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Experimental test of TOYOBO membranes for seawater desalination at Las Palmas, Spain
Abstract
CEDEX (Centro de Estudios y Experimentacion de Obras Publicas) and EMALSA (Empresa Mixta de Aguas de Las Palmas, S.A.) had been performing experimental tests for seawater desalination at Las Palmas, Gran Canaria Is., Spain, using a TOYOBO hollow-fiber membrane. A Hollosep HM10255FI module made by TOYOBO is used in the largest desalination plants around the world, especially in the Middle East. CEDEX and EMALSA confirm that the Hollosep module can produce stable water production and high-quality water for long-term operation without any chemical cleanings during 4600h operation thanks to the its high chlorine resistance and anti-biofouling tolerance.
... Many approaches [1,2] have been conducted to identify the robust membranes and appropriate operating conditions to overcome bio-fouling, but none of them has fundamentally addressed the problem. At the same time, with the improvements of membrane materials and modules [3], the cellulose triacetate (CTA) hollow fiber (HF) RO membranes manufactured by TOYOBO [4] exhibited the superiority on chlorine tolerance over the polyamide RO membranes. Because these polyamide membranes have a low chlorine tolerance (less than 0.1 mg/L), the no residual chlorine requirement in the feed prior to or in the SWRO membranes results in the breeding of bacteria and other microorganisms compromising the properties and performance of the RO membrane. ...
... Chlorine injecting systems are mainly classified into intermittent chlorine injection (ICI) and continuous chlorine injection (CCI), which are indispensable to HF SWRO system. Some literatures reported that ICI could eliminate bio-fouling more efficiently, while CCI was not as effective as ICI [4,5]. For example, the required minimum chlorine concentration and injecting time of ICI based on the experiments of the growth and sterilization rates of microorganisms in seawater of Middle East were simulated, and the operational results proved that ICI was the most effective chlorine injection mode to achieve best RO performance of desalination [6]. ...
... m 3 /d/ module. These operating conditions such as operating pressure and system recovery were a little lower than the previous work [4] which applied operating pressure of 6.5 MPa and system recovery of 45-50%. During testing period of about 150 h, the differential pressure increased differently for each mode, which indicates that modes of chlorine injection can influence not only the feed quality but also the differential pressure, and the increase in differential pressure could be prevented efficiently by the better chlorine injecting mode. ...
Bio-fouling results in deterioration of permeate quality and flux in reverse osmosis (RO) process. Cellulose triacetate hollow fiber membrane used for RO in SWRO has anti-chlorine property that makes technical sense compared to polyamide spiral-wound RO for overcoming bio-fouling. Mode of chlorine injection is the controlling factor of sterilization in SWRO system. This work evaluated the effects of five different modes of chlorine injecting system as well as HCl injection on the performance of HF RO system. In addition, effects of HCl and anti-scalants on anti-scale performance of HF RO system were also investigated, respectively. A brief list of chemical costs under different abovementioned operating conditions was covered in a cost analysis. The results indicated that the injecting mode that employed continuous chlorine with a relatively low concentration of 0.3–0.4 mg/L at pH 5.8–6.2 was preferable in the aspects of total bacterial count (TBC) removal, permeate flow rate, differential pressure, permeability (Pp), performance factor (η) and chemical costs. HCl injection could improve the sterilization and prevent scaling on the membrane surface efficiently. The expense of anti-scalant (MDC220) was higher than HCl.
... A comparison of the desalination performance of a modified PBI HF and a commercial HF module (made by Toyobo) is shown in Figure 12. The Toyobo product is Hollosep MH10255FI membrane, and its permeability is calculated according to the reported A value (1.5 × 10 −6 cm 3 /cm 2 s·[kg/cm 2 ]) [36]. Both our modified PBI HF and the Hollosep provide over 99% salt rejection and their water permeability is comparable. ...
... A comparison of the desalination performance of a modified PBI HF and a commercial HF module (made by Toyobo) is shown in Figure 12. The Toyobo product is Hollosep MH10255FI membrane, and its permeability is calculated according to the reported A value (1.5 × 10 −6 cm 3 /cm 2 s ·[kg/cm 2 ]) [36]. Both our modified PBI HF and the Hollosep provide over 99% salt rejection and their water permeability is comparable. ...
High-performance polybenzimidazole (PBI) hollow-fiber membranes (HFMs) were fabricated through a continuous dry-jet wet spinning process at SRI International. By adjusting the spinning air gap from 4″ (10.2 cm) to 0.5″ (1.3 cm), the HFM pore sizes were enlarged dramatically without any significant change of the fiber dimensional size and barrier layer thickness. When fabricated with an air gap of 2.5″ (6.4 cm) and a surface modified by NaClO solution, the PBI HFM performance was comparable to that of a commercial reverse osmosis (RO) HFM product from Toyobo in terms of salt (NaCl) rejection and water permeability. The PBI RO HFM was positively surface charged in acidic conditions (pH < 7), which enhanced salt rejection via the Donnan effect. With an air gap of 1.5″ (3.8 cm), the PBI HFM rejected MgSO4 and Na2SO4 above 95%, a result that compares favorably with that achieved by nanofiltration. In addition, the PBI HFM has a defect-free structure with an ultra-thin barrier layer and porous sublayer. We believe PBI HFMs are ideal for water purification and can be readily commercialized.
... However, especially operation at elevated temperatures affords continuous or at least intermittent (1 h/ 24 h) chlorination to avoid the attack of micro- organisms [14]. Due to the element construction, the maximum SDI 15 at which HOLLOSEP elements can be operated is SDI 4, whereas spiralwound elements allow operation up to SDI 5. Consequently the raw water quality and/or the pretreatment for HOLLOSEP membranes has to be better [14,15]. Due to constant hydrolysis of CTA membranes and the loss of salt rejection, the typical replacement rate of these membranes is about 20% per year [8], which is about 3 times the replacement rate of spiral-wound PA membranes. ...
Until the end of the 90's the RO desalination technology for medium and large capacities was based mainly upon two configurations of membrane modules: spiral-wound elements and hollow fiber bundles (HF). The retirement of Permasep ® HF (DuPont) leaving HOLLOSEP ® (Toyobo) as being the only alternative for the direct replacement of Permasep, brought a challenge to the makers of spiral elements in the sense of system retrofit to convert existing HF membrane plants into some of the most advanced spiral-wound membrane plants. The major criteria for success was to achieve substantial improvements in the economy and quality of the permeate produced at limited capital expenditure. Such improvements have become feasible with the considerable development of spiral-wound membranes in the recent years. In this paper the technical changes needed for the retrofitting have been systematically studied. After a short historical review, the paper discusses basic options for two existing Permasep installations on the Canary Islands and in the Middle East, respectively. Specific characteristics, advantages and costs of various possible solutions are presented. Two case studies are discussed for the 3×4,700 m 3 /d seawater RO plant in Agragua on the Canary Islands and for the 4×4,200 m 3 /d seawater RO plant in Gela in Sicily. Plant performance data for 8 months and 19 months respectively is presented.
During the last decades, the utilization of osmotic pressure-driven forward osmosis technology for wastewater treatment has drawn great interest, due to its high separation efficiency, low membrane fouling propensity, high water recovery and relatively low energy consumption. This review paper summarizes the implementation of forward osmosis technology for various wastewater treatment including municipal sewage, landfill leachate, oil/gas exploitation wastewater, textile waste-water, mine wastewater, and radioactive wastewater. However, membrane fouling is still a critical issue, which affects water flux stability, membrane life and operating cost. Different membrane fouling types and corresponding fouling mechanisms, including organic fouling, inorganic fouling, biofouling and combined fouling are therefore further discussed. The fouling control strategies including feed pre-treatment, operation condition optimization, membrane selection and modification, membrane cleaning and tailoring the chemistry of draw solution are also reviewed comprehensively. At the end of paper, some recommendations are proposed.
Non-woven fabric (NWF) has become one of the most important segments in filtration field. Herein, a new type of polyethylene-terephthalate (PET) NWF reinforced “sandwich” cellulose triacetate (CTA) composite reverse osmosis (RO) membrane (NCR membrane) was prepared by melting method. Moreover, the structure and performance of NCR membranes with different separation layer thickness were investigated by ATR-FTIR, SEM, and mechanical property and so on. The results indicated that the NWF supporting layer not only provided well interfacial bonding state with separation layer but also overcame the negative effect of CTA RO membrane's permeate flux loss, due to its easy compaction at a moderate or high operating pressure. Furthermore, all the same ATR-FTIR spectrum of NCR membranes indicated that NWF was wrapped up by CTA melt. Besides, the mechanical property exhibited that the tensile strength increased from 7.5 to 19.5 MPa when introducing the NWF into membrane matrix. Also, based on both membrane morphologies and performance, the optimal membrane thickness was 150 μm with adequate permeate flux and higher salt rejection. Finally, the long-term stable RO testing also exhibited that introducing NWF supporting layer with suitable thickness of separation layer was useful for compaction resistance and stable permeability of NCR membranes.
The rejection behaviours of 41 trace organic chemicals (TrOCs) by a hollow fibre cellulose triacetate (CTA) reverse osmosis (RO) membrane for potable water reuse were evaluated. Results reported here suggest that the rejection behaviours of TrOCs by the CTA RO membrane are mostly similar to those previously reported for the polyamide (PA) RO membrane. However, in comparison to the PA based RO membrane, hydrophobic interaction plays a greater role while electrostatic interaction is less significant in governing the rejection of TrOCs by the CTA RO membrane. No difference in rejection between positively and negatively charged compounds by the CTA RO membrane could be observed. The rejection of neutral TrOCs by the CTA RO membrane varied significantly from 25% to over 95%. Molecular size (i.e. minimum projection area) was found to be an important factor governing the rejection of neutral TrOCs. Further investigation using N-nitrosamines reveals that in addition to molecular size, hydrophobicity could significantly influence their rejection by the CTA RO membrane, while N-nitrosamine rejection by the PA RO membrane was mostly governed by molecular size. In contrast to the neutral TrOCs, most charged TrOCs selected in this investigation exhibited over 90% rejection, regardless of molecular size.
This paper presents the results of research work conducted as part of a doctoral thesis and undertaken with the aim of resolving the problem of accelerated fouling of reverse osmosis membranes (made from spiral-wound polyamide), as a result of the deposition of colloidal particles (particulate fouling), the precipitation of inorganic salts (scaling) and the accumulation of living and/or dead biological matter (biofouling). The reverse osmosis modules affected form part of the Las Palmas III (LP3) desalination plant run by the company EMALSA (Spanish initials: Empresa Mixta de Aguas de Las Palmas). This plant is located on the island of Gran Canaria (Spain) and supplies potable water to around half a million people.
Pre-treatment systems in reverse osmosis seawater desalination plants can be relatively simple or complex depending upon the direct function of the physical, chemical and microbiological quality of the water which is fed through the reverse osmosis membranes which separate the salts and the other disperse matter (colloids and micro-organisms) which are present in the processed water which, according to type and quantity, will produce a progressive or accelerated process of fouling of the same. Thus, the less quality of water to be desalinated, the greater or more intensive will be the pre-treatment system. The process water which is the result of systems of open intake is less recommendable since the characteristics are lower in quality, above all, the micro-biological parameters (the worst). All of this has a basic repercussion by increasing the cost per unit of the cubic metre of water produced and supplied to the end consumer or by reducing the profits for the companies exploiting the seawater desalination plant.
The methods and mechanisms of nonsolvent induced phase separation have been studied for more than fifty years. Today, phase inversion membranes are widely used in numerous chemical industries, biotechnology, and environmental separation processes. The body of knowledge has grown exponentially in the past fifty years, which suggests the need for a critical review of the literature. Here we present a review of nonsolvent induced phase separation membrane preparation and characterization for many commonly used membrane polymers. The key factors in membrane preparation discussed include the solvent type, polymer type and concentration, nonsolvent system type and composition, additives to the polymer solution, and film casting conditions. A brief introduction to membrane characterization is also given, which includes membrane porosity and pore size distribution characterization, membrane physical and chemical properties characterization, and thermodynamic and kinetic evaluation of the phase inversion process. One aim of this review is to lay out the basics for selecting polymer−solvent−nonsolvent systems with appropriate film casting conditions to produce membranes with the desired performance, morphology, and stability, and to choose the proper way to characterize these properties of nonsolvent induced phase inversion membranes.
Cellulose triacetate (CTA) membranes have strong resistance to chlorine. The effect of the concentration of chlorine and temperature on the resistance performance was studied. However, the effect of heavy metal ion and pH on it has not been studied well. We studied the effect of various kinds of heavy metal ion, concentration of chlorine, temperature and pH. We measured the reverse osmosis (RO performance, acetylation degree (combined acetic acid content) and molecular weight of CTA. From the experiments it is seen that some heavy metal ions such as copper and cobalt strongly affect the oxidation of CTA by chlorine; and it was also found that the oxidation degree depends on temperature, pH and concentration of chlorine. Furthermore, we investigated the masking agents which reduce the effect of heavy metal ion, and we found some effective masking agents.
Toyobo succeeded in developing a single-pass seawater desalination RO module composed of hollow fiber type membranes made of cellulose triacetate in 1978, and then in 1979 began production of the first commercially available double-element module. This double-element module has many advantages suitable for seawater desalination. It has high chlorine tolerance and high salt rejection, derived from the properties of the membrane material, and it is highly resistant to fouling and scaling matters due to the unique flow pattern and fiber bundle configuration. These advantages help to explain why the Toyobo double-element module has been used so successfully at the many seawater desalination plants around the world.In this report we show the simulated water flow rate, bulk concentration, concentration polarization coefficient and concentration at the membrane surface in double-element modules and present actual operating data from desalination plants in Chigasaki (Japan), Seraya (Singapore),and Helgoland (Germany). Using these monitoring data we analyzed RO performance, A value and B value, thereby demonstrating the advantages of the Toyobo double-element module.
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