JP5834707B2 - Treatment method of organic sludge - Google Patents

Description

  The present invention relates to a method for treating organic sludge.

  Conventionally, organic sludge generated from organic wastewater such as sewage, human waste treatment plant and food industry is dehydrated with a screw decanter (centrifugal dehydrator), screw press type dehydrator, belt press, etc. using a polymer flocculant. Landfilled or incinerated. For dewatering organic sludge, cationic polymer flocculants are widely used depending on the properties of the sludge. Examples of such cationic polymer flocculants include polydialkylaminoalkyl (meth) acrylate salts or quaternary ammonium salts, polydialkylaminoalkyl (meth) acrylamide salts or quaternary ammonium salts, poly ( An acrylic cationic polymer such as a Mannich modified product of meth) acrylamide or a quaternary ammonium salt thereof is used.

  However, in recent years, the amount of sludge generated has increased due to the development of sewers, etc., and the sludge properties have deteriorated due to an increase in the amount of organic matter in the sludge, decay and the like. For this reason, the cationic polymer flocculants as described above, which are mainly used at present, are increasingly unable to perform sufficient treatment. In particular, when the moisture content of the dehydrated cake is increased due to the deterioration of the sludge properties, the cost for incineration of the dehydrated cake is increased, and a dehydration method or a polymer flocculant that lowers the moisture content is required.

  As a dehydration treatment method for reducing the moisture content of the water-containing cake, after adding and mixing the polymer flocculant to the organic sludge and then adding and mixing the inorganic coagulant (Patent Document 1), the organic sludge is inorganic agglomerated. There has been proposed a method (Patent Document 2) in which an amphoteric polymer flocculant is added and mixed and then dehydrated after the agent is added and mixed. However, in these methods, although the moisture content of the dewatered cake is reduced, a large amount of inorganic flocculant is added to the sludge. There is a problem that the number of metals such as iron and aluminum increases.

  Further, as a dehydrating agent for reducing the water content of the water-containing cake, a cationic polymer flocculant containing an amidine ring structural unit (hereinafter referred to as “amidine-based polymer flocculant”) has been proposed (Patent Document 3). Amidine-based polymer flocculants have excellent dewatering performance for organic sludge dewatering, but depending on the nature of the target organic sludge, the dehydrated separation liquid foams violently and contaminates the surroundings, A processing capability is reduced by foaming, and a sufficient effect may not be obtained, and a method for suppressing foaming is desired.

  The cause of foaming of the dehydrated separation liquid is considered as follows. That is, most of the cationic polymer flocculant added to the organic sludge reacts with the organic sludge to form a floc and is discharged out of the system together with the dehydrated cake, but a part remains in the dehydrated separation liquid. This contributes to foaming of the separation liquid. Compared to the commonly used aminoalkyl (meth) acrylate cationic flocculants, amidine polymer flocculants are thought to foam more vigorously due to polymer structure and the like.

  As a method for suppressing foaming of the dehydrated separation liquid, a method of adding silicone oil as an antifoaming agent to a polymer flocculant (Patent Document 4), a lower alcohol-based antifoaming agent as an antifoaming agent, A method of adding an organic polar compound-based antifoaming agent (Patent Document 5) has been proposed. However, the organic compound-based antifoaming agent is expensive and is an economic burden.

JP 2002-166300 A JP 63-158200 A JP-A-5-192513 JP-A-62-53800 JP-A 61-245806

  An object of the present invention is to treat organic sludge using an amidine-based polymer flocculant, and suppress the foaming of the dehydrated separation liquid without impairing the cohesiveness and dewatering property of the organic sludge. An object of the present invention is to provide an organic sludge treatment method capable of preventing a reduction in treatment performance and performing an efficient dehydration treatment.

  As a result of studying a technique capable of reducing the amidine-based polymer flocculant remaining in the dehydrated separation liquid without adversely affecting the flocculation / dehydration treatment, the inventors have obtained the following knowledge. Obtained. That is, an amidine polymer flocculant is added to and mixed with organic sludge, and then an alkaline earth metal salt of a polyvalent anion is added and mixed so that the amidine flocculant remaining in the liquid and the polyvalent anion are ion complexed. Is formed and insolubilized and removed together with the dehydrated cake, and foaming of the dehydrated separation liquid is suppressed.

  Incidentally, the monovalent anionic salt does not form a complex, and the foaming suppression effect cannot be obtained. Further, there is no effect when an alkali metal salt of a polyvalent anion is added and mixed before the amidine polymer flocculant is added to and mixed with the organic sludge. Further, there is no effect in the case of a general aminoalkyl (meth) acrylate cationic flocculant other than the amidine polymer flocculant. Furthermore, metal salts such as polyiron sulfate and aluminum sulfate, which are used as inorganic flocculants instead of alkali metals as polyvalent anion salts, have the effect of suppressing foaming, but break down the flocs finely. Since it has a bad influence on a dehydration process, it is not preferable.

The present invention has been completed on the basis of the above findings, and the gist thereof is that after adding and mixing an amidine polymer flocculant to organic sludge, an alkali metal salt of a polyvalent anion is further added and mixed in the liquid. The present invention resides in a method for treating organic sludge, characterized in that a dehydration treatment is performed after forming an ion complex of the remaining amidine flocculant and a polyvalent anion .

  The present invention makes it possible to suppress foaming of the dehydrated separation liquid without impairing the dewatering effect in the organic sludge treatment method using the amidine polymer flocculant.

  Hereinafter, the present invention will be described in detail. The amidine polymer flocculant used in the present invention contains an amidine structural unit represented by the following general formula (1) and / or an amidine structural unit represented by the following general formula (2).

（ただし、一般式（１）、（２）中、Ｒ^１、Ｒ^２は、それぞれ独立に水素原子又はメチル基であり、Ｘ⁻は陰イオンである。）

(However, in general formula (1), (2), R < ¹ >, R < ² > is a hydrogen atom or a methyl group each independently, and X < ^- > is an anion.)

  The amidine polymer flocculant can be produced, for example, by the method described in Japanese Patent No. 2624089. Specifically, N-vinylformamide and acrylonitrile are copolymerized, and the synthesized copolymer is hydrolyzed under hydrochloric acid acidity, followed by heat treatment and the primary amino group and cyano group of the inner chain of the molecule are cyclized to form an amidine ring. To do. The molecular weight (weight average molecular weight) of the amidine polymer flocculant is usually 100,000 to 5,000,000, preferably 1,000,000 to 5,000,000. A molecular weight of less than 100,000 reduces cohesion, while it is currently difficult to produce a polymer with a molecular weight greater than 5 million on a commercial basis.

  The amidine polymer flocculant may be used alone or in combination with an amphoteric polymer flocculant and / or an aminoalkyl (meth) acrylate cationic flocculant.

  The amphoteric polymer flocculant used in the present invention has a carboxyl group, a sulfonic acid group as an anionic group in the molecule, and a tertiary amine, a neutralized salt thereof, a quaternary salt, etc. as a cationic group. In addition to these ionic components, non-ionic components may be included.

  Cationic monomer units used in amphoteric polymer flocculants include dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylamide, diethylaminopropyl (meth) acrylamide, allyldimethylamine or these And nonionic monomer units include (meth) acrylamide, N, N-dimethyl (meth) acrylamide and the like. Any of these monomers can be used alone or in combination of two or more. The molecular weight of the amphoteric polymer flocculant is usually several million or more and is not particularly limited.

  The aminoalkyl (meth) acrylate cationic flocculant used in the present invention is a polymer obtained by copolymerizing an aminoalkyl (meth) acrylate cationic monomer alone or with a nonionic monomer.

  As aminoalkyl (meth) acrylate cationic monomers, hydrochloric acid of dialkylaminoalkyl (meth) acrylate such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate and diethylamino-2-hydroxypropyl (meth) acrylate Tertiary salts such as salts and sulfates; quaternary salts such as alkyl halide adducts such as methyl chloride adducts of dialkylaminoalkyl (meth) acrylates and aryl halide adducts such as benzyl chloride; N, N-dimethyl Dialkyl (meth) acrylamides such as (meth) acrylamide hydrochlorides and tertiary salts such as sulfates; Halogenated alkyl halides such as methyl chloride adducts of dialkyl (meth) acrylamides and halogenated benzyl chloride adducts Aryl adduct, etc. Include the grade salt. Any of these monomers can be used alone or in combination of two or more.

  The polymerization method of the amphoteric flocculant and aminoalkyl (meth) acrylate cationic flocculant used in the present invention includes precipitation polymerization, bulk polymerization, dispersion polymerization, aqueous solution polymerization and the like, but is not particularly limited.

  The cation equivalent value Cv in the aminoalkyl (meth) acrylate cationic flocculant is not particularly limited, and good dehydrating performance can be obtained by adjusting the mixing ratio with the amidine polymer flocculant. In addition, the intrinsic viscosity [η] indicating the molecular weight of the flocculant is appropriately 5 dl / g or more, and the higher [η], the larger the flocs and the better the dehydration process. If [η] is less than 5 ml / g, the flocs are small and weak, and the dehydrating properties in centrifugal dehydration and screw press dehydration are deteriorated, which is not preferable.

  The mixing ratio of the amidine polymer flocculant and the amphoteric polymer flocculant and / or the aminoalkyl (meth) acrylate cationic flocculant is not particularly limited, but the ratio of the amidine polymer flocculant is 50% or more. Is preferred. Moreover, the amphoteric flocculant and the aminoalkyl (meth) acrylate cationic flocculant to be blended may be one kind or plural kinds. The addition amount of the amidine polymer flocculant is not particularly limited, and it is preferable to add an appropriate addition amount corresponding to the sludge properties.

  In the present invention, in addition to the polymer flocculant, a solid acid may be added for the purpose of improving the solubility and improving the storage stability of the solution. Examples of the solid acid include sulfamic acid and acidic sodium sulfite.

  Examples of the alkali metal salt of a polyvalent anion used in the present invention include sodium sulfate (a dead glass), sulfate such as potassium sulfate, phosphate such as sodium phosphate, and carbonate such as sodium carbonate. Moreover, the alkali metal salt of the polyvalent anion to be used may be used alone or in combination with a plurality of drugs.

  The alkali metal salt of polyvalent anion is used by dissolving in water. The dissolution concentration is not particularly limited, and may be used within a concentration range in which dissolution is possible. The addition amount of the alkali metal salt of the polyvalent anion is generally preferably 300 mg / L or more based on the organic sludge, although it depends on the amount of the remaining amidine polymer flocculant. The upper limit is not particularly limited, and even if added in excess, there is no particular problem, but in consideration of economy, it is preferably 2,000 mg / L or less.

  The order of addition of the alkali metal salt of the polyvalent anion is essential to be added and mixed after adding and mixing the amidine polymer flocculant to the organic sludge. When added prior to the amidine polymer flocculant, the foaming suppression effect of the dehydrated separation liquid does not appear. As a method of such multi-stage addition, a plurality of tanks are installed, each flocculant is added to separate tanks and mechanically stirred, the addition position is shifted to the same tank and mechanically stirred, waste water line In the case of adding to the mixture and mixing the lines, a method of adding by shifting the position can be considered.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, these do not limit this invention at all. In the dehydration test of the examples, the polymer flocculants shown in Table 1 were used as 0.3 wt% aqueous solutions. In the following examples and comparative examples, each characteristic was measured by the following method.

<Measurement and evaluation method>
(1) TS concentration (evaporation residue): Measured based on a standard method (edited by Japan Sewerage Association, “Sewerage Test Method, Vol. 1997, p. 296-297)”.
(2) VTS value (ignition loss): Measured based on an ordinary method (edited by Japan Sewerage Association, “Sewerage Test Method, Vol. 1997, p297”).
(3) Aggregated floc average particle diameter: measured visually.
(4) Foamability of dehydrated separation liquid:
A: Reduced by 50% or more with respect to the amount of foaming without addition of a polyvalent anionic alkali metal salt. ○: Reduction by 20 to 40% with respect to the amount of foaming without addition of a polyvalent anionic alkali metal salt. About 10% reduction compared to the amount of additive-free foam

Examples 1-11:
A dehydration test was conducted using sewage digested sludge having a pH of 7.4, a TS of 1.6%, and a VTS of 63.2% according to the following procedure.

(1) Collect 300 ml of the sludge in a 500 ml beaker.
(2) A predetermined amount of amidine polymer flocculant is added, and mixed with a spatula for 30 seconds at a stirring speed of about 200 rpm.
(3) Further, a predetermined amount of a polyvalent anionic alkali metal salt is added and stirred and mixed for 10 seconds at the same rotational speed.
(4) The aggregated sludge is filtered through a Nutsche lined with a filter cloth, and the amount of filtrate is measured to evaluate the dewaterability.
(5) Take 100 ml of dehydrated separation liquid in a 300 ml glass graduated cylinder, inject air with an air stone at an air flow rate of 0.2 L / min for 30 seconds, and measure the amount of foam.

  Table 2 shows the results of the dehydration test. Each of Examples 1 to 11 was a result of suppressing the foaming of the dehydrated separation liquid without adversely affecting the particle diameter of the formed floc and the drainage.

Comparative Example 1:
Comparative Example 1 was carried out in the same manner as Example 1 except that no polyvalent anionic alkali metal salt was added. The dehydrated separation liquid was large in foaming.

Comparative Examples 2 and 3:
In Comparative Examples 2 and 3, a monovalent anionic alkali metal salt was added instead of the polyvalent anionic alkali metal salt. There was no foam suppression effect of the dehydrated separation liquid.

Comparative Example 4:
In Comparative Example 4, polysulfuric acid iron (PS), which is a polyvalent anionic metal salt, was added in place of the polyvalent anionic alkali metal salt. Foaming of the dehydrated separation liquid was satisfactorily suppressed, but the aggregated floc was small, the drainage was deteriorated, and the results were inferior to those of the examples.

Comparative Example 5:
In Comparative Example 5, polyaluminum chloride (PAC), which is a monovalent anion metal salt, was added in place of the polyvalent anion alkali metal salt. Both the suppression of foaming of the dehydrated separation liquid and the drainage were inferior to the examples.

Comparative Example 6:
In Comparative Example 6, a general aminoalkyl (meth) acrylate cationic flocculant was used instead of the amidine polymer flocculant, and a polyvalent anionic alkali metal salt was added. There was no foaming suppression effect of the dehydrated separation liquid, and the aggregation floc was small, resulting in poor drainage.

Comparative Example 7:
In Comparative Example 7, the polyvalent anionic alkali metal salt was added before the amidine polymer flocculant was added and mixed. There was no foam suppression effect of the dehydrated separation liquid.

The meanings of the signs of the types of additives in Table 2 and Tables 3 and 4 described below are as follows.

Examples 12-14:
A dehydration test was conducted in the same procedure as in Example 1 using sewage mixed raw sludge having a pH of 5.5, TS 2.7%, and VTS 79.8%. A dehydration test was performed in the same manner as in Example 1 except that the flocculant used was amidine polymer flocculant (P1) / DME polymer flocculant (K3) = 50/50 wt%. The results are shown in Table 3. Each of Examples 12 to 14 was a result of suppressing foaming of the dehydrated separation liquid without adversely affecting the particle diameter of the formed floc and the drainage.

Comparative Example 8:
Comparative Example 8 was carried out in the same manner as Example 12 except that no polyvalent anionic alkali metal salt was added. The formed floc had a good particle size and drainage, but the dehydrated separation liquid had a large foam.

Comparative Examples 9 and 10:
In Comparative Examples 9 and 10, a monovalent anionic alkali metal salt was added instead of the polyvalent anionic alkali metal salt. There was no foam suppression effect of the dehydrated separation liquid.

Comparative Example 11:
In Comparative Example 11, polyiron sulfate (PS), which is a polyvalent anionic metal salt, was added instead of the polyvalent anionic alkali metal salt. Foaming of the dehydrated separation liquid was satisfactorily suppressed, but the aggregated floc was small, the drainage was deteriorated, and the results were inferior to those of the examples.

Comparative Example 12:
In Comparative Example 12, polyaluminum chloride (PC), which is a monovalent anionic metal salt, was added in place of the polyvalent anionic alkali metal salt. Both the foaming suppression and drainage of the dehydrated separation liquid were inferior to those of the examples.

Comparative Example 13:
In Comparative Example 13, the polyvalent anionic alkali metal salt was added before the polymer flocculant was added and mixed. There was no foam suppression effect of the dehydrated separation liquid.

Examples 15-17:
A dehydration test was carried out in the same procedure as in Example 1 using food surplus sludge having a pH of 6.3, TS 0.9%, and VTS 86.5%.

  Table 4 shows the results of the dehydration test. Each of Examples 15 to 17 was a result that the foaming of the dehydrated separation liquid could be suppressed without adversely affecting the particle size and the drainage of the formed floc.

Comparative Example 14:
Comparative Example 14 was carried out in the same manner as Example 15 except that no polyvalent anionic alkali metal salt was added. The formed floc had a good particle size and drainage, but the dehydrated separation liquid had a large foam.

Comparative Examples 15 and 16:
In Comparative Examples 15 and 16, a monovalent anionic alkali metal salt was added instead of the polyvalent anionic alkali metal salt. There was no foam suppression effect of the dehydrated separation liquid.

Comparative Example 17:
In Comparative Example 17, polyiron sulfate (PS), which is a polyvalent anionic metal salt, was added instead of the polyvalent anionic alkali metal salt. Foaming of the dehydrated separation liquid was satisfactorily suppressed, but the aggregated floc was small, the drainage was deteriorated, and the results were inferior to those of the examples.

Comparative Example 18:
In Comparative Example 18, polyaluminum chloride (PC), which is a monovalent anion metal salt, was added instead of the polyvalent anion alkali metal salt. Both the foaming suppression and drainage of the dehydrated separation liquid were inferior to those of the examples.

Comparative Example 19:
In Comparative Example 19, the polyvalent anionic alkali metal salt was added before the polymer flocculant was added and mixed. There was no foam suppression effect of the dehydrated separation liquid.

Claims (2)

Addition and mixing of amidine polymer flocculant to organic sludge, and then add and mix polyvalent anion alkali metal salt to form an ion complex of amidine flocculant and polyanion remaining in the liquid, followed by dehydration treatment A method for treating organic sludge.   The method for treating organic sludge according to claim 1, wherein the polyvalent anion is at least one selected from the group consisting of sulfate ion, phosphate ion and carbonate ion.