Electrocoagulation pretreatment of seawater prior to ultrafiltration: Pilot-scale applications for military water purification systems

The objectives were to investigate the performance of a pilot-scale electrocoagulation (EC) reactor and to determine the feasibility of using in-line EC as a pretreatment to ultrafiltration (UF) of seawater. Work was conducted at Port Hueneme, CA, using components of a U.S. military water purification system. Ferric chloride in-line coagulation was also tested. Both the EC and ferric chloride pretreatments improved UF membrane performance compared to UF without in-line coagulation. EC resulted in slightly greater increases in transmembrane pressure (TMP) than observed following ferric chloride pretreatment during sub-critical flux UF. Substantial accumulation of precipitates developed on the EC electrodes during the testing period. X-ray diffraction identified magnetite, maghemite, lepidocrocite, and akaganeite phases. Accumulation of these precipitates was due in part to conservative hydraulic design of the EC unit. It is recommended that EC units should be designed with short hydraulic retention times and higher electrode current density in order to increase upflow (scour) velocity and thus inhibit accumulation on the electrodes. Progressively longer cycling times for polarity reversal are also recommended. This research indicates that EC offers the potential for a feasible and effective pretreatment strategy for mobile water production facilities.     

Effect of different operating parameters on the recovery of proteins from casein whey using a rotating disc membrane ultrafiltration cell

In this study, effects of different operating parameters in ultrafiltration (UF) of casein whey in rotating disk ultrafiltration module, fitted with a 30 kD followed by a 5 kD molecular weight cut-off (MWCO) membrane have been analyzed and the benefits of membrane rotation with respect to stationary membrane module are highlighted. Prior to UF, centrifugation and microfiltration (MF) were carried out with the raw casein whey with an aim to remove the major membrane foulants like colloidal matters, suspended casein particles and lipid. The effects of pH, membrane rotation and transmembrane pressure (TMP) on UF flux and rejection were studied thoroughly, giving an emphasis on the effect of operating conditions in pressure and mass transfer controlled region as well. It was observed that solution pH was having a strong effect on UF flux and rejection for treating casein whey, which was explained in terms of prevailing monomer-dimer equilibrium of β-lactoglobulin, a major constituent of casein whey, as well as due to conformational changes of protein molecules with respect to isoelectric point. It was observed that for the 30 kD membrane, after 20 min of operation, 28.5% higher flux was obtained at pH 2.8 compared to pH 5.5 at a pressure of 490 kPa for stationary membrane, whereas the same figure for rotating membrane was 49.5%. Further, 38.7% higher UF flux at 300 rpm membrane speed compared to stationary membrane in 20 min of operation at pH 2.8 and TMP 490 kPa suggests the importance of shear across the membrane in minimizing the effects of concentration polarization. In the 5 kD membrane α-lactalbumin, which was mainly in the permeate stream from the 30 kD membrane, was separated from the other low molecular weight component of whey, such as lactose.     

两种内压式超滤膜组件在反渗透预处理中的应用

选取两种内压式中空纤维超滤膜组件,从膜材质、运行参数和出水水质等方面对这两种组件在海水淡化反渗透预处理中的应用进行比较。结果表明:2#膜组件跨膜压差和膜通量的稳定性较1#组件好,两种膜组件出水水质比较接近,但2#膜出水水质稳定性较1#膜好。在进水浊度小于20NTU时,2#膜组件更适合应用于反渗透的预处理工艺。     

Immersed Membrane BioReactor (IMBR) for treatment of combined domestic and dairy wastewater in an isolated farm: An exploratory case study implementing the Facet Analysis (FA)

In many regions dairy farms and milk processing industries, discharge large quantities of their wastes to the surroundings which pose serious environmental risks. With the purpose of treating the combined dairy and domestic wastewater from a small dairy farm in the Negev Desert of Israel, the use of a recent emerging technology of Immersed Membrane BioReactor (IMBR) was evaluated over the course of 500 test hours, under a variety of wastewater feed quality conditions.Field experiments were performed at the Kornmehl farm, an isolated dairy farm located 30 km south of Beer-Sheva, in the Negev Desert of Israel. The operating conditions for this experiment included constant product flow of 7 (L/h)], and the transmembrane pressure was increased smoothly during the experiment from 0.05 to 0.13 bar. Temperatures ranged between 30 °C and 37 °C, pH ranged between 4 and 9, TSS varied between 353 mg/L to 1000 mg/L and COD changed from 900 mg/L to 12,800 mg/L.The overall performance of a pilot-scale Ultrafiltration (UF) IMBR process for a combined domestic and dairy wastewater was analyzed based on the Facet Analysis (FA) method. Preliminary results of the FA model indicate: (i) the Trans-Membrane Pressure (TMP); the pH and the temperature do not have an effect on the performance of the permeate normalized flux and on the specific normalized flux, and; (ii) the bioreactor is characterized by high concentration of organic matters and it can be estimated that the IMBR normalized flux decline is dependent on other variables (air blower performance, backwash procedure and chemical cleaning).     

Spiral-wound new thin film composite membrane for a single-stage seawater desalination by reverse osmosis

New thin film composite membrane system, designated PEC-1000, formed by the acid catalyzed polymerization on the surface of a reinforced-porous supporting membrane, make it possible to produce potable water from seawater by reverse osmosis in a single-stage with a high recovery operation. TDS rejection over 99.9% and stable water fluxes of 0.20–0.30 m³/m²-day (5.0–7.4 gal/ft²-day) have been attained with 3.5% synthetic seawater at an applied pressure of 56Kg/cm²(800psi). For brackish water, sodium chloride rejections of 99.6–99.9% and fluxes of 0.61–0.81m³/m²-day(15.0-20.0 gal/ft²-day) have been attained with 5000 ppm sodium chloride feed at an applied pressure of 40Kg/cm² (571psi). TDS rejection of 99.8% and water flux of 0.30 m³/m²-day (7.4 gal/ft²-day) have been attained with two- or four-inch diameter PEC-1000 composite membrane elements at an applied pressure of 56Kg/cm²(800psi) in a single-stage synthetic seawater desalination test. This performance is kept for more than 1500 hours in PEC-1000 thin film composite membrane and two-inch diameter element. 280 ppm in TDS and water flux of 0.11 m³/m² day (2.7 gal/ft²-day) are observed at an applied pressure of 56Kg/cm²-40% water recovery with one four-inch diameter spiral-wound PEC-1000 composite membrane element in a single-stage seawater desalination. This membrane shows high selectivity for low molecular weight valuable organic materials such as ?-caprolactam, dimethylsulfoxide, dimethylformamide. The thickness of ultrathin salt barrier of the composite membrane is found to be 300Å by the Electron Microscopy with special ultrathin section techniques.     

A new thin-film composite seawater reverse osmosis membrane

During the past year a new thin-film composite reverse osmosis membrane that shows excellent potential for single-pass seawater operation has been developed. This membrane, designated FT-30, is formed by depositing a proprietary thin polymer coating on a microporous polysulfone support layer.Membrane samples, tested at an operating pressure of 1000 psi with synthetic seawater, yielded fluxes of about 30 gallons per square foot per day (gfd) and salt rejections as high as 99.6 percent. At 800 psi the flux dropped to 23 gfd with little decrease in salt rejection. Membrane tested with other raw waters, including tapwater at a pressure of 50 psi and brackish waters at 200-600 psi, also provided excellent results. The membrane appears to be suitable for a variety of applications, ranging from water conditioning to single-pass seawater operation.Other important performance characteristics of the new membrane are that it appears to be chlorine-resistant (not damaged by chlorine concentrations of 100 ppm in three-day immersion tests), can be operated over a wide range of pH (3–11), is resistant to compaction, and can operate at tempreatures as high as 60°C without damage.     

Assessment of pretreatment to microfiltration for desalination in terms of fouling index and molecular weight distribution

In this study, different processes such as flocculation with ferric chloride (FeCl₃) and deep bed filtration (sand filtration and dual media filtration) as a pre-treatment to microfiltration (MF) were used for seawater desalination. The performance of these pre-treatments was determined in terms of silt density index (SDI) and modified fouling index (MFI) and flux decline in MF. Flux decline of MF with seawater was 45% without any pre-treatment, 42% after pre-treatment of FeCl₃ flocculation, 24% after pre-treatment of sand filtration with in-line coagulation and 22% after pre-treatment of dual media filtration (sand and anthracite), respectively. MFI and SDI also indicated that deep bed filtration with in-line flocculation was better pre-treatment than flocculation alone. Detailed molecular weight distribution (MWD) of seawater organic matter was examined after different pretreatments. MWD of the initial seawater mainly ranged from 1510 Da to 130 Da. Deep bed filtration with in-line flocculation removed relatively large molecular weight of organic matter (1510-1180 Da), while the small molecular weights (less than 530 Da) were not removed.     

高浓度含盐含酸有机废水预处理及膜清洗初试

以聚合氯化铝（PAC）为絮凝剂,结合杂萘联苯聚芳醚砜酮（PPESK）超滤膜技术处理高浓度含盐含酸有机废水,考察了絮凝剂最佳投药量,同时研究超滤膜的清洗恢复情况,主要考察了水力清洗以及不同化学清洗剂和清洗时间的影响下,膜通量的恢复情况,从而确定了最佳的膜清洗方法。结果表明：PAC最佳投加量为100mg／L,废水絮凝效果最好,COD及SS去除率分别达到30％、90％。EDTA碱液反洗有很好的再生效果,渗透通量恢复率高至98．3％。     

The FT-30 seawater reverse osmosis membrane--element test results

A thin-film composite reverse osmosis (RO) membrane has been developed that provides excellent performance when used in single-pass seawater systems. This membrane, designated FT-30, gives superior performance in such areas as flux, salt rejection, chemical stability, and microbiological resistance. In addition, it is resistant to some oxidizing disinfectant agents, although it is not fully resistant to chlorine; elements fabricated from the membrane have shown damage after 2,000 to 2,500 hours exposure to seawater at 0.5 milligrams per liter (mg/l) active chlorine. It appears that the membrane can operate continuously at active chlorine concentrations below 0.2 mg/l.Several long-term studies were carried out at the OWRT Wrightsville Beach Test Facilities. In actual trials in seawater systems, salt rejections as high as 99.5 percent and fluxes of 23 gfd have been obtained when tested at 800 psi and 25°C. Some of the elements have been in continuous operation for over 4, 000 hours with no deterioration in salt rejection and with only the normal flux decline usually associated with compaction and scaling. Other elements have been installed in small seawater systems with normal intermittant use for almost two years with no serious loss in performance.     

Integration of immersed membrane ultrafiltration with the reuse of PAC and alum sludge (RPAS) process for drinking water treatment

Effects of PAC and alum sludge generated from water treatment process on the effluent quality and fouling of immersed UF membrane were systematically investigated with representative source of natural water and the efficiency of coagulation, PAC adsorption and RPAS to treat natural surface water prior to UF were compared. It was found that the average turbidity removal by RPAS could reach up to 80.2%, and the turbidity removal of immersed membrane UF was independent of the influent, which could be kept at 99%. Particulates were reduced after being pre-treated by different processes, and particles with sizes ranging from 0.5 to 3.5 μm and larger than 13.5 μm were effectively removed by RPAS. UF coupled with RPAS pre-treatment got the best removal for DOM compared to other processes with average DOC and UV₂₅₄ removal 54.1% and 47.2% due to the high removal in the influent of UF. The residual alum content in the effluent of RPAS with UF was less than coagulation and bacteria were almost all removed by membrane. The membrane-fouling was mitigated by pre-treatment processes at different degrees, TMP of UF coupled with RPAS process was relatively stable in 15 d of run, the adsorption of PAC and large number of Al(OH)₃ complexes and precipitates for the foulant molecules might be an important mechanism.     

Reducing pollution from the deliming–bating operation in a tannery. Wastewater reuse by microfiltration membranes

This paper presents experimental results from the implementation of two measures aimed at reducing the nitrogen concentration in a tannery wastewater. Specifically, this research has focused on the wastewater from the deliming/bating operations. The proposed measures are the replacement of ammonium salts by carbon dioxide in the deliming process and the reuse of wastewater and chemicals after membrane filtration of the deliming/bating liquor. The experimental study covered different wastewater pretreatment alternatives and experiments with two membranes (with different separation properties): one in the range of microfiltration (MF) and one in the range of the ultrafiltration (UF). Results of the pretreatment study indicated that neither settling nor protein precipitation were feasible. Only a security filtration prior to membrane filtration was recommended. The tested MF membrane was selected due to the higher flux (around 25 L/(m² h)) in comparison with the UF membrane. The MF permeate was successfully reused in the deliming/bating process. The delimed leather quality was excellent according to both visual and organoleptic inspection from process technicians and phenolphthalein test, confirming the technical feasibility of the proposal. Globally, the implementation of the above mentioned two measures resulted in 53% total nitrogen reduction.     

Parameters affecting backwash variables of RO membranes

The optimal setup of backwash (BW) cleaning methods was determined by analyzing the parameters affecting BW flux: accumulated volume during the process, and permeate salinity. An investigation was carried out on the parameters affecting BW flux and accumulated volume based on existing data and the 2D time-dependent FEM model developed in a previous study. According to this model, the absence or presence of feed velocity and applied pressure relates to Case 1 or Case 2 of BW cleaning methods, respectively. The main parameters affecting BW flux and accumulated volume are BW time t_BW and feed concentration C_f. Effects of membrane thickness, salt and water diffusivities, and feed velocity on BW flux are negligible within ± 10% change. Results show that BW flux based on Case 1 is higher than fluxes of Case 2. This result provides a clear advantage of BW cleaning methods to Case 1 over Case 2 methods. Permeate salinity increases with C_f and t_BW and decreases with desalination time t_RO and feed pressure P_f. A preferable BW cleaning method resulting from this study is a cleaning method based on Case 1 for t_RO > 20 min, at a t_BW as short as possible and C_f around 31 kg/m³.     

Characteristics and potential applications of a novel forward osmosis hollow fiber membrane

There has been a resurgence of interest in forward osmosis (FO) as a potential means of desalination, dewatering and in pressure retarded osmosis, which Sidney Loeb was advocating over 3 decades ago. This paper describes the characteristics and potential applications of a newly developed FO hollow fiber membrane, which was fabricated by interfacial polymerization on the inner surface of a polyethersulfone (PES) hollow fiber. This FO membrane presents excellent intrinsic separation properties, with a water flux of 42.6 L/m² h using 0.5 M NaCl as the draw solution and DI water as the feed with the active layer facing the draw solution orientation at 23 °C. The corresponding ratio of salt flux to water flux was only 0.094 g/L, which is superior to all other FO membranes reported in the open literature. To evaluate different application scenarios, various NaCl solutions (500 ppm (8.6 mM), 1 wt.% (0.17 M) and 3.5 wt.% (0.59 M)) were used as the feed water to test the performance of the FO membrane. The membrane can achieve a water flux of 12.4 L/m² h with 3.5 wt.% NaCl solution as the feed and 2 M NaCl as the draw solution, suggesting it has good potential for seawater desalination.     

PAC-UF组合系统在饮用水处理中的试验研究

试验考察了粉末活性炭(PAC)的投加对超滤膜(UF)运行性能的影响，结果表明：PAC投加到蒸馏水中使膜通量产生微小下降。单独用UF膜系统处理自来水时，膜的通量急剧下降，而PAC作为UF膜的预处理方式处理相同水量时，可以明显延长膜的运行周期；随PAC投量的增加膜稳定运行时间延长，通量下降率降低。物理清洗方式对PAC-UF组合系统中膜通量的恢复效果较好，而化学清洗方式对单独UF膜系统中膜通量的恢复效果较好。     

Cellulose triacetate membranes for seawater desalination

Experimental data on reverse osmosis using a sodium chloride solution by cellulose triacetate membranes are presented. The investigation involved studies on the composition of membrane casting solutions and their effects on the performance. A higher polymer concentration (11–13%) is found suitable for production of a uniform and highly salt rejecting membrane. Salt rejection of 99.0% and 4–5 GFD product water flux were obtained at 1000 psi operating pressure using 30,000 ppm TDS seawater in the initial experiments.     

Facilitated transport separation of propylene–propane: Experimental and modeling study

Supported liquid membrane, as one type of facilitated transport membranes, was used for the separation of propylene–propane mixtures. The effect of trans-membrane pressure and carrier concentration on membrane separation performance were evaluated in terms of mixed-gas selectivity, propylene and propane permeances and propylene and propane permeation fluxes. A general dimensionless model for the transport of components across the membrane was proposed and solved numerically by orthogonal collocation method. Experimental results showed that for a 70:30 (vol.%) propylene–propane mixture, at pressure 120 kPa and carrier concentration 20 wt.%, a propylene permeation flux of 1.46 × 10⁻⁴ mol/m² s was obtained. Mathematical results are in well agreement with experimental results. The average deviation between experimental and modeling results was found to be 5.3% for propylene permeation flux and 0.03% for propane permeation flux.     

浸没式超滤海水预处理工艺

目前渤海湾反渗透海水淡化工程多采用新型的超滤膜法预处理工艺,为提高预处理效果,主要进行超滤膜材料和性能改进以及膜组件运行参数的优化,而对超滤膜前预处理的研究相对较少。本实验研究了超滤与混凝/超滤作为反渗透海水淡化预处理工艺的处理效果。考察了两种预处理工艺条件下浸没式超滤膜比通量(SF)、进水水质、产水水质,膜孔孔径变化、反洗效果及膜表面污染情况。结果表明,超滤与混凝/超滤两种预处理工艺都能达到产水SDI₁₅<2.0;混凝处理可以大幅度降低海水中颗粒数目,降低颗粒物在膜表面沉积和吸附的概率,减轻超滤膜的污染。当采用混凝/超滤工艺时超滤膜表面滤饼层疏松多孔,膜孔孔径变化较小,超滤膜比通量的衰减速度减缓,反洗时超滤膜比通量恢复率较高。     

Electro-ultrafiltration of amylase enzymes: Process design and economy

Electro-ultrafiltration (EUF) has previously resulted in flux improvements in the order of 3-7 times during filtration of amylase enzymes [Enevoldsen, A.D., Hansen, E.B., Jonsson, G., 2007. Electro-ultrafiltration of industrial enzyme solutions. Journal of Membrane Science 299, 28-37]. To determine the energy balance for EUF, the influence of TMP, crossflow velocity and conductivity of the enzyme solution is studied and compared to conventional ultrafiltration (UF). EUF is favorable when filtering solutions of high concentration, while UF is favorable when filtering solutions of low concentration. The dimension of the feed channel, especially the height and the conductivity are crucial for the feasibility of the EUF process. The channel height should be below 1.0 mm and the conductivity less that 2 mS/cm before EUF is economically feasible.     

Separation of casein from whey proteins by dynamic filtration

It has been proven that functional properties of milk proteins can improve the quality and nutritional value of foods. This paper investigates the separation of whey proteins from casein micelles using a Multi Shaft Disk (MSD) module and a rotating disk dynamic filtration module. The MSD module was equipped with 6 ceramic membranes of 0.2 µm pores. PVDF and Nylon membranes of 0.2 µm pores were tested in the rotating disk module. Permeate flux with the MSD module increased with TMP and rotation speed, reaching a maximum of 132 L h^− 1 m^− 2 at 1931 rpm. α-Lactalbumin (α-La) and β-Lactoglobulin (β-Lg) transmissions also increased with rotation speed, ranging from 25% at 1044 rpm to 40% at 1931 rpm . With a Nylon membrane, the rotating disk module yielded lower permeate fluxes than the MSD module, while when equipped with a PVDF membrane it provided higher permeate fluxes than the MSD, but casein micelles rejection was lower. α-La and β-Lg transmissions were higher with the rotating disk module, using Nylon and PVDF membranes, than for the MSD. From this comparison, it can be concluded that the MSD module gave the best compromise between high permeate flux, high α-La and β-Lg transmissions and high casein micelles rejection.     

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.