JPH0325225B2 - - Google Patents

Description

[Detailed description of the invention]

Chlorine has become ubiquitous as a disinfectant in public water supplies, bringing with it its own complex health hazards. It has been shown that chlorine reacts with humic substances present in tap water to produce trihalomethanes (THMs) such as chloroform. The Environmental Protection Agency has recognized trihalomethanes as carcinogens in animals and has announced that the maximum contamination level for all THMs in public water systems is 0.10 mg/liter (100 ppb). (Volume 44 of the Federal Register, November 29, 1979
No. 231 (U.S. Environmental Protection Agency's ``Management of Trihalomethanes in Drinking Water'' in ``Major Domestic Drinking Water Interim Regulations'' final version) Attempts to remove trihalothanes from chlorinated drinking water have so far not been very successful. It can not be said. Even if THM is removed, if chlorine and humic substances remain, THM will be regenerated. If activated chlorine is removed using granular activated carbon, etc., the water will need to be chlorinated again in order to pass the standard.
If you do so, there is a risk that THM will be generated again. Another method is to remove humic substances, which are precursors of THM. Humic substances are commonly found in natural waters, probably leached from organic substances found in soil, and are usually present in high concentrations in surface waters and generally at low concentrations in groundwater.
Materials previously used to remove humic substances from water include adsorbents such as granular activated carbon, coagulants such as alum and ferric sulfate, and conventional ion exchange resins, particularly weakly basic anion exchange resins. There is. A common difficulty with all such methods is that relatively large amounts of treatment agents need to be added to the drinking water to effectively reduce THM precursors to levels below acceptable temperatures. It is. In addition, as mentioned above, each method has its own problems. It is therefore an object of the present invention to minimize the amount of treatment agents that must be added to water in order to significantly reduce the THM precursor content, and another object is to provide a method that does not interfere with conventional drinking water disinfection methods. is to remove THM precursors. Further objects will become apparent upon consideration of the method of disclosure below. In accordance with the present invention, a method for removing trihalomethane precursors from water, particularly drinking water containing trihalomethane precursors, comprises treating the water with very small amounts of ultrafine particle ion exchange resin having a diameter of less than about 1.5 μm. was discovered. The ultrafine ion exchange particles may be used alone or in the form of aggregates in combination with cation exchange particles.
Such ultrafine ion exchange particles are surprisingly effective at removing THM precursors, and at surprisingly low concentrations. The treatment level for removing THM precursors from drinking water is less than 50 mg per liter of water, preferably less than 25 mg per liter of water;
Depending on the content of the precursor, effective treatment is possible even with about 1 to about 10 mg. An advantageous method of treating water, such as drinking water, according to the method of the present invention is to introduce an ultrafine anion exchange resin in the form of an emulsion into the water prior to the purification of the drinking water, particularly the sedimentation and filtration treatments commonly applied. Alternatively, there is a method of introducing water in which aggregates of anion and cation exchange resin are suspended. It is advantageous to combine coagulant treatment and ultrafine anion exchange resin treatment. Coagulant treatment is a well-known water treatment method, and the coagulants used are also well-known, such as cationic and anionic coagulants including polyacrylic acid and soluble polymer quaternary amines. , or nonionic soluble polymer electrolytes. Coagulants include aluminum, ferrous and ferric sulfates and hydrochlorides,
It may also be a metal salt such as magnesium carbonate or aluminum silicate containing clay. Other coagulants will be apparent to those skilled in the art. The coagulant treatment may be performed prior to, simultaneously with, or after the ultrafine ion exchange resin treatment, but it is preferably performed before the filtration step. In the absence of a coagulant or flocculant to flocculate the excess ultrafine cation exchange resin, either present in the water prior to processing or introduced as described above, the resin will pass through the subsequent filter. It passes through and creates turbidity. Dissolved cationic coagulant or ultrafine cation exchange resin treatment is necessary to prevent said turbidity. Conventional sedimentation and filtration steps remove the aggregated resin and with it the THM precursors. Although chlorination or other disinfection steps may be included at any point during the water treatment process, preferably the disinfectant should be introduced after ultrafine ion exchange resin treatment, and more preferably after its removal. When sterilized with chlorine before treatment with ultra-fine ion exchange resin, THM
The precursors would react with the chlorine before being removed, defeating the purpose of the process of the present invention, and chlorinating the ultrafine ion exchange resin before removing it would result in the resin itself reacting with the chlorine. Although the consequences of the latter reaction are unknown, it is believed to be undesirable insofar as it results in the introduction of chlorinated organics into drinking water. The ultrafine ion exchange particles that can be used in the method of the present invention have a diameter of 1.5 μm or less, and have a diameter of approximately
It is a resin with 0.7 to about 1.5 ion exchange functional groups. Such ultra-fine ion exchange resin is the subject of a U.S. patent no.
Since it can be prepared by the method taught in No. 4200695, it is cited here as a reference. The following test examples are provided to explain the present invention in detail, and are not intended to limit its scope. All drugs used were commercially available products of good quality and all percentages and proportions are by weight unless otherwise indicated. In the test examples, raw water was treated with the resin used in the method of the present invention, and in the comparative examples, it was treated with a conventional method. Raw water was collected from the Delaware River in Philadelphia, Pennsylvania, and filtered through coarse mesh and glass wool before testing. Raw water samples were collected by the U.S. Environmental Protection Agency from the Ohio River in Cincinnati, Ohio, and the Preston Water Treatment Plant in Hialeah, Florida, and were tested in situ. The experimental procedures used were similar to each of the test examples below. For the small-scale experimental example, the test material was added to 800 ml of the specific test water in a 1000 ml beaker. The ultrafine ion exchange resin was added as a 6.25% solids suspension and the other THM precursor removers were added as dry solids. The test water containing the THM precursor remover was
Stirring was performed for 5 minutes at 100 rpm using a Bird flocculant test apparatus, followed by an additional 20 minutes of stirring at 30 rpm. The water was then allowed to stand to allow the solids to settle. At the 30th and 60th minutes of settling time, measure the water turbidity with a Herige turbidity meter.
APHA Method No. 163b (APHA Standard Method, 13th Edition, 1971)
Measured using If the sample containing ultrafine anion exchange resin still appeared cloudy after 60 minutes of settling, a small amount of ultrafine cation exchange resin was added to flocculate the excess anion exchange resin. After the settling period, the water samples were filtered using Watzmann No. 1 filter paper. Several 50ml water samples were prepared after filtration, and each sample was chlorinated to a different chlorine level. At this time, dissolve chlorine gas in water and add about 4000−
A stock solution with a concentration of 6000 ppm was used. The chlorinated sample was left undisturbed in a dark room for 24 hours and then subjected to APHA method No. 114.
Chlorine was analyzed spectrophotometrically using 1.0 to 1.0 g after 24 hours (APHA standard method, 13th edition, 1971).
A residual chlorine content of 1.5 ppm was measured. After 24 hours, the sample containing such a specific amount of chlorine is 0.25 ml of 0.1
Treatment with regular sodium thiosulfate reduced free chlorine and prevented further chlorination during analysis.
THM generated during 24 hours was measured using a gas-liquid chromatograph equipped with an electron capture detector by directly injecting a water sample and similarly injecting a standard aqueous solution of chloroform. The results of Test Examples 1 to 29 are shown in Table 1, and these show that the THM precursor was removed by the strongly basic hydroxyl type ultrafine anion exchange resin treatment used in the present invention, and as a result, the THM precursors were removed after overnight chlorination treatment. This exemplifies the reduction in THM of The sample water used in Test Examples 1-10 and 23-29 was from the Delaware River, Test Examples 11-16 was sedimented water from the Ohio River, and Test Examples 17-22 was from water from the Delaware River in Hialeah, Florida. Raw water from the Preston Water Treatment Plant was used as a sample.

【table】

TABLE The results for Sample Examples 30-34 are shown in Table 2 and illustrate the removal of trihalomethane precursors from Delaware River water samples by the strongly basic chloride ultrafine ion exchange resins of the present invention. ing.

[Table] Table 3 shows the results of Test Examples 35 to 39, which were made by mixing the strongly basic ultrafine ion exchange resin and the strongly acidic ultrafine ion exchange resin of Test Examples 1 to 29. This is a reference example of the removal of trihalomethane precursors from Delaware River water by flocculation treatment.

Table: Test Example 40 illustrates the removal of trihalomethane precursors from Delaware River water by treatment with a mixture of 10 mg ferric sulfate (a well-known coagulant) and 9 mg strongly basic ultrafine ion exchange resin. ing.
Comparative Examples 41-45 illustrate the removal of trihalomethane precursors from Delaware River water when treated with ferric sulfate alone. Test example 40 and comparative examples 41 to 45
The results are shown in Table 4.

TABLE The results of Comparative Examples 46-54 are shown in Table 5 and illustrate the removal of trihalomethane precursors from Delaware River water by conventional treatment with alum or aluminum sulfate hexahydrate.

[Table] The results of Comparative Examples 55 and 56 are shown in Table 6, which illustrates the removal of trihalomethane precursors from Delaware River water by conventional treatment using activated carbon (Pittsburgh RC Fine Powder Grade, manufactured by Calgon). There is.

TABLE The results of Comparative Examples 57-61 are shown in Table 7 and illustrate the removal of trihalomethane precursors from Delaware River water by treatment with a dissolved cationic polymer (Betz 1175). Such a comparative example compares the effect of a low-level treatment using the insoluble ultrafine ion exchange resin of the present invention with the treatment effect of an ionic soluble substance that has been conventionally used to remove anionic substances from water. I went there to do that.

[Table] Previously used ionic water-soluble substances, such as those used in Comparative Examples 57 to 61,
Even if the THM removal effect is shown, it is difficult to remove excess soluble polymer from the processing solution. In contrast, the ultrafine ion exchange particles of the present invention are superior in that they are insoluble and can be easily removed from the treated liquid. The results of Test Examples 62 to 67 are shown in Table 8.
62 to 64 are the resins used in the present invention with an anion exchange capacity of 3.8 meq/g (dry resin) used in all the test examples described above, and the resins in test examples 65 to 67 are the resins used in test examples 62 to 64. It has the same size as the resin and has an anion exchange capacity of 2.8meq/g. From this table, it can be seen that differences in the anion exchange capacity of the resins used in the present invention do not have a large effect on the removal of THM precursors.

[Table] Table 9 shows lime 220mg/and lime 220mg/
Add unpulverized gel resin (A) or (B) or unpulverized porous resin (A) or (B) to THM
An example of processing water containing a precursor is shown below. The particle size of these resins is 380 to 600 μm,
The anion exchange capacity of conventional resins in the particle size range of 50μm to 2mm is 4.1±0.3mg/g (dry resin)
The gel resin (B) had a lower degree of crosslinking than the gel resin (A), and the porous resin (B) had a higher porosity than the porous resin (A).

[Table] Thresin (B)
Comparing Tables 1, 2, 4, and 8 showing the above-mentioned test examples with Tables 4 to 7 and 9 showing comparative examples, it is found that the resin used in the present invention is
It is clear that very small amounts (less than 25 mg/treatment level) have a significant effect.

Claims (1)

[Claims] 1. After treating water containing a trihalomethane precursor with an ultrafine anion exchange resin having an average particle size of less than 1.5 micrometers at a rate of 1 milligram to 25 milligrams per liter of water containing the trihalomethane precursor, the resin A method for removing a trihalomethane precursor, the method comprising removing the precursor from water. 2. The method of claim 1, wherein water is treated with the resin at a rate of 1 to 10 milligrams per liter of water. 3. The method of claim 1, wherein the resin is separated from the water by filtration. 4. The method of claim 3, wherein the filtration separation of the resin is facilitated by adding to the water an ultrafine cation exchange resin having an average particle size of less than 1.5 micrometers before filtering the resin from the water. 5. The method of claim 1, wherein the resin is introduced in water in the form of an aqueous emulsion. 6. Claim 1, wherein the resin is introduced into water in the form of an agglomerate together with an ultrafine cation exchange resin having an average particle size of less than 1.5 micrometers.
The method described in section. 7. The method of claim 1, wherein water is treated with the resin in the presence of a metal salt coagulant. 8. The method according to claim 7, wherein the metal salt coagulant is clay. 9. The method according to claim 7, wherein the metal salt coagulant is ferric sulfate. 10. The method of claim 7, wherein the metal salt coagulant is present in the water at a level greater than 5 milligrams per liter of water. 11. The method of claim 1, wherein the resin is in the hydroxyl form. 12. The method of claim 1, wherein the resin is in halide form.