Method for treating organic sludge, apparatus for treating organic sludge, and coagulant for dewatering organic sludge.

Abstract

The present invention provides a method for treating organic sludge, an organic sludge treatment apparatus, and a flocculant for dewatering organic sludge, which can produce a dewatered cake with low water content and excellent handling properties using bio-derived raw materials. [Solution] This method for treating organic sludge involves adding a coagulant to organic sludge to form flocculated flocs, followed by dewatering. The method involves adding a coagulant containing a chitosan-based coagulant to the organic sludge such that the ratio of the colloidal charge of the coagulant to the absolute value of the colloidal charge of the organic sludge is 0.50 to 5.00, and then performing dewatering to produce separated water with a colloidal charge of -0.30 to 1.40 meq / L and a dewatered cake.

Description

Technical Field

[0005]

[0001] The present invention relates to a method for treating organic sludge, an apparatus for treating organic sludge, and a flocculant for dehydrating organic sludge.

Background Art

[0002] Organic sludge generated from sewage treatment plants, sewage treatment plants, or industrial wastewater treatment facilities is dehydrated into dehydrated cakes and then transported to landfill disposal sites, incinerators, or cement factories for reuse purposes. In recent years, it has become more common to dry the dehydrated cake, compost it, and then return it to agricultural land as organic fertilizer.

[0003] [[ID=1​​​​​​​​​​​​​​​​​​ [Patent Document 2] Japanese Patent Application Publication No. 58-58200 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, as described in Patent Documents 1 and 2, the use of chitosan alone as a flocculant in the flocculation treatment of activated sludge and organic sludge has been considered to result in insufficient floc strength and limited dewatering effect. For this reason, Patent Documents 1 and 2 describe a two-agent treatment method using chitosan in combination with a basic metal chloride salt or anionic polymer that has the opposite charge to chitosan.

[0007] On the other hand, as mentioned above, from the perspective of safety for agricultural products, there is a growing demand for dehydrated cakes that contain as few metal salts and organic polymer flocculants as possible, as described in Patent Documents 1 and 2. If it is possible to obtain a dehydrated cake with low water content and excellent handling properties using bio-derived raw materials such as chitosan-based flocculants, it would be useful from the perspective of effective utilization of the dehydrated cake, including its return to farmland.

[0008] In view of the above issues, the present invention aims to provide a method for treating organic sludge, an organic sludge treatment apparatus, and a flocculant for dewatering organic sludge, which can produce a dewatered cake with low water content and excellent handling properties using biologically derived raw materials. [Means for solving the problem]

[0009] As a result of diligent research to solve the above problems, the inventors of this invention have found that adding a chitosan-based flocculant to organic sludge under specific conditions is useful.

[0010] In one aspect, the present invention relates to a method for treating organic sludge, in which a coagulant is added to organic sludge to form flocculated flocs, followed by dewatering. The method involves adding a coagulant containing a chitosan-based coagulant to the organic sludge such that the ratio of the colloidal charge of the coagulant to the absolute value of the colloidal charge of the organic sludge is 0.50 to 5.00, and then performing dewatering to produce separated water with a colloidal charge of -0.30 to 1.40 meq / L and a dewatered cake.

[0011] In one embodiment of the organic sludge treatment method according to the present invention, a chitosan-based flocculant with a 1% salt viscosity of 50 to 1500 mPa·s is used.

[0012] In another embodiment of the organic sludge treatment method according to the present invention, a chitosan-based flocculant containing 0.01 to 5.0% by weight of chitosan is used.

[0013] In yet another embodiment of the method for treating organic sludge according to the present invention, the coagulant further comprises a cationic polymer coagulant other than a chitosan-based coagulant.

[0014] In yet another embodiment of the organic sludge treatment method according to the present invention, the organic sludge is digested sludge generated from a sewage treatment plant.

[0015] In another aspect, the present invention is an organic sludge treatment apparatus comprising: a means for adding a chitosan-based flocculant to organic sludge as a flocculant; a flocculation treatment tank for mixing the organic sludge and the chitosan-based flocculant to form flocculated flocs; a dewatering means for dewatering the flocculated water obtained in the flocculation treatment tank to produce separated water with a colloidal charge of -0.30 to 1.40 meq / L and a dewatered cake; and a control means for controlling the amount of flocculant added to the organic sludge so that the ratio of the colloidal charge of the flocculant to the absolute value of the colloidal charge of the organic sludge is 0.50 to 5.00.

[0016] In yet another aspect, the present invention provides a flocculant for dehydrating organic sludge, which contains chitosan, has a 1% salt viscosity of 1000 to 1500 mPa·s, and has a ratio of the colloid charge amount of the flocculant to the absolute value of the colloid charge amount of the organic sludge of 2.00 to 5.00, and is added to the organic sludge.

[0017] In yet another aspect, the present invention provides a flocculant for dehydration treatment, which contains chitosan, has a 1% salt viscosity of 100 to 1000 mPa·s, and has a ratio of the colloid charge amount of the flocculant to the absolute value of the colloid charge amount of the organic sludge of 2.00 to 4.50, and is added to the organic sludge.

[0018] In yet another aspect, the present invention provides a flocculant for dehydrating organic sludge, which contains chitosan, has a 1% salt viscosity of 50 to 100 mPa·s, and has a ratio of the colloid charge amount of the flocculant to the absolute value of the colloid charge amount of the organic sludge of 0.70 to 4.50, and is added to the organic sludge.

Advantages of the Invention

[0019] According to the present invention, there are provided a method for treating organic sludge, a device for treating organic sludge, and a flocculant for dehydrating organic sludge, which can produce a dehydrated cake with low water content and excellent handleability using bio-derived raw materials.

Brief Description of the Drawings

[0020] [Figure 1] It is a schematic diagram for explaining an example of a device for treating organic sludge according to an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0021] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this specification, the “%” indication regarding components means weight % unless otherwise specified.

[0022] (Method for Treating Organic Sludge) The method for treating organic sludge according to an embodiment of the present invention is a method for treating organic sludge in which a flocculant is added to the organic sludge to form flocculated flocs and then dewatering treatment is performed. A flocculant containing a chitosan-based flocculant is added to the organic sludge so that the ratio of the colloid charge amount of the flocculant to the absolute value of the colloid charge amount of the organic sludge is 0.50 to 5.00. By the dewatering treatment, separated water having a colloid charge amount of -0.30 to 1.40 meq / L and a dewatered cake are generated.

[0023] Examples of the organic sludge include primary sewage sludge, excess sewage sludge, or mixed raw sludge obtained by mixing primary sewage sludge and excess sewage sludge, digested sewage sludge, excess sludge in manure treatment, coagulated sedimentation sludge, septic tank sludge, raw manure, or mixtures thereof, and sludge generated by treating industrial wastewater. As the organic sludge, sludge after treatment by the activated sludge method, sludge generated from pulp waste liquid, sludge generated from food processing factories, etc. can also be used. In particular, in the present embodiment, digested sludge generated from a sewage treatment plant known as difficult-to-dewater sludge is preferably used.

[0024] The organic sludge has, for example, a pH of 3.0 to 11.0, preferably 4.0 to 10.0, more preferably 5.0 to 9.0, and still more preferably 6.0 to 8.0. The evaporation residue (TS) of the organic sludge is generally about 0.5 to 50.0 g / L, preferably 2.0 to 40.0 g / L, more preferably 4.0 to 30.0 g / L, and still more preferably 5.0 to 20.0 g / L.

[0025] The organic sludge is not limited thereto, but typically has a colloid charge amount of -10.00 to 0.50 meq / L. The colloid charge amount of the organic sludge is preferably -8.00 to 0.50 meq / L, more preferably -5.00 to 0.10 meq / L, and still more preferably -2.00 to 0.00 meq / L.

[0026] In the method for treating organic sludge according to an embodiment of the present invention, a chitosan-based flocculant containing chitosan is used as a bio-derived raw material. The chitosan used in the chitosan-based flocculant is obtained by deacetylating chitin present in crustaceans such as crabs and shrimps. When deacetylating, chitosan-based flocculants having various acetylation rates and viscosities can be produced by adjusting the concentration of caustic soda, the reaction temperature, and the reaction time.

[0027] From the viewpoint of handling properties, it is preferable to use powdered (flake-shaped) chitosan as the chitosan used in the chitosan-based flocculant. Although not limited to the following, chitosan powder having a particle size of 3.0 mm or less and an ash content of 2.0% or less is preferably used as the chitosan raw material constituting the chitosan-based flocculant.

[0028] The chitosan-based flocculant preferably contains 0.01 to 5.0% of chitosan, more preferably 0.1 to 5.0%, still more preferably 0.1 to 3.0%, and even more preferably 0.2 to 2.0%. If the chitosan concentration in the chitosan-based flocculant is too high, dissolution may become difficult. If the chitosan concentration in the chitosan-based flocculant is too low, it may be difficult to appropriately control the floc diameter and the sedimentation rate of the flocs when mixed with organic sludge.

[0029] Chitosan itself is insoluble in water, but by treating it with an acid or dissolving it in an acid solution, a chitosan salt is formed and it becomes a solution state. Examples of the acid include formic acid, acetic acid, propionic acid, maleic acid, benzoic acid, tartaric acid, malic acid, citric acid, lactic acid, sulfamic acid, hydrochloric acid, nitric acid, and the like.

[0030] The 1% salt viscosity of the chitosan-based flocculant is preferably about 50 to 1500 mPa·s, more preferably 60 to 1300 mPa·s, and even more preferably 100 to 200 mPa·s. When the 1% salt viscosity of the chitosan-based flocculant is less than 50 mPa·s, a sufficient cross-linking effect cannot be obtained, and it may be difficult to form large flocs with good dehydration properties. When the 1% salt viscosity of the chitosan-based flocculant exceeds 1500 mPa·s, the flocs formed by the flocculation treatment or the separated water obtained by the dehydration treatment may become viscous. As a result, the flocs and the separated water may clog the pipes. In this embodiment, the 1% salt viscosity indicates the value measured at a temperature of 25°C using a B-type rotational viscometer with a spindle rotor at a rotational speed of 30 to 60 rpm for the chitosan-based flocculant.

[0031] In the method for treating organic sludge according to the embodiment of the present invention, the addition of the flocculant is controlled so that the ratio of the colloidal charge amount of the flocculant to the absolute value of the colloidal charge amount of the organic sludge falls within a predetermined range. Specifically, the ratio of the colloidal charge amount of the flocculant to the absolute value of the colloidal charge amount of the organic sludge, that is, the ratio of "(colloidal charge amount of the flocculant) / (absolute value of the colloidal charge amount of the organic sludge)" (hereinafter also referred to as "colloidal charge ratio") is 0.50 to 5.00, and a flocculant containing a chitosan-based flocculant is added to the organic sludge.

[0032] Organic sludge is mainly negatively charged, and by adding a positively charged flocculant, charge neutralization occurs, making it easier to aggregate as flocs. In the case of a flocculant using a bio-derived raw material such as a chitosan-based flocculant, it is difficult to easily form strong flocs that are good for the dehydration treatment of organic sludge. However, by performing the dehydration treatment with the above colloidal charge ratio, it becomes possible to produce a dehydrated cake with a low moisture content and excellent handling properties.

[0033] The colloidal charge ratio is preferably 1.20 to 4.50, more preferably 2.00 to 4.00, and even more preferably 2.30 to 3.80.

[0034] For example, when adding a high-viscosity chitosan-based flocculant with a 1% salt viscosity of 1000 to 1500 mPa·s to organic sludge, it is preferable to add the flocculant to the organic sludge so that the colloidal charge ratio is 2.00 to 5.00, more preferably 2.30 to 4.60, and even more preferably 4.00 to 4.50.

[0035] For example, when adding a medium-viscosity chitosan-based flocculant with a 1% salt viscosity of 100 to 1000 mPa·s, more typically 100 to 200 mPa·s, to organic sludge, it is preferable to add the flocculant to the organic sludge so that the colloidal charge ratio is 2.00 to 4.50, more preferably 2.50 to 4.30, and even more preferably 3.00 to 3.80.

[0036] For example, when adding a medium-viscosity chitosan-based flocculant with a 1% salt viscosity of 80 to 150 mPa·s to organic sludge, it is preferable to add the flocculant to the organic sludge so that the colloidal charge ratio is 3.00 to 4.00, and more preferably 3.20 to 3.80.

[0037] Using a chitosan-based flocculant alone is preferable from the viewpoint of simplifying the equipment, improving efficiency, and ensuring safety for agricultural land conversion. On the other hand, it is also preferable to use a cationic polymer flocculant other than a chitosan-based flocculant in combination with a chitosan-based flocculant, to the extent that the objectives of the present invention can be achieved.

[0038] For example, when adding a flocculant (mixture) containing a chitosan-based flocculant and a cationic polymer flocculant other than the chitosan-based flocculant, with a 1% salt viscosity of 50 to 100 mPa·s, to organic sludge, it is preferable to set the colloidal charge ratio of the mixture to 0.70 to 4.00. The mixing ratio of the chitosan-based flocculant to the flocculant containing the cationic polymer flocculant other than the chitosan-based flocculant can be 70:30 to 95:5, and is more preferably 80:20 to 90:10.

[0039] In addition to chitosan-based flocculants, cationic polymer flocculants that have a cationic monomer as an essential component and consist of a homopolymer or copolymer of cationic monomers, or a copolymer of a cationic monomer and a nonionic monomer, cationic polymer flocculants having a crosslinking structure within the molecule, and cationic polymer flocculants having amidine units within the molecule can be preferably used.

[0040] Examples of cationic monomers include acrylate monomers or methacrylate monomers, various acrylamide compounds or methacrylamide compounds, their neutralized salts, and quaternaries.

[0041] Examples of acrylate monomers and methacrylate monomers include dimethylamino(methyl, ethyl, propyl, or butyl) acrylate or methacrylate, diethylamino(methyl, ethyl, propyl, or butyl) acrylate or methacrylate, di-n-propylamino(methyl, ethyl, propyl, or butyl) acrylate or methacrylate, diisopropylamino(methyl, ethyl, propyl, or butyl) acrylate or methacrylate, di-n-butylamino(methyl, ethyl, propyl, or butyl) acrylate or methacrylate, di-sec-butylamino(methyl, ethyl, propyl, or butyl) acrylate or methacrylate, and diisobutylamino(methyl, ethyl, propyl, or butyl) acrylate or methacrylate.

[0042] Examples of acrylamide compounds or methacrylamide compounds include dimethylamino(methyl, ethyl, propyl, or butyl) acrylamide or methacrylamide, diethylamino(methyl, ethyl, propyl, or butyl) acrylamide or methacrylamide, di-n-propylamino(methyl, ethyl, propyl, or butyl) acrylamide or methacrylamide, diisopropylamino(methyl, ethyl, propyl, or butyl) acrylamide or methacrylamide, di-n-butylamino(methyl, ethyl, propyl, or butyl) acrylamide or methacrylamide, di-sec-butylamino(methyl, ethyl, propyl, or butyl) acrylamide or methacrylamide, and diisobutylamino(methyl, ethyl, propyl, or butyl) acrylamide or methacrylamide.

[0043] Examples of the neutralized salts mentioned above include salts produced by hydrogen halides, sulfuric acid, nitric acid, and acetic acid. Examples of quaternaries include quaternaries produced by alkyl halides, benzyl halides, dimethyl sulfate, and diethyl sulfate.

[0044] Furthermore, cationic polymer flocculants having a crosslinked structure can also be used. Cationic polymer flocculants having a crosslinked structure can be produced by using a crosslinking agent in combination during polymerization. Examples of crosslinking agents include N,N'-methylenebis(meth)acrylamide, triallylamine, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, divinyl compounds such as divinylbenzene, vinyl-based methylol compounds such as methylolmethacrylamide, vinyl-based aldehyde compounds such as acrolein, and vinyl compounds such as methylacrylamide glycolate methyl ether. It is preferable to blend the crosslinking agent in a proportion of 0.0005 to 0.003% by weight relative to the total amount of monomer.

[0045] Furthermore, cationic polymer flocculants having the amidine structure shown in the following general formulas (1) and (2) can also be used.

[0046] [ka]

[0047] [ka]

[0048] For example, in this embodiment, an acrylamide-dimethylaminoethyl acrylate copolymer with a molecular weight of 1.5 million to 15 million can be preferably used as a cationic polymer flocculant.

[0049] Furthermore, to the extent that the objectives of the present invention can be achieved, it is also preferable to use amphoteric polymer flocculants other than chitosan-based flocculants in combination with chitosan-based flocculants. Examples of amphoteric polymer flocculants include polymers obtained by copolymerizing vinyl-based cationic monomer units, vinyl-based anionic monomer units, and vinyl-based nonionic monomer units within the molecule. Examples of vinyl-based cationic monomers copolymerized with anionic or nonionic monomers include neutralized salts represented by the above general formula (1), or quaternary compounds. One of these vinyl-based cationic monomers may be used, or two or more may be used in combination.

[0050] Examples of vinyl anionic monomers include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, vinyl sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid, 2-acrylamidoethanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamidoethanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, 2-acryloyloxyethanesulfonic acid, 3-acryloyloxypropanesulfonic acid, 4-acryloyloxybutanesulfonic acid, 2-methacryloyloxyethanesulfonic acid, 3-methacryloyloxypropanesulfonic acid, 4-methacryloyloxybutanesulfonic acid, and metal salts or ammonium salts of these, such as alkali metals and alkaline earth metals. These anionic monomers may be used individually or in combination of two or more.

[0051] Suitable vinyl-based nonionic monomers for copolymerization include (meth)acrylamide, (meth)acrylic acid esters, (meth)acronitrile, and vinyl acetate, with acrylamide being particularly desirable. Cationized starch, cationized cellulose, and cationized guar gum can also be used.

[0052] The mixing ratio of the chitosan-based flocculant to the cationic polymer flocculant described above can be arbitrarily adjusted depending on the sludge properties and the dewatering machine used. For example, the mixing ratio of the chitosan-based flocculant to the cationic polymer flocculant or amphoteric polymer flocculant is preferably 10% or more, more preferably 50% or more, and more preferably 70% or more.

[0053] The chitosan-based flocculant and the cationic polymer flocculant may be mixed together during dissolution, or they may be dissolved separately and then mixed with organic sludge simultaneously or sequentially to induce flocculation.

[0054] It is also possible to floccate organic sludge by using a chitosan-based flocculant according to an embodiment of the present invention, or by using a chitosan-based flocculant in combination with a cationic polymer flocculant other than a chitosan-based flocculant, and then to form flocculated flocs using known anionic or nonionic polymer flocculants.

[0055] Examples of anionic polymer flocculants include polyacrylamide partial hydrolysates, copolymers of anionic monomers, and copolymers of anionic monomers with nonionic monomers such as acrylamide. Examples of anionic monomers include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, vinyl sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid, 2-allylamide ethanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methallylamide ethanesulfonic acid, 2-methacrylamide-2-methylpropanesulfonic acid, 2-acryloyloxyethanesulfonic acid, 3-acryloyloxypropanesulfonic acid, 4-acryloyloxybutanesulfonic acid, 2-methacryloyloxyethanesulfonic acid, 3-methacryloyloxypropanesulfonic acid, 4-methacryloyloxybutanesulfonic acid, and their alkali metal, alkaline earth metal, or ammonium salts. These anionic monomers may be used individually or in combination of two or more. Examples of nonionic monomers include acrylamide, methacrylamide, methacrylonitrile, and vinyl acetate. These nonionic monomers may be used individually or in combination of two or more.

[0056] Preferred copolymers are acrylamide-acrylate copolymers and acrylamide-2-acrylamido-2-methylpropanesulfonic acid copolymers. Carboxymethylcellulose and sodium alginate can also be used. Nonionic polymer flocculants are polymers or copolymers of the above nonionic monomers, but polyacrylamide is preferred.

[0057] After adding the above-mentioned coagulant to the organic sludge, a dewatering treatment is performed to obtain separated water and dewatered cake. From an efficiency standpoint, mechanical dewatering using, for example, a dewatering machine equipped with a concentration section and a dewatering section is more preferable.

[0058] By appropriately controlling the colloidal charge of the separated water obtained by the dehydration process, the dehydration effect of adding a coagulant can be guaranteed, and a dehydrated cake with low moisture content and excellent handling properties can be obtained. The appropriate range for the colloidal charge of the separated water obtained by the dehydration process is -0.30 to 1.40 meq / L, preferably -0.18 to 1.30 meq / L, more preferably -0.15 to 0.10 meq / L, and even more preferably -0.14 to -0.01 meq / L. If the colloidal charge of the separated water is less than -0.30 meq / L, the chitosan-based coagulant will be insufficient, resulting in poor dehydration and making it difficult to obtain a dehydrated cake with low moisture content and excellent handling properties. If the colloidal charge of the separated water exceeds 1.40 meq / L, the chitosan-based coagulant will be in excess, worsening the dehydration situation and making it difficult to obtain a dehydrated cake with excellent handling properties.

[0059] In mechanical dewatering treatment, an inorganic flocculant or an organic polymer flocculant may be added during or after the concentration process of the organic sludge before dewatering in order to improve the dewatering effect. As inorganic flocculants, known aluminum sulfate, polyaluminum chloride (PAC), polyferric sulfate (polyferric iron), ferric chloride, or mixtures thereof can be used.

[0060] Examples of organic polymer flocculants include condensed polyamines, dicyandiamide-formaldehyde condensates, polyethyleneimines, polyvinylimidalins, polyvinylpyridines, diallylamine salt-sulfur dioxide copolymers, polydimethyldiallylammonium salts, polydimethyldiallylammonium salt-sulfur dioxide copolymers, polydimethyldiallylammonium salt-acrylamide copolymers, polydimethyldiallylammonium salt-diallylamine hydrochloride derivative copolymers, and allylamine salt polymers.

[0061] Examples of condensation polyamines include condensates of alkylenedichlorides and alkylene polyamines, condensates of aniline and formalin, condensates of alkylenediamines and epichlorohydrin, and condensates of ammonia and epichlorohydrin. Examples of alkylenediamines that condense with epichlorohydrin include dimethylamine, diethylamine, methylpropylamine, methylbutylamine, and dibutylamine.

[0062] According to the organic sludge treatment method of the embodiment of the present invention, a dewatered cake with a water content of 85.0% or less, more preferably 84.5% or less, even more preferably 84.0% or less, and even more preferably 83.0% or less, can be obtained, which has good detachability and excellent handling properties. Since this dewatered cake uses a flocculant made from biological raw materials, mainly chitosan-based flocculants, it can be effectively used as compost with higher safety for agricultural crops compared to conventional dewatered cakes.

[0063] (Organic sludge treatment device) As shown in Figure 1, an organic sludge processing apparatus according to an embodiment of the present invention comprises: a flocculant adding means 1 for adding a chitosan-based flocculant to organic sludge as a flocculant; a flocculation treatment tank 2 for mixing the organic sludge and the chitosan-based flocculant to form flocculated flocs; a dewatering means 3 for dewatering the flocculated water obtained in the flocculation treatment tank 2 to produce separated water with a colloidal charge of -0.30 to 1.40 meq / L and a dewatered cake; and a control means 4.

[0064] From the coagulant adding means 1, a coagulant containing the chitosan-based coagulant described above is added to the organic sludge. The coagulant adding means 1 may add the coagulant to the organic sludge in the coagulation treatment tank 2, or it may add the coagulant via an injection point such as a pipe that supplies the organic sludge. The dewatering means 3 can typically be composed of a dewatering machine equipped with a concentration section and a dewatering section. In the dewatering means 3, the coagulation treatment water is separated into dewatered cake and separated water.

[0065] The control means 4 controls the amount of coagulant added to the organic sludge based on the measured colloidal charge of the organic sludge and the measured colloidal charge of the coagulant, so that the ratio of the colloidal charge of the coagulant to the absolute value of the colloidal charge of the organic sludge is between 0.50 and 5.00. The colloidal charge of the organic sludge and the coagulant can be measured using a method based on the sewage testing method. The colloidal charge of the organic sludge is measured by sampling the organic sludge at predetermined intervals. Based on the measurement results, the control means 4 controls the amount of coagulant added so that the ratio of the colloidal charge of the coagulant to the absolute value of the colloidal charge of the organic sludge is within an appropriate range.

[0066] According to the organic sludge processing apparatus according to an embodiment of the present invention, the control means 4 controls the ratio of the colloidal charge of the coagulant to the absolute value of the colloidal charge of the organic sludge to be appropriate. Therefore, regardless of fluctuations in the properties of the organic sludge, it is possible to stably produce a dewatered cake with low water content and excellent handling properties using biologically derived raw materials.

[0067] (Coagulant for dewatering organic sludge) The coagulant for dewatering organic sludge according to an embodiment of the present invention is a chitosan-based coagulant that contains chitosan, has a 1% salt viscosity of 50 to 1500 mPa·s, and is added to organic sludge such that the ratio of the colloidal charge of the coagulant to the absolute value of the colloidal charge of the organic sludge is 0.50 to 5.00.

[0068] The chitosan-based flocculant preferably contains 0.01 to 5.0% chitosan, more preferably 0.1 to 5.0%, even more preferably 0.1 to 3.0%, and even more preferably 0.2 to 2.0%. The 1% salt viscosity of the chitosan-based flocculant is preferably 50 to 1500 mPa·s, more preferably 60 to 1300 mPa·s, and even more preferably 100 to 200 mPa·s.

[0069] Chitosan-based flocculants can be prepared, for example, by dissolving powdered chitosan with a particle size of 3.0 mm or less, an ash content of 2.0% or less, a viscosity of 5.0 mPa·s to several thousand mPa·s in a 0.5-1.0% solution at 20°C, and a degree of deacetylation of 95% or more, in the above-mentioned acid or acidic solution, and then diluting it with water to adjust it to a predetermined chitosan concentration.

[0070] In one embodiment, the coagulant for dewatering organic sludge according to the embodiment of the present invention is a chitosan-containing chitosan-based coagulant that is added to organic sludge such that the 1% salt viscosity is 1000 to 1500 mPa·s, more preferably 1200 to 1300 mPa·s, and the ratio of the colloidal charge of the coagulant to the absolute value of the colloidal charge of the organic sludge is 2.00 to 5.00, preferably 2.30 to 4.60, more preferably 4.00 to 4.50.

[0071] In another embodiment, the coagulant for dewatering organic sludge according to an embodiment of the present invention is a chitosan-containing chitosan-based coagulant that is added to organic sludge such that the 1% salt viscosity is 100 to 1000 mPa·s, more preferably 100 to 200 mPa·s, more preferably 120 to 170 mPa·s, and the ratio of the colloidal charge of the coagulant to the absolute value of the colloidal charge of the organic sludge is 2.00 to 4.50, preferably 2.50 to 4.30, more preferably 3.00 to 3.80.

[0072] In yet another embodiment, the coagulant for dewatering organic sludge according to the embodiment of the present invention is a chitosan-containing chitosan-based coagulant that is added to organic sludge such that the ratio of the colloidal charge of the coagulant to the absolute value of the colloidal charge of the organic sludge is 2.00 to 4.50, preferably 2.50 to 4.10.

[0073] In yet another embodiment, the coagulant for dewatering organic sludge according to the embodiment of the present invention is a chitosan-based coagulant containing chitosan, which is added to organic sludge such that the 1% salt viscosity is 50 to 100 mPa·s, more preferably 60 to 90 mPa·s, and the ratio of the colloidal charge of the coagulant to the absolute value of the colloidal charge of the organic sludge is 0.70 to 4.50, preferably 0.70 to 4.10.

[0074] According to the coagulant for dewatering organic sludge according to an embodiment of the present invention, it is possible to stably produce a dewatered cake with a low water content and excellent handling properties from organic sludge using biologically derived raw materials.

[0075] Although the present invention has been described by the embodiments described above, the descriptions and drawings that constitute part of this disclosure should not be understood as limiting the invention. This disclosure is not limited to the embodiments described above, and its components can be combined and modified to embody it without departing from its spirit. [Examples]

[0076] Examples of the present invention are shown below along with comparative examples. These examples are provided to help you better understand the present invention and its advantages, and are not intended to limit the invention.

[0077] (Examples 1-5) 200 mL of digested sludge (pH: 7.7, TS: 10.5 g / L, colloidal charge: -0.89 meq / L) generated from a sewage treatment plant was placed in a 300 mL beaker, and chitosan-based coagulants (chitosan A, chitosan B, chitosan C) consisting of a 0.2% chitosan aqueous solution were added in the colloidal charge ratios shown in Table 1. Chitosan A and B were prepared by dissolving chitosan powder in sulfamic acid. Chitosan C was prepared by dissolving chitosan powder in hydrochloric acid. The mixture was stirred at 700 rpm for 10 seconds using a commercially available hand mixer to generate flocculated sludge. After visually measuring the size of the flocculated sludge, the flocculated sludge was gravity-dewatered using a cylindrical filter (filter section 70 mmφ polyester filter cloth). The sludge after gravity filtration was sandwiched between two filter cloths and compressed at a pressure of 2 kg / cm for 2 minutes using a piston-type dewatering machine to obtain separated water and dewatered cake. The results are shown in Table 1.

[0078] (Examples 6-8) 200 mL of digested sludge, similar to that used in Examples 1-5, was placed in a 300 mL beaker. Chitosan B and the powder of cationic polymer flocculant X (acrylamide-dimethylaminoethyl acrylate copolymer (molecular weight 5.5 million)) were prepared in the proportions shown in Table 1. A mixture dissolved in 0.2% of the prepared powder was added as a flocculant at the colloidal charge ratio shown in Table 1. The same treatment as in Examples 1-5 was carried out to obtain separated water and dehydrated cake. The results are shown in Table 1.

[0079] [Table 1]

[0080] (1% salt viscosity) The 1% salt viscosity was measured for chitosan-based flocculants (Chitosan A, Chitosan B, Chitosan C) and a mixture of chitosan-based flocculants and cationic polymer flocculants (X:B) using a Type B rotational viscometer (TVB-10 viscometer, manufactured by Toki Sangyo Co., Ltd.) at a temperature of 25°C with a predetermined spindle rotor. Chitosan A was measured using a spindle rotor (No. 1 rotor, manufactured by Toki Sangyo Co., Ltd.) at a rotation speed of 30 rpm. Chitosan B and C were measured using a spindle rotor (No. 2 rotor, manufactured by Toki Sangyo Co., Ltd.) at a rotation speed of 30 rpm. The mixture (X:B) was measured using a spindle rotor (No. 1 rotor, manufactured by Toki Sangyo Co., Ltd.) at a rotation speed of 60 rpm.

[0081] (Colloidal charge) The colloidal charge of organic sludge and the separated water after dewatering was measured according to the method described in Section 15, Dewatering Evaluation, of the Sewage Testing Methods (2012 Edition). First, 10 mL of the sample was placed in a 200 mL beaker and 90 mL of pure water was added. Next, 2 mL of N / 400 methyl glycol chitosan (PVSK) solution was added and stirred. Then, 1 to 2 drops of toluidine blue were added to the sample solution and titrated with N / 400 PVSK solution, with the endpoint being the point at which the color of the sample solution changed from blue to reddish-purple. The colloidal charge of the coagulant was measured similarly according to the method described in Section 15, Dewatering Evaluation, of the Sewage Testing Methods (2012 Edition). First, 1 g of 0.5% coagulant solution was placed in a 100 mL beaker and 69 g of pure water was added. Next, the pH of the coagulant solution was adjusted to 4.0, and 1-2 drops of toluidine blue were added. The solution was then titrated with N / 400 PVSK solution while stirring. The endpoint was defined as the point at which the solution changed color from blue to reddish-purple.

[0082] (Colloidal charge ratio) The colloidal charge ratio was evaluated using the formula "(colloidal charge of coagulant) / (absolute value of colloidal charge of organic sludge)" relative to the absolute value of the colloidal charge of organic sludge.

[0083] (Cake release properties) The cake detachability of the dewatered cake was evaluated based on the state of the dewatered cake after the sludge following gravity filtration was sandwiched between two filter cloths and compressed for 2 minutes at a pressure of 2 kg / cm using a piston-type dewatering machine, according to the following criteria. ◎: The entire amount of dewatered cake is attached to one of the two filter cloths. ○: Dehydrated cake is adhering to two filter cloths in a ratio of 9:1 to 7:3. △: Dehydrated cake is adhering to two filter cloths in a ratio of 6:4 or 5:5. ×: The dehydrated cake is evenly distributed across the two filter cloths.

[0084] (Cake moisture content) The moisture content of the dehydrated cake was determined by taking 25.0 g of dehydrated cake in an evaporating dish, drying it in a forced-air constant-temperature dryer (Toyo Seisakusho Co., Ltd., DRM620DE) at 105°C for 12 to 24 hours, and then allowing it to cool in a desiccator for 30 minutes before weighing it. The moisture content of the cake was calculated by subtracting the weight after drying from the amount of sample before drying.

[0085] As shown in Table 1, in all of Examples 1 to 8, flocs with a diameter of 1.5 mm or more were appropriately formed during the flocculation process, and the cake moisture content was reduced to 85.0% or less.

[0086] (Examples 9-15, Comparative Examples 1-5) 200 mL of digested sludge (pH: 7.6, TS: 11.6 g / L, colloidal charge: -0.95 meq / L) generated from a sewage treatment plant was placed in a 300 mL beaker. A chitosan-based flocculant (chitosan A, chitosan B, chitosan C) consisting of a 0.2% chitosan aqueous solution and a powder of chitosan B and cationic polymer flocculant X (acrylamide-dimethylaminoethyl acrylate copolymer (molecular weight 5.5 million)) were prepared in the proportions shown in Table 2, and the mixture dissolved in 0.2% solution was added as a flocculant in the colloidal charge ratio shown in Table 2. The mixture was stirred at 700 rpm for 10 seconds using a commercially available hand mixer to generate flocculated flocs. After visually measuring the size of the flocculated flocs, the flocculated sludge was dewatered by gravity using a cylindrical filter (filter section 70 mmφ polyester filter cloth). The sludge after gravity filtration was sandwiched between two filter cloths and compressed at a pressure of 2 kg / cm for 2 minutes using a piston-type dewatering machine to obtain separated water and dewatered cake. The results are shown in Table 2.

[0087] [Table 2]

[0088] In all of Examples 9 to 15, flocs with a diameter of 2 mm or more were properly formed during the flocculation process, and the cake moisture content was kept below 85.0%. On the other hand, in Comparative Examples 1 to 5, where the colloidal charge of the separated water was not within an appropriate range, flocculation was not properly formed, making dewatering difficult. [Explanation of Symbols]

[0089] 1: Method for adding a flocculant 2: Coagulation treatment tank 3: Dehydration means 4: Control means

Claims

1. In a method for treating organic sludge, in which a coagulant is added to organic sludge to form coagulated flocs, and then dewatering is performed, A flocculant containing a chitosan-based flocculant is added to the organic sludge such that the ratio of the colloidal charge of the flocculant to the absolute value of the colloidal charge of the organic sludge is 0.50 to 5.

00. A method for treating organic sludge, characterized in that the dewatering treatment generates separated water with a colloidal charge of -0.30 to 1.40 meq / L and a dewatered cake.

2. The method for treating organic sludge according to claim 1, characterized in that a chitosan-based flocculant having a 1% salt viscosity of 50 to 1500 mPa·s is used.

3. The method for treating organic sludge according to claim 2, characterized in that the chitosan-based flocculant containing 0.01 to 5.0% by weight of chitosan is used.

4. The method for treating organic sludge according to any one of claims 1 to 3, characterized in that the flocculant further comprises a cationic polymer flocculant other than the chitosan-based flocculant.

5. The method for treating organic sludge according to any one of claims 1 to 3, characterized in that the organic sludge is digested sludge generated from a sewage treatment plant.

6. A method for adding a coagulant to organic sludge, which involves adding a chitosan-based coagulant as a coagulant, A flocculation treatment tank for mixing the aforementioned organic sludge and the aforementioned chitosan-based flocculant to form flocculated flocs, A dewatering means for dewatering the coagulated water obtained in the aforementioned coagulation treatment tank to produce separated water with a colloidal charge of -0.30 to 1.40 meq / L and a dewatered cake, A control means for controlling the amount of coagulant added to the organic sludge such that the ratio of the colloidal charge of the coagulant to the absolute value of the colloidal charge of the organic sludge is 0.50 to 5.

00. An organic sludge treatment apparatus characterized by comprising the following:

7. It contains chitosan and has a 1% salt viscosity of 1000 to 1500 mPa·s. A coagulant for dewatering organic sludge, characterized in that it is added to the organic sludge such that the ratio of the colloidal charge of the coagulant to the absolute value of the colloidal charge of the organic sludge is 2.00 to 5.

00.

8. It contains chitosan and has a 1% salt viscosity of 100 to 1000 mPa·s. A coagulant for dewatering organic sludge, characterized in that it is added to the organic sludge such that the ratio of the colloidal charge of the coagulant to the absolute value of the colloidal charge of the organic sludge is 2.00 to 4.

50.

9. It contains chitosan and has a 1% salt viscosity of 50 to 100 mPa·s. A flocculant for dewatering organic sludge, characterized in that it is added to the organic sludge such that the ratio of the colloidal charge of the flocculant to the absolute value of the colloidal charge of the organic sludge is 0.70 to 4.50.

Images