METHOD FOR IMPROVING SOLID-LIQUID SEPARATION IN WASTE WATER PROCESSES OR CONDITIONING POTABLE WATER

Abstract

The invention relates to the use of a composition comprising a non-ionic surfactant and an ionic polymer and method of preparation of the composition. The compositions are useful inter alia as flocculation auxiliaries for solid-liquid separation processes, for example in sludge dewatering/waste water purification and as retention aids or other additives in paper manufacture.

Claims

1. A method for improving solid-liquid separation in waste water processes or conditioning potable water comprising: i. introducing a solid flocculation auxiliary composition comprising a non-ionic surfactant R.sup.1O-A-OR.sup.2, wherein the residue O-A-O is derived from a polyalkylene glycol HO-A-OH that comprises monomer units derived from an (C.sub.2-C.sub.6)-alkylene glycol or a mixture of at least two different (C.sub.2-C.sub.6)-alkylene glycols; and R.sup.1 is selected from the group consisting of H, (C.sub.8C.sub.20)-alkyl, (C.sub.8C.sub.20)-alkenyl, (CO)(C.sub.8-C.sub.20)-alkyl and C(O)(C.sub.8-C.sub.20)-alkenyl, and R.sup.2 is selected from the group consisting of H, (C.sub.1-C.sub.6)-alkyl, -benzyl, (CO)(C.sub.8-C.sub.20)-alkyl and C(O)(C.sub.8-C.sub.20)-alkenyl; and (ii) a water-soluble or water swellable ionic polymer, wherein the water-soluble or water swellable ionic polymer is derived from a monomer composition containing a) one or more non-ionic ethylenically unsaturated monomers, and/or b) one or more cationic ethylenically unsaturated monomers, and/or c) one or more anionic ethylenically unsaturated monomers; and wherein the water-soluble ionic polymer is derived from a monomer composition (i) not comprising any cross-linking monomers, or (ii) containing not more than 50 ppm cross-linking monomers, relative to the total content of monomers in the monomer composition; wherein the non-ionic surfactant R.sup.1O-A-OR.sup.2 is present in an amount of from 0.05 wt.-% to 2.0 wt.-%, based on the total weight of the composition; wherein the relative weight ratio of the non-ionic surfactant R.sup.1O-A-OR.sup.2 to the ionic polymer is within the range of from 0.05:100 to 2:100; and wherein the moisture content of the composition does not exceed 12 wt.-%, into the waste water or the potable water.

2. The method according to claim 1, wherein the residue O-A-O is derived from a polyalkylene glycol HO-A-OH that comprises monomer units derived from ethylene glycol or a mixture of ethylene glycol and propylene glycol.

3. The method according to claim 1, wherein the residue O-A-O is derived from a polyalkylene glycol HO-A-OH that comprises 2-130 monomer units derived from ethylene glycol and 0-60 monomer units derived from propylene glycol.

4. The method according to claim 3, wherein the monomer units derived from the ethylene glycol and the monomer units derived from the propylene glycol are present in any order or form two or more separate blocks.

5. The method according to claim 1, wherein the non-ionic surfactant R.sup.1O-A-OR.sup.2 is represented by general formula (A) ##STR00007## wherein R.sup.1 is selected from the group consisting of H, (C.sub.8C.sub.20)-alkyl, (C.sub.8-C.sub.20)-alkenyl, (CO)(C.sub.8-C.sub.20)-alkyl and C(O)(C.sub.8-C.sub.20)-alkenyl, R.sup.2 is selected from the group consisting of H, (C.sub.1-C.sub.6)-alkyl, -benzyl, C(O)(C.sub.8-C.sub.20)-alkyl and C(O)(C.sub.8-C.sub.20)-alkenyl, o and p are integers of from 0 to 130, and a sum of o and p is within a range of from 2 to 130; q and r are integers of from 0 to 60, and a sum of q and r is within a range of from 0 to 60; and optionally with the proviso that if R.sup.1 and R.sup.2 are both H, the sum of q and r is not 0.

6. The method according to claim 1, wherein the non-ionic surfactant R.sup.1O-A-OR.sup.2 has a HLB not exceeding 14. The method according to claim 1, wherein the non-ionic ethylenically unsaturated monomer is selected from the group consisting of a non-ionic monomer of general formula (I) ##STR00008## wherein R.sup.3 represents hydrogen or C.sub.1-C.sub.3-alkyl, and R.sup.4 and R.sup.5 each independently represent hydrogen, C.sub.1-C.sub.5-alkyl or C.sub.1-C.sub.5-hydroxyalkyl; and a non-ionic amphiphilic monomer of formula (II) ##STR00009## wherein Z.sub.1 represents O, NH or NR.sup.9 with R.sup.9 being C.sub.1-C.sub.3-alkyl, R.sup.6 represents hydrogen or C.sub.1-C.sub.3-alkyl, R.sup.7 represents C.sub.2-C.sub.6-alkylene, R.sup.8 represents hydrogen, C.sub.8-C.sub.32-alkyl, C.sub.8-C.sub.32-aryl; C.sub.8-C.sub.32-aralkyl, or a combination thereof; and n represents an integer between 1 and 50; and the cationic ethylenically unsaturated monomer is a monomer of formula (III) ##STR00010## wherein R.sup.10 is hydrogen or C.sub.1-C.sub.3-alkyl; Z.sub.2 is O, NH or NR.sup.11 with R.sup.11 being C.sub.1-C.sub.3-alkyl; and Y.sub.0 is C.sub.2-C.sub.6-alkylene, substituted with one or more hydroxy groups, Y.sub.1, Y.sub.2, Y.sub.3, independently of each other, are C.sub.1-C.sub.6-alkyl, and X.sup. is a halogen, pseudo-halogen, acetate or SO.sub.4CH.sub.3.sup.; and the anionic ethylenically unsaturated monomer is selected from the group consisting of (c1) ethylenically unsaturated carboxylic acids, carboxylic anhydrides, and water-soluble alkali metal salts, alkaline earth metal salts, and ammonium salts thereof, (c2) ethylenically unsaturated sulfonic acids and water-soluble alkali metal salts, alkaline earth metal salts, and ammonium salts thereof, (c3) ethylenically unsaturated phosphonic acids and water-soluble alkali metal salts, alkaline earth metal salts, and ammonium salts thereof, and (c4) sulfomethylated and/or phosphonomethylated acrylamides and water-soluble alkali metal salts, alkaline earth metal salts, and ammonium salts thereof.

Description

EXAMPLES

[0257] The following examples further illustrate the invention but are not to be construed as limiting its scope.

Example 1

[0258] Lab tests were performed by dewatering sludge samples (obtained from central wastewater treatment plant In Dusseldorf-Ilverich) by the sieve method described here below.

[0259] Two flocculation auxiliaries were tested:

[0260] Comparative flocculation auxiliary: copolymer of acrylamide with cationic acrylic acid derivative

[0261] Inventive flocculation auxiliary: copolymer of acrylamide with cationic acrylic acid derivative and 0.5% non-ionic surfactant (reaction product of a C.sub.12-C.sub.18 fatty alcohol, ethylene oxide and propylene oxide) applied in the preparation process of the copolymer before the drying process.

[0262] In a 600 ml beaker, a 0.1 wt.-% aqueous solution of the respective flocculating auxiliary (50010 ml) was prepared and sheared by means of a dispersing device Ultra Turrax T 25 N with dispersing tool S 25 N 18 G (Janke & Kunkel) at a rotation speed of 24,000 min.sup.1, flocculating auxiliary solution) flocculating auxiliary dose: 200 g(weight solids)/m.sup.2 four-blade stainless stirrer (RW 20 DZM Janke & Kunkel) at 100020 min.sup.1 for 100.5 seconds and dewatered by a drainage screen (stainless steel, 15050 mm: 200 m mesh). The resulting filtrate (centrate) was subjected to a foaming test.

[0263] Foam test conditions: 300 ml filtrate, 100 L air/hour, foam height in mm

[0264] The resulting foam heights over time periods are depicted in the table here below and in FIG. 1:

TABLE-US-00004 foam height (mm) time Comp. (min.) Example Example 1 1 266 212 2 212 158 3 187 133 4 173 122 5 176 119 6 176 115 7 176 108 8 176 104 9 176 97 10 173 90 15 137 72 20 104 65 25 79 64 30 68 50

[0265] A clearly reduced foaming tendency could be seen in the lab trial.

Examples 2-4

[0266] The inventive flocculation auxiliary of Example 1 was tested at three different wastewater treatment plants (WWTP). Two plants are purely municipal sewage treatment plants, each with a design capacity of 137,000 and 120,000 population equivalents. The third treatment plant has a design capacity of 1,200 000 population equivalent.

[0267] All water treatment plants described here set to a degradation of organic constituents in the sludge digestion tanks. Then the sludge is drained with the addition of powdered flocculating auxiliaries using modem high performance decanters.

Example 2

[0268] Design capacity 1.2 million inhabitants.

[0269] In this new facility the inflowing water consists of 75% from industry and 25% from municipal sources. The biological process is divided here into high-and low-load range. The resulting excess sludge is thickened using a decanter and then fed to the digester.

[0270] The sludge is dewatered by a total of three Sharpless decanters at a rotation speed of 2700 min-1. During the operational testing centrifuge 1 was charged with 40 m3/h sludge. The dosing of the flocculating auxiliary was 265 g/m.sup.3. The resulting centrate was fed into a process water tank and after nitrogen elimination and neutralization re-added to the inflow of sewage. Since development of foam would be disruptive approximately 16 I/day of defoamer (suspension of polyethylene wax in mineral oil} are dosed into the centrate, normally.

[0271] Comparative operational tests were conducted with the comparative flocculation auxiliary and the inventive flocculation auxiliary according to Example 1. By adding an additional defoamer (suspension of polyethylene wax in mineral oil), the foam height was kept constant.

[0272] 1) Pump for defoamer when using the comparative flocculation auxiliary: 50 strokes per minute

[0273] 2) Pump for defoamer when using the inventive flocculation auxiliary: 25 strokes/minute

[0274] In summary, the dosage of additional defoamer could be cut by half.

Example 3

[0275] Design capacity 137,000 inhabitants.

[0276] Mainly municipal wastewater is processed in this treatment plant. The biological return sludge is thickened using a decanter and then fed to the digester. After a digestion period of 20 days 220 g/m.sup.3 flocculating auxiliary are dosed and dehydrated with a modern high performance decanter of the company KHD.

[0277] As no antifoam agent is used in this application the formation of foam in the centrate limits the volume flow of the machine. Foam formation is a massive handicap. With no or less foam development, the flow rate and, therefore, productivity can be increased.

[0278] 1) Maximum throughput when using the comparative flocculation auxiliary: 27 m.sup.3/h

[0279] 2) Maximum throughput when using the Inventive flocculation auxiliary Example 1: 32 m.sup.3/h.

[0280] I.e. 19% performance increase.

[0281] The higher mud flow shortens the run time of the decanter and, thus, saves energy and costs.

Example 4

[0282] Design capacity 120,000 inhabitants

[0283] This sewage plant is processing almost exclusively domestic sewage. The sludge is processed in a biology stage, thickened with a flotation and fed to the digester. After an appropriate residence time, the sludge is dewatered. Then 163 g/m.sup.3 flocculating auxiliaries is added and the dewatering is performed by using a modem high performance decanter with a throughput of 43 m.sup.3/h. Since there is a great tendency to foam a defoamer from Ashland (suspension of a polyethylene wax in mineral oil) is dosed.

[0284] 1) Output power for the pump for defoaming agent when using the comparative flocculation auxiliary: 120%

[0285] 2) Output power for the pump for defoaming agent when using the inventive flocculation auxiliary: 20%

[0286] In Examples 2-4, no negative effect could be observed on the drainage behavior in the decanter such as lower separation rate or dry solids.

Examples 5 to 11

[0287] In a series of experiments (polymerization reactions of acrylamide and various ionic comonomers) the influence of cross-linkers (contained in the starting material and/or specifically added in predetermined amounts) on undesirable gel formation was studied.

[0288] In Examples 5, 8, 10 and 11, a technical grade of cationic monomer was employed that already contained about 30 ppm cross-linking monomer (N-allylacrylamide, NAA). In Example 9, an analytical grade of the same cationic monomer was employed that did not contain any detectable amount of cross-linker.

[0289] In Examples 5, 6 and 7, N,N-methylenebisacrylamide (MBA) was separately added as cross-linker in various predetermined amounts. In Examples 8 and 9, N-alkylacrylamide (NAA) was separately added as cross-linker in various predetermined amounts.

[0290] The composition of the reaction mixtures, the experimental conditions as well as the measured salt viscosities and gel amounts are summarized in the table here below. The gel amounts measured for Examples 5 to 9 are additionally depicted in FIG. 2:

TABLE-US-00005 results cross-linking time catalysis [gel salt monomer ionic monomer degassing [start [amount in viscosity batch [type] [amount.sup.6] [type] [min] temp in ppm] mL] [mPas].sup.7 obs. Example 5 (catalysis: ABAH 500 ppm; TBHP/Nads 10/15 ppm; full light exposure // 1% Al) a 0 DIMAPA Quat nd 5 200 35 300 b MBA 5 DIMAPA Quat nd 5 200 105 340 c MBA 10 DIMAPA Quat nd 5 200 275 770 3 d MBA 200 DIMAPA Quat nd 5 200 120 nd 1 Example 6 (catalysis ABAH 500 ppm; full light exposure // 1% Al) a 0 ADAME Quat nd 5 0 7 1450 b MBA 5 ADAME Quat nd 5 0 175 nd 1 c MBA 10 ADAME Quat nd 5 0 195 nd 1 d MBA 200 ADAME Quat nd 5 0 100 nd 1 Example 7 (catalysis ABAH 500 ppm, TBHP/Nads 113 ppm; full light exposure // 1% Al) a 0 acrylic acid nd 3 0 12 270 b MBA 5 acrylic acid nd 3 0 38 260 c MBA 10 acrylic acid nd 3 0 100 nd 1 d MBA 200 acrylic acid nd 3 0 48 nd 1 Example 8 (catalysis: ABAH 500 ppm; TBHP/Nads 10115 ppm; full light exposure // 1% Al) a 0 DIMAPA Quat nd 0 150 2 210 b NAA 10 DIMAPA Quat nd 0 150 62 300 c NAA 30 DIMAPA Quat nd 0 150 300 1140 d NAA 100 DIMAPA Quat nd 0 150 210 310 Example 9 (catalysis: ABAH 500 ppm; TBHP/Nads 10115 ppm; full light exposure // 1% Al) a NAA 0 DIMAPA Quat nd 3 100 34 410 2 b NAA 15 DIMAPA Quat nd 3 100 105 530 2 c NAA 40 DIMAPA Quat nd 3 100 300 1070 2 Example 10 (catalysis: ABAH 500 ppm; TBHP/Nads 10115 full light exposure // 1% Al) a 0 DIMAPA Quat nd 0 200 4 200 b 0 DIMAPA Quat nd 0 100 30 340 c 0 DIMAPA Quat <45 0 150 20 320 d 0 DIMAPA Quat 45 0 100 42 400 Example 11 (catalysis: ABAH 500 ppm; TBHP/Nads 10115 full light exposure & 1% Al) a 0 DIMAPA Quat nd 3 100 22 350 b MBA 5 DIMAPA Quat nd 3 100 150 530 c NAA 10 DIMAPA Quat nd 3 100 160 620 nd = not determined DIMAPA Quat = N,N,N-trimethylammoniumpropylacrylamide chloride ADAME Quat = N,N,N-trimethylammoniumethyl(meth)acrylate chloride NAA = N-allylacrylamide MBA = N,N-methylenebisacrylamide ABAH = 2,2-azo-bis(2-amidinopropane)dihydrochloride TBHP = tertbutylhydroperoxide Nads = sodium disulfite AI = defoamer 1 completely cross-linked, only swells, measuring viscosity not possible 2 starting material not containing detectable amounts of cross-linker 3 conclusions can hardly be drawn from viscosity, as liquid is very diluted and swollen particles disturb measurement by increasing viscosity 4 starting material contains about 30 ppm cross-linker (and varying amounts of regulator) 5 starting material not containing detectable amounts of cross-linker .sup.6relative to total amount of active substance .sup.7at velocity 10

[0291] Additional differences between the polymers contained in the composition according to the invention and the polymer of Example 5 have been demonstrated by measuring the particle shape and spherical particle content. By using a PartAn 2001 L, a photo-optical image analyzing system, the non-spherical parameter (NSP), a shape factor of these polymer particles was measured. These measurements showed for the particles of the polymer of Example 5 a deviation of the NSP from an ideal spherical shape of approx. 14% and for the polymers of Example 7 and 9 a deviation of approximately 76%.

[0292] When comparing the above experimental data with the teaching of U.S. Pat. No. 5,684,107, the following can be concluded:

[0293] When employing the polymer compositions according to the invention in the intended application, products having an excellent water-solubility are needed, as insoluble parts do not provide any functional properties or even cause problems in these applications. In nearly all intended applications some kind of flocculation or coagulation mechanism is the key to product performance. Only water-soluble polyelectrolytes possess the ability to interact with material in the intended way. Further, insoluble parts (gel particles) may lead to clogging of protective filters or, e.g. in paper production, may lead to holes or even breaks of the paper sheets which is a very cost intensive problem for paper manufacturers. Therefore, for the purposes of the polymer dispersions according to the invention, it is always desirable to produce polymer products (e.g. powders) that easily dissolve and form smooth solutions without or only with a very low formation of insoluble parts.

[0294] To prove the good solubility of the products according to the invention, solubility tests and gelling tests have been conducted. Based upon long application experience, in standard applications the gel/insoluble limit should certainly not exceed 30 ml/L (cf. values in the 3rd column in above table). For other applications like e.g. paper production, even more demanding limits are set, e.g. below 10 ml/L, below 5 ml/L or even below 1 ml/L. As evidenced by the above experimental data, gel contents below these limits can only be achieved at very low contents or in absence of cross-linkers.

[0295] At contents of cross-linker amounting to 50 ppm or more according to U.S. Pat. No. 5,684,107, the resultant products are wide out of specification. The exemplified compositions of U.S. Pat. No. 5,684,107 contain such inacceptable high quantities of cross-linkers. Further, if no cross-linkers would be added to the reaction mixtures according to U.S. Pat. No. 5,684,107, the subsequent azeotropic (in general thermal) dewatering step in presence of polyalkylene glycol would lead to crosslinking/gel formation with acid groups connected to the polymer backbone.