JP7777484B2 - Residual chlorine removal filter body - Google Patents

Description

The present invention relates to a residual chlorine removal filter body designed to remove free and combined residual chlorine from water.

Sodium hypochlorite is mainly used to disinfect tap water, and the hypochlorous acid and hypochlorite ions produced when sodium hypochlorite dissolves in water are called free residual chlorine. Free residual chlorine has a bactericidal or disinfecting effect. However, the reaction between ammonia and nitrogen oxides present in natural water and the added hypochlorous acid and hypochlorite ions produces combined residual chlorine, such as chloramines. Combined residual chlorine and free residual chlorine are collectively called residual chlorine. Odor can often become a problem depending on the condition of the raw water taken, the amount of free residual chlorine added, and even the amount of chloramines.

Water purifiers are used to remove residual chlorine from drinking water such as tap water. These purifiers are constructed with an adsorption member made of an inorganic material such as activated carbon or ceramic, and, if necessary, an organic polymer membrane for filtration. In recent years, in response to demand for higher performance in water purifiers and air purifiers, activated carbon is widely used in these filters. For example, because chloramine and ammonia are basic, activated carbon with acidic functional groups on its surface is thought to be effective (see, for example, Patent Document 1). In other words, removal (decomposition) efficiency is improved through chemical reactions that utilize acid-base reactions.

Furthermore, a filter in which activated carbon and calcium sulfite are solidified using a porous polymer has also been proposed (see Patent Document 2). In so-called dry filters, filters have been developed that, even for small filters, increase the density of the activated carbon to improve water purification performance and limit the particle size of the calcium sulfite, thereby accelerating the dissolution of calcium sulfite and maintaining the ability to remove free residual chlorine while ensuring a stable water flow rate.

Hospitals often have independent water sources, such as wells or other groundwater sources, and if the source water is contaminated, it may contain relatively high levels of ammonia. As mentioned above, this can lead to the generation of bound residual chlorine, such as chloramines, when disinfected with free residual chlorine. Bound residual chlorine is difficult to adequately remove using activated carbon filters or reverse osmosis membranes, and in the past, it has been mixed into dialysis water, causing hemolysis in patients. For this reason, water from which residual chlorine has been removed is particularly desirable for use in artificial dialysis in hospitals, and filter media with high removal performance for residual chlorine, including free and bound residual chlorine, are in demand.

In response, a residual chlorine removal filter has been proposed in which activated carbon is mixed with calcium sulfite, molded, and integrated (see Patent Document 3). It has good water permeability and can maintain a high level of residual chlorine removal performance, including both free and bound residual chlorine. It has also been proposed to use porous carbon materials made from raw materials with a high nitrogen content as a chloramine decomposition catalyst (see Patent Document 4).

Japanese Patent Application Laid-Open No. 2002-338222 Japanese Patent Application Laid-Open No. 2008-207174 Japanese Patent Application Laid-Open No. 2020-179374 WO2020/137849 publication

In particular, because hospitals consume large amounts of water with residual chlorine removed for use in artificial dialysis, the filter that removes residual chlorine is required to not only have high residual chlorine removal performance, but also to be highly durable. Furthermore, because of its intended use, it is conceivable that filters will be replaced earlier than their performance limit from a safety standpoint, so demand for highly durable residual chlorine removal filters is increasing.

Furthermore, tap water in Japan is often managed to keep the residual chlorine concentration low to suppress the chlorine odor, and there is a demand for residual chlorine removal filters that can effectively remove chlorine even at low concentrations in water and maintain good removal performance over the long term.

The present invention has been developed in consideration of the above points and provides a residual chlorine removal filter body that combines activated carbon adsorbent and calcium sulfite, and that can maintain high levels of residual chlorine removal performance, including both free and bound residual chlorine, for long periods of time by controlling the amount of sulfite ions eluted when water is passed through it.

That is, the first invention relates to a residual chlorine removal filter body characterized by comprising a first filter section formed by mixing an activated carbon adsorbent and a fibrillated fiber binder in water to form a mixed slurry, adsorbing the mixed slurry onto the side of a hollow cylindrical core member while sucking it, and heating and drying the adsorbed material; and a second filter section filled with calcium sulfite having a particle size of 0.7 to 5.0 mm.

The second invention relates to a residual chlorine removal filter body according to the first invention, in which calcium sulfite having a particle size of 0.1 to 0.5 mm is further mixed into the mixed slurry.

The third invention relates to the residual chlorine removal filter element of the first or second invention, in which the amount of sulfite ions eluted 10 minutes after the start of water flow is 5 to 20 mg/L.

The fourth invention relates to a residual chlorine removal filter body according to any one of the first to third inventions, in which the activated carbon adsorbent is one or more of fibrous activated carbon, granular activated carbon, and powdered activated carbon.

The fifth invention relates to a residual chlorine removal filter body according to any one of the first to fourth inventions, in which the activated carbon adsorbent has an iodine adsorption capacity of 800 to 2000 mg/g.

The sixth invention relates to a residual chlorine removal filter body according to any one of the first to fifth inventions, in which the fibrillated fiber binder is made of acrylic fiber.

The seventh invention relates to a residual chlorine removal filter body according to any one of the first to sixth inventions, which has a combined residual chlorine removal performance of 50 L/mL or more.

The residual chlorine removal filter body of the first invention comprises a first filter section formed by mixing an activated carbon adsorbent and a fibrillated fiber binder in water to form a mixed slurry, which is then sucked onto the side of a hollow cylindrical core member to form an adsorbed material, and the adsorbed material is then heated and dried. The filter body also comprises a second filter section filled with calcium sulfite having a particle size of 0.7 to 5.0 mm. By increasing the particle size and weight of the calcium sulfite, the amount of sulfite ions eluted during the initial water flow is reduced, and sulfite ions are continuously eluted into the water. This controls the amount of sulfite ions eluted during water flow, making it possible to maintain high levels of residual chlorine removal performance, including both free and bound residual chlorine, for long periods of time.

The residual chlorine removal filter body of the second invention is the same as that of the first invention, except that calcium sulfite having a particle size of 0.1 to 0.5 mm is further mixed into the mixed slurry. This increases the weight of calcium sulfite supported on the filter body, and allows sulfite ions to be continuously eluted into water, making it possible to maintain high levels of residual chlorine removal performance, including both free and bound residual chlorine, for long periods of time.

According to the residual chlorine removal filter body of the third invention, in the first or second invention, the amount of sulfite ions eluted 10 minutes after the start of water flow is 5 to 20 mg/L, so the amount of sulfite ions eluted in the early stages of water flow can be suppressed so that sulfite ions are continuously eluted into the water.

The residual chlorine removal filter body of the fourth invention, in any of the first to third inventions, has excellent free residual chlorine removal performance because the activated carbon adsorbent is one or more of fibrous activated carbon, granular activated carbon, and powdered activated carbon.

The residual chlorine removal filter body according to the fifth invention is the same as that according to any of the first to fourth inventions, because the activated carbon adsorbent has an iodine adsorption capacity of 800 to 2000 mg/g, it has the general adsorption capacity required of an activated carbon adsorbent.

According to the sixth aspect of the present invention, the residual chlorine removal filter body of any of the first to fifth aspects of the present invention is characterized in that the fibrillated fiber binder is made of acrylic fibers, thereby extending the service life of the filter body.

The residual chlorine removal filter body of the seventh invention, in any of the first to sixth inventions, has a combined residual chlorine removal capacity of 50 L/mL or more, thereby providing good residual chlorine removal performance.

FIG. 2 is a schematic process diagram showing the manufacturing process of the residual chlorine removal filter body.

The residual chlorine removal filter body of the present invention is intended to remove residual chlorine, including free residual chlorine such as hypochlorous acid dissolved in water and bound residual chlorine such as chloramines. The residual chlorine removal filter body of the present invention is installed in, for example, a water purifier or is used in areas where residual chlorine removal is required, such as the water filtration section of an artificial dialysis machine. Filter bodies for liquids such as water include so-called dry filters and wet filters. Dry filters are made by melting a thermoplastic resin to hold an activated carbon adsorbent, which serves as a filter medium. Wet filters are made by mixing a fibrous component, such as resin fiber, as a binder with an activated carbon adsorbent, which serves as a filter medium, and then aspirating and molding the resulting aqueous slurry into a predetermined shape. Wet filters have a structure in which the fibrous component and filter medium are intertwined and integrated.

The residual chlorine removal filter body of the present invention uses a wet filter. Compared to dry filters, wet filters have superior water permeability due to the use of fibrous components as a binder. Furthermore, dry filters have the advantage of a high density and therefore a large amount of activated carbon adsorbent. However, because the activated carbon adsorbent is held in place by melting a thermoplastic resin, the surface of the activated carbon adsorbent may become coated with resin, potentially reducing adsorption performance. In the residual chlorine removal filter body of the present invention, the activated carbon adsorbent and calcium sulfite are held in place by a fibrillated fiber binder, ensuring residual chlorine removal performance while maintaining water permeability.

Activated carbon adsorbents have excellent adsorption performance for residual chlorine, particularly free residual chlorine. The residual chlorine removal filter body of the present invention uses one or more of fibrous activated carbon, granular activated carbon, or powdered activated carbon as the activated carbon adsorbent of the filter medium. The adsorption capacity of the fibrous activated carbon, granular activated carbon, or powdered activated carbon used in the residual chlorine removal filter body of the present invention is comparable to that of general fibrous activated carbon, granular activated carbon, or powdered activated carbon. Specifically, activated carbon is used that has an iodine adsorption capacity of 800 to 2000 mg/g when measured in accordance with JIS K 1474 (2014) and JIS K 1477 (2007).

Activated carbon can be made from raw materials such as wood (waste wood, thinnings, sawdust), coffee bean pulp, coconut shells, bark, and fruit. These naturally derived raw materials are more susceptible to pore development when carbonized and activated. Furthermore, because they are secondary waste materials, they can be procured inexpensively. Other materials that can be used include tires, petroleum pitch, burned synthetic resins such as urethane resin and phenolic resin, and even coal. In particular, fibrous activated carbon can be obtained by carbonizing and activating fibers from various carbon materials, including plants, minerals, natural materials, and synthetic materials.

The activated carbon raw material is heated and carbonized at temperatures between 200°C and 600°C, forming micropores. The activated carbon raw material is then activated by being exposed to water vapor and carbon dioxide at temperatures between 600°C and 1200°C. This results in activated carbon with various types of developed pores. Other activation methods include zinc chloride activation. Sequential washing is also performed.

When the particle size of the granular activated carbon is small or when powdered activated carbon is used, the density of the filter body increases, improving its ability to adsorb free residual chlorine. On the other hand, when the particle size increases, the density of the filter body decreases, improving water permeability. Also, if the particle size is too fine, problems such as clogging when water is passing through are more likely to occur. For this reason, it is best to select the appropriate size depending on the desired adsorption performance and the structure of the filter being used.

Fiber-type activated carbon also has excellent water permeability due to its fibrous shape. If the average fiber diameter is too large, the surface area will be small relative to the amount used, which is undesirable in terms of improving adsorption capacity. Fibrous activated carbon with a small average fiber diameter has excellent adsorption performance and particle filtration capabilities. By setting the average fiber diameter of fibrous activated carbon to 20 μm or less, it is possible to form a filter body that is easy to handle, has excellent adsorption performance, and ensures excellent water permeability.

The activated carbon adsorbent may be composed of only one of fibrous activated carbon, granular activated carbon, or powdered activated carbon, or a combination of multiple types. Granular activated carbon and powdered activated carbon are generally inexpensive. Adding a large amount of granular activated carbon or powdered activated carbon improves the density of the filter body, increasing the amount of activated carbon adsorbent per volume. As mentioned above, fibrous activated carbon has excellent water permeability and high adsorption performance per unit weight. Therefore, it is best to determine the blending ratio of fibrous activated carbon, granular activated carbon, or powdered activated carbon appropriately, taking into account the functionality and economy of the filter body.

The binder of the residual chlorine removal filter body of the present invention is made of a fibrillated fiber binder. It is particularly preferable to use a fibrillated fiber binder made of acrylic fiber, aramid fiber, polyethylene fiber, or the like. Acrylic fiber binders do not melt when heated during drying, so the fibrous structure of the binder remains. This also extends the service life of the filter body. The fiber binder acts as a structural material that holds the activated carbon adsorbent together. Being fibrillated is useful because it allows the activated carbon adsorbent to be held more efficiently.

The bound residual chlorine that is the target of removal by the residual chlorine removal filter of the present invention includes monochloramine, dichloramine, and trichloramine. Monochloramine is typically used to disinfect tap water, and the residual chlorine removal filter of the present invention is particularly effective at removing monochloramine.

As mentioned above, activated carbon adsorbents have high adsorption performance for free residual chlorine, and filter bodies that use activated carbon adsorbents as a filter material have high free residual chlorine removal performance. Therefore, the residual chlorine removal filter body of the present invention combines activated carbon adsorbents, a filter material that primarily removes free residual chlorine, with calcium sulfite as an ingredient that primarily removes bound residual chlorine. The calcium sulfite incorporated into the filter body releases sulfite ions that dissolve into the water and react with bound residual chlorine such as chloramines, decomposing and reducing the bound residual chlorine, thereby removing the bound residual chlorine.

Next, we will use Figure 1 to explain the manufacturing process for the first filter section of the residual chlorine removal filter body. First, activated carbon adsorbent 20 (granular activated carbon 21, fibrous activated carbon 22), fibrillated acrylic fiber binder 23, and, if necessary, calcium sulfite 24 are added to water W and thoroughly mixed to prepare a mixed slurry 30.

A porous mold rod 35 is inserted into the hollow cylindrical core 11 to vacuum-suck the mixed slurry. The hollow cylindrical core 11 has small holes (not shown) for permeation, and the mold rod 35 is made of porous stainless steel. The combined hollow cylindrical core 11 and mold rod 35 are lowered into the mixed slurry 30, and vacuum-sucking is performed through the mold rod 35, causing the mixed slurry 30 to adhere to the side of the hollow cylindrical core 11. As shown in the cutout, a slurry-adhered portion 26 is formed on the surface of the hollow cylindrical core 11. After a predetermined amount of the slurry-adhered portion 26 has formed, the hollow cylindrical core 12 is pulled out of the mixed slurry, and the mold rod 35 is removed. This results in an adsorbed adherend 25 with the slurry-adhered portion 26 on the surface of the hollow cylindrical core 12. The adsorbed adherend 25 is then heated and dried in a dryer 40.

The temperature and time for heat drying are optimally set taking into consideration the melting temperature of the resin component, the size of the adsorbed material itself, the amount of mixed slurry to be adhered, production efficiency, etc. The drying temperature is generally 80-120°C. The acrylic fiber binder does not melt when heated during heat drying, so the fibrous structure of the binder remains.

Calcium sulfite may also be mixed into the mixed slurry. By supporting calcium sulfite in the first filter body as well and increasing the amount of calcium sulfite held in the residual chlorine removal filter body, it becomes possible to release sulfite ions more continuously into the water, and the residual chlorine removal performance can be maintained for an even longer period of time. The calcium sulfite mixed into the first filter section is produced by vacuum-suctioning the slurry, so if the particle size is too large, it will be difficult to suction it evenly, and if the particle size is too small, it will cause clogging when water is passed through or cloudiness in the early stages of water flow. For this reason, a particle size of 0.1 to 0.5 mm is recommended.

To ensure safe drinking water, Article 17, Paragraph 3 of the Water Supply Act Enforcement Regulations (Ministry of Health, Labour and Welfare Ordinance) stipulates that water discharged from taps (faucets) must be disinfected with chlorine to maintain a free residual chlorine level of 0.1 mg/L (0.4 mg/L for combined residual chlorine). When the combined residual chlorine concentration in the raw water is low, it is possible to remove at least the amount of sulfite ions eluted. If the calcium sulfite particle size is small, sulfite ions will be eluted at a high rate in the early stages of water flow, and the amount of sulfite ions eluted will then rapidly decrease. If the calcium sulfite particle size is relatively coarse, sulfite ions will be eluted gradually, allowing sulfite ion elution to be maintained for a long period of time. For this reason, it is recommended that the calcium sulfite particle size in the second filter section be relatively large, between 0.7 and 5.0 mm.

The second filter section is filled with calcium sulfite particles with a particle size of 0.7 to 5.0 mm. Larger particle sizes of calcium sulfite particles have a smaller external surface area per unit volume, which allows for the suppression of sulfite ion elution in the initial stage of water flow. By using calcium sulfite particles with a relatively large particle size in the second filter section, the amount of sulfite ion elution 10 minutes after the start of water flow is set to 5 to 20 mg/L. By suppressing sulfite ion elution in the initial stage of water flow, the occurrence of a temporary peak in elution amount is suppressed, and sulfite ion elution into the water can be controlled continuously.

[Activated carbon adsorbent]
The inventors used the following raw materials as activated carbon adsorbents to prepare a residual chlorine removal filter body.
Granular activated carbon: Futamura Chemical Co., Ltd.: coconut shell activated carbon "CW8150SZ" (average particle size: 0.16 mm)
(Hereinafter referred to as C1.)
Fibrous activated carbon: Futamura Chemical Co., Ltd.: "Phenol-based fibrous activated carbon" (average fiber diameter: 15 μm)
(Hereinafter referred to as C2.)

[Fibrillating binder]
The inventors used fibrillated acrylic resin fibers (trade name: Vipal, manufactured by Nippon Exlan Kogyo Co., Ltd.) as a fibrillation binder to prepare a residual chlorine removal filter body.

[Calcium sulfite]
Calcium sulfite manufactured by Tomita Pharmaceutical Co., Ltd. was used, and the powder was pulverized and separated by average particle size using a sieve. Here, the average particle size was measured as a mass average particle size with reference to JIS K 1474 (2014).
Calcium sulfite classified through a 4/10 mesh (4.75/1.7 mm) sieve to have an average particle size of 1.83 mm is designated as S1.
Calcium sulfite classified through a 10/22 mesh (1.7/0.71 mm) sieve to have an average particle size of 1.15 mm is designated as S2.
Calcium sulfite classified through a 30/100 mesh (0.5/0.15 mm) sieve to have an average particle size of 0.16 mm is designated as S3.
Calcium sulfite classified through a 100/330 mesh (0.15/0.045 mm) sieve to have an average particle size of 0.09 mm is designated as S4.

[Preparation of first filter part]
According to the raw materials and their formulations (unit: parts by weight) listed in Tables 1 to 3, activated carbon adsorbent, fibrillated fiber binder, and calcium sulfite were thoroughly mixed in water to prepare mixed slurries corresponding to each prototype and comparative example. The amount of water in the mixed slurries was 20 times the weight of the added solids. A hollow cylindrical core member for the first filter section was prepared, made of polypropylene, with an outer diameter of 47 mm, an inner diameter of 43 mm, a total length of 113 mm, and pores of 2 mm in diameter. A porous stainless steel mold rod was inserted and fixed into the hollow cylindrical core member and then immersed in the mixed slurry. The solids were then drawn from the mixed slurry by vacuum suction, adhering to a depth of approximately 9 mm on the surface of the hollow cylindrical core member (slurry-adhered portion). The mold rod was then removed from the hollow cylindrical core member, yielding an adsorbent adsorbent, which was an integrated product of the slurry-adhered portion and the hollow cylindrical core member. The adsorbent was then heated and dried in a dryer at 100°C for 12 hours to produce a first filter section for each prototype and comparative example. Each first filter section was a cylindrical body with a diameter of 65 mm and a total length of 113 mm, including a hollow cylindrical core member. The surface of the filter body was covered with a nonwoven fabric made of a polyethylene and polypropylene blend fiber.

[Preparation of second filter part]
A hollow cylindrical core member for the second filter section made of polypropylene was prepared, having an outer diameter of 34 mm, an inner diameter of 30 mm, a total length of 113 mm, and pores of 2 mm in diameter. The first filter section, with a polypropylene cap attached to one side, was inserted into the hollow cylindrical core member, and calcium sulfite was filled between the hollow cylindrical core member and the first filter section. Once calcium sulfite was filled sufficiently to prevent voids, a polypropylene cap was attached. This produced the filter bodies of each prototype and comparative example, and each filter body was a cylinder with a total length of 125 mm.

[Preparation of residual chlorine removal filter body]
The residual chlorine removal filter bodies were prepared as the following prototypes 1 to 5 and comparative examples 1 to 4. Tables 1 and 2 show the raw materials and their compositions (unit: parts by weight).

[Preparation of mixed slurry and preparation of prototypes and comparative examples]
<Prototype example 1>
A first filter section of Prototype Example 1 was prepared by mixing 39 parts by weight of granular activated carbon (C1), 25 parts by weight of fibrous activated carbon (C2), 30 parts by weight of calcium sulfite (S3) having an average particle size of 0.16 mm, and 6 parts by weight of fibrillated acrylic resin fibers to form a slurry. Furthermore, 45 g of calcium sulfite (S1) having an average particle size of 1.83 mm was packed inside the first filter section to form a second filter section of Prototype Example 1, and the filter body of Prototype Example 1 was obtained.

<Prototype Example 2>
A filter body of Sample 2 was obtained in the same manner as Sample 1, except that the calcium sulfite in the second filter portion was changed to calcium sulfite (S2) having an average particle size of 1.15 mm.

<Prototype Example 3>
A filter body of Prototype Example 3 was obtained in the same manner as in Prototype Example 1, except that calcium sulfite was not blended into the first filter part, and a mixed slurry of 57 parts by weight of granular activated carbon (C1), 37 parts by weight of fibrous activated carbon (C2), and 6 parts by weight of fibrillated acrylic resin fiber was used.

<Prototype Example 4>
A filter body of Sample 4 was obtained in the same manner as Sample 1, except that the calcium sulfite in the second filter portion was changed to calcium sulfite (S3) having an average particle size of 0.16 mm.

<Prototype 5>
A filter body of Prototype Example 5 was obtained in the same manner as Prototype Example 1, except that the calcium sulfite in the second filter portion was changed to calcium sulfite (S4) having an average particle size of 0.09 mm.

Comparative Example 1
A filter body of Comparative Example 1 was obtained in the same manner as in Prototype Example 1, except that calcium sulfite was not filled in the second filter portion.

Comparative Example 2
An attempt was made to produce a filter body in the same manner as in Comparative Example 1, except that the calcium sulfite in the first filter section was changed to calcium sulfite (S2) with an average particle size of 1.15 mm. However, the particle size of the calcium sulfite was too large, and the first filter body could not be formed by vacuum suction.

Comparative Example 3
A filter body of Comparative Example 3 was obtained in the same manner as Comparative Example 1, except that the calcium sulfite in the first filter portion was changed to calcium sulfite (S4) having an average particle size of 0.09 mm.

Comparative Example 4
A filter body of Comparative Example 4 was obtained in the same manner as in Prototype Example 3, except that calcium sulfite was not filled in the second filter portion.

[Evaluation items]
<Free residual chlorine removal performance>
The filter bodies of each prototype and comparative example were subjected to a test for the removal performance of free residual chlorine and combined residual chlorine as follows. The test for the removal performance of free residual chlorine was conducted in accordance with JIS S 3201 (2010) for household water purifiers. Water was passed through each filter body at a water temperature of 20°C, a free residual chlorine concentration of 2 ppm (mg/L), and a water flow rate of 2.5 L/min. The free residual chlorine concentration at the inlet and outlet of each filter body was measured to calculate the removal rate. The water flow rate at which the removal rate fell below 80% was defined as the breakthrough point, and the water flow rate (L) until the breakthrough point was reached was measured.

<Removal of combined residual chlorine>
In the combined residual chlorine removal performance test, ammonium chloride and sodium hypochlorite were added to activated carbon filtered water, and the mixture was stirred to prepare sample water with a combined residual chlorine concentration of 0.2 ppm (mg/L). The test was conducted at a water temperature of 20°C and a flow rate of 2.5 L/min. The combined residual chlorine concentration at the inlet and outlet of each filter was measured to calculate the removal rate. The breakthrough point was defined as the amount of water flowing when the removal rate fell below 80%, and the amount of water flowing (L) until the breakthrough point was reached was measured. In the free residual chlorine and combined residual chlorine removal performance tests, the chlorine concentration was quantitatively measured using DPD absorptiometry. The combined residual chlorine concentration was calculated by subtracting the free residual chlorine concentration from the total chlorine concentration. The combined residual chlorine removal performance (L/mL) per unit volume of the filter was also calculated.

<Amount of sulfite ions eluted>
The amount of sulfite ions eluted (mg/L) 10 minutes after the start of water flow was measured and used as the initial amount of sulfite ions eluted. The sulfite ions contained in the water passed through each filter were measured by a calibration curve method using a high-performance liquid chromatograph (HPLC) (Shimadzu Corporation, "Prominence"). The analytical conditions are shown below.
Detector: CDD-10A VP
Column: Shim-pack IC-A3

The test and measurement results for each prototype and comparative example are shown in Tables 3 and 4. Note that for Comparative Example 2, the first filter section could not be molded, so tests could not be performed and this is indicated by "-" in the table.

[Results and Discussion]
Based on the trends in all examples (except Comparative Example 2, in which the filter body could not be formed), it appears that the removal performance of bound residual chlorine is proportional to the particle size of calcium sulfite, and that the removal performance improves as the particle size increases.

Prototypes 1, 2, 4, and 5, in which the particle size of the calcium sulfite in the second filter section was varied, were compared. In this test, in which the concentration of bound residual chlorine was low, Prototypes 1 and 2, in which the particle size of calcium sulfite in the second filter section was larger, demonstrated better bound residual chlorine removal performance. It can be seen that when the particle size of calcium sulfite is larger, the amount of sulfite ions eluted in the initial stage of water flow is suppressed, and the amount of sulfite ions eluted tends to be maintained for a long period of time. This is thought to be why the performance of removing bound residual chlorine was improved. Conversely, when the particle size of calcium sulfite in the second filter section was small, as in Prototypes 4 and 5, the amount of sulfite ions eluted in the initial stage of water flow was large, preventing stable, continuous elution of sulfite ions and resulting in a short-term effect. Based on the above, it is thought that the particle size of calcium sulfite used in the second filter section should be between 0.7 and 5.0 mm.

Furthermore, even in prototype 3, which does not contain calcium sulfite in the first filter section, it was found that good combined residual chlorine removal performance was achieved because calcium sulfite with large particle size was used in the second filter section.

Comparative Examples 1 and 3, which do not contain calcium sulfite in the second filter section, and Comparative Example 4, which does not contain calcium sulfite in the first filter section, showed poor combined residual chlorine removal performance. Furthermore, considering that Comparative Example 1 has a higher combined residual chlorine removal performance than Comparative Example 3, and the moldability of the wet filter, a particle size of 0.1 to 0.5 mm is considered appropriate for the calcium sulfite contained in the first filter section.

Regarding free residual chlorine removal performance, a consistent level of performance was demonstrated in all cases in which water flow tests were conducted. In particular, the free residual chlorine removal performance of prototype 3 was higher than that of prototypes 1 and 2, suggesting that increasing the amount of activated carbon incorporated improves free residual chlorine removal performance.

From the above, it was found that by creating a filter that appropriately contains activated carbon adsorbent as a free residual chlorine remover and calcium sulfite as a bound residual chlorine remover, it is possible to create a residual chlorine removal filter body with good residual chlorine removal performance. It was also shown that by adjusting the particle size of the calcium sulfite, good bound residual chlorine removal performance can be maintained for a long period of time.

By controlling the amount of sulfite ions eluted during water flow, the residual chlorine removal filter of the present invention can maintain high levels of residual chlorine removal performance, including both free and bound residual chlorine, for extended periods of time. This makes the filter suitable for removing residual chlorine from raw water, as well as for filtering and preparing purified water for artificial dialysis.

REFERENCE SIGNS LIST 11 hollow cylindrical core member 20 activated carbon adsorbent 21 granular activated carbon 22 fibrous activated carbon 23 acrylic fiber binder 24 calcium sulfite 25 adsorbed material 26 slurry-adhered portion 30 mixed slurry material 35 mold rod member 40 dryer W water

Claims (7)

a first filter portion obtained by mixing an activated carbon adsorbent and a fibrillated fiber binder in water to form a mixed slurry, adsorbing the mixed slurry onto a side surface of a hollow cylindrical core member while sucking the mixed slurry onto the side surface of the hollow cylindrical core member to form an adsorbed material, and then heating and drying the adsorbed material;
and a second filter portion filled with calcium sulfite having an average particle size of 0.7 to 5.0 mm. The residual chlorine removal filter body according to claim 1, wherein calcium sulfite having a particle size of 0.1 to 0.5 mm is further mixed into the mixed slurry. 3. The residual chlorine removing filter element according to claim 1, wherein the amount of sulfite ions eluted 10 minutes after the start of water flow is 5 to 20 mg/L. The residual chlorine removal filter body according to any one of claims 1 to 3, wherein the activated carbon adsorbent is one or more of fibrous activated carbon, granular activated carbon, and powdered activated carbon. The residual chlorine removal filter body according to any one of claims 1 to 4, wherein the activated carbon adsorbent has an iodine adsorption capacity of 800 to 2000 mg/g. The residual chlorine removal filter body according to any one of claims 1 to 5, wherein the fibrillated fiber binder is made of acrylic fiber. 7. The residual chlorine removing filter body according to claim 1, wherein the combined residual chlorine removing capacity is 50 L/mL or more.