JPH0847697A - Method for removing ammoniacal nitrogen in raw water for city water - Google Patents

Abstract

PURPOSE:To remove ammoniacal nitrogen in the raw water for city water without need for intricate instrumentation equipment or maintenance by sterilizing the beads of the crushed oyster shell with sodium hypochlorite, packing the sterilized beads in a tower or tank, propagating nitrifying bacteria in the tower or tank and then passing the raw water through the tower or tank. CONSTITUTION:The beads 2 obtained by crushing the oyster shell are sterilized with sodium hypochlorite and closely packed in a tower 3. Air is blown into an aeration tank 1 by a compressor 5 to increase the dissolved oxygen concn. in the raw water, and the propagation of the nitrifying bacteria is promoted. The aerated raw water is introduced into the tower 3 by a transfer pump 6 through flowmeter to oxidize the ammoniacal nitrogen in the raw water to nitrate nitrogen by the nitrifying bacteria, and the ammoniacal nitrogen is removed. The grain size of the beads is controlled to 3-50mm. The raw water is circulated between the aeration tank 1 and the tower 3 packed with the beads 2 until the nitrifying bacteria are sufficiently propagated.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a method for treating raw water for water supply,
In particular, it relates to a novel purification treatment method for removing ammoniacal nitrogen in raw water for tap water.

[0002]

2. Description of the Related Art Groundwater is used as raw water for tap water, but usually cannot be supplied as tap water as it is. Therefore, after filtering and treating chemicals, water quality standards required by the Water Supply Act It is supplied after satisfying.

The main chemical treatment of raw water is chlorine injection for the purpose of sterilizing groundwater (chlorine treatment method). At that time, the presence of ammoniacal nitrogen contained in groundwater poses a serious problem. . Ammoniacal nitrogen reacts with chlorine and eventually becomes nitrogen gas and is released into the air, but in the process of this reaction, more than half of chlorine becomes chlorine ions, which are ineffective for sterilization.

Therefore, it is sufficient to inject a large amount of chlorine in anticipation of the amount of chlorine that reacts with ammoniacal nitrogen, but the concentration of ammoniacal nitrogen in the raw water for tap water is 0.5-.
It varies in the range of about 3.0 ppm, and raw water with a constant concentration is not the target of treatment. Generally, the chlorine treatment method requires about 10 times as much chlorine as the concentration of ammonia nitrogen in the raw water, but if a large amount of chlorine is present in the treated water, the reaction between organic matter and chlorine causes trihalomethane, which is a carcinogen, to be generated. Therefore, it is necessary to change the chlorine injection amount without excess or deficiency according to the ammonia nitrogen concentration. For this reason,
The labor cost and equipment cost for adjusting the amount of chlorine injection by periodically measuring the concentration of ammonia nitrogen in the raw water becomes very large. Moreover, the concentration of free chlorine in the treated water is 0.
Since it has to be controlled in the range of about 1 to 1.0 ppm, a highly accurate control device is required.

As a method for removing ammoniacal nitrogen from raw water for tap water, a so-called biological treatment method is known in which the action of nitrifying bacteria is used to oxidize ammoniacal nitrogen into nitrate nitrogen. The biological treatment method is to oxidize ammoniacal nitrogen in raw water to nitric acid using sludge in water containing nitrifying bacteria, nitrifying bacteria support fixed in water, or carrier supporting nitrifying bacteria, and then sterilize with chlorine. Is. As a biological treatment method, there are an immersion filter bed method, a rotating disk method, a biological filtration method, and the like, and sand, a plastic structure, activated carbon, etc. are known as carriers for nitrifying bacteria. However, when these carriers are used, the growth of nitrifying bacteria is insufficient, and the nitrifying action is not efficiently performed in many cases, and there are many problems in terms of maintenance and management of equipment.

[0006]

As a result of repeated studies to solve such problems, the present inventors have found that oyster shells that have been sterilized, especially oysters treated with a chemical solution using sodium hypochlorite. The inventors have found that the use of a crushed shell can effectively remove ammoniacal nitrogen in raw water for tap water without requiring complicated instrumentation equipment and maintenance, and completed the present invention.

That is, according to the present invention, shell beads obtained by crushing an oyster shell are sterilized with sodium hypochlorite, and the sterilized shell beads are packed in a tower or a tank. After propagating nitrifying bacteria in the water, the raw water for tap water is passed through the tower or tank, and the nitrifying bacteria in the tower or tank oxidize the ammoniacal nitrogen in the raw water for tap water to nitrate nitrogen. The present invention provides a method for removing ammoniacal nitrogen in raw water for tap water.

The method of the present invention will be described in detail. The shell beads used in the present invention contain calcium carbonate as a main component, but the oyster shells are washed with water, crushed with a suitable crusher, and sieved to have a particle size of 3 to 50 mm, preferably 5 to 15 m.
m is a coarsely crushed product. This is immersed in an aqueous solution of sodium hypochlorite for sterilization. Sterilization is performed by immersing shell beads after sterilization in pure water to extract dissolved components,
It is essential that the extract is tested to the extent that nitrite nitrogen is not detected by the water quality test specified in the Water Supply Act. Generally, a suitable concentration of the sodium hypochlorite aqueous solution is about 0.01 to 1%.

As described above, the shell beads treated with the chemical solution are washed with water until sodium hypochlorite is no longer recognized, and the sterilized shell beads obtained are filled in a tower or a tank.

The filling amount of the shell beads can be appropriately determined in consideration of the water quality of the raw water and the scale of equipment, and is not particularly limited, but 4.0 to 1 per 1 m ³ (bulk volume) of the shell beads.
A guideline is about 0.0 m ³ / h. Further, the size and shape of the column or tank for filling the shell beads may be determined as appropriate under ordinary chemical engineering design.

In the present invention, the particle size of the shell beads is selected to be in the range of 3 mm to 50 mm because the shell beads having a larger particle size are too bulky and the packing column or tank becomes too large, and the shell beads are also selected. Since the contact surface area of is small, the water flow rate becomes small. On the other hand, if the particle size is smaller than this, the water resistance increases, and if pressure is applied, fine powder may flow out, which may cause clouding of the treated water, which is not preferable.

In the present invention, the sterilization treatment of the shell beads with an aqueous solution of sodium hypochlorite is carried out by another sterilization treatment method, for example, a method of heat treatment, in which unevenness occurs and the strength of the shell beads is lowered, and hydrochloric acid is added. Such treatment with an acid is not preferable because the shell beads are dissolved, but treatment with an aqueous solution of sodium hypochlorite does not have such drawbacks and a desired sterilization treatment can be easily performed.

By using the shell beads crushed to the above particle size, voids can be formed in the packed bed, and nitrifying bacteria colonies are generated in the voids, and the nitrifying efficiency is increased together with the nitrifying bacteria adhering to the surface of the shell beads. Increase. Further, since the shell beads are stacked flatly, the contact frequency between the raw water and the nitrifying bacteria increases when the raw water passes through the shell beads layer.

The shell beads used in the present invention are obtained by crushing oyster shells. Compared to other shells, the oyster shells are easier to pulverize and easily obtain the desired particle size. In addition, the shell forms a layer corresponding to the growth process, which allows the drug solution to penetrate into the interior, and the desired sterilization treatment can be performed by one dipping treatment. In addition, since the oyster shell is porous and the size of its pores is suitable for capturing and supporting nitrifying bacteria, it is more advantageous for breeding nitrifying bacteria than other shells.

Nitrifying bacteria, which are autotrophic bacteria, require trace amounts of phosphorus, potassium, calcium, magnesium, etc. in addition to ammonia nitrogen, but raw water is passed through a tower or tank filled with shell beads. It is considered that by doing so, these nutrients in the shell beads are eluted and conditions suitable for the growth of nitrifying bacteria are created.

Furthermore, in the conventional method using a carrier, the pH of the treated water is lowered due to nitric acid generated by nitrifying bacteria oxidizing ammonia nitrogen, but in the present invention, nitric acid is generated by the alkali content in the shell beads. Are neutralized, and the pH of the treated water can be prevented from lowering. Therefore, the pH in the apparatus is maintained at 7.0 to 7.5 which is the optimum pH range for nitrifying bacteria, and no equipment for pH adjustment is required.

Next, the nitrifying bacteria are sufficiently propagated in the tower or tank filled with shell beads. The breeding of nitrifying bacteria is
Raw water or water prepared separately may be passed through the tower or tank to fill the tower or tank with water, and the nitrifying bacteria culture solution may be added thereto and left for a while. The amount of nitrifying bacteria added is not particularly limited. The breeding condition of nitrifying bacteria can be known by detecting the concentration of ammonium nitrogen discharged from the tower or tank.

In the present invention, the raw water is passed through the aeration tank before the raw water for tap water such as ground water is passed through the tower or tank filled with the shell beads as described above to be treated with nitrifying bacteria. Then, it is preferable to increase the dissolved oxygen concentration in the raw water. If the dissolved oxygen concentration in the raw water is low, the growth of nitrifying bacteria will be insufficient, which is not preferable. The method of aeration treatment may be a known method such as using an aeration tank, and the degree of aeration treatment may be appropriately determined.

Further, in the present invention, a device for aerating the raw water for tap water until the nitrifying bacteria have sufficiently propagated, for example, a process or equipment for circulating between the aeration tank and the tower or tank filled with shell beads. From the viewpoint of.

When the nitrifying bacteria have sufficiently propagated in the tower or tank filled with the shell beads, the raw water for tap water is passed through for treatment, and the flow rate of the raw water or the residence time in the tower or the tank depends on the ammonia in the treated water. It is necessary to adjust the nitrogen concentration so that it does not interfere with the chlorine sterilization process.

In the method for removing ammoniacal nitrogen of the present invention, it is preferable to carry out the purification treatment of the present invention before the chlorine sterilization step.

According to the method of the present invention, ammoniacal nitrogen in raw water can be effectively oxidized to nitrate nitrogen. Further, according to the method of the present invention, even if the concentration of ammonia nitrogen in the raw water changes, the concentration of ammonia nitrogen in the treated water hardly changes, so that the chlorine injection amount for sterilization can be kept constant. Further, the shell beads consumed by the treatment of the raw water can be easily and stably operated continuously by simply replenishing them, so that the present invention is a very useful invention.

The oysters are cultivated and consumed in large quantities, and the disposal of their shells poses a problem. However, the present invention also makes effective use of such wastes and improves the environment. It is a significant invention from the viewpoint of.

[0024]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 Shafts were washed with water, crushed with a crusher, and sieved to 5 m.
Shell beads with a particle size of m to 20 mm were selected. 40 kg of the shell beads were immersed in 200 liters of a 0.03% sodium hypochlorite solution for 24 hours, and then washed with water until sodium hypochlorite was not observed. The CaCO ₃ content in the used shell beads was 94 to 95%.

34 kg of the shell beads thus obtained was packed in a vinyl chloride column having an inner diameter of 250 mm and a length of 1300 mm. Ground water was passed through this tower to fill the tower with water, and then a nitrifying bacteria culture solution was added. In this example, the apparatus shown in FIG. 1 was used, and raw water was circulated between the tower and the aeration tank until the nitrifying bacteria were sufficiently propagated. The raw water was circulated until the concentration of ammonia nitrogen discharged from the tower became about 1/8 of the concentration of ammonia nitrogen in the raw water.

After confirming the growth of nitrifying bacteria in the tower in this way, in this embodiment, before passing the raw water through the tower filled with shell beads, the raw water was passed through the aeration tank to check the dissolved oxygen concentration. Raised. Table 1 shows the dissolved oxygen concentration of raw water and aerated treated water.

[0028]

[Table 1]

[0029] while the aeration process of the above, the raw water ^{(1) 0.3m 3 /h,(2)0.6m 3 /} h, (3)
Raw water was passed through the tower at a flow rate of 0.9 m ³ / h for purification treatment. The treated water had a significantly reduced amount of ammonia nitrogen, and both were compatible with the water quality test stipulated by the Water Supply Act.
Table 2 shows the main items in the test results.

[0030]

[Table 2]

The apparatus used in this example is shown in FIG. A brief description of this device is as follows. FIG.
The apparatus shown in (1) is composed of an aeration tank 1, a shell beads packed tower 3, a flow meter 6 and the like, and a piping system connecting them. Air is blown into the aeration tank 1 by the air compressor 5 in order to increase the dissolved oxygen concentration in the raw water and promote the growth of nitrifying bacteria. The packed column 3 is made of vinyl chloride, and the shell beads 2 are densely packed therein. Also, in order to know the pressure before and after the packed bed and inside the bed, a pressure gauge 7
Is attached, and the pressure loss can be known. The raw water that has been subjected to aeration is passed to the tower 3 through the flow meter 6 by the transfer pump 8. In addition, this device is equipped with a pipe connecting the upper part of the tower and the aeration tank, and raw water can be circulated until the nitrifying bacteria are sufficiently propagated. As the measuring instruments and pumps, general commercially available products may be used, and a valve is provided in the vinyl chloride piping system to adjust the flow rate. Groundwater to be treated passes through the inside of this device from the lower part of the packed tower, nitrifying bacteria in the tower remove ammoniacal nitrogen, and the treated water is discharged from the upper part of the tower.

Comparative Example 1 In the above example, when raw water was treated without performing aeration treatment before passing through the shell beads packed tower, ammonia nitrogen was not removed at any flow rate. It was

Comparative Example 2 In the above-mentioned example, when activated carbon was filled instead of shell beads and treated in the same manner, the ammonia nitrogen concentration was 0.3 m ³ / h, 90% of the raw water in the case of passing water, 0.
In the case of 6 m ³ / h water flow, only a removal rate of about 40% of raw water was obtained.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of an apparatus used in the method of the present invention.

[Explanation of symbols]

 1 ... Aeration tank 2 ... Shell beads 3 ... Shell beads packing tower 4 ... Intake pump 5 ... Air compressor 6 ... Flowmeter 7 ... Pressure gauge 8 ... Transfer pump

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hozumi Igarashi 5-2-3 Numatarigashi Higashi, Niigata City, Niigata Prefecture

Claims (4)

[Claims] 1. Shell beads obtained by crushing an oyster shell are sterilized with sodium hypochlorite, and the sterilized shell beads are packed in a tower or tank, and nitrification is carried out in the tower or tank. After propagating the bacteria, the raw water for tap water is passed through the tower or tank, and nitrifying bacteria in the tower or tank oxidize ammoniacal nitrogen in the raw water for tap water to nitrate nitrogen. Method for removing ammoniacal nitrogen from raw water for tap water. 2. The particle size range of the shell beads is from 3 mm to 5
The method for removing ammoniacal nitrogen in raw water for tap water according to claim 1, which is 0 mm. 3. The raw water for tap water is subjected to aeration treatment before passing through a tower or tank filled with shell beads to increase the dissolved oxygen concentration in the raw water for tap water.
Or the method for removing ammoniacal nitrogen in raw water for tap water according to 2. 4. Raw water for tap water is circulated between a device for performing aeration treatment and a tower or tank filled with shell beads until the nitrifying bacteria are sufficiently propagated.
The method for removing ammoniacal nitrogen from raw water for tap water according to any one of 1.