurizing the permeate through a hydroturbine. A PRO model was developed to predict water flux and power density under specific experimental conditions. The model relies on experimental determination of the membrane water permeability coefficient (A), the membrane salt permeability coefficient (B), and the solute resistivity (K). A and B were determined under reverse osmosis conditions, while K was determined under forward osmosis (FO) conditions. The model was tested using experimental results from a bench-scale PRO system. Previous investigations of PRO were unable to verify model predictions due to the lack of suitable membranes and membrane modules. In this investigation, the use of a custom-made laboratory-scale membrane module enabled the collection of experimental PRO data. Results obtained with a flat-sheet cellulose triacetate (CTA) FO membrane and NaCl feed and draw solutions closely matched model predictions. Maximum power densities of 2.7 and 5.1 W/m² were observed for 35 and 60 g/L NaCl draw solutions, respectively, at 970 kPa of hydraulic pressure. Power density was substantially reduced due to internal concentration polarization in the asymmetric CTA membranes and, to a lesser degree, to salt passage. External concentration polarization was found to exhibit a relatively small effect on reducing the osmotic pressure driving force. Using the predictive PRO model, optimal membrane characteristics and module configuration can be determined in order to design a system specifically tailored for PRO processes.     

The Perspective and Challenge of Nanomaterials in Oil and Gas Wastewater Treatment

Oil and gas wastewater refers to the waste stream produced in special production activities such as drilling and fracturing. This kind of wastewater has the following characteristics: high salinity, high chromaticity, toxic and harmful substances, poor biodegradability, and a difficulty to treat. Interestingly, nanomaterials show great potential in water treatment technology because of their small size, large surface area, and high surface energy. When nanotechnology is combined with membrane treatment materials, nanofiber membranes with a controllable pore size and high porosity can be prepared, which provides more possibilities for oil–water separation. In this review, the important applications of nanomaterials in wastewater treatment, including membrane separation technology and photocatalysis technology, are summarized. Membrane separation technology is mainly manifested in ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). It also focuses on the application of semiconductor photocatalysis technology induced by TiO₂ in the degradation of oil and gas wastewater. Finally, the development trends of nanomaterials in oil and gas wastewater treatment are prospected.     

高回收率膜法苦咸水淡化工艺的应用研究进展

膜法苦咸水淡化过程中,符合环境保护要求的浓排水处理方法成本高昂,所以只有当回收率达到较高值时,在实际运行中才具有经济可行性。目前,在不加剧膜污染的条件下进一步提高苦咸水淡化系统回收率的方法已成为该领域研究热点。本文详细综述了高回收率膜法苦咸水淡化工艺的应用研究进展,包括基于反渗透、纳滤、正渗透、膜蒸馏、电渗析和电容去离子化淡化工艺过程,以及这些过程面临的热点问题,并对此提出了建议。     

Study on the thin-film composite nanofiltration membrane for the removal of sulfate from concentrated salt aqueous: Preparation and performance

Thin-film composite (TFC) nanofiltration (NF) membrane was prepared through the interfacial polymerization between piperazine (PIP) and trimesoyl chloride (TMC) on the polysulphone support membrane. The chemical structure of membrane surface was studied by attenuated total reflectance infrared (ATR-IR) and X-ray photoelectronic spectroscopy (XPS). Parametric studies were conducted by varying reaction time, curing temperature, curing time and additives in PIP solution for obtaining the optimum polymerization conditions. Systematic performance studies were conducted with different feed solutions, feed concentrations, feed pHs, operating temperatures and pressures. Continuous and comparative tests were also conducted to determine the performance stability and separation efficiency of the thin-film composite NF membrane prepared. High performance thin-film composite NF membrane for the selective sulfate removal from concentrated sodium chloride aqueous with the water permeability coefficient of 75 L/(m² h MPa) could be prepared under specific conditions. Experimental results on concentrated mixed solution of NaCl and Na₂SO₄ demonstrated that the NF membrane developed could be successfully used for the removal of sodium sulfate from the concentrated brine of chloralkali industry with high permeate flux, selectivity and performance stability.     

On the behaviour of asymmetric membranes in pervaporation

Symmetric and asymmetric membranes of the Loeb type are compared with respect to their performance in pervaporation. The experiments are carried out with water—isopropanol mixtures, employing cellulose acetate membranes of different structure, but of the same total thickness. These results are compared with calculations based on a 2-layer model for asymmetric membranes. Design criteria for optimal asymmetric membranes for pervaporation, as well as the performance characteristics for the two possible modes of installation — active layer facing the feed or facing the permeate — are discussed. Contrary to reverse osmosis, the installation of the membrane with the active layer facing the permeate proves to be superior — at least for low permeabilities of the membrane material. The interdependencies between thickness and permeability of the active layer, and porosity and thickness of the support layer are much stronger than in reverse osmosis.     

Chemical pretreatment of feed water for membrane distillation

Membrane distillation was used to produce demineralized water from ground water. The influence of feed water pretreatment carried out in a contact clarifier (softening with Ca(OH)₂ and coagulation with FeSO₄ · 7H₂O) followed by filtration, on the process effectiveness was evaluated. It was found that the chemical pretreatment decreased the membrane fouling; however, the degree of water purification was insufficient because precipitation of small amounts of deposit on the membrane surface during the process operation was still observed. The permeate flux was gradually decreasing as a result of scaling. The morphology and composition of the fouling layer were studied using scanning electron microscopy coupled with energy dispersion spectrometry. The presence of significant amounts of silica, apart from calcium and magnesium, was determined in the formed deposit. The removal of foulants by heterogeneous crystallization performed inside the filter (70 mesh), assembled directly at the module inlet, was found to be a solution preventing the membrane scaling. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.