JP5038587B2 - Dewatering method for sewage digested sludge - Google Patents

Description

  The present invention relates to a method for dewatering sewage-digested sludge having excellent cohesive strength and dewaterability, high filtration speed, and excellent various coagulation and dewatering performances such that an excellent floc can be obtained.

Organic sludge generated from sewage, human waste treatment plant, organic industrial wastewater, and the like is dehydrated using a dehydrating device such as a screw press, screw decanter or belt press with the addition of a polymer flocculant.
The sludge cake after dehydration is landfilled or incinerated, but reducing the moisture content in the sludge cake by 1% can reduce the cost of about 10% of the fuel used for incineration, so the sludge cake Various studies have been conducted in order to reduce the moisture content therein.
By the way, in a sewage treatment plant, when there is much organic content contained in sludge, anaerobic treatment is made to organic sludge. In recent years, digested sludge obtained by anaerobic treatment of organic sludge has properties that are extremely difficult to dehydrate by conventional dehydration methods because of its extremely low fiber content and containing a septic sticky substance.

As a method for dewatering digested sludge, for example, polyiron sulfate is used as an inorganic flocculant, and nonionic, anionic, or cationic polymer flocculants are added alone to form a floc for dehydration (Patent Document 1). ) And after adding an inorganic flocculant, there is a method (Patent Document 2) in which the pH is adjusted to 5 to 8 and an amphoteric polymer flocculant is added thereto, but it is necessary to use a large amount of flocculant. In some cases, the cost of using the flocculant becomes high, or the sludge dewatering performance becomes insufficient.
Recently, as a method for treating digested sludge, a method using polyamidine (Patent Document 3) and a method using an inorganic flocculant and an acrylate cationic polymer flocculant in combination (Patent Document 4) are known. The former method using polyamidine is an excellent method for the sludge dewatering method due to the high cationic property of polyamidine, and the latter method using an inorganic flocculant and an acrylate-based cationic polymer flocculant in combination is also described above. It is an excellent method for the sludge dewatering method. However, the obtained floc is insufficient in terms of cohesiveness and filterability, the moisture content of the dehydrated cake is insufficient, and there is a problem that the amount of coagulant used must be increased. .

JP 58-51998 A (Claims) JP-A-63-158200 (Claims) JP-A-5-192513 (Claims) JP-A-7-214100 (Claims)

  The present inventors have intensively studied to find a method for dewatering sludge that can obtain flocs excellent in cohesiveness and filterability and can reduce the moisture content of the dewatered cake with respect to sewage digested sludge. It was.

As a result of various studies to solve the above problems, the present inventor added an inorganic flocculant and an amphoteric polymer flocculant having a specific cation equivalent and an anion equivalent to sewage digested sludge. The present invention has been completed by finding out that the above problems can be solved.
The present invention is described in detail below.
In this specification, acrylate or methacrylate is represented as (meth) acrylate, acrylamide or methacrylamide is represented as (meth) acrylamide, acrylic acid or methacrylic acid is represented as (meth) acrylic acid, acrylonitrile or methacrylonitrile. Is represented as (meth) acrylonitrile.

In the present invention, after adding an inorganic flocculant to sewage digested sludge, the cation equivalent value is 3.5 meq / g or more and the anion equivalent value is 1.0 meq / g or less , and dimethylaminoethyl (meth) acrylate 4 80 to 99.5 mol% of the grade salt monomer unit, 0.5 to 15 mol% of the (meth) acrylic acid and alkali metal salt or ammonium salt monomer unit, and the (meth) acrylamide monomer unit The present invention relates to a sludge dewatering method in which an amphoteric polymer flocculant having 0 to 19.5 mol% is added.
Hereinafter, each component requirement will be described.

1. Sewage Digested Sludge The sewage digested sludge to which the present invention can be applied is applicable to various sludges as long as the organic sludge generated at the sewage treatment plant is subjected to anaerobic digestion. There is no restriction | limiting in particular as organic sludge, Specifically, what digested mixed raw sludge of primary sedimentation sludge and excess sludge etc. are mentioned.

2. Inorganic flocculant As the inorganic flocculant, those usually used in sludge dewatering can be used. Specific examples include aluminum sulfate, polyaluminum chloride, ferric chloride, ferrous sulfate, and polyiron sulfate.

3. Amphoteric polymer flocculant In the present invention, the amphoteric polymer flocculant has a cation equivalent value (hereinafter referred to as “Cv”) of 3.5 meq / g or more and an anion equivalent value (hereinafter referred to as “Av”) of 1.0 meq. An amphoteric polymer having a / g or less (hereinafter simply referred to as an amphoteric polymer) is used.
Cv is preferably 3.8 to 5.5 meq / g, and Av is preferably 0.1 to 0.9 meq / g.
If Cv is less than 3.5 meq / g, the charge neutralization of sludge becomes insufficient, dehydration becomes insufficient, and floc granulation is insufficient, and Av exceeds 1.0 meq / g. , Floc granulation is poor, and amphoteric polymer flocculants must be used in large amounts.

  In the present invention, Cv and Av of the amphoteric polymer are values determined by the colloid titration method shown below.

1) Cv measurement
(1) Titration method Take 90 ml of deionized water in a conical beaker, add 10 ml of a 500 ppm sample solution, bring the pH to 3.0 with an aqueous hydrochloric acid solution, and stir for about 1 minute. Next, 2-3 drops of toluidine blue indicator is added and titrated with N / 400 potassium potassium sulfate reagent (hereinafter referred to as N / 400 PVSK).
The titration rate is 2 ml / min, and the end point is the time when the sample water changes from blue to magenta for 10 seconds or longer.

(2) Preparation of sample 500 ppm aqueous solution 0.2 g (not converted to dry product) of sample is precisely weighed, taken into a triangular corben with a stopper, and dissolved in 100 ml of deionized water. The 25 ml is made up with deionized water in a 100 ml volumetric flask.

(3) Calculation method

2) Measurement of Av
(1) Titration method Take 90 ml of deionized water in a conical beaker, add 10 ml of a 500 ppm sample, adjust the pH to 7.0 with aqueous caustic soda, and stir for about 1 minute. Next, 2-3 drops of toluidine blue indicator is added and titrated with N / 400 potassium potassium sulfate reagent (hereinafter referred to as N / 400 PVSK).
The titration rate is 2 ml / min, and the end point is the time when the sample water changes from blue to magenta for 10 seconds or longer.

(2) Preparation of sample 500 ppm aqueous solution 0.2 g (not converted to dry product) of sample is precisely weighed, taken into a triangular corben with a stopper, and dissolved in 100 ml of deionized water. The 25 ml is made up with deionized water in a 100 ml volumetric flask.

(3) Calculation method

As the amphoteric polymer, dimethylaminoethyl (meth) acrylate quaternary salt monomer unit is 80 to 99.5 mol% , (meth) acrylic acid and alkali metal salt or ammonium salt monomer unit is 0.5. Amphoteric polymers having ˜15 mol% and (meth) acrylamide monomer units of 0 to 19.5 mol% can be used.

The cationic monomer is a dimethylaminoethyl (meth) acrylate quaternary salt monomer .

Examples of the anionic monomer include (meth) acrylic acid and alkali metal salts such as sodium salts or ammonium salts .

As the amphoteric polymer, a nonionic monomer can be used as necessary.

There is no restriction | limiting in particular about the manufacturing method of an amphoteric polymer, A general polymerization method can be employ | adopted using the above-mentioned monomer. For example, in the case of aqueous solution polymerization, thermal radical polymerization using potassium persulfate, ammonium persulfate, 2,2′-azobis (2-amidinopropane) dihydrochloride, a redox polymerization initiator or the like as a polymerization initiator. Or radical photopolymerization by ultraviolet irradiation using a benzoin and acetophenone type photopolymerization initiator. In the case of reverse phase emulsion polymerization, the polymerization may be carried out using a water-insoluble initiator such as azobisisobutyronitrile or benzoyl peroxide in addition to the polymerization initiator.

The obtained gel polymer is then cut and chopped by a known method. The chopped polymer is dried at a temperature of about 60 to 150 ° C. using a dryer such as a band dryer, a rotary dryer, a far-infrared dryer, or a vibratory fluid dryer, and a roll mill. Etc. to obtain a powdery copolymer, and the particle size is adjusted.
As the amphoteric polymer of the present invention, a powdery product is preferably used.

The amphoteric polymer in the present invention preferably has a 0.5% salt viscosity of 10 to 120 mPa · s, which is an index of molecular weight, and more preferably 15 to 90 mPa · s in order to achieve a stable dehydration treatment.
In the present invention, 0.5% salt viscosity means that a sample obtained by dissolving 0.5% of an amphoteric polymer in a 4% sodium chloride aqueous solution at 25 ° C. using a B-type viscometer, rotor No. The value measured at 60 rpm using 1 or 2.

  As the amphoteric polymer flocculant of the present invention, in addition to the amphoteric polymer, sodium bisulfate, sodium sulfate, sulfamic acid and the like may be mixed with known additives as long as they do not adversely affect the dehydration treatment.

4). TECHNICAL FIELD The present invention is a sludge dewatering method in which an inorganic flocculant is added to sewage digested sludge and then the amphoteric polymer flocculant is added.
The flock formation method may be a known method.

  As an addition ratio with respect to the sludge of an inorganic flocculant, 500-50,000 ppm is preferable and 0.01-20 mass% is preferable with respect to TS.

In the present invention, it is preferable to adjust the pH to 4 to 8 after adding the inorganic flocculant because the sludge can be treated more effectively.
As a method for adjusting pH, after adding an inorganic flocculant, if the pH value is satisfied, pH adjustment is not particularly required, but if the range limited by the present invention is not satisfied, acid or alkali is added. Adjust.
Examples of the acid include hydrochloric acid, sulfuric acid, acetic acid and sulfamic acid. Examples of the alkali include caustic soda, caustic potash, slaked lime, and ammonia.

  The addition ratio of the amphoteric polymer flocculant to the sludge is preferably 50 to 1,000 ppm, and preferably 0.1 to 5% by mass with respect to TS. When the amphoteric polymer flocculant and other polymer flocculants described later are used in combination, it is preferable that the total amount of all the polymer flocculants satisfies the addition ratio.

  In the present invention, in addition to the inorganic flocculant and the amphoteric polymer flocculant, an organic cationic compound, a cationic polymer flocculant and an anionic polymer flocculant can be used in combination as necessary.

  Examples of organic cationic compounds include polymer polyamines, polyamidines, and cationic surfactants.

  Examples of the cationic polymer flocculant include a homopolymer of the aforementioned cationic monomer and a copolymer of the aforementioned cationic monomer and nonionic monomer.

  Examples of the anionic polymer flocculant include a homopolymer of the aforementioned anionic monomer and a copolymer of the aforementioned anionic monomer and nonionic monomer.

  The stirring speed and stirring time after adding the sludge dehydrating agent may follow the conventional dehydrating conditions.

  The flocs thus formed are dehydrated using a known means to obtain a dehydrated cake.

  Examples of the dehydrator include a screw press dehydrator, a belt press dehydrator, a filter press dehydrator, a screw decanter, and the like.

The sludge dewatering agent of the present invention can also be applied to a dewatering method using a granulation concentration tank having a filtration part.
Specifically, after adding an inorganic flocculant to the sludge and further adding a sludge dewatering agent, or together with the sludge dewatering agent, the sludge is introduced into a granulation concentration tank having a filtration part, and filtered from the filtration part. Examples include a method of taking out the liquid and granulating, and dehydrating the granulated product with a dehydrator.

  According to the sludge dewatering method of the present invention, flocs excellent in cohesiveness and filterability can be obtained with respect to sewage digested sludge, and the water content of the dewatered cake can be reduced.

The present invention, in sewage digestion sludge, after adding an inorganic flocculant, Ru dehydration process der sludge adding an amphoteric polymer flocculant comprising the amphoteric polymer.

<Examples 1 and 2 and Comparative Examples 1 and 2>
As the polymer flocculant, a monomer shown in Table 1 below was polymerized in an aqueous solution, and the resulting gel polymer was cut, chopped and dried.
In Table 1, DAC means methyl chloride quaternary salt of dimethylaminoethyl acrylate, AA means acrylic acid, and AM means acrylamide.

To 200 ml of sewage digested sludge (TS = 1.8 mass%) placed in a 300 ml beaker, 1,000 ppm of polysulfate was added and stirred at 150 rpm for 30 seconds using a stirrer. Subsequently, a 0.2% aqueous solution of a polymer flocculant shown in Table 1 was added at 200 ppm in terms of solid content, and similarly stirred for 180 seconds to produce sludge flocs, and the particle size was measured.
Thereafter, the sludge floc dispersion was gravity filtered using an 80 mesh net as a filter. The filtrate volume after 10 seconds was measured and used as the filtration rate.
The obtained cake was squeezed and dehydrated with a mini belt press (surface pressure 0.5 kg / cm, 3 stages), and the moisture content was measured. These results are shown in Table 2.

As is clear from the examples and comparative examples, the sludge dewatering method of any of the examples uses an amphoteric flocculant whose Av exceeds the range specified in the present invention (Comparative Example 1) and has an anionic group. Compared with the cationic polymer flocculant that does not (Comparative Example 2), the floc particle size is large, the filtration rate is excellent, and the water content is also reduced.

The sludge dewatering method of the present invention is useful as a method for dewatering sewage digested sludge.

Claims (1)

After adding an inorganic flocculant to the sewage digestion sludge that has been subjected to anaerobic digestion treatment of organic sludge generated at a sewage treatment plant, the cation equivalent value is 3.5 meq / g or more and the anion equivalent value is 1.0 meq / g or less. 80 to 99.5 mol% of dimethylaminoethyl (meth) acrylate quaternary salt monomer units based on all constituent monomer units, (meth) acrylic acid and alkali metals thereof Adding an amphoteric polymer flocculant composed of an amphoteric polymer having a salt or ammonium salt monomer unit of 0.5 to 15 mol% and a (meth) acrylamide monomer unit of 0 to 19.5 mol%. Characterized sludge dewatering method.