JPH10249376A - Treatment of organic waste water such as sewage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new technique by which the amts. of both the green sludge and excess sludge generated from the equipment for treating an org. waste water such as sewage are remarkably and rationally decreased. SOLUTION: The org. sewage is separated into solid and liq., the SS is removed as separated sludge, and then the separated water is aerobically treated by this method. The separated sludge is anaerobically digested, the residue 12 from an anaerobic digestion tank 5, etc., is supplied to an aerobic treating tank 2, etc. and a part of the sludge from the aerobic treating tank 2, etc. is extracted and supplied to an ozonization tank 6. The ozonized sludge is preferably supplied to the aeration tank 2 using an oxygen-contg. gas. Meanwhile, a high molecular flocculant 8 is added to the org. sewage in the solid liq. separation to conduct flocculation and separation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique capable of substantially eliminating sludge discharge in an organic sewage treatment facility for sewage or the like, and remarkably streamlining sludge treatment and disposal.

[0002]

2. Description of the Related Art Organic sewage such as sewage is treated as water of such a quality that it can be discharged after being subjected to various treatments. As a treatment method, an aerobic biological treatment method is most widely used. ing. The aerobic biological treatment method of the organic sewage will be described by taking sewage treatment, which is a typical organic sewage, as an example. From the sewage treatment facilities, a large amount of raw sludge discharged from the sedimentation basin and surplus biological sludge that is proliferated in the aerobic biological treatment process are generated in large quantities every day. Conventionally, these sludges are dewatered with a mechanical dehydrator by adding a sludge dewatering aid such as a polymer, and the separated dewatered cake is incinerated there. Dewatering equipment costs, auxiliary fuel costs for incineration, incinerator equipment costs, etc., have become enormous and are a great burden. In addition, the company is also struggling with the disposal of incinerated ash.
There are problems, such as high maintenance costs.

[0003] Conventionally, as one method of sludge reduction method,
Although the anaerobic digestion method is known, even if the anaerobic digestion is performed for a long time, a large amount of digestion residue that cannot be decomposed remains, and this disposal is a difficult task. Japanese Patent Application Laid-Open No. Hei 7-116865 discloses a technology for reducing the amount of sludge in which excess biological sludge is oxidized with ozone to increase the biodegradability of the sludge and then returned to an aerobic biological treatment tank such as an aeration layer of the activated sludge method. Although it is known and known, the above-mentioned known technique does not initially provide a sedimentation tank,
Since it is based on direct aerobic biological treatment, there is no disclosure of a method for treating and disposing of raw sludge from a primary sedimentation basin generated in a larger amount than excess biological sludge in sewage treatment. In other words, even though the above-mentioned known technology is effective in reducing the amount of excess biological sludge, no idea or specific means for how to rationally treat and dispose of raw sludge has been disclosed.

[0004]

DISCLOSURE OF THE INVENTION The present invention combines a anaerobic digestion method and a sludge reduction technique using ozone in a novel manner, thereby enabling a new technique capable of remarkably reducing both raw sludge and excess biological sludge. The task is to provide

[0005]

The above object is achieved by a method for treating sewage in which the aerobic biological treatment method, anaerobic digestion method and sludge reduction technology using ozone according to the present invention are combined in a novel manner. That is, (1) after the organic sludge is subjected to solid-liquid separation to remove SS as separated sludge, and then the separated water from the solid-liquid separation is subjected to aerobic biological treatment. Organic, wherein the digestion residue from the anaerobic digestion step is supplied to the aerobic biological treatment step, and a part of the sludge from the aerobic biological treatment step is withdrawn and supplied to the ozone treatment step. Of wastewater treatment. (2) The method for treating organic sewage according to (1), wherein the sludge discharged from the ozone treatment step is further supplied to an aeration step using an oxygen-containing gas. (3) The method for treating organic sewage according to (1), wherein the organic sewage is subjected to coagulation separation by adding a polymer coagulant to the organic sewage as solid-liquid separation. (4) The method for treating organic sewage according to (1), wherein an inorganic flocculant is added to the purified effluent discharged from the aerobic biological treatment step to perform flocculation and separation. The aerobic biological treatment step referred to in the present invention is an activated aerobic aeration tank at least in the steps of activated sludge method, anaerobic aerobic activated sludge method, biological nitrification denitrification method, carrier-added activated sludge method, biofilm method, etc. Means a general term for biological treatment methods.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described with reference to the drawings. One embodiment of the present invention will be described with reference to FIG. In FIG. 1, sewage 7 first flows into the sedimentation basin 1, and SS in the sewage is settled and separated. The separated sludge is referred to as raw sludge 9. At this time, when a high-molecular flocculant 8 (preferably a cationic polymer) is added to the sewage 7 to flocculate and remove SS organic substances to a high degree, the amount of excess biological sludge generated from the subsequent aerobic biological treatment step is greatly reduced. This is very preferable since the required amount of ozone in the ozone oxidation step described later is significantly reduced. The sediment separation water from the first sedimentation basin 1 is supplied to an aerobic biological treatment step (such as an aeration tank 2 for activated sludge treatment) to remove BOD. The slurry discharged from the aeration tank 2 (a tank for performing an aerobic biological treatment such as an activated sludge process) is separated and separated in the final sedimentation basin 3 for solid-liquid separation, and purified treated water 17 is obtained. Most of the sludge settled in the final sedimentation basin 3 is returned to the aeration tank 2 as returned sludge 16 and contributes to the adjustment of the concentration of MLSS in the aeration tank 2. Part of the settled sludge from the final settling tank 3 is transferred to the ozone oxidation tank 6 as drawn sludge 15, where it is oxidized with ozone and the biodegradability of the sludge is improved. The ozone oxidized sludge is returned to the aeration tank 2 and is decomposed into carbon dioxide and water by the aerobic biological treatment and disappears.

On the other hand, the raw sludge 9 precipitated in the first settling tank 1 is separated from the concentrated sludge 10 and the separated water 1 in the sludge concentration step 4.
1 is subjected to solid-liquid separation. In the sludge concentration step 4, a centrifugal concentrator,
Means such as flotation concentration and precipitation concentration are used. The concentrated sludge 10 whose solid matter concentration has been increased in the sludge concentration step 4 is supplied to the anaerobic digestion tank 5, where methane fermentation of organic matter is performed to reduce sludge. However, in this anaerobic digestion, about 30% of the SS weight of the supplied concentrated sludge 10 remains as digestion residue (total of indigestible sludge and anaerobic microbial cells). In the present invention, this digest residue 12 is supplied to the activated sludge aeration tank 2 in the sewage treatment step, and an aerobic biological treatment such as an activated sludge method is performed together with the sediment separation water. The anaerobic digestion residue 12 is converted from an anaerobic state to an aerobic state in an activated sludge aeration tank, and a part thereof is decomposed and reduced by aerobic microorganisms.

In the aerobic biological treatment using activated sludge in the aeration tank 2, BOD is removed. First, water separated from the sedimentation tank 1 and digestion residue 1 from the anaerobic digestion tank 5 are removed.
With the inflow of 2, SS flows in and the amount of sludge increases in the system. Therefore, the increase in sludge is suppressed by the following means. That is, a part of the sludge from the aerobic biological treatment step (aeration tank 2) is withdrawn, the extracted sludge 15 is oxidized with ozone to improve the biodegradability of the sludge, and then returned to the aeration tank 2.
When subjected to ozone oxidation, ozone has a strong oxidizing effect, and extracellular macromolecules of microbial cells constituting sludge are oxidized and decomposed to low molecular weight. In addition, the strength of the microbial cell wall is also weakened, and it is considered that the sludge turns into food for aerobic microorganisms. As a result, both digestion residue and excess biological sludge from anaerobic digestion are almost completely eliminated and eliminated, and sludge to be discharged out of the system is substantially eliminated.

In the present invention, as the aerobic biological treatment tank for supplying the ozone-oxidized sludge, besides the method using an activated sludge aeration tank (aeration tank 2 in FIG. 1) for sewage purification, FIG. As shown in the figure, an aerobic biological treatment is performed by providing an aeration tank A separately from the sewage aerobic biological treatment, and the aerated sludge 18, which is a part of the treated sludge, is activated sludge aeration for sewage purification outside the system. A method may be adopted in which the processing is transferred to the tank 2 and the like, and the circulating sludge 19 as another part is transferred to the ozone oxidation tank B and the sludge oxidized in the ozone oxidation tank B is returned to the aeration tank A. Aerobic biological treatment of ozone oxidized sludge produces a considerable amount of non-degradable COD in parallel with sludge decomposition and reduction.
However, in the method of FIG. 2, since the sludge is circulated and processed many times in the aeration tank A and the ozone oxidation tank B, it is recognized that the generation of persistent COD is suppressed. The aerobic sludge extracted from the aerobic biological treatment step is anaerobically digested together with the raw sludge, the biological sludge is decomposed by the anaerobic microorganisms, and the digested residue is allowed to flow into the aerobic biological treatment step. This is preferable because the amount of sludge to be ozonated is reduced and the cost of ozonation is reduced.

In the conventional standard aerobic biological treatment method, phosphate ions in sewage are partly absorbed and removed by activated sludge, and are removed outside the system as excess sludge. Although the phosphorus of the treated sewage is considerably lower than that of the raw water, in the present invention in which the sludge is reduced, excess biological sludge is not discharged out of the system, so that the phosphate ion removal rate becomes zero in principle. Therefore, when the removal of phosphorus is desired, the present invention adds an inorganic coagulant such as aluminum sulfate, PAC, polyiron, iron chloride, etc. to the treated sewage (final sedimentation tank effluent) and performs coagulation separation. The inconsistency was resolved. In general, in the anaerobic digestion step, as shown in FIG. 3, the anaerobic digestion sludge treated in the anaerobic digestion tank C is subjected to solid-liquid separation by a solid-liquid separation device D such as membrane separation or centrifugation. It is preferable to maintain anaerobic bacteria in the digestion tank in order to improve the anaerobic decomposition rate of raw sludge.

Next, the ozone oxidation step will be supplementarily described. If the amount of sludge supplied to the ozone oxidation tank is 3 to 4 times the amount of surplus biological sludge generated in the aerobic biological treatment step in the present invention, the sludge can be almost completely eliminated. When the amount of added ozone is set to about 30 to 80 g · ozone / kg · SS per solid of sludge supplied to the ozone treatment step, the biodegradability of the sludge is sufficiently improved. Although an ozone contact tank can be adopted, sludge foams violently when it is oxidized with ozone, so a defoaming machine or equipment for adding a defoaming agent is provided.

As described above, the present invention provides the following:
Applying the new concept described in (1), raw sludge and excess biologically treated sludge in the treatment facility for organic wastewater can be eliminated very rationally, eliminating the need for sludge dewatering, incineration, and melting of incinerated ash. . That is, raw sludge is anaerobically digested, a part of the sludge is first decomposed and reduced, and then the digested residue is supplied to an aerobic biological treatment step together with organic sewage, and the digested residue is further decomposed by aerobic microorganisms. In this process, reducing substances (hydrogen sulfide, sulfide, etc.) contained in digestion residue are oxidized by aerobic bacteria to reduce ozone consumption. A part of the sludge is withdrawn from an aerobic biological treatment step that supplies organic sewage and anaerobic digestion residue, and is subjected to aerobic biological treatment by ozone oxidation. Alternatively, the extracted sludge is aerated after aerobic biological treatment. By adding a polymer flocculant to organic wastewater and flocculating and removing SS to a high degree, and then performing aerobic biological treatment, the generation amount of excess biological sludge is reduced and the required amount of ozone is reduced.

[0013]

The present invention will be described below in detail with reference to examples. However, the present invention is not limited to only these examples. Example 1 A proof test of the present invention was performed on sewage based on the process shown in FIG. The quality of sewage used for treatment is the first
It is shown in the table.

[0014]

[Table 1]

[0015] The test conditions in the processing method of the present invention are the following.
The results are shown in Tables, Tables 3 and 4. Table 2 shows that a polymer flocculant was added to sewage, a concentrated sludge obtained by concentrating sewage agglomerate (raw sludge) precipitated in a sedimentation tank was subjected to aerobic biological treatment, and solid-liquid separation was performed in a final sedimentation tank. The conditions of the activated sludge treatment for obtaining the treated water are shown. Table 3 shows the conditions for anaerobic digestion of concentrated raw sludge in some anaerobic digesters, and Table 4 shows sludge extracted from aerobic biological treatment (excess biological sludge) and digestion residue from the anaerobic digester. The processing conditions of the sludge volume reduction bypass step in which a part of the material is subjected to the ozone oxidation treatment are shown.

[0016]

[Table 2]

[0017]

[Table 3]

[0018]

[Table 4]

Under the above conditions, a test was conducted to purify the sewage without pulling out sludge for 8 months without disposing the sludge for 8 months. As a result, the MLSS in the aeration tank for activated sludge was maintained after 8 months.
Maintained the condition of 3000-3500 mg / liter. Therefore, according to the present invention, it was recognized that both the raw sludge and the surplus biological sludge were almost completely decomposed. The SS removal rate in the first settling basin was as high as about 80% due to the effect of the polymer flocculant. The treated water (final sedimentation basin effluent) of the present invention has excellent water quality as shown in Table 5.

[0020]

[Table 5]

Example 2 After adding 120 mg / l of aluminum sulfate to the final sedimentation basin effluent of Example 1 (water quality shown in Table 5), 1 mg of an anionic polymer (Ebagrose A153) was added.
Per liter and coagulated and precipitated by a jar tester, the quality of the supernatant water was 2 mg / L for SS, 3 mg / L for BOD, and 5.2 mg / L for COD.
Liter, phosphorus 0.14mg / liter, CO
D and phosphorus could be remarkably reduced, and the problem of deterioration of treated water quality due to sludge volume reduction could be solved.

Comparative Example 1 First, the sedimentation basin and the anaerobic digestion tank were removed from the process of FIG. 1, and the sewage was discharged as shown in the known art (the technology described in Japanese Patent Application Laid-Open No. Hei 7-116865). Was directly treated with activated sludge, and the sludge reduction treatment with ozone was attempted.
Although the amount of generated sludge was almost completely suppressed, the required amount of ozone increased 3.7 times that of the present invention, and the ozone cost was too high to be practical. Moreover, the COD of the treated water is 18.3.
mg / liter, and the C of the treated water of Example 1 of the present invention.
It became worse than the value of OD. This is because the amount of sludge to be oxidized by ozone increases, and the amount of persistent COD produced increases accordingly.

[0023]

According to the present invention, the following effects can be obtained. (1) Raw sludge generated from an organic wastewater purification treatment facility is reduced by anaerobic digestion, and only sludge from biological treatment is subjected to ozone treatment so that the amount can be reduced including the biological treatment process. Therefore, both raw sludge and surplus biological sludge can be rationally eliminated and eliminated, and the required amount of ozone is greatly reduced. (2) After removing SS in organic sewage to a high degree with a polymer flocculant, aerobic biological treatment reduces the amount of excess biological sludge generated in the biological treatment process, and thus requires ozone. The amount can also be reduced. (3) Since almost no excess biological sludge is discharged, a sludge dewatering machine, a sludge dewatering aid, a sludge incinerator, and a sludge incineration ash melting furnace become unnecessary. (4) By adding an inorganic coagulant to the treated water from the final sedimentation basin, the problem of deterioration of phosphorus in the treated water due to sludge reduction can be solved without contradiction.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one example of a flow of an organic wastewater treatment method of the present invention.

FIG. 2 is an explanatory diagram showing an example of ozone oxidation treatment performed in a separate step from aerobic biological treatment of sewage.

FIG. 3 is an explanatory diagram showing an example of a flow of an efficient anaerobic digestion process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 First sedimentation tank 2 Aeration tank 3 Final sedimentation tank 4 Sludge concentration 5 Anaerobic digestion tank 6 Ozone oxidation tank 7 Sewage 8 Polymer flocculant 9 Raw sludge 10 Condensed sludge 11 Separated water 12 Digestation residue 13 Digestion gas 14 Ozone 15 Withdrawal Sludge 16 Returned sludge 17 Treated water 18 Aerated sludge 19 Circulated sludge 20 Separated water A Aeration tank B Ozone oxidation tank C Anaerobic digestion tank D Solid-liquid separation device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C02F 11/06 C02F 11/06 A 11/08 11/08

Claims (4)

[Claims] Claims: 1. A method of solid-liquid separating organic wastewater to remove SS as separated sludge, and then subjecting the separated water from the solid-liquid separation to aerobic biological treatment. Organic, wherein the digestion residue from the anaerobic digestion step is supplied to the aerobic biological treatment step, and a part of the sludge from the aerobic biological treatment step is withdrawn and supplied to the ozone treatment step. Of wastewater treatment. 2. The method for treating organic wastewater according to claim 1, wherein the sludge discharged from the ozone treatment step is further supplied to an aeration step using an oxygen-containing gas. 3. The method for treating organic sewage according to claim 1, wherein the organic sewage is subjected to coagulation separation by adding a polymer coagulant to the organic sewage. 4. The method for treating organic sewage according to claim 1, wherein an inorganic coagulant is added to the purified water discharged from the aerobic biological treatment step to perform coagulation separation.