Organic wastewater treatment apparatus and polymer coagulant

Abstract

To provide a method for treating organic wastewater, an apparatus for treating organic wastewater, and a polymer coagulant, capable of performing stable dehydration treatment even for organic wastewater, particularly hardly dehydrated organic wastewater.SOLUTION: A method for treating organic wastewater includes adding a polymer coagulant which satisfies the following conditions that: (1) salty viscosity at 0.5% salt concentration is 10 to 90 mPa s; and (2) a component ratio of cationic monomers in the total monomers constituting the copolymer contained in the polymer coagulant, out of the molar number of the cationic monomers, the molar number of anionic monomers and the molar number of nonionic monomers, is 25 to 90 mol%, and the component ratio of the sum of the anionic monomers and the nonionic monomers is 10 to 75 mol%, followed by coagulation treatment and then concentration treatment, and dehydration of the concentrated sludge for hardly dehydrated organic wastewater containing at least either night soil or septic tank sludge.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for treating organic wastewater, an apparatus for treating organic wastewater, and a polymer flocculant, and in particular to a method for treating organic wastewater, an apparatus for treating organic wastewater, and a polymer flocculant that are suitable for treating difficult-to-dewater organic wastewater that contains at least human waste or septic tank sludge. [Background technology]

[0002] In recent years, there has been an increase in treatment methods for directly dehydrating organic wastewater generated from human waste or septic tanks. Because organic wastewater from human waste or septic tanks contains a large amount of impurities, the impurities are removed as necessary, followed by direct dehydration, and the dehydrated separated liquid is then subjected to biological treatment, dilution treatment, or the like.

[0003] In such dehydration treatment, a large amount of dehydrated cake of organic sludge is generated, and therefore, various measures for reducing the volume of the dehydrated cake have been studied. Also, in order to reuse the obtained dehydrated cake as a combustion improver, compost, etc., it is necessary to reduce the moisture content. Therefore, a method is being carried out in which a flocculant is added to organic wastewater derived from human waste or a septic tank to flocculate the flocs, and then the flocs are dehydrated.

[0004] Human waste and septic tank sludge are generally collected separately and transported to human waste treatment plants. However, the amount of sludge transported and the properties of the sludge at the time of transport are not constant, and the mixing ratio fluctuates, so the properties of the sludge subjected to dehydration treatment vary greatly. In particular, because human waste contains a large amount of chloride, a high mixing ratio of human waste can result in poor dehydration. Therefore, it is necessary to frequently adjust the amount of polymer flocculant added or change the type of polymer flocculant used depending on the properties of the sludge.

[0005] One way to solve this problem is to condition the sludge by adding inorganic coagulants such as polyferric sulfate or aluminum sulfate before flocculating it with a polymer coagulant. However, this method is not a sufficient solution. In particular, if the pH of the sludge to be dewatered is low, adding an inorganic coagulant will further lower the pH, causing the metal salts of the inorganic coagulant to dissolve, so it may not be possible to add it.

[0006] Japanese Patent Laid-Open No. 2014-159000 (Patent Document 1) describes that by alternately performing a process of adding a flocculant to a mixed sludge of human waste, organic sludge, and excess sludge to dehydrate it, and a process of dehydrating the mixed sludge without adding a flocculant and subjecting the separated liquid to biological treatment, it is possible to reduce the moisture content and volume of the resulting dehydrated cake.

[0007] Japanese Patent Application Laid-Open No. 2020-100917 (Patent Document 2) describes an example of a method for using a polymer to remove micro-pitch with a particle diameter of 150 μm or less from separated white water in the paper manufacturing process. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2014-159000 A [Patent Document 2] Japanese Patent Application Publication No. 2020-100917 Summary of the Invention [Problem to be solved by the invention]

[0009] Patent Document 1 describes the use of ordinary inorganic flocculants or polymer flocculants for treatment. However, the amount and properties of organic sludge, such as human waste or septic tank sludge, vary greatly depending on the time of day and season when it is delivered. When treating organic sludge with inconsistent amounts and properties at the time of delivery, the sludge subjected to dewatering treatment becomes difficult to dewater. Conventional polymer flocculants may not be suitable for such difficult-to-dewater organic sludge. Furthermore, Patent Document 2 is an invention related to a method and apparatus for treating pitch-containing water, but does not describe its application to organic wastewater, and its effects are unclear.

[0010] In view of the above problems, the present invention provides a method for treating organic wastewater, an apparatus for treating organic wastewater, and a polymer flocculant, which are capable of stably dehydrating organic wastewater, particularly organic wastewater that is difficult to dehydrate. [Means for solving the problem]

[0011] In order to solve the above problems, the present inventors have conducted extensive research and found that it is effective to carry out a flocculation treatment using a specific polymer flocculant for difficult-to-dewater organic wastewater, followed by a dewatering treatment.

[0012] One aspect of the embodiment of the present invention, which was completed based on the above findings, is a method for treating organic wastewater, which comprises adding a polymer flocculant that satisfies the following conditions to difficult-to-dewater organic wastewater containing at least either human waste or septic tank sludge: (1) a 0.5% salt viscosity of 10 to 90 mPa·s, and (2) a cationic monomer content of 25 to 90 mol% out of the total molar amounts of cationic monomer, anionic monomer, and nonionic monomer contained in the copolymer of the polymer flocculant, and the total molar amount of anionic monomer and nonionic monomer is 10 to 75 mol%, followed by a flocculation treatment, followed by a concentration treatment, and then dewatering the concentrated sludge.

[0013] In another embodiment of the method for treating organic wastewater according to the present invention, the cationic equivalent value of the polymer flocculant at pH 4 is 1.0 to 5.0 meq / g, and the cationic equivalent value at pH 10 is 4.5 meq / g or less.

[0014] In yet another embodiment of the method for treating organic wastewater according to the present invention, one or more copolymers selected from the group consisting of a quaternary methyl chloride salt of dimethylaminoethyl acrylate, a quaternary methyl chloride salt of dimethylaminoethyl methacrylate, acrylamide, and acrylic acid are used as the polymer flocculant.

[0015] In yet another embodiment of the method for treating organic wastewater according to the present invention, the conductivity of the difficult-to-dewater organic wastewater is 50 to 1500 mS / m, the difference between the evaporation residue and the suspended solids is 1500 mg / L or more, the cation demand is -0.01 to -2.00 meq / L, and the capillary suction time (CST) is 300 seconds or more.

[0016] In yet another embodiment of the method for treating organic wastewater according to the present invention, the method further comprises subjecting the concentrated separated liquid and the dehydrated separated liquid obtained by the concentration treatment and the dehydration treatment to biological treatment, and adding the excess sludge obtained by the biological treatment to the difficult-to-dewater organic wastewater.

[0017] In another aspect, the present invention provides an organic wastewater treatment apparatus comprising: a reaction tank into which difficult-to-dewater organic wastewater containing at least one of human waste and septic tank sludge is introduced; a polymer flocculant having a 0.5% salted viscosity of 10 to 90 mPa·s, in which, among the molar amounts of cationic monomers, anionic monomers, and nonionic monomers contained in all monomers constituting the copolymer, the cationic monomers account for 25 to 90 mol% and the total molar amount of the anionic monomers and nonionic monomers is 10 to 75 mol%; a flocculant addition means for adding the polymer flocculant to the reaction tank; a concentration means for concentrating the organic wastewater to which the polymer flocculant has been added; and a dehydration means for dehydrating the concentrated sludge obtained by the concentration means.

[0018] In one embodiment of the organic wastewater treatment device according to the present invention, the flocculant adding means further adds an inorganic flocculant to the organic wastewater.

[0019] In another embodiment, the organic wastewater treatment device according to the present invention further comprises a control means capable of controlling the addition rate of the polymer flocculant added by the flocculant addition means based on the properties or supply amount of the organic wastewater.

[0020] In yet another embodiment, the organic wastewater treatment device according to the present invention further comprises a sewage receiving tank for receiving sewage, a pretreatment device for removing impurities contained in the sewage, a sewage storage tank for storing a pretreatment liquid treated in the pretreatment device, and a delivery means for delivering the pretreatment liquid to a reaction tank or a storage tank for storing organic wastewater to be delivered to the reaction tank, and for adjusting the flow rate of the organic wastewater in the reaction tank or storage tank.

[0021] In yet another aspect, the present invention provides a polymer flocculant for difficult-to-dewater organic wastewater containing at least one of sewage and septic tank sludge, which satisfies the following conditions: (1) a 0.5% salt viscosity of 10 to 90 mPa·s, and (2) of the molar numbers of cationic monomers, anionic monomers, and nonionic monomers contained in all monomers constituting the copolymer contained in the polymer flocculant, the cationic monomers constitute a proportion of 25 to 90 mol%, and the total molar ratio of the anionic monomers and nonionic monomers is 10 to 75 mol%. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a method for treating organic wastewater, an apparatus for treating organic wastewater, and a polymer flocculant that can stably dehydrate organic wastewater, particularly organic wastewater that is difficult to dehydrate. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a schematic diagram illustrating an example of an organic wastewater treatment device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an example of the configuration of an apparatus upstream of the storage tank in FIG. [Figure 3] FIG. 10 is a schematic diagram illustrating a modified example of the organic wastewater treatment device according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] (organic wastewater) The organic wastewater to be treated can be organic wastewater containing organic substances such as sewage, human waste, and kitchen waste, particularly difficult-to-dewater organic wastewater containing at least one of human waste and septic tank sludge. The method can particularly stably treat difficult-to-dewater organic wastewater having properties such as a conductivity of 50 to 1500 mS / m, a difference between the total solids (TS) and suspended solids (SS) in the organic wastewater of 1500 mg / L or more, a cation demand of -0.01 to -2.00 meq / L, and a capillary suction time (CST) of 300 seconds or more, preferably 500 seconds or more.

[0025] In one embodiment, the conductivity of the organic wastewater to be treated is 50 mS / m or more, further 100 mS / m or more, and even more 400 mS / m or more. The upper limit of the conductivity is 1500 mS / m, but in the case of organic wastewater containing at least one of human waste and septic tank sludge, in one embodiment, it is 1500 mS / m or less, 1200 mS / m or less, or 1100 mS / m or less. The conductivity is measured according to the electrical conductivity measurement method in accordance with JIS K0102 (2021).

[0026] The TS of the organic wastewater is not limited to, but in one embodiment is 2000 mg / L or more, further 5000 mg / L or more, and even more 7000 mg / L or more. The upper limit of the TS of the organic wastewater is not particularly limited, but in the case of organic sludge containing at least one of human waste and septic tank sludge, it is 30000 mg / L or less, further 25000 mg / L or less.

[0027] The SS of the organic wastewater is not limited to, but in one embodiment is 2000 mg / L or more, further 5000 mg / L or more, and even more 7000 mg / L or more. The upper limit of the SS of the organic wastewater is not particularly limited, but in the case of organic sludge containing at least one of human waste and septic tank sludge, it is 28500 mg / L or less, further 23500 mg / L or less.

[0028] Organic wastewater with a difference between TS and SS (TS-SS) of 1500 mg / L or more is difficult to dehydrate, and even if a dehydration treatment is performed after adding a conventional flocculant, the moisture content of the dehydrated cake may not be significantly improved. In one embodiment, the difference between TS and SS (TS-SS) of organic wastewater is 1500 mg / L or more, further 2000 mg / L or more, and even 3000 mg / L or more. The upper limit of the difference between TS and SS (TS-SS) is not particularly limited, but in the case of organic sludge containing at least one of human waste and septic tank sludge, it is 6000 mg / L or less, further 4000 mg / L or less. Here, TS is measured according to the Sewage Testing Method (2012), by measuring the weight of the evaporation residue after heating at 105°C for 2 hours. SS is measured according to the Sewage Testing Method (2012), by measuring the weight of the sediment after centrifugation at 3000 rpm for 10 minutes.

[0029] When the cation demand of organic wastewater is between -0.01 and -2.00 meq / L, more typically between -0.4 and -1.50 meq / L, or even between -0.43 and -1.00 meq / L, it is difficult to dewater, and even if a general coagulant is added and then dewatered, the moisture content of the dewatered cake may not be significantly improved. The cation demand is measured after centrifuging the sludge and separating the liquid phase in accordance with the Sewage Testing Method (2012).

[0030] In one embodiment, the CST of organic wastewater exhibiting poor dewaterability is 300 seconds or more, and even 500 seconds or more. While the upper limit of the CST is not particularly limited, it is typically within the above range for organic sludge containing at least one of human waste and septic tank sludge. The CST is measured in accordance with the Sewage Testing Method (2012).

[0031] (polymer flocculant) As the polymer flocculant, a cationic polymer flocculant or an amphoteric polymer flocculant is used. As the cationic polymer flocculant, a flocculant obtained by copolymerizing a cationic monomer or a cationic monomer with a nonionic monomer is used. The cationic monomer constituting the copolymer of the cationic polymer flocculant is preferably a cationic vinyl monomer, and examples thereof include neutralized salts or quaternized products of various acrylate or methacrylate monomers such as those listed below. Specific examples of cationic vinyl monomers include dimethylaminoethyl acrylate or methacrylate, diethylaminoethyl acrylate or methacrylate, diethylaminopropyl acrylamide or methacrylamide, dimethylaminopropyl acrylamide or methacrylamide, and their neutralized salts with hydrogen halides, sulfuric acid, nitric acid, acetic acid, etc., and quaternized products with alkyl halides, benzyl halides, dimethyl sulfate, diethyl sulfate, etc.

[0032] Cationic polymer flocculants also include those obtained by copolymerizing the above-mentioned cationic monomers with nonionic monomers. As the nonionic monomer, nonionic vinyl monomers are preferred, and specific examples include acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, (meth)acrylic acid esters such as dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate, and vinyl acetate, with acrylamide being particularly preferred.

[0033] As the amphoteric polymer flocculant, a polymer copolymerized with a cationic monomer, an anionic monomer, and, if necessary, a nonionic monomer is used. Typically, the amphoteric polymer flocculant preferably has a polymer copolymerized with a vinyl cationic monomer unit, a vinyl anionic monomer unit, and a vinyl nonionic monomer unit in the molecule. Examples of the vinyl cationic monomer copolymerized with the anionic monomer or nonionic monomer include neutralized salts or quaternized products of cationic vinyl monomers. These vinyl cationic monomers may be used alone or in combination of two or more.

[0034] The anionic monomer used in the amphoteric polymer flocculant is preferably an anionic vinyl monomer, specifically 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 such as alkali metals or ammonium salts thereof. These anionic monomers may be used alone or in combination of two or more.

[0035] As the nonionic monomer used in the amphoteric polymer flocculant, a nonionic vinyl monomer is preferred, and specific examples include acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, (meth)acrylic acid esters such as dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate, and vinyl acetate, among which acrylamide is particularly desirable.

[0036] In this embodiment, a polymer flocculant having a crosslinked structure is preferred. Generally, when a polymer flocculant is added to sludge containing a large amount of soluble inorganic salts, it is thought that the flocculant will cause thread clumping, and a sufficient flocculation effect cannot be obtained. However, a polymer flocculant having a crosslinked structure can prevent thread clumping and form flocs sufficient for dewatering treatment.

[0037] A polymer flocculant having a crosslinked structure can be produced by using a crosslinking agent during polymerization. Examples of crosslinking agents include divinyl compounds such as N,N'-methylenebis(meth)acrylamide, triallylamine, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, and divinylbenzene, vinyl-based methylol compounds such as methylol methacrylamide, vinyl-based aldehyde compounds such as acrolein, and vinyl-based compounds such as methyl acrylamidoglycolate methyl ether. The crosslinking agent is preferably blended in an amount of 0.0005 to 0.003 wt% based on the total amount of monomers.

[0038] As the polymer flocculant, a cationic polymer flocculant having an amidine structure can also be used. By using a cationic polymer flocculant having an amidine structure, the viscosity of the flocculated sludge does not decrease even when heated, and the filtrate becomes easy to separate, so that the moisture content of the dehydrated cake can be reduced without causing problems such as leakage from the screen holes.

[0039] Specific examples of cationic polymer flocculants having an amidine structure include: (a) Cationic polymers containing repeating units of the azimine structure represented by the following (A) and / or (B) can be used. [ka] [ka] (R in the formula 1 , R 2 represents a hydrogen atom or a methyl group, and X- represents an anion)

[0040] Such a cationic polymer flocculant having an amidine structure can be mixed with a known cationic polymer flocculant and / or an amphoteric polymer flocculant within a range that allows the object of the present invention to be achieved.

[0041] The mixing ratio of polyamidine to the polymer mainly composed of aminoalkyl (meth)acrylate is preferably 10% by weight or more, more preferably 50% by weight or more, and even more preferably 70% by weight or more of polyamidine.

[0042] If the blending ratio of polyamidine is less than 10% by weight, the effect of reducing the moisture content of the cake will not be sufficient, and strong flocs that can withstand squeezing in a dehydrator will not be formed. The blending ratio of polyamidine to the polymer mainly composed of aminoalkyl (meth)acrylate can be adjusted as desired depending on the properties of the organic wastewater and the dehydrator used.

[0043] As the polymer flocculant, a polymer flocculant that satisfies the following conditions (1) and (2) is used. (1) 0.5% salt viscosity is 10 to 90 mPa·s, (2) When the sum of the number of moles (C) of cationic monomers, the number of moles (A) of anionic monomers, and the number of moles (N) of nonionic monomers contained in all monomers constituting the copolymer contained in the polymer flocculant is taken as 100 mol%, the constituent ratio of cationic monomers {C / (C+A+N)} is 25 mol% to 90 mol%, and the total constituent ratio of anionic monomers and nonionic monomers {(A+N) / (C+A+N)} is 10 mol% to 75 mol%.

[0044] The 0.5% salt viscosity of the polymer flocculant is more typically 17 to 80 mPa·s, and even more typically 20 to 70 mPa·s. The 0.5% salt viscosity refers to the viscosity at 25°C of a sample in which 0.5% by mass of the polymer flocculant is dissolved in a 4% by mass NaCl solution.

[0045] If the cationic monomer composition ratio {C / (C+A+N)} is less than 25 mol% or more than 90 mol%, the floc diameter of the flocs does not significantly increase during the flocculation treatment, and the moisture content of the dehydrated cake in the subsequent dehydration treatment may not significantly improve. The cationic monomer composition ratio {C / (C+A+N)} is more preferably 40 mol% to 90 mol%, and even more preferably 45 mol% to 80 mol%.

[0046] If the total composition ratio of the anionic monomer and the nonionic monomer {(A+N) / (C+A+N)} is less than 10 mol% or exceeds 75 mol%, the floc diameter of the flocs does not significantly increase during the flocculation treatment, and the moisture content of the dehydrated cake in the subsequent dehydration treatment may not significantly improve. The total composition ratio of the anionic monomer and the nonionic monomer {(A+N) / (C+A+N)} is more preferably 10 mol% to 65 mol%, and even more preferably 15 mol% to 60 mol%.

[0047] The polymer flocculant preferably has a cation equivalent value of 1.0 to 5.0 meq / g at pH 4 and 4.5 meq / g or less at pH 10. Use of such a polymer flocculant increases the frequency of contact between the polymer flocculant and organic wastewater containing at least one of human waste and septic tank sludge, making it possible to produce flocs with a relatively large floc diameter, and to stably treat difficult-to-dewater organic wastewater.

[0048] The cationic equivalent value of the polymer flocculant at pH 4 is more preferably 1.1 to 4.5 meq / g, and even more preferably 2.0 to 3.5 meq / g. The cationic equivalent value at pH 10 is more preferably 3.0 meq / g or less, even more preferably 1.0 meq / g or less, and even more preferably 0.65 meq / g or less. The lower limit of the cationic equivalent value at pH 10 is not particularly limited, but is typically 0.01 meq / g or more, more preferably 0.25 meq / g or more.

[0049] The cation equivalent value of a polymer flocculant is measured according to the following procedure. First, the polymer flocculant is dissolved in water to prepare a 500 mg / L polymer flocculant sample solution. Next, 90 mL of pure water and 10 mL of the polymer flocculant sample solution are mixed to prepare a polymer flocculant aqueous solution, which is then adjusted to pH 4.0 or pH 10.0 with 0.1 N dilute hydrochloric acid or dilute sodium hydroxide, respectively. Toluidine blue is added to this solution, and while stirring with a magnetic stirrer, titration is performed with a polyvinyl potassium sulfate solution (N / 400 PVSK solution) for colloid titration. The titration rate is 2 mL / min. The end point is the point at which the color changes from blue to reddish purple and this color persists for at least 20 seconds. The sample PVSK titer is then measured. A blank test is performed using 100 mL of pure water, and the blank PVSK titer is measured. The colloid equivalent is then calculated based on the sample PVSK titer and the blank PVSK titer, and this colloid equivalent is used as the cation equivalent value. Colloid equivalent (meq / g) = {(PVSK titration amount - blank PVSK titration amount) × F} / 2 (F is a factor, typically 1.0)

[0050] Polymerization methods for polymer flocculants can include precipitation polymerization, bulk polymerization, dispersion polymerization, and aqueous solution polymerization. As an example, but not limited to, a production method using a quaternary methyl chloride salt of dimethylaminoethyl acrylate and acrylamide is described below. First, a predetermined amount of a quaternary methyl chloride salt of dimethylaminoethyl acrylate, acrylamide, and ion-exchanged water is weighed, adjusted to a predetermined temperature, and then placed in an insulated container. Dissolved oxygen is replaced with nitrogen gas, and chemicals such as a polymerization initiator are added. The polymerization initiator is not particularly limited; common azo initiators can be used. As the polymerization progresses, the temperature reaches its peak, and the mixture is aged for a certain period of time. The polymer gel is then removed from the reaction vessel, cut, dried, and pulverized to obtain a powdered polymer flocculant.

[0051] The molecular weight of the polymer flocculant is typically 3 to 25 million, more typically 3 to 15 million. The polymer flocculant can be used in either powder or liquid form. When a polymer flocculant having a crosslinked structure is used, the crosslinked polymer obtained as an emulsion liquid may be granulated or powdered by spray drying using a spray dryer or the like to form dried granules or powder.

[0052] The polymer flocculant is preferably added to the organic wastewater as an aqueous solution in which it is dissolved in water. The concentration of the aqueous solution of the polymer flocculant is not particularly limited, but is usually 0.05 to 0.8 mass %, more typically 0.1 to 0.5 mass %. The addition rate of the polymer flocculant to the organic wastewater varies depending on the properties of the organic wastewater, but can be approximately 0.2 to 5 mass % relative to the solids in the organic wastewater, and can be 100 to 500 mg / L, or even 150 to 350 mg / L for the organic wastewater according to this embodiment.

[0053] (Other flocculants) In addition to the polymer flocculant, other inorganic flocculants or organic coagulants may be added. Examples of inorganic flocculants include aluminum sulfate, aluminum chloride, polyaluminum chloride (PAC), ferric chloride, and polyferric sulfate. Examples of organic flocculants that can be used include one or more selected from polyamines, dicyandiamides, polydicyandiamides, polydiallyldimethylammonium chlorides (also called "polyDADMAC"), amino condensation systems, and melamine acid colloids.

[0054] More specifically, one or more of the following can be used: polyalkylpolyamine, polyethyleneimine, diallyldimethylammonium chloride, ethylenediamine-epichlorohydrin polycondensate, methylolmelamic acid colloid, dicyandiamide-ammonium chloride-formaldehyde polycondensate, polyethylene-polyamine-dimethylamine-epichlorohydrin polycondensate, dialkylamine-epichlorohydrin polycondensate (especially dimethylamine-epichlorohydrin polycondensate), polyallylamine hydrochloride, polydiallylmethylamine hydrochloride, copolymers of diallyldimethylammonium chloride and sulfur dioxide, copolymers of diallyldimethylammonium chloride and acrylamide, and copolymers of diallylamine hydrochloride and sulfur dioxide. The addition rate of other flocculants to organic wastewater varies depending on the properties of the organic wastewater, but is typically around 100 to 5000 mg / L, or even around 1000 to 4000 mg / L.

[0055] When flocculation treatment is performed using the above-mentioned polymer flocculant and / or other flocculants, the floc diameter of the flocs in the organic wastewater is typically more than 2 mm and not more than 10 mm. If the floc diameter is about 3 to 10 mm, even if the organic wastewater is difficult to dewater, the dewatering treatment can be performed stably while suppressing the occurrence of dewatering defects.

[0056] The amount of sewage and septic tank sludge delivered and the sludge properties at the time of delivery vary from moment to moment depending on the receiving conditions and the season, which can significantly affect the properties of the sludge subjected to dehydration. In particular, because sewage contains a large amount of chloride, a high mixing ratio of sewage to sludge can lead to poor dehydration. Controlling the amount of flocculant added is one solution, but daily control changes can be practically difficult. The polymer flocculant according to the embodiment of the present invention can coarsen fine flocs during the flocculation process to produce strong flocculants, even in response to such fluctuations in sludge properties that vary from moment to moment depending on the receiving conditions and the season. This allows for easy dehydration without poor dehydration. Therefore, stable treatment can be achieved over a long period of time without the need for detailed control of the amount of flocculant added depending on the fluctuations in sludge properties.

[0057] The polymer flocculant according to the embodiment of the present invention can easily dehydrate organic wastewater or sludge containing at least one of human waste and septic tank sludge, which has a high salt concentration and is difficult to dehydrate, by coarsening fine flocs in the flocculation treatment to produce strong flocs, thereby preventing poor dehydration. Therefore, stable treatment can be carried out for a long period of time regardless of the amount of human waste or septic tank sludge brought in and fluctuations in its properties.

[0058] (Organic wastewater treatment equipment) Next, an organic wastewater treatment device according to an embodiment of the present invention will be described. As shown in Figure 1, the organic wastewater treatment device according to the embodiment of the present invention includes a storage tank 30 for storing organic wastewater, a reaction tank 40 connected to the storage tank 30, a flocculant addition means 90 for adding a polymer flocculant to the organic wastewater in the reaction tank 40, a concentration means 50 connected to the reaction tank 40 for concentrating the organic wastewater to which the polymer flocculant has been added, a dewatering means 60 for dewatering the concentrated sludge obtained by the concentration means 50, a storage tank 70, a biological treatment tank 80, and a control means 100 for controlling the amount of polymer flocculant added by the flocculant addition means 90.

[0059] Organic sludge containing at least one of human waste and septic tank sludge is stored in the storage tank 30. The human waste and septic tank sludge may be directly placed in the storage tank 30 when transported from an external facility, or the human waste and septic tank sludge may be received separately and then sent to the storage tank 30. For example, as shown in FIG. 2, an organic wastewater treatment device may further include a human waste receiving tank 10 for receiving the human waste, a pretreatment device 11 for removing impurities contained in the human waste, a human waste storage tank 12 for storing a pretreated solution of the human waste obtained in the pretreatment device 11, and a supply means such as a pump for supplying the pretreated solution to the storage tank 30 or the reaction tank 40 and controlling the flow rate thereof so as to adjust the properties of the organic wastewater in the storage tank 30 or the reaction tank 40, such as SS, TS, conductivity, cation demand, and CST. In addition, the organic wastewater treatment device may be equipped with a septic tank sludge receiving tank 20 for receiving septic tank sludge, a pretreatment device 21 for removing impurities and the like contained in the septic tank sludge, and a septic tank storage tank 22 for storing the pretreated septic tank sludge liquid obtained in the pretreatment device 21.

[0060] By feeding the pretreated liquid, which has been subjected to a predetermined pretreatment in pretreatment devices 11 and 21 on human waste and septic tank sludge, to the storage tank 30, the properties of the mixed liquid fed to the storage tank 30 can be adjusted to a state suitable for subsequent treatment. Of course, pretreatment devices 11 and 21 and the tanks shown in Figure 2 may be added or omitted depending on the scale and receiving capacity of the human waste treatment plant or sewage treatment plant. The organic wastewater stored in the storage tank 30 is fed to the reaction tank 40.

[0061] As shown in Fig. 1, a polymer flocculant is added to the organic wastewater in a reaction tank 40 via a flocculant addition means 90 to perform flocculation treatment. The reaction tank 40 may be provided with an agitator (not shown) to thoroughly stir the polymer flocculant in the organic wastewater in the reaction tank 40. As shown in Fig. 3, a separate reaction tank 41 may be provided upstream of the reaction tank 40, and an inorganic flocculant and / or an organic coagulant may be added in the reaction tank 41 to perform conditioning treatment of the organic wastewater. The organic wastewater in the reaction tank 40 to which the polymer flocculant has been added is sent to a concentration means 50.

[0062] The concentrating means 50 is a means for concentrating organic wastewater to which a polymer flocculant has been added (hereinafter also referred to as "flocculated sludge") to obtain concentrated sludge and concentrated separated liquid, and various commonly available concentrating devices can be used. As the concentrating means 50, it is preferable to use a mechanical concentrating device from the viewpoint of improving treatment efficiency.

[0063] For example, an elliptical plate concentrator equipped with a gravity thickening section in which a slit-shaped elliptical plate rotates relative to the flocculated sludge delivered from the reaction tank 40 and a water collector located below the gravity thickening section for capturing the concentrated separated liquid can be used as the thickening means 50 in Figure 1. Because the elliptical plate thickener does not require wash water, the amount of wash water required for the typical thickening process of excess sludge can be reduced, resulting in a more environmentally friendly thickening process. Furthermore, because the elliptical plate thickener has a relatively compact exterior, the space required for installation can be reduced, allowing for a more compact system. To further stabilize the thickening process in the thickening means 50, inorganic flocculants and / or organic coagulants may be added to the flocculated sludge. The thickened sludge thickened by the thickening means 50 is sent to the dewatering means 60, and the concentrated separated liquid is sent to the storage tank 70 via piping or the like.

[0064] The dewatering means 60 is a means for dewatering the concentrated sludge concentrated by the concentration means 50 to obtain dewatered sludge and dewatered separated liquid. As the dewatering means 60, a centrifugal dehydrator, a belt press dehydrator, a filter press dehydrator, a screw press dehydrator, a rotary press dehydrator, an electroosmotic dehydrator, or the like can be used. In particular, a screw press dehydrator is preferred because it can achieve a low moisture content with low power consumption.

[0065] For example, a screw press dehydrator has a cylindrical outer tube with a screw shaft and screw blades concentric with the cylindrical outer tube. It has a thickening section on the mixed sludge supply side and a squeezing section on the dehydrated cake discharge side, where the space between the cylindrical outer tube and the screw shaft gradually narrows in the direction of the mixed sludge flow. The cylindrical outer tube is provided with multiple openings for discharging separated liquid. A sliding-shaft screw press dehydrator has a mechanism in which the screw shaft moves parallel to the dehydrated sludge outlet direction and forcibly discharges the dehydrated sludge. Use of such a screw press dehydrator can significantly reduce the moisture content of the dehydrated cake. In addition to dehydrators that combine separate screens and dehydrators, dehydrators that integrate a screen and dehydrator, including a thickening section in the front stage that performs the function of a screen and a squeezing section in the rear stage, are more preferable because they do not require a separate screen and simplify the device configuration. In order to facilitate the dehydration treatment in the dehydration means 60 , an inorganic flocculant and / or an organic coagulant may be added to the dehydration means 60 via a flocculant adding means 90 .

[0066] The concentrated separated liquid obtained by solid-liquid separation in the concentration means 50 and the dehydrated separated liquid obtained by solid-liquid separation in the dehydration means 60 are stored in a storage tank 70 and then subjected to biological treatment in a biological treatment tank 80, and are subjected to dilution treatment or the like as necessary. The biological treatment is not particularly limited, but examples thereof include aerobic biological treatment using an activated sludge method (a conventional activated sludge method, a membrane separation activated sludge method, a batch activated sludge method), a biofilm treatment method (a fixed-bed biofilm method, a fluidized-bed biofilm method), or the like.

[0067] The concentrated separated liquid produced by the concentration means 50 and the dehydrated separated liquid produced by the dehydration means 60 can also be used as raw water for phosphorus recovery. Alternatively, excess sludge produced in the biological treatment tank 80 is allowed to flow into the storage tank 30 and mixed with the human waste and septic tank sludge from the human waste receiving tank 10 and the septic tank sludge receiving tank 20 shown in Figure 2. By circulating the excess sludge from the biological treatment tank 80 to the storage tank 30, the amount of sludge generated and discharged outside the treatment system as a whole can be reduced.

[0068] The control means 100 is connected to a pump 31 that supplies organic wastewater from the storage tank 30 to the reaction tank 40 (reaction tank 41 in FIG. 3 ), and to a flocculant addition means 90. The control means 100 controls the supply of a polymer flocculant and an inorganic flocculant or an organic coagulant by the flocculant addition means 90. For example, the control means 100 can control the addition rate and type of flocculant to be added according to the amount of organic wastewater supplied into the reaction tank 40 via the pump 31.

[0069] The control means 100 may control the type and amount of flocculant supplied to the reaction tanks 40, 41, the concentration means 50, and the dewatering means 60 depending on the properties of the organic wastewater contained in the storage tank 30. For example, when easily dewaterable organic wastewater having properties such that a sufficient flocculation effect can be obtained even when a general polymer flocculant or inorganic flocculant as described in Patent Document 1 is added from the storage tank 30 to the reaction tanks 40, 41, the control means 100 adds a generally available normal flocculant to the reaction tank 40. On the other hand, when the organic wastewater supplied from the storage tank 30 to the reaction tank 40 is difficult to dewater due to fluctuations in the properties of the organic wastewater caused by seasonal fluctuations, climate change, fluctuations in the amount and timing of delivery, etc., the control means 100 adds a polymer flocculant according to an embodiment of the present invention to the reaction tank 40.

[0070] In this way, the control means 100 can control the type of polymer flocculant based on the properties of the organic wastewater in the storage tank 30, thereby optimizing and improving the efficiency of the treatment. In this case, when treating organic wastewater that is difficult to dewater, by using the polymer flocculant according to this embodiment, the dewatering treatment can be carried out stably without causing dewatering defects, etc., and therefore, more efficient and stable treatment can be achieved than in the past.

[0071] The properties of the organic wastewater in the storage tank 30 may be measured manually. Alternatively, a measuring device for measuring the properties of the organic wastewater inside the storage tank 30, such as the conductivity and cation demand, may be installed inside the storage tank 30. Based on the measurement results of the measuring device, the control means 100 may output a control signal for selecting the type of flocculant to the flocculant addition means 90. In addition to the type of flocculant, the control means 100 can appropriately control the flocculant addition rate, addition time, start and end of addition, etc.

[0072] (Method for treating organic wastewater) An example of a method for treating organic wastewater according to an embodiment of the present invention will be described below, using the organic wastewater treatment apparatus shown in Figures 1 to 3. The method for treating organic wastewater according to an embodiment of the present invention includes adding a polymer flocculant that satisfies the following conditions (1) and (2) to difficult-to-dewater organic wastewater containing at least one of human waste and septic tank sludge, and having, for example, a conductivity of 50 to 1500 mS / m, a difference between evaporation residue and suspended solids of 1500 mg / L or more, a cation demand of -0.01 to -2.00 meq / L, and a capillary suction time (CST) of 300 seconds or more, flocculating the organic wastewater, followed by concentrating the flocculating treatment, and then dehydrating the concentrated sludge obtained by the concentration treatment. (1) 0.5% salt viscosity is 10 to 90 mPa·s, (2) When the sum of the number of moles (C) of cationic monomers, the number of moles (A) of anionic monomers, and the number of moles (N) of nonionic monomers contained in all monomers constituting the copolymer contained in the polymer flocculant is taken as 100 mol%, the constituent ratio of cationic monomers {C / (C+A+N)} is 25 mol% to 90 mol%, and the total constituent ratio of anionic monomers and nonionic monomers {(A+N) / (C+A+N)} is 10 mol% to 75 mol%.

[0073] In the coagulation treatment, the polymer coagulant is added to the organic wastewater having the above properties to form coagulated flocs with a diameter of about 2 to 10 mm in the liquid. An inorganic coagulant and / or an organic coagulant may be added before or after the condensation treatment.

[0074] In the concentration treatment, an inorganic flocculant and / or an organic coagulant may be added as necessary to the flocculated sludge containing the flocs obtained in the coagulation treatment. The concentrated sludge obtained in the concentration treatment is then dehydrated using a dehydrator or the like to obtain dehydrated sludge (dehydrated cake). In this concentration treatment, the flocculated sludge obtained in the coagulation treatment is preferably treated using an elliptical plate thickener equipped with a gravity thickening section in which a slit-shaped elliptical plate rotates and moves, and a water collector provided below the gravity thickening section for capturing the concentrated separated liquid. This allows for efficient and stable treatment of the flocculated sludge.

[0075] In the dehydration treatment, in order to stably dehydrate poorly dewaterable organic wastewater containing at least one of human waste and septic tank sludge, it is preferable to dehydrate the concentrated sludge obtained in the concentration treatment, for example, using a screw press dehydrator, to obtain dehydrated sludge and dehydrated separated liquid. The concentrated separated liquid and dehydrated separated liquid obtained by the concentration treatment and dehydration treatment are stored in a storage tank 70 and then introduced into a biological treatment tank 80 for biological treatment. By returning the excess sludge generated in the biological treatment to the storage tank 30 and mixing it with the organic wastewater containing at least one of human waste and septic tank sludge, the amount of excess sludge generated in the system can be reduced and treatment efficiency can be improved.

[0076] According to the method for treating organic wastewater according to the embodiment of the present invention, it is possible to stably dehydrate sludge including human waste and / or septic tank sludge, which are prone to fluctuations in properties. [Example]

[0077] Examples of the present invention will be described below together with comparative examples. These examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the invention.

[0078] (Test 1) As the polymer flocculants, polymer flocculants A to H were prepared having the compositions and properties shown in Table 1. The abbreviations for the components constituting the polymer flocculants are as follows. DAA: Methyl chloride quaternary salt of dimethylaminoethyl acrylate DAM: methyl chloride quaternary salt of dimethylaminoethyl methacrylate AAm: acrylamide AA: acrylic acid

[0079] The 0.5% salt viscosity of the polymer flocculant was measured at 25°C using a Brookfield viscometer, with the viscosity of a sample prepared by dissolving 0.5% by mass of the polymer flocculant in a 4% by mass NaCl solution.

[0080] The cation equivalent value of the polymer flocculant at pH 4 and 10 was measured in the same manner as described above. That is, the polymer flocculant was dissolved in water to prepare a 500 mg / L polymer flocculant sample solution, which was then adjusted to pH 4.0 or pH 10.0 with 0.1 N dilute hydrochloric acid or dilute sodium hydroxide, respectively, and then titrated with a polyvinyl potassium sulfate solution (N / 400 PVSK solution) for colloid titration. The colloid equivalent was calculated based on the sample PVSK titer and the blank PVSK titer, and this was used as the cation equivalent.

[0081] [Table 1]

[0082] In Test 1, 200 ml of sewage (pH: 7.5, conductivity: 973 mS / m, TS: 9,100 mg / L, SS: 5,700 mg / L, TS-SS: 3,400 mg / L; cation demand: -0.91 meq / L, CST: 735 seconds) delivered to a certain sewage treatment plant was placed in a 500 ml beaker, to which 310 mg / L of a 0.2% aqueous solution of polymer flocculants A to H listed in Table 1 was added. The mixture was stirred for 10 seconds at 800 rpm using a commercially available hand mixer to obtain flocculated sludge. This flocculated sludge was gravity filtered through a 60-mesh nylon filter cloth, and the volume of filtered water after 30 seconds was measured. The flocculated sludge on the filter cloth was quickly transferred to a beaker, and polyferric sulfate was added dropwise. The sludge was re-flocculated by stirring 10 times with a spatula. The resulting flocculated sludge was then sandwiched between two filter cloths and dehydrated using a dehydrator at 2 kg / cm. 2 The resulting dehydrated cake was measured for moisture content. The results are shown in Table 2.

[0083] In the following, "floc self-supporting ability" was evaluated as "Good" if the sludge stood on its own when placed on the filter cloth in the dehydrator according to the above procedure, "Good" if it protruded from the filter cloth, and "Poor" if it did not fit on the filter cloth at all. "Floc diameter" was evaluated by visually evaluating the overall floc diameter of the sludge when placed on the filter cloth in the dehydrator according to the above procedure, and the average value was taken as the floc diameter. "Moisture content of dehydrated cake" was evaluated based on the change in weight of the sludge before and after dehydration treatment.

[0084] [Table 2]

[0085] The human waste used in Test 1 was difficult to dewater, with a high salt concentration, a TS-SS of 3,400 mg / L, and an extremely high CST value. However, by using polymer flocculants A to D, the self-sustaining properties of the flocs improved, allowing for easy dewatering. As a result, dewatered cake with a low moisture content of 69.9% to 72.6% was consistently obtained. On the other hand, when polymer flocculants E to H were used, the floc diameter was too small or flocculation did not occur, preventing stable filtration. The addition of inorganic flocculants was not effective, and it was difficult to measure the moisture content of the dewatered cake. The self-sustaining properties of the flocs were also poorly evaluated.

[0086] (Test 2) As the polymer flocculants, polymer flocculants I to M having the compositions and properties shown in Table 3 were prepared.

[0087] [Table 3]

[0088] In Test 2, 100 ml of a mixed sludge of sewage and septic tank sludge delivered to a certain sewage treatment plant (pH: 7.1, conductivity: 1,040 mS / m, TS: 10,400 mg / L, SS: 7,000 mg / L, TS-SS: 3,400 mg / L; cation demand: -0.96 meq / L, CST: 1,625 seconds) was placed in a 300 ml beaker, and 170 mg / L of a 0.2% aqueous solution of polymer flocculants I to M with the physical properties shown in Table 3 was added. The mixture was stirred at 800 rpm for 10 seconds using a commercially available hand mixer. The flocculated sludge was gravity filtered through a 60-mesh nylon filter cloth, and the amount of filtered water after 30 seconds was measured. The sludge was then sandwiched between two filter cloths and dewatered using a dehydrator at a rate of 2 kg / cm. 2 The resulting dehydrated cake was measured for moisture content. The results are shown in Table 4.

[0089] [Table 4]

[0090] The mixed sludge of sewage and septic tank sludge used in Test 2 was difficult to dewater, with a high salt concentration, a TS-SS of 3,400 mg / L, and an extremely high CST value. However, by using polymer coagulants I to L, the flocculated flocs became more self-sustaining, allowing for easy dewatering. As a result, dewatered cakes with moisture contents of approximately 75.5% to 76.3% were consistently obtained. On the other hand, when polymer coagulant M was used, the floc diameter did not become coarse, and the amount of filtered water was reduced compared to when polymer coagulants I to L were used. When polymer coagulant M was used, the flocculated sludge did not adhere to the filter cloth during dewatering, and the moisture content of the dewatered cake could not be measured.

[0091] (Test 3) As the polymer flocculants, polymer flocculants N to V having the compositions and properties shown in Table 5 were prepared.

[0092] [Table 5]

[0093] In Test 3, 200 ml of a mixed sludge of sewage and septic tank sludge delivered to a certain sewage treatment plant (pH: 7.2, conductivity: 429 mS / m, TS: 7,300 mg / L, SS: 5,800 mg / L, TS-SS: 1,500 mg / L; cation demand: -0.44 meq / L, CST: 835 seconds) was placed in a 300 ml beaker, and 150 mg / L of a 0.2% aqueous solution of polymer flocculants N-V with the physical properties shown in Table 5 was added. The mixture was stirred at 800 rpm for 10 seconds using a commercially available hand mixer. The flocculated sludge was gravity filtered through a 60-mesh nylon filter cloth, and the amount of filtered water after 30 seconds was measured. Next, the sludge was passed through two filter cloths using a dehydrator at 2 kg / cm. 2 The resulting dehydrated cake was then measured for moisture content. The results are shown in Table 6. [Table 6]

[0094] The mixed sludge of sewage and septic tank sludge used in Test 3 was difficult to dewater, with a TS-SS of approximately 1,500 mg / L. However, the use of polymer coagulants P to T improved the self-sustaining properties of the flocs, allowing for easy dewatering. As a result, dewatered cakes with moisture contents of approximately 81.2% to 84.3% were consistently obtained. Polymer coagulant N had poor self-sustaining properties due to the floc diameter being too small, making it difficult to handle and more difficult to dewater than polymer coagulants P to T. Polymer coagulant U had a moisture content of 82.5%, and was able to achieve the same level of dewatering as polymer coagulants S and T. However, the amount of filtered water was less than that of polymer coagulants S and T, and the floc diameter was too small, resulting in poor self-sustaining properties of the flocs, making stable dewatering difficult. Although it was possible to carry out dewatering treatment with polymer flocculants O and V, as the floc diameter was small and the floc self-sustaining ability of the flocculants was poor, the moisture content of the dewatered cake was higher than when polymer flocculants P to T were added, and it was more difficult to carry out stable dewatering treatment compared to polymer flocculants P to T.

[0095] (Test 4) As the polymer flocculants, polymer flocculants W to Z and AA to DD having the compositions and properties shown in Table 7 were prepared.

[0096] [Table 7]

[0097] In Test 4, 200 ml of a mixed sludge of sewage and septic tank sludge delivered to a certain sewage treatment plant (pH: 7.5, conductivity: 486 mS / m, TS: 7,300 mg / L, SS: 5,800 mg / L, TS-SS: 1,500 mg / L; cation demand: -0.66 meq / L, CST: 987 seconds) was placed in a 300 ml beaker, and 150 mg / L of a 0.2% aqueous solution of polymer flocculants W-Z and AA-DD with the physical properties shown in Table 7 was added. The mixture was stirred at 800 rpm for 10 seconds using a commercially available hand mixer. The flocculated sludge was gravity filtered through a 60-mesh nylon filter cloth, and the amount of filtered water after 30 seconds was measured. Next, the sludge was passed through two filter cloths and dewatered using a dehydrator at 2 kg / cm. 2 The resulting dehydrated cake was measured for moisture content. The results are shown in Table 8.

[0098] [Table 8]

[0099] The mixed sludge of sewage and septic tank sludge used in Test 4 was difficult to dewater, with a TS-SS of approximately 1,500 mg / L. However, the addition of polymer coagulants Y-Z and AA-BB improved the self-sustaining properties of the flocs, making dewatering easy. As a result, dewatered cakes with moisture contents of approximately 76.5% to 81.1% were consistently obtained. Polymer coagulants W and U had too small a floc diameter, resulting in poor self-sustaining properties and poor handling, making dewatering more difficult than with polymer coagulants P-T. Polymer coagulants X, CC, and DD also had small floc diameters and poor self-sustaining properties, making dewatering possible. However, the moisture content of the dewatered cake was higher than with polymer coagulants Y-Z and AA-BB, making stable dewatering more difficult than with polymer coagulants Y-Z and AA-BB. [Explanation of symbols]

[0100] 10...Urine receiving tank 11...Pretreatment device 12...Urine storage tank 20...Septic tank sludge receiving tank 21...Pretreatment device 22...Septic tank storage tank 30...Reservoir 31...Pump 40...Reaction tank 41...Reaction tank 50...Concentration means 60...Dehydration means 70...Reservoir 80...Biological treatment tank 90...Flocculant addition means 100...Control means

Claims

1. A polymer flocculant is used for difficult-to-dewater organic wastewater containing at least one of human waste and septic tank sludge under the following conditions: (1) 0.5% salt viscosity is 10 to 90 mPa·s; (2) Of the molar number of cationic monomers, the molar number of anionic monomers, and the molar number of nonionic monomers contained in the total monomers constituting the copolymer contained in the polymer flocculant, the constituent ratio of the cationic monomers is 25 to 90 mol%, and the total constituent ratio of the anionic monomers and the nonionic monomers is 10 to 75 mol%, 1. A method for treating organic wastewater, comprising the steps of: adding a polymer flocculant satisfying the above requirement to carry out a flocculation treatment; thereafter, concentrating the flocculated sludge; and dehydrating the concentrated sludge.

2. 2. The method for treating organic wastewater according to claim 1, wherein the polymer flocculant has a cation equivalent value of 1.0 to 5.0 meq / g at pH 4 and a cation equivalent value of 4.5 meq / g or less at pH 10.

3. 3. The method for treating organic wastewater according to claim 1, wherein the polymer flocculant is one or more copolymers selected from the group consisting of quaternary methyl chloride salt of dimethylaminoethyl acrylate, quaternary methyl chloride salt of dimethylaminoethyl methacrylate, acrylamide, and acrylic acid.

4. The method for treating organic wastewater according to any one of claims 1 to 3, characterized in that the difficult-to-dewater organic wastewater has an electrical conductivity of 50 to 1500 mS / m, a difference between evaporation residue and suspended solids of 1500 mg / L or more, a cation demand of -0.01 to -2.00 meq / L, and a capillary suction time (CST) of 300 seconds or more.

5. The method for treating organic wastewater according to any one of claims 1 to 4, further comprising subjecting the concentrated separated liquid and the dehydrated separated liquid obtained in the concentration treatment and the dehydration treatment to biological treatment, and adding excess sludge obtained in the biological treatment to the difficult-to-dehydrate organic wastewater.

6. a reaction tank into which difficult-to-dewater organic wastewater containing at least one of human waste and septic tank sludge is introduced; a polymer flocculant having a 0.5% salted viscosity of 10 to 90 mPa·s, in which, among the molar numbers of cationic monomers, anionic monomers, and nonionic monomers contained in all monomers constituting the copolymer, the constituent ratio of the cationic monomers is 25 to 90 mol %, and the total constituent ratio of the anionic monomers and the nonionic monomers is 10 to 75 mol %; a flocculant adding means for adding the polymer flocculant to the reaction tank; a concentrating means for concentrating the organic wastewater to which the polymer flocculant has been added; a dehydration means for dehydrating the concentrated sludge obtained by the concentration means; An organic wastewater treatment device comprising:

7. 7. The organic wastewater treatment device according to claim 6, wherein the flocculant adding means further adds an inorganic flocculant to the organic wastewater.

8. 8. The organic wastewater treatment device according to claim 6 or 7, further comprising a control means capable of controlling the addition rate of the polymer flocculant added by the flocculant addition means based on the properties or supply amount of the organic wastewater.

9. a wastewater receiving tank for receiving the wastewater; a pretreatment device for removing impurities contained in the human waste; a sewage storage tank for storing the pretreated liquid treated by the pretreatment device; a supply means for supplying the pretreatment liquid into the reaction tank or a storage tank for storing the organic wastewater to be supplied to the reaction tank, and adjusting the flow rate of the organic wastewater in the reaction tank or the storage tank; The organic wastewater treatment device according to any one of claims 6 to 8, further comprising:

10. A polymer flocculant for difficult-to-dewater organic wastewater containing at least one of human waste and septic tank sludge, The polymer flocculant satisfies the following conditions: (1) 0.5% salt viscosity is 10 to 90 mPa·s; (2) Of the molar number of cationic monomers, the molar number of anionic monomers, and the molar number of nonionic monomers contained in the total monomers constituting the copolymer contained in the polymer flocculant, the constituent ratio of the cationic monomers is 25 to 90 mol%, and the total constituent ratio of the anionic monomers and the nonionic monomers is 10 to 75 mol%, A polymer flocculant characterized by satisfying the above.

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