WO2001025156A1

WO2001025156A1 - Cationic polymers for sludge dewatering

Info

Publication number: WO2001025156A1
Application number: PCT/SE2000/001922
Authority: WO
Inventors: Josep Lluis Bisbal Tudela; Franz Cresta; Enrico Celli
Original assignee: Kemira Kemi Ab
Priority date: 1999-10-06
Filing date: 2000-10-05
Publication date: 2001-04-12
Also published as: EP1242316A1; WO2001025156A8; KR20020080327A; CN1384806A; SE9903594L; AU7978700A; SE9903594D0

Abstract

A method and a composition for dewatering sludges are described. The method for dewatering sludges includes treating the sludge with a flocculant aid and with a flocculant, whereafter the sludge is dewatered. The method is characterised in that the flocculant aid is an inorganic compound; the flocculant aid and the flocculant are provided as a solid composition comprising 0.1-10 parts by weight of flocculant aid per part by weight of flocculant; water is added to the composition to provide an aqueous solution or dispersion of the composition; said aqueous composition is added to the sludge; and that the sludge is dewatered. The composition for dewatering sludges is characterised in that it comprises a mixture of a solid inorganic flocculant aid with a solid flocculant at a ratio of 0.1-10 parts by weight of flocculant aid per part by weight of flocculant.

Description

CATIONIC POLYMERS FOR SLUDGE DEWATERING

Field of the Invention

This invention relates to a process for dewatering of sludges from municipal and industrial wastes and to a composition for carrying out the process. Background of the Invention

Catiomcally charged water-soluble or water-disper- sible polymers are utilized in processes that involve the dewatering of aqueous suspensions . Dewatering of sludges may be augmented by mixing into them chemical reagents m order to induce a state of coagulation or flocculation which thereby facilitates the process of separation of water. For this purpose, different synthetic high-molecular weight polymers have been extensively used for chemically conditioning sludges. High-molecular weight poly- acrylamides have been commonly applied. These poly- electrolytes have been used alone or in combination with inorganic coagulants or organic highly ionic low-molecular weight polymeric coagulants . The most frequently employed inorganic and organic coagulants are iron salts, commonly ferric chloride, and polymers of diallyl dimethyl ammonium chloride (DADMAC) and epichlorohydrm dimethyl amine (epi-DMA) . It is generally accepted that each individual sludge has a different characterization and treatment, which indicates the suitable coagulant and flocculant material to be added.

It is well known that, prior to flocculating a suspension, it is often desirable to add first a conditioning or coagulation agent, which can be inorganic polyvalent compounds, such as iron or aluminium salts, or relatively low-molecular weight catiomc polymers. In JP-B-5133867 for instance, a process is described m which sewage sludge is treated with polyvalent metal salt, low-molecular weight catiomc polymer and high- molecular weight catiomc polymer, which is preferably added last. WO 94/02424 discloses a method for purifica- tion of sludge containing mainly water, which comprises a two-step process: first a water-containing coagulation mixture is added, which contains a ferric salt and a low- molecular weight organic polymer and then a high-molecu- lar weight polyelectrolyte . US-5,846,435 discloses a chemical method for the dewatering of biological sludge digested by thermophilic bacteria, which comprises the sequential addition of a quaternized polyacrylamide, having a polyquaternary amine as part of its polymer chain and a cationic polyacrylamide.

According to JP 56058598 (abstract from Derwent and PAJ) it is known to treat muddy water containing suspended clays by adding directly, in the powdered state, a treating agent comprising 1 part by weight of a polymer coagulant and 1-100 parts by weight of water-soluble inorganic Ca, Mg or Fe(II) salt (s) . The treating agent does not contain any flocculant .

On the other hand, EP 479 616 patent discloses a method of dewatering, where both an organic coagulant polymer, preferably diallyl dimethyl ammonium chloride (DADMAC) , and a flocculant polymer are added simultaneously to the sludge as preformed aqueous solutions or as a single preformed solution containing both the cationic coagulant polymer and the cationic flocculant polymer. US 3,642,619 also discloses a simultaneous addition of a ferric salt and a high-molecular weight polymer, prepared as a solid blend consisting of from 0.05 to 5 percent by weight of polymer and the remainder a ferric-containing salt. These references show the better performance of the two-component treatment compared with those sludge dewatering methods which only use a polyvalent metal ion conditioner, a low-molecular weight cationic organic polymer or a high-molecular weight cationic flocculant polymer. In most cases, there is a preference for the sequential rather than the simultaneous addition of coagulant and flocculant, which implies a more complex process than a one-product treatment.

The conventional existing sludge dewatering systems, using either a flocculant or a combination of coagulant and flocculant, try to avoid overdosing and the subsequent formation of large gelatinous floes, which can prevent an optimum release of water. This results in a lower volume of processed sludge and a lower dry solids content of the sludge cake. The gelatinous sticky floes also tend to result in the formation of a cake that does not release well from the filter press cloth (in belt and filter presses) . Moreover, variations often occur in sludge from a source, which lead to a variety of particle types to remove. Furthermore, it is not uncommon to encounter sludges which are not amenable to flocculation by any of the known polymeric flocculating agents.

The present invention aims at minimizing or overcoming the aforementioned problems, increasing the dewatering efficiency of the existing sludge dewatering systems. Summary of the Invention

In the present invention, a sludge from municipal or industrial waste-water is flocculated and then dewatered. Flocculation is effected by a solid mixture of a flocculant aid and a flocculant polymer, prepared as a prefor- med solution of both components.

Generally and in connection with the present invention, the word "flocculant" describes a high-molecular weight material which has the ability to aggregate adjacent suspended particles of an aqueous suspension by attaching to and bridging them. The molecular weight of a flocculant is normally more than 1 x 10⁶ and is usually 5-20xl0⁶ or higher. The flocculant may be non-ionic or ionic, i.e. a polyelectrolyte .

Further, by the word "flocculant aid" used herein is meant either an ordinary coagulant or a mineral. The word "coagulant" describes a highly ionic low-molecular weight material (MW<1^»10⁶) that achieves its effect primarily by absorbing on to the surface of the suspended particles and changing the surface charge thereof, while "mineral" describes an inorganic material which has the ability to react with the impurities in the sludge and which also binds to and forms a network with the flocculant.

The choice of suitable flocculant and flocculant aid materials depends upon the particular process and the particular suspension that is to be dewatered.

It has been found that by mixing both components, i.e. the flocculant and the flocculant aid, in solid state, preparing the corresponding aqueous solution and adding both components simultaneously to the sludge, a surprising improvement in the dewatering efficiency is obtained, namely the use of the novel composition gives an unexpected synergistic result, which improves the dewatering of sludge compared to treatment by prior art methods .

The present invention thus provides a method for dewatering sludges, where the sludge is treated with a flocculant and a flocculant aid, whereafter the sludge is dewatered, characterised in that the flocculant aid is an inorganic compound; the flocculant aid and the flocculant are provided as a solid composition comprising 0.1-10 parts by weight of flocculant aid per part by weight of flocculant; water is added to the composition to provide an aqueous solution or dispersion of the composition; said aqueous composition is added to the sludge; and that the sludge is dewatered.

The present invention further provides a composition for dewatering sludges, characterised in that it comprises a mixture of a solid inorganic flocculant aid with a solid flocculant at a ratio of 0.1-10 parts by weight of flocculant aid per part by weight of flocculant . Further features and advantages of the present invention will appear from the following description and the appended claims.

Detailed Description of the Invention The novel composition comprises a water-soluble or water-dispersible, particulate mixture of an inorganic flocculant aid and a flocculant polymer.

According to an aspect of the invention, flocculation of a sludge from industrial or municipal waste comprises dissolving or dispersing the described particulate mixture in water to form a treatment solution, mixing the treatment solution with the sludge and thereby flocculating and dewatering the sludge.

The solid inorganic flocculant aid of the present invention is a water-soluble or water-dispersible iron- or aluminium-containing salt, a mineral or mixtures thereof. Preferred solid iron salts are ferric salts such as ferric chloride, ferric sulphate, ferric hydroxide, ferric nitrate and ferric nitrate sulphate . Preferred aluminium salts are aluminium sulphate, aluminium hydrate and prepolymerised polyaluminium compounds, e.g. polyaluminium chloride hydroxide, polyaluminium chloride hydroxide sulphate, polyaluminium chloride silicate, polyaluminium hydroxide sulphate, polyaluminium hydroxide sulphate phosphate and the like. Suitable minerals are silicon-containing compounds such as silica (Si0₂), alkali metal metasilicates, aluminium silicates, alkali metal silicates, alkali metal aluminium silicates or mixtures thereof. Preferred silicon-containing compounds are talc, kaolin, natural or synthetic zeolite and bentonite .

Inorganic alkali metal salts or alkaline earth metal salts can be present together with the flocculant aid or the flocculant polymer. Suitably the salt has a cation which is sodium, calcium, magnesium, ammonium, potassium or mixtures thereof. Suitable salts include sodium chloride, sodium sulphate, calcium sulphate, magnesium sulphate, ammonium sulphate and potassium sulphate. The flocculant polymer used in the invention may be nonionic, cationic or mixtures thereof. Preferred nonionic flocculants are water-soluble high-molecular weight polyacrylamides which include homopolymers of (meth) acrylamide and copolymers of (meth) acrylamide and up to about 25 percent of other nonionic comonomers . Some of the nonionic comonomers are diacetone acrylamide, hydroxy ethyl acrylate, hydroxi ethyl methacrylate, ethyleneoxide, n-butyl acrylamide and methacrylamide . Preferred cationic flocculants include homo- or copolymers of (meth) acrylamide with the quaternary or acid salts of diakylaminoalkyl (meth) -acrylamides or - acrylates, especially the quaternised dimethyl or diethyl aminoethyl (meth) acrylates . As an example of other flocculant polymers there may be mentioned polyimines, polyimides, polyethylene oxides and phenolic resins.

The composition is a dry particulate solid. It is possible to form particles containing both types of components, for instance as a result of drying a film of a solution of the mixed components and then flaking the film, but preferably the composition is formed by mixing particles of the flocculant aid with particles of the flocculant polymer. In this case, it is preferred that each component should be of a similar particle size to stay as a substantially uniform mixture which facilitates the uniform dosing of the components in the treatment solution.

If the flocculant aid has characteristics such that it is difficult to form a homogeneous stable mixture, then the flocculant aid may be mixed with a carrier.

Thus, the coagulant may be distributed thoughout beads of a matrix material that will liberate the flocculant aid upon contact with water. A suitable matrix material is a carbohydrate, such as starch, or an inorganic carrier material.

The amount by weight of the flocculant aid per part by weight of the flocculant polymer is at least 0.1 parts and can be as high as 10 parts, but preferably the amount is in the range from 0.1 to 1.5 parts by weight, and most preferably 0.2 to 1 part by weight, per part by weight of the flocculant . Sludges which are treatable to effect dewatering thereof by the novel composition are of a diversified character. They comprise industrial sludge, municipal sludge or a combination thereof. They can be primary sludge, activated sludge, waste-activated sludge, chemically precipitated sludge or mixtures thereof. They also comprise raw untreated sludge, anaerobic or aerobic digested sludge, air-flotation sludge or digested elutriated sludge. It is known that particular sludges vary in their dewatering characteristics and in their solids contents. Illustrative of such sludges are those which contain from about 1 to about 5 weight percent of solids .

The novel composition should be dissolved or dispersed in water. The addition to the sludge is usually effected by adding an aqueous solution or dispersion of the composition, preferably having a concentration of 0.01 to 1.5 percent by weight and, most preferably, from 0.1 to 0.2 percent by weight . The total amount of the composition added may vary considerably according to the sludge being treated and according to the degree of dewatering required. Typical addition rates for a sewage sludge would be in the range 0.1 to 0.5 percent by weight of the composition, based on the total weight of sludge solids. Addition may be effected by conventional methods and some agitation of the mixture of the sludge and the composition is necessary to bring about flocculation. Thereafter separation of the separated solids from liquid may be effected by conventional methods, such as filtration, centrifugation or sedimentation. Compared to dual or two-component systems the invention presents an advantage in the ease of using a single dry composition. The novel composition when added to the sludge as a preformed solution gives results that are superior to those obtained when either of its components is used alone, and surprisingly even when its components are sequentially added to the sludge in whatever order, as preformed solutions, or when its components as preformed solutions are first mixed and then added to the sludge, or when the composition is added directly in solid form to the sludge. Compared to the processes only using either a low- molecular weight coagulant or a high-molecular weight flocculant polymer, or combinations of both, with a sequential or simultaneous addition of separate solutions thereof to the sludge, the method of the invention provides a much more cost-effective treatment. Moreover, there is a lower tendency to the formation of gelatinous floes, and better drainage and a higher dry solids cake are obtained. Finally, the corresponding aqueous solutions prepared from the novel composition have pH values of from about 3 to about 5 for polymer concentrations of 0.05 to 1 percent by weight, which prevent the potential basic or acidic hydrolysis of the flocculant polymer of the composition.

The invention is further illustrated by the follow- ing non-limiting examples. Parts and percentages relate to parts by weight and percent by weight respectively, unless otherwise stated.

Free drainage (by gravity) tests were used to evaluate the conditioning performance of the polymer on different municipal and industrial sludges. The free drainage test is used to measure the amount of water released from a polymer-treated sludge sample. The test is run using the following general procedure : 1. Measure 200-500 ml of well-mixed untreated sludge. Suspended solids (SS) and volatile suspended solids (VSS) are described for every tested sludge. 2. Prepare an aqueous solution or dispersion of the composition having a concentration of 0.2 percent by weight .

3. Add the polymer solution to the sludge and mix it thoroughly (5 s at 500 rpm followed by 15 s at 50 rpm) .

4. Pour the conditioned sludge into a funnel where a filter has been previously placed.

5. Record the drainage (filtrate weight) in grams during 1 min and measure the turbidity of the filtrate. In the examples below, turbidity is measured in Hach equipment and expressed in NTU (nephelometric turbidity units) .

The weight of water which drains from the floe mixture as well as the filtrate clarity are used to distinguish performance differences between polymers. In general, a high water drainage at lower polymer dosages indicates a very efficient and effective polymer. Example 1 A cationic polyacrylamide (charge: 70 mole%; molecular weight 9-10^»10⁶) was mechanically blended with different amounts of solid ferric sulphate (20.7% Fe) (parts of flocculant aid per part of flocculant are 0, 0.11, 0.25, 0.43 and 0.66). The particle size of each component was approximately the same and was in the range of 100 to 600 μm. Free drainage tests were performed on 500 ml samples of a municipal anaerobic digested sludge (SS = 2.97 weight%; VSS = 47 weight% of SS) . Table I shows the weight of drained water and turbidity of the filtrate for each test. Table I

Dose

Flocculant aid/Flocculant polymer (w/w)

0 0.11 0 25 0 43 0 66

Ppm DrainNTU Drain- NTU DrainNTU DrainNTU DrainNTU age age age age age

⁽g⁾ (9) (g⁾ ⁽g⁾ (g⁾

180 316 14.9 358 11.0 353 15.2 422 22.0 322 11.7

160 213 25.5 351 9.37 321 12.9 408 20.8 305 11.1

140 115 46.6 325 8.01 317 12.2 399 19.0 277 12.1

120 3 383 260 8.5 284 12.3 229 11.6 211 59.6

100 - - 69 80.6 131 33 132 35.3 118 103

From Table I it is evident that the drainage is markedly increased by using the composition of the present invention compared to using a flocculant only. The best results are obtained with the composition containing 0.43 parts by weight of flocculant aid per one part by weight of flocculant, but also the composition containing 0.11 parts by weight of flocculant aid per one part by weight of flocculant gives remarkably good results such as a more than five times higher drainage (284 g vs. 43 g) for an amount of 120 ppm of the composition compared to using the flocculant only. In addition to improved drainage, the turbidity is also improved compared to the use of the flocculant only. Example 2

70 parts of a cationic polyacrylamide (35 mole% charge; molecular weight 6.5^«10⁶) were blended with 30 parts of ferric sulphate (20.7 % Fe; particle size below 0.5 mm) according to the following methods:

Method (A) : The polyacrylamide and the ferric sulphate were mechanically mixed in solid state. An aqueous solution of the mixture having a concentration of 0.2 percent by weight was then prepared. Method (B) : 0.2% by weight aqueous solutions of polyacrylamide and ferric sulphate were separately prepared. 70 ml of the polyacrylamide solution were then mixed with 30 ml of the ferric sulphate solution.

Method (C) : 0.2% by weight aqueous solutions of polyacrylamide and ferric sulphate were separately prepared. In the free drainage tests, the polyacrylamide solution was added first to the sludge and, after 5 s stirring

(500 rpm) , the ferric sulphate solution was added. The amount by weight of the ferric sulphate per part by weight of polyacrylamide was maintained at 0.43. Method (D) : Aqueous solutions of polyacrylamide and ferric sulphate having 0.2% by weight were separately prepared. In the free drainage tests, the ferric sulphate solution was added first to the sludge and, after 5 s stirring (500 rpm) , the polyacrylamide solution was added. The amount by weight of the ferric sulphate per part by weight of polyacrylamide was maintained at 0.43. Free drainage test were performed on 200 ml samples of a primary and secondary mixture of a municipal sludge

(SS = 2.54 weight%; VSS = 53 weight% of SS) , adding the conditioning agents according to the aforementioned four methods. Table II shows the weight (in grams) of drained water and turbidity of the filtrate for each test. The dosages refer to the total amount of both components

(polyacrylamide and ferric sulphate) : Table I I

The results clearly illustrate the unexpected synergistic effects of the novel composition (method A) compared to addition of the pure polyacrylamide, the successive additions of polyacrylamide and the iron salt (methods C and D) , or the addition of a mixture of the two preformed solutions of polyacrylamide and ferric sulphate (method B; no flocculation is noticed in this case) .

Example 3

70 parts of a non-ionic polyacrylamide (molecular weight 8*10⁶) were mechanically blended with 30 parts of talc (PE 8418 from Luzenac; method E) . The particle size of each component was approximately the same and was in the range of 100 to 600 μm. Free drainage tests were performed on 200 ml samples of a primary sludge from a paper mill (SS = 4,5 weight%; VSS = 50 weight% of SS) . The draining performance of the novel composition was compared with the pure non-ionic polyacrylamide and with the blend produced by mechanically mixing 70 parts of the same non-ionic polyacrylamide and 30 parts of a cationic poly DADMAC (Magnafloc 368 from Allied Colloids Limited; method F) . Table III shows the weight of drained water and turbidity of the filtrate for each test.

Table III

The example illustrates again the improved, cost- efficient draining performance of the novel composition compared to pure polyacrylamide or to blends of a polyacrylamide and an organic coagulant such as a poly DADMAC .

A closer study of the data in Table III reveals that compared to the use of the flocculant only (composition PAM) , the use of a composition including the flocculant together with an organic coagulant (composition F) actually gives an inferior drainage. This could be taken as an indication against the use of a combination of coagulant and flocculant for the dewatering of sludge . In contrast to this, however, the composition according to the present invention, which includes the flocculant together with an inorganic flocculant aid (composition E) , very surprisingly gives a markedly better drainage than both the composition including the flocculant only (composition PAM) and the composition including a combination of organic coagulant and flocculant (composition F) . Example 4

70 parts of a cationic polyacrylamide (35 mole% charge, molecular weight 6.5^#10⁶) were mechanically blended with 30 parts of aluminium hydrate (62% Al₂0₃; method G) . Free drainage tests were performed on 200 ml samples of industrial activated sludge (SS = 4.05 weight%; VSS = 52 weight% of SS) . The draining performance of the novel composition was compared with the pure cationic polyacrylamide. Table IV shows the weight of drained water and turbidity of the filtrate for each test .

Table IV

The example shows a slight drainage improvement of the composition of the invention compared to the pure polyacrylamide (PAM) . In addition, the composition of the present invention is decidedly more cost-effective than the pure polyacrylamide. Example 5

A plant test was performed at a municipal wastewater treatment plant with an anaerobic digested sludge (SS = 3.0 weight%; VSS = 48 weιght% of SS) . Dewatering is accomplished on a centrifuge. Normal plant operation requires 5.8 kg/ton of dry substance of a cationic polyacrylamide (70 mole-% charge, molecular weight 9-10^#10⁶) , obtaining a sludge cake dryness of about 17.4% by weight. 70 parts of the same cationic polyacrylamide and 30 parts of ferric sulphate were mechanically mixed. An aqueous solution having 0.2% by weight was then prepared and added to the sludge. In this case, 4.8 kg/ton of dry substance of the novel composition resulted in a sludge cake dryness of 19.16%, clearly improving the performance of the pure polyacrylamide at a lower cost. Example 6

70 parts of a cationic polyacrylamide (35 mole% charge; molecular weight 6.5-10⁶) were blended with 30 parts of solid ferric sulphate (20.7 % Fe; particle size below 0.5 mm) according to the following methods: A. The polyacrylamide and the ferric sulphate were mechanically mixed in solid state. An aqueous solution of the mixture having a concentration of 0.2 percent by weight was then prepared. B. The polyacrylamide and the ferric sulphate were mechanically mixed in solid state. The solid mixture was then added directly to the sludge.

C. 0.2 % by weight aqueous solutions of polyacrylamide and ferric sulphate, respectively, were separately prepared. In the free drainage tests the polyacrylamide solution was added first to the sludge and, after 5s stirring (500 rpm) , the ferric sulphate solution was added. The amount by weight of the ferric sulphate per part by weight of polyacrylamide was maintained at 0.43.

D. 0.2 % by weight aqueous solutions of polyacrylamide and ferric sulphate, respectively, were separately prepared. In the free drainage tests the ferric sulphate solution was added first to the sludge and, after 5s stirring (500 rpm) , the polyacrylamide solution was added. The amount by weight of the ferric sulphate per part by weight of polyacrylamide was maintained at 0.43.

Free drainage tests were performed on 200 mL-samples of a primary and secondary mixture of a municipal sludge (SS = 2.59 weight%; VSS = 55 weight% of SS) , adding the conditioning agents according to the aformentioned four methods. Table V shows the weight (in grams) of drained water and turbidity of the filtrate for each test. The dosages refer to the total amount of both components (polyacrylamide and ferric sulphate) :

Table V

The results clearly illustrate the unexpected synergistic effect of the composition according to the present invention (method A) compared to addition of the pure polyacrylamide; successive additions of the poly- acrylamide and the iron salt (methods C and D) ; or the addition of the mixture in solid state (method B; no flocculation was noticed in this case) .

Claims

1. A method of dewatering sludges, where the sludge is treated with a flocculant aid and with a flocculant, whereafter the sludge is dewatered, c h a r a c t e r i s e d in that the flocculant aid is an inorganic compound; the flocculant aid and the flocculant are provided as a solid composition comprising 0.1-10 parts by weight of flocculant aid per part by weight of flocculant; water is added to the composition to provide an aqueous solution or dispersion of the composition; said aqueous composition is added to the sludge; and that the sludge is dewatered.

2. A method as claimed in claim 1, wherein the flocculant aid and the flocculant are provided as a composition comprising 0.1-1.5 parts by weight of flocculant aid per part by weight of flocculant .

3. A method as claimed in claim 1 or 2 , wherein the composition comprises solid particles of the flocculant aid and the flocculant with a particle size of 100-600 μm.

4. A method as claimed in any one of the preceding claims, wherein water is added to the composition to provide an aqueous solution or dispersion having a concentration of 0.01-1.5 % by weight.

5. A method as claimed in any one of the preceding claims, wherein the aqueous composition is added to the sludge at a ratio of 0.1-0.5 % by weight of total weight of flocculant aid solids and flocculant solids, based on the weight of sludge solids.

6. A composition for dewatering sludges, c h a r a c t e r i s e d in that it comprises a mixture of a solid inorganic flocculant aid with a solid flocculant at a ratio of 0.1-10 parts by weight of flocculant aid per part by weight of flocculant .

7. A composition as claimed in claim 6, wherein the inorganic flocculant aid is selected from the group consisting of iron-containing salts, aluminium-containing salts, minerals, or mixtures thereof.

8. A composition as claimed in claim 7, wherein the iron-containing salts are selected from the group consisting of ferric chloride, ferric sulphate, ferric hydroxide, ferric nitrate and ferric nitrate sulphate; the aluminium-containing salts are selected from the group consisting of aluminium sulphate, aluminium hydrate, polyaluminium chloride hydroxide, polyaluminium chloride hydroxide sulphate, polyaluminium hydroxide sulphate, polyaliminium hydroxide sulphate phosphate, and polyaluminium chloride silicate; and the minerals are selected from the group consisting of silica, alkali metal metasilicates, aluminium silicates, alkali metal silicates, or mixtures thereof.

9. A composition as claimed in claim 8, wherein the minerals are selected from the group consisting of talc, kaolin, zeolites and bentonite.

10. A composition as claimed in any one of claims 6-9, wherein the flocculant is selected from the group consisting of nonionic and cationic homopolymers and copolymers of (meth) acryl amide.