JP2001293483A - Water treating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform highly efficient flocculating/settling treatment in water treatment and to prevent corrosion due to water at the same time. SOLUTION: The slurry of undissolved materials obtained in the production of a slaked lime aqueous solution is poured into the water controlled to pH 6.7-7.3 and 80-160 mg/L calcium bicarbonate concentration by using the slaked lime aqueous solution and carbon dioxide, then the slaked lime aqueous solution and/or carbon dioxide are poured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water purification treatment method for performing coagulation sedimentation treatment and non-corrosion of water. More specifically, the present invention relates to an improved water purification method for injecting a slaked lime aqueous solution and carbon dioxide gas, the slaked lime aqueous solution obtained by providing a slaked lime aqueous solution production apparatus and a carbon dioxide gas injection apparatus in a water purification treatment facility, The present invention relates to a water purification treatment method that simultaneously achieves high-efficiency coagulation sedimentation treatment and non-corrosiveness of water by injecting undissolved matter and carbon dioxide gas that come out of the water purification device into appropriate places in the water purification process.

[0002]

2. Description of the Related Art Conventionally, in a surface water purification system, a coagulation sedimentation / filtration step of adding a coagulant to water to be treated (hereinafter referred to as raw water) is indispensable. PAC) and sulfate bands. In recent years, the amount of coagulant used has tended to increase with the deterioration of surface water quality, especially when the raw water introduced into the landing well is at low temperature, low turbidity, or low alkalinity, the coagulation efficiency is increased. It is necessary to increase the injection rate of the agent. As a result, the amount of flocculant used increases and the amount of sludge generated increases, the flocculant is mixed into the filtered water, the cost of the flocculant increases, and the corrosiveness of the purified water increases due to the increase in chloride ions and sulfate ions derived from the flocculant. The problem of increase arises. Also, when the pH of the raw water introduced into the landing well is high, an acid such as sulfuric acid is injected to lower the pH to perform the coagulation treatment, and thereafter, the appropriate p
An alkaline agent is injected to make the H value. However, since pH buffering properties are low in free carbonic acid and water with low alkalinity, increasing the injection amount of alkaline agent greatly increases the pH and easily exceeds the upper limit of the water supply law (8.6 in Japan). As a result, it is difficult to inject a large amount of slaked lime aqueous solution, and it is not possible to increase the Langeria index, which is an index for judging water corrosion, to improve non-corrosive water. Moreover,
It is feared that aluminum causes Alzheimer's disease. For these reasons, research is being conducted on reducing the amount of purified water sludge and the cost of chemicals, and on reducing the injection rate of PAC and sulfate bands.

On the other hand, a technique for injecting an aqueous slaked lime solution to make water non-corrosive has been spreading with the advent of a device for continuously producing an aqueous slaked lime solution disclosed in, for example, Japanese Patent No. 1459175. In the device disclosed in this publication,
There was a problem that an insoluble material that was difficult to dissolve remained in an aqueous solution having a pH of 12 or more. However, it has been solved by a method in which the insoluble material is treated in water maintained at a pH of 10 or less and then introduced into a landing well. No. 141605). Further, Japanese Patent No. 2048482 discloses that an aqueous slaked lime solution and carbon dioxide gas are used in combination to increase the Langelia index to make water non-corrosive. Further, Japanese Patent Application Laid-Open No. 6-83566 proposes increasing the concentration of hardly soluble flocs generated during the production of slaked lime aqueous solution, introducing the flocs into a mixing pond and using them as an alkaline agent. However, it does not improve coagulation sedimentation. There is a need for a method for simultaneously achieving high-efficiency coagulation sedimentation and non-corrosion of water.

[0004]

In view of such circumstances, the present inventors have studied a method for simultaneously solving high-efficiency coagulation sedimentation and making water non-corrosive, and as a result, conventionally known slaked lime carbonate is known. By improving and developing the combined gas injection method, that is, undissolved matter from the slaked lime dissolving device,
By injecting slaked lime solution and carbon dioxide gas into appropriate places in the water purification process according to the water quality, undissolved substances have the core function of coagulation in the coagulation sedimentation operation, forming heavy flocs and improving water quality. Normally used slaked lime solution and carbon dioxide gas,
In addition, the present inventors have found that the coagulation and precipitation can be effectively performed without requiring the use of an additional agent such as a coagulation aid other than the undissolved matter discharged from the slaked lime dissolving apparatus, and completed the present invention.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a water treatment facility including a landing well, a mixing pond, a sedimentation pond, a filtration pond and a distribution pond.
Provide a slaked lime aqueous solution production device and a carbon dioxide gas injection device, and inject water with slaked lime aqueous solution and carbon dioxide gas to adjust the water quality, measure the pH, alkalinity, calcium hardness, etc. of the water to be treated, and obtain the Langeria index. , PH 7.5-8.3, alkalinity 60-
80 mg / l, determine the injection rate of slaked lime and carbon dioxide gas in an amount that gives a Langerian index of -1 to 0, and in the sedimentation basin of the water purification treatment facility or in a step before it, the undissolved slurry from the slaked lime solution manufacturing apparatus And carbon dioxide gas and slaked lime aqueous solution,
6.7-7.3, calcium bicarbonate concentration 80-160mg / l
The pH is increased so that the pH buffering property is increased, and then the coagulant is injected to perform coagulation, precipitation and filtration. Further, by injecting slaked lime aqueous solution and / or carbon dioxide gas into the filtered water, high efficiency is achieved. This is a water purification method characterized by simultaneously performing coagulation sedimentation and water non-corrosion.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention provides a water purification facility including a landing well, a mixing well, a sedimentation basin, a filtration pond and a distribution pond, with a slaked lime aqueous solution production apparatus and a carbon dioxide gas injection apparatus installed therein. In the step (2), the slaked lime aqueous solution, undissolved slurry and carbon dioxide gas from the slaked lime aqueous solution production apparatus are injected according to the water quality. The undissolved slurry in the present invention refers to a slurry containing undissolved matter that remains without being dissolved in a slaked lime aqueous solution having a pH of 11 or more in a slaked lime aqueous solution manufacturing apparatus. The solid in this undissolved slurry is mainly calcium carbonate, and contains undissolved slaked lime contained in the calcium carbonate and other impurities of the raw slaked lime. As the slaked lime dissolving apparatus, for example, an apparatus described in Japanese Patent No. 1459175, in which water is introduced from a lower part of a stirring tank and a slaked lime aqueous solution is continuously extracted from an upper part, can be used.
The undissolved slurry is taken out from the lower part of the tank after the introduction of water is stopped.

In practicing the present invention, prior to the water purification treatment, the pH, alkalinity, calcium hardness, etc. of the raw water are measured in advance to determine the Langeria index, and the water quality, pH 7, which is preferable from the viewpoint of preventing corrosion of the treated water. .5-8.3,
The injection rate of slaked lime and carbon dioxide gas in such an amount as to have an alkalinity of 60 to 80 mg / l and a Langeria index of -1 to 0 is determined.

[0008] The injection rate of the carbon dioxide gas and the slaked lime aqueous solution is adjusted to adjust the pH of the water during the coagulation operation by using a part or all of the predetermined amount as described above. For example, when the pH of the raw water is higher than a predetermined pH, carbon dioxide gas is injected, and when the pH is low, an aqueous slaked lime solution is injected to adjust the pH to the predetermined pH. This pH adjustment may be performed after the addition of the flocculant, but may be performed by injecting a carbon dioxide gas or / and an aqueous solution of slaked lime before adding the flocculant in anticipation of the degree of the pH decrease due to the addition of the flocculant. it can.
Also, the calcium bicarbonate concentration of water during the coagulation operation is 80 to
Adjust so that it is within the range of 160 mg / l. If the concentration of calcium bicarbonate in the raw water is lower than 80 mg / l, the buffer capacity is small, and even if the pH at the time of adding the flocculant is adjusted within the predetermined range, it is possible to sufficiently sediment and separate the contained floating substances. Can not. Adjustment of calcium hydrogen carbonate concentration is performed using slaked lime and carbon dioxide gas. A typical case will be described below. An amount of the undissolved material according to the properties of the raw water is preferably injected into a landing well, and then carbon dioxide gas and an aqueous solution of slaked lime are injected to obtain properties favorable for coagulation and precipitation, that is,
pH 6.7-7.3, calcium bicarbonate concentration 80-160mg / l,
Preferably pH 6.8-7.2, calcium bicarbonate concentration 90-1
Adjust to 20 mg / l. By performing adjustment using an undissolved material in this way, it is possible to form heavy flocs without using an aggregation aid during aggregation precipitation. When the raw water has a low pH and low alkalinity, first use a slaked lime aqueous solution and carbon dioxide gas as needed, and when the raw water has a high pH, first use a carbon dioxide gas and slaked lime as necessary. After adjusting the properties as close as possible to the aggregation reaction to the extent possible using an aqueous solution, the undissolved substance and the aggregation agent may be added. After adding undissolved matter and flocculant,
Further, the pH and the concentration of calcium hydrogen carbonate may be adjusted. In some cases, the use of a coagulation aid or the like is not excluded. Undissolved matter is preferably 2-3%
Inject with slurry. As the carbon dioxide gas, the whole or a part of the necessary amount for adjusting the previously determined Langeria index to -1 to 0 is injected. In addition, the carbon dioxide gas inlet is provided at an appropriate position deeper than the water depth of 2 m according to the size of the landing well or the mixing well. After the undissolved material is injected into the landing well, carbon dioxide is injected into the landing well or mixing well, and the pH is adjusted to 6.7 to 7.3. When the pH after the above treatment is as low as 6.7 or less, slaked lime aqueous solution is injected to adjust the pH within the above range. When the slaked lime aqueous solution is required, when undissolved matter is taken out from the slaked lime dissolving tank, it can be taken out as a slurry together with a required amount of slaked lime aqueous solution and added to the landing well. If the pH after the above treatment is higher than 7.7, adjust by increasing the injection amount of carbon dioxide gas.

The water thus adjusted has a large buffering capacity, and when a flocculant such as PAC is added, the previously added undissolved material performs the core function of flocculation, forming heavy flocs and causing sedimentation. Speed increases. As a result, the generated floc has a high sedimentation speed, and efficient processing can be performed.
In addition, since the addition of the conventionally used coagulation aid is not required, and since most of the added undissolved material, slaked lime and calcium carbonate, are dissolved, the amount of solids separated is significantly reduced. .

[0010]

[Example 1] Raw water: water temperature 15 ° C, pH 6.7, alkalinity 5 mg
/ l, calcium hardness 5 mg / l, Langeria index -3.8, turbidity
The surface water was highly corrosive at 50 degrees. Water quality improvement target value of pH 7.8, alkalinity 70 mg /
The required injection rates of slaked lime and carbon dioxide were determined experimentally to be 48 mg / l and 57 mg / l, respectively. The total amount of slaked lime required to achieve the water quality improvement target for raw water of 20 m ³ / day was calculated as 1 kg / day, and the carbon dioxide gas amount was calculated as 1.2 kg / day.
Diameter 0.22 m, height 1.5 m, was charged with slaked lime 1.2kg to cylindrical vertical low speed stirrer with dissolver volume 0.06 m ^3, and water from the bottom of the dissolution tank pH12 or more overflow liquid in the intermediate vessel I saved. When 80% of the slaked lime was dissolved and overflowed into the intermediate tank, the water supply to the dissolving tank was stopped, and the undissolved matter remaining at the lower part of the dissolving tank was allowed to stand still for 1 hour, and the undissolved matter was transferred to the undissolved slurry tank. I took it out. The concentration of slaked lime obtained in the intermediate tank was about 1500 mg / l. Undissolved slurry pH 12.0, slurry concentration 2.9%
The components of the undissolved material are calcium carbonate 57%, slaked lime
40%, silicon dioxide 2% and aluminum oxide 0.2%.

The water purification treatment was performed as follows according to the water treatment flow shown in FIG. 20 m ³ / day of the raw water was taken into the landing well, and the undissolved slurry was injected at 0.3 l / h.
It became 0.0. 57 mg / l of carbon dioxide gas was injected into the mixed water, and then 19.3 l / h of an aqueous solution of slaked lime at 1500 mg / l were injected.The pH was 7.1, the alkalinity was 59 mg / l, and the calcium hardness was
The water became 60 mg / l and the concentration of calcium bicarbonate was 98 mg / l.
Here, 25 mg / l of PAC was injected to perform aggregation precipitation. The turbidity of the supernatant was 3 degrees and the coagulation / sedimentation efficiency was 94%. The supernatant water from the sediment was subjected to sand filtration to obtain filtered water having a turbidity of 0.1 °. When 5 l / h of the slaked lime solution was injected into the filtered water, non-corrosive water having a pH of 7.8, an alkalinity of 67 mg / l, a calcium hardness of 72 mg / l, and a Langeria index of -0.5 was obtained.

[0012]

Comparative Example Same raw water, slaked lime aqueous solution and PA
Batch experiments of coagulation sedimentation were performed using C. Injection of the slaked lime aqueous solution alone has no pH buffering property in the raw water.
Injection of l and a small amount of slaked lime raises the pH to 8.6, and the water quality at this time is 7 mg / l alkalinity, 7 mg / l calcium hardness, and the Langeria index is -1.6. PH 7.8, alkalinity 70 mg / l, calcium hardness 7 mg / l, it was not possible to make the Langeria index -0.5. Next, the slaked lime injection rate required to bring the pH for coagulation treatment to 7.1, the same as in the example, was determined, and was 0.8 mg / l. According to the water treatment flow shown in FIG. 1, a slaked lime aqueous solution of 1500 mg / l is added to 20 m ³ / day of raw water.
5 l / h (slaked lime injection rate 6 mg / l) was injected, and PAC was added to this.
Aggregate precipitation was performed by injecting mg / l. The turbidity of the sedimentation supernatant water was as high as 8 ° C, and this was subjected to sand filtration. As a result, the turbidity was 0.5 ° C. When the quality of purified water obtained by injecting the slaked lime aqueous solution into the filtered water so as to have a pH of 7.8 was measured, the calcium hardness was 11 mg / l, the alkalinity was 7 mg / l, and the non-corrosive water was Langeria index of -2.3. And the coagulation sedimentation efficiency was 79%, which was lower than that of the example.

[0013]

Example 2 The raw water temperature was 28 ° C. pH 9.4, alkalinity 5
7.1mg / l, calcium hardness 58.5mg / l, Langeria index 1.3
It was surface water with a turbidity of 30 degrees and high pH. The target value for water quality improvement as purified water is pH 7.8, alkalinity 65mg /
The required injection rates of slaked lime and carbon dioxide gas were determined by experiments, and were determined to be 10 mg / l and 16.1 mg / l, respectively. The total slaked lime required to achieve the above water quality improvement target for 20 m ³ / day of raw water was calculated to be 0.02 kg / day and carbon dioxide 0.32 kg / day. diameter
0.22 m, height 1.5 m, the slaked lime 1.2kg were charged into a cylindrical vertical low speed stirrer with dissolver volume 0.06 m ^3, pooled pH12 or more overflow liquid to the intermediate tank with water from the bottom of the dissolution tank Was. Slaked lime
When 80% was dissolved and overflowed into the intermediate tank, the water supply to the dissolving tank was stopped, and the undissolved matter remaining in the lower part of the dissolving tank was drawn out to the undissolved slurry tank after allowing to stand still for 1 hour. .
The concentration of slaked lime obtained in the intermediate tank was about 1600 mg / l.
The undissolved slurry had a pH of 12.1 and a slurry concentration of 2.9%. The raw water 20 m ³ / day was treated as follows according to the water treatment flow of FIG. That is, raw water is first introduced into the landing well, where the undissolved slurry is 0.06 l / h and carbon dioxide is added at 1
When the solution was injected so as to be 6.1 mg / l, the pH was 7.2, the alkalinity was 58.7 mg / l, the calcium hardness was 60.7 mg / l, and the Langeria index was -1.0. Then about 1600 mg / l slaked lime solution at 3 l / h
Was injected as a pre-alkali and PAC was injected at 36 mg / l, pH 7.3, alkalinity 60.5 mg / l, calcium hardness 6
It was 7.9 mg / l, and the Langeria index was -0.8. When this water was subjected to coagulation sedimentation, the turbidity of the sedimentation supernatant water was 4 degrees, and the coagulation sedimentation efficiency was about 87%. When the supernatant water of this precipitation was subjected to sand filtration, the turbidity of the filtered water was 0.1 °. When 2 l / h of the slaked lime solution was injected into the filtered water, the treated water had a pH of 7.8, an alkalinity of 65 mg / l, a calcium hardness of 71.9 mg / l, and a Langeria index.
-0.2 non-corrosive water was obtained.

[0014]

According to the method of the present invention, regardless of the quality of raw water, low-temperature low-turbidity water, low-alkalinity water, or high-low pH water, coagulation and sedimentation can be performed without using a coagulation aid. Flock can be formed, coagulation and sedimentation can be effectively performed, and non-corrosive water can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an example of water treatment according to the present invention.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C02F 1/66 540 C02F 1/66 540Z 1/52 1/52 Z 1/68 510 1/68 510B 520 520D 520C 530 530A 530K 530L 540 540Z

Claims (1)

[Claims] 1. A slaked lime aqueous solution production device and a carbon dioxide gas injection device are installed in a water treatment facility including a landing well, a mixing well, a sedimentation basin, a filtration pond, and a distribution reservoir, and water quality is adjusted by injecting the slaked lime aqueous solution and carbon dioxide gas. In the water purification process to be performed, p
H, alkalinity, calcium hardness, etc. are measured to determine the Langeria index.
H7.5-8.3, alkalinity 60-80mg / l, Langeria index -1
Determine the injection rate of slaked lime and carbon dioxide gas in an amount to become ~ 0, and inject the undissolved slurry, carbon dioxide gas and slaked lime aqueous solution from the slaked lime aqueous solution manufacturing apparatus into the sedimentation basin or a step before it to adjust the pH to 6.7. 7.3, adjusting the concentration of calcium bicarbonate to 80-160mg / l, coagulating, sedimenting and filtering in the presence of coagulant, injecting slaked lime aqueous solution and / or carbon dioxide gas into the filtered water, high efficiency coagulating sedimentation and water A water purification method that simultaneously makes non-corrosive water.