JPH0155920B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention aims to provide an innovative treatment process for organic wastewater such as sewage and wastewater, and in particular, completely integrates and integrates biological treatment process, advanced treatment process, and sludge treatment process. The present invention relates to a method for treating organic wastewater that makes it possible to significantly streamline the sludge treatment process and advanced treatment process and save resources. In recent years, biological treatment of organic wastewater such as sewage using activated sludge treatment alone has not improved the quality of the treated water (especially
When COD) is insufficient, so-called tertiary treatment or advanced treatment methods, which combine coagulation and separation processes such as coagulation-sedimentation with biological treatment, have attracted much attention, and some have even begun to be implemented on an actual plant scale. There is. The typical treatment steps of this conventional biological treatment and flocculation separation process are quite simple as shown in FIG. 1, and are a collection of processes without any originality. That is, raw water 1-1 flows into an aeration tank 2 and undergoes biological treatment, and after activated sludge is separated in a final settling tank 3-1, inorganic substances such as sulfuric acid and ferric chloride are added to the biologically treated water 4. A flocculant 16 and a polymer flocculant are added as necessary to form a floc in a flocculator 5, which is then sedimented and separated in a coagulation sedimentation tank 6. On the other hand, surplus sludge 7 from the biological treatment system and flocculated sludge After 8-1 is concentrated separately (or mixed in advance), a cationic polymer or ferric chloride and slaked lime are added in the sludge treatment step 24, and mechanical dehydration is performed using a centrifugal dehydrator, a vacuum dehydrator, etc. It is dehydrated in a machine. These conventional methods have the following serious problems, and there is currently a strong need for a new treatment process that can effectively solve these problems. (1) Since a large amount of flocculant is used in the flocculation process, the processing cost becomes enormous. (2) As a result, not only a large amount of agglomerated sludge is generated, but also this sludge, which is mainly composed of aluminum hydroxide or ferric hydroxide, has extremely poor concentration and dewatering properties, which is a serious problem in terms of quality. be. (3) Moreover, since a large amount of dehydrated cake with a high moisture content is generated, it is extremely difficult to find a disposal site such as a landfill. Furthermore, the cost of incineration is extremely high. (4) On the other hand, since a large amount of chemicals must be used for dewatering in the sludge treatment process,
The processing cost is enormous, and the moisture content of the dehydrated cake is high. Although the problems pointed out above are all extremely important, it is considered that they are unavoidable to some extent because there have been no effective solutions to date, and it is impossible to implement the problems while keeping these problems in mind. The current situation is that we have no choice but to do so. The present invention makes it possible to solve the above-mentioned conventional problems all at once using an innovative idea. Or, in a method of processing in a flocculation treatment step in which an iron-based or aluminum-based flocculant is added in the biological treatment step, at least one of the surplus sludge generated from the biological treatment step and the flocculated sludge discharged from the flocculation treatment step. Either by adding mineral acid and then mixing these surplus sludge and flocculated sludge, or by mixing the surplus sludge and flocculated sludge and then adding mineral acid, iron ions or The method is characterized in that aluminum ions are eluted, an oxidizing agent is added to the mixed sludge to perform an oxidation reaction, the water is further dehydrated in a dehydration step, and the obtained dehydrated separated water is reused as a flocculant in the flocculation treatment step. This is a method for treating organic wastewater. Incidentally, as the aggregation treatment step, either a sedimentation separation method or a flotation separation method can be applied. To explain the embodiment of the present invention with reference to the drawings, in Fig. 2 1, organic wastewater 1-2 such as sewage, human waste, industrial wastewater, etc.
or directly into the aeration tank 2 of any biological treatment process such as the activated sludge method (if a biological nitrification-denitrification process or biological dephosphorization process is adopted, it may be allowed to flow directly into the anaerobic tank - not shown). (There are many.)
After flowing into the water and undergoing biological treatment, biological sludge such as activated sludge is separated in a settling tank 3-2, and then the biologically treated water 4 undergoes a coagulation sedimentation process (or coagulation and flotation process)
After flowing into the flocculator 5, it is separated in a coagulation sedimentation tank 6. An inorganic flocculant 16 such as iron sulfate or sulfuric acid salt is added to the flocculator 5. Incidentally, when a biofilm treatment method such as a rotating disk method or a fluidized medium method is employed in the biological treatment step, the sedimentation tank 3-2 can of course also be used as the coagulation sedimentation tank 6. Therefore, surplus sludge 7 (often passed through an anaerobic digestion tank) and flocculated sludge 8-1 from the biological treatment process are transferred to a thickening process (not shown) such as a gravity thickener, flotation thickener, or centrifugal thickener. After being concentrated, it flows into the acid treatment tank 9. In the acid treatment tank 9, a mineral acid 10 such as sulfuric acid is added, and the concentrated sludge 8-
Iron compounds and aluminum compounds such as ferric hydroxide and aluminum hydroxide in 2 are dissolved, and iron ions and aluminum ions are eluted. In this case, as shown in FIG.
If mineral acid 10 is added only to sludge 1 (after making it into thickened sludge 8-2 if necessary) and then mixed with excess sludge 7, the amount of mineral acid 10 consumed can be reduced. Thereafter, an oxidizing agent 12 is added in the first chemical oxidation tank 11 to perform an oxidation reaction treatment. As the oxidizing agent 12, hydrogen peroxide and ozone can be used alone or in combination, but of course it is also possible to use chlorine in combination, or to use these oxidizing agents 12 in combination with ultrasonic waves and heat. be. In addition, in the first chemical oxidation tank 11, a metal salt 22 such as an iron salt or an aluminum salt is added as an auxiliary if desired. Further, it is preferable to add an alkali agent 21 to the sludge from the acid treatment tank 9 in advance to maintain the pH of the reaction liquid in the first chemical oxidation tank 11 at 2 to 5. can be improved. Thus, the effluent sludge from the first chemical oxidation tank 11 is preferably concentrated in advance, and then dehydrated by a dehydrator 13 such as a filter press, and separated into a dehydrated cake 14 and dehydrated separated water 15. In this case, mineral acid 2 is added to the effluent sludge again before dewatering.
It is preferable to add 0.3 to 100% of the sludge, so that iron ions, aluminum ions, etc. in the effluent sludge can be sufficiently dissolved and recovered. The dehydrated separated water 15 is normally recycled as it is to the flocculator 5 and reused as a flocculant, but if desired, the dehydrated separated water 15 may be
In order to remove COD components even more fully, the second
In the chemical oxidation tank 17, an oxidizing agent 18 (such as hydrogen peroxide, which has the same effect as the oxidizing agent 12) may be added, stirred and oxidized for a predetermined period of time, and then recycled as an oxidized liquid 19. That is, since the dehydrated separated water 15 contains a large amount of iron or aluminum as described above, this can be effectively used as a catalyst for increasing the oxidizing power of hydrogen peroxide, etc., and as a result, agglomeration is prevented. Even if the agent is recycled, treated water 20 of good quality can be stably obtained from the coagulation sedimentation tank 6. Although the above is a typical embodiment of the present invention, other embodiments such as the third illustrated example and the fourth illustrated example are possible. The third illustrated example is a case in which a flocculation separation step is provided before the biological treatment step, and the fourth illustrated example is a case in which a flocculant is added during the biological treatment step. The aeration tank 2 also serves as a flocculator 5, and the sedimentation tank 3-2 also serves as a coagulation and sedimentation tank 6. Note that the inorganic flocculant 16 may also be added to the biologically treated water 4, and the oxidized liquid 19 is recycled to at least one of the aeration tank 2 and the biologically treated water 4. In the present invention, the flocculated sludge 8-1 refers to sludge obtained by adding a flocculant to a solid-liquid separator, such as flocculation-sedimentation sludge and flotation separation sludge. To summarize the gist of the technical idea of the present invention, iron compounds and aluminum compounds in coagulated sludge are dissolved in mineral acid to form iron ions and aluminum ions, respectively, and then oxidized with hydrogen peroxide, etc. It was designed to be used as a catalyst to increase the oxidizing power of agents. To recycle dehydrated and separated water as a flocculant in flocculation treatment processes such as flocculation and precipitation. Iron and aluminum in flocculated sludge are used to dehydrate surplus activated sludge, digested sludge, mixed raw sludge, etc. Furthermore, the flocculated sludge itself has been modified to improve its dewatering properties. Further chemical oxidative decomposition of COD components contained in dehydrated separated water using an oxidizing agent such as hydrogen peroxide. Furthermore, iron and aluminum in the dehydrated and separated water are used to increase the oxidizing power of the oxidizing agent. It is based on a completely unprecedented technical idea. As described above, according to the present invention, all the serious problems of the above-mentioned conventional processes are solved,
Industrially important benefits can be obtained and organic wastewater treatment processes can be revolutionized: (i) The need for fresh inorganic flocculants required in the coagulation-sedimentation and coagulation-flotation processes can be eliminated or greatly reduced. (ii) Both biological sludge and flocculated sludge can be modified and dehydrated in an extremely rational manner, and can be easily made into a dehydrated cake with a low moisture content. (iii) The only chemical necessary for dewatering biological sludge is an oxidizing agent such as hydrogen peroxide, which eliminates the need to add fresh iron salts or the like, or the amount added can be reduced to an extremely small amount. can do. (iv) COD components incorporated into flocculated sludge are
It undergoes oxidative decomposition in the sludge treatment process, and if desired, the COD component is further decomposed in the dehydrated water recycling process, so even if the flocculant is reused.
COD components do not circulate and accumulate within the system. (v) Since Fe(OH) ₃ , Al(OH) ₃ , etc. in the flocculated sludge are dissolved in acid and reused, the amount of flocculated sludge generated is extremely small. (vi) As a result, sludge components such as landfilling and incineration are extremely rationalized. Next, an example of the present invention carried out using a pilot plant will be described. Comparative example 1 (conventional method) At the J human waste treatment plant in I city, F prefecture, human waste is treated using the activated sludge method as shown in Figure 1, and then sulfuric acid is added to remove the color and COD components in the final sedimentation tank effluent. 500 to 1000 ppm of clay and 1.0 ppm of anionic polymer (Acofloc A110) were added for coagulation and sedimentation treatment. After the activated sludge surplus sludge and coagulated sedimentation sludge are mixed, a cationic polymer (Sunpoly) is mixed.
CF900) was added at 2% per SS in the sludge and centrifugally dehydrated, but the water content of the dehydrated cake was 85-86%.
This was becoming a problem. Comparative example 2 (conventional method) At the K sewage treatment plant in I city, F prefecture, after treating sewage with the activated sludge method, the chromaticity of the final settling tank effluent,
In order to remove BOD and COD components, 80 to 150 ppm of sulfuric acid clay and 1.0 ppm of anionic polymer (Acofloc A110) were added and subjected to coagulation and sedimentation treatment. After the activated sludge surplus sludge and coagulated sedimentation sludge are mixed, they are mixed with a cationic polymer (Sunpoly).
CF900) was added at 2% per SS in the sludge and centrifugally dehydrated, but the water content of the dehydrated cake was 85-86%.
This was a very high problem. The water quality of the flocculation-sedimentation treated water was as shown in the attached table (described later). Example 1 In order to fundamentally improve the current situation of Comparative Example 1, the embodiment of the present invention shown in FIG. 2 1 was applied. In other words, 300 to 600 ppm of ferric sulfate is added to the final sedimentation tank effluent only at the start of operation.
A110 was added at 1.0 ppm and flocculation and precipitation treatment was performed. Next, coagulation and sedimentation sludge is mixed with the surplus activated sludge, concentrated in a thickener, and then sulfuric acid is added.
The pH was adjusted to 1.0 to 1.5 and stirred for 30 minutes. after that,
The pH was adjusted to about 2 to 4 by adding alkali such as magnesium hydroxide or caustic soda, and 2000 to 3000 ppm of hydrogen peroxide was added, followed by dehydration using a filter press with a squeezing mechanism. However, as a result of recycling the dehydrated separated water as it is into the flocculator as a flocculant for the coagulation-sedimentation process, the amount of fresh ferric sulfate required to be added can be reduced to 30 to 50 ppm, which is 1/10, and the amount of dehydrated cake can be reduced. The moisture content was extremely low at 60-65%. As a result, it is no longer necessary to add the cationic polymer that was conventionally used. Example 2 In order to fundamentally improve the current situation of Comparative Example 2, the embodiment of the present invention shown in FIG. 21 was applied. In other words, 40 to 80 ppm of ferric sulfate is added to the final sedimentation tank effluent only at the start of operation.
A110 was added at 1.0 ppm and flocculation and precipitation treatment was performed. Next, the activated sludge surplus sludge is mixed with flocculated sedimentation sludge, concentrated in a thickener, and then sulfuric acid is added and the pH is 1.0~
1.5 and stirred for 30 minutes. After that, add an alkali such as magnesium hydroxide to make the pH 2-3.
2000 to 3000 ppm of hydrogen peroxide was added and dehydrated using a filter press with a squeezing mechanism.
Afterwards, add hydrogen peroxide to the dehydrated and separated water.
After injecting 500 ppm and stirring for 3 hours, it was recycled into a flocculator. As a result, the required amount of fresh ferric sulfate to be added can be reduced to 1/10, to 3 to 8 ppm, and the moisture content of the dehydrated cake is extremely low at 60 to 65%. Addition of cationic polymer is no longer necessary. In addition,
The quality of the treated water was as shown in the table below.

[Table] As described above, as a result of the present invention, all the problems of the conventional process have been solved.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the system of the conventional method, and Figures 2 to 4
The figure is a system explanatory diagram showing each embodiment of the present invention. 1-1... Raw water, 1-2... Wastewater, 2... Aeration tank, 3-1... Final sedimentation tank, 3-2... Sedimentation tank,
4...biologically treated water, 5...flocculator, 6
... Coagulation sedimentation tank, 7 ... Surplus sludge, 8-1 ... Coagulation sludge, 8-2 ... Thickened sludge, 9 ... Acid treatment tank,
10... Mineral acid, 11... First chemical oxidation tank, 12...
... Oxidizing agent, 13 ... Dehydrator, 14 ... Dehydrated cake, 15 ... Dehydrated separated water, 16 ... Inorganic flocculant,
17... Second chemical oxidation tank, 18... Oxidizing agent, 19
... Oxidation treatment liquid, 20 ... Treated water, 21 ... Alkaline agent, 22 ... Metal salt, 23 ... Mineral acid, 24 ...
...Sludge treatment process.

Claims (1)

[Scope of Claims] 1 Organic wastewater is treated in a biological treatment process and treated in a flocculation treatment process in which an iron-based or aluminum-based flocculant is added before or after the biological treatment process or in the biological treatment process. In the method, mineral acid is added to at least one of the surplus sludge generated from the biological treatment step and the flocculated sludge discharged from the flocculation treatment step, and then these surplus sludge and flocculated sludge are mixed, or the surplus sludge and flocculation are mixed. After mixing the sludge, mineral acid is added to elute iron ions or aluminum ions into the mixed sludge of the surplus sludge and flocculated sludge, an oxidizing agent is added to the mixed sludge to perform an oxidation reaction, and further dewatering is performed. A method for treating organic wastewater, comprising dehydrating the water in the step and reusing the resulting dehydrated separated water as a flocculant in the flocculation treatment step. 2. The treatment method according to claim 1, wherein the oxidizing agent addition step is performed by adding at least one of an iron salt and an aluminum salt in combination. 3. Claim 1 or 2, wherein the mixed sludge from which the iron ions or aluminum ions have been eluted is subjected to the oxidation reaction treatment after being adjusted to pH 2 to 5 by adding an alkaline agent in advance. Treatment method described in section. 4. Claims 1, 2, or 3, wherein the mixed sludge after the oxidation reaction treatment is further treated in the dehydration step after adding mineral acid.
Treatment method described in section. 5. Claim 1, wherein the flocculation treatment step is performed using a liquid obtained by adding at least one of hydrogen peroxide and ozone as an oxidizing agent to the dehydrated separated water from the dehydration step as a flocculant.
2. The treatment method described in Section 2, Section 2, Section 3, or Section 4. 6. The method according to claim 1, 2, 3, 4, or 5, wherein the dehydration step is performed after preliminarily concentrating the mixed sludge after the oxidation reaction treatment. Processing method. 7. Claims 1, 2, 3, 4, 5, or 6, wherein the mineral acid addition step is performed after concentrating the inflowing sludge in advance.
Treatment method described in section.