JPH0581317B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for biologically treating organic wastewater by an activated sludge method, a contact aeration method, or the like.

Organic wastewater such as human waste, chemical factory wastewater, food factory wastewater, alcohol distillation wastewater, and sewage can be biologically treated by activated sludge method (floating method) or contact aeration method (fixed bed aeration method). These methods have been widely used in the past, but when using these methods to treat human waste with a BOD concentration of 10,000 to 12,000 mg, for example, diluted water such as industrial water or groundwater is used that is 10 to 20 times the amount of human waste to be processed. It had been. For this reason, not only is the treatment cost high and uneconomical, but there are also social problems such as ground subsidence due to pumping up groundwater and depletion of drinking water. Therefore, in recent years, no-dilution treatment methods or low-dilution treatment methods have been adopted in place of conventional treatment methods that require large amounts of dilution water.

By the way, in biological treatment, heat generation due to biological metabolic reactions, for example, in the case of BOD oxidation reaction (respiration) of organic matter under aerobic conditions, oxygen consumption 1
It is about 3300 Kcal per Kg- _O2 , but in the case of the above-mentioned non-dilution treatment method and low dilution treatment method, oxygen consumption per unit of treatment amount is large, so even if there is natural heat dissipation, activated sludge tank or contact aeration tank In some cases, the water temperature in biological treatment tanks such as plants exceeds the optimum temperature for microorganisms, 20-35°C, and reaches 40°C or higher. This is particularly noticeable in the summer when the temperature of the influent flowing into the biological treatment tank is high, or when the BOD concentration of the influent exceeds 4000 mg/kg. The amount of heat generated further increases.

In addition, if the treatment before the biological treatment tank in the wastewater treatment system is a wastewater or sludge treatment equipment that involves heat treatment such as heating, or if the treatment is for chemical factory wastewater or food factory wastewater, biological The liquid flowing into the treatment tank itself may be at a high temperature. Conventionally, even in such cases, the temperature of the influent was lowered by dilution water when it entered the biological treatment tank, but with the above-mentioned no-dilution treatment method or low-dilution treatment method, the temperature of the influent was sufficiently reduced. It doesn't get warm.

In any case, if the water temperature in the biological treatment tank exceeds the optimum temperature for microorganisms, the treatment effect will decrease due to death of activated sludge, decrease in activity, etc., and the quality of treated water will deteriorate. Tokukosho is a way to partially solve this problem.
It is proposed in Publication No. 58-6557. This method is
As shown in FIG. 6, after the effluent, which is oxidized treated water or reduced treated water, is cooled through a heat exchanger 1, it is circulated to a mixed decomposition tank 3 that constitutes a biological treatment tank 2. In this method, the denitrified treated water is cooled in a cooling tower 4, and the cooled treated water is used as a refrigerant for the heat exchanger 1.

However, in the method that requires the heat exchanger 1, calcium present in the final treated water and activated sludge mixture (return sludge, etc.) that is the effluent of the biological treatment tank 2, Dissolved inorganic components such as magnesium, phosphorus, sulfuric acid, and carbonate ions, as well as suspended solids such as oil and suspended solids, may adhere as scales to the heat transfer surface of the heat exchanger 1, significantly reducing the cooling effect. Alternatively, there are many problems in terms of equipment, such as clogging of the heat exchanger 1. Also,
In terms of maintenance and management, the cooling equipment must be shut down to disassemble and clean the heat exchanger 1, or scale removal work such as cleaning with chemical solutions must be performed frequently. There were problems such as reduced equipment operating days and increased running costs due to the use of chemicals.

In addition, as another method, as disclosed in Japanese Patent Application Laid-Open No. 59-62392, at least a part of the treated water in the biological treatment process of wastewater is branched off as circulating water, and after being cooled, it is returned to the biological treatment tank. Methods for suppressing water temperature rise in biological treatment processes have also been proposed.

However, even in this method, a heat exchanger is used as a cooling device, so as a way to solve the problem of scale adhesion on equipment, the water used to cool the treatment tank is made of high-quality water that does not contain polluted water substances such as scale. Purified water such as post-processed water is recycled, and unless the water is of high quality, it cannot be cooled through a heat exchanger. As a result, purified water for cooling, which is not originally necessary for the treatment, is forced to flow into the treatment tank, which unnecessarily increases the degree of dilution, resulting in a problem of increasing the size of the treatment apparatus.

The present invention was made in view of the above circumstances, and
A biological treatment method and device capable of efficiently treating organic wastewater in an undiluted or lightly diluted state to obtain treated water of good quality, and in which the device can be operated continuously for a long period of time. The purpose is to provide

In order to achieve the above object, the method of the present invention includes:
The effluent or influent of a biological treatment tank containing an aerobic biological treatment means is partially flash evaporated in a cooling can under an absolute pressure of 45 mmHg or less to reduce its temperature, and then the liquid is subjected to the biological treatment described above. The device is configured to have a biological treatment tank containing an aerobic biological treatment means, and the effluent or inflow of this tank is partially flushed under an absolute pressure of 45 mmHg or less. It is composed of a cooling can which evaporates to reduce the temperature, a vacuum device which reduces the pressure of the cooling can, and a supply means which causes the liquid in the cooling can to flow into the biological treatment tank.

Hereinafter, one embodiment of the apparatus of the present invention will be described with reference to the drawings. In FIG. 1, the reference numeral 10 indicates a well-known biological treatment tank for biologically denitrifying organic wastewater W such as human waste, including a first denitrification tank 11, a nitrification tank 12, and a second denitrification tank. The nitrogen tank 13 and the reaeration tank 14 are connected in series by a flow path 15, and
The first denitrification tank 11 and the nitrification tank 12 are connected to each other by a circulation flow path 16 that circulates and returns a part of the liquid in the nitrification tank 12 to the first denitrification tank 11 as circulating liquid R. A settling tank 17 and, if necessary, an advanced treatment tank 18 are connected to the aeration tank 14 via a flow path 19, and the settling tank 17 and the first denitrification tank 1 are connected to each other by a flow path 19.
1 are connected to each other by a sludge circulation channel 20 that returns part or all of the microbial sludge settled in the settling tank 17 to the first denitrification tank 11 as return sludge S. Further, the circulation passage 16 includes a cooling can 21 for cooling part or all of the circulating liquid R flowing through the circulation passage 16, and a cooling can 21 for cooling part or all of the circulating liquid R flowing through the circulation passage 16, and a cooling can 21 for cooling the circulating liquid R cooled by the cooling can 21 through the first denitrification process. A pump (supply means) 22 for returning the water to the tank 11 is interposed.

Further, a vacuum device 23 for reducing the pressure inside the cooling can 21 is connected to the cooling can 21 via a steam suction channel 24 . The circulating liquid R supplied to the cooling can 21 self-evaporates until it reaches equilibrium with the pressure inside the can, and the latent heat of vaporization is taken away and the temperature is reduced. Gas vacuum device 2
3, the circulating fluid R is continuously taken out from the cooling can 21 and the pressure inside the can is maintained at a predetermined value, whereby the circulating fluid R is cooled to a temperature close to the saturated vapor pressure corresponding to that pressure.

Here, the pressure inside the cooling can 21 is determined based on the capacity, structure, and amount of aeration gas of the biological treatment tank 10.
The absolute pressure is maintained at at least 45 mmHg or less, although it varies depending on the type of bacteria, the amount of cooling liquid supplied from the cooling can 21 to the biological treatment tank 10, etc., and cannot be determined unconditionally. As a result, part of the effluent or inflow that exceeds the upper limit of the optimum temperature (36°C) for aerobic biological treatment at a temperature of 40°C or higher will be evaporated, and the temperature will be below 36°C, which is the saturated steam temperature under this absolute pressure. temperature rise in the processing tank can be effectively suppressed. The cooling can 21 may be of any shape as long as the circulating fluid R is exposed to a reduced pressure inside the can, but since the circulating fluid R self-evaporates, It is preferable to have a structure in which the surface area of the circulating fluid R is as large as possible,
For example, a multi-stage cascade type as shown in Figure 2a and b, or a circulating fluid R as shown in Figure 2c.
There is a structure in which the water flows in the tangential direction of the can and flows down the can wall.

Note that the evaporated vapor from the circulating fluid R is transferred to the vacuum device 23.
If there are a lot of droplets entrained when suctioning, make sure to leave enough space above the evaporated liquid level in the can, or install a baffle plate 25 or the like shown in Figure 2c inside the can or in the vapor suction channel 24. It is recommended to use a demister such as a wire mesh or cyclone to separate droplets. In addition, when the amount of circulating fluid R supplied to the cooling can 21 is large or when the temperature difference to be cooled is large, the cooling can 21
The load on the vacuum device 23 can be reduced by dividing the cooling canister 21 into several chambers, or by providing a plurality of cooling cans 21 to reduce the load on the vacuum device 23.
It is preferable to separate as much gas as possible from the circulating liquid R by once passing it through a deaerator and allowing it to stand still or to slowly stir it, thereby reducing the load on the vacuum device 23.

On the other hand, the vacuum device 23 basically consists of a vacuum pump that discharges evaporated steam and non-condensable gas from the circulating liquid R to the outside of the cooling can 21 to maintain the inside of the can in a predetermined reduced pressure state. And, if necessary,
A condenser is attached to the cooling can 21 to condense the evaporated vapor discharged from the cooling can 21, and a booster is provided to compress the evaporated vapor to a pressure at which it can be condensed when the cooling temperature is low and the evaporated vapor cannot be condensed as it is in the condenser. and the capacitor.

Examples of the vacuum pumps mentioned above include mechanical pumps such as piston pumps, liquid ring pumps (trade name: Natsushi Pump), multi-blade rotary pumps, and oil rotary pumps, and injection pumps such as steam ejectors, air ejectors, and water ejectors. These can be used alone or in combination in multiple stages. In devices that use vacuum oil, such as piston pumps, multi-blade rotary pumps, and oil rotary pumps, a large amount of evaporated vapor contained in the suction fluid condenses inside the pump and mixes with the vacuum oil, causing its function to deteriorate. To prevent this, a water removal device such as a demister or condenser may be installed between the cooling can 21 and the pump, or the oil containing condensed water discharged from the pump may be removed by a centrifuge or oil-water separator. or the like to separate the water and return the purified oil to the pump. In addition, in a liquid ring type pump, sealed water circulates inside the main body, and the pump has the effect of condensing the sucked evaporated vapor within the pump, so the suction capacity is high and there is no problem of condensed water getting mixed in. This liquid ring type pump is used with an air ejector attached to its upstream side. Furthermore, the water ejector generates a vacuum by injecting liquid pressurized by a pump from a nozzle, and, like the liquid ring pump described above, has the effect of condensing evaporated steam and suctioning non-condensable gas. In addition, it has no mechanically moving parts and has a simple structure, making it suitable as the vacuum pump described above. Particularly preferred are multijet condensers with increased condensing function and water jet condensers called jet ejector condensers.

In addition, the liquid ring type pump and water ejector mentioned above are
Performance changes depending on the temperature of the sealing water and the injection water, and the ultimate pressure below the vapor pressure corresponding to the water temperature cannot be obtained.
Therefore, a large amount of cold water is required to obtain a predetermined pressure, but it is preferable to circulate the water through sealing water and injection water, and to remove the heat of condensation of the evaporated steam using a cooling device such as a cooling tower. In this case, it is advantageous to use fresh water for the circulating seal water or circulating jet water from the liquid ring pump or water ejector, as this avoids contamination in the cold water circulation system. In addition, since the condensed water in the liquid ring pump or water ejector is added to the circulating water, makeup water is not particularly required for the chilled water circulation system even when using a cooling tower, and furthermore, the condensed water is Unlike the circulating fluid R and the treated water of the biological treatment tank 10, the water has been evaporated once, so it contains almost no scale matter or suspended matter, and there are almost no problems such as scale formation. FIG. 3a shows the vacuum device 23 constructed using a water jet condenser 26, in which 27 is a cooling device such as a cooling tower, and 28 is a liquid level controller. Also, the third
Figure b shows a vacuum device 30 configured by arranging a plurality of water ejectors 29 in multiple stages. In the figure, 31 is a gas-liquid separation drum, 32 is a cooling device such as a cooling tower, and 33 is a flow rate adjustment valve. .

Next, the method of the present invention will be explained.

The method of the present invention is suitable for treating organic wastewater W that is undiluted or lightly diluted at room temperature and has a BOD concentration of about 4000 mg/min or more even in the diluted state. Below, we will explain this method based on the apparatus with the above configuration. First, we will explain the method using either no dilution or low dilution diluted with dilution water of about 1 to 2 times the flow rate of the raw wastewater (processing amount if the flow rate of raw wastewater is Qm ³ /D). teeth
It will be from 2Q to 3Q. ) is sent to the nitrification tank 12 via the first denitrification tank 11, where organic nitrogen and ammonia nitrogen in the organic wastewater W are nitrified and BOD components are removed. .
At this time, an appropriate amount of air is blown into the mixture of treated water and microbial sludge in the nitrification tank 12, and if necessary, a small amount of sodium hydroxide solution N is added to maintain the pH of the mixture at around 7.5 to 9.0. , maintain the best nitrification conditions.

Next, a part of the mixed liquid or treated water in the nitrification tank 12 containing nitrite nitrogen and nitrate nitrogen generated by nitrification is used as circulating liquid R (generally 20 to 36Q water volume) to the first denitrification tank 11. We will send it back to you, but in that case,
Part or all of the circulating liquid R is passed through the cooling can 21. The circulating fluid R supplied to the cooling can 21 is heated to 45 mmHg inside the can by the vacuum devices 23 and 30.
Since the pressure is reduced to the absolute pressure below, self-evaporation (flash evaporation) occurs until it reaches equilibrium with the pressure inside the can.
The latent heat of vaporization is taken away and the temperature decreases, but at that time,
The evaporated steam and non-condensable gas are taken out of the can by the vacuum devices 23 and 30, and the pressure inside the can is maintained at a predetermined value, and the temperature of the circulating fluid R is brought close to the saturated water vapor pressure temperature corresponding to the pressure inside the can. Go down. Then, the circulating fluid R whose temperature has been reduced is returned to the first denitrification tank 11 by the pump 22.

The inside of this first denitrification tank 11 is maintained under anaerobic environmental conditions, including the organic wastewater W, the circulating liquid R returned from the nitrification tank 12 directly or via the cooling can 21, and the settling tank 17. A mixed waste liquid mixed with return sludge S returned from the tank is retained. Then, the nitrite nitrogen and nitrate nitrogen in the circulating fluid R flowed into this first denitrification tank 11.
BOD components are reduced to nitrogen gas by facultative anaerobes that use them as an organic carbon source;
The mixed waste liquid is denitrified and BOD components are also removed.

Furthermore, the mixed liquid that has passed through the first denitrification tank 11 and the nitrification tank 12 is introduced into the second denitrification tank 13, and the remaining nitrite nitrogen and nitrate nitrogen that were not reduced in the first denitrification tank 11 are added. is denitrified by reducing it to nitrogen gas. In this case, while maintaining the inside of the second denitrification tank 13 in an anaerobic atmosphere, a small amount of methanol M is supplementarily added to the mixed liquid inside to reduce nitrite nitrogen and nitrate nitrogen to nitrogen gas. Promote speed.

The denitrification mixture that has passed through the second denitrification tank 13 is then fed to the re-aeration tank 14, where it is aerated for a short time under air agitation to aerobize the microbial sludge and remove residual BOD components. In addition to performing biological oxidation and deaeration of the gas contained in the microbial sludge, the sludge is sent as it is or diluted with dilution water D with a water volume of 10Q or less and sent to the next settling tank 17, where BOD components and nitrogen are removed. Sedimentation separates into water and microbial sludge. Then, the treated water is sterilized with chlorine via the advanced treatment tank 18 as necessary and discharged into a river, etc., while a part or all of the settled microbial sludge is returned to the first denitrification tank 11 as return sludge S. The microbial sludge concentration in the tank is maintained at a predetermined value.
Here, when only a portion of the microbial sludge is used as return sludge S, excess sludge is appropriately treated and discarded.

As described above, in the method of the present invention, part or all of the circulating fluid R, which is the effluent from the biological treatment tank 10, is guided to the cooling can 21 and once cooled to a predetermined temperature, and then Since the circulating liquid R whose temperature has been reduced is allowed to flow into the biological treatment tank 10, the liquid temperature in the biological treatment tank 10 can be maintained within the appropriate temperature range for microorganisms, and the treatment efficiency can be maintained at a high level. Further, since the temperature of the circulating fluid R is reduced in the cooling can 21 which is depressurized by the vacuum devices 23 and 30 composed of the water ejector 29 and the like, scale does not adhere to the inside of the device. Therefore, there is no need to clean the device with chemicals or the like or to disassemble it, making maintenance easier, reducing running costs, and enabling continuous operation over a long period of time.

By the way, in the above, biological treatment tank 1
The treated water from the nitrification tank 12 or a mixed solution of treated water and microbial sludge was introduced into the cooling tank 21 and cooled as the effluent from the nitrification tank 12. Mixed liquid or returned sludge S
is cooled as the above-mentioned effluent to the biological treatment tank 10.
It may also be allowed to flow into the In addition, in the above, the first
Instead of the denitrification tank 11, a mixed decomposition tank that performs both nitrification and denitrification functions as shown in FIG. May be used. Furthermore, although the biological treatment tank 10 is made up of a plurality of tanks and is used for biological denitrification treatment, it may be a single activated sludge tank when simply removing BOD components. In this case, the effluent or inflow of the biological treatment tank supplied to the cooling can 21 is a mixture of microbial sludge and treated water before flowing into the settling tank 17, or a return sludge S.

In addition, when biological treatment is performed by diluting raw wastewater, treated water from the settling tank 17 or, if necessary, treated water that has been highly treated in the advanced treatment tank 18 is supplied to the cooling can 21. It may be cooled and used as dilution water for the raw wastewater.

Furthermore, FIG. 4 shows a system in which a device 34 that performs heat treatment such as heating is installed in the process before the biological treatment tank 10 in a wastewater treatment system or sludge treatment system. An embodiment of the present invention is shown in which the influent is at a high temperature. The processing equipment 34 that involves the heat treatment is, for example, a gas liquid (ammonium water) containing ammonia, phenol, thiocyanide, cyanide, organic substances, etc. discharged from a coke oven gas cooling process in the iron and gas manufacturing industries.
Ammonia steam stripping equipment in wastewater treatment systems that treat wastewater, heat treatment equipment such as the Portias process that heats human waste, sewage sludge, and surplus sludge to improve dewatering performance, and wet oxidation equipment called the Zimmerman process. etc. are mentioned,
It goes without saying that another treatment device may be provided between the device 34 that involves heat treatment and the biological treatment tank 10.

Furthermore, FIG. 5 shows an embodiment in which the raw wastewater itself is at a high temperature, such as chemical factory wastewater or food factory wastewater, and the basic configuration is the same as the embodiment shown in FIG. 4.

Further, in each of the above embodiments, wastewater is treated using only microbial sludge, but it may be treated using microbial sludge and activated carbon. Furthermore, instead of the floating method, a contact aeration method (fixed bed aeration method) may be used, but in that case, the return sludge S
Since there is no water or circulating fluid R, when applying the embodiment shown in Figure 1, it is sufficient to cool the treated water and perform low dilution treatment, and when applying no dilution treatment, use the embodiments shown in Figures 4 and 5. The following method may be used.

As explained above, in the present invention, the effluent or inflow of a biological treatment tank containing an aerobic biological treatment means is led to a cooling can and the temperature is reduced under a reduced pressure of 45 mmHg or less. Since the liquid is then allowed to flow into the biological treatment tank, the temperature of the liquid in the treatment system can be kept appropriately low to optimally maintain the activity of microorganisms, thus increasing the treatment efficiency. can be retained. Moreover, since there is almost no scale adhesion inside the equipment, there is no need to clean or disassemble the equipment, making maintenance easier, reducing running costs, and making it possible to operate the equipment continuously over long periods of time. It has the effect of being able to do things.

Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

The system shown in Fig. 1, in which only the circulating fluid R flows in its entirety into the cooling can 12, has a wastewater treatment scale of 10 Kl per day, and the system has the same processing scale as the equipment, but uses the heat exchanger 1 instead of the cooling can 21. In the conventional device shown in Fig. 6, human waste is diluted twice (human waste amount: dilution water amount = 1:
1) and treated for one year. As a result, in the apparatus of the present invention shown in FIG. 1, the apparatus is never stopped during the above treatment period, and moreover,
The water temperature in all tanks from 1 to 17 could be maintained at 30 to 35°C even in summer. On the other hand, in conventional equipment, if the operation of the heat exchanger 1 is not stopped once every two weeks and cleaning with chemicals is performed, the cooling efficiency of the heat exchanger 1 decreases and the water temperature is lowered. Moreover, during the treatment period, the heat exchanger 1 became clogged, and it was often necessary to disassemble and clean it.

On the other hand, human waste after dilution has a BOD concentration of 5000 to 6000.
mg/, total nitrogen was 1800-2200 mg/, but after treatment, in any of the above devices,
BOD concentration 60mg/or less, total nitrogen 60mg/or less,
The COD concentration was below 350mg/. However, with conventional equipment, if the heat exchanger 1 is bypassed during washing or disassembly cleaning of the heat exchanger 1 and is operated without cooling the circulating fluid R, the water temperature temporarily rises and the quality of the treated water deteriorates considerably. BOD concentration 180mg/, total nitrogen 1100
mg/, COD concentration was 700 mg/, and a decrease in activated sludge activity was observed.

[Brief explanation of the drawing]

Figure 1 is a flow sheet showing one embodiment of the present invention, Figures 2 a, b, and c are schematic cross-sectional views of a cooling can, and Figure 3
Figures a and b are flow sheets showing configuration examples of a vacuum device and a cooling can, Figures 4 and 5 are flow sheets showing other embodiments of the present invention, and Figure 6 is a flow sheet of a conventional device. be. 10...Biological treatment tank, 21...Cooling can, 2
2... Pump (supply means), 23, 30... Vacuum device, 26... Water jet condenser, 27,
32...Cooling device, 29...Water ejector.

Claims (1)

[Scope of Claims] 1. The effluent or inflow of a biological treatment tank containing an aerobic biological treatment means is placed in a cooling can with a diameter of 45 mm.
1. A biological treatment method for organic wastewater, which comprises partially flash-evaporating the liquid under an absolute pressure of Hg or less to reduce the temperature, and then flowing the liquid into the biological treatment tank. 2. A living organism of organic wastewater according to claim 1, characterized in that evaporated steam generated from a cooling can is condensed and the condensed water is supplied to a cold water circulation system of a vacuum device that depressurizes the cooling can. Scientific processing method. 3. A biological treatment tank containing an aerobic biological treatment means, and the effluent or inflow of the biological treatment tank.
A cooling can whose temperature is lowered by flash evaporation in part under an absolute pressure of 45 mmHg or less, a vacuum device which reduces the pressure of the cooling can, and a supply for causing the liquid whose temperature has been reduced in the cooling can to flow into the biological treatment tank. A biological treatment device comprising: means. 4. The biological treatment device according to claim 3, wherein the vacuum device comprises a water ejector and a cooling device such as a cooling tower that cools the circulating jet water of the water ejector. 5. The biological treatment device according to claim 4, wherein the water ejector is a water jet condenser.