JPH06142685A - Method and device for treating waste fluid containing organic nitrogen - Google Patents

Abstract

PURPOSE:To efficiently execute anaerobic digestion by eliminating efficiently ammonia and other digestion obstructing substance generated by digestion without lowering sludge concentration in an anaerobic digestion tank. CONSTITUTION:Waste fluid containing organic nitrogen is separated into a high SS waste fluid and a low SS waste fluid by a solid-liquid separator 1, and when the high SS waste fluid is led into an anaerobic digestion tank 2 and subjected to anaerobic digestion, in-tank sludge in the anaerobic digestion tank 2 is drawn out to a washing device 3, mixed with a washing liquid, and thereafter, subjected to slid-liquid separation, and the separated solid portion is fed back to the anaerobic digestion tank 2.

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 effluent containing organic nitrogen by an anaerobic digestion method.

[0002]

BACKGROUND ART Anaerobic bacteria such as methanogenic bacteria are used as a treatment method for decomposing and gasifying waste liquid containing organic solids such as human waste, livestock excrement, food-based industrial waste liquid, and water treatment sludge. There is an anaerobic digestion treatment method. In this method, liquefaction and solubilization of solids by the action of different microorganism groups such as organic acid-producing bacteria, acetic acid-producing bacteria, and methanogenic bacteria in the digestion tank,
Since it produces organic acids and methane, it has features such as small excess sludge, low consumption power, and methane (energy) as a reaction product, making it the most effective volume reduction measure for solids and sludge. This is a realistic processing method.

However, since methanogens are relatively sensitive to toxic substances such as hydrogen sulfide, ammonia, and cyan, if these substances or their precursors are present in the stock solution in a certain amount or more, they are hindered. It may become less active and eventually fall into an unprocessable state. In particular, slurry wastes containing organic solids, such as sludge, sludge, livestock excrement, etc., often contain protein-derived organic nitrogen, which are liquefied during the treatment process into ammoniacal nitrogen. Since it is reduced, it is necessary to take measures against ammonia inhibition.

The concentration of ammonia, which affects the methane production reaction, varies depending on operating conditions such as pH and temperature, but it is usually 1,000 to 2,000 as NH ₄ -N concentration.
Inhibition is said to occur at mg / l and above. Ammonia exists in water in two forms, ammonium ion and free ammonia, but free ammonia has a stronger inhibitory action because it has a higher cell membrane permeability. Therefore, the higher the pH is, and the higher temperature digestion around 55 ° C. is more susceptible to ammonia inhibition than the medium temperature conditions around 35 ° C.

The most practical method for preventing such inhibition of ammonia is to dilute the waste liquid with water,
It is often used in livestock manure. However, since the concentration of organic substances is also reduced by diluting, the load of organic substances in the digestion tank with the same residence time is reduced accordingly, which is contrary to the point of efficiency improvement. In addition, depending on the nitrogen concentration of the target effluent, there are cases where the dilution method is not sufficient.

[0006] Conventionally, as a method for removing ammonia in anaerobic digestion, a method in which a liquid in a tank is taken out, ammonia is diffused in an ammonia diffusion tower, and returned to the digestion tank (Japanese Patent Laid-Open No. 253898), and a digestion gas And agitating the gas, and a means for removing ammonia and hydrogen sulfide is provided in the gas circulation path (Japanese Patent Laid-Open No. 185499/1988). However, since both methods are methods of removing ammonia and the like in the gas phase, there is a limit to the amount of ammonia and the like that can be removed.

[0007]

The object of the present invention is to efficiently remove ammonia and other inhibitory substances generated by digestion without lowering the sludge concentration in the digestion tank with a simple device and operation. This is to propose an anaerobic digestion treatment method capable of efficiently performing anaerobic digestion.

[0008]

The present invention provides the following method and apparatus for treating waste liquid containing organic nitrogen. (1) In a method of introducing effluent containing organic nitrogen into an anaerobic digester to perform anaerobic digestion, sludge in the tank of the anaerobic digester is drawn out, mixed with a cleaning liquid, and then separated by solid-liquid separation. A method for treating wastewater containing organic nitrogen, characterized in that solid content is returned to an anaerobic digestion tank for anaerobic digestion. (2) Solid-liquid separation device that separates waste liquid containing organic nitrogen into high SS waste liquid with high solid content and low SS waste liquid containing soluble organic matter, separated high SS discharge Anaerobic digester that anaerobically digests liquid, draws out the sludge in the anaerobic digester, mixes with the cleaning liquid, and then solid-liquid separates, and a cleaning device that returns the separated sludge to the anaerobic digester, and the solid-liquid An apparatus for treating an effluent containing organic nitrogen, comprising a biological treatment apparatus for biologically treating the low SS effluent separated by a separator and the cleaning effluent separated by a cleaning apparatus under anaerobic or aerobic conditions.

The drainage liquid to be treated in the present invention is a drainage liquid containing organic nitrogen, and a drainage liquid in the form of a slurry containing an organic solid content is particularly suitable as a treatment target. The amount of organic nitrogen is not particularly limited, but generally 1,000 mg / l
The above is suitable as a processing target. Such drainage includes human waste, food-based industrial drainage, livestock excrement, and other industrial drainage, water treatment sludge, and the like. Although these effluents may contain inorganic solids, the effluents contain mainly organic solids and almost no inorganic solids (for example, inorganic solids are 20% by weight of total solids). % Or less), the total solid content concentration is 10 by solid-liquid separation.
The anaerobic digestion treatment can be performed in a state of being concentrated to ˜20 wt%.

In the wastewater treatment method of the present invention, such wastewater containing organic nitrogen is introduced into an anaerobic digestion tank to maintain an anaerobic state for anaerobic digestion. The concentration of the effluent for anaerobic digestion is not particularly limited, and the effluent may be directly introduced into the digestion tank, but the total solid content concentration is 5 to 20% by weight, particularly 10 to 20% by weight. It is preferable to perform anaerobic digestion in (1) because the treatment efficiency per unit volume of the digestion tank becomes high.

[0011]

In the drainage treatment apparatus of the present invention, the solid-liquid separator separates the drainage into a high SS drainage and a low SS drainage. As the solid-liquid separation device, it is possible to perform solid-liquid separation by centrifugation, coagulation treatment or the like, and separate into high SS drainage and low SS drainage. The high SS effluent is introduced into an anaerobic digestion tank for anaerobic digestion. The low SS effluent containing a soluble organic substance is introduced into a biological treatment apparatus and subjected to anaerobic or aerobic biological treatment. When the high-load anaerobic treatment is performed, the treated liquid can be used as a cleaning liquid.

The conditions for anaerobic digestion may be the same as those for general anaerobic digestion. That is, the temperature in the digester is 30 to 65 ° C, preferably 35 to 38 ° C for medium temperature digestion and 50 to 60 for high temperature digestion.
Anaerobic digestion is carried out at a retention time of 10 to 60 days, preferably 20 to 30 days, with anaerobic conditions maintained at 0 ° C, continuous or intermittent stirring.

In the anaerobic digester, organic acid-producing bacteria,
By the action of acetic acid-producing bacteria and methanogenic bacteria, the organic solid matter is decomposed through the steps of liquefaction / solubilization, organic acid production, and methanation. In this process, organic nitrogen is decomposed to produce ammonia, and in addition to this, digestive inhibitors such as hydrogen sulfide and cyan are produced.

In the present invention, in order to remove such inhibitor substances such as ammonia, a part or all of the sludge in the tank of the anaerobic digestion tank is extracted and mixed with the cleaning liquid in the cleaning device, and then solid-liquid separated, The separated solid content is returned to the anaerobic digestion tank for anaerobic digestion. The amount of sludge in the tank that is extracted from the anaerobic digestion tank and washed depends on the nitrogen concentration of the supplied waste liquid.
It is necessary to wash an amount that can be maintained at 0.00 to 2000 mg / l or less. For example, total nitrogen is 10,0
When cleaning and circulating the effluent contained in 00 mg / l,
The concentration of ammonia nitrogen in the digestion tank is 2,000 mg / l
Provided that at least 5 of the drainage supplied is maintained
It is necessary to extract more than twice the amount of sludge in the tank and wash it.

The cleaning liquid to be mixed with the sludge in the digestion tank must be neutral and contain no substance that is toxic to methanogens, the temperature is close to the temperature in the digestion tank, and oxygen is not generated. Water that is in a reduced state and does not contain dissolved organic matter is suitable. Especially the total nitrogen concentration is 1000mg
/ L or less, soluble COD _Cr 1000 mg / l or less in an anaerobic state (reduced state) is preferable.

As such a cleaning liquid, various liquids such as industrial water, wastewater of other systems not containing ammonia, and treated water of wastewater can be used. Anaerobic treatment liquids of other systems, for example, the above-mentioned waste liquid The high-load anaerobic treatment liquid with low SS drainage separated by solid-liquid separation at the time of concentration is suitable. The amount of the cleaning liquid used for cleaning is appropriately 3 to 10 times the amount of the liquid to be cleaned, and a plurality of centrifugal separators are arranged in series as a solid-liquid separation device and the cleaning liquid is caused to flow countercurrently to reduce the amount of the cleaning liquid. It is possible.

The drawn sludge in the tank and the cleaning liquid are mixed and then solid-liquid separated. However, the mixing and the solid-liquid separation can be performed in the cleaning device. As the washing device, a device that performs a high degree of solid-liquid separation such as a centrifuge used for solid-liquid separation of waste water is preferable. In the solid-liquid separation, it is preferable that the supply slurry and the recovery slurry have the same volume, and the cleaning liquid and the cleaning waste liquid have the same volume.

By mixing the sludge in the tank and the cleaning liquid, the sludge in the tank is diluted, and ammonia and other inhibitory substances contained in the solid content diffuse into the cleaning liquid. By performing solid-liquid separation in this state, the solid content in which the concentration of ammonia and other inhibitory substances has decreased and the cleaning waste liquid containing ammonia and other inhibitory substances are separated.

When the separated solid content is returned to the anaerobic digestion tank, the concentration of ammonia and other inhibitory substances in the digestion tank decreases, so that the anaerobic treatment is efficiently performed. Moreover, since the solid content concentration does not decrease due to the washing, the efficiency per digester tank volume does not decrease. The cleaning effluent can be treated as wastewater by activated sludge treatment or the like.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments of the drawings. FIG. 1 is a flow chart showing the processing apparatus of the embodiment. In the figure, 1 is a solid-liquid separation device, 2 is an anaerobic digestion tank, 3 is a cleaning device, 4 is a high-load anaerobic treatment device, 5 is an aerobic treatment device, and 6 is a gas storage tank.

The solid-liquid separation device 1 separates the waste liquid supplied from the drain pipe 7 into a high-SS waste liquid having a high solid content and a low-SS waste liquid containing a soluble organic substance. It is composed. As the solid-liquid separator, those having a concentrating mechanism such as a centrifuge and a coagulation separator can be used, but a centrifuge that does not use a coagulant is preferable.

The anaerobic digestion tank 2 is constructed so as to introduce high SS effluent from the flow path 8 for anaerobic digestion, and to decompose organic solids through the steps of liquefying, acid production and methane production. ing. The cleaning device 3 includes the anaerobic digestion tank 2 from the flow path 9.
The sludge in the tank is introduced, the treatment liquid of the high-load anaerobic treatment device 4 is introduced from the flow path 10 as a cleaning liquid, mixed, and then solid-liquid separated. As the cleaning device 3,
A centrifuge is used in the examples. The solid content after the solid-liquid separation is returned to the anaerobic digestion tank 2 through the channel 11, and the cleaning drainage is discharged from the channel 12 to the aerobic treatment apparatus 5.

The high-load anaerobic treatment apparatus 4 is constructed so as to introduce a low SS effluent from the flow path 13 and perform a high-load anaerobic treatment to decompose soluble organic substances. As the high-load anaerobic treatment apparatus, known ones such as UASB method, fixed bed method, fluidized bed method and the like can be used.

The aerobic treatment apparatus 5 is configured to introduce an anaerobic digestion liquid from the flow path 14, an anaerobic treatment liquid from the flow path 15 and a cleaning effluent from the flow path 12 to perform aerobic biological treatment. There is. As an aerobic treatment device, an activated sludge method and its modified method are generally used. Gas storage tank 6 is anaerobic digestion tank 2
Also, gas such as methane generated in the high load anaerobic treatment apparatus 4 is introduced from the flow paths 16 and 17 and stored.

The method for treating waste liquid by the above-mentioned treatment apparatus is as follows:
First, an effluent containing organic nitrogen and organic solids is introduced from the drainage pipe 7 into the solid-liquid separation device 1 to perform solid-liquid separation, and a high solids concentration, preferably a solids concentration of 10 to 20% by weight. Separation into high SS drainage and low SS drainage containing almost no organic solids but soluble organics.

The high SS effluent is introduced into the anaerobic digestion tank 2 through the flow path 8 and kept anaerobic at the optimum temperature of methanogens (35 to 38 ° C.), and the mixture is agitated by gas blowing or mechanically.
Anaerobic digestion is performed with a residence time of ~ 30 days. As a result, the organic solid content is decomposed through the steps of liquefaction, organic acid production, and methane production.

As the organic solids are decomposed, the organic nitrogen is also decomposed to produce ammonia nitrogen and other digestive inhibiting substances. Therefore, the sludge in the tank of the anaerobic digestion tank 2 is washed from the channel 9 to the cleaning device 3 Are continuously or intermittently taken out, and the treatment liquid of the high load anaerobic treatment device 4 is introduced as a washing liquid from the flow path 10 and mixed, and then solid-liquid separation is performed. As a result, ammonia nitrogen and other inhibitory substances contained in the sludge in the tank are diffused into the cleaning liquid and separated as cleaning drainage. By returning the solid content in which the inhibitor concentration has decreased to the anaerobic digestion tank 2 from the flow channel 11, the inhibitor concentration in the digestion tank 2 can be reduced and anaerobic digestion can be efficiently performed. Cleaning drainage is flow path 1
2 is discharged to the aerobic treatment device 5.

In the anaerobic digestion tank 2, the total solid content is 75-80.
% Decomposes and gasifies. The generated gas such as methane is stored in the gas storage tank 6 through the flow path 16. Further, the anaerobic digestion liquid is sent from the flow path 15 to the aerobic treatment device 5. The introduction of the effluent into the anaerobic digestion tank 2 and the ejection of the anaerobic treatment liquid are usually performed once or twice a day, but not limited to this.
On the other hand, in the high load anaerobic treatment device 4, low S
S-effluent is introduced to perform high-load anaerobic treatment. Here, by utilizing the self-immobilization phenomenon of the bacterial cells, the waste liquid is brought into contact with the sludge blanket that holds the methanogen at a high concentration, the fixed bed, and the fluidized bed, so that the soluble organic substances are efficiently decomposed in a short retention time. To do. Here, too, the gas is gasified through the acid generation and methane generation stages, and the generated gas is stored in the gas storage tank 6 through the flow path 17. The temperature in the high load anaerobic treatment apparatus 4 is 25 to 40 ° C, preferably 30 to 38 ° C, the residence time is 4 to 48 hours, and the COD _Cr load is 4 to 15 kg-.
COD _Cr / m ³ · day is suitable. The anaerobic treatment liquid is sent from the flow path 14 to the aerobic treatment device 5. The introduction of the low SS drainage liquid into the high load anaerobic treatment apparatus 4 and the discharge of the anaerobic treatment liquid are normally performed continuously.

In the aerobic treatment apparatus 5, the cleaning effluent introduced from the flow passage 12, the anaerobic digestion liquid introduced from the flow passage 15 and the anaerobic treatment liquid introduced from the flow passage 14 are biologically treated under aerobic conditions. Decomposes residual solids and soluble organics.
Here, any treatment method such as a method of returning sludge like a standard activated sludge method and a method of fixing and holding sludge is adopted. Appropriate residence time of the aerobic treatment apparatus 5 is 4 to 48 hours, preferably 6 to 24 hours. The treatment liquid of the aerobic treatment device 5 is discharged from the treatment liquid pipe 18, and the excess sludge is discharged from the sludge discharge pipe 19. The gas in the gas storage tank 6 is taken out from the flow path 20 and used as fuel or the like.

In the above-mentioned processing apparatus and processing method, since organic solids are highly concentrated for anaerobic digestion, a small volume of high SS effluent can be efficiently anaerobically digested at high solids concentration. You can Since ammonia and other digestive inhibiting substances produced by anaerobic digestion are removed by washing, digestion can be continued with high efficiency even in the case of drainage containing organic nitrogen. In addition, the large-volume low-SS effluent produced by solid-liquid separation can be efficiently treated by the high-load anaerobic treatment with a short residence time. Can be treated efficiently and the amount of sludge generated is small.

Although the solid-liquid separation device 1 is used in the above embodiment, the solid-liquid separation device 1 may be omitted and the effluent may be directly introduced into the anaerobic digestion tank 2 for anaerobic digestion. Further, when the organic solid content concentration is low, a rough solid-liquid separator such as a precipitation tank and a high-grade solid-liquid separator such as a centrifuge can be used in combination. Further, the cleaning device 3 is not limited to the centrifuge and may be another device, and the cleaning liquid is not limited to the anaerobic treatment liquid.

Although the anaerobic treatment device 4 and the aerobic treatment device 5 are used in the above-mentioned embodiments, when the concentration of soluble organic matter in the low SS effluent is low, the BOD is 1000 mg /
In the case of 1 or less, the anaerobic treatment device 4 can be omitted and the treatment can be performed directly by the aerobic treatment device 5. Further, when high treated water quality is not required, such as when discharged to the sewer, the aerobic treatment device 5 can be omitted.

The test examples will be described below. % In the example
Is% by weight. Example 1 TS (total solids): 177,000 mg / l, total COD
_Cr : 234,000 mg / l, soluble COD _Cr : 10,
The SS contained in the dehydrated filtrate of beer lees with 800 mg / l and total nitrogen of 12,700 mg / l was centrifuged in a TS: about 18
%, And anaerobic digestion was performed using a jar fermenter with a working volume of 1 liter as a digestion tank. The amount of sludge supplied is 20 ml / day, HRT is 50 days each, CO
D _Cr load was 4.7kgCOD _Cr / m ³ / day.

5 of the effluent supplied during the process of anaerobic digestion
Double the amount of sludge in the tank (100 ml) once a day, 8
00 ml phosphate buffer + sodium sulfide (50 mg /
l) was used as a washing liquid, and the operation of mixing and solid-liquid separation in a centrifuge was repeated twice to wash, and 100 ml of solid-liquid separation
Minute solids were returned to the digester again.

Comparative Examples 1 and 2 As Comparative Example 1, anaerobic digestion was performed without extracting the sludge in the tank and controlling the pH. As Comparative Example 2, the sludge in the tank was not drawn out, but the pH was controlled to 7 to perform anaerobic digestion.

Each of the above tests is 2 HRT, or 100
As shown in Table 1, in Comparative Examples 1 and 2, the soluble COD _Cr in the tank was increased and the organic acid was accumulated within 1-2 months due to the inhibition of ammonia. As a result, it became impossible to continue processing. In Example 1, good treatment was performed and the decomposition rate of TS and COD _Cr was 80 to 90%.
It was extremely expensive. The gasification rate of organic substances was also high. The results are shown in Table 1.

[0037]

[Table 1]

[0038]

According to the present invention, the sludge in the anaerobic digestion tank is pulled out and washed. Therefore, ammonia generated by digestion without decreasing the sludge concentration in the anaerobic digestion tank, etc. Efficiently removes the digestive inhibitors of
Thereby, anaerobic digestion can be performed efficiently.

[Brief description of drawings]

FIG. 1 is a flowchart showing a processing apparatus according to an embodiment.

[Explanation of symbols]

 1 solid-liquid separation device 2 anaerobic digestion tank 3 cleaning device 4 high-load anaerobic treatment device 5 aerobic treatment device 6 gas storage tank

Claims (2)

[Claims] 1. A method for introducing effluent containing organic nitrogen into an anaerobic digestion tank to anaerobically digest, in which sewage sludge in the anaerobic digestion tank is drawn out, mixed with a cleaning liquid, and then solid-liquid separated, A method for treating wastewater containing organic nitrogen, wherein the separated solid content is returned to an anaerobic digestion tank for anaerobic digestion. 2. A waste liquid containing organic nitrogen is subjected to solid-liquid separation to obtain a high SS liquid liquid having a high solid content concentration and a low S liquid containing a soluble organic substance.
Solid-liquid separator that separates into S effluent, anaerobic digester that anaerobically digests the separated high SS effluent, sludge in the anaerobic digester tank is drawn out, mixed with cleaning solution, and then separated into solid and liquid A cleaning device for returning the sludge to the anaerobic digestion tank, and a biological treatment device for biologically treating the low SS waste liquid separated by the solid-liquid separation device and the cleaning waste liquid separated by the cleaning device under anaerobic or aerobic conditions. An apparatus for treating waste liquid containing organic nitrogen, which comprises: