JPH0929278A - Method for treating waste water and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and device to effect a nitrification treatment of waste water containing nitrogen under pressure. SOLUTION: In a method wherein waste water containing ammonia whose organic matters have been subjected to an aerobic biological treatment and pressurized gas containing oxygen is introduced into a closed treatment tank filled with carriers on which nitrifying bacteria are immobilized to effect a nitrification treatment under pressure, the nitrification treatmant is carried out in the tank under pressure of 1-15kg/cm<2> G, and exhaust gas from the treatment tank is heat-exchanged with a gas supplied by a compressor and thereafter the exhaust gas is reutilized in the aerobic biological treatment of organic matters in the waste water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for treating nitrogen-containing wastewater such as factory wastewater, domestic wastewater, station building wastewater, housing wastewater, and the like. TECHNICAL FIELD The present invention relates to a wastewater treatment method and apparatus for treating and nitrifying.

[0002]

2. Description of the Related Art In recent years, the so-called eutrophication phenomenon has become prominent due to an increase in inflow of wastewater containing nitrogen and phosphorus into sea areas, rivers, lakes, and the like. In addition, a phenomenon in which dissolved oxygen in water is extremely low has been frequently observed. For this reason, problems such as the death of fish and shellfish in sea areas, rivers, lakes and marshes, and changes in microflora macroscopically occur, which have a great effect on ecosystems. Nitrogen-containing wastewater is believed to be a significant factor in such eutrophication phenomena, and removing nitrogen from wastewater is a very important task.

When a wastewater containing organic matter and nitrogen is treated by a general aerobic biological method, the organic matter is converted into carbon dioxide and water to make it harmless, and the nitrogen compound is converted into ammonia by a deamination reaction. When aerobic treatment is further performed in a state where the concentration of organic substances is low, ammonia is oxidized into nitrite and nitric acid by the action of nitrifying bacteria. At this stage, the toxicity of ammonia disappears and it is rendered harmless, but it is further placed in an anaerobic atmosphere to convert nitrous acid and nitric acid into nitrogen gas by the action of denitrifying bacteria. In this reduction reaction,
A hydrogen donor is required, and in addition to methanol and acetic acid, it is common to use organic substances in wastewater as the hydrogen donor.

[0004]

[Problems to be Solved by the Invention] In the case of aerobic oxidation of ammonia, there are mainly Nitrosomonas bacteria as microorganisms that convert to nitrite, and microorganisms that further convert nitrite to nitric acid are mainly Nitrobacter. It is known to be a bacterium. These nitrifying bacteria have a slower growth rate than the oxidizing bacteria of organic substances. Therefore, when the excess sludge is drawn out according to the growth standard of the oxidizing bacteria of the organic substance as in the activated sludge method, it becomes difficult to accumulate nitrifying bacteria having a slow growth rate. Therefore, in order to effectively carry out nitrification after removal of organic matter, the nitrification reaction is often carried out using a carrier to which nitrifying bacteria are attached. The reason is that the bacterial cells adhered and grown on the carrier are fixed on the carrier without flowing out.
Therefore, the nitrification reaction relatively easily proceeds.

However, as described above, since the nitrifying bacteria originally have a slow growth rate, the nitrifying bacteria layer on the carrier is usually
Very thin, nitrification rate is 1/4 to 1 / of organic removal rate
It is often around 5. For this reason, in the case of waste water having a high concentration of nitrogen, the volume of the nitrification tank is considerably large, and sometimes it is as large as the aeration tank for oxidizing organic substances. Therefore, the nitrification tank needs to be upsized, which is an issue in terms of device design and economics. On the other hand, in the denitrification tank in an anaerobic atmosphere after nitrification, the growth rate of the denitrifying bacteria is not so different from that of the organic substance-oxidizing bacteria, and therefore the volume of the denitrifying tank does not become extremely large.

[0006]

Means for Solving the Problems The present invention is directed to an ammonia-containing wastewater and a pressurized oxygen-containing wastewater after aerobically treating organic matter in a wastewater in a closed treatment tank filled with a carrier on which nitrifying bacteria are immobilized. In the method of introducing gas and performing nitrification treatment under pressure, nitrification treatment is performed at a pressure in the tank of 1 to 15 Kg / cm ² G, and the exhaust gas from the treatment tank is treated with the gas supplied by the compressor and heat. After exchanging, it is used again for aerobic biological treatment of organic matter in wastewater, a wastewater treatment method characterized by having a wastewater supply port and a treated water discharge port, and a seal for filling a carrier on which nitrifying bacteria are immobilized. A mold treatment tank, in which a diffuser pipe communicating with an oxygen-containing gas supply port is installed in the lower part of the treatment tank, and a liquid level adjusting means, a pressure adjusting means and a gas outlet are provided in the upper part of the tank, and a treated water outlet is provided. Install a screen immediately before the A discharge port, and a conduit for guiding the oxygen-containing gas supplied from the compressor to the diffuser pipe via the heat exchanger, and the gas discharged from the upper part of the tank via the heat exchanger to the outside of the system. The present invention relates to a wastewater treatment device, which is provided with a conduit for taking out to

According to the present invention, a carrier in which fine threads create a three-dimensional space, such as a gel entrapping immobilization carrier capable of accumulating nitrifying bacteria in a three-dimensional solid body at a high concentration or a synthetic resin non-woven fabric is used. In the entrapping immobilization carrier, nitrifying bacteria are mixed in advance in the synthetic resin gel of the carrier. In the non-woven fabric carrier, the nitrifying bacteria are attached to the yarn surface of the non-woven fabric to be immobilized and gradually grown. By supplying an oxygen-containing gas under pressure to a treatment tank filled with these carriers and increasing the dissolved oxygen concentration, oxygen can reach the inside of the nitrifying bacteria layer and increase the growth rate of nitrifying bacteria. , The nitrification rate increases with proliferation. Further, since the oxygen-containing gas discharged from the nitrification treatment tank utilizes its pressure, it can be reused for aeration of the organic substance oxidation device which is usually connected immediately before the treatment tank.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The pressurized nitrification tank according to the present invention has a drainage supply port and a treated water discharge port, and a gas discharge port at the upper end and a slurry discharge port at the lower end. 3 carriers
A material having a three-dimensional space, for example, a material obtained by previously mixing gel with nitrifying bacteria by a gel encapsulation method and solidifying, or a synthetic resin nonwoven fabric is used as a carrier. These carriers can be used both as a fixed bed and as a fluidized bed. An air diffuser for supplying an oxygen-containing gas is arranged below the carrier packing and at the bottom of the pressurized nitrification tank, and the air diffuser is connected to the discharge port of the compressor. This compressed oxygen-containing gas gives oxygen to nitrifying bacteria in the carrier to cause nitrification reaction. At this time, since the nitrifying bacteria are present in the three-dimensional space or in the gel, the detachment phenomenon of the bacterial cells due to air bubbles is hardly found. In particular, in a fixed bed, there is no collision or contact between the carriers, and the peeling phenomenon is further reduced.

The pressure in the nitrification tank at the time of pressurization is 1 to 15 kg /
cm ² G, preferably ^{2 to} 10 kg / cm ² G, and the dissolved oxygen concentration is 10 mg / liter or more, usually 10 to 4
Set to 0 mg / liter. Due to this pressure, the bubbles of the oxygen-containing gas become smaller according to the pressure value, and the phenomenon of nitrifying bacteria peeling from the carrier due to the bubbles is hardly seen. In addition, by maintaining the dissolved oxygen concentration at 10 mg / liter or more, the diffusion of oxygen into the bacterial layer adhered and fixed in the three-dimensional space is enhanced, and the nitrifying bacteria present inside are effectively supplied with oxygen. Can be supplied and the efficiency of the nitrification reaction can be increased.

On the other hand, the oxygen-containing gas discharged from the treatment tank for performing the nitrification reaction under pressure has a slightly lower oxygen content than that at the time of inflow, but it can be reused sufficiently. , Which can be used as an aeration gas for oxidizing organic substances. Since an ordinary aeration tank for oxidizing organic matter is operated at normal pressure, the oxygen-containing gas discharged from the pressure-type processing tank of the present invention can be supplied without additional power. On the other hand, when supplying this pressurized exhaust gas as an aeration gas for organic matter oxidation, the temperature of the oxygen-containing gas on the discharge side of the compressor must be high in order to prevent the temperature of the gas from decreasing due to sudden pressure reduction to normal pressure. Is used to exchange heat between both gases. For this reason, the device of the invention comprises a heat exchanger, as shown.

The wastewater treated according to the present invention is not particularly limited as long as it is nitrogen-containing wastewater such as ordinary factory wastewater, domestic wastewater, station building wastewater, and collective housing wastewater. Further, the carrier used in the present invention may be one having a three-dimensional space, and specific examples thereof include a gel entrapping immobilization carrier and a synthetic resin non-woven fabric. The gel entrapping immobilization carrier is obtained by incorporating nitrifying bacteria into a gel and immobilizing it in advance, and is usually filled in a tank in a cylindrical shape, a spherical shape, or the like. As the gel used here, polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyacrylamide and the like can be used, but the gel is not limited thereto. Since nitrifying bacteria are present in the carrier from the beginning, the nitrification reaction is carried out at the same time as the start-up of nitrification treatment. Next, as the synthetic resin non-woven fabric, it is possible to use one in which fine fibers of the synthetic resin are entangled with each other and the bonding points of the fibers are adhered and fixed to form a continuous three-dimensional space constituted by the respective fibers inside. it can. When a material such as polypropylene or polyethylene is used as the synthetic resin, the specific gravity becomes smaller than that of water, and the carrier floats in water. However, when a material such as polyvinyl chloride or polyvinylidene chloride is used,
Since the specific gravity is larger than that of water, the carrier precipitates in water. In addition to these, resins such as nylon, acrylic resin, and polyvinyl alcohol can also be used. As a carrier to be actually used, a sheet-shaped carrier is made at regular intervals to form one module, cut into a cube, or processed into a cylindrical shape or a hollow cylindrical shape. In the case of this carrier, nitrifying bacteria are used by adhering and fixing on the surface of the yarn of the non-woven fabric and gradually growing. These carriers can be used both as a fixed bed and as a fluidized bed.

FIG. 1 shows an example of the processing apparatus of the present invention. The present invention will be described below with reference to FIG.
The treatment tank 2 filled with the above-mentioned carrier 1 is of a closed type and is configured such that an upper space 11 is formed during a wastewater purification treatment operation, and a constant pressure state is maintained by a pressure control valve 13 at the upper portion of the tank. The shape, volume, etc. are not particularly limited. Usually, it has a drainage supply port 3 and a treated water discharge port 4 treated in the tank through a pump 19 for supplying drainage, and a screen 5 is installed immediately before the treated water discharge port so that the carrier does not flow out. To be done. The screen spacing used is shorter than the carrier used. Usually, a carrier having a diameter and length of several millimeters to several tens of millimeters is used, and therefore the spacing may be shorter than this length.

At the bottom of the tank, there are provided a slurry discharge port 6 for drawing out the precipitate and an air diffuser 7 for supplying oxygen into the tank. A gas containing oxygen (usually air) passes through the compressor 15 and is introduced into the heat exchanger 17 via the conduit 16,
After heat exchange, the air is supplied from the diffuser pipe 7 as air bubbles into the tank.
The shape, number, arrangement form, etc. of the air diffusers can be appropriately selected according to each condition and are not particularly limited. To take out the treated water, the liquid level adjusting means (level sensor) 8 installed in the tank is activated, and the automatic adjusting valve 10 connected to the treated water discharge port 4 through the transmitter 9 for pressure adjustment depending on the height of the liquid surface. In response to opening and closing. On the other hand, the air bubbles that have risen in the tank are the space 11 above the tank.
The automatic gas adjusting valve 13 is opened and closed by means for adjusting to a predetermined pressure, that is, the transmitter 12, through the gas outlet 14, and enters the heat exchanger 17 through the conduit.

The pressure in the tank varies depending on the type of waste water to be treated, the nitrogen concentration, etc., but is usually 1 to 15 kg /
Keep in the range of cm ² G. In the pressurized state within this range, the dissolved oxygen concentration is maintained at 10 mg / liter (L) or more, preferably 15 mg / L or more, and the upper limit is maintained at about 100 mg / L. By maintaining the dissolved oxygen concentration at 15 mg / liter, it is possible to obtain a nitrification rate that is about twice the nitrification rate of ammonia at normal pressure. However, the dissolved oxygen concentration is 10
When the amount is less than mg / L, the nitrification rate does not increase so much that the effect due to the pressurization is not obtained. On the other hand, if the dissolved oxygen concentration is maintained at about 100 mg / L, a nitrification rate that is about 5 times the nitrification rate of ammonia at normal pressure can be obtained, but in order to create a dissolved oxygen concentration higher than this, 15
Pressurization of at least kg / cm ² G is required, which necessitates a multistage compressor, which is not preferable from the economical viewpoint.

The oxygen-containing gas discharged from the gas discharge port 14 has an oxygen content rate slightly lower than that at the time of inflow,
The present invention reuses this. That is, before performing the nitrification reaction according to the present invention, the organic matter in the wastewater is usually treated by the activated sludge method or the biological contact oxidation method, but a part or all of the air required for this treatment is used. Is covered with the oxygen-containing gas discharged from the gas discharge port 14. In this case, the normal aeration tank for organic substance oxidation is operated at normal pressure, so if the pressurized oxygen-containing gas discharged from the gas outlet is supplied as it is, the temperature of the gas will drop when returning to normal pressure. The present inventors have observed that on the other hand,
In the device of the present invention, the oxygen-containing gas is heated on the discharge side of the compressor 15. For example, air supplied at a pressure of 5 kg / cm ² G has a discharge port temperature of about 200 ° C. Therefore, heat exchange is performed between the discharge side air and the low temperature exhaust gas,
The exhaust gas temperature is raised to about several degrees Celsius to 40 degrees Celsius. The exhaust gas thus heated is used as an aeration gas for oxidizing the organic matter through the conduit 18. As a result, the power of the blower used for the conventional aeration is reduced, and the economical efficiency is increased.

[0016]

Next, the present invention will be described in detail with reference to examples. Example 1 An artificial wastewater having the following composition was used to perform wastewater treatment under the apparatus and operating conditions of the present invention described below. The results of wastewater treatment are shown in Table 1. 1. Equipment Treatment tank volume 200 L (580 mmφ × 760 mmH) Treatment tank effective volume 158 L (580 mmφ × 600 mmH) Carrier filling amount 32 L Carrier filling rate 20% Carrier type Entrapping immobilization carrier mixed with nitrifying bacteria in PVA gel Specific gravity of carrier 1. 03 Carrier shape Cube, 6x6x6mm

2. Components of artificial drainage As described below, ammonia nitrogen was contained at 200 mgN / L, and other components necessary for the growth of microorganisms were added. NH ₄ HCO ₃ 1130 mg / L (200 mg N / L) KH ₂ PO ₄ 44 mg / L MgSO ₄ .5H ₂ O 40 mg / L CaCl ₂ .2H ₂ O 5 mg / L

3. Operating conditions A continuous operation experiment was performed when the pressure was normal pressure and a pressure of 5 kg / cm ² G and the dissolved oxygen concentrations were 1 to 5 mg / L and about 30 mg / L, respectively. The target of treated water quality was ammonia nitrogen concentration of 10 mgN / L or less and nitrification rate of 95% or more, and the nitrogen load that could achieve this target was continuously obtained by changing the amount of wastewater (raw water) supply. The temperature was room temperature (20 ° C.), and the flow in the tank was completely mixed.

4. Results The operation results are shown in Table 1. As is clear from the table, in normal pressure operation, the nitrogen load was 0.3 KgN / m ³ · day, the raw water supply was 10 L / hour, the residence time was 15.8 hours, and the ammonia nitrogen in the treated water was 10 mgN / L or less. became. On the other hand, in the pressure operation of 5 kg / cm ² G, the nitrogen load is 1.0
KgN / m ³ · day, raw water supply rate 33 L / hour, residence time 5.3 hours, ammoniacal nitrogen in treated water is 10 mg
It became less than N / L. From this, the dissolved oxygen concentration of 1 to 5 mg / L at normal pressure operation is about 30 mg / L at pressurization operation.
It was confirmed that by setting L, the nitrogen load increased 3.3 times as compared with the normal pressure operation in order to achieve the same treated water quality (ammonia nitrogen removal rate of 95% or more).

[0020]

[Table 1]

[0021]

EFFECTS OF THE INVENTION According to the present invention, a method and an apparatus for treating wastewater, in which a carrier in which nitrifying bacteria are immobilized is filled in a closed treatment tank, and nitrogen-containing wastewater is aerobically treated under pressure to efficiently perform nitrification. Will be provided.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a wastewater treatment device used in the present invention.

[Explanation of symbols]

 1 Carrier 2 Sealed Treatment Tank 3 Drainage Supply Pipe 4 Treated Water Discharge Port 5 Screen 6 Slurry Discharge Port 7 Diffuser 8 Level Sensor 9 Transmitter 10 Automatic Control Valve 11 Upper Space 12 Transmitter 13 Gas Automatic Control Valve 14 Gas Discharge Port 15 Compression Vessel 16 conduit 17 heat exchanger 18 conduit 19 pump 20 conduit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuo Imamura 2-12-1, Tsurumi Chuo, Tsurumi-ku, Yokohama-shi, Kanagawa Chiyoda Kako Construction Co., Ltd. (72) Takashi Kimura Two, Tsurumi-chuo, Tsurumi-ku, Yokohama Chome 12-1 Chiyoda Kako Construction Co., Ltd. (72) Inventor Koji Kataoka 2-12-1 Tsurumi Chuo, Tsurumi-ku, Yokohama-shi Kanagawa Chiyoda Kako Construction Co., Ltd.

Claims (4)

[Claims] 1. An ammonia-containing wastewater after the aerobic biological treatment of organic matter in the wastewater and a pressurized oxygen-containing gas are introduced into a closed-type treatment tank filled with a carrier on which nitrifying bacteria are immobilized.
In the method of performing nitrification treatment under pressure, the pressure in the tank should be 1
Characterized by nitrification treatment at ~ 15 Kg / cm ² G, the exhaust gas from the treatment tank is heat-exchanged with the gas supplied by the compressor, and then used again for aerobic biological treatment of organic matter in wastewater. Wastewater treatment method. 2. The method according to claim 1, wherein the carrier is a carrier in which nitrifying bacteria are entrapped and immobilized in a synthetic resin gel or a synthetic resin non-woven fabric to which the nitrifying bacteria are attached and immobilized. 3. A closed type treatment tank having a waste water supply port and a treated water discharge port, which is filled with a carrier on which nitrifying bacteria are immobilized.
An air diffuser communicating with the oxygen-containing gas supply port is installed in the lower part of the treatment tank, a liquid level adjusting means, a pressure adjusting means and a gas outlet are provided in the upper part of the tank, and a screen is installed immediately before the treated water outlet. , A slurry outlet is provided at the bottom of the tank, and a conduit for guiding the oxygen-containing gas supplied by the compressor to the diffuser pipe via the heat exchanger and the gas discharged from the upper portion of the tank are connected to the heat exchanger. A wastewater treatment equipment, which is equipped with a conduit for taking it out of the system via the wastewater treatment equipment. 4. The wastewater treatment apparatus according to claim 3, wherein the carrier is a carrier in which nitrifying bacteria are entrapped and immobilized in a synthetic resin gel or a synthetic resin nonwoven fabric to which the nitrifying bacteria are attached and immobilized.