Cationic emulsion terpolymer for dewatering aqueous sludge

Abstract

The present invention relates generally to dewatering aqueous sludge produced by wastewater or sewage treatment facilities, such as from municipal and industrial processes. The method of the invention comprises treating an aqueous sludge with a cationic polyacrylamide terpolymer comprising acrylamide, a first cationic monomer, and a second cationic monomer different from the first monomer, and dewatering the treated aqueous sludge.

Description

Technical Field

[0001] Generally speaking, the present disclosure relates to dewatering aqueous sludge generated from wastewater or sewage treatment facilities (such as from municipal and industrial processes). The method includes treating the aqueous sludge with a cationic polyacrylamide terpolymer comprising the reaction product of acrylamide, a first cationic monomer, and a second cationic monomer different from the first monomer, and dewatering the treated aqueous sludge. Background Art

[0002] The discharge streams from these processes typically contain waste solids that cannot be directly recycled and are transported to wastewater treatment facilities via sewage systems. The discharge streams undergo a series of operations (depending on the specific industry and the setup of the wastewater treatment facility) to concentrate and dewater the waste solids, thereby producing sludge. Ultimately, the industrial discharge streams pass through filter presses, such as chamber filter presses, plate filter presses, frame filter presses, membrane filter presses, screw filter presses, and belt filter presses, or through centrifuges, where the waste solids are concentrated into a primary sludge or filter cake and the filtered wastewater from the filter presses or centrifuges is further processed until it is suitable for discharge or reuse.

[0003] A typical wastewater treatment plant receives raw sewage and produces solids and clarified water. Typically, the raw sewage is treated in a primary sedimentation stage to form primary sludge and a supernatant. The supernatant undergoes biological treatment and then a secondary sedimentation stage to form secondary sludge and a clarified liquor. The clarified liquor is typically further treated before discharge.

[0004] The standard practice for dewatering sludge is to mix a dose of polymer flocculant into the sludge at the dosing point and then almost immediately subject the sludge to a dewatering process, which forms a cake and a reject liquor. The dewatering process can be centrifugal separation or can be through processes such as filter pressing or belt pressing.

[0005] In many countries, most sludge cakes are landfilled for regulatory reasons. For landfilling, the cake must have a dryness of less than 40%, and the amount of sludge entering any landfill must not be greater than 8% (mixture ratio). Therefore, it is desirable to (i) increase the content of separated dry matter (OS), if possible, to above about 40% by weight, i.e., to keep the moisture content of the sludge cake below about 60% by weight using current processes.

[0006] In conventional or standard dewatering processes for aqueous sludge, various ionic, anionic, and cationic polymers are added to the aqueous sludge as polymeric flocculants to induce flocculation of the solid matter in the sludge. Other methods include adding quicklime (CaO) to the aqueous sludge to increase the dry matter content (OS). However, the addition of quicklime is both expensive and labor-intensive. Therefore, a simple sludge dewatering process is needed to achieve a high solids content. Specifically, the goals are to increase the residual dry matter in the dewatered sludge filter cake and to reduce the moisture content in the filter cake, respectively.

[0007] It was therefore an object to provide a copolymer composition which exhibits improved performance as a sludge dewatering aid in wastewater and sewage treatment.

[0008] The compositions currently produced utilize cationic polyacrylamide terpolymers that provide improved results in aqueous sludge dewatering. While not wanting to be bound by theory, it is believed that the second cationic monomer has a methyl group attached directly to the polymer backbone. This provides a harder polymer with a different configuration than conventional or standard CPAM polymers. Summary of the Invention

[0009] The present disclosure relates to a method for dewatering aqueous sludge. The method involves treating the aqueous sludge with a cationic polyacrylamide terpolymer comprising the reaction product of acrylamide, a first cationic monomer, and a second cationic monomer different from the first cationic monomer. The treated aqueous sludge is then dewatered.

[0010] Also disclosed is a method for increasing the dryness of a cake during a sludge dewatering process. The method comprises treating aqueous sludge with a cationic polyacrylamide terpolymer comprising a reaction product of acrylamide, a first cationic monomer, and a second cationic monomer different from the first monomer. The treated aqueous sludge is then dewatered to produce a filter cake, which can be disposed of accordingly.

[0011] This summary is intended to introduce some concepts in a simplified form that will be further described in the detailed description below. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. DETAILED DESCRIPTION

[0012] The following specific embodiments are exemplary only and are not intended to limit the invention or the application and use of the invention. Unless explicitly stated or obvious from the context, the term "about" as used herein should be understood to be within the normal tolerance range in the field, such as within 2 standard deviations of the mean. "About" can be understood to be within 10%, 5%, 1%, 0.5%, 0.1%, 0.05% or 0.01% of the value. "About" can also be understood to imply the exact value. Unless obvious from the context, all numerical values ​​provided herein are modified by the term "about".

[0013] There are no particular limitations on the aqueous sludge to be dewatered by the method according to the present invention. The aqueous sludge used as the starting material may be, for example, mining sludge, municipal sludge, papermaking sludge, and industrial sludge. The aqueous sludge may be digested sludge, activated sludge, crude sludge, raw sludge, or the like, or mixtures thereof.

[0014] In some aspects, the present methods relate to a method for dewatering aqueous sludge. The aqueous sludge is treated with a cationic polyacrylamide terpolymer comprising the reaction product of acrylamide, a first cationic monomer, and a second cationic monomer different from the first cationic monomer. The treated aqueous sludge is then dewatered. The resulting filter cake can then be disposed of accordingly.

[0015] In some aspects of the present method, the first cationic monomer is an acrylate monomer. For example, the first cationic monomer can be [2-(acryloyloxy)ethyl]trimethylammonium chloride (AETAC) (also known as 2-(dimethylamino)ethyl acrylate methyl chloride (ADAME-Q, DMA3Q), or acryloxyethyltrimethylammonium chloride), (3-acrylamidopropyl)trimethylammonium chloride (APTAC, DiMAPA-Q), and combinations thereof.

[0016] In some aspects of the present method, the second cationic monomer is a methacrylate monomer. For example, the second cationic monomer can be [2-(methacryloyloxy)ethyl]trimethylammonium chloride (MADAME-Q) (also known as 2-dimethylaminoethyl methacrylate (MADAME-Q) and ethyl methacrylate trimethylammonium chloride (TMAEMC)), [3-(methacrylamido)propyl]trimethylammonium chloride (MAPTAC, DiMAPMA-Q), and combinations thereof. The second cationic monomer should have a methyl group that can be directly attached to the polymer backbone.

[0017] Typical CPAM polymers are random coils (freely linked chains) in tap water (process water). The terpolymers have methyl groups on their backbones, which hinder the free coiling more and make the coiled configuration wider and stiffer.

[0018] In some aspects of the present methods, the first cationic monomer and the second cationic monomer are present in a weight ratio of about 95:5 weight percent to about 50:50 weight percent.

[0019] In other aspects of the present methods, the terpolymer has a total charge density of from about 50 mol% to about 100 mol% or from about 25 mol% to 100 mol%.

[0020] In some aspects of the methods of the present invention, the dehydration step is further defined as a centrifugation step or process.

[0021] In some aspects of the present method, the dewatering step utilizes at least one of a chamber filter press, a plate filter press, a frame filter press, a membrane filter press, a screw filter press, and a belt filter press.

[0022] In some aspects of the present methods, the aqueous sludge is derived from municipal, industrial, papermaking wastewater, or mining processes.

[0023] In another aspect, the present invention relates to a method for increasing the dryness of a cake during a sludge dewatering process, the method comprising treating aqueous sludge with a cationic polyacrylamide terpolymer comprising the reaction product of acrylamide, a first cationic monomer, and a second cationic monomer different from the first monomer, and subsequently dewatering the treated aqueous sludge to produce a filter cake.

[0024] In yet another aspect of the process, the solids content of the filter cake of the treated aqueous sludge is increased by at least 15% compared to the solids content of the filter cake of the aqueous sludge treated with a standard polymer under the same conditions.

[0025] Example

[0026] Preparation of comparative compositions

[0027] Prepare the aqueous phase by adding 276 g acrylamide (50 wt%), 0.6 g Trilon C, 394 g ADAME Quat (80 wt%), 90 g water, and 2 ppm N,N'-methylenebisacrylamide to a 2-liter (L) beaker. While stirring, adjust the pH to 3 using sulfuric acid. Prepare the organic phase in a second 2-liter beaker by combining 20 g Zephrym 7053, 3 g Degacryl 3059L, 12.7 g Intrasol FA1218 / 5, and 247 g paraffin oil. See Table 1.

[0028] The aqueous phase is then added to the oil phase under vigorous stirring, followed by mixing with a homogenizer to obtain a stable water-in-oil inverse emulsion. The inverse emulsion is added to a 2 L glass reaction vessel equipped with an anchor stirrer, thermometer, and distillation apparatus, and the emulsion is evacuated. The temperature of the emulsion is adjusted to 63 ± 1°C. After 30 minutes of air stripping or distillation to remove any volatile organic compounds (VOCs), polymerization is initiated by initially adding 1 wt % V-65 in oil, based on the total weight of the emulsion. The amount of distillate under negative pressure is 110 milliliters (ml). After distillation, the vacuum is removed. The residual monomer reacts adiabatically, typically reaching a maximum temperature of approximately 70°C. The emulsion is stirred for an additional 15 minutes, and vacuum is applied again until the vessel cools to 40°C. The vacuum is discontinued, and 2 grams (g) of sodium persulfate (25 wt %) and 11 grams of sodium bisulfite (25 wt %) are added to the vessel to reduce the monomer content. Finally, an activator is added to the vessel under stirring to facilitate the conversion of the inverse emulsion in water in the final product. If the inverse emulsion is added to water, the polymer dissolves in the water after inversion.

[0029] Preparation of novel compositions

[0030] The novel composition was prepared in the same manner as the standard composition, except that both ADAME Quat and MADAME Quat monomers were added to the aqueous phase: 276 g acrylamide (50 wt%), 276 g ADAME Quat (80 wt%), 126 g MADAME-Q (75 wt%), and 2 ppm N,N'-methylenebisacrylamide. The total monomer concentration remained 450 g (see Table 1).

[0031] Table 1 - Recipe

[0032]

[0033] Water-containing sludge samples were obtained from three different wastewater treatment facilities in Germany, namely Cologne, Angertal, and Essity Mannheim. Two 500 milliliter (ml) sludge samples from each facility were treated with two different doses of a standard drainage aid used as a baseline for the study. The sludge from each facility was treated with two different dosage levels as shown in Tables 2-4. The samples were sheared for 10-20 seconds using a four-claw stirrer at 1000 rpm to simulate the centrifuge used in the dewatering facility. The water-containing sludge was dewatered using a 315 micron (μm) metal sieve. The dewatering time of 300 ml of filtrate was measured and the clarity of the filtrate was determined using a graduated measuring wedge.

[0034] The filter cake remaining in the sieve was covered with a Perspex disk and a 10 kg weight was placed on top of the Perspex disk for 1 minute. The compaction of the cake was assessed by visual inspection to determine whether the cake had good, fair, or poor compressibility. Next, a portion of the compressed filter cake (weighed) was placed in a 105°C oven overnight. The dried filter cake was weighed and the total solids content (TS) of the cake was recorded.

[0035] Dehydration time and clarity

[0036] Table 2–KA

[0037]

[0038] Dehydration time (300ml filtrate time): the lower the better

[0039] Clarity (filtrate in turbidity wedge): The higher the better

[0040] TS cake solid content (105℃, overnight): The higher the better

[0041] As can be seen in Table 2, the terpolymer compositions comprising the reaction product of both acrylate and methacrylate monomers have improved efficacy compared to the standard formulation. Table 2 also shows that only selected combinations provide the desired results.

[0042] Table 3-KA Angertal

[0043]

[0044] Dehydration time (300ml filtrate time): the lower the better

[0045] Clarity (filtrate in turbidity wedge): The higher the better

[0046] TS cake solid content (105℃, overnight): The higher the better

[0047] The results in Table 3 show that the new terpolymer composition performs significantly better than the standard formulation.

[0048] Table 4 - Essity Mannheim, Paper Sludge

[0049]

[0050] Dehydration time (300ml filtrate time): the lower the better

[0051] Clarity (filtrate in turbidity wedge): The higher the better

[0052] TS cake solid content (105℃, overnight): The higher the better

[0053] The results in Table 4 show that the new terpolymer composition performs significantly better than the standard formulation.

[0054] Studies have shown that the residual dry matter (OS) in the filter cake can be increased by 15% compared to a standard composition.

[0055] Although at least one exemplary embodiment has been presented in the foregoing detailed description, it should be understood that there are numerous variations. It should also be understood that the one or more exemplary embodiments described herein are merely examples and are not intended to limit the scope, applicability, or configuration of the claimed subject matter in any way. On the contrary, the foregoing detailed description will provide a convenient roadmap for implementing the exemplary embodiments of the subject matter of the present invention to those skilled in the art. It should be understood that various changes may be made to the function and arrangement of the elements described in the exemplary embodiments without departing from the scope of the subject matter of the present invention given in the appended claims.

Claims

1. A method for dehydrating aqueous sludge, the method comprising: include: a) treating aqueous sludge with a cationic polyacrylamide terpolymer comprising the reaction product of: Acrylamide; a first cationic monomer; and a second cationic monomer different from the first cationic monomer; b) dewatering the treated aqueous sludge obtained from step a).

2. The method of claim 1, wherein the first cationic monomer is an acrylate monomer.

3. The method of claim 1, wherein the first cationic monomer is selected from the group consisting of [2-(acryloyloxy)ethyl]trimethylammonium chloride, (3-acrylamidopropyl)trimethylammonium chloride, and combinations thereof.

4. The method of claim 1, wherein the second cationic monomer is a methacrylate monomer.

5. The method of claim 4, wherein the second cationic monomer is selected from [2-(methacryloyloxy)ethyl]trimethylammonium chloride, [3-(methacrylamido)propyl]trimethylammonium chloride, and combinations thereof.

6. The method of any one of claims 1-5, wherein the first cationic monomer and the second cationic monomer are present in a weight ratio of about 95:5 to about 50:

50.

7. The method of any one of claims 1-5, wherein the total charge density of the terpolymer is from about 50 wt% to about 100 wt%.

8. The method of any one of claims 1-5, wherein the dehydration step is further defined as centrifugation.

9. The process according to any one of claims 1 to 5, wherein the aqueous sludge originates from municipal, industrial, papermaking wastewater or mining processes.

10. The method according to any one of claims 1 to 5, wherein the dryness of the cake is increased.

11. The process as claimed in claim 10, wherein the solid content of the filter cake from the treated aqueous sludge is increased by at least 15% as compared to the solid content of the filter cake of the aqueous sludge treated with conventional polymers under the same conditions.

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