Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
2000-08-31
2002-07-02
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C210S728000, C210S734000, C210S790000
Reexamination Certificate
active
06413433
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for dewatering of sludge.
BACKGROUND OF THE INVENTION
A sludge is defined as a mixture of solids and liquids. Usually the liquid in a sludge is water and therefore, usually the desirable portion of the sludge is the liquid. Separation of the solids from the water in a sludge is a common chemical engineering unit operation that comes under the general heading of “water treatment” or “classic solids/liquid separation processes”. More specifically, this separation of the solids from the water in a sludge is usually described as “dewatering” of the sludge.
To conduct solids/liquid separation during water treatment, suspended solids in the sludge are removed from water by a variety of processes, including sedimentation, straining, flotation, filtration, coagulation, flocculation, and emulsion breaking, among others. The amount of solids in sludges being dewatered ranges from as little as several parts per billion of solids to large amounts, up to and including, actual chunks of suspended solids or oils. Sludges being dewatered may contain from about 99.75 weight percent water to about 40 or 50 weight percent water. Obviously, the more water in the sludge, the more processing it takes in order to “dewater” the sludge. After a sludge has been dewatered, the liquid portion is usually processed further according to its intended end use, while the solids portion is typically properly disposed of in compliance with all applicable local, state and federal laws.
While strictly mechanical or physical means have been used to effect solids/liquid separation, modem chemical engineering methods typically rely on mechanical or physical separation techniques that are enhanced by the use of synthetic and natural cationic polymeric materials to accelerate the rate at which sludges can be dewatered. These solid-liquid separation processes include the treatment of sludges with cationic coagulant polymers that function to settle suspended inorganic particulates. Once settled out, the suspended inorganic particulates are readily removed from the liquid using mechanical or physical separation means. This separation of suspended inorganic particulate material makes the water usable for industrial or municipal purposes.
Dewatering of sludge is possible because particles in nature usually have either a cationic or anionic charge. Accordingly, these particles can be agglomerated, such that they can be readily physically separated from a liquid, by the addition to the sludge of a water-soluble coagulant or flocculant polymer having a charge opposite to that of the particles. This is referred to as a “polyelectrolyte enhanced solids/liquid separation process”, wherein a water-soluble or water-dispersible ionically charged polymer is added to a sludge to neutralize the charged particles or emulsion droplets to be separated.
In a typical “polyelectrolyte enhance solids/liquid separation process”, the dosage of these water-soluble or water-dispersible ionically charged polymers is critical to the performance of the process. Too little ionically charged polymer, and the suspended particles will not be charge neutralized and will thus still repel each other. Too much polymer, and the polymer will be wasted, or worse, present a problem in and of itself.
Lime or salts of iron or aluminum have been used to coagulate or flocculate solids; which facilitates the process of separation of these solids from sludge. There are known water-soluble or water-dispersible ionically charged polymers also used for this purpose. There are also known polymers that are of particular value as flocculants for suspensions of organic matter of a proteinaceous or cellulosic nature such as are to be found in sewage treatment effluents. In addition, there are synthetic polyelectrolytes, particularly certain cationic copolymers of acrylamide, that have been found to be of use in the field of sludge dewatering.
U.S. Pat. No. 3,409,546 describes the use of cationic polymers for dewatering of sludge. In this patent, the use of N-(amino methyl)-polyacrylamide polymers, is described in conjunction with other cationic polymers for the treatment of sewage sludges.
U.S. Pat. No. 3,414,514 describes the use of a copolymer of acrylamide and a quaternized cationic methacrylate ester for sludge dewatering.
Another class of cationic polymers used to dewater sludges is described in U.S. Pat. No. 3,897,333. The use of polyethyleneimines and homopolymers of cationic acrylates and methacrylates and other cationic polymers such as polyvinyl pyridines is also known.
Another example of a cationic polymer useful for sludge treatment is described in U.S. Pat. No. 4,191,645. In this patent, cationic copolymers prepared from a nonionic monomer, such as acrylamide, and a cationic monomer, such as trimethylammonium ethylmethacrylate methyl sulfate quaternary (TMAEM.MSQ) or dimethylaminoethylacrylate methyl sulfate quaternary (DMAEA.MSQ) are disclosed as being useful for sludge dewatering.
Further examples of polymeric treatments for sludge dewatering include the 1,4-dichloro-2-butene dimethylamine ionene chloride polymer disclosed in U.S. Pat. No. 3,928,448 and the block copolymers disclosed in U.S. Pat. No. 5,234,604.
Notwithstanding the variety of commercially available polymers that have been found to be capable of flocculating or coagulating sludges, there are various circumstances which tend to limit the usefulness of these reagents. While for certain sludges, economical treatments with these known reagents are feasible, more often sludges require very high and not cost effective dosages of reagents for successful treatment. Moreover, variations often occur in the composition of sludge from any one source. For example, variations in the supply of material to the sludge making process and/or in the oxidizing conditions that may be involved in the production of the sludge lead to a variety of particle types that must be removed. Furthermore, it is not uncommon to encounter sludges that are, for some reason, not amenable to flocculation by any of the known polymeric flocculating agents.
It is therefore desirable to provide additional chemical treatment materials and methods for the dewatering of sludge.
SUMMARY OF THE INVENTION
A process for dewatering of sludge, wherein said sludge comprises solids and water, comprising the steps of.
a) adding a cationic dispersion polymer and a microparticle to said sludge, wherein said cationic dispersion polymer can be added before or after or simultaneous with the addition of said microparticle; and
b) physically separating said solids from said water.
DETAILED DESCRIPTION OF THE INVENTION
Throughout this patent application, the following definitions will be used:
All percentages given for components of polymers are to be understood to mean “mol percent”.
“AcAm” for acrylamide;
“DMAEA.BCQ” for dimethylaminoethyl acrylate.benzyl chloride quaternary salt (also known as ethanaminium, N-benzyl-N,N-dimethyl-2-((1-oxo-2-propenyl)oxy)chloride);
“DMAEA.MCQ” for dimethylaminoethyl acrylate.methyl chloride quaternary salt (also known as ethanaminium, N,N,N-trimethyl-2-((1-oxo-2-propenyl)oxy)chloride); and
“DADMAC” for diallyldimethylammonium chloride;
“Excess sludge” refers to secondary biological sludge which needs to be removed from the system.
“IV” stands for intrinsic viscosity, which is RSV when the limit of concentration is equal to zero.
“Nalco” refers to the Nalco Chemical Company, One Nalco Center, Naperville, Ill. 60563, (630) 305-1000.
“RSV” stands for Reduced Specific Viscosity, which is an indication of polymer chain length and average molecular weight, which are indicative of the extent of polymerization during production. The RSV is measured at a given polymer concentration and temperature and calculated as follows:
RSV
=
[
(
η
/
η
0
)
-
1
]
c
&eegr;=viscosity of polymer solution
&eegr;
o
=viscosity of solvent at the same temperature
c =concentration of polymer in solution.
In this patent application, the units of concentration “c” are
Borelli Massimo
Mattucci Livio
Maury Elise
Sparapany John
Urbani Fernando
Breininger Thomas M.
Brumm Margaret M.
Hruskoci Peter A.
Nalco Chemical Company
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