Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
  • B01D21/01—Separation of suspended solid particles from liquids by sedimentation using flocculating agents
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F11/00—Treatment of sludge; Devices therefor
  • C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
  • C02F11/121—Treatment of sludge; Devices therefor by de-watering, drying or thickening by mechanical de-watering

Definitions

• the present invention relates to a dehydration aid, and more specifically to a fibrous dehydration aid used for dehydrating sludge. It also relates to a method for dehydrating sludge using the dehydration aid.
• Patent Documents 1 and 2 a method has been proposed in which a flocculant and dehydration aid fibers are added to the sludge to make it easier to dehydrate.
• Patent Documents 1 and 2 regenerated cellulose fibers, which have relatively high hydrophilicity, are used as the dehydration aid to improve water dispersibility. This makes it difficult to reduce the moisture content of the dehydrated cake.
• a method has also been proposed in which pulp is used as a dehydration aid, and a surfactant that increases the negative electric potential is applied to it, dispersing the pulp in water, where the mutual repulsion caused by the electric charges causes the pulp to disperse evenly, thereby enhancing its effectiveness as a dehydration aid (Patent Document 3).
• Patent Document 4 a method has been proposed in which a fibrous material made of synthetic fibers, semi-synthetic fibers, regenerated fibers, or natural fibers, the surfaces of which have been treated with a hydrophilic oil agent, is used together with a coagulant.
• the objective of the present invention is to provide a dewatering aid that has uniform dispersibility in sludge, has good dewatering properties after floc formation, and can reduce the water content after dewatering.
• the present invention is a dehydration aid comprising hydrophobic short fibers and a surfactant attached to the surface thereof, the surfactant being 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 when attached to the hydrophobic short fibers, and the nonionic surfactant being a dehydration aid having an HLB of 7 to 13.
• the present invention provides a dewatering aid that is uniformly dispersible in sludge, has good dewatering properties after floc formation, and can reduce the water content after dewatering.
• the hydrophobic staple fiber in the present invention is a hydrophobic staple fiber.
• the hydrophobic fiber in the present invention is a fiber having a moisture regain of 3.0% by weight or less as described in JIS L-1015, and specific examples thereof include polyester fiber, polyolefin fiber, polylactic acid fiber, and acrylic fiber.
• polyester fiber is preferable, and polyethylene terephthalate fiber and polybutylene terephthalate fiber are particularly preferable. That is, as the hydrophobic staple fiber, polyester staple fiber is preferable, and polyethylene terephthalate staple fiber and polybutylene terephthalate staple fiber are particularly preferable.
• the fiber diameter of the hydrophobic short fibers is preferably 3 to 100 ⁇ m, more preferably 4 to 50 ⁇ m, and particularly preferably 5 to 30 ⁇ m. If the fiber diameter is less than 3 ⁇ m, the hydrophobic short fibers will tend to aggregate with each other, making it difficult to disperse uniformly in the water and sludge, which is undesirable. On the other hand, if the fiber diameter exceeds 100 ⁇ m, the capillary effect will be reduced, making it impossible to draw out the water contained in the sludge, which is undesirable.
• Hydrophobic short fibers are used as dehydration aids in the form of a short fiber aggregate consisting of multiple hydrophobic short fibers. It is preferable that each of the hydrophobic short fibers constituting this short fiber aggregate has the same fiber diameter.
• “same fiber diameter” means that the difference between the maximum and minimum fiber diameters is 20% or less, preferably 10% or less.
• the fiber length of the hydrophobic short fibers is preferably 1 to 50 mm, and more preferably 3 to 20 mm. It is preferable that each of the hydrophobic short fibers constituting the short fiber aggregate has the same fiber length.
• the same fiber length means that the difference between the maximum and minimum 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, it is not preferable because it cannot fully exert its effect as a water guide in the capillary phenomenon.
• the hydrophobic short fibers will become entangled with each other, reducing dispersibility in water and sludge, and also causing blockages due to entanglement in the dehydrator filter, which is not preferable.
• Hydrophobic fibers available commercially are treated with oils necessary for spinning.
• the oils consist of mineral oils and nonionic surfactants to emulsify the mineral oils in water and to provide antistatic properties. If these hydrophobic fibers are used as is, they do not disperse well in water containing sludge.
• a cationic surfactant and a nonionic surfactant are further applied to the surface of the hydrophobic short fibers to which the spinning oil has been applied.
• the cationic surfactant used in the present invention is a surfactant that has the property of changing the zeta potential of the hydrophobic short fibers by +50 mV or more when it adheres to the hydrophobic short fibers.
• the zeta potential of the fiber surface of hydrophobic short fibers is generally negative, so in the presence of a cationic surfactant and a nonionic surfactant, the cationic surfactant is adsorbed onto the surface of the hydrophobic short fibers, and at the same time, the hydrophobic group of the nonionic surfactant is adsorbed onto the hydrophobic group of the cationic surfactant.
• nonionic and anionic surfactants are used as the oils added during spinning, but of these, anionic surfactants further reduce the zeta potential of the fibers to - (negative).
• anionic surfactants further reduce the zeta potential of the fibers to - (negative).
• a cationic surfactant is further added to this, neutralizing the charge and, as a result, the zeta potential can be increased.
• hydrophobic short fibers with adsorbed cationic surfactants are adsorbed to the sludge and act as water conduits during dewatering.
• the cationic surfactant in order to obtain a high dehydration rate, it is desirable for the cationic surfactant to neutralize the charge of the anionic surfactant used in the spinning oil and further change the zeta potential of the hydrophobic short fibers in the + (plus) direction. For this reason, the present invention uses as the cationic surfactant a cationic surfactant that has the property of changing the zeta potential by +50 mV or more.
• the surface of hydrophobic short fibers has a negative zeta potential to begin with, and the attachment of spinning oil thereto further shifts the zeta potential in the negative direction.
• the above-mentioned cationic surfactant is attached to the hydrophobic short fibers, thereby shifting the zeta potential of the hydrophobic short fiber surface in the positive direction.
• a quaternary ammonium salt is preferably used as the cationic surfactant that changes the zeta potential of the fiber surface of the hydrophobic short fiber by +50 mV or more.
• the nitrogen concentration in the surfactant attached to the surface of the hydrophobic fiber is derived from the nitrogen element of the quaternary ammonium salt.
• the nitrogen concentration in the surfactant is preferably 500 ppm or more, and more preferably 750 ppm or more.
• the nitrogen concentration in the surfactant is calculated as a value including the nitrogen element of the components contained in the oil that was originally attached to the fiber surface of the hydrophobic short fiber.
• Cationic surfactants contain hydrophobic groups in their molecules. These hydrophobic groups are preferably monoalkyl or dialkyl. In either case, the number of carbon atoms in the alkyl group is preferably 8 to 22, from the viewpoints of dispersibility in water, adhesion to hydrophobic short fibers, and compatibility with nonionic surfactants.
• cationic surfactants include steartrimonium chloride, steartrimonium bromide, cetrimonium chloride, cetrimonium bromide, behentrimonium chloride, distearyldimonium chloride, dicetyldimonium chloride, and isostearyl lauryldimonium chloride.
• Nonionic Surfactant Hydrophobic staple fibers have poor wettability in water and low dispersibility in water.
• the oil applied to the fiber during spinning contains a nonionic surfactant or an anionic surfactant.
• These surfactants are added solely to prepare a water-based oil and to exhibit antistatic properties. They are not added to improve the dispersibility in water of each filament constituting the fiber bundle. For this reason, good dispersibility in water of the filaments constituting the fiber bundle cannot be obtained by simply using commercially available fibers as they are.
• HLB is a scale that indicates the degree of hydrophilicity and lipophilicity (hydrophobicity) of a surfactant, with the stronger the hydrophilicity, the higher the value. HLB ranges from 0 (lipophilic) to 20 (hydrophilic).
• the HLB of the nonionic surfactant exceeds 13
• the dispersibility in water will be good, but the high hydrophilicity will result in high water retention, making it impossible to obtain a good dehydration rate.
• the HLB of the nonionic surfactant is less than 7, although the interaction with the hydrophobic short fibers is strong, the wettability in water will be low and the dispersibility in water will be poor.
• nonionic surfactants with an HLB of 7 to 13 include polyether-polyester copolymers, ester-type nonionic surfactants, and ether-type nonionic surfactants.
• polyether-polyester copolymers examples include copolymers such as terephthalic acid-alkylene glycol-polyalkylene glycol, terephthalic acid-isophthalic acid-alkylene glycol-polyalkylene glycol, terephthalic acid-alkylene glycol-polyalkylene glycol monoether, and terephthalic acid-isophthalic acid-alkylene glycol-polyalkylene glycol monoether.
• the alkylene glycol is preferably ethylene glycol, propylene glycol, tetramethylene glycol, or pentamethylene glycol.
• the polyalkylene glycol is preferably polyethylene glycol, a polyethylene-polypropylene glycol copolymer, or polypropylene glycol.
• the polyalkylene glycol monoether is preferably a polyethylene glycol monoether.
• ester-type nonionic surfactant an ethylene oxide adduct of a higher fatty acid is preferred.
• ether-type nonionic surfactant an ethylene oxide adduct of a higher alcohol is preferred.
• nonionic surfactants contain hydrophobic and hydrophilic groups in their molecules, and the hydrophobic groups interact with the hydrophobic short fibers, while the hydrophilic groups interact with water, resulting in good dispersibility in water.
• a cationic surfactant and a nonionic surfactant in combination, it is possible to achieve uniform dispersion of short fibers in water and good dispersion in sludge, and to obtain good dewatering properties.
• the total nitrogen concentration derived from the cationic surfactant in the surfactant consisting of the cationic surfactant and the nonionic surfactant applied in the present invention is preferably 250 ppm or more, more preferably 500 ppm or more, and even more preferably 1000 ppm or more, based on the dry weight. If it is less than 250 ppm, a large amount of surfactant must be applied in order to sufficiently change the zeta potential of the hydrophobic short fibers to the positive side, which is undesirable in terms of the manufacturing process, handling, and cost.
• Surfactants may contain small amounts of emulsifiers that aid in emulsification into water, as long as they do not affect the zeta potential.
• Hydrophobic short fibers may be used from which the spinning oil adhering to the surface has been removed in advance, in which case the concentration of the cationic surfactant and nonionic surfactant mixture applied can be made lower.
• the surfactant is preferably a mixture of a cationic surfactant and a nonionic surfactant in the form of an aqueous emulsion, which is then attached to the surface of the hydrophobic staple fibers.
• a method for attaching a surfactant to the surface of hydrophobic short fibers a method can be used in which a surfactant is attached to continuous hydrophobic fibers by slit oiling before the continuous hydrophobic fibers are cut into hydrophobic short fibers of a predetermined length, and then the continuous hydrophobic fibers are cut to the predetermined length.
• an aqueous solution of a surfactant may be sprayed onto long hydrophobic fibers, and then the long hydrophobic fibers may be cut to the predetermined length.
• continuous hydrophobic fibers that have been previously degreased of spinning oil can be immersed in a bath of an aqueous surfactant solution, and the excess aqueous solution adhering to the surface of the continuous hydrophobic fibers can be squeezed out with a mangle or sucked out with air, and then the continuous hydrophobic fibers can be cut to the specified length.
• Flocculant As the flocculant, either an inorganic flocculant or a polymer flocculant can be used.
• inorganic coagulants examples include polyferric sulfate (polyiron), polyaluminium chloride (PAC), ferric chloride, aluminium sulfate (aluminum sulfate), hydrated lime and ferrous sulfide.
• polymeric flocculants examples include polyacrylamide, acrylamide-sodium acrylate copolymer, acrylamide-2-methylpropanesulfonate sodium copolymer, alkylamino methacrylate quaternary salt polymer, alkylamino methacrylate quaternary salt-acrylamide copolymer, polyvinylamidine, chitosan, polyglutamic acid, alginic acid, pectin, starch, copolymer of acrylic acid ester and acrylamide, and methacrylic acid ester polymer.
• a dewatering sludge composition containing the dewatering aid of the present invention, sludge and a flocculant is prepared, and this dewatering sludge composition is dewatered.
• the dewatering aid is dispersed in sludge, and a flocculant previously dispersed in water is added thereto and stirred to prepare a flocculated dewatering sludge composition, and this dewatering sludge composition is dewatered.
• sludge examples include sludge from sewage treatment plants, agricultural village drainage facilities, septic tanks, sewage treatment facilities, industrial wastewater treatment facilities, water purification plants, paper factories, and mines. From the viewpoint of handling with a sludge dehydrator, the moisture content of the sludge is preferably 90 to 99.9% by weight, more preferably 95 to 99.5% by weight, and particularly preferably 96 to 99% by weight.
• the dehydration aid of the present invention is preferably added in an amount of 0.3 to 10 parts by weight, more preferably 0.6 to 6 parts by weight, per 100 parts by weight of sludge solids (sludge TS), from the viewpoint of lowering the moisture content of the dehydrated cake while also taking into consideration costs.
• the amount of flocculant added is, for example, 0.1 to 3 parts by weight per 100 parts by weight of sludge TS.
• the dehydration aid of the present invention is a dehydration sludge composition suitable for dehydration using a dehydrator such as a centrifugal dehydrator, a belt press, a screw press, a filter press, a multi-disk type dehydrator, or a double cylinder pressure dehydrator.
• a dehydrator such as a centrifugal dehydrator, a belt press, a screw press, a filter press, a multi-disk type dehydrator, or a double cylinder pressure dehydrator.
• the dehydration aid of the present invention is (Step 1) dispersing the dewatering aid of the present invention in sludge; It can be suitably used in a dewatering method including (step 2) a step of adding a flocculant dispersed in water to sludge and stirring the sludge to flocculate the sludge, and (step 3) a step of dewatering the flocculated sludge.
• Step 1 dispersing the dewatering aid in sludge;
• a method for dewatering sludge comprising, in this order: (step 2) adding a flocculant dispersed in water to the sludge and stirring it to flocculate the sludge; and (step 3) dewatering the flocculated sludge.
• sludge TS is the total evaporation residue of sludge, that is, the total amount of solid matter contained in the sludge slurry.
• Amount of Oil and Surfactant Adhered The amount of oil applied to commercially available hydrophobic fibers and the amount of surfactant consisting of a mixture of a cationic surfactant and a nonionic surfactant applied to the hydrophobic fibers were measured by drying the samples overnight at 105°C, and then using the methanol extraction method specified in JIS L 1013 2010 8.27(c).
• the total nitrogen concentration of the cationic surfactant in the surfactant consisting of a mixture of the cationic surfactant and the nonionic surfactant to be applied and the total nitrogen concentration of the cationic surfactant in the oil and surfactant attached to the hydrophobic fiber surface were measured by the following method. 1) Pretreatment In the case of a surfactant consisting of a mixture of a cationic surfactant and a nonionic surfactant, the mixture was spread thinly and evenly on a petri dish and then vacuum dried at 50° C. until there was no change in weight.
• Zeta potential - ⁇ V ⁇ ⁇ ⁇ k / ( ⁇ ⁇ ⁇ P) ⁇ V: streaming potential
• ⁇ viscosity of the measured solution
• k electrical conductivity of the measured solution
• ⁇ dielectric constant of the measured solution
• ⁇ P pressure loss between the porous plates at both ends
• Dispersion state of dehydration aid in dehydrated cake 3% by weight of dehydration aid based on sludge TS was added to 200 ml of excess sludge, and the mixture was stirred at 150 rpm for 5 minutes with a stirrer. Then, 2% by weight of cationic flocculant based on TS was added, and the mixture was stirred at 150 rpm for 60 seconds, and then stirred at 60 rpm for 5 minutes to obtain a dehydrated sludge composition.
• Reduction rate of amount of dehydrated cake generated was measured according to the following procedure. 1) To sludge having a sludge TS concentration A (wt %), a polymer flocculant is added in an amount of B (wt %) relative to the sludge TS, and the sludge is dehydrated in a dehydrator as is to obtain a dehydrated cake, and the moisture content X (wt %) of the dehydrated cake after dehydration is measured. 2) Using the following formula, calculate the amount of dehydrated cake D 0 (tons) generated when the amount of sludge is 100 tons and no dewatering aid is added.
• Example 1 An aqueous surfactant solution was prepared, which was a mixture of a quaternary ammonium salt type cationic surfactant with a total nitrogen concentration derived from the quaternary ammonium salt type cationic surfactant of 1000 ppm and a nonionic surfactant which is a polyether-ester copolymer with an HLB of 11.
• a dehydration aid was prepared which was a mixture of polyester staple fibers with a single fiber fineness of 0.6 dTex and a length of 10 mm in a weight ratio of 2:1 and polyester staple fibers with a length of 3.3 dTex and a length of 10 mm in which the amount of oil and surfactant adhering to the fiber surface was 1.2% by weight relative to the fiber weight and the total nitrogen concentration in the oil and surfactant adhering to the fiber surface was 500 ppm.
• the zeta potential of the short fibers after deoiling with methanol was -84.6 mV.
• the zeta potential increased by 50.7 mV by applying an aqueous solution of a surfactant consisting of a mixture of a nonionic surfactant and a quaternary ammonium salt type cationic surfactant.
• Example 2 An aqueous surfactant solution was prepared, the aqueous solution being a mixture of a quaternary ammonium salt type cationic surfactant, the total nitrogen concentration of which was 1000 ppm, and a nonionic surfactant which was a polyether-ester copolymer with an HLB of 11. Using this, a dehydration aid was produced, the aqueous solution being made of polyester staple fibers with a single fiber fineness of 0.6 dTex and a length of 10 mm, the amount of oil and surfactant adhering to the fiber surface being 2.4% by weight relative to the fiber weight, and the total nitrogen concentration in the oil and surfactant adhering to the fiber surface being 840 ppm.
• a dehydration aid was produced, the aqueous solution being made of polyester staple fibers with a single fiber fineness of 0.6 dTex and a length of 10 mm, the amount of oil and surfactant adhering to the fiber surface being 2.4% by weight relative to the fiber weight
• the zeta potential of the short fibers after deoiling with methanol was -84.6 mV.
• the zeta potential increased by 70.4 mV by applying an aqueous solution of a surfactant consisting of a mixture of a nonionic surfactant and a quaternary ammonium salt type cationic surfactant.
• Example 3 An aqueous surfactant solution was prepared, the aqueous solution being a mixture of a quaternary ammonium salt type cationic surfactant and a nonionic surfactant which is a polyether-ester copolymer having an HLB of 11, and the total nitrogen concentration derived from the quaternary ammonium salt type cationic surfactant being 1000 ppm.
• a dehydration aid was prepared which was a mixture of polyester staple fibers having a single yarn fineness of 0.6 dTex and a length of 10 mm and polyester staple fibers having a length of 3.3 dTex and a length of 10 mm in a weight ratio of 2:1, in which the amount of oil and surfactant adhering to the fiber surface was 2.0% by weight relative to the fiber weight and the total nitrogen concentration in the oil and surfactant adhering to the fiber surface was 790 ppm.
• the zeta potential of the fiber after deoiling with methanol was -84.6 mV.
• the application of an aqueous solution of a surfactant consisting of a mixture of a nonionic surfactant and a quaternary ammonium salt type cationic surfactant increased the zeta potential by 57.6 mV.
• Comparative Example 1 A dehydration aid was prepared from polyester staple fibers having a single fiber fineness of 0.6 dTex and a length of 10 mm, the fiber surfaces of which had been previously deoiled and to which 1.5% by weight of a nonionic surfactant with an HLB of 15 was applied based on the fiber weight.
• the zeta potential of the short fiber after deoiling with methanol was -84.6 mV, and there was almost no change in the zeta potential by applying the aqueous solution of a nonionic surfactant.
• Comparative Example 2 A dewatering aid was prepared by cutting a commercially available polyester fiber having a single fiber fineness of 0.6 dTex, to which an oil solution containing an anionic surfactant was attached in an amount of 0.5% by weight based on the fiber weight, into polyester staple fibers having a length of 10 mm.
• the dehydration aid of the present invention can be used as a dehydration agent for sludge generated in sewage treatment plants, septic tanks, sewage treatment facilities, industrial wastewater treatment facilities, and other wastewater treatment facilities, sludge generated in water purification plants, sludge generated in paper mills, sludge generated in construction and civil engineering works, and sludge derived from mining wastewater.

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• 2024
  • 2024-04-01 WO PCT/JP2024/013416 patent/WO2024214584A1/ja not_active Ceased
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