CA1055802A - Cationic flocculants for raw water clarification - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Improved clarification of raw waters containing suspended colloidal solid particles results when poly-quaternary flocculants having solution viscosities in the range of about 40-150 centistokes at 25°C. as 37 weight percent aqueous solutions, based on the cationic portion of the polyquaternary compound, are employed.

Description

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This invention relates to an improved process for reducing turbidity in natural raw waters. More particularly, ~ .
it relates to such a process wherein raw water having at .
least a portion of its turbidity associat:ed with suspended 5 particles of extremely, small size is recluced in turbidity .
by treatm~nt with certain polyquaternary flocculants. `.. : `;
Flocculation is a.prDcedure by which the solids present in aqueous dispersions are removed. Aqueous dis-persions are systems wherein solid particles are dispersed in water, which forms the continuous phase. Aqueous dis-persions can cover a wide range of systems having dispersed particles of varying size and composition.
Raw water is a natural source of water such as a river, lake, reservoir and the like used for various pur- ;~
lS poses. Most of these wakers may require treatment prior to their intended use, generally because of turbidity due :
to suspended solidæ therein. ;
An ideal flocculant is generally considered to ~;
be one which readily mixes with the suspension to be floccu~
lated, causes rapid agglomeration of suspended solid particles to form flocs, and then effects quick settling of the flocs formed. With such properties, the ideal flocculant can en- : :
able large volumes of aqueous suspensions to be rapidly treat~ .;
ed in a highly efficient manner. Until recently, the floccu~
25 lants developed for use commercially were far from what ~ :
could be called the ideal flocculants. .
A recent development in the field of flocculants is that of high molecular weight polyquaternary flocculants.
These polyquaternary flocculants have demonstrated increased :~
e~ficiency over prior art flocculants and have shown per-formance that approaches that of ideal flocculants. Xn commercial applications, these high molecular weight poly-quatelnay rlocoulants ha~e been effectively used in Lhe treatment of certain raw waters, indllstrial wastes, and municipal wastes. In specific applicati.ons, such as in dewatering of sewage sludges, the high molecular weight polyquaternary flocculants perform well.
A convenient laborakory method oE evaluat.iny the relative efficiencies of various flocculan-ts is by use of kaolin clay suspensions. These suspensions, properly pxe-paxed, closely resemble many na-tural raw waters. Using kaolin clay suspensions in laboratory tests, it has been demonstrated that polyquaternary flocculants increased in efficiency with increasing molecular weight.
In spite of the numerous advantagesshown by high molecular polyquaternary flocculants, it has been found that when certain raw waters are subjected to clar:ification using high molecular weight polyquaternary flocculants, the extent to which clarification is e~fected is~less than desired. ~:
In attempts to improve performance, numerous modifications '~
in processing and equipment have been introduced. These :::
numerous modification have complicated the clarif.ication pro- ; ;
cess and have not achieved the hi,gh degrees o~ clarification ;~
desired using high molecular weight polyquaternary flocculants~
Accordingly, there exists the need ~or an improved process whereby the high degrees of clarification desired in certain raw waters can be achieved.
In accordance with the present invention, there is provided an improved process for the clarification of raw :~
water containing suspended solids therein, a portion of said suspended solids being colloidal particles of a diameter in the range of 0.09-1~5 millimicrons and contributing at least 0.5 Jackson Turbidity Unit to a total turbidity of said raw water in the range of about 4 to 250 or higher Jackson Turbidity Units, which process comprises: mixing with said raw water an effective amount of a polyquaternary .

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floccula~lt wnich as a 37 weight percent aqueous solution based on the cationic por t.iOII of said polyquaternary has a solution viscosity of 25C. of about 40 to 150 centistokes so as to form initial flocs which remain suspended in the water; allowing said initial Elocs to re:main suspended in sa.id water until an effec-tive or significant amount of said colloidal particles is adsorbed thereto to .form settleable flocs; and thereafter settling the setteable flocs with their adsorbed colloidal particle content.
The process of the present invention when used in clarification of raw waters as defined provides a greater degree of clarification than is obtained when polyquaternary flocculants of higher solution viscosities under the same conditions o~ measurement are employed. This is highly surprising and completely unexpected. The process of the present invention, therefore, provides, in the case of the specififed raw waters, treated waters of greater clarity and redueed contents of suspended solids than previously obtained.
Although the specific manner by which the low molecular weight polymers achieve the improved clarity is not known for certain and applicant does not wish to be bound by any theory, it is thought that the high molecular weight polyquaternary floceeulants, by their rapid floccula-ting ability do not cause the ine suspended colloidal parti-cles to be effècted as much as with the flocculants of the present invention.
In carrying out the process of the present invention, it is necessary to select as the raw water ~o be treated one that has a turbidity in the range of about 4 to 250 ~ackson Turbidity Units and has turbidity of at least about 0.5 r and more generally 0..5 to 10, Jackson Turbidity Units associated with solid suspended colloidal particles having a diameter in '- ` ~ : ' ;3l~V5~
the range of about 0.09 to lo 5 millimicrons. Not all waters fulfill these requirements and, consequently, the process of the invention does not apply to all raw waters.
There are several manners by which the specified nature of the raw water can be determined. A detailed method involves measurements o~ particle sizes of the suspended solids and determination of the contribution of the various size particles to the turbidity value of the water. A more convenient method is to subject the water to clarification using high molecular weight polyquaternary ~locculants in accordance with conventional processes and then to determine the turbidity valuP of the treated water. If the raw water treated has an unacceptable turbidity value, the residual turbidity may be shown to be due to the fine particles speci-fied and the process of the present invention can be e~fecti~e-ly employed to provide an acceptable turbidity value for the raw water under consideration.
Once the specified raw wa-ter has been selected for treatment, it is irst necessary to mix an effective amount Of the polyquaternary flocculant of specified solution vis-cosity therewith. As indicated, the polyquaternary floccu-lant must have a solution viscosity at 25C. as a 37 waight percent aqueous solution based on the cationic portion of the polyquaternary, in the range of about 40 to 150 centi-stokes. When the solutiOn viscosity is above about 150 ~entistokesmeasured as specifi~ed, the advantages in clarification de-crease substantially.
The cationic flocculant useful in the process of the present invention is one obtained by reaction of an epoxy compound with an amine to the extent that the specified solution viscosity is obtained. Preferably, the polyquater-nary is obta~ned by reaction of epichlorohydrin with a major portion of a secondary amine, such as dimethylamine.

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Optionally, minor amounts of a polyfunctional amine may be used in conjunction ~ith a dialkylamine, generally up to 15 mol percent of the total amount of amine usage. Preferred polyfunctional amines arepolyalkylenepolyamines having the 5 formula H2N-CH2CH2-NH~[~H2CH2~NH ~ wherein N is an integer ;~
of 0 to about 4. Preferred polyalkylene;polyamines include ethylenediamine, diethylenetriamine, tri~ethylenetetramine, and tetraethylenepentamine. These polyquaternaries and the process for preparation thereof are known and it is only necessary that the polyquaternary have the solution v:iscosity specified. Another type of polyquaternary flocculant which may be used in the process of the present invention is one obtained by reaction of a primary amine with a difunctional epoxy compound and then quaternarized after polymerization so long as the solution viscosity requirements are met. For example, methylamine can be reacted with epichlorohydrin to form a polymer, and the resulting polymer can be quaternarized with methyl chloride to provide a polyquaternary of suitable solution viscosity~ The descriptions as to polymer prepara-tions given in United States Patent 3,567,659 and 3,738,945,and, the references cited therein are pertinent.
The particular amount of polyquaternary flocculant necessary in the process of the present invention will vary, depending upon the particular raw water being clarified and 25 the specific po~lyquaternary flocculant employed. Generally, ;
the effectlve use le~el may range from about 0.1 part per million to about 100 parts per million, the parts being of real polymer, i.e. cationic plus anionic portions of the poly-quaternary flocculant, based on the weight of water being treated. More usually the usage level will be in the range of l to 40, preferahly 0.5-25, parts per million, same basis.
The actual use level may vary widely at different times of the year due to climatic conditions, level of water in the ~1;35~
raw water source, and othe~ factors which influence the type and amount of suspended solids present in the raw water. The degree of clarification desired will also in~
fluence -to some extent the usage level oi- polyquaternary flocculant. In any eventt the amount of polyquaternary flocculant that is effective in providing the degree of clarification desired is readily determined by trial.
In the practice of the present invention, the poly-quaternary flocculant in desired amount is added to the raw water, preferably under conditions which produce turbulence.
In general, the flocculant is distributed throughout the raw water and maintained in contact with the suspended solids for as long as may be necessary to initiate flocculation.
The treated raw water may be passed into a flocculation zone of a clariiier wherein additional residence time is provided for contact between the flocculant and the suspended flocs and the suspended particles. Longer residence times contri- -bute to clarification; however, it may not always be possible to employ long residence times due to limitations of equip-ment of the plant.in which the process is practiced. It is also possible to practice the present invention in a system in which the flocculant is combined with the raw water under turbulent conditions and within a brief period, for ex-ample 1-S minutes, the treated water is filtered without passing through the usual clarification or settling zone.
Thus, the pipe line through which the raw water is obtained from the source may, in effect, serve as at least a part of the processing equipment. In some instances it may be desir-able to incorporate a precipitant in carrying out the set-tling operation.
The clarified water obtained in accordance with the present process will have a greater clarity than when processed conventionally. The residual turbidity value will .

be at least about 0.5 J.T~U. below that conventionally ob-tained and, more generally, will be at least about 2 to 5 J.T.U. below that conventionally obtained.
In the sole fiqure of drawing, two curves are shown. The curved line shows turbidity remaining after clari-fication in kaolin clay suspensions as a function of solution viscosity of polyquaternary flocculants. The straight line shows turbidity remaining in certain raw waters after clari-fication as a function of solution viscosity of polyquater-nary flocculants~
The invention is more fully illustrated by theexamples which follow, wherein all parts and percentages are by weight unless otherwise specifically designated.
COMPARATIVE EXAMPLE A
A kaolin clay suspension in water is prepared to provide an initial turbidity equivalent to 25 Jackson Turbidity Units(J.T~U.~
A series of polyquaternary flocculants of different solution viscosities at 25C. as 37% aqueous solutions, based on the weight of the cationic portion of the polyquaternary, are evaluated in clarification of the above-prepared kaolin clay suspension. To aliquots of the suspension in individual runs are added 2 parts per million based on the weight of water treated, of real polyquaternary compound, i.e. l00~
basis based on total of cationic and anionic portions. 1he sus-pension is then stirred at 100 r.p.m. for l minute using an `~
electric stirrer, and then stirred at 40 r.p.m. for 15 minutes, followed by settling for 15 minutes. The super-natant liquor is drawn off and analyzed for residual turbi-dity which is calculated as percent of original turbidity pxesent and plotted against the solution viscosity at ~5C.

of the flocculant employed, as a 37% aqueous solution based on the cationic portion of the polyquaternary flocculant.

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The r~sults are shown as the curved line in the accompanying drawing. It can be seen that in flocculating kaolin clay ~-suspension, the percent of turbidity remaining decreases with increasing solution viscosity of the polyquaternary flocculants, as taught in U.S. Patent 3,'738,945, issued June 12, 1973 to Panzer et al.

In this series of examples, the natural raw water clarified is obtained ~rom the Lower Nueces Valley Authority Canal in Texas and has an initial turbidity of 42 J.T.U.
The water has a content of fine suspended colloidal solid -particles which contributes from about 2 to 5 J.T.U. to the turbidity as determined by preliminary tes-ts.
In this series of examples the flocculant is added to aliquots of the raw water and the procedure of Example 1 is followed. The supernatant liquor is then ~rawn , off and analyzed for residual turbidity. Residual turbidity is calculated as percentage of original turbidity,present and plotted against the solution viscosity at 25C. of the flocculant employed as a 37% aqueous solution, based on the cationic portion of the polyquaternary compound.
The polyquaternary flocculants are prepared by reaction of epichlorohydrin and dimethylamine to various solu-tlon viscosities following the proceduxe of U.S. Patent 3,738,945. The various solution viscosities evaluated and results obtained at 2 ppm of flocculants as in Example A are shown in Table I. The percent turbidity remaining plotted against the solution viscosity forms thestraight line given in the accompanying drawing.

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T A B L E

Solution Viscosity* Turbidity Example(centistokes~ - Remaining (%) 1 50 :Ll

2 75 :L7

3 100 21

4 125 '29 1~0 32 :
Comparative B 385 91 *As 37~ aqueous solution based on cationic portion of polyquaternary compound at 25C.
It can be seen from the data in Table I
and from the drawing that in the treatment of the raw water employed, flocculant performance is more effective at decreasing solution viscosity, quite the opposite of the behavior exhibited with kaolin clay sus-pensions. Comparative Example B shows typical performance of high molecular weight polyquaternary compounds used in accordance with the prior art processes.

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Claims (7)

The embodiments of the invention in which an exclusive pro-perty or privilege is claimed are defined as follows:

1. An improved process for the clarification of raw water containing suspended solids therein, a portion of said suspended solids being colloidal particles of a diameter in the range of about 0.09 to 15 millimicrons and contribu-ting 0.5 to 10 Jackson Turbidity Unit to a total turbidity of said raw water in the range of 4 to 250 J.T.U., which process comprises: mixing with said raw water an effective amount of a polyquaternary flocculant which as a 37 weight percent aque-ous solution based on the cationic portion of said polyquater-nary has a solution viscosity at 25°C. of about 40 to 150 centi-stokes so as to form initial flocs which remain suspended in said water; allowing said initial flocs to remain suspended in said water until an effective amount of said colloidal particles are adsorbed thereto to form settleable flocs; and thereafter settling the settleable flocs with their adsorbed colloidal particle content.

2. The process of Claim 1 wherein the polyquater-nary flocculant is obtained by reaction of dimethylamine and epichlorohydrin.

3. The process of Claim 1 wherein the polyquaternary flocculant is obtained by reaction of dimethylamine, a poly-alkylenepolyamine, and epichlorohydrin, said polyalkylenepoly-amine comprising up to 15 mole percent of the total amine usage.

4. The process of Claim 1 wherein the polyquaternary flocculant is obtained by reaction of dimethylamine, ethylene-diamine, and epichlorohydrin.

5. The process of Claim 1 wherein the polyquaternary is obtained by reaction of dimethylamine, a polyalkylenepoly-amine and epichlorohydrin, said polyalkylenepolyamine compris-ing up to 15 mole percent of the total amine usage.

6. The process of Claim 5 wherein the polyquaternary flocculant is obtained by reaction of dimethylamine, ethylene-diamine, and epichlorohydrin.

7. The process of Claim 1 wherein in said settling step an added precipitant is employed.