CA1061022A - Conditioning sewage waste sludges for dewatering - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Waste sludges are conditioned for dewatering by intermixing with the waste sludge prior to dewatering an admixture of a water-soluble, high-molecular weight polymer of methacrylamidopropyltrimethylammonium chloride.

Description

BACKGROUND OF THE INVENTION
This invention relates to the treatment of waste. More particularly, this invention is directed to a process for conditioning sludges from municipal and industrial wastes to obtain an improved de-10 watering step.

Sludge is the major byproduct of industrial and domestic water and waste treating processes. In fact, one of the major problems in a well-run water pollution control prograIn is the sludge conditioning method used in dewatering sludges. The term "sludge dewatering 15 process" as used in the art and as used herein means any process which reduces the water content of the sludge from its usual value of 93 to 99 percent by weight to about 90 percent by weight or less. That is, it concentrates the sludge solids to about 10 percent by weight or gr eater .

Wastewater sludge is basically characterized according to three factors which are: (1) sludge source, (2) sludge processing, and (3) degree of treatment. By "sludge source" is meant whether the sludge is from municipal ~lomestic)wastewater or industrial wastewater or a combination thereof. The sludge processing character-25 istic defines whether the sludge is raw untreated sludge, anaerobic or C-llZ9 aerobic digested sludge, air flotation sludge or digested elutriated sludge. The degree of treatment indicates whether the sludge is primary sludge, activated sludge, waste activated sludge, chemically precipitated sludge, trickling filter humus or a combination of one or 5 more of these such as waste activated sludge combined with primary sludge. It is generally accepted that each individual sludge has a different characterization and this sludge character more or less dictates the dewatering process used.

The various mechanical dewatering processes now commonly 10 used in the art and as used herein are gravity filtration, vacuum filtration, centrifugation, flotation, and sedimentation. However, regardless of the mechanical process used for dewatering, it has be~
come standard practice in the art to chemically condition the sludge prior to dewatering. This chemical conditioning of the sludge enhances 15 the mechanical dewatering process dramatically. The water content of the sludge can be reduced from concentrations in the neighborhood of 93 to 99 percent water to those of about 60 to 90 percent or less by proper chemical conditioning prior to mechanical dewatering.

The most frequently employed chemical for the conditioning of 20 sludge for dewatering is ferric chloride. The ferric chloride may be used alone or in combination with lime and/or other conditioning agents.
Other ferric salts such as ferric sulfate have been widely used alone and in combination with lime. Some ferrous salts, notably ferrous sulfate, have also found use in the chemical conditioning of sludges.

C-l lZ9 More recently, high-molecular weight polyelectrolytes have been extensively used for chemically conditioning sludges. The polyelectrolytes have been used alone and in combination with in-organic chemical conditioning agents such as the ferric and ferrous 5 salts, alum and lime. In most of the combination treatments of the prior art, the sludge is first treated with the inorganic conditioning agent followed by the polyelectrolyte. A few applications use the polyelectrolyte first followed by the inorganic conditioning agent.
For some examples of the prior art methods, see U~ S. Patent No.
10 3, 300,407, which is directed to a chemical conditioning process using an anionic polyelectrolyte followed by an inorganic conditioning agent, U. S. Patent Nos. 3, 142, 638 and 3, 423, 312 which are directed to the chemical conditioning of sewage sludges, U. S. Patent No.
3, 472, 767 which is directed to the conditioning of sewage sludges with 15 a combination of cationic polyelectrolyte and an acid salt containing polyvalent metal ions, U. S. Patent Nos. 3, 066, 095 and 3, 642, 619.

SUMMARY OF THE INVENTION
We have found that the dewatering of waste sludges is greatly enhanced if the sludge is treated prior to dewatering with a water_ 20 soluble, high-molecular weight polymer of methacrylamidopropyl-trimethylammonium chloride. The polymers of our invention are high-molecular weight, water-soluble polymers of methacrylamidopropyl-trimethylammonium chloride (MAPTAC) and may be prepared in any convenient manner, as for example, in the manner taught by U. S.
25 Patent No. 3, 661, 880 or by conventional solution or inverted emulsion polymerization techniques, as for example the procedures disclosed in U. S. Patent No. 3,284, 393.

The polymers `useful in this invention should have high molec-ular weights, preferably of at least 100, 000 and more preferably of at least 1, 000, 000 and should have a solubility in water of at least 0, 25 percent. These polymers may be homopolymers of methacrylamido-propyltrimethylammonium chloride, or, in the preferred embodiment of this invention, they may be copolymers of methacrylamidopropyl-trimethylammonium chloride and acrylamide containing from 10 to 75 percent by weight acrylamide. While the chloride anion is the most preferred quaternary ammonium derivative, other anions such as 10 fluoride, bromide, nitrate, acetate, hydrogen sulfate, and dihydrogen phosphate may be utilized with the cationic polymers of this invention.

Our method of conditioning the sludges comprises adding to the sludge prior ts) dewatering from 300 to 3, 000 ppm. of the polymers of this invention. These polymers may be used alone or in combination 15 with conventional ferric salts such as ferric chloride, f erric sulfate, or alum.

A 50 percent waste activated sludge - 50 percent raw sludge blend was used as test media in a Buchner Funnel Test. 15 inches 20 mercury was used as filtration vacuum and Whatman(~)40 filter paper (11 centimeters in diameter) and a funnel having a diameter of 12. 5 centimeters was used. The Buchner Funnel Test procedure was as follows: (1) 200 ml samples were measured into beakers and mixing containers; (2) the polymer solution was added using pipets; (3) the 25 polymer solution and sludge were mixed at 450 rpm. for 15 seconds C-l 129 1~)6102Z
using the variable-speed mixer; (4) the conditioned sludge sample was poured into a Buchner funnel and vacuum applied, Just prior to filtration, polymer was added to a predetermined volume of sludge ~425 ml) which was stirred at 450 rpm. for 15 seconds. The filtration 5 time required to obtain a 10 percent cake volume is shown in Table 1.

TABLE I
Sample Characteristics Performance Composition (a)Sludge Dewatering ~n]40't) C .
lN NaN03 ~pd. 10% Cake Time poly(MAPTAC) 5, 74 125 mg/l 70 seconds 75/25(MAPTAC/AM) by weight 88 mg/l 69 seconds 90/10(MAPTAC/AM) 138 mg/l 50 seconds 50/50(MAPTAC/AM) 62 mg/l 78 seconds - 25 / 75 (MAPTA C /AM) 82 mg / 1 184 s econds Emul sion 75 /25 (MAPTAC/AM) 125 mg/l 66 seconds -(a) Determined by one-point method.
15 opd = Optimum Polymer Dosage MAPTAC = Methacrylamidopropyltrimethylammonium chloride AM = Acrylamide

Claims (4)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A process for dewatering an aqueous waste sludge comprising conditioning the waste sludge with a polymer of methacrylamidopropyltrimethylammonium chloride.

2. A method as in Claim 1, wherein the polymer is a copolymer of methacrylamidopropyltrimethylammonium chloride and acrylamide.

3. A process as in Claim 1, wherein the concen-tration of the polymer is from 300 to 3,000 ppm. by weight based on the total weight of the aqueous sludge suspension.

4. A process as in Claim 1, wherein the polymer is used in conjunction with an inorganic coagulant.