JP2546750B2 - How to sterilize activated carbon - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for sterilizing activated carbon, and more particularly to a method for effectively sterilizing microorganisms growing in activated carbon used in the production of pure water used for food manufacturing water, semiconductor manufacturing water and the like. .

[0002]

2. Description of the Prior Art Decolorization, deodorization,
A mixed bed type ion exchange tower using activated carbon for removing harmful organic substances or residual chlorine, and a cation resin and anion resin in a mixed bed at the subsequent stage, or a two bed type or further decarbonation tower in which each resin is individually packed A treatment process in which various multi-bed type desalination devices such as an added two-bed, three-column type is installed is used. However, in the treatment process using activated carbon, even if the decolorization, deodorization, removal of harmful organic substances or removal of residual chlorine of activated carbon is sufficient with the passage of water, microorganisms gradually grow in the activated carbon layer and sterilization treatment is performed. Even if almost no microorganisms are detected at the inlet of the activated carbon tower due to factors such as the above, there are many cases in which a general bacterial count of 10 ³ to 10 ⁷ microorganisms / ml is detected in the treated water. Further, in severe cases, microbial slime and mud balls are generated, which deteriorates the performance of activated carbon, and odorous substances and the like generated by decomposition and / or production of microorganisms may leak into the treated water.

The mixed bed type ion exchange tower has a microbial removal rate of 2
Significantly higher than floor type or 2 bed 3 tower type equipment, 99.9%
It is known that the removal rate is obtained, but in the situation where a large amount of microorganisms or odorous components leak from the activated carbon layer as described above, sufficient removal cannot be performed, and the number of general bacteria is 10 to 10. About 10 ⁴ / ml of microorganisms leak into the treated water. As a result, post-contamination by microorganisms occurs in the latter stage of the treatment process as shown in FIG. 3 or 4, particularly in the treated water storage tank. For example, in the field of soft drinks and the like, if an activated carbon tower is provided, there is concern about post-contamination by microorganisms, so steam sterilization or hot water sterilization is usually applied to suppress the growth of microorganisms and reduce leaks. . A method of performing this sterilization with chlorine or ozone was also examined, but the sterilization inside the activated carbon particles could not be performed, and only a support layer for the activated carbon layer (sand, gravel, etc.)
In addition, the effect and application are limited to the sterilization of the outlet side pipe.

In FIG. 3, only the ultraviolet sterilizer (UV) is provided as a sterilizer, and periodic sterilization (CIP treatment) of the treated water storage tank and the piping system is required. In FIG.
Chlorine or ozone is injected again into the treated water as a bactericide to suppress the growth of microorganisms in the treated water storage tank. But raw water,
When used as cleaning water, chlorine is not a problem, so a dechlorination unit has been added. Steam sterilization is a method in which steam is blown directly into the tower, but channeling is likely to occur in the activated carbon layer, and it is difficult to uniformly raise the temperature in the activated carbon layer. It takes 5 to 7 hours for sterilization operation to uniformly raise the temperature in the tower to 80 to 90 ° C, and the energy cost is high because the steam is used transiently.

The hot water sterilization is carried out by forming a hot water circulation system in the treatment process and heating the water in the circulation system to 85 to 90 ° C. in a hot water exchanger. However, a large amount of energy cost is still required to uniformly heat the activated carbon layer to at least 80 ° C or higher.
Further, there are problems such as low efficiency due to indirect heating, large heat loss from the piping system and the activated carbon tower itself as the tower diameter is large, and sterilization operation requires 4 to 5 hours. Therefore, when it is unavoidable to sterilize the product by retort, steam or hot water sterilization is not performed immediately even if a microbial leak occurs from the activated carbon tower, and the sterilization frequency is extended every 7 days to 1 month. You can also see the case. Frequent sterilization operations (every 1 to 7 days) are required for carbonated drinks, beer water, etc. that cannot be sterilized by retort.

Regarding the chemical sterilization of activated carbon, the following results have previously been obtained (Japanese Patent Application No. 2-16031), that is, the bactericidal effect of inorganic acids (hydrochloric acid / sulfuric acid) is excellent, and the pH value is
By bringing the activated carbon into contact with the acid held at 1.5 or less for 30 to 90 minutes, the following good bactericidal effect can be obtained. The duration of the bactericidal effect is 2 to 3 days for hot water sterilization, and 6 to 7 days for acid sterilization. And the number of microorganisms in the activated carbon treated water is 1/1 of that of hot water sterilization.
It is 00 or less. Further, iron manganese and the like that had covered the activated carbon surface with an acid is dissolved and the surface is activated. For example, for removal of residual chlorine, chlorine in the treated water is 0.1 mg / l before acid treatment.
However, it recovers to 0.05 mg / l or less after the acid treatment. However, this sterilization-effective method also requires a long time for washing because of the pH recovery of the treated water after the sterilization treatment, so that the amount of waste water for washing increases.

[0007]

As described above, although steam sterilization and hot water sterilization can surely perform sterilization, the sterilization effect can last for a few days, so almost complete microbial leak prevention is possible. Sterilization every 2-3 days is necessary to achieve. Further, in steam sterilization and hot water sterilization, as the use of activated carbon progresses, the surface layer of activated carbon is covered with inorganic SS such as iron-manganese in raw water, and residual chlorine removal ability and organic matter adsorption ability decrease. Further, although chemical treatment using an inorganic acid also has an effective bactericidal effect, there is a problem in that it takes a long time to recover the pH of the treated water after the treatment and a large amount of cleaning drainage occurs. The present invention aims to solve the above-mentioned problems of the conventional techniques, and to provide an effective sterilization method of microorganisms grown in activated carbon so that the pure water production process can be appropriately and efficiently operated. To do.

[0008]

In order to achieve the above object, in the present invention, after passing through an activated carbon tower, a pure mixed bed type ion exchange tower or a multi-bed type ion exchange tower containing a cation resin and an anion resin is used. In the step of obtaining water, an acid waste solution and / or an alkali waste solution used for the regeneration of a cation resin and an anion resin are passed through the activated carbon tower to sterilize microorganisms in the activated carbon, and It was done. In the sterilization method, the waste liquid is passed through the activated carbon tower by a method (A) in which only the acid waste liquid used to regenerate the ion-exchange resin is used, and the same alkali waste liquid is passed through, and then the acid waste liquid is passed through. The method (B) to be performed is combined appropriately. In particular, in the case (A) in which only the acid waste liquid is passed through the activated carbon, it is preferable that the ion exchange column in the latter stage is passed through an acid first and then an alkali to regenerate the resin.

According to the present invention, for example, in the treatment process for a soft drink as shown in FIG. 5, the activated carbon tower 33 in which the microorganisms are most concentratedly grown and which is one of the sources of microbial contamination of the entire process, This is a chemical sterilization with a regenerant of the mixed bed type ion exchange tower 34 in the latter stage.

[0010]

The present inventor has conducted research on a sterilization method of activated carbon with an inorganic acid, and has obtained the following findings. The bactericidal effect is mainly achieved under strongly acidic conditions of pH 1.5 or less. Although the bactericidal effect is slight under alkaline conditions, SS and slime are peeled off, and a part of organic substances adsorbed on activated carbon can be removed. In the case where a facility using an acid / alkali for regeneration of the ion exchange resin, for example, having a mixed bed type ion exchange tower in the latter stage,
Even if these recycled waste liquids are directly passed through the activated carbon tower, the above effects can be obtained. Therefore, no special chemicals or means such as hot water sterilization are required for sterilization of activated carbon. By this effect, iron, manganese, slime, etc. on the surface of activated carbon are eliminated, and the residual chlorine removal capacity is restored.

When the acid / alkali of the resin-recycled waste liquid is passed through the activated carbon, acid or alkali leaks little by little from the activated carbon layer during the washing with water after the chemical washing, and the treated water has a pH similar to that of raw water.
It takes a long time to recover, and a large amount of cleaning drainage occurs. However, since there is a desalting device such as a mixed bed type ion exchange column in the latter stage of the activated carbon column, the leaked acid / alkali is removed there. The ion load in the cleaning waste water is several% of the ion exchange capacity of the resin, and the amount of pure water collected in the process as a whole is only slightly reduced, which is not a problem in operation.

FIG. 2 shows, as an example, a recovery time of pH and a recovery time when hydrochloric acid alone, caustic soda alone, and first caustic soda and then hydrochloric acid are passed through sterilized activated carbon that has been contaminated with microorganisms. The cleaning method shown here is an example used in the experiment, and the specific conditions for implementation need not be as described above. <Washing method> Packing tower: 50φ x 1300 Hmm acrylic column Activated carbon: 1.5 liters packed, height of packed bed 800 mm Chemical treatment (ii) [2% HCl] 1) Downflow of 2% HCl 1.8 liters ( SV3) Penetration: 24 minutes 2) Retention: 30 minutes 3) Extrusion with raw water (tap water) (SV3): 30 minutes 4) Washing by introducing raw water from the top of the column (SV20): According to Figure 2 (b) [2% NaOH] The same procedure as in (a) was performed.

(C) [2% NaOH-2% HCl] 1) 2 liters of NaOH 1.8 liters in downward flow (SV3) through: 24 minutes 2) Hold: 30 minutes 3) Raw water (tap water) Extrusion (SV3): 30 minutes 4) 1.8 liters of 2% HCl in downward flow (SV3): 24 minutes 5) Retention: 30 minutes 6) Extrusion with raw water (tap water) (SV3): 30 Minute 7) Washing by introducing raw water from the top of the column (SV20): According to FIG. <Properties of raw water> Tap water: pH 7.2, conductivity 240 μs / cm
(At 25 ° C.) chlorine 1-2 mg / l, M alkalinity 40-45 mg
/ L,

In FIG. 2, (a) shows cleaning methods (a) and (c).
The results show that the pH recovery conditions under both conditions were almost the same. Further, (b) shows the result of the cleaning method (b). Table 1 shows the amount of cleaning waste water required until the cleaning end point pH in each cleaning method.

[Table 1]

In addition, in the cleaning methods (a) and (c), when the cleaning is performed from the end pH of each cleaning to the set pH and then water is passed through the mixed bed type ion exchange column, the ion loading amount is generally obtained as shown in Table 2. . Therefore, for example, in the following activated carbon tower-mixed bed type ion exchange tower system, the amount of anion resin consumed by chemical sterilization with an acid waste solution is calculated as shown in Table 3.

[Table 2]

<Example of activated carbon tower-mixed bed type ion exchange tower system design conditions> Raw water load ion amount: 120 mg / l as CaCO ₃ treated water amount: 300 m ³ / c (30 m ³ / hour × 1)
0 hours) Safety factor: Cation resin 1.2 Anion resin 1.45 Flow-through capacity: Cation resin 45 g / lR as
CaCO ₃ anion resin 35 g / lR as CaCO ₃ regenerant amount: HCl 100 kg / c 100
% NaOH 150 kg / c 100% Resin amount: Cationic resin 1000 liters Anion resin 1500 liters

[Table 3]

Thus, the end point of washing the activated carbon is adjusted to pH 2.0.
In that case, 8% of the anion resin in the mixed bed type ion exchange column in the subsequent stage is consumed when the wash water is passed, and the amount of treated water (capacity) per cycle is reduced accordingly, which is a practical problem. However, when the washing end point is set to pH 3.0, the consumption rate of the anion resin is as small as 1.5%, which is not a practical problem. That is, when the cleaning method (a) is sterilized with a hydrochloric acid waste liquid, the cleaning method (c) is first passed through a caustic soda waste liquid, and then when the hydrochloric acid waste liquid is sterilized, if the pH of the cleaning end point is set to 3.0 or more, the anion resin in the subsequent stage is The load is extremely small. The amount of waste water for cleaning up to pH 3.0 of the end of cleaning is 7 l / l-activated carbon, and the cleaning time is 20 minutes at SV20.
Even at the cleaning end point pH of 2.0, it can be practically used by increasing the safety factor of the anion resin by about 10% from the beginning of the design.

If the sterilization of the acid waste liquid through activated carbon is carried out once every 3 to 7 days, the amount of microorganisms at the activated carbon outlet is generally 100 co / ml (maximum 1000 co / ml or less). To be Further, since the microorganism removal rate by the mixed bed type ion exchange tower in the latter stage is 99.0 to 99.9%, the number of general bacteria in the process water after the mixed bed type ion exchange tower is always 1 to 10 co / ml. It is maintained below. This is a very low level as compared with 10 to 10 ⁴ co / ml when the activated carbon is not acid-sterilized. Washing method (C) When a caustic soda waste liquid is passed, at the washing end point pH of 13.0, the load on the cationic resin in the subsequent stage is large and practical use is difficult. At the cleaning end point 12.0, the amount of loaded ions due to the subsequent passage of water is about 2.0 g / l-activated carbon as CaCO _3.
And about 8.8% of the total cationic resin is consumed, and the pH is 1
At 1.0, about 2.2% is consumed. In order to ensure the safety of treated water, it is necessary to wash to a pH of about 11.0, but in this case, the washing time is 65 minutes with SV20, the washing drainage volume is 22 liters / liter-Activated carbon, and about 3 times as much as in the case of hydrochloric acid. It becomes the amount of drainage.

Therefore, the acid waste liquid is followed by the alkali waste liquid (N
The method of sterilizing by passing aOH) requires a long washing time and a large amount of washing waste water, and the process for adjusting the amount of alkali waste liquid to be passed to activated carbon to restore the pH to a proper pH is complicated. However, it can be put to practical use. The method (A) in which only the acid waste liquid is passed through the activated carbon to sterilize it can be completed within the regeneration time of the mixed bed type ion exchange column, for example, by the following method.

<Step> 1) Backwash separation of mixed bed type ion exchange tower 15 minutes 2) HCl feed (upstream flow from mixed bed type ion exchange tower to activated carbon tower) 30 to 40 minutes 3) HCl extrusion (Same as above) 20 minutes 4) NaOH admixture in mixed bed ion exchange tower, activated carbon HCl retention 30-40 minutes 5) NaOH extrusion of mixed bed ion exchange tower activated carbon HCl retention 30 minutes 6) Mixed bed ion exchange tower drain discharge Activated carbon tower backwash 15 minutes 7) Mixed bed type ion exchange tower mixing Activated carbon tower wash 15 minutes 8) Mixed bed type ion exchange tower and activated carbon tower wash 15 minutes

In the above steps, the time during which the acid is in contact with the activated carbon at a pH of 1.5 or less is about 80 to 90 minutes,
Sufficient time is obtained for sterilization, and the time required for regenerated sterilization as a whole process is 170 to 195 minutes. The method (B) of sterilizing the activated carbon by passing the alkaline waste solution first and then the acid waste solution is 1 times every several times of the passing of the acid waste solution only (A).
It may be performed once, or about once every 2 to 4 weeks, for the purpose of sterilizing acid-resistant bacteria and preventing slime.

[0022]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Example 1 A detailed implementation method of the present invention will be described with reference to FIG. 1 by taking a process having an activated carbon column and a mixed bed type ion exchange column as an example. FIG.
In the above, the present invention is carried out as follows using the activated carbon tower 1 filled with the activated carbon 2 and the mixed bed type ion exchange tower 3 filled with the cation resin 4 and the anion resin 5. The cation resin 4 and the anion resin 5 are mixed, the raw water 6 is opened with the valves 7, 8, 9, 10 to pass water through the activated carbon tower 1 and the mixed bed type ion exchange tower 3 to obtain treated water.

Next, a mixed bed type ion exchange tower 3 and an activated carbon tower 1
Recycle backwashing, etc., but normally, that is, when the activated carbon tower is not sterilized, the mixed bed ion exchange tower 3 is used according to the conventional method.
It is sufficient to carry out the reproduction backwash. Further, a method of passing an alkali waste liquid through the activated carbon tower 1 and then passing an acid waste liquid therethrough for sterilization is also a method of passing through only the acid waste liquid described below for sterilization. , NaOH is omitted because it has only been changed in the order of passage. When the acid waste liquid is passed through the activated carbon tower 1 for sterilization, the valves 13 and 14 are opened, and the activated carbon layer is sluged for about 5 minutes to loosen it, and then the HC of the mixed bed ion exchange tower 3 is used.
l Do medicine first. Main valve 23 and valve 1 of HCl metering tank 22
4, 18, 21, and 26 are opened, the cation resin 4 is charged, discharged from the intermediate collector C ₂ , and passed through the activated carbon tower in an upward flow. The main valve 23 is closed and HCl extrusion is carried out within the same flow for 20 minutes or less, and then the activated carbon tower (hereinafter abbreviated as AC tower) of the mixed bed type ion exchange tower (hereinafter abbreviated as MB tower) is in contact with acid. Hold until NaOH extrusion is complete.

The subsequent steps of the MB tower 3 are as follows. The main valve 17 of the NaOH measuring tank 28 is opened, and the valve 1
Open 8, 9, and 26 and carry out NaOH replenishment using raw water 6. The main valve is closed and the NaOH flow is 30
Do within minutes. Next, the valves 16 and 19 are opened and drained to lower the water level in the MB tower to the resin surface layer of 300 to 500 mm. Then, the valve 24 is opened to introduce air, and the valves 12, 1
Open 6 and mix the resin. AC tower 1 is MBO NaO
After the H extrusion is completed, the valves 13 and 14 are opened, and the raw water 6 is backwashed and washed for about 15 minutes. Next, cleaning is performed by opening the valves 7 and 27. During cleaning, the valve 15 is also opened for a short time to fill the inside of the AC tower. MB when cleaning drainage drops below pH 3.0
Start washing the tower with water.

The valves 7, 8, 9, 25 and 16 are opened to perform full water washing. After full water, the valve 16 is closed and washing is continued until the set treated water quality is reached. That is, the sterilization operation in which only the acid waste liquid is passed has been described, but the sterilization operation may be performed by using only the alkali waste liquid or a combination of the acid waste liquid and the alkali waste liquid. A preferred combination is to perform a sterilization operation using only the acid waste liquid and a sterilization operation using the alkali waste liquid / acid waste liquid once every several times.

Example 2 The AC tower was sterilized under the following conditions: AC tower, MB tower, raw water, and regeneration conditions. Raw water load Ion amount Total cation 115 mg / l as CaCO ₃ Total anion 135 mg / l as CaCO ₃ treated water amount 600 liters / c (60 liters / hour × 10 hours) Regenerator amount HCl 200 g / c (100%) NaOH 300 g / c (100%) Resin Dowex MSA-2 (anion resin: trade name) Dowex HCR-W2 (cation resin: trade name) Activated carbon tower Acrylic column 80φ x 1600Hmm AC5 liter Mixed bed type ion exchange tower 180φ x 1800Hmm Activated carbon tower sterilization Frequency: Acid waste solution sterilization 1 time / week Normal operation 6 days / week Regenerator concentration / c MB tower 4% HCl: 4.4 liter / hour 4% NaOH: 6.0 liter / hour ( Inflow concentration is 2% HCl: 8.8 liters / hour)

After the completion of HCl extrusion, the activated carbon tower was subjected to a downward flow pump circulation at a flow rate of 15 liters / hour for 45 minutes. The pH of the circulating liquid at this time was 0.8. Raw water was obtained by further injecting chlorine into tap water to adjust residual chlorine to 1 to 2 mg / liter. The results are as follows. 1) Number of microorganisms (general bacteria)

[Table 4] Other mold yeasts not detected

2) Residual chlorine

[Table 5]

3) Long-term operation The acid waste solution sterilization was repeated once a week. Looking at the progress after acid sterilization after 2-3 months, the number of general bacteria in the water quality at the outlet of the AC tower increased as follows. After that, if it continues for the 6th month, the number will gradually increase, and the maximum (value on the 7th day) will be A.
The number of general bacteria at the outlet of the C tower was 2.2 × 10 ³ cells / ml.

[Table 6]

Example 3 Under the same conditions as in Example 2, acid waste liquid sterilization was performed once a week, and alkali waste liquid (2% NaOH) was sterilized once every four times and then acid waste liquid sterilization. As a result, there was no increase in general bacteria observed in Example 2 after long-term operation, and the following values were obtained even after 6 months. By the way, the 6th month was June of the rainy season, and the water temperature was 22 ° C, which was in a condition where bacteria could easily grow.

[Table 7]

[0031]

The present invention has the following effects. (1) The cost of sterilization is not necessary because the recycled waste liquid from the ion exchange tower in the latter stage is used as it is. (2) By performing the sterilization treatment with the acid waste liquid, the sterilization effect lasts for a long time as compared with hot water sterilization and the like. (3) By combining the treatment with the acid waste liquid and the alkali waste liquid, Fe, Mn, slime, etc. on the surface of the activated carbon were eliminated, the residual Cl ₂ removal ability was recovered, and continuous use for a long time became possible. (4) Acids and alkalis remaining in the activated carbon can be removed by the ion-exchange resin in the latter stage because it is a small amount, and there is no problem in operation.

[Brief description of drawings]

FIG. 1 is a process flow process chart showing a sterilization method of the present invention.

FIG. 2 is a graph showing a cleaning time and a pH recovery state.

FIG. 3 is a process diagram of a conventional pure water production method.

FIG. 4 is a process diagram of another conventional method for producing pure water.

FIG. 5 is a process diagram of a pure water producing method to which the present invention is applied.

[Explanation of symbols]

1: Activated carbon tower, 2: Activated carbon, 3: Mixed bed type ion exchange tower,
4: cation resin, 5: anion resin, 6: raw water, 2
0: treated water, 22: HCl measuring tank, 28: NaOH measuring tank, C ₁ , C ₂ , C ₃ : water collecting device, 31: water receiving tank, 3
2: Pump, 33: Activated carbon tank, 34: Mixed bed type ion exchange tower, 35: Treated water storage tank, 36: Membrane filter, 3
7: UV sterilization, 38: Cl ₂ bactericide

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location C02F 9/00 503 C02F 9/00 503B (72) Inventor Shigeo Miya 1-6, Konan, Minato-ku, Tokyo No. 27 within EBARA Infilco Co., Ltd. (56) Reference JP-A-51-28354 (JP, A) JP-A-50-8368 (JP, A)

Claims (2)

(57) [Claims] 1. An acid used for regeneration of a cation resin and an anion resin when pure water is obtained through a mixed bed type ion exchange column or a multi-bed type ion exchange column having a cation resin and an anion resin after passing through an activated carbon column. A method for sterilizing activated carbon, comprising passing waste liquid and / or alkaline waste liquid through the activated carbon tower to sterilize microorganisms in the activated carbon. 2. A method of passing the waste liquid to the activated carbon tower using only the acid waste liquid used for the regeneration of the ion exchange resin,
2. The method for sterilizing activated carbon according to claim 1, wherein the method of passing the same alkaline waste liquid and then the acid waste liquid is appropriately combined.