JP2005035868A - Processing method of sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an industrially advantageous processing method of sludge that is capable of being eco-friendly discharged or of utilizing it as a fertilizer or a cultivating soil for growing plants. <P>SOLUTION: The processing method of sludge comprises solidifying the sludge by adding a polyvinyl alcohol type resin thereto and disposing the solidified material as wastes or using it as a fertilizer or a cultivating soil for growing plants. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a sludge treatment method. More specifically, improvement of the environment of rivers, lakes or seas by treating so-called sludge such as stagnation parts of river flow, sediments containing organic matter present on the lake or sea bottom, or sedimentation sludge of activated sludge treatment equipment. It is about the method of aiming at.

As a treatment method of sludge such as sediment containing organic matter existing on the bottom of the lake or the sea bottom or sedimentation sludge of activated sludge treatment equipment, the moisture content was reduced by temporarily dehydrating or agglomerating after dredging sludge. Thereafter, a method of landfilling or further incineration is generally used (for example, Patent Document 1). The incinerated ash after incineration may be reused by being used for land reclamation or processed into a molded body such as a brick or a block (for example, Patent Document 2).
Japanese Unexamined Patent Publication No. 07-000998 Japanese Patent Laid-Open No. 08-061634

  In recent years, there has been a movement to reuse sludge itself due to the fact that sludge or incineration ash disposal sites have decreased and the cost of incineration is quite high. The most effective way to reuse sludge is to use the organic matter contained in sludge as a fertilizer. However, when it is reused as a fertilizer, fluidity can be used for handling and transporting the fertilizer. In addition to problems such as difficulty in handling, when it is used as a fertilizer for plants that inhabit relatively shallow water such as rivers, lake shores or coasts, or when organic matter itself is biodegraded in shallow water, redispersion occurs in water, It was difficult to use because it hinders the transmission of sunlight necessary for the activities of living organisms. In order to prevent this, methods such as covering the sludge with soil, aggregating with a polymer flocculant, or spraying sludge with no fluidity with a polymer or inorganic solidifying agent have been tried. Was not enough.

As a result of intensive studies, the present inventors have found that the above problem is caused by adding a polyvinyl alcohol-based resin and solidifying sludge that contains organic matter in rivers, lake bottoms, or sea bottom, or sludge that is the sludge of activated sludge treatment equipment. As a result, the present invention has been completed.
That is, according to the present invention, organic substances contained in sludge are effectively used for plant growth. The solidified product containing sludge obtained by adding polyvinyl alcohol resin to sludge is not easily redispersed in water even if it is disposed on the river, lake shore or coast, for example. Similarly, when it is disposed of in a place, it is biodegraded by microorganisms that inhabit the natural world and is also used as fertilizer or soil for plant cultivation. In addition, according to the present invention, the solidified product is discarded in nature and used as fertilizer or cultivated soil, or is biodegraded by natural force and disappears without damaging the natural environment at all.

The present invention
(1) A treatment method of sludge characterized by adding polyvinyl alcohol resin to sludge and solidifying, and using the solidified product as a fertilizer or soil for plant disposal or plant growth,
(2) The treatment method according to the above (1), wherein the polyvinyl alcohol-based resin is polyvinyl alcohol having a saponification degree of 97 mol% or more,
(3) The processing method according to (1) or (2) above, wherein the solidification uses a sun or a dryer,
(4) The treatment method according to any one of (1) to (3) above, wherein the solidification is performed in the presence of a crosslinking agent for the polyvinyl alcohol resin.
(5) The treatment method according to (3) above, wherein the dryer is a heat dryer, and the heating temperature is 105 ° C. or higher.
(6) The polyvinyl alcohol resin is selected from a saponified product of a copolymer of vinyl acetate and α-olefin, a saponified product of a copolymer of vinyl acetate and diacetone acrylamide, and an acetoacetyl group-containing polyvinyl alcohol. The processing method according to any one of (1) to (5) above,
(7) The sludge treatment method according to any one of (1) to (6) above, wherein the solidified product is a hydrous gel containing water or seawater.
(8) Solidified product characterized by containing sludge and polyvinyl alcohol resin,
(9) Fertilizer or soil for plant growth characterized by containing the solidified material according to (8) above, and
(10) Useful plants cultivated using the solidified product according to (8) above,
About.

  Since the sludge solidified product obtained by the method of the present invention has an appropriate strength, it is excellent in handling properties during storage and transportation. In addition, when it is put into water for the purpose of biodegradation in fertilizer or water, it not only re-disperses and does not block light transmission, but also swells moderately, so it has excellent sustained release of organic matter in the solidified product, Furthermore, since the permeation of oxygen or the like necessary for biodegradation is not inhibited, the organic matter in the solidified product is also efficiently decomposed. In addition, since the polyvinyl alcohol itself has the property of being biodegraded by Pseudomonas bacteria existing in nature, the solidified product itself is degraded.

Hereinafter, the present invention will be described in detail.
The sludge used in the present invention is obtained by collecting sediment containing organic matter present in the sediments of rivers, lakes or marine areas, or sedimentation sludge from an activated sludge treatment facility. The above sediments are generated by the culturing of fish such as sea bream and cormorant, oysters and shellfish such as oyster shellfish, etc. It may be any of those that are formed by depositing feces, etc., and other items that are caused by other factors, and the type is not particularly selected.

  The moisture content of the sludge before being mixed with the polyvinyl alcohol resin and solidifying is preferably 200% or less with respect to the dry weight of the sludge, but the moisture content of sludge just collected by means such as cocoons exceeds 200%. In many cases, it is preferable to subject the sludge to water reduction treatment in order to reduce the moisture content of the sludge (preferably to 200% or less). Such water reduction treatment may be performed when the polyvinyl alcohol-based resin is added to sludge, or may be performed as a pretreatment of the present invention before the addition. Furthermore, it may be performed both at the time of addition and before the addition.

  The treatment means used for the water reduction treatment may be any means as long as it is a means for reducing the moisture content of the sludge, and may be a known treatment means. For example, a chemical treatment means for adding a solidifying agent or a water reducing treatment agent to sludge, or a physical means for dehydrating sludge by mechanical squeezing or the like can be mentioned.

  Examples of the solidifying agent or water reducing agent include a polymeric water-absorbing agent or water-retaining agent, a polymeric flocculant, an inorganic flocculant, a natural flocculant, a microorganism-producing flocculant, a sulfuric acid band, and (baked) gypsum. , Cement, quicklime, bentonite, silica gel, layered silicate, zeolite, (blast furnace) slag, paper sludge incinerated ash, or a mixture containing one or more of these as a main component.

  Examples of the polymer water-absorbing agent or water retention agent include cross-linked polyacrylate resin, isobutylene / maleate resin, starch / polyacrylate resin, polyvinyl alcohol / polyacrylate resin, and crosslinked polyvinyl. Examples thereof include alcohol-based resins and crosslinked cellulose-based resins.

  Examples of the polymer flocculant include synthetic polymer flocculants such as polyaminomethylacrylamide salts, aminoalkyl (meth) acrylate quaternary salt resins, acrylamide / acrylic acid copolymer salts, polyacrylic acid salts, and polyacrylamides. Natural polymers such as chitosan acetate, sodium alginate, gelatin, tannic acid, cellulose and derivatives thereof, starch and derivatives thereof, and the like.

  Examples of the inorganic flocculant include aluminum sulfate (sulfuric acid band), basic aluminum chloride, sodium aluminate, ferrous sulfate, ferric sulfate, calcium oxide, calcium hydroxide, calcium chloride, magnesium sulfate, or chloride. Examples thereof include inorganic flocculants represented by ferric iron.

  Examples of natural product-based flocculants include chitosan or chitosan derivatives such as chitosan acetate, cationized starch, cationized cellulose, cationized guar gum, carboxymethylcellulose, carboxymethylstarch, sodium alginate, crustacean shell powder Examples include the body.

  Examples of the microorganism-producing flocculant include flocculants mainly composed of microorganism-produced monosaccharide, disaccharide, trisaccharide or tetrasaccharide or higher polysaccharide. Moreover, what acetylated the hydroxyl group in these sugars may be used as the microorganism-producing flocculant. More specifically, examples of the sugar include glucose, mannose, glucuronic acid, galactose, arabinose, fructose, trehalose, lactose, maltose, sucrose, raffinose, stachyose, and mixtures thereof. The microorganism-producing flocculant contains an organic acid, preferably a fatty acid such as pyruvic acid, succinic acid, mycolic acid, mycolic acid, palmitic acid, stearic acid, arachidic acid, and the carboxyl group is a sugar hydroxyl group and an ester. You may have a bond. Examples of the microorganism-producing flocculant include polysaccharides bound with organic acids described in claim 1 of JP-A-5-262801.

  Examples of the mixture used as the solidifying agent or water reducing agent include incineration ash, portant cement, sulfate band, anhydrous gypsum, methacrylic acid ester, and lignin sulfonic acid described in JP-A-2002-363560. A mixture of salts, stearate, sodium tripolyphosphate and sodium hydroxide, or a natural mineral mainly composed of incinerated ash, gypsum, silica fume, alumina / silicate, or alkali metal carbonate described in Japanese Patent No. 3274376 Examples thereof include a mixture of a salt and an anionic surfactant.

  In the present invention, the above-described treatment means may be appropriately combined and used for the water reduction treatment, and the water reduction treatment may have a plurality of steps.

  Examples of the physical means for reducing the sludge include vacuum dehydrating means such as a belt filter or an oliver filter, centrifugal dehydrating means, or mechanical squeezing means such as a filter press, belt press or roll press.

  The polyvinyl alcohol-based resin used in the present invention is obtained by saponifying an aliphatic polyvinyl ester obtained by polymerizing an aliphatic vinyl ester. There is no particular limitation on the degree of polymerization and saponification of the polyvinyl alcohol-based resin, but the average degree of polymerization is about 200 or more, preferably about 500 in order to maintain the strength that the solidified product does not collapse during storage, transportation or spraying. It is better to be above. Further, when a polyvinyl alcohol resin (hereinafter also abbreviated as PVA resin) is solidified without using a crosslinking agent or the like, it is difficult to prevent re-dispersion when the solidified product is added to water. The degree of conversion is preferably about 90 mol%, more preferably about 97 mol% or more.

  Examples of the aliphatic vinyl esters used in producing the PVA-based resin of the present invention include vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, and vinyl stearate. Is desirable. Moreover, you may copolymerize the unsaturated monomer and aliphatic vinyl ester which can be copolymerized with aliphatic vinyl ester in the range which does not impair the effect of this invention. Examples of unsaturated monomers copolymerizable with aliphatic vinyl esters include unsaturated dibasic acid monoalkyl esters such as monomethyl maleate and monomethyl itaconate, diacetone acrylamide, acrylamide, dimethyl acrylamide, and N-methylol. Amide group-containing monomers such as acrylamide and N-vinyl-2-pyrrolidone, alkyl vinyl ethers such as lauryl vinyl ether and stearyl vinyl ether, hydroxyl group-containing monomers such as allyl alcohol, dimethylallyl alcohol and isopropenyl allyl alcohol, allyl acetate, Acetyl group-containing monomers such as dimethylallyl acetate and isopropenyl allyl acetate, vinyl halides such as vinyl chloride, vinylidene chloride and vinyl fluoride, trimethoxyvinylsilane, tributyl Nylsilane, vinyl silanes such as diphenylmethyl vinyl silane, alpha olefins such as ethylene and propylene, sulfone group-containing monomers such as sodium allyl sulfonate, sodium methallyl sulfonate and sodium styrene sulfonate, acrylic acid, methacrylic acid, acrylic Acrylic acid monomers such as 2-ethylhexyl acrylate, n-butyl acrylate, 2- (2′-hydroxy-5′-methacryloxyethylphenyl) -2H-benzotriazole, polyoxyethylene (meta ) Acrylate, polyoxypropylene (meth) acrylate, polyoxyethylene (meth) acrylic amide, polyoxypropylene (meth) acrylic amide, polyoxyethylene (meth) allyl ether, polyoxypropylene (meth) allyl ether, polyoxyethylene Down vinyl ether, but the oxyalkylene group-containing monomers such as polyoxypropylene vinyl ether is not limited thereto.

  The polymerization method of the aliphatic vinyl ester may be a known one, and examples thereof include a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. Among them, α, α′- Using an azo or peroxide initiator such as azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), peracetic acid, di-n-propylperoxydicarbonate, etc. A polymerization method is common. A chain transfer agent for adjusting the degree of polymerization such as 2-mercaptoethanol is used for the polymerization, or hydroquinone, 2,2,6,6-tetramethyl-1-piperidinooxy (TEMPO), meta- A polymerization inhibitor / polymerization inhibitor such as dinitrobenzene may be used. Also, a method for removing unreacted monomers and a saponification, drying, and pulverization method may be known methods, and there is no particular limitation.

  The polyvinyl alcohol resins obtained by the above method may be used alone or in combination of two or more.

  The addition amount of the polyvinyl alcohol resin of the present invention is not particularly limited, but it is suitably about 0.1% by mass or more based on the dry solid content of sludge. This is because when the addition amount of the polyvinyl alcohol resin is about 0.1% by mass or more, the strength of the solidified product becomes better, and even when the solidified product is put into water, the stability is excellent. The addition method of the polyvinyl alcohol resin is a method of adding an aqueous solution in which the polyvinyl alcohol resin is dissolved in water or seawater, a method of adding a fine powder having a particle size of about 200 μm or less to the sludge and dissolving it while kneading, A preferable method includes, but is not limited to, a method in which a fine powder of about 200 μm or less is added to sludge and stirred and then melted with heat during molding and drying. However, among these, the method of adding an aqueous polyvinyl alcohol solution is preferable in terms of high efficiency as a binder. A known addition and mixing device for the polyvinyl alcohol resin and sludge may be used, and a twin screw kneader, a twin screw kneading extruder, a tank mixer, or the like is used. These operations may be batch or continuous.

  When mixing or kneading sludge and polyvinyl alcohol resin, wood scraps such as sawdust, aquatic plants, seaweeds, etc. are added to increase the amount of organic matter in the solidified product or to increase voids, and it is more porous. In order to make it, diatomaceous earth, bentonite, activated carbon, silica or the like may be added. In addition, enzymes, fungus bodies and necessary nutrients for making microbial degradation more effective may be added. When used as culture soil, water retention, air permeability, etc. can be changed by adding sand, humus, kanuma soil, akadama soil, vermiculite and the like. Furthermore, binders other than polyvinyl alcohol, for example, cellulose derivatives such as methyl cellulose and carboxymethyl cellulose, starch derivatives such as raw starch, oxidized starch, and phosphorylated starch, vinyl acetate emulsion, EVA as long as the effects of the present invention are not impaired. Emulsion polymer such as emulsion, acrylic emulsion, seaweed such as agar, carrageenan, sodium alginate, animal protein such as glue, casein, gelatin, fermentation mucilage such as pullulan, dextrin, polyacrylamide, polyethyleneimine, polyvinylpyrrolidone, A synthetic polymer such as polyethylene glycol, a polylactic acid emulsion, or the like may be added. An antifoaming agent, a pH adjusting agent, an antioxidant and the like may be added as necessary.

As a method for solidifying sludge to which a polyvinyl alcohol resin is added in the form of an aqueous solution or powder, the following methods are preferable examples.
(I) A method of making a freeze-thaw gel by adding a polyvinyl alcohol-based resin to sludge and then melting sludge frozen at −10 ° C. or lower for 3 hours or more at an appropriate temperature.
(Ii) A method in which a polyvinyl alcohol-based resin is added to sludge and formed into an appropriate shape, and then dried at sun or room temperature to solidify.
(Iii) A method of further drying and heat-treating the molded product at 105 ° C. or higher in order to improve the stain resistance of the molded product of (ii) above,
(Iv) A method in which a polyvinyl alcohol resin is added to sludge and a crosslinking agent is added at the same time, and then placed in a suitable container or formed into a suitable shape and allowed to gel, and (v) polyvinyl alcohol. Preferred examples include a method of adding a cross-linking agent at the same time as adding the resin to the sludge and then putting it in a suitable container or molding it into a suitable shape and drying it.

Among these, (ii) a method in which a polyvinyl alcohol-based resin is added to sludge and formed into an appropriate shape, and then dried and solidified by sunlight or at room temperature is advantageous both in terms of cost and operation.
In addition, when a particularly high water resistance is required when solidifying the deposit, it is preferable to use the above methods (iv) and (v) in which a polyvinyl alcohol resin is used in combination with a crosslinking agent. The cross-linking agent used in the method is appropriately selected depending on the type of polyvinyl alcohol resin and the like. Among polyvinyl alcohol resins that can be used with a crosslinking agent, saponified products of vinyl acetate and diacetone acrylamide are adipic acid dihydrazide, carbohydrazide, tartaric acid dihydrazide, itaconic acid dihydrazide, citric acid trihydrazide, butane. A polyfunctional hydrazide compound such as tricarbohydrazide is useful because it can be easily crosslinked and gelled and water-resistant. Similarly, a saponified product of a copolymer of vinyl acetate and α-olefin is useful because the dry film has high water resistance and higher biodegradability than unmodified polyvinyl alcohol. Similarly, polyvinyl alcohol containing an acetoacetyl group is also useful because it easily crosslinks with aldehydes. Other cross-linking agents that make water resistant polyvinyl alcohol resins generally form complexes with aldehydes such as glyoxal, glutaraldehyde, and aldehyde starch as well as epoxies, polycarboxylic acids, isocyanates, and poval. There are metals, but they are used with consideration for environmental impact.

  A typical example of the processing method of the present invention will be described with reference to FIG. The collected sludge is processed in the sludge pretreatment facility 1 as described above and supplied to the sludge storage tank 3. The polyvinyl alcohol-based resin aqueous solution is stored in the PVA dissolution tank 2. Both are supplied to the mixer 6 through the constant flow pumps 4 and 5 and mixed. When mixing, if necessary, other additives (auxiliaries) described above may be added and mixed. The mixture is dried by, for example, a dryer or sun-dried 10, crushed by the crusher 7, and the obtained solidified product is transferred to the solidified product storage tank 8. The solidified material is sprayed by a transport device 9 such as a belt conveyor or a transport device 9 such as a truck at a treatment site that is a shallow water such as a riverbank, a lake shore, or a coast to biodegrade organic matter in sludge, or as a fertilizer for aquatic plants or seaweeds. Used or transported to crop cultivation area or market. Since the solidified product obtained as described above contains organic matter, it is suitable as a fertilizer for the cultivation and cultivation of useful plants such as cereals, vegetables, flower buds, fruits, medicinal plants, foliage plants, and has water retention and drainage properties. Since it has, it is suitable as a soil for plant cultivation. Plants cultivated in this way are excellent in cultivation results such as harvest, fruit size / number, and number of flowers.

  EXAMPLES Hereinafter, although a specific example is given and this invention is demonstrated further in detail, this invention is not limited at all by these Examples. In the following examples, “%” and “part” are unless otherwise specified. “Mass%” and “parts by mass” are meant.

<Synthesis example of PVA resin>
A reactor equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and pressure gauge was purged with nitrogen. Then, 2800 parts by mass of deoxygenated vinyl acetate monomer and 1000 parts by mass of methanol were charged, and heating was started under stirring. When the internal temperature reached 60 ° C., polymerization was started by separately adding a solution prepared by dissolving 1.5 parts by mass of AIBN as an initiator into 50 parts by mass of methanol. After polymerization at 60 ° C. for 4 hours, the polymerization was stopped by cooling. The solid content concentration in the polymerization solution at this time was 57.3%. The obtained polymerization solution was supplied to a demonomer tower having a multi-stage perforated plate in the tower, and methanol vapor was blown from the bottom of the tower to come into contact with the polymerization solution to remove unreacted vinyl acetate monomer. The solid content concentration of the polyvinyl acetate resin-methanol solution at this time was 44%. 25 parts by mass of 2% sodium hydroxide-methanol solution was added to 1000 parts by mass of this polyvinyl acetate resin-methanol solution, and the mixture was mixed well and allowed to stand at 40 ° C. for 1 hour. The gel obtained after saponification was pulverized with a pulverizer and then dried with a blow dryer at 60 ° C. After drying, pulverization was performed to obtain the PVA resin of the present invention. The polymerization degree was 1700 and the saponification degree was 99.5 mol%.

<Hedro>
As a sludge simulation liquid, a mixture obtained by adding 360 parts by mass of water to 100 parts by mass of Kasaoka clay, 100 parts by mass of bentonite, and 100 parts by mass of silica sand 6 and stirring and kneading was used as a substitute for sludge. In addition, as the actual sludge, we used the bottom sediment of the sea in Tsukiminato Shinmachi, Sakai City, Osaka Prefecture. In addition, as the activated sludge, the settled sludge from our activated sludge treatment equipment was used.

<Evaluation of solidified product; dispersion resistance test>
The solidified product obtained by the method of the present invention is mainly intended to be used as a fertilizer for aquatic plants and seaweeds by spraying it on relatively shallow riversides, lake shores, and coasts. Was placed at 30 ° C. for 24 hours, and then shaken at 150 SPM for 1 hour with an MWA shaker manufactured by IWAKI SANGYO. After shaking, it was visually confirmed whether the solidified product was redispersed and the water was not turbid.

(Example 1)
After adding 50 parts by mass of polyvinyl alcohol having a polymerization degree of 1700 and a saponification degree of 99.5 mol%, which was produced in Synthesis Example 1, to 450 parts by mass of water, a 10% polyvinyl alcohol aqueous solution was prepared by stirring and heating. 90 parts by mass of 10% polyvinyl alcohol aqueous solution was added to 660 parts by mass of the above simulated liquid and kneaded well, and then cast on a Teflon (registered trademark) plate to form a plate having a thickness of 1 cm. The whole Teflon (registered trademark) plate was left in a room at 20 ° C. and 65% RH for 3 days to dry the moisture. The dried product was subdivided into 1 cm square cubes and subjected to a dispersion resistance test. The shape was retained and the dispersed water was not cloudy.

(Example 2)
Instead of polyvinyl alcohol having a polymerization degree of 1700 and a saponification degree of 99.5 mol% in Example 1, an ethylene-modified polyvinyl alcohol having a polymerization degree of 1730, a saponification degree of 97.0 mol% and an ethylene modification degree of 2.2 mol% was used. The test was carried out in the same manner as in Example 1 except that. The dispersion resistance test showed good results as in Example 1.

(Example 3)
The simulated liquid prepared in Example 1 and the polyvinyl alcohol aqueous solution kneaded material were allowed to stand in a freezer refrigerator at −15 ° C. for 15 hours to freeze the kneaded material. Then, it thawed at room temperature of 25 degreeC over 3 hours, and created the freeze-thaw gel. The gel was subdivided into 1 cm square cubes and subjected to a dispersion resistance test. As in Example 1, good results were shown.

(Example 4)
A 10% aqueous solution of diacetone acrylamide copolymer-modified polyvinyl alcohol having a polymerization degree of 1720, a saponification degree of 96.7 mol%, and a diacetone acrylamide content of 2.0 mol% and an adipic acid dihydrazide 10% aqueous solution were added to 660 parts by mass of the simulated liquid. After adding 4.5 parts by mass of the kneaded mixture, the kneaded product is placed in a vinyl tube with a round hole with a diameter of 8 mm at the tip, and the kneaded product is squeezed out of the tube to give a cylinder with a diameter of about 10 mm. A shaped molding was obtained. This molded product was dried at 110 ° C. for 3 hours to obtain a solidified product. The solidified product was cut to a length of 1 cm and subjected to a dispersion resistance test. Good results were obtained as in Example 1.

(Example 5)
Instead of the diacetone acrylamide-modified polyvinyl alcohol of Example 4, a polymerization degree of 650, an acetoacetyl group-modified polyvinyl alcohol containing 3.6 mol% of acetoacetyl groups in the side chain was used, and glyoxal instead of a 10% aqueous solution of adipic acid dihydrazide. The test was conducted in the same manner as in Example 4 except that 5 parts by mass were added. In the dispersion resistance test, good results were obtained as in Example 4.

(Example 6)
Instead of the simulated liquid of Example 1, a concentrated sludge concentrate (water content 180%) of an activated sludge treatment apparatus for treating sodium acetate was used, and the addition amount of 10% polyvinyl alcohol aqueous solution was changed to 150 parts by mass. The test was conducted in the same manner as in Example 1 except for the above. The results of the dispersion resistance test were as good as in Example 1.

(Example 7)
To 500 parts by mass of the settled sludge used in Example 6, 300 parts by mass of Kanuma soil, 250 parts by mass of humus soil, and 100 parts by mass of silica sand No. 6 were mixed, and polyvinyl alcohol having a polymerization degree of 1700 and a saponification degree of 99.5 mol% was added. 70 parts by mass of a dissolved 10% aqueous solution was added and kneaded well. This kneaded material was dried for 5 hours with a blast dryer at 65 ° C. to prepare a soil. Morning glory was cultivated using this soil. The morning glory was well cultivated and bloomed beautifully.

(Example 8)
The test was conducted in the same manner as in Example 1 except that instead of the simulated liquid, sludge (water content 150%) obtained by sedimentation and dehydration treatment of actual sea bottom sediment was used. The results of the dispersion resistance test were as good as in Example 1.

Example 9
120 parts by mass of 10% aqueous solution of diacetone acrylamide copolymer-modified polyvinyl alcohol used in Example 4 and 10 parts by mass of 10% aqueous solution of adipic acid dihydrazide may be added to 400 parts by mass of sludge used in Example 8. Kneaded. The kneaded product was placed in a plastic bag and allowed to stand for 48 hours to prepare a hydrous gel. The results of the dispersion resistance test of this hydrous gel were good.

(Comparative Example 1)
The test was conducted in the same manner except that polyvinyl alcohol was not used in Example 1. As a result of the dispersion resistance test, the clays were redispersed and the water became cloudy.

(Comparative Example 2)
A test was conducted in the same manner except that carboxymethylcellulose having a substitution degree of 1.0 and a 2% aqueous solution viscosity at 20 ° C. of 2600 mPa · s was used instead of the polyvinyl alcohol of Example 1. As a result of the dispersion resistance test, the viscosity was redispersed and the water became cloudy.

  According to the present invention, the environment of a river, a lake or a marine area can be improved. Further, according to the present invention, sludge can be effectively used for plant growth.

Flow chart until polyvinyl alcohol resin and sludge are mixed and solidified

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sludge pretreatment equipment 2 PVA dissolution tank 3 Sludge storage tank 4 Metering pump 5 Metering pump 6 Mixer 7 Crusher 8 Solidified material storage tank 9 Transport device 10 Dryer or sun-dried

Claims (10)

  A method for treating sludge, comprising adding a polyvinyl alcohol-based resin to sludge and solidifying the solid, and using the solidified product as a fertilizer or soil for discarding or growing plants.   The processing method according to claim 1, wherein the polyvinyl alcohol-based resin is polyvinyl alcohol having a saponification degree of 97 mol% or more.   The processing method according to claim 1 or 2, wherein the solidification uses a sun or a dryer.   Solidification is performed in presence of the crosslinking agent of polyvinyl alcohol-type resin, The processing method in any one of Claims 1-3 characterized by the above-mentioned.   The processing method according to claim 3, wherein the dryer is a heat dryer, and the heating temperature is 105 ° C or higher.   The polyvinyl alcohol resin is selected from a saponified product of a copolymer of vinyl acetate and α-olefin, a saponified product of a copolymer of vinyl acetate and diacetone acrylamide, or a polyvinyl alcohol containing an acetoacetyl group. The processing method according to any one of claims 1 to 5.   The method for treating sludge according to any one of claims 1 to 6, wherein the solidified product is a hydrous gel containing water or seawater.   A solidified product containing sludge and polyvinyl alcohol resin.   A fertilizer or cultivated soil for plant growth, comprising the solidified product according to claim 8. Useful plants cultivated using the solidified product according to claim 8.

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