Flocculation of suspended solids from aqueous solutions

Abstract: The use as flocculants of aluminum chloride/­ water-soluble cationic polymer compositions having inorganic:polymer weight ratios of at least 5:1 is disclosed. These compositions are especially effective in low turbidity waters.

Description: BACKGROUND OF THE INVENTION This invention relates to methods of flocculating, accelerating the rate of flocculation and/or accelerating the settling of solids which are suspended in aqueous media by addition thereto of a flocculating composition. US-A-4,450,092 discloses compositions useful for coagulating finely divided solids in turbid waters. These compositions are prepared by mixing inorganic water-soluble compounds such as aluminum chloride, aluminum sulfate, ferric chloride and ferric sulfate with a polymer of diallyl dimethyl ammonium chloride having a molecular weight of at least 2,000. The weight ratio of the inorganic component to the organic component ranges from 0.75:1 to about 4:1. US-A-4,582,627 discloses flocculating agents which are reaction products of sulfate ion-containing polymeric aluminum hydroxy chloride and one or more cationic polymers such as polyacrylic amide, polyamide amine and polyethylene imine. US-A-4,137,165 discloses the use of low molecular weight acrylamide polymers which contain quaternized dimethylamino methyl groups for clarification of turbid waters. US-A-3,489,681 discloses the use of water-soluble copolymers of diacetone acrylamide as flocculating agents. The term flocculation, as used herein, is synonymous with the term coagulation. Flocculation refers to the settling of suspended solid particles from aqueous systems. Turbidity, as used herein, is defined as the cloudiness or haziness of a solution caused by finely suspended particles. Turbidity is measured using NTU's, (nephelometric turbidity units). As used herein, low turbidity systems are systems having a low solids concentration (on a weight basis), i.e., a solids weight percent of 0.1 or less. As a general rule, this corresponds to an approximate turbidity of 50 NTU's or less, but may vary due to nature of the solids or dissolved colored matter. High solids suspensions include those systems containing in excess of 0.1 weight percent suspended solids, which generally corresponds to a turbidity of greater than 50 NTU's. While the instant compositions are especially effective in low turbidity waters, it is not intended that their use be so restricted. In fact, the instant compositions are useful in a wide variety of raw waters and in concentrated wastewaters. Many flocculants are known, including alum (Al₂(SO₄)₃ X H₂0, wherein X is about 14), poly(aluminum chloride), sodium aluminate, iron compounds such as ferric chloride and ferric sulfate, lime and various cationic organic polymers, including but not limited to poly(alkaline amines), poly(diallyl dimethyl ammonium chloride), poly(2-hydroxy propyl-l-N-methyl ammonium chlorides) and quaternized poly (N-N-dimethylaminomethacrylate). The novel compositions of the instant invention are not, however, known or suggested in the art. SUMMARY OF THE INVENTION The instant invention relates to synergistic flocculation compositions of aluminum chloride and at least one water soluble cationic Polymer selected from the group consisting of water-soluble polyamines and water-soluble dialkyl diallyl ammonium polymers, wherein the weight ratio of aluminum chloride to polymer is at least 5:1, on an active basis. Thus, the instant method utilizes a synergistic composition comprising aluminum chloride and at least one water-soluble cationic polymer to accomplish clarification objectives. The novel compositions of this invention are stable when blended together and synergistically settle fine suspended matter from aqueous systems. The instant compositions are especially effective in low-turbidity, low-alkalinity waters, but they are also effective in other waters. Low-alkalinity waters, as used herein, are waters having total alkalinity values of 150 ppm or less. Additionally, the instant compositions are convenient to use since only one product must be added to the system being treated, instead of two or more. DETAILED DESCRIPTION OF THE INVENTION The instant invention relates to a method for reducing turbidity in aqueous systems which comprises adding to said system an effective amount of a composition comprising: (a) aluminium chloride; and (b) at least one water-soluble cationic polymer selected from the group consisting of water-soluble polyamines and water-soluble C₁-C₈ dialkyl diallyl ammonium polymers, wherein the weight ratio of (a) to (b) is at least 20:1. The water soluble polyamine is represented by the following structure: wherein R₁ and R₂, which may he the same or different, are selected from the group consisting of C₁-C₈ straight or branched alkyl, substituted C₁-C₈ straight or branched alkyl and hydrogen and wherein R is selected from the group consisting of C₁-C₈ straight or branched alkyl and substituted C₁-C₈ straight or branched alkyl, and wherein n ranges from 2 to 50,000. Preferably, the molecular weight should range from about 500 to about 200,000, as determined by gel permeation chromatography. Polymers having molecular weights ranging from about 10,000 - 150,000 are more preferred. The most preferred polyamines are epichlorohydrin-dimethylamine polymers. Any water soluble C₁-C₈ alkyl diallyl ammonium polymer can he used. The preferred polymers are polydimethyl diallyl ammonium chloride (polyDMDAAC), polydiethyldiallyl ammonium chloride (polyDEDAAC), polydimethyl diallyl ammonium bromide (polyDMDAAB)and polydiethyl diallyl ammonium bromide (polyDEDAAB). The most preferred dialkyl diallyl ammonium polymer is a homo polymer of dimethyl diallyl ammonium chloride. The molecular weight of the dialkyl diallyl ammonium polymer preferably ranges from about 1,000 to about 5,000,000, as determined by gel permeation chromatography. The ratio of aluminum chloride to polymer is critical, and should he at least 20:1, by weight, on an active basis. Preferably, the ratio should range from 20:1 to about 100:1, and most preferably from 20:1 to about 30:1. These compositions synergistically reduce turbidity in aqueous systems, particularly low-turbidity, (i.e., systems containing 0.1 or less weight percent of suspended solids) , low-alkalinity systems (i.e., 150 ppm or less). As used herein, the phrase "effective amount" refers to that amount of an aluminum chloride/polymer composition which is necessary to reduce turbidity in the system being treated. Generally, the effective amount will range from 0.1 ppm of the instant compositions, on an active basis, to 100 ppm of the instant compositions. The key to this invention is that the inventors have discovered a synergistic relationship between aluminum chloride and certain cationic polymers. While use of these components, individually, is known in the art, the use of the instant compositions is not known. The synergistic benefit of the combined components, as demonstrated by the examples, is surprising and unexpected. The method of the invention is especially effective in low turbidity, low alkalinity waters. However, the inventors do not intend that the inventive method he restricted to use in such systems, as the instant compositions are effective flocculants in a wide range of aqueous systems. Other important aspects of the instant invention are that the components of the compositions are compatible and that the compositions are stable. Preferably, the compositions are applied in the method of the invention as aqueous solutions. Thus, an aluminium chloride/cationic polymer composition is added to water, forming an aqueous solution. The maximum weight percent of the composition in water depends upon its solubility limit; generally, however, it is preferred that the aqueous solution contain from about 0.1 to about 20%, by weight, of the instant aluminium chloride/cationic polymer composition, wherein the weight ratio of aluminium chloride to cationic polymer is at least 20:1, on an active basis. EXAMPLES The following examples demonstrate the invention in greater detail. These examples are not intended to limit the scope of the invention in any way. In the examples, the following products were used: AlCl₃ is an aluminum chloride solution available from Hardwicke Chemical Company (which is 26-28% active (weight basis), with 2-5 weight % aluminum bromide), Reheis Chemical Company (28 weight % active), Courtney Industries (28 weight % active) or Vista Chemical Company (25 weight % active). Alum is a 50% active aqueous solution of aluminum sulfate, Al₂ (SO₄)₃ . 14 H₂0. High MW PolyDMDAAC is 20 weight % active polydimethyl diallyl ammonium chloride (MW = 1,000,000-2,000,000), available from Calgon Corporation as Cat-Floc L. Medium MW Poly DMDAAC is 20 weight % active polydimethyl diallyl ammonium chloride (MW = 150,000 ± 50,000), available from Calgon Corporation as Cat-Floc TL. Low MW Poly DMDAAC is 30 weight % active polydimethyl diallyl ammonium chloride (MW = 3,000 - 4,000), available from Calgon Corporation as Varikem 110. Dry Poly DMDAAC is 100% active polydimethyl diallyl ammonium chloride (MW = approximately 200,000), available from Calgon Corporation as E-921. High MW Polyamine is a 50 weight % active epichlorohydrin - dimethylamine polymer (MW = 100,000), available from American Cyanamid as CA-260. Low MW Polyamine is a 50 weight % active epichlorohydrin dimethylamine polymer (MW = 20,000), available from American Cyanamid as CA-250. Alum/Medium MW Poly DMDAAC (5:1) is Cat Floc K-5, available from Calgon Corporation, which is 5 parts, by weight, a 50% alum solution (by weight) and 1 part Catfloc C, a 40%, by weight, active polyDMDAAC having a molecular weight of approximately 150,000. Alum/Medium MW Poly DMDAAC (10:1) is Cat Floc K-10, available from Calgon Corporation, which is 10 parts, by weight, a 50% alum solution (by weight) and 1 part Catfloc C, a 40%, by weight, active polyDMDAAC having a molecular weight of approximately 150,000. Examples 1-16 In Examples 1-16, jar tests were run on Watauga River water having an initial turbidity of 4.0 - 4.5 NTU's. The water had a total alkalinity of 60-70 ppm. The jar tests were run under the following conditions: 1 min @ 100 rpm 20 min @ 45 rpm 10 min @ 0 rpm After a 10 minute settling period, 30 ml samples of supernatant were drawn, and turbidity was measured using a Bausch & Lomb Mini-20 Spectrophotometer/Nephelometer. For filtration index measurements, 100 ml samples of supernatant were drawn, and the time was measured for each 100 ml sample to pass through a sheet of 0.3 micron filter paper. The filtration index values were then calculated by dividing the time obtained by the time required for 100 mls of deionized water to pass through a sheet of 0.3 micron filter paper. Results are shown in Table I. Example Number Flocculant As Product Dosage (ppm) Supernatant Clarity (NTU'S) (10 min.) Filtration Index 1 Alum 10 4.4 - 2 Alum 15 4.0 2.37 3 Alum 20 3.7 2.30 4 Alum 30 2.4 2.22 5 Alum 40 2.4 - 6 Alum 50 2.9 - 7 Alum/DMDAAC (10:1) 10 4.3 - 8 Alum/DMDAAC (10:1) 15 3.6 - 9 Alum/DMDAAC (10:1) 20 2.9 1.93 10 Alum/DMDAAC (10:1) 25 2.3 - 11 AlCl₃ 10 4.1 - 12 AlCl₃ 15 3.9 1.96 13 AlCl₃ 20 2.6 - 14 AlCl₃ 25 2.2 1.63 15 AlCl₃/Low MW Polyamine (20:1) 15 2.3 1.48 16 AlCl₃/High MW DMDAAC (20:1) 15 3.2 1.81 Examples 17-63 In Examples 17-63, jar tests were run on feed water having a turbidity of approximately 12 NTU's. Total alkalinity was approximately 150 ppm. The jar tests were run under the following conditions: 1 min @ 100 rpm 3 min @ 50 rpm 6 min @ 20 rpm 5 min @ 0 rpm After a 5 minute settling period, 10 ml samples of supernatant were drawn, and turbidity was measured using a Bausch & Lomb Mini-20 Spectrophotometer/Nephelometer. Results are shown in Table II.

Claims: A method for reducing the turbidity of an aqueous system comprising adding to said system an effective amount of a composition comprising: (a) aluminium chloride; and (b) at least one water-soluble polymer selected from the group consisting of; (i) water-soluble polyamines represented by structure I wherein R₁ and R₂, which may be the same of different, are selected from the group consisting of straight or branched C₁-C₈ alkyl, substituted straight or branched C₁-C₈ alkyl and hydrogen; wherein R is selected from the group consisting of straight or branched C₁-C₈ alkyl and substituted or branched C₁-C₈ alkyl; and wherein n ranges from 2-50,000; and (ii) water-soluble C₁-C₈ dialkyl diallyl ammonium polymers; wherein the weight ratio of (a):(b) is at least 20:1. The method of claim 1 wherein (b) is an epichlorohydrin dimethylamine polymer. The method of Claim 1, wherein (b) is selected from the group consisting of polydimethyl diallyl ammonium chloride, polydiethyl diallyl ammonium chloride, polydimethyl diallyl ammonium bromide and polydiethyl diallyl ammonium bromide. The method of Claim 1, wherein (b) is polydimethyl diallyl ammonium chloride. The method of any of Claims 1 to 4, wherein said aqueous system contains 0.1 weight percent, or less, suspended solids. The method of any one Claims 1 to 5, wherein said effective amount is from 0.1 to 100 ppm of said composition.

Inventors: HASSICK DENIS E, MIKNEVICH JOSEPH, HASSICK, DENIS E., MIKNEVICH, JOSEPH
Applicants: CALGON CORP, CALGON CORPORATION
Application year: 1988
Main classification: C02F1
IPC codes: B01D21, C02F1