JP2007325999A - Method for restraining bulking of activated sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To propose a method for effectively restraining the bulking of activated sludge by a simple constitution and a simple operation. <P>SOLUTION: The method for restraining the bulking of activated sludge comprises a step of adding a cationic polymer flocculant and colloidal silica to the bulked activated sludge in a system for treating waste water with activated sludge to flocculate the bulked activated sludge, in the concrete, the steps of: adding the cationic polymer flocculant into an aeration tank 1 through a first injection line 11 in the system for treating waste water with activated sludge; and adding colloidal silica in a return sludge line 4 through a second injection line 12. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for suppressing bulking in an activated sludge treatment system, and more particularly to a method for inhibiting bulking by adding a cationic polymer flocculant to the activated bulk sludge in a wastewater activated sludge treatment system.

  In the activated sludge treatment method for organic wastewater, the wastewater is mixed with activated sludge in the aeration tank and aerated, and the sludge is separated in the solid-liquid separation tank, and the separated liquid is discharged as treated water, while part of the separated sludge Is returned to the aeration tank as returned sludge. In such an activated sludge treatment method, organic matter in the wastewater is aerobically decomposed by the activated sludge in which bacteria such as zoom glare are dominant. In the treatment of sewage and other ordinary organic wastewater, bacteria such as zoom glare are dominant in activated sludge, and sludge with excellent sedimentation is generated. Sludge is easily separated by sedimentation in a solid-liquid separation tank. Solid-liquid separation.

  However, depending on the properties of raw water and various treatment conditions, “filamentous bulking” in which filamentous bacteria such as Sphaerotilus natans grow in activated sludge, “dispersed bulking” in which sludge disperses without forming sludge flocs, and physical Bulking such as “demolition bulking” in which sludge is disassembled due to excessive force occurs, and the sedimentation property of sludge deteriorates. When these bulkings occur, it becomes difficult to separate the sludge in the solid-liquid separation tank, and the sludge flows out together with the treated water, so that sufficient return sludge cannot be secured, and the treatment performance deteriorates.

  Conventionally, various methods have been proposed to eliminate the bulking phenomenon of activated sludge. For example, fungicides and surfactants can be used to biologically or chemically suppress filamentous bacteria that cause bulking. There are methods such as a method of denaturing, a method of physically activating activated sludge with a coagulant, an inorganic agent, and the like, which are not always satisfactory.

  Patent Document 1 (Japanese Patent Application Laid-Open No. 62-186997) proposes a method of adding a cationic polymer flocculant and an inorganic porous powdery microbial carrier. As the inorganic porous powdery microorganism carrier, fine particles having a particle size of 10 μm or less such as pumice, siliceous ore, clay and the like are used. This method is understood to be a method in which sludge settles by aggregating sludge with a cationic polymer flocculant using an inorganic porous powdery microorganism carrier as a core. However, this method has a problem that sludge with low compaction and low specific gravity does not settle even if it aggregates.

In Patent Document 2 (Japanese Patent Laid-Open No. 8-257583), after adding a cationic polymer flocculant and sand having a particle size of 500 μm or less to a biological treatment liquid, surplus sludge introduced into the settling tank and taken out from the settling tank is added. A method has been proposed in which sludge and sand are separated by a cyclone and the sand is recycled. In this method, by adding a cationic polymer and sand in combination, the sand is effectively taken into the sludge floc, and the sedimentation property of the sludge floc is surely and remarkably enhanced and settles quickly in the settling tank. It is supposed to be. However, this method has the same problems as described above, and a more effective method has been demanded.
JP-A 62-186997 JP-A-8-257583

  An object of the present invention is to propose a bulking suppression method capable of effectively suppressing bulking with a simple configuration and operation.

The present invention is the following bulking suppression method.
(1) A bulking suppression method comprising adding a cationic polymer flocculant and colloidal silica to bulked activated sludge in an activated sludge treatment system for wastewater.
(2) The method according to (1) above, wherein the cationic polymer flocculant is added to the bulked activated sludge in the wastewater activated sludge treatment system, and then colloidal silica is added.
(3) The method according to (1) or (2) above, wherein a cationic polymer flocculant is added to an aeration tank in an activated sludge treatment system for wastewater, and colloidal silica is added to the returned sludge and returned.
(4) The method according to any one of (1) to (3), wherein 5 to 100 mg / L is added to the activated sludge bulked with colloidal silica.

  In the present invention, the bulking suppression target is bulking sludge in the activated sludge treatment system, particularly bulked activated sludge in the wastewater activated sludge treatment system. The bulking includes all bulking in which sludge is dispersed and flocs are formed, such as the aforementioned “filamentous bulking”, “dispersion bulking”, and “dismantling bulking”. The case is also effective. Here, sludge having an SVI value of 300 or more can be used as bulking sludge.

  The cationic polymer flocculant used in the present invention is a polymer flocculant having a cationic property, and those conventionally used are used, and a water-soluble linear polymer compound having a cationic group is preferable. Such a cationic polymer flocculant has a number average molecular weight of 5 to 20 million, preferably 10 to 15 million, a colloid equivalent value of 2.5 to 5.0 meq / L, preferably 4.0 to 5.0 meq. Highly cationic / L is preferred. Representative examples of the “cationic polymer flocculant” used in the present invention include quaternary ammonium salts of dialkylaminoethyl (meth) acrylate polymers and quaternary ammonium salts of dialkylaminopropyl (meth) acrylamide polymers. And quaternary ammonium salts of polyamines, and the like. Particularly preferred is a homopolymer of methyl chloride quaternary ammonium salt of dimethylaminoethyl methacrylate. The cationic polymer flocculant can be added as a 0.1 to 0.2% by weight aqueous solution.

  The colloidal silica used in the present invention is an aqueous dispersion in which ultrafine particles of silica (anhydrous silicic acid) having a particle diameter of 5 to 100 nm, preferably about 10 to 20 nm, are dispersed in a colloidal form and have a silica concentration of 20 to 40% by weight. The thing is marketed and a commercial item can be used. Colloidal silica can be added with the above aqueous solution as it is.

  In the present invention, bulking is suppressed by adding the cationic polymer flocculant and colloidal silica to the bulked activated sludge in the activated sludge treatment system for wastewater to cause aggregation. The addition of the cationic polymer flocculant and colloidal silica is preferably added to the activated sludge when bulking occurs. In addition to the cationic polymer flocculant and colloidal silica, a pH adjuster and other auxiliary agents may be added at any stage.

  The cationic polymer flocculant and the colloidal silica are preferably added to the bulked activated sludge after the cationic polymer flocculant is added and stirred, and then the colloidal silica is added and further stirred. These can be added to any place in the sludge treatment system, but are preferably added to different places. When added in the above order, the cationic polymer flocculant is added to the aeration tank and agitated by aeration, and the colloidal silica is mixed with the return sludge and returned to the aeration tank. It can add to the sludge after adding, and also can complete aggregation by stirring by aeration.

  The addition amount of the cationic polymer flocculant and the colloidal silica varies depending on the addition position, mLSS, and SVI value, but generally the cationic polymer with respect to a liquid containing activated sludge, for example, a mixed liquid in an aeration tank. The coagulant is 5 to 200 mg / L, preferably 10 to 100 mg / L, colloidal force 5 to 100 mg / L, preferably 10 to 50 mg / L (all as pure components). The amount to be added can be determined by measuring the sedimentation in advance by a jar test or the like and evaluating in advance.

  As an evaluation method, the sludge liquid to which each chemical is applied is put into a 1 L beaker, a 0.2% aqueous solution of a cationic polymer flocculant is added, 180 rpm is added for 1 minute with a jar tester, and then colloidal silica is added. The sample can be stirred again with a jar tester under the same conditions, the sample can be transferred to a 1 L graduated cylinder, the SVI value can be measured, and sedimentation can be confirmed. It is desirable to determine each addition amount so that the SVI value is 300 or less, preferably 150 or less.

  In the present invention, the above-mentioned cationic polymer flocculant and colloidal silica are added to the activated sludge bulked in the activated sludge treatment system for wastewater to cause aggregation, thereby improving the sedimentation property of sludge and suppressing bulking. be able to. At this time, colloidal silica has a lighter specific gravity than other inorganic agents, so it is easily held by the sludge floc and does not settle at the bottom. Therefore, the amount added is small and the handling property is excellent. Further, since colloidal silica is a liquid, there is very little possibility of scattering during addition.

  According to the present invention, by adding a cationic polymer flocculant and colloidal silica to the bulked activated sludge in the wastewater activated sludge treatment system, it is possible to effectively suppress bulking with a simple configuration and operation. it can.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flow chart of an activated sludge treatment system for waste water in an embodiment, where 1 is an aeration tank and 2 is a solid-liquid separation tank. In the activated sludge treatment system shown in FIG. 1, wastewater is introduced into the aeration tank 1 from the raw water channel 3, return sludge is introduced from the return sludge channel 4, air is sent from the air supply channel 5 and diffused from the diffuser 6. Then, mixed aeration is performed. A part of the mixed solution is sent from the aeration tank 1 to the solid-liquid separation tank 2 through the transfer path 7 and separated into solid-liquid separation, and the separated liquid is discharged from the treatment water path 8 as treated water. A part of the separated sludge is discharged from the excess sludge passage 9 and the remaining portion is returned to the aeration tank 1 from the return sludge passage 4 as return sludge.

  When bulking occurs in the activated sludge treatment system, a cationic polymer flocculant is injected into the aeration tank 1 from the first injection path 11 and added to the bulked activated sludge, and then stirred and mixed by aeration, and then the second injection. Colloidal silica is injected into the return sludge of the return sludge passage 4 from the passage 12, mixed by the static mixer 13, returned to the aeration tank 1, and mixed with the floc aggregated by the cationic polymer flocculant to grow the floc. Thereby, the activated sludge floc increases the sedimentation property, the solid-liquid separation in the solid-liquid separation tank 2 is favorably performed, and bulking is suppressed.

  FIG. 2 (a) is a flow chart of an activated sludge treatment system for wastewater in another embodiment, and FIG. 2 (b) is a perspective view of a triangular weir for measuring flow rate. The triangular weir 14 for flow rate measurement is normally provided in the return sludge passage 4, and the colloidal silica is added to the return sludge by connecting the second injection passage 12 to the falling part thereof, and the aeration tank is mixed by dropping the return sludge. 1 to send back. Thus, colloidal silica can be added using an existing apparatus in place of the static mixer 13 to suppress bulking.

  Examples of the present invention will be described below. In each example,% indicates wt%.

<Example 1>:
In an activated sludge treatment system for food industry wastewater, a highly cationic high-dissolving solution in which bulking sludge (mixed solution in an aeration tank) predominated by filamentous bacteria is placed in a 1 L beaker and dissolved to form a 0.2% aqueous solution. A molecular flocculant (a homopolymer of methyl chloride quaternary ammonium salt of dimethylaminoethyl methacrylate, number average molecular weight of 12 million) was added to a pure content of 50 mg / L. After stirring for 1 minute at 180 rpm with a jar tester (Miyamoto Seisakusho Co., Ltd.), 50 mg / L of colloidal silica (particle size 10-20 nm, 30% aqueous solution) is added as a pure component, and again stirred under the same conditions with a jar tester. did. Those samples were transferred to a 1 L graduated cylinder, and SV (sludge volume) and SVI (volume occupied by 1 g of sludge) were measured as sedimentation properties. Since SV and SVI had a high concentration of 4400 mg / L of the original sludge, it was diluted twice and measured at a sludge concentration of 2200 mg / L. The results are shown in Table 1.

<Comparative Examples 1-8>:
In Example 1, instead of colloidal silica, the additives shown in Table 1 were added and tested in the same manner. The results are shown in Table 1.

  From Table 1, all the systems using the cationic polymer flocculant and the inorganic agent in combination confirmed better sedimentation than the system using only the cationic polymer flocculant. The system to which the compound containing silica was added obtained better sedimentation, but the improvement of the sedimentation of the system to which colloidal silica was added became more remarkable. As a result, it can be seen that the system in which the cationic polymer flocculant and the colloidal silica are added is more effective than the system in which the conventional sand and other inorganic agents are used in combination.

<Examples 2 and 3, Comparative Examples 9 and 10>:
The filamentous bulking sludge in which the filamentous bacteria predominate in Example 1 and the dispersible bulking sludge in which sludge was dispersed in the activated sludge treatment system of other food industry wastewater were put in a 1 L beaker, 0.2% A high cationic polymer flocculant dissolved in an aqueous solution of 50 mg / L was added. After stirring at 180 rpm for 1 minute with a jar tester (manufactured by Miyamoto Seisakusho), 50 mg / L of colloidal silica was added, and the mixture was again stirred under the same conditions with a jar tester. The sample was transferred to a 1 L graduated cylinder and the sedimentation property was measured. The results are shown in Table 2.

  From Table 2, both the fibrous bulking and the dispersible bulking were obtained by using a cationic polymer flocculant and colloidal silica in combination, and by adding them individually, good sedimentation was obtained. It can be seen that is applicable.

<Examples 4 to 11 and Comparative Example 11>:
The bulking sludge predominated by filamentous bacteria in Example 1 was placed in a 1 L beaker, and a high cationic polymer flocculant dissolved in a 0.2% aqueous solution was added at the concentrations shown in Table 3. After 180 rpm for 1 minute with a jar tester (manufactured by Miyamoto Seisakusho Co., Ltd.), 50 mg / mL of each of the chemicals shown in Table 3 was added and stirred again under the same conditions with a jar tester. These samples were transferred to a 1 L graduated cylinder and sedimentation was measured. The results are shown in Table 3.

  From Table 3, the colloidal silica was added in an amount of 0 to 50 mg / L, and the anionic crosslinking was increased by increasing the concentration, and the sedimentation was improved in proportion thereto. However, when the colloidal silica is 125 mg / L or more, the effect of improving the sedimentation property is small, and it can be seen that the amount of colloidal silica added to the bulked activated sludge is preferably 5 to 100 mg / L.

<Example 12>:
In Example 1, the test was performed by changing the order of adding the drugs. The results are shown in Table 4 together with the results of Example 1 and Comparative Examples 7 and 8.

  From the results of Table 4, it can be seen that the addition of the colloidal silica after the addition of the high cationic polymer flocculant exhibits an effect superior to the reverse order.

  INDUSTRIAL APPLICABILITY The present invention can be used in a method for improving the sedimentation property of bulked activated sludge in an activated sludge treatment system for wastewater and suppressing bulking.

It is an activated sludge processing system flow chart of drainage in an embodiment. (A) is the activated sludge processing system flow chart of the waste_water | drain in other embodiment, (b) is a perspective view of the triangular weir for flow measurement.

Explanation of symbols

1 aeration tank,
2 Solid-liquid separation tank 3 Raw water channel 4 Return sludge channel 5 Air supply channel 6 Air diffuser 7 Transfer channel 8 Treatment water channel 9 Excess sludge channel 11 First injection channel 12 Second injection channel 13 Static mixer 14 Triangular weir for flow measurement

Claims (4)

A bulking suppression method comprising adding a cationic polymer flocculant and colloidal silica to bulked activated sludge in an activated sludge treatment system for wastewater. The method according to claim 1, wherein the cationic polymer flocculant is added to the bulked activated sludge in the activated sludge treatment system for waste water, and then colloidal silica is added. The method according to claim 1 or 2, wherein a cationic polymer flocculant is added to an aeration tank in an activated sludge treatment system for wastewater, and colloidal silica is added to the returned sludge and returned. The method according to any one of claims 1 to 3, wherein 5 to 100 mg / L is added to the activated sludge bulked with colloidal silica.

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