Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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
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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.
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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.
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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.
EXAMPLE 1
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
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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.
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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
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