JP2000233198A - Treatment of organic waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance treated water quality in aerobic biological treatment and to prevent functional trouble such as the generation of scum, bulking or the like in a succeeding solid-liquid separation process in a treatment method subjecting waste water containing an org. solid to anaerobic biological treatment and aerobic biological treatment successively. SOLUTION: Org. waste water is subjected to solid-liquid separation treatment in a solid-liquid separation means 1 and the separated liquid is subjected to anaerobic biological treatment in an anaerobic biological treatment process 2 while the separated sludge is subjected to aerobic biological treatment along with anaerobically and biologically treated water in an aerobic biological treatment process 5. In this treatment method, a denitrification treatment process 5B is provided to the aerobic biological treatment process 5 or the separated sludge is subjected to aerobic treatment and denitrification treatment before supplied to the aerobic biological treatment process.

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 containing organic solids (beer, starch, potato-processed wastewater, etc.), and more particularly to an aerobic organism after treating this organic wastewater with an anaerobic organism. The present invention relates to a treatment method for improving the quality of treated water in an aerobic biological treatment, and preventing scum generation and bulking in a subsequent solid-liquid separation step.

[0002]

2. Description of the Related Art As a method for treating wastewater containing organic solids such as beer, starch and potato wastewater, as shown in FIG. 4, the wastewater is solid-liquid separated by a solid-liquid separation means 1 by sedimentation or sludge flotation. After separation, the separated water (hereinafter sometimes referred to as “pre-sedimentation supernatant”) is subjected to UASB (Upflow Anaerob).
In a high-load anaerobic biological treatment process 2 such as an ic sludge blanket (upward-flow anaerobic sludge bed), anaerobic biological treatment is performed to decompose to methane, which may be referred to as separated sludge (hereinafter referred to as “pre-sedimentation sludge”). ) Is mixed with this anaerobic treated water and subjected to aerobic biological treatment with activated sludge in the aeration tank 3, and the obtained aerobic treated water is
There is a method of performing solid-liquid separation in the precipitation tank 4. In this method, when solids flow into and accumulate in the anaerobic biological treatment step 2, particularly the high-speed UASB reaction tank, the effective capacity of the reaction tank decreases, the activity of sludge decreases, and the treatment capacity decreases. For,
Solid matter has been removed in the solid-liquid separation means 1 in advance.

[0003]

As shown in FIG. 4, in the conventional organic wastewater treatment method, the solids separated in the preceding stage of the anaerobic biological treatment step 2 are sent to the aeration tank 3 together with the anaerobic treated water. Activated sludge treatment is performed.In this activated sludge treatment step, when the inflow of solid organic matter increases and the proportion of soluble organic matter decreases, floc formation often becomes unstable and floc tends to disperse. As a result, fine SS flows out into the treated water, and the visibility decreases significantly. Depending on the load fluctuation, scum and sludge float in the sedimentation tank 4 at the subsequent stage, and foaming in the aeration tank 3 becomes remarkable. For example, the operation of the activated sludge treatment becomes very unstable. In particular, anaerobic treated water has a low proportion of easily decomposable organic substances,
Since the value of OD _Cr / BOD ₅ becomes as large as about 4 to 5,
Such a phenomenon is likely to occur.

In order to prevent such a phenomenon, the amount of water passing through the anaerobic biological treatment process is actually limited, and a part of the raw water (organic wastewater) (about 30% of the total water amount) is directly aerated in the subsequent stage. Although a part of the raw water is supplied to the aeration tank 3 as described above, it is necessary to reduce the amount of sludge generated by employing the anaerobic biological treatment, The effect of reducing the aeration power is impaired, which is not preferable.

[0005] The problem in the activated sludge treatment process is as follows.
Because of the pre-sedimentation sludge, this pre-sedimentation sludge has been attempted to be directly dehydrated without being introduced into the aeration tank 3 for treatment. Dehydration has a problem of odor generation and is practically impossible.

[0006] The present invention solves the above-mentioned conventional problems, and in a treatment method for treating effluent containing organic solids by anaerobic biological treatment and then aerobic biological treatment, the quality of treated water in aerobic biological treatment is improved. It is an object of the present invention to provide a method for preventing functional troubles such as scum generation and bulking in the solid-liquid separation step.

[0007]

According to the present invention, there is provided a method for treating organic waste water, comprising the steps of: solid-liquid separation of the organic waste water to separate organic solids in the waste water; An anaerobic biological treatment step of anaerobically biologically treating the liquid separated in the step, and an anaerobic biological treatment water discharged from the anaerobic biological treatment step and an organic solid separated in the solid-liquid separation step. And an aerobic biological treatment step for aerobic biological treatment.

According to the first aspect of the present invention, the aerobic biological treatment step is provided with a denitrification treatment step. Preferably, the organic solids separated in the solid-liquid separation step are subjected to the aerobic treatment step. Then, it supplies to the said aerobic biological treatment process.

According to the third aspect of the present invention, the organic solid separated in the solid-liquid separation step is supplied to the aerobic biological treatment step after passing through an aerobic treatment step and a denitrification treatment step.

The present inventors have conducted intensive analysis on the problem in the above-mentioned conventional method and found that the cause of this problem is largely affected by decomposition of solids in the pre-set sludge and its metabolites. That is, in many food wastewaters, the organic SS in the pre-sedimentation sludge contains solid nitrogen-containing organic matter mainly derived from proteins, and the residence time (SRT) in the aeration tank is about 5 days or less. If it takes longer, this nitrogen-containing organic matter is decomposed in the order of soluble nitrogen-containing organic matter → ammonia → nitrous acid → nitric acid in the course of decomposition by activated sludge, and mainly in the sedimentation tank 4 into which the activated sludge treated water flows. Problems such as sludge floating and scum are generated due to the denitrification phenomenon by nitric acid and nitrous acid.
In general, it is economical to stabilize the sludge and reduce the amount of excess sludge generated as much as possible. Therefore, it is often the case that the operation is performed with a long SRT of the aeration tank. Under the operating conditions that increase the SRT, the above-mentioned obstacles caused by nitrification cannot be avoided. Conversely, if the SRT in the aeration tank is shortened to suppress the decomposition of organic SS, the concentration of sludge must be reduced, and the ratio of bacterial cells present in the sludge is low. The operation is performed in a state where the amount of solid organic matter is relatively large, and bulking occurs due to overload, and a remarkable foaming phenomenon occurs. In addition, in order to perform anaerobic biological treatment in the previous stage of the aeration tank, the operating temperature of the aeration tank is usually about 30 ° C.,
Under such temperature conditions, even if the SRT is kept short, the nitrification reaction is likely to occur, and the generated nitrous acid or nitric acid and the solid organic matter remaining in the sludge react in the sedimentation tank to cause denitrification. This causes problems such as floating of sludge and generation of scum.

Therefore, in order to fundamentally solve the problems in the conventional method, the SRT in the aeration tank is set relatively long to promote the decomposition of the organic SS in the pre-set sludge and the activated sludge treated water It is necessary to prevent problems such as floating of sludge and generation of scum due to the denitrification reaction as described above in the sedimentation tank into which water flows.

In the method for treating organic waste water according to the first aspect, the denitrification process is provided in the aerobic biological treatment process, so that the nitric acid and nitrous acid generated by the decomposition in the aerobic biological treatment process are separated from the wastewater. It is removed during the denitrification process. Therefore, the amount of nitric acid and nitrous acid in the activated sludge treatment water flowing into the subsequent settling tank is significantly reduced, and the problems of sludge floating and scum generation due to these are eliminated.

According to a second aspect of the present invention, there is provided the method of treating an organic wastewater according to the first aspect, wherein only the pre-sedimentation sludge is previously dissolved in the aerobic treatment step to solubilize and reduce the molecular weight, and then the aerobic biological treatment is performed. By feeding the sludge to the process, it is possible to promote the decomposition of solids and reduce the amount of excess sludge generated.

According to a third aspect of the present invention, there is provided a method for treating organic waste water, wherein the pre-set sludge is subjected to an aerobic treatment step and a denitrification treatment step, whereby nitrogen-containing organic matter in the pre-set sludge is directly nitrified and denitrified. And remove. For this reason, the residual amounts of nitric acid and nitrous acid in the activated sludge treatment water flowing into the settling tank are significantly reduced, and the problems of sludge floating and scum generation due to these are eliminated.

[0015]

Embodiments of the present invention will be described below in detail.

FIGS. 1 to 3 are system diagrams showing an embodiment of the method for treating organic waste water according to the present invention.

In the method shown in FIG. 1, raw water is first solid-liquid separated by a solid-liquid separation means 1 such as a sedimentation tank, a flotation tank or a decanter, and the solid-liquid separated liquid (pre-sedimentation supernatant) is anaerobic. Anaerobic biological treatment is performed in the biological treatment step (methane fermentation step) 2, and 80 to 90% of the contained organic matter is decomposed into methane.

The anaerobic biological treatment step 2 may be a single-phase system or a two-phase system of acid generation and methane generation. The sludge holding method may be any of the UASB method, the floating method, and the like.

The anaerobic treated water is subjected to the aerobic biological treatment in the aerobic biological treatment step 5 together with the solid matter (pre-sedimentation sludge) separated by the solid-liquid separation means 1 to decompose the residual organic matter. In this embodiment, the aerobic biological treatment step 5 is divided into three regions by a partition wall.
After the aerobic biological treatment is performed in the second region (first aeration unit) 5A, the denitrification treatment is performed in the second region (denitrification unit) 5B under anaerobic conditions, and thereafter, the third treatment is performed. The aerobic biological treatment is performed in the region (second aeration unit) 5C.

That is, in the first aeration unit 5A, decomposition of organic substances in the pre-sedimentation sludge and anaerobic treated water, ammoniaation and nitrification of organic nitrogen are performed, and denitrification is performed in the denitrification unit 5B. (2) The residual organic matter is decomposed in the aeration section 5C, the dissolved oxygen is increased, and the treated water is fed to the settling tank 4.

The sludge holding system in the aerobic biological treatment step 5 may be any of a floating system, a fixed bed system, a fluidized bed system, and a biofilm system.

The denitrification section 5B in the aerobic biological treatment step 5
If the volume ratio is excessively large, the function of the aerobic biological treatment process will be impaired. If the volume ratio is excessively small, the effect of the present invention due to the provision of the denitrification unit cannot be obtained. Therefore, the denitrification unit 5B
Is 10 to 5 of the volume of the aerobic biological treatment step 5 (the total volume of the first aeration unit 5A, the denitrification unit 5B, and the second aeration unit 5C).
It is preferably set to 0%, particularly about 20 to 30%.

As shown in FIG. 1, the denitrification section 5B in the aerobic biological treatment step 5 is provided between the first aeration section 5A and the second aeration section 5B. It is also possible to constitute a part and an aeration part at the subsequent stage, and return a part of the effluent of the aeration part to the denitrification part and circulate it.

The denitrification section 5B is capable of converting nitrate ions and nitrite ions with nitrogen gas by denitrifying bacteria under anaerobic conditions, that is, by not performing aeration at all or by limiting the amount of oxygen supplied even if aeration is performed. In the denitrification reaction in the denitrification section 5B, even in the case of endogenous denitrification using organic matter contained in sludge as a hydrogen donor, raw water or pre-sedimentation is required to increase the denitrification efficiency. A part of the supernatant (preferably about 3 to 20%, more preferably about 5 to 10%) is shown by a broken line in FIG.
It may be introduced directly into the denitrification section 5B. Direct denitrification unit 5B using raw water or part of the pre-sedimentation supernatant as hydrogen donor
In general, the denitrification rate and the denitrification efficiency are increased, and treated water with better water quality can be obtained.

As shown in FIG. 1, by providing the denitrification unit 5B in the aerobic biological treatment step 5, nitrous acid and nitric acid generated in the aerobic biological treatment are denitrified in the denitrification unit 5B. Denitrification does not occur in the sedimentation tank 4, and therefore, floating of sludge and generation of scum in the sedimentation tank 4 are prevented.

The aerobic treated water sent from the second aeration unit 5C to the settling tank 4 is separated into solid and liquid in the settling tank 4, and the supernatant water is discharged out of the system as treated water. On the other hand, the separated sludge is returned to the aerobic biological treatment step 5 as returned sludge. In addition,
The sludge of the aerobic biological treatment step 5 or a part of the separated sludge is discharged out of the system as surplus sludge as necessary.

As described above, the denitrification phenomenon is prevented in the sedimentation tank 5, and the floating of sludge and the generation of scum due to the denitrifying phenomenon are prevented. Therefore, the deterioration of the treated water quality due to the outflow of floating sludge and fine flocs is prevented. From the sedimentation tank 5, high-quality treated water can be obtained.

As the solid-liquid separation means for the aerobic treated water, a membrane separation device may be used instead of the precipitation tank 5.

The method shown in FIG. 2 is characterized in that a sludge stabilization tank 6 is provided, and the pre-sedimentation sludge is subjected to aerobic biological treatment in this sludge stabilization tank 6 and then fed to the aerobic biological treatment step 5. Are different from the method shown in FIG.

In this method, only the pre-sedimentation sludge is subjected to the aerobic biological treatment in the sludge stabilization tank 6 so that the residence time can be prolonged. By feeding, the decomposition of solid matter can be promoted and the amount of excess sludge generated can be reduced. A part of the returned sludge is sent to the sludge stabilization tank 6 to maintain the cell concentration in the sludge stabilization tank 6. In this method, nitric acid and nitrous acid are generated in the nitrification reaction of organic nitrogen also in the sludge stabilization tank 6, and the generated nitric acid and nitrous acid are denitrified in the aerobic biological treatment step 5 in the same manner as in the method of FIG. It is denitrified in the part 5B.

In the method shown in FIG. 3, the sludge stabilization tank 6 is divided into two areas by a partition wall, and the inflow sludge is subjected to anaerobic biological treatment in the first area (denitrification section) 6A. Then, aerobic biological treatment is performed in the second area (aeration section) 6B, and a part of the treated water in the aeration section 6B is denitrified by the denitrification section 6A.
The configuration shown in FIG. 2 is different from the method shown in FIG.

Similarly to the denitrification unit 5B, the denitrification unit 6A is subjected to nitric acid by denitrifying bacteria under anaerobic conditions, that is, by not performing aeration at all or by limiting the amount of supplied oxygen even if aeration is performed. Therefore, this method promotes solubilization and low-molecularization of pre-sedimentation sludge in the sludge stabilization tank 6, as in the method shown in FIG. At the same time, the organic nitrogen derived from solid matter in the pre-sedimentation sludge is removed by the denitrification section 6A and the aeration section 6B of the sludge stabilization tank 6.
It is removed by nitrification and denitrification.

In the method shown in FIG. 3, since the organic nitrogen in the pre-sedimentation sludge is nitrified and denitrified in the sludge stabilization tank 6, the denitrification part 5B in the aerobic biological treatment step 5 is not necessarily required. Instead, the aerobic biological treatment step 5 may include only the aeration unit.

In the method shown in FIG. 3 as well, the organic nitrogen is removed by the nitrification and denitrification in the sludge stabilization tank 6 and further in the aerobic biological treatment step 5, whereby the aerobic organism introduced into the sedimentation tank 4 is obtained. The amounts of nitric acid and nitrous acid in the treated water are reduced, and floating of sludge in the sedimentation tank 4 due to the denitrification phenomenon, generation of scum, and deterioration of the treated water quality due to these are prevented.

When the denitrification section 6A is provided in the sludge stabilization tank 6 as described above, the volume ratio of the denitrification section 6A depends on the presence or absence of the denitrification section in the aerobic biological treatment step 5. If there is no denitrification part in the step 5, the denitrification part 6A is about 20 to 50% of the total volume of the sludge stabilization tank 6, and if the denitrification part is provided in the aerobic biological treatment step 5, It is preferable that the nitrogen content 6A is about 10 to 30% of the total volume of the sludge stabilization tank 6.

This sludge stabilization tank 6 can also be of a three-phase type consisting of an aeration section, a denitrification section and an aeration section without circulation, as in the aerobic biological treatment step 5.

Note that the method shown in FIGS. 1 to 3 is an embodiment of the present invention, and the present invention is not limited to the illustrated method unless it exceeds the gist.

For example, as described above, raw water or pre-sedimentation supernatant is directly supplied to the denitrification section of the aerobic biological treatment step as a hydrogen donor supply source to the denitrification section of the aerobic biological treatment step. You may.

[0039]

The present invention will be described more specifically below with reference to examples and comparative examples.

In the following Examples and Comparative Examples, the effluent from the beer factory was separated into solid and liquid, and the pre-sedimentation supernatant was replaced with U
After the anaerobic biological treatment by ASB, the aerobic biological treatment was performed together with the pre-sedimentation sludge, and each method was applied to a treatment system for solid-liquid separation of the aerobic treated water.

The water quality of the pre-settling supernatant, pre-settling sludge and UASB treated water in this treatment system is as shown in Table 1.

[0042]

[Table 1]

Comparative Example 1 (conventional example shown in FIG. 4) Aeration tanks made of PVC were arranged in series, a first aeration tank (capacity: 5.0 L), a second aeration tank (capacity: 2.5 L), and a third aeration tank Each tank was subjected to aerobic biological treatment in a capacity of 2.5 L. The flow rate of the UASB treated water into the first aeration tank was 21 L /
The amount of sludge withdrawal was adjusted so that the inflow of day and pre-sedimentation sludge was 1.2 L / day, and the MLSS of each aeration tank was about 6000 to 7000 mg / L. Processing temperature is about 25
-30 ° C. The load of the first aeration tank was as shown in Table 2. The amount of sludge returned was twice the amount of raw water.

When the treatment was continued in this manner, the time-dependent changes in the transparency of the treated water (supernatant water in the sedimentation tank) and the concentrations of nitric acid and nitrite nitrogen in the treated water SS and the treated water were respectively shown in FIG. 6 and 7.

Example 1 (Method of the Present Invention Shown in FIG. 1) In Comparative Example 1, anaerobic biological treatment was performed without performing aeration in the second aeration tank (that is, the second aeration tank was a denitrification tank). Except for this, processing was performed in the same manner as in Comparative Example 1.
As shown in Table 2, the load of the first aeration tank at this time is equivalent to that of Comparative Example 1.

When the treatment was continued in this manner, the time-dependent changes in the visibility of the treated water (supernatant water in the sedimentation tank) and the concentrations of nitric acid and nitrite nitrogen in the treated water SS and the treated water were respectively shown in FIG. 6 and 7.

Example 2 (the method of the present invention shown in FIG. 2) In Example 1, a first sludge stabilization tank (capacity 1.
5L) and a second sludge stabilization tank (capacity 1.5 L) are arranged in series, and the pre-set sludge is subjected to aerobic biological treatment in these first and second sludge stabilization tanks and then supplied to the first aeration tank. The treatment was performed in the same manner as in Example 1 except that 2.2 L / day of the pre-settle supernatant was directly fed to the second denitrification tank. In addition, 10% of the sludge separated in the sedimentation tank was returned to the first sludge stabilization tank, and the remainder was returned to the first aeration tank.

The load of the first aeration tank at this time is as shown in Table 2.

When the treatment was continued in this manner, the time-dependent changes in the transparency of the treated water (supernatant water in the sedimentation tank) and the concentrations of nitric acid and nitrite nitrogen in the treated water SS and the treated water were respectively shown in FIG. 6 and 7.

Example 3 (the method of the present invention shown in FIG. 3) In Example 2, anaerobic biological treatment was performed without aeration in the first sludge stabilization tank, and 30% of the effluent of the second sludge stabilization tank was used.
0% was circulated to the first sludge stabilization tank, and the pre-sedimentation supernatant was treated in the same manner as in Example 2 except that the entire amount was sent to the anaerobic biological treatment step. The load on the first aeration tank at this time is as shown in Table 2.

When the treatment was continued in this manner, the time-dependent changes in the visibility of the treated water (supernatant water in the settling tank) and the concentrations of nitric acid and nitrite nitrogen in the treated water SS and the treated water were respectively shown in FIG. 6 and 7.

[0052]

[Table 2]

The following is clear from the results of Comparative Example 1 and Examples 1 to 3.

That is, in Comparative Example 1 according to the conventional method, scum was frequently generated in the sedimentation tank, and the visibility of the treated water was low.
In Examples 1 and 3, the denitrification was performed only by endogenous denitrification, and nitrogen was not completely removed in the denitrification tank provided in the aerobic biological treatment process.
Was higher than that of Example 2. In Example 2, by directly introducing a part of the pre-sedimentation supernatant as a hydrogen donor, the NO _x -N removal in the denitrification tank provided in the aerobic biological treatment step was almost completely performed, and the residual NO _x- Since N was small, the treated water SS and the visibility were the best.

[0055]

As described above in detail, according to the method for treating organic wastewater of the present invention, the wastewater containing organic solids is treated anaerobically and then aerobicly treated.
The retention time of the aerobic biological treatment step is sufficiently long to improve the quality of the treated water, and scum generation and bulking in the subsequent solid-liquid separation step are prevented, and stable and efficient treatment can be performed.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a method for treating organic wastewater according to claim 1;

FIG. 2 is a system diagram showing an embodiment of a method for treating organic wastewater according to claim 2;

FIG. 3 is a system diagram showing an embodiment of an organic wastewater treatment method according to claim 3;

FIG. 4 is a system diagram showing a conventional method.

FIG. 5 is a graph showing changes in treated water visibility in Examples 1 to 3 and Comparative Example 1.

FIG. 6 shows treated water SS in Examples 1 to 3 and Comparative Example 1.
5 is a graph showing the transition of.

FIG. 7: Treated water NO in Examples 1 to 3 and Comparative Example 1
It is a graph which shows transition of _x- N.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid-liquid separation means 2 Anaerobic biological treatment process 3 Aeration tank 4 Sedimentation tank 5 Aerobic biological treatment process 6 Sludge stabilization tank

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Noriaki Ono 3-7-7 Nishishinjuku, Shinjuku-ku, Tokyo F-term Kurita Kogyo Co., Ltd. 4D040 BB01 BB04 4D059 AA07 AA08 BA31

Claims (3)

[Claims] 1. A solid-liquid separation step of solid-liquid separation of an organic waste water to separate organic solids in the waste water, and an anaerobic biological treatment of the liquid separated in the solid-liquid separation step in an anaerobic manner. An anaerobic biological treatment step, and an aerobic biological treatment step of aerobically biologically treating the anaerobic biological treatment water discharged from the anaerobic biological treatment step and the organic solids separated in the solid-liquid separation step. A method for treating organic wastewater, comprising: a denitrification treatment step provided in the aerobic biological treatment step. 2. A method for treating organic wastewater, wherein an organic solid separated in the solid-liquid separation step is supplied to the aerobic biological treatment step after passing through an aerobic treatment step. 3. A solid-liquid separation step of solid-liquid separation of the organic wastewater to separate organic solids in the wastewater, and an anaerobic biological treatment of the liquid separated in the solid-liquid separation step in an anaerobic manner. An anaerobic biological treatment step, and an aerobic biological treatment step of aerobically biologically treating the anaerobic biological treatment water discharged from the anaerobic biological treatment step and the organic solids separated in the solid-liquid separation step. In the method for treating organic waste water, the organic solids separated in the solid-liquid separation step are supplied to the aerobic biological treatment step after undergoing an aerobic treatment step and a denitrification treatment step. Characteristic organic wastewater treatment method.