Dehydration aid and sludge dehydration method

Abstract

The present invention provides a dehydration aid comprising a hydrophobic short fiber and a surfactant attached to the surface of the hydrophobic short fiber, the surfactant comprising a cationic surfactant and a nonionic surfactant, the cationic surfactant is a surfactant in which the zeta potential of the hydrophobic short fibers is changed by + 50 mV or more by adhering to the hydrophobic short fibers, the nonionic surfactant has an HLB of 7-13, and the dehydration aid can be uniformly dispersed in water and has good dehydration properties after formation of sludge and flocculate. And the water content after dehydration is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to a dewatering aid, and more particularly to a fibrous dewatering aid for dewatering sludge. It also relates to a dewatering method for sludge using the dewatering aid. BACKGROUND

[0002] In recent years, in order to reduce environmental load, biological treatment of organic wastewater such as domestic wastewater and factory wastewater has been increasing, and the resulting excess sludge has also been increasing. Generally, the excess sludge is disposed of or reused after being reduced in amount by dewatering.

[0003] In the case of disposal, most of it is incinerated, but if the moisture content of the sludge is high, the energy load during incineration and transportation becomes high. Therefore, it is desirable to reduce the water content of the dewatered sludge.

[0004] Among them, a dewatering method is proposed in which a flocculant and a dewatering aid fiber are added to the dewatered sludge, making it easy to dewater the sludge (Patent Documents 1 and 2). In this method, as the dewatering aid, regenerated cellulose fiber having a high hydrophilicity is used in order to improve water dispersibility. Therefore, it can become an obstacle to reducing the water content of the dewatered filter cake.

[0005] In addition, a method is proposed in which the effect as a dewatering aid is improved, in which a surfactant that increases the negative (-) potential is made to act on paper pulp using the paper pulp as a dewatering aid, and the paper pulp is uniformly dispersed by mutual repulsion of charges in a state of being dispersed in water (Patent Document 3).

[0006] In the case of using this method, since the zeta potential of the sludge is negative (-), in order to form a flocculate suitable for dewatering, a cationic high-molecular flocculant needs to be mixed in a large amount, resulting in an increase in cost.

[0007] Furthermore, a method is proposed in which a fibrous material obtained by treating the surface of synthetic fiber, semi-synthetic fiber, regenerated fiber, and natural fiber with a hydrophilic oil agent and a flocculant are used (Patent Document 4).

[0008] In the case of using this method, it is assumed that the uniform dispersibility of the fiber into water is made good by the hydrophilic oil agent, but since the composition acting on the sludge contains the hydrophilic oil agent due to the addition of the flocculant thereto, the dewaterability is not necessarily improved.

[0009] Patent Document 1: Japanese Patent No. 4817431

[0010] Patent Document 2: Japanese Patent No. 5658107

[0011] Patent Literature 3: Japanese Patent No. 6411182

[0012] Patent Literature 4: Japanese Patent Application Laid-Open No. 2018-167191 SUMMARY

[0013] An object of the present application is to provide a dewatering aid which is uniformly dispersed in sludge and has good dewatering properties after flocculation, and which can reduce the water content after dewatering.

[0014] That is, the present application provides a dewatering aid characterized by comprising hydrophobic short fibers and a surfactant attached to the surface thereof, the surfactant comprising a cationic surfactant and a nonionic surfactant, the cationic surfactant being a surfactant which changes the zeta potential of the hydrophobic short fibers by +50 mV or more by being attached to the hydrophobic short fibers, and the nonionic surfactant having an HLB of 7 to 13.

[0015] According to the present application, a dewatering aid which is uniformly dispersed in sludge and has good dewatering properties after flocculation, and which can reduce the water content after dewatering can be provided. DETAILED DESCRIPTION

[0016] Hereinafter, the present application will be described in detail.

[0017] 〔Hydrophobic short fibers〕

[0018] The hydrophobic short fibers in the present application are short fibers of hydrophobic fibers. The hydrophobic fibers in the present application are fibers having a moisture content of 3.0% by weight or less as described in JIS L-1015, and specifically, polyester fibers, polyolefin fibers, polylactic acid fibers, acrylic fibers can be exemplified. Among them, polyester fibers are preferred, and polyethylene terephthalate fibers, polybutylene terephthalate fibers are particularly preferred. That is, as the hydrophobic short fibers, polyester short fibers are preferred, and polyethylene terephthalate short fibers, polybutylene terephthalate short fibers are particularly preferred.

[0019] The fiber diameter of the hydrophobic short fibers is preferably 3 to 100 μm, further preferably 4 to 50 μm, and particularly preferably 5 to 30 μm. If the fiber diameter is less than 3 μm, the coagulation of the hydrophobic short fibers with each other becomes strong, and it is difficult to uniformly disperse in water and sludge, which is not preferred. On the other hand, if the fiber diameter exceeds 100 μm, the capillary phenomenon effect becomes low, and thus the retained water in the sludge cannot be extracted, which is not preferred.

[0020] In the state of the short fiber aggregate in which the hydrophobic short fibers are aggregated, the hydrophobic short fibers are used as a dewatering aid. The fiber diameters of the 1 by 1 hydrophobic short fibers constituting the short fiber aggregate are preferably the same. Here, the fiber diameters being the same means that the difference between the maximum value and the minimum value of the fiber diameters is 20% or less, and preferably 10% or less.

[0021] The fiber length of the hydrophobic short fibers is preferably 1 to 50 mm, and further preferably 3 to 20 mm. The fiber lengths of the 1 by 1 hydrophobic short fibers constituting the short fiber aggregate are preferably the same. Here, the fiber lengths being the same means that the difference between the maximum value and the minimum value of the fiber lengths is 20% or less, and preferably 10% or less. If the fiber length of the hydrophobic short fibers is less than 1 mm, the effect as a water guide path of the capillary phenomenon cannot be sufficiently exerted, and this is not preferred. On the other hand, if the fiber length exceeds 50 mm, entanglement of the hydrophobic short fibers with each other occurs, and the dispersibility in water and sludge becomes poor, and in addition, clogging of the filter screen of the dewatering machine occurs due to entanglement, and thus this is not preferred.

[0022] [Surfactant]

[0023] The hydrophobic fibers available as a commercial product are given a spin finish required for spinning. In general, the spin finish is constituted of a mineral oil and a nonionic surfactant and an anionic surfactant, and the nonionic surfactant and the anionic surfactant are used to emulsify the mineral oil in water, and in addition, to impart antistatic properties. If the hydrophobic fibers are simply used as they are, the dispersibility in water containing sludge is not good.

[0024] In the present application, a cationic surfactant and a nonionic surfactant are further given to the surface of the hydrophobic short fibers to which the spin finish is attached.

[0025] [Cationic Surfactant]

[0026] The cationic surfactant used in the present application is a surfactant having the property of changing the zeta potential of the hydrophobic short fibers by +50 mV or more by being attached to the hydrophobic short fibers.

[0027] Since the zeta potential of the fiber surface of the hydrophobic short fibers is generally negative (-), in the presence of the cationic surfactant and the nonionic surfactant, the cationic surfactant is adsorbed to the surface of the hydrophobic short fibers, and at the same time, the hydrophobic group of the nonionic surfactant is adsorbed to the hydrophobic group of the cationic surfactant.

[0028] As the oil agent to be imparted at the time of spinning, generally, nonionic surfactants and anionic surfactants are used, but among them, the anionic surfactants further lower the zeta potential of the fiber to negative (-). In the present application, by further imparting a cationic surfactant thereto, the charge is neutralized, as a result of which, it is possible to increase the zeta potential.

[0029] Since the sludge has a negative (-) zeta potential, the hydrophobic short fibers to which the cationic surfactant is adsorbed play a role as a water conduit at the time of dewatering by being adsorbed to the sludge.

[0030] Here, in order to obtain a high dewatering rate, it is desired that the cationic surfactant neutralize the charge of the anionic surfactant used for the spinning oil agent, and that the zeta potential of the hydrophobic short fibers further change in the positive (+) direction. Therefore, in the present application, as the cationic surfactant, a cationic surfactant having a property of changing the zeta potential by +50 mV or more is used.

[0031] The surface of the hydrophobic short fibers originally has a negative (-) zeta potential, by further causing the spinning oil agent to adhere to the surface of the hydrophobic short fibers, the zeta potential is further shifted in the negative (-) direction. In the present application, by causing the above-described cationic surfactant to adhere to the hydrophobic short fibers, the zeta potential of the surface of the hydrophobic short fibers is shifted in the positive (+) direction. As a result, the sludge which originally has a negative (-) zeta potential and the above-described hydrophobic short fibers form good floes via the coagulant, and it is possible to improve the dewatering rate of the sludge.

[0032] As the cationic surfactant which changes the zeta potential of the fiber surface of the hydrophobic short fibers by +50 mV or more, a quaternary ammonium salt is preferably used. In this case, the nitrogen concentration in the surfactant adhering to the surface of the hydrophobic fibers is derived from the nitrogen element of the quaternary ammonium salt. In order to change the zeta potential of the surface of the hydrophobic short fibers by +50 mV or more using the cationic surfactant, it is preferable that the nitrogen concentration in the surfactant be 500 ppm or more, and further preferably 750 ppm or more. It should be noted that the nitrogen concentration in the surfactant is calculated as a value including the nitrogen element contained in the components originally adhering to the fiber surface of the hydrophobic short fibers.

[0033] As the cationic surfactant, a hydrophobic group is contained in the molecule thereof. The hydrophobic group is preferably a monoalkyl type or a dialkyl type. In either case, from the viewpoints of dispersibility in water, adhesiveness to the hydrophobic short fibers, and compatibility with nonionic surfactants, and the like, the number of carbon atoms of the alkyl group is preferably 8 to 22 in either case.

[0034] As such cationic surfactants, specifically, stearyltrimethylammonium chloride, stearyltrimethylammonium bromide, cetrimonium chloride, cetrimonium bromide, behenyltrimethylammonium chloride, distearyldimethylammonium chloride, dicetyl dimethylammonium chloride, isostearyl lauryl dimethylammonium chloride can be exemplified.

[0035] [Nonionic surfactant]

[0036] Hydrophobic short fibers are originally poor in wettability in water and low in dispersibility in water. In general, among the oil agent imparted to the fibers at the time of spinning, a nonionic surfactant, an anionic surfactant are contained. These surfactants are added only for the purpose of making water-based oil agent and for the purpose of exhibiting antistatic function. They are not added for the purpose of improving the dispersibility in water of the filaments constituting the fiber bundle one by one. Therefore, if only commercially available fibers are directly used, good dispersibility in water of the filaments constituting the fiber bundle cannot be obtained.

[0037] The dispersibility in water of the dewatering aid of the present application is borne by the nonionic surfactant having HLB of 7 to 13 attached to the surface of the hydrophobic short fibers. HLB is a scale indicating the degree of hydrophilicity and lipophilicity (hydrophobicity) of a surfactant, and the stronger the hydrophilicity, the larger the value. HLB takes a value between 0 (lipophilicity) and 20 (hydrophilicity). In nonionic surfactants, HLB is calculated by Griffin's formula described below.

[0038] HLB = 20 Mw / Mn

[0039] Here, Mw is the molecular weight of the hydrophilic group, and M is the molecular weight of the nonionic surfactant.

[0040] If the HLB of the nonionic surfactant exceeds 13, the dispersibility in water is good, but since the hydrophilicity becomes high, the water retention becomes high, and a good dewatering rate cannot be obtained. On the other hand, if the HLB of the nonionic surfactant is less than 7, only the interaction with the hydrophobic short fibers is strong, but the wettability in water is low, and the dispersibility in water is poor.

[0041] As the nonionic surfactant having HLB of 7 to 13, polyether polyester copolymer, ester-type nonionic surfactant, ether-type nonionic surfactant.

[0042] As the polyether polyethylene glycol terephthalate, polyethylene glycol isophthalate, polyethylene glycol terephthalate-polyethylene glycol isophthalate, polyethylene glycol terephthalate-polyethylene glycol isophthalate monoether, and the like.

[0043] Here, as the alkylene glycol, ethylene glycol, propylene glycol, tetramethylene glycol, and pentamethylene glycol are preferable. As the polyalkylene glycol, polyethylene glycol, polypropylene glycol, and the like are preferable. polypropylene glycol copolymer, polypropylene glycol. As the polyalkylene glycol monoether, polyethylene glycol monoether is preferable.

[0044] As the ester-type nonionic surfactant, an ethylene oxide adduct of a higher fatty acid is preferable. In addition, as the ether-type nonionic surfactant, an ethylene oxide adduct of a higher alcohol is preferable.

[0045] Thus, the nonionic surfactant contains a hydrophobic group and a hydrophilic group in its molecule, and therefore the hydrophobic group interacts with the hydrophobic short fibers and the hydrophilic group interacts with water, whereby good dispersibility in water can be obtained.

[0046] In the present application, by using both the cationic surfactant and the nonionic surfactant, uniform dispersion of the short fibers in water and good dispersion in sludge can be achieved, and good dewaterability can be obtained.

[0047] The total nitrogen concentration from the cationic surfactant in the surfactant composed of the cationic surfactant and the nonionic surfactant given in the present application is preferably 250 ppm or more, further preferably 500 ppm or more, and further preferably 1000 ppm or more, in the dry weight thereof. If it is less than 250 ppm, a large amount of the surfactant needs to be given in order to sufficiently change the zeta potential of the hydrophobic short fibers to the positive side, which is not preferable in terms of manufacturing process, handling, and cost.

[0048] In a range that does not affect the zeta potential, a small amount of an emulsifier or the like that contributes to emulsification in water can be contained in the surfactant.

[0049] As the hydrophobic short fibers, hydrophobic short fibers from which spinning oil adhering to the surface has been previously removed can be used, in which case the concentration of the cationic surfactant and the nonionic surfactant mixture given can be further reduced.

[0050] [Manufacturing method]

[0051] For the surfactant, a mixture of a cationic surfactant and a nonionic surfactant is preferably adhered to the surface of the hydrophobic short fiber in the form of an aqueous emulsion.

[0052] As a method of adhering the surfactant to the surface of the hydrophobic short fiber, a method can be used in which the surfactant is adhered to the continuous fiber of the hydrophobic fiber before the hydrophobic short fiber is cut to a prescribed length by slit oiling, and then the continuous fiber of the hydrophobic fiber is cut to a prescribed length. Alternatively, the hydrophobic fiber can be sprayed with an aqueous solution of the surfactant, and then cut to a prescribed length.

[0053] Alternatively, a method can be used in which the continuous fiber of the hydrophobic fiber, from which a spinning oil has been previously removed, before the hydrophobic short fiber is cut to a prescribed length, is immersed in a bath of an aqueous solution of the surfactant, the excess aqueous solution adhered to the surface of the continuous fiber of the hydrophobic fiber is squeezed out with a mangle or sucked up with air, and then the continuous fiber of the hydrophobic fiber is cut to a prescribed length.

[0054] [Coagulant]

[0055] As the coagulant, either of an inorganic coagulant and a high-molecular coagulant can be used.

[0056] As the inorganic coagulant, polyferric sulfate (polyferric), polyaluminum chloride (PAC), ferric chloride, aluminum sulfate, slaked lime, ferrous sulfide can be exemplified.

[0057] As the high-molecular coagulant, polyacrylamide, acrylamide sodium acrylate copolymer, sodium acrylamide-2-methylpropane sulfonate copolymer, alkylamino methacrylate quaternary salt polymer, alkylamino methacrylate quaternary salt acrylamide copolymer, polyvinyl amidine, chitosan, polyglutamic acid, alginic acid, pectin, starch, copolymer of acrylate and acrylamide, and methacrylate polymer.

[0058] [Sludge composition for dewatering]

[0059] When dewatering sludge using the dewatering aid of the present application, a sludge composition for dewatering composed of the dewatering aid of the present application, sludge, and a coagulant is prepared, and the sludge composition for dewatering is dewatered. Specifically, the dewatering aid is dispersed in the sludge, a coagulant previously dispersed in water is added thereto and stirred, thereby preparing a coagulated sludge composition for dewatering, and the sludge composition for dewatering is dewatered.

[0060] As the sludge, sludge from a sewage treatment plant, an agricultural settlement drainage facility, a purification tank, a manure treatment facility, an industrial drainage treatment facility, a water purification plant, a paper mill, and a mine can be exemplified. From the viewpoint of the treatment of a sludge dewatering machine, the moisture content of the sludge is preferably 90 to 99.9% by weight, further preferably 95 to 99.5% by weight, and particularly preferably 96 to 99% by weight.

[0061] From the viewpoint of reducing the moisture content of the dewatered filter cake on the basis of simultaneously considering the cost, the dewatering aid of the present application is preferably added at 0.3 to 10 parts by weight, and further preferably added at 0.6 to 6 parts by weight, with respect to 100 parts by weight of the sludge solid component (sludge TS). The amount of the coagulant to be added is, for example, 0.1 to 3 parts by weight, with respect to 100 parts by weight of the sludge TS.

[0062] The dewatering aid of the present application is a dewatering sludge composition suitable for dewatering using a centrifugal dewatering machine, a belt filter press, a screw press, a filter press, a multiple disc type dewatering machine, a double cylinder press dewatering machine, or the like.

[0063] [Dehydration method]

[0064] The dewatering aid of the present application can be suitably used in a dewatering method including the following steps:

[0065] (Step 1) a step of dispersing the dewatering aid of the present application in the sludge,

[0066] (Step 2) a step of adding a coagulant dispersed in water to the sludge and stirring to coagulate the sludge, and

[0067] (Step 3) a step of dewatering the coagulated sludge.

[0068] That is, according to the present application, it is possible to provide a dewatering method of sludge sequentially including the following steps:

[0069] (Step 1) a step of dispersing the dewatering aid of the present application in the sludge,

[0070] (Step 2) a step of adding a coagulant dispersed in water to the sludge and stirring to coagulate the sludge, and

[0071] (Step 3) a step of dewatering the coagulated sludge.

[0072] Examples

[0073] Hereinafter, the present application will be described in detail with examples. The measurement and evaluation were performed using the following methods. Note that the sludge TS is the total evaporation residue of the sludge, that is, the entire amount of the solid substance contained in the slurry of the sludge.

[0074] (1) Oil and surfactant attachment amount

[0075] The amount of oil agent imparted to the hydrophobic fiber obtained in the market and the amount of the surfactant consisting of a mixture of a cationic surfactant and a nonionic surfactant imparted to the hydrophobic fiber were determined by JIS L 1013 2010 8.27 (c) methanol extraction method after drying the sample at 105°C overnight.

[0076] (2) Total nitrogen concentration

[0077] The total nitrogen concentration of the cationic surfactant in the surfactant consisting of a mixture of a cationic surfactant and a nonionic surfactant imparted and the total nitrogen concentration of the cationic surfactant in the oil agent and the surfactant adhered to the surface of the hydrophobic fiber were determined by the following method.

[0078] 1) Pretreatment

[0079] In the case of the surfactant consisting of a mixture of a cationic surfactant and a nonionic surfactant, it was thinly and uniformly spread on a culture dish and vacuum dried at 50°C until the weight did not change.

[0080] In addition, in the case of the oil agent adhered to the surface of the hydrophobic fiber and the imparted surfactant, the methanol-extracted solution in the above (1) was moved to a culture dish, the methanol was removed in a desiccator at 50°C, and then vacuum dried at 50°C until the weight did not change.

[0081] 2) Total nitrogen analysis

[0082] A TN-2100H manufactured by Sibata Scientific Technology Ltd. was used as a micro total nitrogen analysis device, and quantitative analysis of nitrogen was performed by oxidation combustion chemiluminescence method.

[0083] (3) Zeta potential of short fibers

[0084] A sample of short fibers was placed in a measuring column, densely packed between the two end porous plates so that the sample would not move, and the resulting streaming potential was measured at each pH by applying pressure in such a way that a certain pressure was applied from one direction, and the zeta potential was calculated by the following formula. At this time, in the case where the pH is changed in the direction of lowering, hydrochloric acid diluted with pure water was added to adjust the pH, and on the other hand, in the case where the pH is changed in the direction of rising, potassium hydroxide diluted with pure water was added to adjust the pH.

[0085] Zeta potential = - ΔV x η x k / (ε x ΔP)

[0086] ΔV: Streaming potential

[0087] η: viscosity of the test solution

[0088] k: conductivity of the test solution

[0089] ε: dielectric constant of the test solution

[0090] ΔP: pressure loss between the two porous plates

[0091] (4) Dispersed state of the dewatering aid in the sludge

[0092] A dewatering aid was added to 200 ml of the remaining sludge at 3% by weight relative to the TS of the sludge, and stirred for 5 minutes at 150 rpm using a blender.

[0093] The state at this time was visually observed, and evaluated using the following criteria.

[0094] Uniformly dispersed to 1 fiber A

[0095] Mass with a small amount of fiber bundles B

[0096] Mass with fiber bundles C

[0097] (5) Dispersed state of the dewatering aid in the dewatered filter cake

[0098] A dewatering aid was added to 200 ml of the remaining sludge at 3% by weight relative to the TS of the sludge, and stirred for 5 minutes at 150 rpm using a blender. Then, a cationic coagulant was added at 2% by weight relative to the TS, and stirred for 60 seconds at 150 rpm, and then stirred for 5 minutes at 60 rpm, to obtain a dewatering sludge composition. This was subjected to gravity filtration on a filter cloth (Nakao Filter PP9A25) for about 30 seconds, and then a piston-type dewatering machine using compressed air was used to press for 5 minutes at a pressure of 0.6 MPa, to obtain a dewatered filter cake.

[0099] The state of the dewatered filter cake at this time was visually observed, and evaluated using the following criteria.

[0100] Uniformly dispersed to 1 fiber A

[0101] Mass with a small amount of fiber bundles B

[0102] Mass with fiber bundles C

[0103] (6) Moisture content of the dewatered filter cake

[0104] The moisture content of the dewatered filter cake obtained in the above (5) was measured according to the following procedure.

[0105] 1) The empty weight X (g) of an aluminum cup was measured.

[0106] 2) The dewatered filter cake as the measurement object is moved into an aluminum cup, and the total weight Y (g) of the dewatered filter cake and the aluminum cup is measured.

[0107] 3) The dewatered filter cake is placed into a dryer along with the aluminum cup, and dried at 105°C overnight.

[0108] 4) After cooling, the total weight Z (g) of the dewatered filter cake and the aluminum cup is measured along with the aluminum cup.

[0109] 5) The water content of the dewatered filter cake is calculated by the following calculation formula.

[0110] Water content (wt%) = (Y - Z) / (Y - X)

[0111] (7) Dewatered filter cake production reduction rate

[0112] The dewatered filter cake production reduction rate is measured according to the following procedure.

[0113] 1) A polymer flocculant is added to sludge having a TS concentration A (wt%) at B (wt%) relative to the TS of the sludge, and dewatered using a dewatering machine to produce a dewatered filter cake, and the water content X (wt%) of the dewatered filter cake after dewatering is measured.

[0114] 2) The dewatered filter cake production D0 (tons) in the case where the sludge amount is 100 tons and no dewatering aid is added is calculated using the following calculation formula.

[0115] D0 = (100 tons x A (wt%) + 100 tons x A (wt%) x B (wt%)) / (1 - X (wt%))

[0116] 3) A dewatering aid is added to sludge having a TS concentration A (wt%) at C (wt%) relative to the TS of the sludge and stirred, and a polymer flocculant is further added at B (wt%) relative to the TS of the sludge and stirred. Then, dewatering is performed using a dewatering machine to produce a dewatered filter cake, and the water content Y (wt%) of the dewatered filter cake is measured.

[0117] 4) The dewatered filter cake production D1 (tons) in the case where the sludge amount is 100 tons and a dewatering aid is added is calculated using the following calculation formula.

[0118] D1 = (100 tons x A (wt%) + 100 tons x A (wt%) x (B + C) (wt%)) / (1 - Y (wt%))

[0119] 5) The dewatered filter cake production reduction rate is calculated using the following calculation formula.

[0120] Dewatered filter cake production reduction rate (wt%) = (1 - D1 / D0) x 100

[0121] Example 1

[0122] An aqueous solution of a surfactant composed of a mixture of a nonionic surfactant of an ester copolymer having HLB = 11 and a cationic surfactant of a quaternary ammonium salt type having a total nitrogen concentration of 1000 ppm from the quaternary ammonium salt type cationic surfactant was prepared. Using this aqueous solution, a dewatering aid was produced in which the attached amount of the oil agent and the surfactant attached to the fiber surface was 1.2% by weight with respect to the fiber weight, the total nitrogen concentration in the oil agent and the surfactant attached to the fiber surface was 500 ppm, and the weight ratio of polyester staple fibers of 0.6 dTex and 10 mm in length to polyester staple fibers of 3.3 dTex and 10 mm in length was 2: 1.

[0123] The zeta potential of the staple fibers of the dewatering aid at pH = 7.5 after attachment of the aqueous solution of the surfactant composed of a mixture of the nonionic surfactant and the cationic surfactant of the quaternary ammonium salt type was -33.9 mV. In addition, the zeta potential of the above staple fibers after deoiling with methanol was -84.6 mV. That is, by imparting the aqueous solution of the surfactant composed of a mixture of the nonionic surfactant and the cationic surfactant of the quaternary ammonium salt type, the zeta potential increased by 50.7 mV.

[0124] The dispersion state of the dewatering aid in the sludge, the dispersion state of the dewatering aid in the dewatering filter cake, the water content of the dewatering filter cake, and the reduction rate of the amount of the dewatering filter cake were measured. The results are shown in Table 1.

[0125] Example 2

[0126] An aqueous solution of a surfactant composed of a mixture of a nonionic surfactant of an ester copolymer having HLB = 11 and a cationic surfactant of a quaternary ammonium salt type having a total nitrogen concentration of 1000 ppm from the quaternary ammonium salt type cationic surfactant was prepared. Using this aqueous solution, a dewatering aid was produced in which the attached amount of the oil agent and the surfactant attached to the fiber surface was 1.2% by weight with respect to the fiber weight, the total nitrogen concentration in the oil agent and the surfactant attached to the fiber surface was 500 ppm, and the weight ratio of polyester staple fibers of 0.6 dTex and 10 mm in length to polyester staple fibers of 3.3 dTex and 10 mm in length was 2: 1.

[0127] ​​The zeta potential of the short fiber at pH = 7.5 after the attachment of the aqueous solution of the surfactant composed of the mixture of the nonionic surfactant and the cationic surfactant of the quaternary ammonium salt type was -14.2 mV. In addition, the zeta potential of the above short fiber after the deoiling with methanol was -84.6 mV. That is, the zeta potential was increased by 70.4 mV by imparting the aqueous solution of the surfactant composed of the mixture of the nonionic surfactant and the cationic surfactant of the quaternary ammonium salt type.

[0128] The dispersion state of the dewatering aid in the sludge, the dispersion state of the dewatering aid in the dewatered filter cake, the moisture content of the dewatered filter cake, and the reduction rate of the amount of the dewatered filter cake were measured. The results are shown in Table 1.

[0129] [Example 3]

[0130] An aqueous solution of a surfactant composed of a mixture of a cationic surfactant of the quaternary ammonium salt type having a total nitrogen concentration of 1000 ppm and a nonionic surfactant of a polyoxyethylene alkyl ether copolymer having an HLB of 11 was prepared. Using this aqueous solution, a dewatering aid was produced in which the attached amount of the oil agent and the surfactant attached to the surface of the fiber was 2.0% by weight with respect to the weight of the fiber, the total nitrogen concentration in the oil agent and the surfactant attached to the surface of the fiber was 790 ppm, and the weight ratio of a mixture of polyester short fibers having a single yarn fineness of 0.6 dTex and a length of 10 mm and polyester short fibers having a single yarn fineness of 3.3 dTex and a length of 10 mm was 2:1.

[0131] The zeta potential of the short fiber at pH = 7.5 after the attachment of the aqueous solution of the surfactant composed of the mixture of the nonionic surfactant and the cationic surfactant of the quaternary ammonium salt type was -27.0 mV. In addition, the zeta potential of the fiber after the deoiling with methanol was -84.6 mV. That is, the zeta potential was increased by 57.6 mV by imparting the aqueous solution of the surfactant composed of the mixture of the nonionic surfactant and the cationic surfactant of the quaternary ammonium salt type.

[0132] The dispersion state of the dewatering aid in the sludge, the dispersion state of the dewatering aid in the dewatered filter cake, the moisture content of the dewatered filter cake, and the reduction rate of the amount of the dewatered filter cake were measured. The results are shown in Table 1.

[0133] [Comparative Example 1]

[0134] A dewatering aid composed of polyester short fibers having a single yarn fineness of 0.6 dTex and a length of 10 mm to which a nonionic surfactant having an HLB of 15 was imparted at 1.5% by weight with respect to the weight of the fiber was produced.

[0135] The zeta potential of the short fiber at pH = 7.5 after the attachment of the nonionic surfactant aqueous solution was -79.3 mV. In addition, the zeta potential of the short fiber after the deoiling with methanol was -84.6 mV, and by imparting the nonionic surfactant aqueous solution, the zeta potential hardly changed.

[0136] The dispersion state of the dewatering aid in the sludge, the dispersion state of the dewatering aid in the dewatered filter cake, the moisture content of the dewatered filter cake, and the reduction rate of the amount of the dewatered filter cake were measured. The results are shown in Table 1.

[0137] [Comparative Example 2]

[0138] A dewatering aid was produced by cutting a polyester fiber having a single yarn fineness of 0.6 dTex to which 0.5% by weight of an oil agent containing an anionic surfactant with respect to the weight of the fiber was attached and which was obtained as a commercial product to a length of 10 mm to become a polyester short fiber.

[0139] The zeta potential of the short fiber at pH = 7.5 was -125.9 mV. The zeta potential of the short fiber after the deoiling with methanol was -84.6 mV. That is, the zeta potential was reduced by 41.3 mV by the oil agent containing an anionic surfactant.

[0140] The dispersion state of the dewatering aid in the sludge, the dispersion state of the dewatering aid in the dewatered filter cake, the moisture content of the dewatered filter cake, and the reduction rate of the amount of the dewatered filter cake were measured. The results are shown in Table 1.

[0141] [Table 1]

[0142]

[0143] Industrial Availability

[0144] The dewatering aid of the present application can be used as a dewatering agent used in sludge generated from sewage treatment plants, purification tanks, excrement treatment facilities, industrial drainage treatment facilities, other drainage treatment facilities, plants, sludge generated at water purification plants, sludge generated at paper manufacturing plants, sludge generated at construction sludge generated from civil engineering, sludge from mine wastewater, and the like.

Claims

1. A dehydration aid characterized in that, The hydrophobic short fibers and the surfactant attached to the surface thereof, the surfactant being composed of a cationic surfactant and a nonionic surfactant, the cationic surfactant being a surfactant that changes the zeta potential of the hydrophobic short fibers by +50 mV or more by being attached to the hydrophobic short fibers, and the nonionic surfactant having an HLB of 7 to 13.

2. The dehydration aid of claim 1, wherein, The cationic surfactant is a quaternary ammonium salt, and the nitrogen concentration in the surfactant attached to the surface of the hydrophobic fibers is 500 ppm or more.

3. The dehydration aid of claim 1, wherein, The hydrophobic short fibers are polyester short fibers.

4. A dewatering sludge composition composed of the dewatering aid according to any one of claims 1 to 3, sludge, and a coagulant.

5. A coagulated dewatering sludge composition obtained by dispersing the dewatering aid according to any one of claims 1 to 3 in sludge, adding a coagulant previously dispersed in water thereto, and stirring.

6. A dewatering method for sludge, sequentially comprising the following steps: a step (step 1) of dispersing the dewatering aid according to any one of claims 1 to 3 in sludge, a step (step 2) of adding a coagulant dispersed in water to the sludge and stirring to coagulate the sludge, and a step (step 3) of dewatering the coagulated sludge.

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