CA2558038C - Sewage sludge dewatering process - Google Patents
Sewage sludge dewatering process Download PDFInfo
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- CA2558038C CA2558038C CA2558038A CA2558038A CA2558038C CA 2558038 C CA2558038 C CA 2558038C CA 2558038 A CA2558038 A CA 2558038A CA 2558038 A CA2558038 A CA 2558038A CA 2558038 C CA2558038 C CA 2558038C
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- Prior art keywords
- flocculant
- suspension
- polymer
- dewatering
- process according
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- 238000000034 method Methods 0.000 title claims abstract description 41
- 230000008569 process Effects 0.000 title claims abstract description 35
- 239000010801 sewage sludge Substances 0.000 title claims description 11
- 239000000725 suspension Substances 0.000 claims abstract description 78
- 229920000642 polymer Polymers 0.000 claims abstract description 71
- 239000002245 particle Substances 0.000 claims abstract description 36
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 23
- 230000016615 flocculation Effects 0.000 claims abstract description 16
- 238000005189 flocculation Methods 0.000 claims abstract description 16
- 239000007900 aqueous suspension Substances 0.000 claims abstract description 12
- 230000003311 flocculating effect Effects 0.000 claims abstract description 9
- 230000008719 thickening Effects 0.000 claims abstract description 8
- 125000002091 cationic group Chemical group 0.000 claims description 25
- 239000000203 mixture Substances 0.000 claims description 17
- -1 methyl chloride quaternary ammonium salt Chemical class 0.000 claims description 11
- 239000007788 liquid Substances 0.000 claims description 10
- 238000002156 mixing Methods 0.000 claims description 10
- 229920002401 polyacrylamide Polymers 0.000 claims description 9
- HRPVXLWXLXDGHG-UHFFFAOYSA-N Acrylamide Chemical compound NC(=O)C=C HRPVXLWXLXDGHG-UHFFFAOYSA-N 0.000 claims description 8
- NEHMKBQYUWJMIP-UHFFFAOYSA-N anhydrous methyl chloride Natural products ClC NEHMKBQYUWJMIP-UHFFFAOYSA-N 0.000 claims description 8
- 229940050176 methyl chloride Drugs 0.000 claims description 7
- 239000011248 coating agent Substances 0.000 claims description 6
- 238000000576 coating method Methods 0.000 claims description 6
- 230000006835 compression Effects 0.000 claims description 5
- 238000007906 compression Methods 0.000 claims description 5
- NIXOWILDQLNWCW-UHFFFAOYSA-M Acrylate Chemical compound [O-]C(=O)C=C NIXOWILDQLNWCW-UHFFFAOYSA-M 0.000 claims description 4
- 239000002202 Polyethylene glycol Substances 0.000 claims description 4
- 229920001223 polyethylene glycol Polymers 0.000 claims description 4
- 229920001296 polysiloxane Polymers 0.000 claims description 2
- 239000002002 slurry Substances 0.000 claims description 2
- 239000008394 flocculating agent Substances 0.000 description 30
- 239000010802 sludge Substances 0.000 description 22
- 239000007787 solid Substances 0.000 description 19
- 239000000178 monomer Substances 0.000 description 18
- 238000007792 addition Methods 0.000 description 15
- 125000000129 anionic group Chemical group 0.000 description 14
- 239000000243 solution Substances 0.000 description 11
- 229920006317 cationic polymer Polymers 0.000 description 10
- 239000000701 coagulant Substances 0.000 description 7
- 239000008367 deionised water Substances 0.000 description 5
- 239000006185 dispersion Substances 0.000 description 5
- 239000000839 emulsion Substances 0.000 description 5
- 150000003839 salts Chemical class 0.000 description 5
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 4
- 150000001412 amines Chemical class 0.000 description 4
- 125000004985 dialkyl amino alkyl group Chemical group 0.000 description 4
- 238000001914 filtration Methods 0.000 description 4
- 229910052500 inorganic mineral Inorganic materials 0.000 description 4
- 239000011707 mineral Substances 0.000 description 4
- 239000011368 organic material Substances 0.000 description 4
- 239000002244 precipitate Substances 0.000 description 4
- 239000000047 product Substances 0.000 description 4
- 238000011282 treatment Methods 0.000 description 4
- 229920002554 vinyl polymer Polymers 0.000 description 4
- 229920003169 water-soluble polymer Polymers 0.000 description 4
- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 description 3
- 229940048053 acrylate Drugs 0.000 description 3
- 230000009471 action Effects 0.000 description 3
- 239000011324 bead Substances 0.000 description 3
- 239000004744 fabric Substances 0.000 description 3
- 239000000706 filtrate Substances 0.000 description 3
- 238000004898 kneading Methods 0.000 description 3
- 238000000926 separation method Methods 0.000 description 3
- 239000010865 sewage Substances 0.000 description 3
- 239000000758 substrate Substances 0.000 description 3
- JKNCOURZONDCGV-UHFFFAOYSA-N 2-(dimethylamino)ethyl 2-methylprop-2-enoate Chemical class CN(C)CCOC(=O)C(C)=C JKNCOURZONDCGV-UHFFFAOYSA-N 0.000 description 2
- DPBJAVGHACCNRL-UHFFFAOYSA-N 2-(dimethylamino)ethyl prop-2-enoate Chemical class CN(C)CCOC(=O)C=C DPBJAVGHACCNRL-UHFFFAOYSA-N 0.000 description 2
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonia chloride Chemical compound [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 2
- 239000002253 acid Substances 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 150000001409 amidines Chemical class 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 239000003245 coal Substances 0.000 description 2
- 229920001577 copolymer Polymers 0.000 description 2
- GQOKIYDTHHZSCJ-UHFFFAOYSA-M dimethyl-bis(prop-2-enyl)azanium;chloride Chemical compound [Cl-].C=CC[N+](C)(C)CC=C GQOKIYDTHHZSCJ-UHFFFAOYSA-M 0.000 description 2
- 229920000620 organic polymer Polymers 0.000 description 2
- 239000011780 sodium chloride Substances 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- 239000004753 textile Substances 0.000 description 2
- 239000002562 thickening agent Substances 0.000 description 2
- 239000007762 w/o emulsion Substances 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- 239000002351 wastewater Substances 0.000 description 2
- PQUXFUBNSYCQAL-UHFFFAOYSA-N 1-(2,3-difluorophenyl)ethanone Chemical compound CC(=O)C1=CC=CC(F)=C1F PQUXFUBNSYCQAL-UHFFFAOYSA-N 0.000 description 1
- SMZOUWXMTYCWNB-UHFFFAOYSA-N 2-(2-methoxy-5-methylphenyl)ethanamine Chemical compound COC1=CC=C(C)C=C1CCN SMZOUWXMTYCWNB-UHFFFAOYSA-N 0.000 description 1
- JAHNSTQSQJOJLO-UHFFFAOYSA-N 2-(3-fluorophenyl)-1h-imidazole Chemical compound FC1=CC=CC(C=2NC=CN=2)=C1 JAHNSTQSQJOJLO-UHFFFAOYSA-N 0.000 description 1
- XHZPRMZZQOIPDS-UHFFFAOYSA-N 2-Methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid Chemical compound OS(=O)(=O)CC(C)(C)NC(=O)C=C XHZPRMZZQOIPDS-UHFFFAOYSA-N 0.000 description 1
- NIXOWILDQLNWCW-UHFFFAOYSA-N 2-Propenoic acid Natural products OC(=O)C=C NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 1
- OMIGHNLMNHATMP-UHFFFAOYSA-N 2-hydroxyethyl prop-2-enoate Chemical compound OCCOC(=O)C=C OMIGHNLMNHATMP-UHFFFAOYSA-N 0.000 description 1
- 229920001661 Chitosan Polymers 0.000 description 1
- ROSDSFDQCJNGOL-UHFFFAOYSA-N Dimethylamine Chemical compound CNC ROSDSFDQCJNGOL-UHFFFAOYSA-N 0.000 description 1
- WHNWPMSKXPGLAX-UHFFFAOYSA-N N-Vinyl-2-pyrrolidone Chemical compound C=CN1CCCC1=O WHNWPMSKXPGLAX-UHFFFAOYSA-N 0.000 description 1
- 229920002873 Polyethylenimine Polymers 0.000 description 1
- OFOBLEOULBTSOW-UHFFFAOYSA-N Propanedioic acid Natural products OC(=O)CC(O)=O OFOBLEOULBTSOW-UHFFFAOYSA-N 0.000 description 1
- 229920002472 Starch Polymers 0.000 description 1
- NJSSICCENMLTKO-HRCBOCMUSA-N [(1r,2s,4r,5r)-3-hydroxy-4-(4-methylphenyl)sulfonyloxy-6,8-dioxabicyclo[3.2.1]octan-2-yl] 4-methylbenzenesulfonate Chemical compound C1=CC(C)=CC=C1S(=O)(=O)O[C@H]1C(O)[C@@H](OS(=O)(=O)C=2C=CC(C)=CC=2)[C@@H]2OC[C@H]1O2 NJSSICCENMLTKO-HRCBOCMUSA-N 0.000 description 1
- 150000003926 acrylamides Chemical class 0.000 description 1
- 150000001252 acrylic acid derivatives Chemical class 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 235000019270 ammonium chloride Nutrition 0.000 description 1
- 229920006318 anionic polymer Polymers 0.000 description 1
- 229920006320 anionic starch Polymers 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000006085 branching agent Substances 0.000 description 1
- 239000002775 capsule Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 229920006037 cross link polymer Polymers 0.000 description 1
- 239000003431 cross linking reagent Substances 0.000 description 1
- LDHQCZJRKDOVOX-NSCUHMNNSA-N crotonic acid Chemical compound C\C=C\C(O)=O LDHQCZJRKDOVOX-NSCUHMNNSA-N 0.000 description 1
- 230000018044 dehydration Effects 0.000 description 1
- 238000006297 dehydration reaction Methods 0.000 description 1
- 230000001934 delay Effects 0.000 description 1
- 230000002939 deleterious effect Effects 0.000 description 1
- VAYGXNSJCAHWJZ-UHFFFAOYSA-N dimethyl sulfate Chemical compound COS(=O)(=O)OC VAYGXNSJCAHWJZ-UHFFFAOYSA-N 0.000 description 1
- BNIILDVGGAEEIG-UHFFFAOYSA-L disodium hydrogen phosphate Chemical compound [Na+].[Na+].OP([O-])([O-])=O BNIILDVGGAEEIG-UHFFFAOYSA-L 0.000 description 1
- 239000004815 dispersion polymer Substances 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000012458 free base Substances 0.000 description 1
- 238000000227 grinding Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 229920001519 homopolymer Polymers 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- VZCYOOQTPOCHFL-UPHRSURJSA-N maleic acid Chemical compound OC(=O)\C=C/C(O)=O VZCYOOQTPOCHFL-UPHRSURJSA-N 0.000 description 1
- 239000011976 maleic acid Substances 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- FQPSGWSUVKBHSU-UHFFFAOYSA-N methacrylamide Chemical compound CC(=C)C(N)=O FQPSGWSUVKBHSU-UHFFFAOYSA-N 0.000 description 1
- LVHBHZANLOWSRM-UHFFFAOYSA-N methylenebutanedioic acid Natural products OC(=O)CC(=C)C(O)=O LVHBHZANLOWSRM-UHFFFAOYSA-N 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 229910000403 monosodium phosphate Inorganic materials 0.000 description 1
- 235000019799 monosodium phosphate Nutrition 0.000 description 1
- 229920005615 natural polymer Polymers 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920000768 polyamine Polymers 0.000 description 1
- 229920001451 polypropylene glycol Polymers 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- UIIIBRHUICCMAI-UHFFFAOYSA-N prop-2-ene-1-sulfonic acid Chemical compound OS(=O)(=O)CC=C UIIIBRHUICCMAI-UHFFFAOYSA-N 0.000 description 1
- 150000003242 quaternary ammonium salts Chemical class 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 239000012266 salt solution Substances 0.000 description 1
- 150000003335 secondary amines Chemical class 0.000 description 1
- 229940047670 sodium acrylate Drugs 0.000 description 1
- AJPJDKMHJJGVTQ-UHFFFAOYSA-M sodium dihydrogen phosphate Chemical compound [Na+].OP(O)([O-])=O AJPJDKMHJJGVTQ-UHFFFAOYSA-M 0.000 description 1
- 235000019698 starch Nutrition 0.000 description 1
- 239000008107 starch Substances 0.000 description 1
- 229920001059 synthetic polymer Polymers 0.000 description 1
- VZCYOOQTPOCHFL-UHFFFAOYSA-N trans-butenedioic acid Natural products OC(=O)C=CC(O)=O VZCYOOQTPOCHFL-UHFFFAOYSA-N 0.000 description 1
- LDHQCZJRKDOVOX-UHFFFAOYSA-N trans-crotonic acid Natural products CC=CC(O)=O LDHQCZJRKDOVOX-UHFFFAOYSA-N 0.000 description 1
- NLVXSWCKKBEXTG-UHFFFAOYSA-N vinylsulfonic acid Chemical compound OS(=O)(=O)C=C NLVXSWCKKBEXTG-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
- C02F1/54—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using organic material
- C02F1/56—Macromolecular compounds
-
- 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
- C02F11/14—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents
Landscapes
- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Separation Of Suspended Particles By Flocculating Agents (AREA)
- Treatment Of Sludge (AREA)
Abstract
A process of dewatering aqueous suspension employing a flocculating system comprising treating the suspension with a flocculating amount of a first flocculant and a dewatering amount of a second flocculant, and subjecting the suspension to mechanical dewatering to form a cake, wherein the first flocculant brings about flocculation and assists thickening of the suspension and the second flocculant is a water-soluble or water swellable polymer that is mixed into the suspension is a water-soluble or water swellable particulate polymer having a particle diameter of at least 20 microns.
Description
Sewage Sludge Dewaterind Process The present invention concerns the flocculation and dewatering of aqueous suspensions to form a dewatered cake.
It is well known to apply flocculants to aqueous suspensions in order to separate solids from the suspension. For instance it is common practice to flocculate and then dewater suspensions containing either suspended solid organic material or mineral solids. For instance it is common practice to flocculate sludges such as sewage sludge, waste waters, textile industry effluents, red mud from the Bayer Alumina process and suspensions of coal tailings etc. Flocculation is usually achieved by mixing into the suspension the flocculent, allowing the suspended particles to flocculate and then dewatering the flocculated suspension to form a dewatered cake.
In the dewatering of suspensions it is known to add a high molecular weight, water soluble polymer as a flocculent to the suspension in order to remove the liquid from the suspension and greatly increase the dry solids of the suspension.
High molecular weight flocaulants may be cationic, anionic, nonionic or amphoteric in nature. The choice of polymeric flocculent will largely depend upon the susbstrate, which is being treated. For instance it is common practice to use high molecular weight cationic flocculants to treat aqueous suspensions comprising suspended organic material, for instance sewage sludge. In paper-making it is known to use either cationic, nonionic, anionic or amphoteric flocculants. Flocculation of mineral suspensions is frequently effected by use of anionic flocculants.
It is standard practice to apply polymers as aqueous compositions to flocculate suspensions containing suspended organic material. Generally the compositions of polymers are relatively dilute, for instance no more than 1%
and usually no more than 0.5%, and can be as low as 0.2% by weight or lower.
It is well known to apply flocculants to aqueous suspensions in order to separate solids from the suspension. For instance it is common practice to flocculate and then dewater suspensions containing either suspended solid organic material or mineral solids. For instance it is common practice to flocculate sludges such as sewage sludge, waste waters, textile industry effluents, red mud from the Bayer Alumina process and suspensions of coal tailings etc. Flocculation is usually achieved by mixing into the suspension the flocculent, allowing the suspended particles to flocculate and then dewatering the flocculated suspension to form a dewatered cake.
In the dewatering of suspensions it is known to add a high molecular weight, water soluble polymer as a flocculent to the suspension in order to remove the liquid from the suspension and greatly increase the dry solids of the suspension.
High molecular weight flocaulants may be cationic, anionic, nonionic or amphoteric in nature. The choice of polymeric flocculent will largely depend upon the susbstrate, which is being treated. For instance it is common practice to use high molecular weight cationic flocculants to treat aqueous suspensions comprising suspended organic material, for instance sewage sludge. In paper-making it is known to use either cationic, nonionic, anionic or amphoteric flocculants. Flocculation of mineral suspensions is frequently effected by use of anionic flocculants.
It is standard practice to apply polymers as aqueous compositions to flocculate suspensions containing suspended organic material. Generally the compositions of polymers are relatively dilute, for instance no more than 1%
and usually no more than 0.5%, and can be as low as 0.2% by weight or lower.
Various alternative methods of introducing a flocculant into a suspension have been proposed. WO-A-02/079099 describes in a method in which at least one flocculant emulsion and is added directly to a solids liquid separation process and inverted in situ such that flocculant is released directly into the application.
The emulsion is added specifically at the solids liquid separation process and subjected to an effective amount of high shear for sufficient time and pressure to ensure rapid inversion of the emulsion and complete release of the flocculant into the bulk suspension before any initial separation.
WO-A-98/31749 and WO-A-98/31748 and of both concerned with preparing dispersions of high intrinsic viscosity cationic polymers in an aqueous and medium containing dissolved low intrinsic viscosity cationic polymer. The product thus formed is an aqueous dispersion of undissolved high intrinsic viscosity cationic polymer which is a convenient way of providing high molecular weight flocculants. The dispersion polymer can be dissolved in water to a conventional concentration or can be added directly to a suspension.
It is also known to use two different polymeric flocculants in the same process.
In commercial practice the dewatering of sewage sludge may involve the addition of two polymeric flocculants which have the same charge (co-ionic).
In other processes it is known to apply two polymers of opposite charge (counter-ionic). Where two polymeric flocculants are applied to an aqueous suspension they may be added simultaneously or more usually sequentially.
W09950195 describes a process of dewatering an aqueous suspension of suspended organic solids by adding to the suspension an aqueous composition comprising a first water-soluble ionic polymeric flocculant and a second water-soluble ionic polymeric flocculant. The first flocculant is in excess over the second flocculant and both flocculants are counterionic. It is a requirement that the first flocculant and second flocculant form particles of counterionic precipitate. The counter Ionic precipitate Is designed to rupture In order to release the second flocculent and contained within the counter ionic precipitate.
US 6063291 discloses flocculation of suspensions using the addition of a mixture of counter Ionic flocculants In which one of the fiocculants is particulate.
US 5112500 discloses separate addition of dry cationic polymer particles and =
dry anionic polymer particles to a suspension to flocculate it.
Such counter ionic flocculent systems can bring about deleterious effects when attempting to dewater certain sludges, especially sludges that contain significant, amounts of organic components, such as sewage sludges.
WO-A-01/05712 reveals a process of dewatering a suspension by adding.to the suspension concentrated a dilute solution of polymeric flocculants substantially simultaneously. Both the concentrated and diluted solutions of polymer and are added at conventional concentrations of no more than 1% and usually much =
less than this.
WO-A-02/72482 describes a process of flocculating and dewatering an aqueous suspension of suspended solids In which a polymer composition comprising 40% and 60% by weight polymer and a polymer composition comprising =
between 0.05 and 0.2% by weight polymer are introduced simultaneously.
Although the process brings about some improvements In filtration and free drainage, it would be desirable to improve upon the cake solids obtained in dewatering suspensions, especially for sewage sludges. =
WO 2004/022493 describes a method of dewatering a suspension employing a coMposItion comprising a cationic polymer flocculent and a coagulant in which the coagulant Is encapsulated. After free drainage of the suspension the coagulant is released into the suspension for example by rupturing of the capsules which enclose the coagulant or by migration from a matrix in which the coagulant is entrapped. Although significant improvements in cake solids can be obtained in it would be desirable to provide equivalent or improved cake solids using flocculant products that can be more easily manufactured and/or applied.
However, achieving high cake solids can sometimes be difficult, particularly in the dewatering of sewage sludges. It is also known to add a flocculant or coagulant to assist the initial dewatering of a suspension followed by further addition of flocculant or coagulant and then further dewatering to achieve high cake solids. Such processes are described in JP-A-10-249398, JP-A-61-257300, JP-A-06-343999, JP-A-06-344000 and EP-A-1035077. However, these processes have the disadvantage that they require two stages of dewatering involving two separate treatments with flocculant.
It would be desirable to provide an improved process that results in dewatering of suspensions to provide increased cake solids. In particular it would be desirable to provide such a process that involves treatment agents that can be more easily and conveniently manufactured and applied. A further objective of the present invention is to provide a process that avoids the necessity of employing flocculant additions in two separate steps.
According to the present invention we provide a process of dewatering aqueous suspension employing a flocculating system comprising treating the suspension = 25 with a flocculating amount of a first flocculant and a dewatering amount of a second flocculant, and subjecting the suspension to mechanical dewatering to form a cake, wherein the first flocculant brings about flocculation and assists thickening of the suspension and the second flocculant further dewaters the suspension, characterised in that the second flocculant is a water-soluble or water swellable polymer that is mixed into the suspension in the form of a water-soluble or water swellable particulate polymer having a particle diameter of at least 20 microns, wherein the first and second flocculants are not counter ionic.
According to another aspect of the present invention, there is provided a process of dewatering aqueous suspension which is a sewage sludge employing a 5 flocculating system comprising i) treating the suspension with a flocculating amount of a first flocculant having a molecular weight of at least one million and a dewatering amount of a second flocculant, which second flocculant is in the form of a particulate polymer, ii) thickening the suspension involving initial flocculation and release of free water, iii) during mixing or mechanical dewatering, the particulate second flocculant integrates into the suspension, and (iv) subjecting the suspension to mechanical compression dewatering to form a cake, wherein the first flocculant brings about flocculation and assists thickening of the suspension and the second flocculant further dewaters the suspension, wherein the second flocculant is a water-soluble or water swellable polymer formed from 80 to 100% by weight methyl chloride quaternary ammonium salt of dimethyl amino ethyl (meth)acrylate and 0 to 20%
by weight acrylamide, the second flocculant being of intrinsic viscosity between and 10 dl/g that is mixed into the suspension in the form of a water-soluble or water swellable particulate polymer having a particle diameter of at least 50 microns, and the first flocculant is a cationic acrylamide polymer.
It is important that first and second flocculants do not form a counterionic precipitate. For instance, the first flocculant may be nonionic whilst the second flocculant can be anionic but preferably is cationic. Alternatively, the first flocculant may either be cationic or anionic and the second flocculant would be nonionic. It is especially preferred that both the first and second flocculants are co-ionic so that both flocculants are either anionic but most preferably are cationic.
5a The invention is applicable to any suitable suspensions in which it Is desirable concentrate the suspended solids. This Includes waste waters, and textile industry effluents mineral suspensions such as red mud from the Bayer Alumina process or coal tailings, In paper mill wastes such as cellulosic sludges. The process is particularly applicable to the dewatering of sewage sludge.
In the dewatering processes the suspension is first thickened following the addition of the first flocculent. This stage involves the initial flocculation and release of free water to produce the thickened suspension. Generally the release of free water may be achieved by free drainage or filtration and it is common to employ mechanical means such as a belt thickener, belt press rotary drum thickener or centrifuge. The flocculent should be applied In sufficient quantity to bring about initial flocculation and partial dewatering of the suspension. Preferably the suspension is thickened to produce a semi solid sludge paste. In general this first flocculent will be a polymer added at a conventional concentration, for instance 0.1% to 1% by weight, especially 0.2%
to 0.5%.
Typically addition of the first flocculent and second flocculent would be Into the initial bulk suspension.
The emulsion is added specifically at the solids liquid separation process and subjected to an effective amount of high shear for sufficient time and pressure to ensure rapid inversion of the emulsion and complete release of the flocculant into the bulk suspension before any initial separation.
WO-A-98/31749 and WO-A-98/31748 and of both concerned with preparing dispersions of high intrinsic viscosity cationic polymers in an aqueous and medium containing dissolved low intrinsic viscosity cationic polymer. The product thus formed is an aqueous dispersion of undissolved high intrinsic viscosity cationic polymer which is a convenient way of providing high molecular weight flocculants. The dispersion polymer can be dissolved in water to a conventional concentration or can be added directly to a suspension.
It is also known to use two different polymeric flocculants in the same process.
In commercial practice the dewatering of sewage sludge may involve the addition of two polymeric flocculants which have the same charge (co-ionic).
In other processes it is known to apply two polymers of opposite charge (counter-ionic). Where two polymeric flocculants are applied to an aqueous suspension they may be added simultaneously or more usually sequentially.
W09950195 describes a process of dewatering an aqueous suspension of suspended organic solids by adding to the suspension an aqueous composition comprising a first water-soluble ionic polymeric flocculant and a second water-soluble ionic polymeric flocculant. The first flocculant is in excess over the second flocculant and both flocculants are counterionic. It is a requirement that the first flocculant and second flocculant form particles of counterionic precipitate. The counter Ionic precipitate Is designed to rupture In order to release the second flocculent and contained within the counter ionic precipitate.
US 6063291 discloses flocculation of suspensions using the addition of a mixture of counter Ionic flocculants In which one of the fiocculants is particulate.
US 5112500 discloses separate addition of dry cationic polymer particles and =
dry anionic polymer particles to a suspension to flocculate it.
Such counter ionic flocculent systems can bring about deleterious effects when attempting to dewater certain sludges, especially sludges that contain significant, amounts of organic components, such as sewage sludges.
WO-A-01/05712 reveals a process of dewatering a suspension by adding.to the suspension concentrated a dilute solution of polymeric flocculants substantially simultaneously. Both the concentrated and diluted solutions of polymer and are added at conventional concentrations of no more than 1% and usually much =
less than this.
WO-A-02/72482 describes a process of flocculating and dewatering an aqueous suspension of suspended solids In which a polymer composition comprising 40% and 60% by weight polymer and a polymer composition comprising =
between 0.05 and 0.2% by weight polymer are introduced simultaneously.
Although the process brings about some improvements In filtration and free drainage, it would be desirable to improve upon the cake solids obtained in dewatering suspensions, especially for sewage sludges. =
WO 2004/022493 describes a method of dewatering a suspension employing a coMposItion comprising a cationic polymer flocculent and a coagulant in which the coagulant Is encapsulated. After free drainage of the suspension the coagulant is released into the suspension for example by rupturing of the capsules which enclose the coagulant or by migration from a matrix in which the coagulant is entrapped. Although significant improvements in cake solids can be obtained in it would be desirable to provide equivalent or improved cake solids using flocculant products that can be more easily manufactured and/or applied.
However, achieving high cake solids can sometimes be difficult, particularly in the dewatering of sewage sludges. It is also known to add a flocculant or coagulant to assist the initial dewatering of a suspension followed by further addition of flocculant or coagulant and then further dewatering to achieve high cake solids. Such processes are described in JP-A-10-249398, JP-A-61-257300, JP-A-06-343999, JP-A-06-344000 and EP-A-1035077. However, these processes have the disadvantage that they require two stages of dewatering involving two separate treatments with flocculant.
It would be desirable to provide an improved process that results in dewatering of suspensions to provide increased cake solids. In particular it would be desirable to provide such a process that involves treatment agents that can be more easily and conveniently manufactured and applied. A further objective of the present invention is to provide a process that avoids the necessity of employing flocculant additions in two separate steps.
According to the present invention we provide a process of dewatering aqueous suspension employing a flocculating system comprising treating the suspension = 25 with a flocculating amount of a first flocculant and a dewatering amount of a second flocculant, and subjecting the suspension to mechanical dewatering to form a cake, wherein the first flocculant brings about flocculation and assists thickening of the suspension and the second flocculant further dewaters the suspension, characterised in that the second flocculant is a water-soluble or water swellable polymer that is mixed into the suspension in the form of a water-soluble or water swellable particulate polymer having a particle diameter of at least 20 microns, wherein the first and second flocculants are not counter ionic.
According to another aspect of the present invention, there is provided a process of dewatering aqueous suspension which is a sewage sludge employing a 5 flocculating system comprising i) treating the suspension with a flocculating amount of a first flocculant having a molecular weight of at least one million and a dewatering amount of a second flocculant, which second flocculant is in the form of a particulate polymer, ii) thickening the suspension involving initial flocculation and release of free water, iii) during mixing or mechanical dewatering, the particulate second flocculant integrates into the suspension, and (iv) subjecting the suspension to mechanical compression dewatering to form a cake, wherein the first flocculant brings about flocculation and assists thickening of the suspension and the second flocculant further dewaters the suspension, wherein the second flocculant is a water-soluble or water swellable polymer formed from 80 to 100% by weight methyl chloride quaternary ammonium salt of dimethyl amino ethyl (meth)acrylate and 0 to 20%
by weight acrylamide, the second flocculant being of intrinsic viscosity between and 10 dl/g that is mixed into the suspension in the form of a water-soluble or water swellable particulate polymer having a particle diameter of at least 50 microns, and the first flocculant is a cationic acrylamide polymer.
It is important that first and second flocculants do not form a counterionic precipitate. For instance, the first flocculant may be nonionic whilst the second flocculant can be anionic but preferably is cationic. Alternatively, the first flocculant may either be cationic or anionic and the second flocculant would be nonionic. It is especially preferred that both the first and second flocculants are co-ionic so that both flocculants are either anionic but most preferably are cationic.
5a The invention is applicable to any suitable suspensions in which it Is desirable concentrate the suspended solids. This Includes waste waters, and textile industry effluents mineral suspensions such as red mud from the Bayer Alumina process or coal tailings, In paper mill wastes such as cellulosic sludges. The process is particularly applicable to the dewatering of sewage sludge.
In the dewatering processes the suspension is first thickened following the addition of the first flocculent. This stage involves the initial flocculation and release of free water to produce the thickened suspension. Generally the release of free water may be achieved by free drainage or filtration and it is common to employ mechanical means such as a belt thickener, belt press rotary drum thickener or centrifuge. The flocculent should be applied In sufficient quantity to bring about initial flocculation and partial dewatering of the suspension. Preferably the suspension is thickened to produce a semi solid sludge paste. In general this first flocculent will be a polymer added at a conventional concentration, for instance 0.1% to 1% by weight, especially 0.2%
to 0.5%.
Typically addition of the first flocculent and second flocculent would be Into the initial bulk suspension.
The dewatering process involves the action of the second flocculent on the thickened suspension in which the second flocculent is in the form of polymer particles having a particle diameter of at least 20 microns. The particulate second flocculent may be partially hydrated although it is preferred that it is substantially dry. We find that the particulate second flocculant does not substantially mix into the bulk suspension prior to thickening but it does integrate into the thickened suspension during mixing and/or mechanical dewatering and brings about further release of water to produce a dewatered cake. The polymeric particles can be easily mixed into the thickened suspension and distributed throughout using conventional mixing equipment.
Suitable mixing equipment includes for instance ribbon type mixers on or kneading mixers. Ribbon type mixers consist of helical or spiral mixing blades that sweep across nearly the entire surface of the mixing vessel. Kneading mixers consist of two kneading arms that intermesh as well as form a close tolerance to the mixer wall. Alternatively the second flocculent can be distributed throughout the thickened sludge during mechanical dewatering.
Typically, this mechanical dewatering will normally involve compression and can for instance be any of belt press, filter press, screw press or centrifuge.
When this treated thickened suspension is subjected to mechanical dewatering unexpectedly high cake solids are achieved.
Usually the second flocculent will be a particulate polymer having a particle diameter of at least 50 microns. The polymeric particles may have a particle diameter as high as 2000 or 3000 microns or higher or can be as low as 10 or 20 microns or lower, although usually will not be below 50 microns. Generally the particle diameter will be in the range of 50 microns to 2000 microns.
Preferably, the particles will have an diameter between above 100 and 800 microns, for instance 120 or 160 to 800 microns. More preferably the particles will range between 250 and 750 microns. The particles may also be defined by weight average particle diameter generally this will be between 50 and 1000 microns, preferably 100 to 800 microns and more preferably between 300 and 700 microns.
The first and second flocculants may be any suitable natural or synthetic polymeric flocculent and typically will be high molecular weight Natural polymers include for instance cationic starch, anionic starch and chitosan etc.
Synthetic polymers include linear, branched and cross-linked polymers of ethylenically unsaturated monomers. The first flocculent may be the same as the second flocculent or alternatively the two flocculants may be different.
Usually the polymer of the first flocculent and second flocculent will be of molecular weight in excess of 600,000, usually at least one million and normally 5 million up to 30 million.
The first and second flocculants of the present invention may be cationic, anionic, nonionic in nature. The choice of polymeric flocculent will largely depend upon the substrate, which is being treated. For instance it is common practice to use high molecular weight cationic flocculants to treat aqueous suspensions comprising suspended organic material, for instance sewage sludge. In treating paper-mill waste it is known to use either cationic, nonionic, anionic or amphoteric flocculants. Flocculation of mineral suspensions is frequently effected by use of anionic flocculants. As indicated previously either the first and second flocculants should be co ionic or that at least one of them may be non-ionic. Hence, the first and second flocculants should not be counter-ionic.
The polymer may be prepared by polymerisation of a water soluble monomer or water soluble monomer blend. By water soluble we mean that the water soluble monomer or water soluble monomer blend has a solubility in water of at least 5g in 100 ml of water. The polymer may be prepared conveniently by any suitable polymerisation process.
Suitable mixing equipment includes for instance ribbon type mixers on or kneading mixers. Ribbon type mixers consist of helical or spiral mixing blades that sweep across nearly the entire surface of the mixing vessel. Kneading mixers consist of two kneading arms that intermesh as well as form a close tolerance to the mixer wall. Alternatively the second flocculent can be distributed throughout the thickened sludge during mechanical dewatering.
Typically, this mechanical dewatering will normally involve compression and can for instance be any of belt press, filter press, screw press or centrifuge.
When this treated thickened suspension is subjected to mechanical dewatering unexpectedly high cake solids are achieved.
Usually the second flocculent will be a particulate polymer having a particle diameter of at least 50 microns. The polymeric particles may have a particle diameter as high as 2000 or 3000 microns or higher or can be as low as 10 or 20 microns or lower, although usually will not be below 50 microns. Generally the particle diameter will be in the range of 50 microns to 2000 microns.
Preferably, the particles will have an diameter between above 100 and 800 microns, for instance 120 or 160 to 800 microns. More preferably the particles will range between 250 and 750 microns. The particles may also be defined by weight average particle diameter generally this will be between 50 and 1000 microns, preferably 100 to 800 microns and more preferably between 300 and 700 microns.
The first and second flocculants may be any suitable natural or synthetic polymeric flocculent and typically will be high molecular weight Natural polymers include for instance cationic starch, anionic starch and chitosan etc.
Synthetic polymers include linear, branched and cross-linked polymers of ethylenically unsaturated monomers. The first flocculent may be the same as the second flocculent or alternatively the two flocculants may be different.
Usually the polymer of the first flocculent and second flocculent will be of molecular weight in excess of 600,000, usually at least one million and normally 5 million up to 30 million.
The first and second flocculants of the present invention may be cationic, anionic, nonionic in nature. The choice of polymeric flocculent will largely depend upon the substrate, which is being treated. For instance it is common practice to use high molecular weight cationic flocculants to treat aqueous suspensions comprising suspended organic material, for instance sewage sludge. In treating paper-mill waste it is known to use either cationic, nonionic, anionic or amphoteric flocculants. Flocculation of mineral suspensions is frequently effected by use of anionic flocculants. As indicated previously either the first and second flocculants should be co ionic or that at least one of them may be non-ionic. Hence, the first and second flocculants should not be counter-ionic.
The polymer may be prepared by polymerisation of a water soluble monomer or water soluble monomer blend. By water soluble we mean that the water soluble monomer or water soluble monomer blend has a solubility in water of at least 5g in 100 ml of water. The polymer may be prepared conveniently by any suitable polymerisation process.
When the water soluble polymer is nonionic the polymer may be formed from one or more water soluble ethylenically unsaturated nonionic monomers, for instance acrylamide, methacrylamide, hydroxyethyl acrylate, N-vinylpyrrolidone.
Preferably the polymer is formed from acrylamide.
When the water soluble polymer is anionic the polymer is formed from one or more ethylenically unsaturated anionic monomers or a blend of one or more anionic monomers with one or more of the nonionic monomers referred to previously. The anionic monomers are for instance acrylic acid, nnethacrylic acid, maleic acid, crotonic acid, itaconic acid, vinylsulphonic acid, allyl sulphonic acid, 2-acrylamido-2-methylpropane sulphonic acid and salts thereof. A
preferred polymer is the copolymer of sodium acrylate with acrylamide.
Preferably the water soluble polymer is cationic and is formed from one or more ethylenically unsaturated cationic monomers optionally with one or more of the nonionic monomers referred to herein. The cationic polymer may also be amphoteric provided that there are predominantly more cationic groups than anionic groups. The cationic monomers include dialkylamino alkyl (meth) acrylates, dialkylamino alkyl (meth) acrylamides, including acid addition and quaternary ammonium salts thereof, diallyldimethyl ammonium chloride.
Preferred cationic monomers include the methyl chloride quaternary ammonium.
salts of dimethylamino ethyl acrylate and dimethyl aminoethyl methacrylate. A
particularly preferred polymer includes the copolymer of acrylamide with the methyl chloride quaternary ammonium salts of dimethylamino ethyl acrylate.
The polymers may be linear in that they have been prepared substantially in the absence of branching or cross-linking agent. Alternatively the polymers can be branched or cross-linked, for example as in EP-A-202780.
Desirably the polymer may be prepared by reverse phase emulsion polymerisation, optionally followed by azeotropic dehydration to form a dispersion of polymer particles in oil. Alternatively the polymer may be provided in the form of beads by reverse phase suspension polymerisation, or as a powder by aqueous solution polymerisation followed by comminution, drying and then grinding. The polymers may be produced as beads by suspension polymerisation or as a water-in-oil emulsion or dispersion by water-in-oil emulsion polymerisation, for example according to a process defined by EP-A-150933, EP-A-102760 or EP-A-126528.
It is particularly preferred that the second flocculent is formed from at least 30%
by weight cationic monomer or monomers. Even more preferred are polymers comprising at least 40 or 50% by weight cationic monomer units. It may be desirable to employ cationic polymers having very high cationicities, for instance up to 80 or even 100% cationic monomer units. It is especially preferred when the cationic second flocculent polymer is selected from the group consisting of cationic polyacrylamides, polymers of dialkyl dially1 ammonium chloride, dialkyl amino alkyl (meth) -acrylates (or salts thereof) and dialkyl amino alkyl (meth)-acrylamides (or salts thereof).
As stated previously the second flocculent is desirably of relatively high molecular weight. Normally the second flocculent will be a polymer that exhibits an intrinsic viscosity of at least 0.5 dl/g. Typically the intrinsic viscosity will be the least 3 dl/g, and often it can be as high as 20 or 30 dl/g but preferably will be between 4 and 10 dl/g.
Intrinsic viscosity of polymers may be determined by preparing an aqueous solution of the polymer (0.5-1% w/w) based on the active content of the polymer. 2 g of this 0.5-1% polymer solution is diluted to 100 ml in a volumetric flask with 50 ml of 2M sodium chloride solution that is buffered to pH 7.0 (using 1.56 g sodium dihydrogen phosphate and 32.26 g disodium hydrogen phosphate per litre of deionised water) and the whole is diluted to the 100 ml mark with deionised water. The intrinsic viscosity of the polymers are measured using a Number 1 suspended level viscometer at 25 C in 1M buffered salt solution.
One particularly useful cationic polymer type for use as the second flocculant 5 includes 50 to 100% by weight methyl chloride quaternary ammonium salt of dimethyl amino ethyl (meth) acrylate and 0 to 50 % by weight acrylamide of intrinsic viscosity between 4 and 10 dl/g. Preferably the cationic polymer comprises at least 80% methyl chloride quaternary ammonium salt of dimethyl amino ethyl (meth) acrylate.
Preferably the polymer is formed from acrylamide.
When the water soluble polymer is anionic the polymer is formed from one or more ethylenically unsaturated anionic monomers or a blend of one or more anionic monomers with one or more of the nonionic monomers referred to previously. The anionic monomers are for instance acrylic acid, nnethacrylic acid, maleic acid, crotonic acid, itaconic acid, vinylsulphonic acid, allyl sulphonic acid, 2-acrylamido-2-methylpropane sulphonic acid and salts thereof. A
preferred polymer is the copolymer of sodium acrylate with acrylamide.
Preferably the water soluble polymer is cationic and is formed from one or more ethylenically unsaturated cationic monomers optionally with one or more of the nonionic monomers referred to herein. The cationic polymer may also be amphoteric provided that there are predominantly more cationic groups than anionic groups. The cationic monomers include dialkylamino alkyl (meth) acrylates, dialkylamino alkyl (meth) acrylamides, including acid addition and quaternary ammonium salts thereof, diallyldimethyl ammonium chloride.
Preferred cationic monomers include the methyl chloride quaternary ammonium.
salts of dimethylamino ethyl acrylate and dimethyl aminoethyl methacrylate. A
particularly preferred polymer includes the copolymer of acrylamide with the methyl chloride quaternary ammonium salts of dimethylamino ethyl acrylate.
The polymers may be linear in that they have been prepared substantially in the absence of branching or cross-linking agent. Alternatively the polymers can be branched or cross-linked, for example as in EP-A-202780.
Desirably the polymer may be prepared by reverse phase emulsion polymerisation, optionally followed by azeotropic dehydration to form a dispersion of polymer particles in oil. Alternatively the polymer may be provided in the form of beads by reverse phase suspension polymerisation, or as a powder by aqueous solution polymerisation followed by comminution, drying and then grinding. The polymers may be produced as beads by suspension polymerisation or as a water-in-oil emulsion or dispersion by water-in-oil emulsion polymerisation, for example according to a process defined by EP-A-150933, EP-A-102760 or EP-A-126528.
It is particularly preferred that the second flocculent is formed from at least 30%
by weight cationic monomer or monomers. Even more preferred are polymers comprising at least 40 or 50% by weight cationic monomer units. It may be desirable to employ cationic polymers having very high cationicities, for instance up to 80 or even 100% cationic monomer units. It is especially preferred when the cationic second flocculent polymer is selected from the group consisting of cationic polyacrylamides, polymers of dialkyl dially1 ammonium chloride, dialkyl amino alkyl (meth) -acrylates (or salts thereof) and dialkyl amino alkyl (meth)-acrylamides (or salts thereof).
As stated previously the second flocculent is desirably of relatively high molecular weight. Normally the second flocculent will be a polymer that exhibits an intrinsic viscosity of at least 0.5 dl/g. Typically the intrinsic viscosity will be the least 3 dl/g, and often it can be as high as 20 or 30 dl/g but preferably will be between 4 and 10 dl/g.
Intrinsic viscosity of polymers may be determined by preparing an aqueous solution of the polymer (0.5-1% w/w) based on the active content of the polymer. 2 g of this 0.5-1% polymer solution is diluted to 100 ml in a volumetric flask with 50 ml of 2M sodium chloride solution that is buffered to pH 7.0 (using 1.56 g sodium dihydrogen phosphate and 32.26 g disodium hydrogen phosphate per litre of deionised water) and the whole is diluted to the 100 ml mark with deionised water. The intrinsic viscosity of the polymers are measured using a Number 1 suspended level viscometer at 25 C in 1M buffered salt solution.
One particularly useful cationic polymer type for use as the second flocculant 5 includes 50 to 100% by weight methyl chloride quaternary ammonium salt of dimethyl amino ethyl (meth) acrylate and 0 to 50 % by weight acrylamide of intrinsic viscosity between 4 and 10 dl/g. Preferably the cationic polymer comprises at least 80% methyl chloride quaternary ammonium salt of dimethyl amino ethyl (meth) acrylate.
10 .
Other suitable polymeric second flocculants include polyvinyl amidine and polyvinyl amines of intrinsic viscosity greater than 1 dl/g, preferably greater than 2 dl/g.
Another particularly suitable category of second fiocculants are Mannich addition polyacrylamides. ideally such polymers will exhibit an intrinsic viscosity greater than 1 dl/g and quite often can be at least 4 dl/g, for instance at least 7 or 8 dl/g. Such polymers may be made by reacting formaldehyde / amine adducts with polyacrylamide. The amine may for instance be dimethylarnine or other secondary amines. Preferably the Mannich addition polyacrylamides are quatemised salts and these could be prepared by reacting the free base Mannich with a suitable quaternising agent such as methyl chloride or dimethyl sulfate.
Another suitable polymer as the second flocculant includes poly dimethyl diallyl ammonium chloride of intrinsic viscosity greater than 0.5 dig, preferably at least 1 dl/g.
Effective dewatering of suspensions can be achieved when these polymers are , used as the second flocculant.
Other suitable polymeric second flocculants include polyvinyl amidine and polyvinyl amines of intrinsic viscosity greater than 1 dl/g, preferably greater than 2 dl/g.
Another particularly suitable category of second fiocculants are Mannich addition polyacrylamides. ideally such polymers will exhibit an intrinsic viscosity greater than 1 dl/g and quite often can be at least 4 dl/g, for instance at least 7 or 8 dl/g. Such polymers may be made by reacting formaldehyde / amine adducts with polyacrylamide. The amine may for instance be dimethylarnine or other secondary amines. Preferably the Mannich addition polyacrylamides are quatemised salts and these could be prepared by reacting the free base Mannich with a suitable quaternising agent such as methyl chloride or dimethyl sulfate.
Another suitable polymer as the second flocculant includes poly dimethyl diallyl ammonium chloride of intrinsic viscosity greater than 0.5 dig, preferably at least 1 dl/g.
Effective dewatering of suspensions can be achieved when these polymers are , used as the second flocculant.
The dose of aqueous composition depends on the substrate and usually this will be a conventional amount Typically for sewage sludge treatment the dose of the aqueous composition (second flocculent) found to be an effective dewatering amount is often at least 50 mg active polymer per litre of suspension. Usually the amount would be higher for instance up to 400 mg per litre. Preferred doses are between 60 and 300 mg per litre. The quantity of first flocculent used will usually be at least 50 mg active polymer per litre of suspension and can be as high as 500 or 600 mg per litre. Preferred doses would be between 100 and 400 mg per litre.
.
Various polymers may be used as thefirst flocculent in order to obtain a suitably thickened suspension for treatment with the second flocculent. Preferably the first flocculent is a cationic organic polymer. This is particularly true when the suspension is a sewage sludge. Preferred cationic polymers include polymers selected from the group consisting of acrylamide polymers, polyvinyl amidine, polyvinyl amine, poly dimethyl diallyl ammonium chloride, poly amines;
. polyethyleneimines, mannich polyacrylamides and quaternised mannich polyacrylamides. .
The first and second flocculants may be added sequentially and in which case usually the second flocculent is added to the suspension first although the reverse order may be employed. Normally the first and second flocculants are added in close proximity and preferably they are added substantially simultaneously. When the two flocculants are added in this way they can desirably be added separately although in some situations the first flocculant and the second flocculent are combined into a single composition with beneficial _ results. In one preferred aspect the single composition is a particulate polymer product in which the first flocculent comprises particles having a diameter below 10 microns and the second flocculent comprises particles having a diameter above 20 microns, preferably above 50 microns. The particle size of the second flocculent may be as defined previously. We have found the first flocculent tends to act substantially immediately on the suspension and brings about flocculation and thickening and then the larger particle size second flocculent can distribute easily throughout the thickened suspension to bring about further dewatering.
Particularly effective results can be achieved when the first and second flocculants are added to the sludge simultaneously but separately. Without being limited to theory it is believed that the first flocculent results in flocculation of the sludge and the undispersed polymer of the second flocculent becomes trapped within the flocculated structure but does not bring about any significant dewatering until the flocculated sludge is thickened and then by mixing the polymer of the second flocculent is allowed to distribute throughout and integrate with the sludge and achieve further dewatering.
In a further embodiment the second flocculent comprises polymeric particles having a coating applied to the surface. The coating delays the dissolution of the second flocculent particles so that on addition to the suspension the first flocculent acts on the suspension to bring about flocculation and produce a thickened suspension and the coated second flocculent particles are distributed throughout the thickened suspension and bring about further dewatering. The coating may for instance be a silicone compound or alternatively it may be a water-soluble wax. The water-soluble wax and can for instance be a polyethyleneglycol or a polypropylene glycol. A suitable water-soluble wax is for instance polyethyleneglycol with a molecular weight of 600 (PEG600) or above.
It may be desirable to combine first and second flocculants into a single composition in which the second flocculent comprises coated particles.
In a still further embodiment of the present invention, the second flocculent may be introduced in the suspension in the form of a slurry of second flocculent polymer particles in a liquid. The liquid may be a suitable liquid that does not adversely interact with either the particles of the second flocculant or the suspension. Suitably the liquid can be a polyethyleneglycol.
The following example is an illustration of the invention.
.
Various polymers may be used as thefirst flocculent in order to obtain a suitably thickened suspension for treatment with the second flocculent. Preferably the first flocculent is a cationic organic polymer. This is particularly true when the suspension is a sewage sludge. Preferred cationic polymers include polymers selected from the group consisting of acrylamide polymers, polyvinyl amidine, polyvinyl amine, poly dimethyl diallyl ammonium chloride, poly amines;
. polyethyleneimines, mannich polyacrylamides and quaternised mannich polyacrylamides. .
The first and second flocculants may be added sequentially and in which case usually the second flocculent is added to the suspension first although the reverse order may be employed. Normally the first and second flocculants are added in close proximity and preferably they are added substantially simultaneously. When the two flocculants are added in this way they can desirably be added separately although in some situations the first flocculant and the second flocculent are combined into a single composition with beneficial _ results. In one preferred aspect the single composition is a particulate polymer product in which the first flocculent comprises particles having a diameter below 10 microns and the second flocculent comprises particles having a diameter above 20 microns, preferably above 50 microns. The particle size of the second flocculent may be as defined previously. We have found the first flocculent tends to act substantially immediately on the suspension and brings about flocculation and thickening and then the larger particle size second flocculent can distribute easily throughout the thickened suspension to bring about further dewatering.
Particularly effective results can be achieved when the first and second flocculants are added to the sludge simultaneously but separately. Without being limited to theory it is believed that the first flocculent results in flocculation of the sludge and the undispersed polymer of the second flocculent becomes trapped within the flocculated structure but does not bring about any significant dewatering until the flocculated sludge is thickened and then by mixing the polymer of the second flocculent is allowed to distribute throughout and integrate with the sludge and achieve further dewatering.
In a further embodiment the second flocculent comprises polymeric particles having a coating applied to the surface. The coating delays the dissolution of the second flocculent particles so that on addition to the suspension the first flocculent acts on the suspension to bring about flocculation and produce a thickened suspension and the coated second flocculent particles are distributed throughout the thickened suspension and bring about further dewatering. The coating may for instance be a silicone compound or alternatively it may be a water-soluble wax. The water-soluble wax and can for instance be a polyethyleneglycol or a polypropylene glycol. A suitable water-soluble wax is for instance polyethyleneglycol with a molecular weight of 600 (PEG600) or above.
It may be desirable to combine first and second flocculants into a single composition in which the second flocculent comprises coated particles.
In a still further embodiment of the present invention, the second flocculent may be introduced in the suspension in the form of a slurry of second flocculent polymer particles in a liquid. The liquid may be a suitable liquid that does not adversely interact with either the particles of the second flocculant or the suspension. Suitably the liquid can be a polyethyleneglycol.
The following example is an illustration of the invention.
Example Dewatering of aqueous suspensions via a one-stage addition of a conventional solution and dry particles of organic polymer flocculants Polymers Polymer A is a linear, high molecular weight, high cationic acrylamide based polymer of intrinsic viscosity 12 dl/g in the form of a dehydrated emulsion (liquid dispersion product). Polymer B is a linear, low -medium molecular weight, cationic homopolymer of quatemised dimethyl amino ethyl methacrylate of intrinsic viscosity 5 dl/g based polymer in bead form.
Unless otherwise stated intrinsic viscosity is measured using a Number 1 suspended level viscometer, in 1M sodium chloride buffered to pH 7 in accordance with the information given in the description.
Test substrate Dewatering tests were conducted on a sample of a digested, mixed primary/activated sludge. The sample had a dry solids content of 3.28%.
Experimental procedure (A) One-stage addition of polymer(s) i) Polymer A was first dissolved in deionised water to give a homogeneous 1% w/v solution and further diluted to 0.25%w/v prior to use. Polymer B was dissolved in deionised water to give a 1%w/v solution. The 1%w/v solution was further diluted with deionised water to 0.25%w/v prior to use.
ii) 250 ml of a digested, mixed primary/activated sludge was placed in a 1 litre plastic beaker (120cm diameter by 120cm tall). A standard laboratory stirrer was secured over the beaker with the stirrer shaft located through a hole in the centre of the beaker lid. The stirrer is a four bladed, fiat =
5 crosshead type (each paddle is 25cm width by 1.1cm).
ill) An appropriate volume of a 0.25% solution of Polymer A, and a 0.25%
solution or substantially dry particles (250-500 micron) of Polymer B, were added simultaneously to the sludge and the lid secured to the 10 beaker. The sludge was flocculated by stirring at 1500rpm for 15s. The flocculated sludge was poured into a filtration cell, which had a filter membrane, comprising an 8cm diameter belt-press filter cloth and the filtrate collected in a measuring cylinder.
Unless otherwise stated intrinsic viscosity is measured using a Number 1 suspended level viscometer, in 1M sodium chloride buffered to pH 7 in accordance with the information given in the description.
Test substrate Dewatering tests were conducted on a sample of a digested, mixed primary/activated sludge. The sample had a dry solids content of 3.28%.
Experimental procedure (A) One-stage addition of polymer(s) i) Polymer A was first dissolved in deionised water to give a homogeneous 1% w/v solution and further diluted to 0.25%w/v prior to use. Polymer B was dissolved in deionised water to give a 1%w/v solution. The 1%w/v solution was further diluted with deionised water to 0.25%w/v prior to use.
ii) 250 ml of a digested, mixed primary/activated sludge was placed in a 1 litre plastic beaker (120cm diameter by 120cm tall). A standard laboratory stirrer was secured over the beaker with the stirrer shaft located through a hole in the centre of the beaker lid. The stirrer is a four bladed, fiat =
5 crosshead type (each paddle is 25cm width by 1.1cm).
ill) An appropriate volume of a 0.25% solution of Polymer A, and a 0.25%
solution or substantially dry particles (250-500 micron) of Polymer B, were added simultaneously to the sludge and the lid secured to the 10 beaker. The sludge was flocculated by stirring at 1500rpm for 15s. The flocculated sludge was poured into a filtration cell, which had a filter membrane, comprising an 8cm diameter belt-press filter cloth and the filtrate collected in a measuring cylinder.
15 iv) After 30s drainage the thickened sludge retained on the filter cloth was subjected to a 'furrowing' technique, whereby a spatula was slowly , drawn across the sludge in several directions to encourage release of more water. Furrowing was carried out for 30s. The volume of filtrate was noted.
v) The thickened sludge was transferred to a 250m1 beaker and stirred by hand for 45s with a spatula, using a slow, circular folding action.
vi) The thickened sludge was then transferred to a piston-press device and subjected to a compression dewatering stage. Dewatering was commenced using a pressure of 20psi for 2 minutes, followed by = increases of lOpsi, at one minute intervals, for a further 3 minutes to a maximum of 60psi. Pressure was maintained at 60psi for a further 5 minutes, giving a total compression dewatering time of 10 minutes. The wet cake was removed and the cake solids conten:t was determined by heating at 110 C overnight.
v) The thickened sludge was transferred to a 250m1 beaker and stirred by hand for 45s with a spatula, using a slow, circular folding action.
vi) The thickened sludge was then transferred to a piston-press device and subjected to a compression dewatering stage. Dewatering was commenced using a pressure of 20psi for 2 minutes, followed by = increases of lOpsi, at one minute intervals, for a further 3 minutes to a maximum of 60psi. Pressure was maintained at 60psi for a further 5 minutes, giving a total compression dewatering time of 10 minutes. The wet cake was removed and the cake solids conten:t was determined by heating at 110 C overnight.
(B ) One-stage addition of oolvmer(a) excluding mixing of the thickened sludge.
The procedure was exactly the same as that described in Section (A) except:
Section v) was omitted (C) Control ¨ Addition of dry polymer particles in a two-stage process The procedure was as that given in Section (A) except:
Section iii) ¨ the appropriate volume of a 0.25% solution of Polymer A
was added to the sludge using a syringe and the lid secured to the beaker. The sludge was flocculated by stirring at 1500rpni for 10s. The flocculated sludge was poured into a filtration cell comprising an 8cm diameter belt-press filter cloth and the filtrate collected in a measuring cylinder.
Section v) - the thickened sludge was transferred to a 250m1 beaker. The appropriate weight of substantially dry particles of Polymer B (250-500 micron) was added into the thickened sludge. To mix in the polymer the treated thickened sludge was stirred by hand for 45s with a spatula, using.a slow, circular folding action.
Results The results are given in Table 1
The procedure was exactly the same as that described in Section (A) except:
Section v) was omitted (C) Control ¨ Addition of dry polymer particles in a two-stage process The procedure was as that given in Section (A) except:
Section iii) ¨ the appropriate volume of a 0.25% solution of Polymer A
was added to the sludge using a syringe and the lid secured to the beaker. The sludge was flocculated by stirring at 1500rpni for 10s. The flocculated sludge was poured into a filtration cell comprising an 8cm diameter belt-press filter cloth and the filtrate collected in a measuring cylinder.
Section v) - the thickened sludge was transferred to a 250m1 beaker. The appropriate weight of substantially dry particles of Polymer B (250-500 micron) was added into the thickened sludge. To mix in the polymer the treated thickened sludge was stirred by hand for 45s with a spatula, using.a slow, circular folding action.
Results The results are given in Table 1
Claims (11)
1. A process of dewatering aqueous suspension which is a sewage sludge employing a flocculating system comprising i) treating the suspension with a flocculating amount of a first flocculant having a molecular weight of at least one million and a dewatering amount of a second flocculant, which second flocculant is in the form of a particulate polymer, ii) thickening the suspension involving initial flocculation and release of free water, iii) during mixing or mechanical dewatering, the particulate second flocculant integrates into the suspension, and (iv) subjecting the suspension to mechanical compression dewatering to form a cake, wherein the first flocculant brings about flocculation and assists thickening of the suspension and the second flocculant further dewaters the suspension, wherein the second flocculant is a water-soluble or water swellable polymer formed from 80 to 100% by weight methyl chloride quaternary ammonium salt of dimethyl amino ethyl (meth)acrylate and 0 to 20% by weight acrylamide, the second flocculant being of intrinsic viscosity between 3 and 10 dl/g that is mixed into the suspension in the form of a water-soluble or water swellable particulate polymer having a particle diameter of at least 50 microns, and the first flocculant is a cationic acrylamide polymer.
2. A process according to claim 1, in which the mechanical dewatering employs an apparatus selected from the group consisting of belt press, filter press, screw press and centrifuge.
3. A process according to claim 1 or 2, in which the particulate polymer of the second flocculant has a particle diameter of 100 to 2000 microns.
4. A process according to any one of claims 1 to 3 in which the second flocculant has an intrinsic viscosity of 4 to 10 dl/g.
5. A process according to any one of claims 1 to 4 in which the first flocculant and second flocculant are added substantially simultaneously.
6. A process according to any one of claims 1 to 5 in which the first flocculant and second flocculant are combined into a single composition.
7. A process according to any one of claims 1 to 6 in which the second flocculant comprises polymeric particles having a coating applied to the surface.
8. A process according to claim 7 in which the coating is a silicone.
9. A process according to claim 7 in which the coating is a water-soluble wax.
10. A process according to any one of claims 1 to 9 in which the second flocculant is introduced into the suspension in form of a slurry in a liquid.
11. A process according to claim 10 in which the liquid is polyethylene glycol.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
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GB0405505.9 | 2004-03-12 | ||
GBGB0405505.9A GB0405505D0 (en) | 2004-03-12 | 2004-03-12 | Dewatering process |
PCT/EP2005/002079 WO2005097687A1 (en) | 2004-03-12 | 2005-02-28 | Dewatering process |
Publications (2)
Publication Number | Publication Date |
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CA2558038A1 CA2558038A1 (en) | 2005-10-20 |
CA2558038C true CA2558038C (en) | 2013-10-01 |
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ID=32117481
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Application Number | Title | Priority Date | Filing Date |
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CA2558038A Expired - Fee Related CA2558038C (en) | 2004-03-12 | 2005-02-28 | Sewage sludge dewatering process |
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US (1) | US7754087B2 (en) |
EP (1) | EP1723081A1 (en) |
KR (1) | KR101204283B1 (en) |
CN (1) | CN1930090B (en) |
AU (1) | AU2005231565B2 (en) |
CA (1) | CA2558038C (en) |
GB (1) | GB0405505D0 (en) |
NZ (1) | NZ549350A (en) |
WO (1) | WO2005097687A1 (en) |
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WO2011050440A1 (en) | 2009-10-30 | 2011-05-05 | Suncor Energy Inc. | Depositing and farming methods for drying oil sand mature fine tailings |
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WO2012062359A1 (en) * | 2010-11-10 | 2012-05-18 | Yara International Asa | Method to support an emission-free and deposit-free transport of sulphide in sewer systems to waste water treatment plants and agent for use therein |
US20150075561A1 (en) * | 2011-01-06 | 2015-03-19 | Perigee Solutions International Llc | Process for removing polymeric fouling |
CN102267795A (en) * | 2011-06-17 | 2011-12-07 | 中国科学院武汉岩土力学研究所 | Dewatered sludge drying method of wastewater treatment plant |
CA2789678C (en) * | 2011-09-16 | 2015-04-07 | Syncrude Canada Ltd. In Trust For The Owners Of The Syncrude Project | Oil sands fine tailings flocculation using dynamic mixing |
US8721896B2 (en) | 2012-01-25 | 2014-05-13 | Sortwell & Co. | Method for dispersing and aggregating components of mineral slurries and low molecular weight multivalent polymers for mineral aggregation |
WO2014046979A1 (en) * | 2012-09-19 | 2014-03-27 | Hercules Incorporated | Process for filtration enhancement of aqueous dispersions |
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US20140238943A1 (en) * | 2013-02-22 | 2014-08-28 | Cedrick Favero | Method For Treating Suspensions Of Solid Particles In Water Using Post Hydrolyzed Polymers |
CA2812275C (en) | 2013-04-10 | 2019-01-08 | Imperial Oil Resources Limited | Systems and methods for separating mine tailings from water-absorbing polymers and regenerating the separated water-absorbing polymers |
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US10106443B2 (en) * | 2013-04-25 | 2018-10-23 | S.P.C.M. Sa | Composition for treating suspensions of solid particles in water and method using said composition |
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AR101419A1 (en) * | 2014-08-28 | 2016-12-14 | Dow Global Technologies Llc | COMPOSITIONS FOR WATER TREATMENT AND METHODS OF USE |
JP2016120464A (en) * | 2014-12-25 | 2016-07-07 | 三菱レイヨン株式会社 | Sludge dewatering method |
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JP7216967B2 (en) * | 2017-04-28 | 2023-02-02 | ハイモ株式会社 | Organic wastewater treatment method and its use |
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-
2004
- 2004-03-12 GB GBGB0405505.9A patent/GB0405505D0/en not_active Ceased
-
2005
- 2005-02-28 WO PCT/EP2005/002079 patent/WO2005097687A1/en not_active Application Discontinuation
- 2005-02-28 KR KR1020067018516A patent/KR101204283B1/en not_active IP Right Cessation
- 2005-02-28 NZ NZ549350A patent/NZ549350A/en not_active IP Right Cessation
- 2005-02-28 AU AU2005231565A patent/AU2005231565B2/en not_active Ceased
- 2005-02-28 US US10/591,878 patent/US7754087B2/en not_active Expired - Fee Related
- 2005-02-28 CA CA2558038A patent/CA2558038C/en not_active Expired - Fee Related
- 2005-02-28 EP EP05758482A patent/EP1723081A1/en not_active Withdrawn
- 2005-02-28 CN CN2005800074150A patent/CN1930090B/en not_active Expired - Fee Related
Also Published As
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AU2005231565A1 (en) | 2005-10-20 |
KR20070032297A (en) | 2007-03-21 |
AU2005231565B2 (en) | 2010-06-17 |
EP1723081A1 (en) | 2006-11-22 |
CA2558038A1 (en) | 2005-10-20 |
US7754087B2 (en) | 2010-07-13 |
US20070187333A1 (en) | 2007-08-16 |
NZ549350A (en) | 2010-07-30 |
CN1930090A (en) | 2007-03-14 |
WO2005097687A1 (en) | 2005-10-20 |
KR101204283B1 (en) | 2012-11-26 |
GB0405505D0 (en) | 2004-04-21 |
CN1930090B (en) | 2010-06-16 |
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