Method for flocculating solid particles and use of high shear treatment

Abstract

The invention relates to a method for flocculating solid particles in a liquid-solid separation process. The method comprises obtaining a flocculant solution comprising a cationic biopolymer having a charge density in the range of 0.5 to 2.6 meq / g and selected from the group consisting of a cationically crosslinked alpha-1, 3-glucan polymer, a cationic graft copolymer of dextran and alpha-1, 3-glucan, or any mixture thereof. The flocculant solution is subjected to a high shear treatment. The flocculant solution is contacted after a high shear treatment with a suspension in which solid particles are dispersed in a continuous aqueous phase, and the solid particles are flocculated. The flocculated solid particles are then separated from the continuous aqueous phase.

Description

[0001] The present invention relates to a method for flocculation of solid particles and use of high shear treatment according to the preamble of the independent claims.

[0002] Many industrial processes comprise a step in which solid particles are separated from a liquid phase to provide two separate fractions, a solid fraction and a liquid fraction. Such a liquid-solid separation step is for example used in water treatment processes, in the manufacture of pulp, paper, board, etc., and in the mining industry. One typical example of a liquid-solid separation step is sludge dewatering in water treatment. Sludge typically comprises various solid particles and / or microorganisms suspended in an aqueous phase. The success of a liquid-solid separation step depends on the clarity of the liquid fraction after separation and the dryness of the solid fraction. The solid fraction of sludge can be further treated, for example deposited, used as fertilizer, or incinerated for energy production.

[0003] Often the liquid-solid separation step comprises flocculation of the solid particles present in the liquid phase. Flocculation and / or coagulation chemicals are used in order to improve the formation of flocs and / or to improve the quality of the formed flocs. For example, in water treatment processes, sludge can be conditioned prior to the dewatering step by the addition of flocculants, such as inorganic compounds of iron and lime, or synthetic organic polymers. These flocculants are added to the sludge in order to improve sludge handling and to enhance the dewatering effect in the liquid-solid separation.

[0004] Synthetic cationic polymers based on petroleum are often used as flocculants in liquid-solid separations. Due to the non-degradable nature of synthetic polymers, when synthetic cationic polymers are used in a liquid-solid separation step, the solid fraction separated from the wastewater treatment can not be used for landfill, composting or for soil improvement. Furthermore, there is currently a growing incentive to push industrial processes towards more sustainable directions and to encourage the use of bio-based and / or biodegradable chemicals. This desire to use bio-based and / or biodegradable chemicals has triggered a strong interest in finding alternatives to synthetic cationic polymers based on petroleum. In addition, the rising price of petroleum reduces its attractiveness as a raw material. Therefore, there is a constant search for more sustainable alternatives that still provide suitable process behavior and separation results.

[0005] It is an object of the present invention to minimize or even eliminate the drawbacks present in the prior art.

[0006] It is also an object to provide a more sustainable method for flocculation in a liquid-solid separation process, in particular for sludge dewatering in a water treatment process.

[0007] It is a further object of the present invention to provide a method that provides efficient flocculation and high solids content for the separated solids after a liquid-solid separation step. It is a further object of the present invention to provide a method that provides efficient flocculation and high solids content for the separated solids after a liquid-solid separation step.

[0008] These objectives are achieved by the invention having the features presented in the characterizing portion of the independent claims. Some preferred embodiments are disclosed in the dependent claims.

[0009] The embodiments mentioned herein relate to all aspects of the invention where applicable, even if not always mentioned separately.

[0010] A typical method for flocculating solid particles during liquid-solid separation includes:

[0011] - Obtain a suspension in which solid particles are dispersed in a continuous aqueous phase;

[0012] - Obtain a flocculant solution comprising a cationic biopolymer having a charge density in the range of 0.5 to 2.6 meq / g and selected from cationic crosslinked α-1,3-glucan polymers, cationic graft copolymers of dextran and α-1,3-glucan, or any mixture thereof;

[0013] - subject the flocculant solution to high shear treatment;

[0014] - The high-shear treated flocculant solution is brought into contact with the suspension, causing the solid particles to flocculate; and

[0015] - Separate flocculated solid particles from the continuous aqueous phase.

[0016] A typical application of high-shear treatment according to the invention is for increasing the cationicity of flocculant solutions containing cationic biopolymers having a charge density in the range of 0.5 to 2.6 meq / g and selected from cationic crosslinked α-1,3-glucan polymers, cationic graft copolymers of dextran and α-1,3-glucan, or any mixture thereof.

[0017] It has been unexpectedly discovered that subjecting flocculant solutions containing specific cationic biopolymers to high shear treatment significantly improves the flocculation capacity of these solutions. High shear treatment significantly enhances the dehydration efficiency of these cationic biopolymers, making them even suitable for industrial-scale use. The specific cationic biopolymers used in this invention have a charge density in the range of 0.5 to 2.6 meq / g and are selected from cationic crosslinked α-1,3-glucan polymers, cationic graft copolymers of dextran and α-1,3-glucan, and any mixtures thereof. The effects obtained by subjecting these biopolymers to high shear treatment are completely unexpected, as similar effects cannot be obtained, for example, with cationic linear α-1,3-glucan polymers. Therefore, this invention provides a flocculant solution that is biodegradable and available from renewable resources.

[0018] A flocculant solution containing a cationic biopolymer is used to flocculate an aqueous suspension in which solid particles are dispersed or suspended in a continuous aqueous phase. The cationic biopolymer is selected from cationic cross-linked α-1,3-glucan polymers, cationic graft copolymers of dextran and α-1,3-glucan, or any mixture thereof. It is assumed that the cationic biopolymer interacts with the solid particles, subsequently forming flocs.

[0019] In the context of this invention, the terms "α-1,3-glucan polymer" and "α-1,3-glucan" refer to a polymer structure having a polysaccharide backbone comprising D-glucose units linked together by glycosidic bonds. At least 70%, preferably at least 80%, more preferably at least 90% or at least 95%, and sometimes even at least 99% or 100% of the glycosidic bonds are α-1,3-bonds.

[0020] In this context, the term "dextran" refers to an α-glucan in which at least 50%, preferably at least 60%, more preferably at least 70%, even more preferably at least 80% or at least 90% of the glycosidic bonds are α-1,6-glycosidic bonds, wherein the balance to 100% is typically α-1,3-glycosidic bonds. Dextran has a substantially linear structure, meaning that it has 0% to 5% branching before forming a graft copolymer with α-1,3-glucan. The branches that may exist within dextran itself are typically short, ranging in length from one to three glucose monomers.

[0021] According to one embodiment, the flocculant solution may comprise or be composed of a cationic biopolymer, which is a cationically crosslinked α-1,3-glucan polymer. The cationically crosslinked α-1,3-glucan polymer suitable for use in this invention comprises cationic substituents attached to its structure. The cationic substituents may be substituted ammonium groups, preferably quaternary ammonium groups, more preferably trialkylammonium groups. The alkyl group in the trialkylammonium group may be, for example, methyl, hydroxymethyl, hydroxyethyl, or hydroxypropyl. The substituted ammonium group may be, for example, a trimethylammonium group. It is assumed that the cationic substituents of the α-1,3-glucan polymer are capable of interacting with solid particles present in an aqueous suspension and providing floc formation. Further assumption is made that, without being bound by theory, high-shear treatment in some way releases the cationic groups or makes the cationic groups more readily interactable.

[0022] The crosslinked α-1,3-glucan polymer suitable for use in this invention can be obtained by contacting the α-1,3-glucan polymer with a crosslinking agent and a solvent (e.g., water). The amount of crosslinking agent used, calculated by the dry weight of the polymer, can be from 20 to 5000 ppm, preferably from 100 to 5000 ppm. According to one embodiment, a crosslinking agent selected from the group consisting of glyoxal and diglycidyl ethers, such as polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, glycerol diglycidyl ether, poly(dimethylsiloxane) diglycidyl ether, and trimethylolpropane triglycidyl ether, can be used.

[0023] Alternatively, the flocculant solution used in this invention may comprise or be composed of a cationic biopolymer, which is a cationic biopolymer selected from cationic ester derivatives or ether derivatives of dextran and α-1,3-glucan graft copolymers. Suitable graft copolymer derivatives, their preparation methods, and methods for determining their glycosidic bond spectra are described, for example, in WO 2021 / 247810. The graft copolymer has a branched structure comprising dextran and α-1,3-glucan chains linked together. The degree of polymerization of the α-1,3-glucan in the graft copolymer can be in the range of 20 to 3000, preferably 500 to 2000. For example, the degree of polymerization can be in the range of 20 to 2000 or 55 to 1000. The degree of polymerization here refers to the number of glucose units contained within a single α-1,3-glucan chain.

[0024] According to one embodiment of the invention, the flocculant solution may comprise or consist of a cationic graft copolymer, the cationic graft copolymer comprising 5 to 75% by weight, preferably 10 to 70% by weight, more preferably 20 to 60% by weight, or even more preferably 30 to 50% by weight, of dextran based on the dry weight of the graft copolymer prior to esterification or etherification. The cationic graft copolymer may comprise, for example, 35 to 95% by weight, preferably 30 to 90% by weight, more preferably 40 to 80% by weight, or even more preferably 50 to 70% by weight, of α-1,3-glucan (e.g., α-1,3-glucan side chains) based on the dry weight of the graft copolymer prior to esterification or etherification.

[0025] Ester or ether derivatives of dextran-α-1,3-glucan graft copolymers may contain one or more cationic groups linked to the graft copolymer via ester or ether bonds. The cationic group may include substituted ammonium groups, such as primary, secondary, tertiary, or quaternary ammonium groups, preferably quaternary ammonium groups, more preferably trialkylammonium groups. The ammonium groups may be substituted with alkyl and / or aryl groups, for example, with C1-C4 or C6-C24 alkyl groups. One of the substituted ammonium groups contains a carbon atom or carbon chain linked to the graft copolymer via an ether or ester bond.

[0026] According to one embodiment, the cationic biopolymer can be a cationic graft copolymer comprising a dextran backbone and an α-1,3-glucan side chain, wherein preferably the side chain is linked to the dextran backbone via α-1,2 and / or α-1,3 and / or α-1,4 bonds. The α-1,3-glucan side chain may contain at least 70%, preferably at least 80%, more preferably at least 90% or at least 95%, and sometimes even 99% or 100% α-1,3-glycosidic bonds.

[0027] According to one embodiment of the invention, the flocculant solution comprises a cationic biopolymer as defined above, which may have a degree of cationic substitution in the range of 0.05 to 1.2, preferably 0.1 to 1.0, more preferably 0.1 to 0.7, and even more preferably 0.15 to 0.6, as determined after high-shear treatment. The degree of substitution refers to the average number of hydroxyl groups substituted by cationic groups in each glucose unit of a graft copolymer or crosslinked copolymer via ether or ester bonds or other bonds. High cationicity improves the water solubility of the biopolymer. However, excessive cationicity is preferably avoided, as it may be ecotoxic to aquatic organisms. The high-shear treatment according to the invention enables an increase in the availability of the cationic groups of the biopolymer for interaction with solid particles in an aqueous suspension. This means that effective dehydration results can be achieved even when using biopolymers with even lower cationicity. Biopolymers with lower cationicity may also contain fewer impurities, making them more suitable for applications such as drinking water.

[0028] According to one embodiment, the cationic biopolymer is water-soluble. The cationic biopolymer may be partially or completely water-soluble. In the context of this invention, water solubility is defined as the amount of insoluble matter in the biopolymer solution, which is measured using the procedure described in the experimental section of Example 12. For example, the cationic biopolymer may preferably have <25%, more preferably <20%, or even more preferably <15% insoluble matter as measured before high-shear treatment. After high-shear treatment, the amount of insoluble matter in the flocculant solution containing the cationic biopolymer may be <10%, preferably <5%, more preferably <3%, as measured as described in the experimental section.

[0029] The cationic biopolymer has a charge density in the range of 0.5 to 2.6 meq / g. It has been observed that if the charge density is too high, no increase in charge density is observed after high-shear treatment. The flocculant solution may contain the cationic biopolymer having a charge density of 0.6 to 2.6 meq / g, preferably 1.0 to 2.5 meq / g, more preferably 1.5 to 2.5 meq / g, and even more preferably 1.9 to 2.4 meq / g, as determined before high-shear treatment. The charge density may, for example, be in the range of 1.0 to 2.4 meq / g, preferably 1.1 to 2.4 meq / g, or 1.8 to 2.3 meq / g, as determined before high-shear treatment. The charge density is measured by Mütek titration as described in the experimental section.

[0030] According to one embodiment of the invention, the flocculant solution may comprise a cationic graft copolymer of dextran and α-1,3-glucan. Crosslinking can be performed using the same crosslinking agent defined above. The crosslinking of the branched structure of the graft copolymer further alters the three-dimensional configuration of the cationic biopolymer.

[0031] Cationic biopolymers can have a salt viscosity of 50 to 150,000 mPas or 100 to 100,000 mPas, measured at a 2% wt% biopolymer concentration before high-shear treatment. According to one embodiment, the cationic biopolymer can have a salt viscosity in the range of 50 to 10,000 mPas, preferably 50 to 5,000 mPas, and sometimes 200 to 4,000 mPas, measured at a 2% wt% biopolymer concentration before high-shear treatment. This measurement method has been described in detail in the experimental section. Salt viscosity can be used to measure or estimate the molecular size of the biopolymer. It has been observed that when the viscosity of the cationic biopolymer is within a given range, the cationic biopolymer can provide a particularly effective dehydration effect.

[0032] A flocculant solution containing a selected cationic biopolymer is subjected to a high-shear treatment in which a shear power of at least 5 W / kg, preferably at least 20 W / kg, and more preferably at least 35 W / kg is applied to the flocculant solution containing or composed of cationic biopolymers. According to a preferred embodiment, the flocculant solution may be subjected to a shear power in the range of 5 to 1000 W / kg, preferably 20 to 500 W / kg, more preferably 35 to 300 W / kg, and even more preferably 35 to 209 W / kg during the high-shear treatment. The shear power can sometimes be as high as 500 W / kg. The duration of the high-shear treatment may preferably be up to 600 s, preferably 1 to 600 s, more preferably 5 to 400 s, and even more preferably 10 to 300 s. The duration of the high-shear treatment may, for example, be 10 to 180 s or 30 to 150 s. Generally, the higher the power used in the high-shear treatment, the shorter the duration of the high-shear treatment can be, and vice versa.

[0033] During high-shear treatment, the flocculant solution may contain 0.01 to 5% by weight, preferably 0.05 to 4% by weight, of a cationic biopolymer, calculated based on the weight of the flocculant solution.

[0034] A flocculant solution containing or composed of cationic biopolymers can be subjected to high-shear treatment in any suitable high-shear device or apparatus capable of generating appropriate high-shear power in an aqueous system. For example, cationic biopolymers can be subjected to high-shear treatment in homogenizers, high-speed mixers, dispersers, rotor-stator mixers, mixers with two counter-rotating rotors, centrifugal pumps providing direct or counter-rotating flow, high-pressure equipment, shear pumps, etc. In some cases, ultrasonic treatment can also be used as a high-shear treatment. Suitable high-shear mixing equipment and homogenizers are well known to those skilled in the art and are commercially available, for example, under trade names such as Ultra Turrax®, Polytron®, Atrex®, Silverson®, Ystral®, Cavitron™, and Waukesha shear pumps™. For example, the cationic biopolymer can be dissolved in water, subjected to high-shear homogenization, and then contacted with an aqueous suspension containing the solid particles to be flocculated. High-shear homogenization can be achieved, for example, by using a rotational speed of at least 2000 rpm. Suitable shear power can alternatively be achieved in a high-shear treatment in which the selected cationic biopolymer is subjected to high shear power via a centrifugal pump or the like, for example during pumping after the cationic biopolymer has been dissolved or dispersed in water.

[0035] Prior to high-shear treatment, the flocculant solution containing the selected cationic biopolymer can be heat-treated at a temperature of 60°C to 115°C, preferably 85°C to 100°C.

[0036] Following high-shear treatment, the flocculant solution is contacted with the aqueous suspension, thereby allowing the cationic biopolymer to interact with the solid particles and flocculate the solid particles. This invention is applicable to the flocculation of aqueous suspensions in which solid particles are dispersed in a continuous aqueous phase during a liquid-solid separation process, in which the liquid phase and solid particles are separated from each other. For example, this invention is applicable to conditioning drinking water. According to a preferred embodiment, the liquid-solid separation process can be a wastewater treatment process (such as municipal or industrial wastewater), or it can be a sludge dewatering step in such wastewater treatment processes. The aqueous suspension undergoing the liquid-solid separation process can be municipal wastewater sludge or agricultural sludge, or it can be derived from biological treatment processes of wastewater and / or sewage. The liquid-solid separation process can be a sludge treatment process (such as primary sludge, secondary sludge, tertiary sludge, or digested sludge derived from wastewater treatment). Liquid-solid separation can be a treatment process for suspensions derived from food or beverage production or processing.

[0037] According to one embodiment, an aqueous suspension (such as wastewater or sludge) comprises a continuous aqueous liquid phase and organic and / or inorganic solid materials and / or particles suspended in the aqueous liquid phase. The suspension may be rich in bacterial-derived materials, especially when it is sludge derived from water treatment or agricultural processes. The aqueous liquid phase of the suspension may also contain dissolved organic matter, such as polysaccharides, humic substances, and fatty acids. The suspension (such as wastewater or sludge) may have a biological oxygen demand (BOD) >50 mg / L, a chemical oxygen demand (COD) in the range of 15 to 45 g / L, preferably 20 to 40 g / L, and / or a dry solids content in the range of 5 to 80 g / L, preferably 10 to 60 g / L, more preferably 20 to 55 g / L. The pH of the suspension may be in the range of pH 6 to pH 9, preferably pH 7 to pH 8. The conductivity of the suspension can be in the range of 5 to 14 mS / cm, preferably 5 to 10 mS / cm, and / or the charge density can be in the range of -5.5 to -1.5 μeq / g, preferably -5.0 to -1.8 μeq / g. The total phosphorus value of the suspension can be in the range of 400 to 1400 mg / l, preferably 450 to 1200 mg / l, and / or the total nitrogen value can be in the range of 1.2 to 3.5 g / l, preferably 1.5 to 3.0 g / l.

[0038] According to a preferred embodiment, the suspension comprises solid organic particles dispersed in a continuous aqueous phase. This means that an aqueous suspension (such as wastewater or sludge) comprises a continuous aqueous liquid phase and at least organic solid material and / or particles suspended in that aqueous liquid phase. Flocculant solutions containing cationic biopolymers are particularly suitable for flocculating organic materials and / or particles that may otherwise be difficult to flocculate and / or dehydrate after high-shear treatment.

[0039] The flocculant solution containing cationic biopolymers interacts directly with solid materials and / or particles suspended in the aqueous liquid phase of the suspension. Preferably, the method of the present invention does not include a pretreatment step in which the suspension is contacted with anionic flocculants, anionic additives, or anionic modifiers before being contacted with the flocculant solution.

[0040] The flocculant solution can be contacted with the aqueous suspension in an amount providing 1 to 30 kg of cationic biopolymer per ton of dry suspension, preferably 2 to 20 kg of cationic biopolymer per ton of dry suspension, more preferably 3 to 15 kg of cationic biopolymer per ton of dry suspension.

[0041] The flocculated solid particles are separated from the continuous aqueous phase in any suitable manner. For example, the separation of the aqueous phase (i.e., the dewatering of the flocculated solid particles) is carried out by using mechanical dewatering devices such as centrifuges, belt filter presses, or box filter presses, preferably centrifuges.

[0042] experiment

[0043] Some embodiments of the present invention are described in the following non-limiting examples.

[0044] Characterization of cationic biopolymers

[0045] The cationic biopolymers used in the examples were characterized by measuring their charge density at pH 4 and by measuring their salt viscosity. Charge density was also measured after high-shear treatment.

[0046] Charge density

[0047] The charge density at pH 4 was determined using a BTG Mütek PCD-04 particle charge titrator. Each cationic biopolymer to be tested was first dissolved in deionized water to form a 0.20 wt% flocculant solution. The flocculant solution was diluted to a concentration of 0.01 to 0.05 wt% for measurement, depending on the charge density of the biopolymer. The pH was adjusted to 4.0 using 0.1 M acetic acid. The charge density was determined using a 0.001 N sodium polyethanesulfonate (PES-Na) solution as the titrant. During titration, the pH was typically increased by 0.1 to 0.3 pH units. The charge density is expressed in meq / g dry matter.

[0048] Salt viscosity

[0049] The salt viscosity (hereinafter referred to as "salt viscosity") of a cationic biopolymer solution in the presence of salt was determined using a Brookfield DV-1 viscometer equipped with a small sample adapter at 25°C, using either a #18 or #31 rotor (depending on the viscosity level). The pH of the biopolymer solution was not adjusted because pH has no effect on the measured viscosity results. The pH of the solution is typically in the range of pH 6 to pH 11.4. Salt viscosity was measured using the maximum possible rotation speed. The cationic biopolymer was first dissolved in deionized water at a 2 wt% solution. Then, sodium chloride (NaCl) was added at a weight ratio of 5:1 (NaCl: cationic biopolymer) and dissolved under mixing, and the salt viscosity was then measured. This means that the salt viscosity of the cationic biopolymer was determined in an aqueous solution containing 9.1 wt% NaCl at a concentration of 1.8 wt% cationic biopolymer.

[0050] Conductivity

[0051] The conductivity of 0.5 wt% cationic biopolymer in deionized water was measured using a Knick Portavo 902 COND conductivity meter equipped with a Knick SE 204 sensor.

[0052] High-shear treatment of cationic biopolymers

[0053] The high-shear treatment of the cationic biopolymer was performed by mixing 150 ml of freshly prepared 2% or 200 ml of 0.2% cationic biopolymer solution at 16,000 rpm for 3 to 5 minutes using an IKA T25digital Ultra Turrax® homogenizer equipped with an S 25 N-25 F blade. In the examples, samples subjected to high-shear treatment were labeled “UT Post-Treatment”.

[0054] sludge dewatering test

[0055] Digested sludge collected from a wastewater treatment plant in Finland was used in the examples. The pH and solids content of each type of sludge, as well as the CST time (indicated in parentheses as 'zero test') for sludge without any added chemicals, are given in the relevant examples.

[0056] Sludge dewatering was tested using a Triton 319 multi-functional CST (Triton Electronics Ltd., UK) via capillary suction time (CST) testing. Mixing was performed using a Heidolph RZR 2021 or IKA RW 20 digital mixer with a four-blade agitator having a total blade width of 30 mm and a blade height of 15 mm.

[0057] In the CST test, the mixing speed was 1000 rpm. The cylinder used had a diameter of 18 mm. A flocculant solution containing cationic biopolymers was added to 100 g of digested sludge in a 250 ml beaker, and mixed for 10 s after addition. After mixing for 10 s, 4.5 ml of the sample was transferred to a graduated cylinder and the CST value was measured. A low CST value indicates good dewatering performance.

[0058] The flocculant solution for CST testing is prepared as follows: First, the selected cationic biopolymer is dissolved overnight in a 0.5% solution, and then diluted to a 0.2% solution for testing. These solutions can be used as is or after high-shear treatment.

[0059] Example 1

[0060] The sludge used had a dry solids content of 2.6%, a pH of 7.2, and a CST time of 350 s (zero test).

[0061] The biopolymers used as flocculant solutions are cationic graft copolymers of dextran and α-1,3-glucan (labeled αG1 and αG2). The properties of biopolymers αG1 and αG2 before and after high-shear treatment are shown in Table 1. As can be seen from Table 1, high-shear treatment increases the charge density and viscosity of the biopolymers.

[0062] Table 1. Properties of the biopolymer used in Example 1.

[0063]

[0064] The effects of temperature treatment on dehydration performance were also investigated. Therefore, samples of biopolymer αG2 were aged at 95°C for 1 h and then used as flocculant solutions, regardless of whether they had undergone high-shear treatment.

[0065] The efficiency of biopolymers as flocculant solutions was tested using the sludge dewatering test described above, regardless of whether they underwent high-shear treatment. The results are shown in Table 2.

[0066] The results in Table 2 show that high-shear treatment significantly improved the dehydration performance of the biopolymer, as evidenced by a significantly lower CST value at the corresponding dosage level. It also shows that heat treatment alone only provided a moderate improvement in dehydration efficiency, but high-shear treatment resulted in a significant increase. Furthermore, it can be concluded that temperature treatment did not interfere with the effects achievable through high-shear treatment.

[0067] Table 2. Sludge dewatering test results of Example 1.

[0068]

[0069] kg of active biopolymer per ton of dry sludge

[0070] Example 2

[0071] The sludge used had a dry solids content of 2.4%, a pH of 7.6, and a CST time of 296 s (zero test).

[0072] The biopolymers used as flocculant solutions are cationic graft copolymers of dextran and α-1,3-glucan (denoted as αG3, αG4, and αG5). Their properties before and after high-shear treatment are shown in Table 3. As can be seen from Table 3, when the charge density before high-shear treatment was 1.5 meq / g or lower, a significant increase in charge density was observed after high-shear treatment. An increase in the viscosity of the flocculant solution was observed in all samples.

[0073] Table 3. Properties of the biopolymer used in Example 2.

[0074]

[0075] The efficiency of biopolymers as flocculant solutions was tested using the sludge dewatering test described above, regardless of whether they underwent high-shear treatment. The results are shown in Table 4.

[0076] Table 4. Sludge dewatering test results of Example 2.

[0077]

[0078] kg of active biopolymer per ton of dry sludge

[0079] As shown in Table 4, when the biopolymer is used as a flocculant solution, high-shear treatment significantly improves its dehydration performance. The increased efficiency is manifested in a significantly lower CST value at the corresponding dosage level.

[0080] Example 3

[0081] The sludge used had a dry solids content of 2.4%, a pH of 7.2, and a CST time of 342 s (zero test).

[0082] The biopolymers used as flocculant solutions are a cationic graft copolymer of dextran and α-1,3-glucan (denoted as αG7) and a cross-linked α-1,3-glucan polymer (denoted as αG8). Their properties before and after high-shear treatment are shown in Table 5. As can be seen from Table 5, high-shear treatment provides a significant increase in charge density for both biopolymers. The viscosity value of αG8 decreases after high-shear treatment. On the other hand, high-shear treatment leads to a significant increase in the viscosity of αG7.

[0083] Table 5. Properties of the biopolymer used in Example 3.

[0084]

[0085] Viscosity too high to measure

[0086] The efficiency of biopolymers as flocculant solutions was tested using the sludge dewatering test described above, regardless of whether they underwent high-shear treatment. The results are shown in Table 6.

[0087] Table 6. Sludge dewatering test results of Example 3.

[0088]

[0089] kg of active biopolymer per ton of dry sludge

[0090] As shown in Table 6, high shear treatment improved the dehydration properties of the biopolymer, as evidenced by significantly lower CST values ​​at corresponding dosage levels. High shear treatment also improved the CST test performance of αG8, even though the increase in charge density was moderate.

[0091] Example 4

[0092] The sludge used had a dry solids content of 2.3%, a pH of 7.2, and a CST time of 244 s (zero test).

[0093] The biopolymer used as the flocculant solution is a cross-linked α-1,3-glucan polymer (denoted as αG9). The properties of αG9 before and after high-shear treatment are shown in Table 7. As can be seen from Table 7, high-shear treatment provides a significant increase in charge density and a decrease in salt viscosity.

[0094] Table 7. Properties of the biopolymers used in Example 4.

[0095]

[0096] The effects of temperature treatment on the dehydration properties of biopolymer αG9 were also investigated. Therefore, a portion of αG9 was aged at 95°C for 1 h and then used as a flocculant solution, regardless of whether it had undergone high-shear treatment.

[0097] The efficiency of biopolymer αG9 as a flocculant was tested using the sludge dewatering test described above, regardless of whether it underwent high-shear treatment. The results are shown in Table 8.

[0098] Table 8. Sludge dewatering test results of Example 4.

[0099]

[0100] kg of active biopolymer per ton of dry sludge

[0101] It can be seen that high-shear treatment improves the dehydration performance of biopolymer αG9. Temperature treatment alone only provides a moderate improvement in dehydration efficiency, but significant improvement can be obtained when temperature-treated biopolymers are subjected to high-shear treatment.

[0102] Example 5

[0103] The sludge used had a dry solids content of 3.2%, a pH of 7.3, and a CST time of 285 s (zero test).

[0104] The biopolymer used as the flocculant solution is a cationic graft copolymer of dextran and α-1,3-glucan (denoted as αG10). The properties of αG10 before and after high-shear treatment are shown in Table 9. It can be seen that high-shear treatment provides a moderate increase in the charge density of the biopolymer, but reduces the salt viscosity of the biopolymer.

[0105] Table 9. Properties of the biopolymer used in Example 5.

[0106]

[0107] The efficiency of biopolymer αG10 as a flocculant was tested using the sludge dewatering test described above, with or without high-shear treatment. The results are shown in Table 10. It can be seen that high-shear treatment improves the dewatering performance of biopolymer αG10.

[0108] Table 10. Sludge dewatering test results of Example 5.

[0109]

[0110] kg of active biopolymer per ton of dry sludge

[0111] Example 6

[0112] The sludge used had a dry solids content of 3.2%, a pH of 7.3, and a CST time of 285 s (zero test).

[0113] The biopolymers used as flocculant solutions are cationic graft copolymers of dextran and α-1,3-glucan (labeled αG11, αG12, and αG13). Their properties before and after high-shear treatment are shown in Table 11. As can be seen from Table 3, a significant increase in charge density (de) can be observed after high-shear treatment. An increase in the viscosity of the flocculant solution was observed in all samples.

[0114] The efficiency of biopolymers as flocculant solutions was tested using the sludge dewatering test described above, regardless of whether they underwent high-shear treatment. The results are shown in Table 12. As can be seen from Table 12, high-shear treatment significantly improved the dewatering performance of biopolymers αG11, αG12, and αG13.

[0115] Table 11 Properties of the biopolymer used in Example 6.

[0116]

[0117] Table 12. Sludge dewatering test results of Example 6.

[0118]

[0119] kg of active biopolymer per ton of dry sludge

[0120] Comparative Example 7

[0121] The sludge had a dry solids content of 3.2%, a pH of 7.3, and a CST time of 337 s (zero test).

[0122] The biopolymers used as flocculant solutions are cationic linear α-1,3-glucan polymers (denoted as αG16, αG17, and αG19). Their properties before and after high-shear treatment are shown in Table 13. It can be seen that high-shear treatment did not provide any significant change in charge density, even though an increase in salt viscosity could be observed.

[0123] Table 13 shows the properties of the biopolymer used in Comparative Example 7.

[0124]

[0125] The efficiency of biopolymers as flocculant solutions was tested using the sludge dewatering test described above, with or without high-shear treatment. The results are shown in Table 14. High-shear treatment did not provide any improvement in the sludge dewatering efficiency of the tested linear biopolymers.

[0126] Table 14 shows the sludge dewatering test results of Comparative Example 7.

[0127]

[0128] Comparative Example 8

[0129] The sludge had a dry solids content of 2.5%, a pH of 7.3, and a CST time of 392 s (zero test).

[0130] The biopolymers used as flocculant solutions are cationic linear α-1,3-glucan polymers (denoted as αG20 and αG21). Their properties before and after high-shear treatment are shown in Table 15. It can be seen that high-shear treatment did not provide any significant change in charge density.

[0131] Table 15 shows the properties of the biopolymer used in Comparative Example 8.

[0132]

[0133] The efficiency of biopolymers as flocculant solutions was tested using the sludge dewatering test described above, with or without high-shear treatment. The results are shown in Table 16. High-shear treatment did not provide any improvement in the sludge dewatering efficiency of the tested linear biopolymers.

[0134] Table 16 shows the sludge dewatering test results of Comparative Example 8.

[0135]

[0136] Comparative Example 9

[0137] The sludge had a dry solids content of 3.0%, a pH of 7.3, and a CST time of 238 s (zero test).

[0138] The biopolymer used as the flocculant solution is a cationic linear α-1,3-glucan polymer (denoted as αG22). Its properties before and after high-shear treatment are shown in Table 17. It can be seen that high-shear treatment did not provide any significant change in charge density.

[0139] Table 17 shows the properties of the biopolymer used in Comparative Example 9.

[0140]

[0141] The efficiency of biopolymers as flocculant solutions was tested using the sludge dewatering test described above, regardless of whether they underwent high-shear treatment. The results are shown in Table 18. High-shear treatment did not provide any improvement in the sludge dewatering efficiency of the tested linear biopolymers.

[0142] Table 18 shows the sludge dewatering test results of Comparative Example 9.

[0143]

[0144] Comparative Example 10

[0145] The sludge had a dry solids content of 3.0%, a pH of 7.3, and a CST time of 344 s (zero test).

[0146] The biopolymers used as flocculant solutions are cationic graft copolymers of dextran and α-1,3-glucan (denoted as αG23, αG24, and αG25). Their properties before and after high-shear treatment are shown in Table 19. It can be seen that high-shear treatment did not provide any increase in charge density or salt viscosity.

[0147] Table 19 shows the properties of the biopolymer used in Comparative Example 10.

[0148]

[0149] The efficiency of biopolymers as flocculant solutions was tested using the sludge dewatering test described above, with or without high-shear treatment. The results are shown in Table 20. High-shear treatment did not provide any improvement in the sludge dewatering efficiency of the tested linear biopolymers.

[0150] Table 20 shows the sludge dewatering test results of Comparative Example 10.

[0151]

[0152] Comparative Example 11

[0153] The sludge used had a dry solids content of 3.2%, a pH of 7.3, and a CST time of 285 s (zero test).

[0154] The biopolymers used as flocculant solutions are cationic linear α-1,3-glucan polymers (denoted as αG14 and αG15). Their properties before and after high-shear treatment are shown in Table 21. It can be seen that high-shear treatment did not provide any significant change in charge density. An increase in the viscosity of the flocculant solution can be observed.

[0155] Table 21 shows the properties of the biopolymer used in Comparative Example 11.

[0156]

[0157] The efficiency of biopolymers as flocculant solutions was tested using the sludge dewatering test described above, regardless of whether they underwent high-shear treatment. The results are shown in Table 22. Table 22 shows that high-shear treatment did not improve the performance of linear α-1,3-glucan polymers αG14 and αG15.

[0158] Table 22 shows the sludge dewatering test results of Comparative Example 11.

[0159]

[0160] kg of active biopolymer per ton of dry sludge

[0161] Example 12.

[0162] In biopolymer solutions containing biopolymers αG7, αG11, and αG13, the amount of insoluble matter was determined before and after high-shear treatment.

[0163] The method for determining insoluble matter is as follows:

[0164] Mix 1 g of biopolymer into 900 ml of tap water (25°C) at 450 rpm for 60 minutes, then filter the solution through a 300 pm sieve. Rinse the beaker thoroughly with cold tap water and pour the rinse water through the sieve. Rinse the sieve under cold tap water until the effluent is free of polymer (approximately 5 to 10 minutes). Drain the sieve. If any insoluble matter remains on the sieve, weigh the cooled pre-conditioning tray on an analytical balance (=W1), scrape the insoluble matter from the sieve onto the tray, and dry it at 110°C to 120°C for at least 240 minutes. Weigh the tray with the dried insoluble matter on an analytical balance (=W2).

[0165] The percentage of insoluble matter is calculated as ((W2-W1) / 1 g)×100%.

[0166] If the amount of insoluble matter is too small to be collected and weighed, but is still visible, then the insoluble matter (gel particles) is counted. In this case, the result is close to 0%.

[0167] The results are shown in Table 23.

[0168] Table 23 Insolubles in biopolymers before and after high-shear treatment.

[0169]

[0170] It can be seen that high shear treatment improved the solubility of all tested biopolymers.

[0171] For biopolymer αG2, the amount of insoluble matter was also measured in both the uncooked and conditioned states. The amount of insoluble matter was 9.6% in the uncooked state and 0.2% after conditioned. This indicates that the improved dehydration effect of biopolymer αG2 is not due to a reduction in the amount of insoluble matter.

[0172] Even though the present invention has been described with reference to the most practical and preferred embodiments, it should be understood that the present invention is not limited to the above-described embodiments, but is also intended to cover different modifications and equivalent technical solutions within the scope of the appended claims.

Claims

1. A method for flocculating solid particles in a liquid-solid separation process, the method comprising: - obtaining a suspension in which solid particles are dispersed in a continuous aqueous phase; - obtaining a flocculant solution comprising a cationic biopolymer having a charge density in the range of 0.5 to 2.6 meq / g and selected from a cationically cross-linked alpha-1,3-glucan polymer, a cationic graft copolymer of dextran and alpha-1,3-glucan, or any mixture thereof; - subjecting the flocculant solution to a high shear treatment; - contacting the flocculant solution after the high shear treatment with the suspension and flocculating the solid particles; and - separating the flocculated solid particles from the continuous aqueous phase.

2. The method of claim 1, wherein, The cationic biopolymer has a cationic degree of substitution in the range of 0.05 to 1.2, preferably 0.1 to 1.0, more preferably 0.1 to 0.7, even more preferably 0.15 to 0.6, determined after the high shear treatment.

3. The method according to claim 1 or 2, characterized in that, The cationic biopolymer has a charge density in the range of 0.6 to 2.6 meq / g, preferably 1.0 to 2.5 meq / g, more preferably 1.5 to 2.5 meq / g, even more preferably 2.0 to 2.4 meq / g, determined before the high shear treatment.

4. The method according to claim 1, 2 or 3, characterized in that, In the high shear treatment, the flocculant solution is subjected to a shear power in the range of 5 to 1000 W / kg, preferably 20 to 500 W / kg, more preferably 35 to 209 W / kg.

5. The method of claim 4, wherein, The high shear treatment has a duration of 1 to 600 s, preferably 5 to 400 s, more preferably 10 to 300 s.

6. The method according to any of the preceding claims 1 to 5, characterized in that, The cationic graft copolymer comprises 5 to 75 wt%, preferably 10 to 70 wt%, more preferably 20 to 60 wt%, even more preferably 30 to 50 wt% of dextran, calculated on the dry weight of the graft copolymer.

7. The method according to any of the preceding claims 1 to 6, characterized in that, The cationic graft copolymer comprises 35 to 95 wt%, preferably 30 to 90 wt%, more preferably 40 to 80 wt%, even more preferably 50 to 70 wt% of alpha-1,3-glucan, calculated on the dry weight of the graft copolymer.

8. The method according to any of the preceding claims 1 to 7, characterized in that, The cationic graft copolymer is selected from an ester derivative or an ether derivative of a graft copolymer of dextran and alpha-1,3-glucan.

9. The method according to any of the preceding claims 1 to 8, characterized in that, The cationic graft copolymer is cross-linked.

10. The method according to any of the preceding claims 1 to 9, characterized in that, The cationically cross-linked biopolymer is obtained by using a cross-linking agent selected from the group comprising glyoxal and a diglycidyl ether such as polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, glycerol diglycidyl ether, poly(dimethylsiloxane) diglycidyl ether and trimethylolpropane triglycidyl ether.

11. The method according to any of the preceding claims 1 to 10, characterized in that, The flocculant solution comprising the cationic biopolymer is subjected to a heat treatment at a temperature of 60°C to 115°C, preferably 85°C to 100°C, before the high shear treatment.

12. The method according to any of the preceding claims 1 to 11, characterized in that, The flocculant solution comprises 0.01 to 5 wt.-%, preferably 0.05 to 4 wt.-%, of the cationic biopolymer, calculated on the weight of the flocculant solution.

13. The method according to any of the preceding claims 1 to 12, characterized in that, The liquid-solid separation process is a treatment process of wastewater, such as municipal wastewater or industrial wastewater, or a treatment process of sludge, such as raw sludge, secondary sludge, tertiary sludge or digested sludge derived from wastewater treatment.

14. The method of claim 13, wherein, The wastewater has a biological oxygen demand (BOD) of more than 50 mg / l, and / or a chemical oxygen demand (COD) in the range of 15 to 45 g / l, preferably 20 to 40 g / l, and / or a dry solids content in the range of 5 to 80 g / l, preferably 10 to 60 g / l, more preferably 20 to 55 g / l.

15. The method according to any of the preceding claims 1 to 14, characterized in that, The flocculant solution is contacted with the suspension in an amount to provide 1 to 30 kg of the cationic biopolymer per ton of dry suspension, preferably 2 to 20 kg of the cationic biopolymer per ton of dry suspension, more preferably 3 to 15 kg of the cationic biopolymer per ton of dry suspension.

16. Use of high shear treatment for increasing the cationicity of a flocculant solution comprising a cationic biopolymer, the cationic biopolymer having a charge density in the range of 0.5 to 2.6 meq / g, and being selected from a cationically crosslinked alpha-1,3-glucan polymer, a cationic graft copolymer of dextran and alpha-1,3-glucan, or any mixture thereof.

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