JPH105789A - Treatment of methane fermentation treating liquid and treating facility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the efficiency of the treatment by a subsequent activated sludge method by decreasing the nitrogen quantity and, above all, the concn. of the ammonia nitrogen in a methane fermentation treating liquid. SOLUTION: The fermentation liquid obtd. by executing the methane fermentation treatment is subjected to an ammonia stripping treatment in a stripping vessel, by which the ammonia form nitrogen in the fermentation liquid is removed and simultaneously, the total nitrogen quantity is decreased so as not to hinder the activity of activated sludge. In addition, the sepn. of solid from the liquid of the treated water is executed by a filter membrane, by which the MLSS in the aeration tank is increased and the treating capability is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating wastewater having a high concentration and a large amount of nitrogen, such as livestock wastewater, and more particularly, to a fermentation solution obtained by methane fermentation using an activated sludge method. It is an object of the treatment method to improve the treatment efficiency by the subsequent activated sludge method by reducing the amount of nitrogen in the methane fermentation treatment liquid, particularly the concentration of ammonia nitrogen.

Another object of the present invention is to ensure the solid-liquid separation of the treated water and stabilize the properties of the discharged water regardless of the change in the properties of the activated sludge.

[0003] Still another object of the present invention is to increase the concentration of activated sludge in an aeration tank for performing activated sludge treatment to improve the treatment capacity.

[0004]

2. Description of the Related Art Livestock effluent discharged from livestock barns such as piggers and barns is compared with domestic effluent discharged from ordinary households.
It has the special feature of high solids content and high biochemical oxygen demand (BOD). Therefore, it has been proposed to use a treatment system combining a methane fermentation method suitable for high-load wastewater treatment and an activated sludge method with excellent purification ability for the treatment of livestock wastewater.

The activated sludge method decomposes organic matter in wastewater into carbon dioxide gas and water by contacting activated sludge, which is a block of aerobic microorganisms, with wastewater while aerating it. It has the advantage that low and high clarity treated water can be obtained. However, the activated sludge method is not suitable for high-load treatment, and if livestock wastewater having a high concentration is treated as it is, the activated sludge activity may be reduced or microorganisms may be killed. Therefore, if the digestion and decomposition of livestock wastewater is advanced to a certain extent in advance by the methane fermentation method suitable for high-load wastewater treatment as the first-stage treatment, wastewater treatment utilizing the excellent purification capacity of the activated sludge method can be realized. Becomes

[0006] The methane fermentation method is a treatment method in which organic substances are mainly decomposed into methane gas and carbon dioxide gas by the action of anaerobic microorganisms. It is said that methane gas, which is a decomposition product, can be recovered and used as a heat energy source. Has advantages.

FIG. 2 shows an outline of a conventional livestock wastewater treatment facility for purifying a treatment liquid obtained by a methane fermentation method using an activated sludge method. The treatment equipment is a storage tank for fermented liquid obtained by subjecting livestock wastewater discharged from livestock barns such as piggers and barns to methane fermentation and then dewatering with a dehydrator, and purifying treatment with activated sludge while aerating the fermented liquid. And a sedimentation tank that separates and removes solids such as activated sludge from the treated wastewater. Fermented liquid pump P ₄ for transferring the fermentation solution is installed in the storage tank, a screen for solids removal is arranged between the fermentation liquid reservoir and aeration tank. At the bottom of the aeration tank, there is provided an air diffuser for blowing out the air supplied from the blower. The sedimentation tank, pump P ₅ for taking an active sludge sedimentation
And a pipe, which communicates with the aeration tank and the outside.

Although illustration is omitted, following the sedimentation tank,
Disinfection tanks for disinfection of discharged water are often provided.

[0009] The outline of the processing steps of livestock wastewater by the above-mentioned processing equipment is as follows. In the livestock wastewater discharged from the barn, organic solids in the wastewater are digested to a certain extent in the methane fermentation tank, and after the fermentation liquid is extracted by the dehydrator, it is temporarily stored in the fermentation liquid storage tank, and then the pump P ₄ Is transferred to the aeration tank. The solids remaining in the fermentation liquor are captured and removed by a screen in the middle.

[0010] In the aeration tank, air is continuously or intermittently supplied to the fermentation liquor by a blower and a diffuser tube, and the fermentation liquor is brought into contact with activated sludge, so that the fermentation liquor is further decomposed and digested. The activated sludge treatment method includes a floating aeration method in which activated sludge flows freely in the tank, a contact aeration method in which activated sludge is attached to a filter medium fixed in the tank, and a filter medium with activated sludge attached in the tank. Although there is a rotary filter bed type for rotating, etc., which one to adopt may be appropriately selected according to the implementation situation.

The wastewater that has been purified by activated sludge in the aeration tank is led to a sedimentation tank, where sedimented solids such as activated sludge and the like are separated and then only the supernatant liquid is discharged. Separated activated sludge in the sedimentation tank is taken out by the pump P _5, a portion thereof is returned to the aeration tank, the remainder is out as excess sludge.

[0012]

The wastewater treatment method in the above-mentioned conventional treatment equipment has the following drawbacks. Since the ammonia concentration in the fermentation liquor obtained by the methane fermentation treatment is extremely high, it may adversely affect the activity of the activated sludge in the aeration tank. Generally, when a protein is anaerobically treated, ammonia is generated as a decomposition product, so that the amount of ammonia nitrogen after the methane fermentation treatment is larger than that of raw water. Livestock wastewater has a total nitrogen content of 1500-5000
In addition to the high concentration of mg / l, the ratio of ammonia nitrogen originally derived from night soil to the total nitrogen is high. For this reason, the ammonia nitrogen concentration of the methane fermentation liquor becomes extremely high. As a result, the activated sludge in the aeration tank is inhibited by ammonia, resulting in poor treatment, and the suspended solids concentration (SS) and BOD of the treated water are sufficiently reduced. It cannot be reduced.

The methane fermentation liquor has a high total nitrogen content and B
The ratio to OD is also high. For this reason, when the air supply in the aeration tank becomes excessive, the nitrification effect of generating nitric acid and nitrous acid from ammonia by microorganisms in activated sludge exceeds the denitrifying effect of converting nitric acid and nitrous acid to nitrogen gas. ,nitric acid·
Nitrite may accumulate. As a result, the pH in the aeration tank falls below a range suitable for the activity of the activated sludge, and there is a possibility that the treatment of wastewater may be poor.

The capacity of the wastewater in the aeration tank depends on the amount of activated sludge. Conventionally, however, the solid-liquid separation of the treated water flowing out of the aeration tank is performed by the sedimentation separation method in the sedimentation tank. Therefore, the suspended solids concentration (MLSS) in the aeration tank is set too high so as not to deteriorate the properties of the supernatant. Can not do. Conventionally, the MLSS of the aeration tank is 2000 to 5000
mg / l, and if this value is increased,
Although the processing capacity can be improved because the amount of activated sludge increases, there is a possibility that the properties of the supernatant liquid discharged are adversely affected. Therefore, in the conventional processing equipment, the capacity of the aeration tank must be increased in order to increase the purification processing capacity.

If the BOD of the fermentation liquor is very large and of high concentration, it is necessary to dilute the fermentation liquor in or before introduction into the aeration tank, since the processing capacity of the aeration tank cannot be so high.

The properties of the supernatant obtained by solid-liquid separation in the sedimentation tank by the sedimentation separation method are easily affected by the amount of water flowing into the sedimentation tank and the properties of activated sludge. That is,
When the amount of water flowing into the sedimentation tank fluctuates or the property of the activated sludge changes, there is a risk that the treatment failure such as an increase in the SS of the discharge water may occur.

[0017]

SUMMARY OF THE INVENTION The present invention provides a method and equipment capable of efficiently treating wastewater having a high concentration and high nitrogen content, such as livestock wastewater. The feature of the treatment method according to the present invention is a method of purifying a treatment liquid by a methane fermentation method using an activated sludge method,
Activated sludge treatment after treatment by the ammonia stripping method.

The solid-liquid separation of the treated water obtained by the activated sludge treatment can be performed using a filtration membrane.

In this case, it is conceivable that a filtration membrane is arranged in an aeration tank for performing activated sludge treatment to perform solid-liquid separation of treated water.

Further, in the method of the present invention in which solid-liquid separation is performed by a filtration membrane, the suspended solids concentration (MLSS) of the aeration tank for performing the activated sludge treatment can be set to 5,000 to 20,000 mg / l.

On the other hand, the feature of the processing equipment according to the present invention is that it comprises a stripping tank and an aeration tank.

In such a treatment facility, it is desirable to install a solid-liquid separator using a filtration membrane in the aeration tank.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION A treatment method according to the present invention is an aeration tank for performing a sludge treatment of a high-concentration, high-nitrogen content fermented solution obtained by subjecting livestock wastewater and the like to methane fermentation treatment and then dehydrating with a dehydrator. The biggest feature of this method is that an ammonia stripping treatment is performed prior to the transfer to the fermentation liquor to reduce the concentration of ammonia nitrogen in the fermentation liquor in advance.

Prior to subjecting the fermented liquor obtained by the methane fermentation treatment to activated sludge treatment, the reason for removing the ammonia nitrogen in the fermented liquor is as follows. Livestock wastewater is BO
Not only is the amount of D and total nitrogen very high, but it also has the characteristic that the proportion of ammonia nitrogen in total nitrogen is large. Moreover, when the methane fermentation treatment is performed, the ammonia concentration of the fermentation liquor is generally higher than that of the raw water due to the production of ammonia accompanying the decomposition of the protein. For this reason,
Fermented liquor obtained by subjecting livestock wastewater to methane fermentation has an extremely high ammonia concentration.

However, the aerobic microorganisms in the activated sludge are:
If the ammonia concentration is high, the activity is inhibited. Also BOD
An environment in which the ratio of nitrogen to nitrogen is high is not suitable for obtaining good treated water. Suitable total nitrogen in aeration tank /
The value of BOD is usually about 1/5 to 1/10, and when the nitrogen ratio is increased, the production amount of nitric acid and nitrous acid is increased and the inside of the tank is acidified, and the activity of activated sludge is reduced. Therefore, when the fermentation liquor having a large amount of total nitrogen and a high ammonia concentration is directly introduced into the aeration tank, the ability of the activated sludge to treat wastewater is reduced, and in some cases, aerobic microorganisms may be killed. Therefore, it is necessary to remove ammonia nitrogen as much as possible from the fermentation liquor in advance in order to perform good wastewater treatment.

FIG. 1 shows an example of a processing facility for carrying out the method of the present invention. The treatment equipment comprises a storage tank, a stripping tank, and an aeration tank for the fermentation liquid sent from the methane fermentation tank, and between the fermentation liquid storage tank and the stripping tank, to remove solids. Screen is interposed. Further, the stripping tank and the aeration tank are provided with air diffusers for jetting air supplied from the blower in each tank. In addition, a dehydrator for extracting the fermentation liquid is provided between the methane fermentation tank and the fermentation liquid storage tank.

The stripping tank is provided with an alkali agent supply device and an absorption tower for collecting ammonia gas.

In the aeration tank, ultrafiltration (particle size = 0.001)
To 0.01 μm) or microfiltration (particle size = 0.
01~10μm together with a solid-liquid separator with porous filtration membrane made of a polymer material or the like for performing the target) is placed, a pipe for taking out the treated water by the pump P ₂ from the solid-liquid separator, and, a pipe for withdrawing the excess sludge by the pump P ₃ is connected. In addition, the pore diameter of the filtration membrane is 0.1 to 0.1.
It is considered that the thickness should be about 4 μm, but this range is not limited. Also, the type of the membrane module is appropriately selected from a flat membrane shape, a tubular shape, a spiral shape, a hollow fiber membrane shape, and the like. Seems practical.

Next, an embodiment of the method of the present invention will be described with reference to FIG. Livestock effluent discharged from piggers, barns, and other barns is subjected to methane fermentation treatment, and organic matter is decomposed into methane gas and carbon dioxide gas by the action of microorganisms, or is converted into a form easily susceptible to subsequent activated sludge treatment.

The methane fermentation fermentation solution obtained is digested with after extraction with dehydrator, after transferred to the fermentation liquor reservoir, pumped P _1, the residual solid was removed by passing through a middle of the screen And then feed it to the stripping tank.

In a stripping tank, an alkaline agent is added to the fermentation liquor, and the pH is in the range of 8 to 10 (preferably 9.
5 or more) and air is blown out from an air diffuser connected to a blower for 3 to 20 hours (preferably 5 to 8 hours).
Aeration). Note that a strong alkali compound such as sodium hydroxide is used as the alkali agent.

The ammonia nitrogen is removed from the fermentation liquor by the ammonia stripping treatment. The mechanism is considered to be roughly as follows. Ammonia N
H ₃ hardly exists in an ionic state in a solution, but is dissolved in a hydrated state, and has a property that its solubility is reduced in an alkaline environment. In general, the gas has a property that the solubility of the gas decreases as the water temperature increases. Therefore,
By adjusting the fermentation liquor, which has been heated to 25 ° C. or more by methane fermentation, to alkalinity and aeration, dissolved ammonia is diffused into the gas phase, and as a result, the ammonia concentration of the fermentation liquor is reduced. Experiments have shown that pH = 9.5.
-It is possible to remove about 60% of the ammonia nitrogen dissolved in the fermentation liquor in 5 hours of aeration time, pH = 10.5 and about 80% in 20 hours of aeration time.

Means for removing ammonia in the wastewater include, besides the stripping method, a biological denitrification method utilizing the metabolism of microorganisms, a treatment method for chemically removing nitrogen by adding hypochlorous acid, and an ionizing method. An ion exchange method using an exchange resin may be mentioned, but all have the following disadvantages as compared with the stripping method. Biological denitrification involves decomposing ammonia to nitrogen gas through the cooperative action of aerobic microorganisms, nitric acid bacteria, nitrite bacteria and denitrifying bacteria. Not generally suitable for wastewater treatment. In the chemical treatment method using hypochlorite HClO, chlorine remains in the treated water, so that post treatment is required. In the ion exchange method, since the ion exchange resin is expensive, the processing cost is extremely high.

On the other hand, the stripping method is suitable for removing ammonia from high-concentration wastewater, and the methane fermentation liquor is maintained at a relatively warm water temperature of 25 ° C. or higher, which is advantageous for ammonia stripping. It can be said that it is superior to any of the above-mentioned treatment methods in that the equipment cost and running cost are inexpensive, and that post-treatment of the treated water is unnecessary.

The ammonia gas generated by the ammonia stripping treatment is collected in an absorption tower and released to the atmosphere as it is, or is discarded after being subjected to an appropriate treatment.

On the other hand, the fermented liquor with reduced ammonia concentration is transferred to an aeration tank and subjected to a purification treatment with activated sludge. The aeration process is intermittent aeration in which the interval between aeration and stop is 0.5 to 2 hours, and the MLSS of the aeration tank is 500
Set between 0 and 20000 mg / l.

In the aeration tank, the aerobic microorganisms present in the activated sludge metabolize the organic matter in the fermentation liquor and decompose it into carbon dioxide and water, thereby significantly reducing the BOD. Further, the remaining nitrogen is converted into nitrogen gas by the synergistic action of the nitrification action of nitric acid bacteria and nitrite bacteria and the denitrification action of denitrifying bacteria, and is removed out of the system.

[0038] The required purification processes finished treated water, after sucked by pump P ₂ which is a pipe connected to the solid-liquid separator, and the solids, such as activated sludge and passed through a filtration membrane is separated off, discharged to the outside I do. The solid-liquid separation method using a filtration membrane with a small pore size requires a large amount of MLSS in the aeration tank,
It is possible to obtain high-clarity effluent water with a small amount of water, and it is also possible to remove bacteria depending on the membrane pore size. Moreover, since it is not necessary to settle the activated sludge, there is an advantage that the solid-liquid separation performance is hardly affected even if the sludge properties change due to bulking or the like.

Various conditions such as the material of the filtration membrane, the type of the membrane module, the membrane pore size, the membrane permeation flow rate, the MLSS of the aeration tank, and the amount of aeration depend on the properties of the fermentation liquor to be treated and the discharge environment.
What is necessary is just to set suitably within the range which can perform stable solid-liquid separation without causing membrane blockage. For reference, in order to obtain a stable solid-liquid separation state using a flat membrane filter having a membrane pore size of 0.4 μm made of a polyolefin polymer, the membrane permeation flow rate is 250
MLSS = 10000m under the condition of ml / min
g / l, aeration amount = 0.6 m ³ / hour, MLSS
= 14000 mg / l, aeration amount = 1.2 m ³ /
Set it to time.

The amount of activated sludge in the aeration tank gradually increases due to the growth of microorganisms during the purification treatment. Therefore, in order to maintain the value of MlSS in the aeration tank within a predetermined range, the increased amount of the activated sludge is drawn out through a pipe and eliminated.

The embodiments of the present invention can be applied to other than the above. For example, the present invention is suitable for treating livestock wastewater, but does not prevent application to treatment of agricultural wastewater or general domestic wastewater.

Further, the processing equipment according to the present invention may be provided with a disinfection tank for discharged water at a stage subsequent to the aeration tank in addition to the one shown in the figure.

Further, although not shown, instead of installing the solid-liquid separator in the aeration tank, a storage tank for the treated water is connected to the aeration tank, and the solid-liquid separator is installed in this storage tank. It is also conceivable to carry out solid-liquid separation by using a liquid. Alternatively, as in the prior art, a sedimentation tank is provided after the aeration tank, and after the solid-liquid separation of the treated water after the sludge treatment is performed in the sedimentation tank, the discharge of the treated water is not prevented.

The conditions for the ammonia stripping treatment and the activated sludge treatment may be appropriately set according to the properties of the wastewater to be treated, the scale of the treatment equipment, and the like.

In addition, the embodiments of the present invention can be appropriately changed according to the situation.

[0046]

According to the present invention, the fermented liquor obtained by subjecting livestock wastewater or the like to methane fermentation is subjected to ammonia stripping to remove ammonia nitrogen in advance and simultaneously reduce the total nitrogen amount. Since the activated sludge treatment is performed, there is no danger that the activity of the activated sludge will be inhibited and the wastewater treatment capacity will be reduced. Accordingly, wastewater treatment utilizing the excellent purification ability of the activated sludge method can be performed on high-load wastewater such as livestock wastewater, so that treated water with a small amount of BOD and residual nitrogen can be obtained.

Since the ammonia stripping method is used as the means for removing ammonia from the fermentation liquid, it is possible to efficiently perform the ammonia removal treatment even on a high-concentration fermentation liquid. Therefore, it is possible to perform drainage treatment that is easy to maintain and has excellent stability.

By performing the solid-liquid separation of the treated water obtained by the activated sludge treatment in the aeration tank using a filtration membrane, the sedimentation tank can be omitted, and it can be surely performed regardless of the change in the properties of the activated sludge. Discharge water with a small SS value and high clarity is obtained. Bacteria can also be removed depending on the pore size of the membrane. Therefore, it is possible to make post-treatment of the effluent unnecessary or to reuse the effluent.

By performing solid-liquid separation of the treated water by a filtration membrane, the ML in the aeration tank can be maintained without impairing the clarity of the discharged water.
It is possible to increase the value of SS. Conventionally, the value of the MLSS in the aeration tank is about 2000 to 5000 mg / l, and if it is set to a value higher than that, there will be an adverse effect on the properties of the discharged water such as SS. In contrast, in the present invention, the MLSS is set to 5000
Since it can be set in the range of ２０20,000 mg / l, the amount of activated sludge can be increased to 2 to 10 times that of the conventional aeration tank of the same volume, and the wastewater treatment capacity can be increased accordingly.

Alternatively, for the same reason as described above, the present invention can exert the same or higher purification ability in the aeration tank smaller than the conventional one. In combination with the elimination of a sedimentation tank, the required installation space of the processing equipment according to the present invention is about half that of the conventional equipment.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a processing facility according to the present invention.

FIG. 2 is a schematic diagram showing a conventional processing facility.

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Yutaka Yamashita 1 Kokufu-cho, Tochigi-city, Tochigi Pref. Mitsui Mining Co., Ltd.

Claims (6)

[Claims] 1. A method for purifying a treatment liquid obtained by a methane fermentation method by an activated sludge method, wherein the treatment liquid is treated by an ammonia stripping method and then subjected to an activated sludge treatment. 2. A wastewater treatment method, wherein solid-liquid separation of treated water obtained by the activated sludge treatment according to claim 1 is performed using a filtration membrane. 3. The wastewater treatment method according to claim 2, wherein a solid-liquid separator using a filtration membrane is installed in an aeration tank for performing activated sludge treatment, and solid-liquid separation of treated water is performed. 4. The method according to claim 2, wherein the concentration of suspended solids in the aeration tank for performing the activated sludge treatment is 5,000 to 2,000.
Wastewater treatment method set to 0 mg / l. 5. A methane fermentation treatment liquid treatment facility comprising a stripping tank and an aeration tank. 6. The facility for treating a methane fermentation treatment solution according to claim 5, wherein a solid-liquid separator using a filtration membrane is installed in the aeration tank.