JP2010137224A - Method for cleaning water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for cleaning water which simultaneously carries out highly efficient coagulation sedimentation treatment and anti-corrosion of water. <P>SOLUTION: The charge rate of slaked lime is decided by finding the Langelier index of water to be treated to achieve pH 7.5-8.3 for the suitable water quality for anti-corrosion and the Langelier index of -1 to 0. Undissolved slurry is charged to adjust pH 6.7-7.3 in a sedimentation pond or before its process. In the presence of a coagulation agent, coagulation, sedimentation, and filtration are carried out, and a slaked lime aqueous solution is charged to filtered water to achieve pH 7.5-8.3 and the Langelier index of -1 to 0. Thus, the efficient coagulation sedimentation treatment and anti-corrosion of water are simultaneously carried out. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a water purification method for performing coagulation sedimentation treatment and non-corrosion of water. Specifically, it is an improved method of a water purification treatment method for injecting a slaked lime aqueous solution and carbon dioxide gas, and is provided with a slaked lime aqueous solution production apparatus and a carbon dioxide gas injection apparatus in a water purification treatment facility, and the slaked lime aqueous solution production apparatus The present invention relates to a water purification treatment method that simultaneously achieves high-efficiency coagulation sedimentation treatment and non-corrosion of water by injecting undissolved slurry from water and carbon dioxide into appropriate portions of the water purification step.

  Conventionally, in a surface water treatment plant, a coagulation-precipitation / filtration process in which a coagulant is added to the water to be treated (hereinafter referred to as raw water) is indispensable. As coagulants, polyaluminum chloride (PAC) and sulfate bands are used. Is used. In recent years, the amount of flocculant used tends to increase with the deterioration of surface water quality, especially in order to increase the flocculation efficiency when the raw water introduced into the landing well is at low temperature, low turbidity, or low alkalinity. It is necessary to increase the injection rate of the agent. As a result, the amount of flocculant used is increased, the amount of sludge generated is increased, the flocculant is mixed into the filtered water, the cost of the flocculant is increased, and the corrosiveness of the purified water is increased due to the increase in chloride and sulfate ions derived from the flocculant. The problem of increase arises. Further, 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 a coagulation treatment, and then an alkaline agent is injected to obtain an appropriate pH value. However, in free carbonic acid and water with low alkalinity, the pH buffering property is small, so increasing the injection amount of the alkaline agent will greatly increase the pH and easily exceed the upper limit value (8.6 in Japan). Therefore, it is difficult to inject a large amount of slaked lime aqueous solution, and it is impossible to increase the Langeria index, which is an index for determining the corrosion of water, to improve noncorrosive water. Furthermore, there is concern that aluminum will cause Alzheimer's disease. For these reasons, studies are being made to reduce the amount of purified water sludge generated and chemical costs, and to reduce the injection rate of PAC and sulfuric acid bands.

  On the other hand, a technique for injecting a slaked lime aqueous solution for non-corrosion of water is also becoming widespread with the advent of an apparatus for continuously producing a slaked lime aqueous solution disclosed in, for example, Japanese Patent No. 1459175. In the apparatus disclosed in other publications, there is a problem that an undissolved part (undissolved substance) that is difficult to dissolve remains in an aqueous solution having a pH of 12 or higher, but the undissolved part (undissolved substance) is maintained at a pH of 10 or less. This is solved by a method of introducing it into a landing well after treatment in water (Patent Document 1). Further, Patent Document 2 discloses that a slaked lime aqueous solution and carbon dioxide gas are used in combination to increase the Langeria index and make water non-corrosive. Furthermore, Patent Document 3 proposes that the concentration of the hardly soluble floc produced during the production of the slaked lime aqueous solution is increased, and the floc is introduced into the mixing pond and used as an alkali agent. It does not improve precipitation. There is a need for a method that achieves high-efficiency coagulation precipitation and non-corrosion of water at the same time.

Japanese Patent No. 1416054 Japanese Patent No. 2048482 JP-A-6-63566

  In view of the current situation, the present inventors have studied a method for simultaneously solving high-efficiency coagulation sedimentation and non-corrosion of water, and as a result, improved and developed a conventionally known slaked lime carbon dioxide combined injection method. That is, by injecting undissolved slurry, slaked lime solution and carbon dioxide gas from the slaked lime aqueous solution manufacturing apparatus into appropriate portions of the water purification treatment process according to the water quality, the undissolved slurry is agglomerated in the coagulation sedimentation operation. Use of additional chemicals such as coagulant aids in addition to the slaked lime solution and carbon dioxide gas normally used to improve water quality and undissolved slurry from the slaked lime aqueous solution production equipment, which has a nuclear function and forms a heavy floc The present invention has been completed by finding that the coagulation and precipitation can be carried out effectively without the necessity of the above.

  The present invention typically includes a slaked lime aqueous solution production device and a carbon dioxide gas injection device in a water purification treatment facility including a landing well, a mixing pond, a sedimentation basin, a filtration pond, and a distribution basin. In the water purification treatment to be adjusted, the pH, alkalinity, calcium hardness, etc. of the water to be treated are measured to obtain the Langeria index, pH 7.5 to 8.3, alkalinity 60 to 80 mg / l which is a preferable water quality from the viewpoint of corrosion prevention Then, determine the injection rate of slaked lime and carbon dioxide gas in an amount that makes the Langeria index -1 to 0, and in the settling basin of the water purification treatment facility or the process before that, undissolved slurry and carbon dioxide gas from the slaked lime aqueous solution production apparatus And slaked lime aqueous solution is injected, pH is adjusted to 6.7 to 7.3, calcium bicarbonate concentration is adjusted to 80 to 160 mg / l, and after increasing pH buffering property, flocculant is injected to aggregate, precipitate, Perform filtration, and further sterilize the filtered water By injecting an aqueous solution and / or carbon dioxide, a water treatment method characterized by performing high efficiency flocculation and non-corrosive of water at the same time.

  According to the method of the present invention, a heavy floc can be formed without using an agglomeration aid when coagulating and sedimenting regardless of whether the raw water is low-temperature, low-turbidity water, low-alkaline water or pH-high water quality. Therefore, coagulation and precipitation can be performed effectively, and non-corrosive water can be easily obtained.

It is a flow which shows an example of the water treatment by this invention.

  The present invention provides a slaked lime aqueous solution production device and a carbon dioxide gas injection device in a water purification treatment facility including a landing well, a mixing well, a sedimentation basin, a filtration pond, and a distribution basin. Slaked lime aqueous solution, undissolved slurry and carbon dioxide gas coming out of the apparatus are injected according to the water quality. The undissolved material slurry in the present invention refers to a slurry containing undissolved material remaining without being dissolved in a slaked lime aqueous solution having a pH of 11 or more in a slaked lime aqueous solution production apparatus. The solid in the undissolved slurry is mainly calcium carbonate and contains impurities of undissolved slaked lime and other raw material slaked lime contained in the calcium carbonate. As an apparatus for producing slaked lime aqueous solution, for example, a device as described in Japanese Patent No. 1459175 can be used which introduces water from the lower part of the stirring tank and continuously takes out the slaked lime aqueous solution from the upper part. Undissolved slurry is removed from the bottom of the tank after the introduction of water is stopped.

  In carrying out the present invention, prior to the water purification treatment, the pH, alkalinity, calcium hardness and the like of raw water are measured in advance to determine the Langeria index, and pH 7.5 to pH 7.5, which is a preferable water quality from the prevention of water corrosion after treatment. 8.3, The injection rate of slaked lime and carbon dioxide gas in an amount that makes the alkalinity 60-80 mg / l and Langeria index -1-0 is determined.

  The injection rate of carbon dioxide and slaked lime adjusts the pH of the water during the coagulation operation using 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 is injected, and when the pH is low, a slaked lime aqueous 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 also be performed by injecting carbon dioxide gas and / or slaked lime aqueous solution before the addition of the flocculant in anticipation of the degree of pH decrease due to the addition of the flocculant. it can. Moreover, it adjusts so that the calcium hydrogencarbonate density | concentration of the water at the time of aggregation operation may be in the range of 80-160 mg / l. When the concentration of calcium hydrogen carbonate in 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 specified range, the contained floating substances can be sufficiently settled and separated. Can not. The calcium bicarbonate concentration is adjusted using slaked lime and carbon dioxide. A typical case will be described below. The amount of the undissolved slurry according to the properties of the raw water is preferably injected into the landing well, and then carbon dioxide gas and slaked lime aqueous solution are injected, and preferable properties for coagulating precipitation, that is, pH 6.7 to 7.3, hydrogen carbonate The calcium concentration is adjusted to 80 to 160 mg / l, preferably pH 6.8 to 7.2, and the calcium bicarbonate concentration is adjusted to 90 to 120 mg / l. Thus, by adjusting using an undissolved substance slurry, it becomes possible to form a heavy floc even if it does not use an aggregation auxiliary agent at the time of 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. If the raw water has a high pH, first use carbon dioxide gas and slaked lime as needed. The aqueous solution may be used to adjust the properties close to those preferable for the aggregation reaction as much as possible, and then the undissolved slurry and the aggregating agent may be added. After adding the undissolved slurry and the flocculant, the pH and calcium bicarbonate concentration may be further adjusted. In some cases, the use of a coagulant aid or the like is not excluded. Undissolved slurry is preferably injected as a 2-3% slurry. Carbon dioxide is injected as a whole or a part of the necessary amount for adjusting the Langelia index determined in advance to -1 to 0. The carbon dioxide gas inlet is provided at a position deeper than the appropriate depth of 2 m depending on the size of the landing well or the mixing well. After injecting the undissolved slurry into the landing well, carbon dioxide is injected into the landing well or the mixing well, and the pH is adjusted to 6.7 to 7.3. If the pH after treatment is as low as 6.7 or less, slaked lime aqueous solution is injected to adjust the pH to be within the above range. When the slaked lime aqueous solution is required, when taking out the undissolved material from the slaked lime dissolving tank, it can be taken out as a slurry together with a required amount of the slaked lime aqueous solution and added to the landing well. When the pH after the above treatment is higher than 7.7, the amount of carbon dioxide injection is increased.

  The water adjusted in this way has a large buffering capacity, and when a flocculant such as PAC is added, the undissolved material added previously performs the core function of aggregation, forming a heavy floc and increasing its sedimentation rate. Become. As a result, the settling speed of the generated floc is high and efficient processing becomes possible. Moreover, since the addition of the coagulant aid used conventionally is not required and most of the added slaked lime, which is the main component of the undissolved material, dissolves, the amount of solid matter to be separated is significantly reduced.

The raw water was a highly corrosive surface water with a water temperature of 15 ° C., pH 6.7, alkalinity 5 mg / l, calcium hardness 5 mg / l, Langeria index −3.8, and turbidity 50 °. As the water quality improvement target value as pH 7.8, alkalinity 70mg / l, calcium hardness 70mg / l, Langeria index -0.5 as purified water with low corrosiveness, the required injection rate of slaked lime and carbon dioxide was obtained by experiment, 48 mg / l and 57 mg / l. The total amount of slaked lime required to achieve the water quality improvement target value for raw water of 20 m ³ / day was calculated as 1 kg / day, and the amount of carbon dioxide was calculated as 1.2 kg / day. Diameter 0.22 m, height 1.5 m, capacity cylindrical vertical low speed stirrer with dissolver of 0.06 m ³ to (slaked lime solution producing apparatus) was charged with slaked lime 1.2 kg, pH 12 or more spilled with water from the bottom of the dissolution tank The flowing liquid was stored in the intermediate tank. When 80% of the slaked lime is dissolved and overflows to the intermediate tank, the water supply to the dissolution tank is stopped and the undissolved slurry remaining in the lower part of the dissolution tank is left undissolved slurry after being allowed to settle for 1 hour. Extracted into the tank. The concentration of slaked lime obtained in the intermediate tank was approximately 1500 mg / l. The undissolved slurry had a pH of 12.0 and a slurry concentration of 2.9%, and the components of the undissolved material were calcium carbonate 57%, slaked lime 40%, silicon dioxide 2%, and aluminum oxide 0.2%.

The water purification process was performed as follows by the water treatment flow shown in FIG. The raw water 20m ³ / day was taken into the landing well and the undissolved slurry was injected at 0.3 l / h, resulting in a pH of 10.0. When 57 mg / l of carbon dioxide was injected into this mixed water and then 19.3 l / h of 1500 mg / l of slaked lime aqueous solution, pH 7.1, alkalinity 59 mg / l, calcium hardness 60 mg / l, calcium bicarbonate concentration It became 98 mg / l water. PAC was injected at a dose of 25 mg / l to perform aggregation precipitation. The turbidity of the sediment supernatant was 3 degrees, and the efficiency of coagulation sedimentation was 94%. The precipitate supernatant was subjected to sand filtration to obtain filtrate having a turbidity of 0.1 degree. When 5 l / h of 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.

[Comparative example]
Using the same raw water, slaked lime aqueous solution and PAC as in the examples, a batch experiment of coagulation precipitation was performed. Since injection of slaked lime aqueous solution alone does not provide pH buffering to raw water, injection of a small amount of slaked lime, 1.8 mg / l, raises the pH to 8.6, and the water quality at this time is 7 mg / l for alkalinity and 7 mg / l for calcium hardness. It was impossible to set the Langeria index to -0.5 at a pH of 7.8, an alkalinity of 70 mg / l, a calcium hardness of 7 mg / l, which is a preferable water quality value for clean water with low corrosivity, and a Langeria index of -1.6. . Subsequently, the slaked lime injection rate required for setting the pH for the coagulation treatment to the same 7.1 as in the example was 0.8 mg / l. According to the water treatment flow shown in Fig. 1, 0.5 mg / l of slaked lime aqueous solution of 1500 mg / l is injected into raw water 20 m ³ / day, and PAC is injected 25 mg / l into this, Aggregation precipitation was performed. The turbidity of the precipitate supernatant was as high as 8 degrees, and when this was subjected to sand filtration, the turbidity was 0.5 degrees. The quality of the purified water obtained by injecting slaked lime aqueous solution to this filtered water so as to have a pH of 7.8 was measured and found to be non-corrosive water with a calcium hardness of 11 mg / l, alkalinity of 7 mg / l and Langeria index -2.3. In addition, the coagulation precipitation efficiency was 79%, which was lower than that of the example.

The raw water was a surface water having a water temperature of 28 ° C., pH 9.4, alkalinity 57.1 mg / l, calcium hardness 58.5 mg / l, Langeria index 1.3 and turbidity 30 degrees, and was a high pH water. Water quality improvement target values as purified water were set at pH 7.8, alkalinity 65 mg / l, calcium hardness 58.5 mg / l, Langeria index -0.2, and the required injection rates of slaked lime and carbon dioxide were determined experimentally, 10 mg / l each. l, 16.1 mg / l. It was calculated as 0.02 kg / day of total slaked lime and 0.32 kg / day of carbon dioxide required to achieve the above water quality improvement target values for raw water of 20 m ³ / 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 it. When 80% of the slaked lime is dissolved and overflows to the intermediate tank, the water supply to the dissolution tank is stopped and the undissolved slurry remaining in the lower part of the dissolution tank is left undissolved slurry after being allowed to settle for 1 hour. Extracted into the tank. The concentration of slaked lime obtained in the intermediate tank was approximately 1600 mg / l. The undissolved slurry had a pH of 12.1 and a slurry concentration of 2.9%. The raw water 20m ³ / day was treated as follows by the water treatment flow of FIG. That is, first, raw water was taken into the landing well, and undissolved slurry was injected here to 0.06 l / h and carbon dioxide gas to 16.1 mg / l, pH 7.2, alkalinity 58.7 mg / l, calcium hardness It was 60.7 mg / l and the Langeria index -1.0. Next, about 1600 mg / l of slaked lime aqueous solution was injected as 3 l / h as a pre-alkali, and PAC was injected at 36 mg / l, pH 7.3, alkalinity 60.5 mg / l, calcium hardness 67.9 mg / l, Langeria index − 0.8. When this water was coagulated, the turbidity of the sediment supernatant was 4 ° C., and the coagulation efficiency was about 87%. When this precipitated supernatant was subjected to sand filtration, the turbidity of the filtrate was 0.1 degree. When 2 l / h of slaked lime aqueous solution was injected into the filtered water, non-corrosive water having a pH of 7.8, an alkalinity of 65 mg / l, a calcium hardness of 71.9 mg / l and a Langeria index of -0.2 was obtained.

Claims (4)

  In the purified water treatment facility, the slaked lime aqueous solution manufacturing device is installed in the water treatment facility, and the undissolved slurry obtained separately from the device, and the slaked lime aqueous solution is injected to adjust the water quality. Determine the rate of injection of slaked lime, which is the preferred water quality (pH 7.5 to 8.3), the amount of Langeria index -1 to 0, and inject the undissolved slurry into the sedimentation basin or the previous step to adjust the pH to 6.7. Adjust to ~ 7.3, perform coagulation, precipitation and filtration in the presence of coagulant, inject slaked lime aqueous solution into the filtered water to adjust pH 7, 5-8.3, Langeria index -1 to 0, and water non-corrosion Water purification method that performs at the same time.   In the purified water treatment where the slaked lime aqueous solution production device and the carbon dioxide gas injection device are installed in the water purification treatment facility and the water quality adjustment is performed, the Langeria index of the water to be treated is obtained and the water quality is preferable from the prevention of corrosion (pH 7.5 to 8.3). Determine the injection rate of slaked lime and carbon dioxide gas in an amount of index -1 to 0, and in the sedimentation basin or the previous process, undissolved slurry obtained from the slaked lime aqueous solution production device, carbon dioxide obtained from the carbon dioxide gas injection device Adjust the pH to 6.7 to 7.3 by injecting gas, perform aggregation, precipitation, and filtration in the presence of a flocculant, inject slaked lime aqueous solution and / or carbon dioxide gas into the filtered water, pH 7.5 to 8.3, Langeria index -1 A water purification method that simultaneously performs coagulation sedimentation treatment to make it 0 and non-corrosion of water.   3. A water purification treatment for simultaneously performing coagulation sedimentation treatment and non-corrosion of water according to claim 1 or 2, wherein the pH is adjusted to 6.7 to 7.3 by injecting undissolved slurry and slaked lime aqueous solution into the sedimentation basin or the previous step. Method.   The coagulation sedimentation treatment and water non-corrosion treatment according to any one of claims 1 to 3, wherein the pH is adjusted to 6.7 to 7.3 and the calcium bicarbonate concentration is adjusted to 80 to 160 mg / l in the sedimentation basin or the step prior thereto. Water purification method to perform.

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