JP3339801B2 - Septic sludge treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for treating putrefactive sludge, and more particularly, to a method effective for treating hardly dehydrated sludge in which putrefaction has progressed.

[0002]

2. Description of the Related Art At present, biological treatment is widespread in municipal sewage treatment, and as a result, the resulting excess or mixed sludge is generally subjected to flocculation treatment using a flocculant. On the other hand, especially in the city center, since the sewage treatment plant requires a vast site, a centralized treatment method for transporting and treating sludge by piping is being studied. However, with long-term sludge retention and long-distance transportation, decay of sludge progresses,
It becomes so-called hardly dewatered sludge, and there are problems such as a decrease in sludge dewatering efficiency.

As a method of solving the above problem, a method of increasing the amount of a coagulant is used. However, in addition to increasing the cost, if the amount is too large, there is a high possibility of redispersion and efficient treatment is performed. A method is needed. Various methods have been studied to solve such problems. For example, it is also known that a cationic polymer flocculant having an amidine ring structure is effective for sludge having advanced putrefaction.

[0004] However, the above method is mainly a method of combining a cationic polymer flocculant having an amidine ring structure with a belt press type dehydrator, not a method of combining with a centrifugal dehydrator. By the way, the centrifugal dewatering machine is relatively compact and has a high sludge treatment capacity, and it is preferable to use the centrifugal dewatering machine. However, compared with the belt press type dewatering machine, a strong G is applied to the aggregated sludge (flock) by centrifugal force. Solid-liquid separation may be performed in a broken state, and there has been a need for an agent capable of forming a strong floc.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for treating a so-called hardly dewatered sludge in which sludge has been spoiled. It is an object of the present invention to provide an efficient method for treating putrefactive sludge, which is less expensive, does not redisperse costly and can be combined with a centrifugal dehydrator.

[0006]

That is, the gist of the present invention is to provide a method for coagulating septic sludge containing a volatile organic acid of 100 mg / l or more by the following general formula (I) or (II):
The viscosity of a 0.2% aqueous solution of a cationic polymer having a structural unit represented by the following formula: is not less than 80 centipoise (measured at 25 ° C. with a B-type viscometer) . The method for treating putrefactive sludge is characterized in that after treating the putrefaction sludge with a certain coagulant, it is dewatered with a centrifugal dehydrator. In the formula, R ¹ and R ^{2 each} independently represent a hydrogen atom or a methyl group, and X ⁻ represents an anion.

[0007]

Embedded image

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The cationic polymer used in the present invention is a cationic polymer having a structural unit represented by the general formula (I) or the general formula (II), and the content of the amidine ring is usually 30 to It is in the range of 95 mol%, preferably 35-90 mol%. Amidine ring structural unit (I) in this flocculant
The quantification of (II) and (II) is measured by the total amount of (I) and (II) by nuclear magnetic resonance spectroscopy or infrared spectroscopy. Amidine ring structural unit When the content of amidine ring is less than 30 mol%, p
Although the sludge having a low H is effective, the sludge in the medium to weak alkaline region has a higher degree of dissociation with an amidine group than an amino group, and therefore, a higher amidine conversion rate is more effective.

It is important that the viscosity of the cationic polymer used in the present invention is not less than 80 centipoise as measured at 25 ° C. using a B-type viscometer as a 0.2% aqueous solution in deionized water. If the viscosity of the cationic polymer is less than 80 centipoise, an aggregate having high floc strength cannot be obtained.

The above-mentioned cationic polymer usually copolymerizes acrylonitrile or (meth) acrylonitrile with a monomer which forms a vinylamine unit after polymerization, and then forms a vinylamine unit in the obtained copolymer. The side chain group of the monomer is chemically modified with an acid to form a primary amino group.
Subsequently, by heating, the primary amino group is reacted with acrylonitrile or the nitrile group of (meth) acrylonitrile to form an amidine ring.

The above-mentioned monomer which forms a vinylamine unit by modification after polymerization includes N-vinylformamide, N-vinylacetamide, N-vinylpropionamide, N-vinylphthalimide and the like.

The molar ratio of the monomer (A), which forms a vinylamine unit by modification after polymerization, to acrylonitrile or (meth) acrylonitrile (B) is usually 20:80 to (A) :( B). 95: 5, preferably 3
0:70 to 90:10, more preferably 40:60 to 8
The range is 0:20, but is not limited to this range.

As the above-mentioned copolymerization method, any method of bulk polymerization, solution polymerization, precipitation polymerization, suspension polymerization, and reversed-phase emulsion polymerization can be generally used. Aqueous solution precipitation polymerization or suspension polymerization is preferred from the viewpoint of easy handling such as transfer. Further, the concentration of the monomer, the polymerization temperature, the type of the reaction vessel, and the like are appropriately selected in consideration of the molecular weight of the target polymer and the heat generated by the polymerization. For example, the following polymerization method can be mentioned. A method in which water is used as a solvent and polymerization is carried out in the form of an aqueous solution at a monomer concentration of 5 to 60% by weight to obtain a polymer as a hydrogel or a precipitate of a precipitate. The monomer concentration is 20 to 60% by weight. % Aqueous solution is emulsified in oil-in-water or water-in-oil using a hydrophobic solvent and an emulsifier, and an aqueous solution having a monomer concentration of 20 to 60% by weight is mixed with a hydrophobic solvent and a dispersion stabilizer. Used in a water-in-oil dispersion state to obtain a polymer. Among these copolymerization methods, a precipitation polymerization method in water is preferred. In the case of this precipitation polymerization, it is preferable to use an inorganic or organic salt, a surfactant, a water-soluble polymer or the like as a dispersion stability and a precipitation accelerator.

As the polymerization initiator used in the above-mentioned copolymerization method, a general radical polymerization initiator can be used, but an azo compound, particularly a water-soluble azo compound is preferred from the viewpoint of polymerization yield. Specific examples thereof include hydrochloride and acetate of 2,2′-azobis-2-amidinopropane,
Sodium salt of 4,4'-azobis-4-cyanovaleric acid, hydrochloride and sulfate of azobis-N, N'-dimethyleneisobutylamidine and the like can be mentioned. The ratio of the polymerization initiator used is usually 0.01 to 1 based on the weight of the monomer.
% By weight, preferably in the range of 0.02 to 0.9% by weight. The polymerization reaction temperature is usually in the range of 20 to 100C, preferably 30 to 90C.

The obtained copolymer is converted into a solution, dispersion, or powder, and then modified under acidic conditions to be modified into a copolymer containing vinylamine units. As a denaturing method, a method of hydrolysis in water under acidic conditions,
Hydrolysis in a hydrophilic solvent such as an alcohol containing water may be mentioned.

As the acidic denaturing agent used for the above denaturation, hydrochloric acid, bromic acid, hydrofluoric acid, sulfuric acid, nitric acid, phosphoric acid,
Sulfamic acid, alkanesulfonic acid and the like can be mentioned, but hydrochloric acid is preferred. The proportion of the acidic modifier used is usually 0.1 to 2 moles, preferably 0.2 to 1.5 moles per mole of the group that forms vinylamine units in the copolymer.
The range is twice as large. The denaturation reaction may be performed under pressure, and the reaction temperature is usually 30 to 130 ° C, preferably 40 to 130 ° C.
To 110 ° C. In order to prevent gelation (water insolubilization) of the denatured product at the time of denaturation, the hydroxyamine is usually used in an amount of 0.1 to 20% by weight, preferably 1 to 10% by weight based on the total amount of the copolymer. (See JP-A-5-86127).

The above-mentioned modified copolymer is used in the present invention by making it into a solution, dispersion or powder, and further heating it at a temperature of usually 70 to 130 ° C., preferably 80 to 110 ° C. (Hereinafter also referred to as a polyamidine type flocculant).

The method of the present invention is also effective for mixed raw sludge and excess sludge in which decay has not progressed very much. However, the method of the present invention is effective for sludge which remains in pipes and storage tanks for a long time and becomes hardly dewatered sludge. Significantly better than other flocculants. For example, sludge that has been left standing for 24 hours or more during the coagulation treatment after being concentrated is putrefactive. As the sludge decay progresses and the bacteria die, the cells are broken down, become water-soluble polymers mainly composed of proteins, and dissolve in water. In addition, volatile organic acids are also generated.

The decay status of the sludge can be determined based on the amount of the water-soluble polymer component derived from microorganisms such as the above-mentioned microorganisms and the amount of the generated volatile organic acid. That is, the amount of the water-soluble polymer component can be determined by centrifugal sedimentation of the sludge and the amount of the organic component dissolved in the supernatant. Specifically, the total amount of organic carbon (T) in the supernatant obtained by centrifuging and removing the sludge at 3000 rpm for 10 minutes
When OC) was measured, it was found that the total amount of organic carbon increased to about 2 to 5 times before and after standing at 30 ° C. for 24 hours. are doing. This water-soluble polymer is negatively charged near neutrality, forms a polymer complex with the cationic flocculant added for sludge treatment, consumes the flocculant, and forms the complex formed. Becomes like a water-absorbing gel and dehydration becomes difficult. Therefore, as the decay progresses, it becomes difficult to dewater the sludge.

Since the volatile organic acid is extremely small in fresh surplus sludge, it is considered that the volatile organic acid was produced by putrefaction unless an acid flows in from the initial sedimentation. By doing so, it can be a measure of corruption. The degree of decay varies depending on the season, temperature, etc., but is usually 100 mg / l, preferably 300 mg / l.
If there is an increase in the amount of the volatile organic acid of mg / l, it can be said that sludge decay has considerably progressed.

The polyamidine type flocculant used in the present invention has a higher charge density than the conventionally used (meth) acrylic acid type polymer flocculant, and thus has a high water solubility derived from the cells. Since the polymer complex has a sufficient cationic group and a high charge density even if consumed to a certain extent, the formed polymer complex is densely ion-crosslinked, and as a result, it is difficult to swell with water, and the water content of the aggregate is reduced. It is thought to decrease.

Conventionally, polyamidine-type flocculants are inferior to polyacrylic acid ester-type flocculants in terms of floc strength, and it is thought that their effects cannot be sufficiently exhibited unless they are combined with a belt press type dehydrator. Came. However, in the present invention, by using a polyamidine-type flocculant having a specific viscosity or more, an aggregate having a strong floc strength is obtained even with a polyamidine-type flocculant, and as a result, septic sludge can be treated even with a centrifugal dehydrator. Becomes
Effective septic sludge treatment became possible.

The polyamidine type flocculant according to the present invention comprises:
It is effective enough when used alone, but used in combination with cationic, amphoteric, anionic, or nonionic water-soluble polymers, and inorganic coagulation such as sulfate band, ferric chloride, ferric sulfate, and polyaluminum chloride. You may use together with an agent.

The sludge to be treated in the present invention is sewage, particularly municipal sewage having a long transfer time. Specific examples thereof include primary sludge sludge settled from sewage in an urban sewage treatment plant, surplus sludge settled from effluent from an activated sludge tank, and mixed raw sludge that is a mixture thereof. The method of the present invention is generally applied to the treatment after the above-mentioned sludge is concentrated by gravity sedimentation or mechanically concentrated.

The proportion of the amidine-type coagulant used in the present invention is usually in the range of 0.01 to 3.0% by weight, preferably 0.1 to 1.0% by weight, based on the solid content of the sludge. .

[0026]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist. In the following examples, each physical property was evaluated according to the following methods.

<Measurement Method of Aqueous Solution Viscosity> The aqueous solution viscosity was measured using a B-type viscometer N as an aqueous solution having a concentration of 0.2% in deionized water.
The measurement was performed at 25 ° C. using an O1 rotor, and the measurement results were shown in centipoise.

<Measurement Method of Volatile Organic Acid> The volatile organic acid in the sample was distilled by steam distillation in the presence of sulfuric acid, and the obtained distillate was titrated with an aqueous solution of sodium hydroxide to obtain a low-grade organic acid. The total amount of fatty acids was expressed as the equivalent amount of acetic acid (mg / l).

<Measurement Method of Suspended Substances> The suspension in water in the sample was filtered through a glass fiber filter paper having a pore size of 1 μm, evaporated to dryness, the residue on the filter paper was weighed, and the number of mg per liter was determined. The “suspended matter” amount “ss” was obtained.

In the following examples, N-vinylformamide and acrylonitrile were copolymerized and then hydrolyzed to obtain the composition (functional group composition) and elimination of the structural units (I) and (II). Cationic polymers having the viscosity of a 0.2% aqueous solution of salt water as shown in Table 1 below were used.

The functional group composition of each cationic polymer was determined by nuclear magnetic resonance spectroscopy and infrared spectroscopy.
It was measured by a mold viscometer. The composition of the amidine group represents the total amount of the structural units (I) and (II).

[0032]

[Table 1]

Example 1 Septic mixture having a pH of 5.28, a volatile organic acid of 320 mg / l and a suspended substance of 11,000 mg / l when left in a sludge storage tank of a sewage treatment plant for 36 hours. The raw sludge and the aqueous solution having a cationic polymer concentration of 0.2% of each sample shown in Table 1 above were decanted (centrifugal separator: Tomoe) at a ratio of 1.0% by weight of cationic polymer (to sludge SS). (Manufactured by Kogyo Co., Ltd.) with a donut-shaped cross section to supply sludge to the inner pipe at a sludge supply rate of 10 m ³ / hr, and an aqueous solution of a cationic polymer to the outer pipe. After the mixture was mixed and agglomerated in the apparatus, the mixture was dehydrated by a centrifugal dehydrator having a residence time of 12 minutes under the condition that the acceleration of gravity due to centrifugal force was 2500 G. The cake moisture content was measured from the loss on drying and the weight of the wet cake under the suspended solids recovery rate according to the sewer test method and drying conditions at 105 ° C. for 2 hours. Table 2 shows the measurement results.

Example 2 In Example 1, the pH was 6.57 and the volatile organic acid was 12 in a sludge storage tank at a sewage treatment plant for 24 hours.
0 mg / l and suspended matter is 11,500 mg / l
In the same manner as in Example 1, except for using the putrefaction mixed raw sludge, the suspended solids recovery rate and cake moisture content of the cationic polymer shown in Table 1 were determined.
Table 3 shows the measurement results.

Example 3 In Example 1, the pH was 6.57 and the volatile organic acid was 60 m in a sludge storage tank at a sewage treatment plant for 6 hours.
g / l and the suspended solids of the cationic polymer shown in Table 1 shown in Table 1 were recovered in the same manner as in Example 1 except that the septic mixed raw sludge having a suspended substance of 12,000 mg / l was used. And the cake moisture content were determined. Table 4 shows the measurement results.

[0036]

[Table 2] Polymer: cationic polymer (the same applies hereinafter)

[0037]

[Table 3]

[0038]

[Table 4]

[0039]

As described above, the method for treating putrefactive sludge of the present invention described above is effective by adding a small amount of coagulant, and can be treated by a centrifugal dewatering machine having a high treating capacity. Especially useful for.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Katsunori Tanaka 2-2-1-1, Nishigotanda, Shinagawa-ku, Tokyo Inside Hyomo Corporation (72) Inventor Toshinori Nishizono 1-1 Kurosaki Castle Stone, Yawatanishi-ku, Kitakyushu, Fukuoka Mitsubishi Kurosaki Office, Chemical Co., Ltd. (72) Koji Mori, Inventor 1000 Kamoshita-cho, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Mitsubishi Chemical Co., Ltd. Yokohama Research Laboratory (56) References JP-A-8-299999 (JP, A) JP-A Heihei JP-A 8-243600 (JP, A) JP-A 8-229600 (JP, A) JP-A 8-215700 (JP, A) JP-A 8-188699 (JP, A) JP-A 8-155500 (JP, A) A) JP-A-7-223000 (JP, A) JP-A-7-178399 (JP, A) JP-A-7-100500 (JP, A) JP-A-6-246300 (JP, A) JP-A-6 -238300 (JP, A) JP-A-6-218400 (JP, A) JP-A-6-218399 (JP, A) JP-A-5-192513 (JP, A) JP-A-8-19796 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) B01D 21/01 C02F 1/52-1/56 C02F 11/00-11/20

Claims (5)

(57) [Claims] Claims: 1. A volatile organic acid containing at least 100 mg / l.
In the coagulation treatment of putrefaction sludge having the following general formula (I)
Alternatively, the viscosity of a 0.2% aqueous solution of a cationic polymer having a structural unit represented by (II) in deionized water is 80 centipoise (measured at 25 ° C. with a B-type viscometer).
The method for treating putrefactive sludge, comprising treating the putrefaction sludge with a coagulant having a value of not less than the above, and then dewatering with a centrifugal dehydrator. Embedded image (Wherein, R ¹ and R ^{2 each} independently represent a hydrogen atom or a methyl group, and X ⁻ represents an anion.) 2. The method according to claim 1, wherein the cationic polymer is represented by the general formula (I) or (I)
The processing method according to claim 1, which comprises 35 to 90 mol% of the structural unit represented by I). 3. The treatment method according to claim 1, wherein the average residence time from the time when the septic sludge leaves the concentration tank to the time when the coagulant is mixed is 24 hours or more. 4. A method according to any one of claims 1 to 3, rotting sludge contains volatile organic acid or 300 mg / l. 5. A method according to any one of claims 1-4 sludge is mixed raw sludge or excess sludge of the sewage.