GB2339155A

GB2339155A - Ultrafiltration using hollow cellulose acetate fibres

Info

Publication number: GB2339155A
Application number: GB9911972A
Authority: GB
Inventors: Yoskiaki Nakanishi; Kazuhisa Kumami; Tsuyoshi Hirata
Original assignee: DAICEN MENBRANE SYSTEMS Ltd; Daicel Chemical Industries Ltd
Current assignee: DAICEN MENBRANE SYSTEMS Ltd; Daicel Corp
Priority date: 1998-05-22
Filing date: 1999-05-21
Publication date: 2000-01-19
Also published as: JP2001000842A; GB9911972D0

Description

2339155

TITLE OF THE INVENTION

MODULE FOR CONCENTRATING PATHOGENIC PROTOZOA AND CONCENTRATION METHOD USING THE SAME BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a concentration module and a concentration method for detecting pathogenic protozoa such as cryptosporidiums and giardias existing in-water by use of a specific ultrafiltration membrane.

2. Description of Related Art

In quantitative analysis of pathogenic protozoa existing in water, e.g., cryptosporidiums and giardias, a process of concentrating sample water is required.

Usually, this is because protozoa exist in water in such a low concentration that an enormous volume of sample water must be analyzed in order to ensure an accurate determination.

According to a concentration procedure in "Provisional Test Method for Detecting Oocysts of Cryptosporidiums with regard to Water Supply" issued by the Ministry of Health and Welfare of Japan in October 1996, 40 liters or more of & sample water from a hydrant, a water distribution pool or a water purification pool or 20 liters of sample of raw water for water supply is to be concentrated by use of a disk filter of cellulose acetate having a diameter of 47mm or 90mm. (pore diameter is 1.2 um or smaller).

In reality, this is inefficient because it takes eight to ten hours to filtrate 40 liters of tap water with a sheet of a filter of 47mm diameter for concentration. So in general practice, several f ilters of the same size are arranged in parallel for working a less time-consuming concentration. Cryptosporidiums thus concentrated on the filters are collected as sediments by dissolving the filters with acetone and removing an acetone phase by centrifugation.

The filtration by this method is def ective in that it requires a lot of care and takes a lot of time. As an improvement of this method, a sampling capsule having 2 a microfiltration (MF) membrane (membrane area is 0.13 M2) is available under the trade name of "Envirocheck" from Gelman Sciences, for example. This product is a module including a pleated membrane of a 5 polyethersulfone which has pores of 1gm diameter. Using this product is certainly advantageous since the time necessary for concentration by filtration is shortened, but that it is disadvantageous since the collection ratio for cryptosporidiums, which is of major importance, is extremely low, that is, about 20% or lower.

Further to the above, it is said that an examination technique is required to exhibit a reproducible collection ratio of at least 80% constantly in order to be admitted as an established method.

SUMMARY OF THE INVENTION

The development of the present invention began with AL logical examination about where the defects of the above-described methods lay. More particularly, it was examined why the above-described module in which themicrofiltration membrane of the polyethersulfone having pores of 1,um diameter was pleated- exhibited only a poor collection ratio for cryptosporidiums. This examination has lead to the following presumptions:- As 3 a first conclusion, the material for the membrane is not suitable. As a second conclusion, the pore diameter of the membrane is not proper. As a third conclusion, the type of the module which resulted from the formation of 5 the membrane is not proper.

Accordingly, one of the major objects of the present invention is to provide a novel membrane module adopted to solve the above three problems.

In order to accomplish the above-mentioned object, the inventors have carried out intensive study and achieved the present invention.

The invention provides a module for concentrating pathogenic protozoa which is constructed to concentrate raw water by filtration using an ultraf iltration membrane having a contact angle of 60' or less and a water absorption of 4.7wt% or higher. Preferably the module is a module of an external pressure mode comprising a hollow fiber ultraf iltration membrane of cellulose acetate which has a permeability of 150 liters/m' h or more to water. The invention also provides a method for concentrating raw water by use of the module with a view to detecting pathogenic protozoar that is, a method for concentrating pathogenic protozoa.

In another aspect, the present invention provides a module for concentrating pathogenic 4 protozoa which comprises a bundle of a plurality of hollow fiber ultrafiltration membranes having end portions and having a contact angle of 600 or less and a water absorption of 4.7wt% or higher, the end portions of the hollow fiber ultrafiltration membranes being bound with resin, and a case for accommodating the bundle of hollow fiber ultrafiltration membranes to provide liquid-tight partition between a raw-water side and a filtrate-water side. The case is provided with a raw-water inlet and a concentrate-water outlet on the raw-water side and a filtrate-water outlet on the filtrate-water side.

In still another aspect, the present invention provides a module for concentrating pathogenic protozoa which includes a cartridge including a U-shaped bundle of a plurality of holl.ow f iber ultraf iltration membranes having a contact angle of 60 or less and a water absorption of 4.7wt% or higher, with end portions of the hollow f iber ultraf iltration membranes being integrally bound with a resin so that said end portions of the hollow fiber ultraf i1tration membranes adhere to each other to form a bound portion, and a seal member for the cartridge provided at an outer periphery of the bound portion, and a case including a cylindrical case body, a cap for closing an opening of the case body and a seal member for the cap provided therebetween, the case providing liquid-tight partition between a raw-water side and filtrate-water side, by accommodating the cartridge to bring the seal member for the cartridge in close contact with the cylindrical case body. The bound portion has a seal seating member for setting -o-t the seal member for the cartridge, the seal seating member being located on the outer periphery of the bound portion within 5mm from an edge of the bound portion where the bundle of hollow fiber membranes is exposed.

In summary, the present invention is concerned with positively collecting protozoa, which can be gathered on hollow fiber ultrafiltration membranes, by constructing a cartridge of a U-shaped bundle of hollow fiber ultrafiltration membranes having ends which are bound with resin to form a bound portion, and a seal member provided on the bound portion, and by providing a seal seating for setting the seal member at a specific position of the bound portion.

These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of 6 illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 5 BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a sectional view of an exemplary module f or concentrating pathogenic protozoa in accordance with the present invention; Fig. 2 is a sectional view of a hollow f iber module of aa internal pressure mode of Comparative Example 1; Fig. 3 is a schematic view illustrating a liquid flow in a concentration test using a module for concentrating pathogenic protozoa in accordance with the present invention; Fig. 4 is a schematic view illustrating a liquid flow in a concentration test using Comparative Example Fig. 5 is a side view of an exemplary hollow f iber membrane cartridge for collecting protozoa using a U-shaped bundle of hollow fiber membranes in accordance with the present invention; Fig. 6 is a view of a cross-sectional face of the exemplary hollow f iber membrane cartridge-f or collecting protozoa shown in Fig. 5; 25 Fig. 7 is a sectional view taken along line B-B 7 of Fig.5; Fig. 8 is a sectional view of an exemplary module using the hollow f iber membrane cartridge for collecting protozoa shown in Figs. 5 to 7. 5 DESCRIPTION OF THE PREFERRED EMBODIMENTS EMBODIMENT 1

As regards the material for the membrane mentioned in the aforesaid first conclusion, there has been paid attention to the adsorption of cryptosporidiums on the surface of membranes. It is a well-known fact that hydrophilic and hydrophobic properties of membranes much affect releasability of fine particles adhering to the surface of the membranes and that the more hydrophilic the membranes are, the more releasable the particles are. The most common indications for judging the hydrophilicity hydrophobicity of membranes are contact angle and water absorption. The contact angle of separatory membranes is determined using flat ones. More particularly, in the present invention, f lat membranes were obtained by dissolving cellulose acetate polymer in a solvent of dimethylsulfoxide (DMSO) so that the concentration of cellulose acetate was 1 Bwt%, f low-casting the resulting mixture onto a glass plate, and drying the flow-cast 8 mixture in an oven at 180C for about two days. The contact angle was determined by an automatic contact angle meter CA-Z produced by Kyowa Kaimen Kagaku Co., Ltd., Japan in a prescribed manner. More specifically, the contact angle was measured by a liquid-drop shape method, according to which drops of water were dropped on the membranes and the angle defined by the drops and the membranes when they contacted each other were measured. The contact angle of the cellulose acetate membranes was f ound to be 5 0 0 to 5 5 0. on the other hand, the contact angle of polyethersulf one membranes measured in the same manner was 650 to 700.

Another indication of hydrophilicity is that of water absorption of flat membranes. The water absorption is calculated by the following equation:

Water absorpion = 100 ( (WI - WO) / Wo) % wherein W,, is weight of an absolutely dry f lat membrane which has been dried in an oven at 180T for two days and W, is weight of the same flat membrane which has been immersed in pure water at 250C for a day, taken out of the water and wiped with Kim wipes (manufactured by Kimberly-Clark Corp.) quickly so that water drops on its surface are removed. when measured in this way, the water absorption of cellulose acetate membranes was 4.7 wt% to 6.5 wt% and that of polyethersulfone, membranes 9 was 0.40 wt% to 0.43 wt%.

The thus obtained contact angle and water absorption values both indicate that the cellulose acetate membranes are much more hydrophilic than the polyethersulf one membranes. As such, it maybe expected that cryptosporidiums adhering to cellulose acetate membranes are more releasable.

As to the aforesaid second conclusion, it is considered that the pore diameter affects the sticking of cryptosporidiums to membranes. In both the Provisional Test Method and the conventional art concentration filter, the pore diameter of a membrane is around 1 gm, which is within the range of microfiltration. Accordingly, the surface of the membrane has a network-like structure and has rough depressions and projections, as seen from a scanning electron microscopic photograph. When a sample water containing cryptosporidium is concentrated by filtration, a pressure of about 50 kPa to about 100 kPa is applied for a long time. The shape of cryptosporidium oocysts is nearly spherical, but they readily deform. Presumably, the cryptosporidium oocysts are present on the surface of the membrane, sticking into its network-like structure. This is considered to be the reason the collection ratio of cryptosporidium oocysts is not improved even when they are collected after concentration, either with or after shaking. It is thought that this problem may be solved by smoothing. the surf ace of the membrane and decreasing the surface pore diameter of the membrane by an order of magnitude A& compared with microfiltration membranes.

More particularly, the collection ratio can be expected to improve greatly with use of an ultraf iltration grade membrane. Since it is said that 10 the pore diameter of an ultraf iltration membrane having a cut-of f molecular weight of 2, 000, 000 daltons is about 0.01 um, a membrane having a cut- off molecular weight of 2, 000, 000 daltons or less is considered to be suitable for this application. However, with a view of improving the collection ratio further, it is preferable to use an ultrafiltration membrane having a cut-off molecular weight of 500,000 daltons or less.

The third problem relates to the type of the module. In the conventional module with a pleated membrane, valley portions of the membrane contact each other closely, and cryptosporidium oocysts adhering to the valley portions do not come off easily. This is assumed to be a cause which suppresses the collection of cryptosporidium oocysts. Changing the type of the module into one such that surfaces of membranes do not contact each other and using hollow fiber membranes of an external pressure mode, which have a large f ilter area per unit occupied volume, are expected to bring about great improvement in the filtration efficiency and 5 collection ratio.

From the above-mentioned views, the present invention provides a novel module for detecting cryptosporidium which uses hollow f iber ultraf iltration membranes of an external pressure mode which are made of cellulose acetate.

As regards cellulose acetate as material for the hollow fiber membranes of the present invention, its acetic acid content is not particularly limited as far as it can be dissolved in typical organic solvents.

However one having an acetic acid content within the range of 40% to 62% is usually used, and one having an acetic acid content within the range of 55% to 62% is preferably used. The average polymerization degree is to 360, preferably 140 to 280.

In the present invention, a membrane-forming solution suitable for producing the desired hollow fiber membranes may preferably be a solution of cellulose acetate in a polar organic solvent which has a 10 wt% to 30 wt% content of cellulose acetate with respect to the total weight of the membrane-f orming solution. More 12 preferably, the content of cellulose acetate is 15 wt% to 23 wt%. As the polar organic solvent, 1,4-dioxane, dimethyl sulfoxide, N,N-dimethyl formamide, N- methyl-2-pyrrolidone and 2-pyrrolidone can be mentioned as examples, but the polar organic solvent is not particularly limited to these compounds. A non-solvent such as ethylene glycol and polyethylene glycol may be used in addition to the above-mentioned solvent.

Especially, ethylene glycol may be used as an additive preferably for forming the target membrane structure.

Since the viscosity of the membrane-forming solution increases with an increase in the addition amount of these additives, the addition amount may preferably be 1 to 30 wt% with respect to the total amount of the membrane- forming solution in view of spinability. The addition of plasticizers such as triethyl phosphate and diethylene glycol dimethyl ether causes inconveniences such as the thickening of a dense layer and prevention of generation of voids, and therefore is unpreferable because the required water permeability is not obtained.

For producing the hollow f iber membranes f rom the above-described membrane-forming solution, the conventionally employed process for producing hollow fiber membranes may be applied. More particularly, the membrane- forming solution is extruded from an outer tube 13 of a double-tube type nozzle while flowing an inside coagulating agent out from an inner tube of the nozzle, and coagulated in a coagulating bath by dry-wet spinning or by wet spinning, thereby to obtain a hollow fiber membrane. The temperature of the inside coagulating agent or of the coagulating bath may preferably be 30C to 800C. If the temperature is lower than 300C, the dense layer forms thick on the surface of the membrane and therefore the target permeability cannot be obtained. If the temperature exceeds 80'C, a normal hollow fiber membrane cannot be obtained. Inthe case of the dry-wet spinning, the distance from the extruding end of the nozzle to the surface of the coagulating bath, which distance def ines a dry area, may be suitably 0.1 cm to 50 cm, more suitably 0.5 cm to 30 Cm. The membrane-f orming solution may be introduced in the coagulating bath after being passed through the air for 0.2 seconds or more. Usable as the inside coagulating agent and coagulating bath for the production of the membrane are water, ethylene glycol, polyethylene glycol and the like which are non-solventa to cellulose acetate, a combination thereof, and a combination of at least one of these non-solvents and at least one of the above- mentioned solvents. Especially, water and a 14 combination of water with polyethylene glycol are preferable since they have good membrane forming characteristics and the target average pore diameter can be obtained. In the case of the combination of water and polyethylene glycol, a weight ratio of water to polyethylene glycol of 70 to 1 / 30 to 99 is preferable since membrane-formation characteristics and membrane properties are well balanced. Further, polyethylene glycol preferably having an average molecular ratio of about 200 is preferable.

Since the hollow fiber membranes of the present invention are operated under external pressure, the membranes have the dense layer on the outside surface thereof. Where the dense layer has a small average pore diameter, a practical water permeability cannot be obtained. For this reason, the average pore diameter on the surfaceof the dense layermay preferably be 0.001 Umto 0.05 gm, more preferably within the rangeof 0.005 /-tm to 0.03 m, which is equivalent-to a cut-off molecular weight of 10,000 to 500,000 daltons.

The thickness of the hollow fiber membranes of the present invention is adjusted within the range of gm to 500 /Lm in order to obtain a Larger membrane strength and a higher water permeability. If the thickness is smaller than 50/um, the strength in use is poor. on the other hand, if the thickness is larger than 500 gm, the membrane strength increases but the water permeability declines. Since such thickness is not practical, the thickness is preferably within the range of 100,um to 400 gm. with a thickness in this range, a water permeability of 150 liters /M2 -h or higher may be ensured.

The most preferable embodiment of the module for concentrating pathogenic protozoa according to the present invention is a hollow fiber membrane module of an external pressure mode using hollow fiber ultraf iltration membranes of cellulose acetate which are suitable for concentrating cryptosporidiums.

Fig. 1 is a sectional view of an exemplary module in accordance with the present invention. The figure shows a non- limitative example for applying the invention to this use. -More particularly, the arrangement of the hollow fiber membranes and the membrane area to be used can be optionally selected. The packing ratio of hollow fiber membranes packed in a module case is selected from the range of 5% to 50%, preferably 10% to 35%. Here the packing ratio is calculated by dividing the total cross-sectional areas of the hollow f ibers inserted inside the case in terms of outer diameter by the cross-sectional area of the 16 module case in terms of inner diameter. If the packing ratio is less than 10%, the module has the defect that the concentration coefficient is poor and the concentration operation takes a long time. If the packing ratio exceeds 35%, the surfaces of the membranes are so close to each other that the collection ratio of cryptosporidiums adhering to the surfaces of the membranes may decline.

The present invention is now described in f urther detail by way of examplea thereof.

Properties, i.e., water permeability and cut off molecular weight, of hollow fibers of the present invention were determined by the following methods.

(1) Water permeability A module was produced which was composed of ten hollow fibers having an effective length of 50cm, which were bundled to form the shape of a letter U and accommodated in a case of 2cm inner diameter and 30cm length, as shown in Fig. 1.

In other words, a module 1 for concentrating pathogenic protozoa included a hollow fiber ultrafiltration membrane bundle 8 and a case (having a cap 3 and a body 7) which accommodated the hollow fiber membrane bundle 8. The hollow fiber membrane bundle 8 was made up of a plurality of hollow fiber 17 ultraf iltration membranes which had a specific contact angle and a specific water absorption and were bundled in U-shape, and both end portions of the hollow fiber membrane bundle were bound with resin. The inside of the case was partitioned liquid-tight into a raw-water side and a filtrate-water side by the hollow fiber membrane bundle 8 accommodated therein. A raw-water nozzle 2 which served as a raw-water inlet and a concentrate-water outlet was provided on the raw-water side, and a filtrate-water nozzle 6 which served as a f iltrate-water outlet was provided on the f iltrate-water side. Reference numeral 4 is a vent nozzle. Pure water at 25C was supplied into this module under a transmembrane pressure of 98.1kPa by a dead end filtration method. The amount of water penetrating inside the hollow f ibers was measured and converted in terms of a unit area. (2) Cut-off molecular weight Solutions of the below-mentioned substances in a phosphoric acid buffer solution (pH 7) having a concentration of 100mg/L (Cl) were each supplied by the dead end filtration method into the module used for the above-described determination of the water permeability. Twenty minutes af ter the solution began to be supplied, the concentration of filtrate solution (C2) and that of 18 the solutions remaining in the module case (C3) were determined. The stopping ratio R of the hollow fiber ultra f iltrat ion membrane was calculated by the following equation. 5 R = 200 (C2) / (CI + C3) (%) The dissolved substances were bovine serum albumin (molecular weight was 68, 000 daltons), y globulin(molecular weight was 150,000 daltons) and urease (molecular weight was 480,000 daltons). The solute rejection to the solutions and the molecular weights of the substances were plotted in ordinate and in abscissa, respectively. Molecular weight corresponding to a solute rejection of 90% on the resultant curve was assumed to be the cut-off molecular weight of the hollow fiber ultrafiltration membrane.

Example I

A membrane-forming liquid containing 19 wt% cellulose acetate (acetylation degree was 56. 1%, average polymerization degree was 180, contact angle was 510 water absorption was 6.1 wt%, manufactured by Daicel Chemical industries, Ltd.), 20 wt% ethylene glycol and 61% N-methyl-2-pyrrolidone was extruded from the outer tube of a double-tube type nozzle while at the same time an inside coagulating agent containing 100 wt% water at 19 70C was extruded from the inner tube of the doubletube type nozzle. The extruded liquid was passed in the air for 2 seconds, coagulated from the inside surface and the outside surface in a coagulating bath at 70C, and then immersed in water and desolvated. Hollow fibers of 0.6mm inner diameter and 0.9mm. outer diameter were thus obtained. The water permeability of the hollow f iber membranewas 600 liters/m' - h and the cut-of f molecular weight was 150,000 daltons. one hundred and fifty of the hollow fiber membranes, which had an effective length of 33cm, were curved in U-shape and made into the module shown in Fig. 1. Ef f ective membrane area of this module was 0. 14 M2, and the packing ratio was 27%. The case of the module 1, including both cap 3 and body 7, was made of acrylic resin. The case was 27cm. in length and the outer diameter of the body 7 of the case was 3.6cm. The end portions of the hollow f iber membrane bundle 8 were bonded to the case with an adhesive of urethane resin, Fig. 3 illustrates a system including this module which system was employed for concentrating cryptosporidiums. Referring o Fig. 3, liquid which contained 298 cryptosporidium oocysts per 100 liters of raw water was prepared, and 100 liters of the liquid were poured in a raw-water tank 9. The module 1, provided with a water stopper 5, was connected to the raw-water tank 9 via a roller pump 10. At this stage, the module 1 was set in such a manner that the f iltrate-water nozzle 6 was on the top and attention was paid so that air in tubing and the module 1 could be removed by the vent nozzle 4. The roller pump 10 was operated to send 100 liters of raw water to the raw-water nozzle 2 at a rate of 30 liters/h or less. After the concentration by filtration was finished, the moule 1 was detached from the system. water stopping tubes were attached to the raw-water nozzle 2 and the f iltrate-water nozzle 6. The eluting solution used for a capsule filter in U.S.EPA Method 1622, 80ml, was introduced in the module 1 from the vent nozzle 4. The module 1 was shaken for five minutes by a shaker (wrest-action shaker 3589JPN produced by Kanto Chemicals, Co., Ltd., Japan). Here the U.S.EPA Method 1622 is a test method established by the U.S. Environmental Protection Agency for detecting cryptosporidiums in water. According to detailed preparation of the eluting solution used for the method described in 117. 0 Reagents and Standards" of the above-mentioned Method 1622, the eluting solution is prepared as follows: one gram of Laureth-12 is put in a glass beaker together with IOOmL of reagent-grade pure water and dissolved well using a hot plate or microwave.

21 The resulting mixture is then transferred into a 10OOmL cylinder, to which 10ml of Tries buffer (pH 7-4), 2ML of EDTA solution (pH 8.0) and 150gL of Antiform A were added. Further 10OOmL of reagent-grade pure water is added. Methods 1622, 7.4 also provides makers I name and products, numbers regarding all reagents to be used in this method.

After shaking the module, the eluting solution was recovered into a centrifugal tube. Then 80ml of the eluting solution was added again to wash the inside of the module and was recovered.

The recovered eluting solution was diluted to 200ml with water purified by a water-purifier (trade-name: Milli-Q produced by Nihon Milipore, Ltd Japan), 50ml of which was filtered by ten filters of cellulose acetate (5ml per filter). After staining, oocysts were counted. The total count of oocysts on the ten filters was 73.

Accordingly, the module exhibited a remarkably high recovery of cryptosporidium oocysts, that is, (73 X 4 / 298) X 100 = 98%.

Comparative EXample 1 The same hollow f iber membranes as used in Example 1 were formed into a module of an internal pressure mode 22 as shown in Fig. 2 which included a case of th I e same material as used in Example 1. The size of the module was 27 cm in total length and the outer diameter of the case body was 3.6 cm, as the external pressure mode module.

Five hundred sixty (560) hollow fibers of 16cm effective length were put in the case. Both ends of the case were sealed with a urethane-base adhesive. The configuration of the module and the arrangement of the hollow fiber membranes are shown in Fig. 2. Referring to Fig. 2, raw water was fed from a raw-water nozzle 12 provided at a cap 13 at one end of the module 11. Raw water flew through the inside of the hollow fiber membranes 17 and the filtrate water having passed through the membranes was discharged from the filtrate-water nozzle 14. A water stopper was attached to a concentrate-water outlet nozzle 16 provided at a cap 13 at the other end of the module 11 during normal concentration operation.

The effective membrane area of the module was 0.17 M2 in terms of inner surface area and the packing ratio was 50%. Fig. 4 shows a system for concentrating cryptosporidium-containing liquid using this module 11.

As shown in Fig. 4, 100 liters of raw water containing 298 cryptosporidiums (concentration was 298/100 liters) were put in a raw-water tank 18. The water stopper 15 was attached to the concentrate-water outlet nozzle 16 of the module 11. That is, by the deadend filtration method, 100 liters of raw water were all sent to the raw-water nozzle 12 using a roller pump 19 and filtered by the internal pressure mode. Next, for recovering cryptosporidiums adhering to the inner surface of the membranes, a water stopper was attached to the filtrate-water nozzle 14 of themodule 11, and themodule 11 was stood up vertically with the raw-water nozzle 12 at the bottom. The tip of the raw-water nozzle 12 was put into a centrifugal tube (2 2 5ml). The water stopper 15 on the concentrate-water outlet nozzle 16 was removed and 20ml of eluting solution was fed. Subsequently, water stoppers 15 were attached to the raw-water nozzle 12 and the concentrate-water outlet nozzle 16. The water stopper on the f iltrate- water nozzle 14 was removed and 60ml of eluting solution was poured therefrom. This eluting solution was the same as that used in Example 1. Nitrogen gas was introduced at a pressure of 30kPa from the f iltrate- water nozzle 14 to allow the eluting solution to penetrate into the hollow f ibers. The water stopper was again attached to the f iltrate- water nozzle 14. The module was stood up vertically and the tip of the raw-water noz z le 12 was put into the centrifugal tube.

24 The water stopper 15 was removed from the concentrate-water outlet nozzle 16 to let the eluting solution flow into the centrifugal tube. Subsequently, 40ml of the eluting solution was fed from the concentrate-outlet nozzle 16. Nitrogen gas was introduced from the concentrate-water outlet nozzle 16 under a pressure of 30kPa for five minutes, and the eluting solution was recovered.

The recovered eluting solution was diluted into 200ml with water purified by Milli-Q, 60ml of which was filtered by six filters of cellulose acetate and stained for counting the number of oocysts. The total count of recovered cryptosporidium oocysts on the six filters was 25. Given that the count of cryptosporidium oocysts in 200ml was assumed to be 83, the recovery was 28%.

EMBODTMENT 2 Attention is paid to the fact that, in a cartridge wherein both end portions of the bundle of hollow fiber membranes are bound with resin, water puddles on the concentrate-water side is a cause of decline in reliability when protozoa are taken out of the cartridge. So the construction of the cartridge is so simplified that less water is stagnant at the bound portion of the cartridge.

A cartridge according to the present invention includes a U-shaped bundle of specif ic ultraf iltration membranes, of which end portions are bound integrally using resin to form a bound portion, and a ring-form seal member provided around the outer periphery of the resin-bound portion. usable as the ring-form seal member are any seal members that are usually used in the art, including an O-ring, for example. The cross- sectional configuration of the seal member may be circular, square, stellar or the like as commonly seen in the art. materials therefor are not particularly limited, but f luororubbers, ethylene propylene rubbers, nitrile rubbers, silicone rubbers and natural rubbers may be mentioned for example.

The cartridge of this embodiment of the present invention is composed at least of a bundle of hollow f iber membranes with a seal-binding member therefor and a ring-form seal member. In the case where the sealbinding member is made of a resilient resin, the seal-binding member is readily deformed by the ringform seal member. In such a case, a rigid ring-f orm seal member may be used at the out periphery of the bundle of hollow fiber membranes and the seal-binding member of resin, for preventing deformation. Material for the ring-formed sealing member in this case is not 26 particularly limited, but may be a rigid resin or a metal, for example. Material for the seal-binding member are not particularly limited, but in general a synthetic resin is often used. Examples of such resins are epoxy 5 resins, polyurethane resins, silicone resins and polyolef in resins. Especially resins which can be used as adhesives are preferred.

The hollow fibers used in the present invention pref erably have an inner diameter of about 0. 1 mm to about 3 mm, more preferably about 0.2 mm. to about 1 mm.

Material therefore is not particularly limited, but cellulose acetate resins, polyacrylonitrile resins, polysulfone resins, polyethersulfone resins, polyolef in resins, polyvinyl alcohol resins, polyimide resins, polyamide resins, resins containing fluorine groups and silicon resins may be mentioned for example.

Further, for protecting the hollow fiber membranes, a protective net and/or a perforated protective cylinder which is usually used in the art may be used in the present invention.

The size of the cartridge of the present invention is not particularly limited, but may be, for example, about 5 0 mm. to about 2, 0 0 0 mm in length, preferably about 100 mm to about 500 mm. in length, because a cartridge having such length can easily be adapted for use 27 according to the present invention. The number of hollow f iber membranes used in the cartridge may be about to 100,000, preferably about 10 to 1,000, though it depends on the outer shape of the cartridge.

As to the position of the ring-form seal member, it is suitably mounted at a distance of 5mm or less from a border of the bound portion where the hollow fiber membranes are exposed, that is, from the border on the filtration side. with this construction, substantially no puddles of water are f ormed on the raw-water side where protozoa are being concentrated. Therefore, reliable collection of protozoa can be realized. More preferably, this distance maybe 2mmor less. Still more preferably, the ring-form seal member is fixed to the bound portion of the bundle not by means of a groove formed around the border on the hollow fiber membrane exposing side, but by means of a falling step or a cut formed there. This construction improves reliability even more.

Preferably, in the cartridge of the present invention, the bundle of hollow fiber membranes forms a curved portion of the shape of U on the side opposite to the bound portion thereof and there the hollow fiber membranes are not bound to adjacent hollow f iber members.

This construction can reduce puddles of water.

In the case where the hollow fiber membranes is 28 formed in a U shape, it is preferable that the cartridge includes two or more U-shaped bundles of hollow fiber membranes, which cross each other at the curved portions of the U shape. With the curved portions crossing each other, the bundles of hollow fiber membranes do not become thick at the curved portions, and the hollow f iber membranes do not come in close contact with adjacent hollow fiber membranes easily at the curved portions. Therefore puddles of water are not formed readily. If the number of bundles in the cartridge are too large, the production process becomes complicated and production costs rise unnecessary and uneconomically. The number of bundles is preferably about two to ten, more preferably two to four.

The module (also referred to as a cartridge module) proposed by the present invention has a construction in which the periphery of open edges of the hollow fiber membranes is pressed by a cap. The cap may be connected to a housing, i.e., a case body, for accommodating the cartridge by any means that provides a detachable connection. For example, the cap may be connected to the housing by threads which engage the inside of the cap and the circumference of the housing. A seal member, e.g., an O-ring, may be located between the cap and the housing. Alternatively, a one-touch 29 coupling or a clump may be used for connection. A portion inside the cap at which the cap presses the cartridge is not particularly limited, but may have a configuration which allows engagement with a pressed face of the cartridge. A rubber member may be provided to function as a buffer.

With the above construction, the hollow fiber membrane cartridge can easily be held inside of the housing, and can easily be attached to and detached from the housing. Materials for the cap and the housing are not particularly limited, but may generally be rigid synthetic resins or metals, including acrylic resins, polyolefin resins, polysulfone resins, polycarbonate resins, nylon resins, polyvinyl chloride resins, ABS resins, As resins, resins containing fluorine and stainless steel, for example.

On a side wall of the case (i.e., the housing) containing the bundle of hollow fiber membranes, provided are an inlet for introducing untreated liquid and a small-sized nozzle for discharging and introducing air. On an opposing side wall, provided is another small-sized nozzle for discharging and introducing air. If air stays in the housing, filtration cannot be performed effectively. An air filter may be added for drawing out air, but puddles may form around the air filter. For this reason, the small-sized nozzles for discharging and introducing air are provided at specific positions for effectively d is charging air without giving rise to puddles. 5 An exemplary module according to the present invention is shown in Figs. 5 to 8, which should not be construed to limit the scope of the present invention. Figs. 5 to 7 illustrate an exemplary hollow fiber membrane cartridge for collecting protozoa according to the present invention. Figs. 5 and 6 are a side view and a cross- sectional face view of the exemplary cartridge using a U-shaped bundle of hollow fiber membranes, and Fig. 7 is a cross-sectional view taken along line B - B' of Fig. 5.

In a cartridge 20 shown in Figs. 5 to 7, two U-shaped bundles 21 of hollow fiber membranes cross each other at curved portions of the shape of U. Both end portions of the hollow fiber membrane bundles 21 are adhesive-sealed (bound) integrally using a sealing resin 24. Further, a ring member 23 is engaged on the outer periphery of the sealing resin 24 so as to form a bound portion. On the outer periphery of this ring member 23 in the bound portion, disposed is an O"ring 22 as the ring-form seal member along a groove 25 provided as a seal seating on the ring member 23. The distance between 31 the O-ring 22 and an fiber membranes exposing edge of the bound portion is denoted by A in Fig. 5 and should not exceed 5mm. A protective net or a protective cylinder is usually used for protecting the U-shaped hollow fiber membrane bundles, but is not shown in the figures for simplicity of illustration.

Fig. 8 is a cross-sectional view illustrating an exemplary hollow fiber membrane cartridge module for collecting protozoa according to the present invention.

More specifically, the cartridge module of Fig. 8 is one having the hollow fiber membrane cartridge for collecting protozoa shown in Figs. 5 to 7 accommodated in a space def ined by a housing, i.e., a cylindrical case body 27, and a cap 28 for closing an opening of the case body. The case body 27 and the cap 28 are connected to each other by engaging threads and sealed liquid-tight with an O-ring 29. The ring member 23 of the cartridge is pressed against the inside wall of the housing and is also sealed liquid-tight to the case body 27 by the O-ring 22. Sample liquid is introduced to the inside of the housing via an untreated-liquid inlet 32. Air in the housing is discharged outside the housing via an air discharging/introducing nozzle 30 as a first small- sized nozzle or via an air discharging/ introducing nozzle 31 as a second small-sized nozzle by loosening 32 the nozzle 30 or 31. The nozzles 30 and 31 are much smaller than the untreated- 1 iqu id inlet 32. The nozzle 31 opposes the untreated- liquid inlet 32. When all air in the housing is replaced with the sample liquid, the nozzles are closed. The sample liquid, as introduced into the housing, is filtered by the hollow fiber membranes 21. Filtered liquid from which protozoa have been removed is discharged outside the module via a filtrate liquid discharge nozzle 33 of the cap 28.

Concentrate liquid in which protozoa have been concentrated stays in a space defined by inner walls of the case body 27, outer surfaces of the hollow fiber membranes and the O-ring 22. At this time, where the position of the O-ring 22, i.e., the value of A, is within 5 mm from the hollow fiber membrane exposing edge, puddles may be suppressed. Besides, since the nozzles provided on the side walls of the case body 27 are of required minimum size, only a little amount of liquid stays there. With these ideas, the concentrate liquid can be collected most effectively, which allows reliable examination of liquid.

Referring to the module of Fig. 8, the cartridge will readily come off the housing without need to be operated by hands if pressure is applied from the untreated-liquid inlet 32 after the cap is removed 28.

33 A small pressure of 98kPa or lower may be enough for detaching the cartridge. Thus, removal of the cartridge is found to be very convenient.

Example 2

Two U-shaped bundles were prepared, each comprised of forty hollow fiber ultrafiltration membranes of cellulose acetate having an inner diameter of 0.8 mm and an outer diameter of 1.3 mm (FUC1582 having a contact angle of 540 and a water absorption of 5.7 wt%, produced by Daicen Membrane-Systems, Ltd., Japan). The bundles were put together to cross each other at their curved portions and inserted through a ring member of acrylic resin having an outer diameter of 40 mm, an inner diameter of 34 mm and a value of 2 mm for the distance A. Both end portions of the hollow fiber membrane bundles were adhesive-sealed with an urethane resin adhesive (Coronate 4403, Nippollan 4221 produced by Nippon Polyurethane Industry Co., Ltd., Japan) while distributing the hollow fiber membranes uniformly. Thus a cartridge having an effective membrane area of 0.1 M2 (in terms of outer diameters of hollow fiber membranes) as shown in Figs. 5 to 7 is provided. An O- ring of nitrile rubber of 2.62mm thickness was engaged with the groove. This cartridge was inserted in a 34 transparent housing (case) of acrylic resin as shown in Fig. 8, thereby to produce a hollow fiber membrane cartridge module for collecting protozoa. The size of the module was 220 mm, (L) x 55 MM (0).

For the purpose of determining retention of liquid within the module as an index, a sample liquid containing 0.2g of Bentonite (produced by Wako Purechemical Industries, Ltd., Japan) dispersed in pure water was filtered by the above-described module by the external pressure method. Then, 140ml of concentrate liquid were taken out of the untreated-liquid side. Subsequently, 50ml of pure water was added into the module to rinse the inside thereof and then recovered. This operation was repeated twice in total. All the recovered liquid was evaporated and the amount of remaining solid substance was determined. The amount was 0.17g. Comparative Example 2 20 A hollow fiber membrane cartridge module was produced in the same manner as in Example 1 except that the distance A for the ring member was 10mm. For obtaining an index representative of the retention of liquid within this module, the amount of remaining solid substance was determined in the same manner as in Example 2. The amount was 0.13g.

As shown above, the hollow fiber membrane cartridge module for collecting protozoa in Embodiment 2 can collect concentrate liquid with high reliability after protozoa are concentrated. Therefore reliable detection of protozoa can be realized.

Also the providing of hollow fiber membranes in the form of a cartridge may reduce the amount of wastes and the number of components, thereby reducing production costs. Thus the present invention has economical advantage.

Though the hollow fiber membrane cartridge and cartridge module of the present invention is intended for collection of protozoa, the invention may also be applied to any use that requires similar operation and functions such as collection of fungi, viruses or a trace of values by concentration.

The module f or concentrating pathogenic protozoa according to present invention exhibits an excellent filtration efficiency and has enabled achievement of a f ar higher collection ratio f or pathogenic protozoa than conventional modules, by use of hydrophilic ultraf iltration membranes having a contact angle of 600 or leas and a water absorption of 4.7 wt% or more, more 36 suitably by conducting concentration of the external pressure type by the dead end filtration method by use of hydrophilic hollow fiber ultrafiltration membranes of cellulose acetate which have a larger filter area per occupied volume than do conventional flat membrane filters.

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Claims

What is claimed is:

1. A module for concentrating pathogenic protozoa constructed to concentrate raw water by filtration, comprising: an ultrafiltration membrane having a contact angle of 600 or less and a water absorption of 4.7wt% or higher.

2. A module for concentrating pathogenic protozoa according to claim 1, wherein the ultrafiltration membrane is a hollow f iber membrane of cellulose acetate.

3. A module for concentrating pathogenic protozoa according to claim 2, wherein the hollow fiber membrane has an external pressure mode.

4. A module for concentrating pathogenic protozoa according to any one of claims 1 to 3, wherein the ultrafiltration membrane has a permeability of 150 liters/m' - h or higher to pure water at 25T under a trans-membrane pressure dif f erence of 98. 1kPa across the membrane.

5. A module for concentrating pathogenic protozoa comprising% 38 a bundle of a plurality of hollow fiber ultraf iltration membranes having end portions and having a contact angle of 600 or less and a water absorption of 4.7wt% or higher, the end portions of the hollow fiber ultraf iltration membranes being bound with a resin, and a case for accommodating the bundle of hollow fiber ultrafiltration membranes to provide sl liquid-tight partition between a raw-water side and a filtrate- water side thereof, the case being provided with a raw-water inlet and a concentrate-water outlet on the raw-water side thereof and a filtrate-water outlet on the filtrate-water side thereof.

6. A module for concentrating pathogenic protozoa according to claim 5, wherein the plurality of hollow fiber ultrafiltration membranes are bundled into a U-shaped bundle.

7. A module for concentrating pathogenic protozoa comprising:

a cartridge including a U-shaped bundle of a plurality of hollow fiber ultrafiltration membranes having end portions and having a contact angle of 60' or less and a water absorption of 4.7wt% or higher, the end portions of the hollow fiber ultrafiltration 39 membranes being integrally bound with resin so that said end portions of the hollow fiber ultrafiltration membranes adhere to each other to form a bound portion, and a seal member for the cartridge provided at an outer periphery of the bound portion; and a case including a cylindrical case body, a cap for closing an opening of the case body and a seal member for the cap provided therebetween, the case providing liquid-tight partition between a raw-water side and a filtrate-water side thereof by accommodating the cartridge to bring the seal member for the cartridge in close contact with the cylindrical case body, wherein the bound portion has a seal seating for setting the seal member for the cartridge, the seal seating being located on the outer periphery of the bound portion within 5mm. f rom an edge of the bound portion where the bundle of hollow fiber membranes is exposed.

8. A module for concentrating pathogenic protozoa according to claim 7, wherein the hollow fiber ultraf iltration membranes are hollow f iber membranes of cellulose acetate.

9. A module for concentrating pathogenic protozoa according to claim 7, comprising at least two U-shaped bundles of hollow fiber ultrafiltration membranes, wherein one of the U-shaped bundles crosses another one of the U-shaped bundles in proximity of a curved portion of U-shape.

10. A module for concentrating pathogenic protozoa according to claim 7, wherein the cylindrical case body has on a trunk portion thereof a raw-water inlet for supplying raw water, a f irst small nozzle for introducing or discharging air into or from the cylindrical case body and a second small nozzle for introducing or discharging air into or from the cylindrical case body, the second nozzle being opposed to the raw-water inlet.

11. A method for concentrating pathogenic protozoa existing in raw water, comprising:

supplying raw water to an ultrafiltration membrane having a contact angle of 600 or more and a water absorption of 4.7wt% or higher and filtering the raw water with the ultrafiltration membrane.

12. A method for concentrating pathogenic protozoa according to claim 11, wherein the ultrafiltration membrane is a hollow f iber membrane of a cellulose ester.

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13. A method for concentrating pathogenic protozoa according to claim 12, wherein the filtration is carried 5 out under an external pressure.

14. A module for concentrating pathogenic protozoa, substantially as hereinbefore described in examples 1 and 2 and as shown in figures 1, 3 and 5-8. 10

15. An apparatus for concentrating pathogenic protozoa existing in water, comprising a module as claimed in any of claims 1-10 and 14.

16. A method for concentrating pathogenic protozoa, comprising supplying raw-water to a module as claimed in any of claims 1-10 and 14, or an apparatus as claimed in claim 15.

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