Use of oxidized cationic starch in flocculation and dewatering of municipal sludge
United States Patent 11 1 1111 3,875,054  
 Hunt et al. Apr. 1, 1975 USE OF OXIDIZED CATIONIC STARCH IN 3.157.594 11/1964 Nevers 260/233 R FLOCCULATION AND DEWATERING OF 3,397,139 8/1968 Sak 1 210/53 3,624,070 11/1971 Hunt 260/233 R MUNICIPAL SLUDGE Inventors: Walter G. Hunt, Bridgeton; Ray J.  
 Belz, Mehlville, both of Mo.  
 Anheuser-Busch Incorporated, St. Louis, Mo.  
 Filed: Mar. 4, 1974 Appl. No.: 447,656  
 Related US. Application Data Division of Ser. No. 335.518, Feb. 26. 1973, Pat. No. 3.835.114.  
 Assignee:  
 References Cited UNITED STATES PATENTS Primary E.\&#39;anzinerSamih N. Zaharna Assistant Examiner-Peter A. Hruskoci Attorney, Agent, or FirmGravely, Lieder &amp; Woodruff [57] ABSTRACT This disclosure covers the use of a cationic oxidized starch in the flocculation and dewatering o1- municipal raw primary sludge. From 0016 to 0.189591 (based on the dry weight of the sludge) of the treated starch of 35 to 60 fluidity and 1.75 to 2.25% oxidation is added to the municipal sludge and contacted with the sewage for a period of 3 to 5 minutes before being de-&#39; watered to a moisture content below about 70% moisture, which is the moisture level at which the solids will adequately sustain combustion. The starch has from 0.15 to 0.25 degree substitution of an amine butene halide, specifically, 1-ch1oro-4-butenyltrimethylammonium chloride.  
 5 Claims, No Drawings USE OF OXIDIZED CATIONIC STARCH IN FLOCCULATION AND DEWATERING OF MUNICIPAL SLUDGE This is a division of application Ser. No. 335,518, filed Feb. 26, 1973, now U.S. Pat. No. 3,835,114v  
 BACKGROUND OF THE INVENTION Presently treatment of raw sewage is a very important problem in the United States, and particularly to the larger cities which discharge part of the sewage treatment product into nearby rivers. In the treatment of municipal raw primary sewage, the sewage generally is initially deposited in a settling basin and the effluent is pumped directly to a river or other depository. The effluent may be further treated, in a secondary treatment process. The solids or sludge from the settling basins are filtered (generally on a rotary drum filter) and the filter cake is taken directly to an incinerator. This filter cake material usually needs to have about 30% solids so that it will adequately sustain combustion in the incinerator. This is called a primary sewage treatment and most cities either have or soon will have such processes in operation.  
  The sludge is negatively charged and an anionic polymer usually is added to the sludge before the cationic polymer is added. If only a cationic polymer is added the sludge does not flocculate as well as when the anionic material is used in combination.  
  The cationic material causes the sludge to fiocculate so that the sludge is more easily filtered and a greater percentage of water can be removed by the filter. As mentioned, the dewatering apparatus presently used in a rotary vacuum filter. The present state of the art also utilizes lime and ferric chloride as chemical coagulants in the treatment of raw primary sludge prior to vacuum filtration. Certain acrylic-type polymers also are useful in the treatment of sludge to condition. it for vacuum filtration.  
  There are certain teachings of the use of quaternary ammonium starch ethers as flocculants, particularly in the patents of Paschal] U.S. Pat. No. 2,995,513 and Caldwell U.S. Pat. No. 2,975,124. Both of these patents relate &#39;to the use of starch ethers as fiocculants. However, neither of these patents disclose the specific starch ether of the present invention (which contains a double bond) or its use as a sludge flocculant, and it is, therefore, a principal object of this invention to provide a cationic oxidized starch ether of specific characteristics which is useful as a flocculant in the treatment of primary sewage sludge at a reasonable cost. It is also an object of this invention to provide an oxidized starch product which has both anionic and cationic properties and which is very useful as a flocculating agent in the treatment of sewage sludge. These and other objects and advantages will become apparent hereinafter.  
  This invention comprises the use of an oxidized gelatinized cationic starch as a flocculating agent for primary sewage sludge.  
 DETAILED DESCRIPTION In Hunt U.S. Pat. No. 3,624,070 (assigned to the owner of the present invention), there is shown the preparation of granular gelatinizable quaternary ammonium starch ethers from starch and an amine alkene halide. In the present application an oxidized starch is gelatinized prior to reaction with the amine alkene halide so that a more random type of substitution is obtained. This enhances the flocculating effect of the starch ether. Also, the starch must be gelatinized prior to use, and the gelatinization prior to reaction also has the advantage of preparing a ready-to-use final product.  
  As will be described in detail hereinafter, it is important that the starch be oxidized to a specific range; that it be gelatinized prior to adding amine alkene halide; that the substitution be within a specified range, and that a specific amount of the starch ether be added to the sludge in order for the invention to be effective.  
  Hunt U.S. Pat. No. 3,624,070 discloses methods of making the amine butene halide starch ether. However, this patent discloses the reaction with the starch in granular form. In the present invention, the starch is initially treated with sodium hypochlorite until it is oxidized to an available chlorine content of about 2.2%. The starch preferably is dent corn starch, but can be other non-waxy starches such as wheat, potato, sago and rice. The oxidation treatment preferably is with sodium hypochlorite but can be any other suitable oxidizing treatment, such as sodium periodate.  
  The dent corn starch is oxidized to an available chlorine content of about 1.75 to about 2.25%. This oxidation treatment can be carried on by any suitable method, but should be carried to the extent that it is equivalent to a sodium hypochlorite treated corn starch of this available chlorine content. Preferably, the available chlorine content is about 2.2%. The fluidity of the oxidized starch is about 35 to about 60.  
  In making up the amine butene halide reagent, we prefer to use the tertiary amines, since under the conditions used, they do not further react with halides to form a variety of products as do the primary and secondary amines, thereby reducing the yields and purity of the reagent. Of the tertiary amines, trimethylamine appears to offer the most advantages, not only because it is the most economical but also because of its reactivity in this reaction; however, other teritary amines such as dimethyl benzyl, dimethyl lauryl (Armeen DM12D), and triethyl are also very reactive. Higher molecular weight teriary amines such as tri-n-propyl, N-methyl morpholine, N-methyl piperidine, methyl diallylamine, and pyridine may also be used, but the alkylation reaction rates are considerably diminished. All tertiary amines capable of quarternizing with dichlorobutene also fall within the scope of this invention. Though the free amines are preferred, the corresponding amine salts may also be used after adding sufficient alkali to revert them to the free amines.  
 PROCESS FOR SODIUM HYPOCHLORITE TREATING CORN STARCH In reacting sodium hypochlorite with dent corn starch, from about 2.0 to 2.25% by weight (based on the dry weight of the starch) available chlorine is reacted at to F. with about 42 to 50% by weight starch (dry basis) based on the combined water and starch which has been adjusted to pH 9.0 with a 2.0%  
 NaOH solution. The sodium hypochlorite is added then adjusted to pH 6.5 to 5.0 with lzlHcl and diluted with excess water to 15Be, filtered on Buchner funnel. reslurried to 15Be, filtered again and dried.  
  The amine butene halide reagent described in Hunt US. Pat. No. 3,624,070 is the same reagent that is used in this invention. This reagent is known as amine alkene halide salt and this term is understood to include qua ternary ammonium alkene halide salts. The reagent is represented by the following structural formula:  
  R X-G-IL RX Where X is halide, R is methyl or ethyl and G is alkenylene. The alkenylene has from 1 to 4 carbons.  
  This product is reacted with gelatinized oxidized dent starch to produce the following product:  
  if Starch-O-G-N RC1 Where R is methyl or ethyl and G is alkenylene of 1 to 4 carbons.  
  One main difference between the starch reaction product of Patent No. 3,624,070 and the starch reaction product of this invention is the greater amount of amine butene halide added to the starch of the present reaction. Also, the starch is reacted in gelatinized condition rather than being reacted in granular form.  
  In reacting the amine butene halide (particularly 1- chloro-4-butenyltrimethylammonium chloride) with starch, from about 50m 55% by weight (based on the dry weight of the starch) of the amine alkene halide is reacted with oxidized gelatinized starch for 4 to 5 hours at a temperature of about 65 to 75C. using the technique of Ex. No. 1. The final product has a carboxyl number of about 0.1% to about 0.3% which corresponds to a degree of substitution (D.S.) of about 0.0036 to about 0.0108. The average molecular weight is about 89000.  
 EXAMPLE NO. 1  
 &#39; ring. Specifically, the starch is treated with steam at a temperature of 212 to 220F. for a period of 5 to minutes while being stirred.  
  The temperature is adjusted to 70C. and the stirring is continued. At this point 32 g. of a NaOH solution is added to the mixture of gelatinized starch and water with continued stirring. The NaOH is added as a catalyst and not as a gelatinizing agent. From about 12 to about 18% by weight NaOH (based on the dry weight of the starch) can be added. The temperature can be to 75C.  
  At this point, 1 l l g. of a 50% TAC solution 1- chloro-4-butenyltrimethylammonium chloride) is added. This reagent is prepared as hereinbefore described. This solution is allowed to react for 4 hours with stirring at C. before it is diluted to 25% solids by weight with water to product a gelatinized oxidized cationic starch.  
  From about 50 to about 55% by weight (based on the dry weight of starch) of the amine butene halide can be used. This reaction between the amine butene halide and the starch can continue for 4 to 5 hours at a temperature of 65 to C.  
  Following are Examples of treating raw primary sewage with the cationic oxidized starch of this invention.  
 EXAMPLE NO. 2  
  A mixture of 108 g. (dry basis) 7303 (lightly oxidized dent starch) in 300 ml. water is gelatinized with steam and diluted with 300 ml. water. The dent starch had a chlorine content of 2.20 The gelatinized starch is transferred to a 70C. water bath and 32 g. of 50% NaOH solution and 11 1 g. 50% TAC solution are added. The TAC is 1-ch1oro-4-butenyltrimethylammonium chloride. This mixture is reacted for 4 hours at 70C. The resultant product is 21% solids by weight and has a degree of substitution of 0.25.  
  Composite samples of primary sludge were picked up from a municipal sewage treatment plant. Cationic starch at a concentration of 0.5% was examined using the following method:  
  A predetermined amount (based on the dry weight of the sludge) of a 0.05% by weight aqueous solution of an anionic polyelectrolyte is added to 200 ml. of raw primary sludge and mixed back and forth 10 times between two beakers. This anionic polyelectrolyte is a very high molecular weight synthetic water soluble hydrolyzed polyacrylamide labeled under the tradename Purifloc A-23 and made by the Dow Chemical Company. (In all of the following Examples this anionic polyelectrolyte will simply be referred to as Purifloc A-23).  
 A specific weight (based on the dry weight of the sludge) of a 0.5% by weight aqueous solution of cationic polyelectrolyte prepared according to Example No. 3 is then added, mixed back and forth at 76F. 10; times between two beakers, and transferred to a Buchner funnel fitted with Whatman No. 1 filter paper. The pressure in the filtrate receiver was reduced to 13 inches Hg and the filtrate collected after 30, 60, and seconds determined. Results are as follows:  
 I Sludge Amount of Amount of Run (ml.) 70 Solids Anionic Cationic l Polyelectrolyte Oxidized ml. Filtrate 7: Solids Added Starch at (seconds) After Added 30 60 90 120 Filtration 6 Sludge Amount of Amount of Run (ml.) /1 Solids Anionic Cationic Polyelcctrolyte Oxidized ml. Filtratc 7r Solids Added (/z) Starch at (seconds) After Added 192 Filtration 4 200 1 1.4 .022 .098 60 97 120 32.6 5 200 .5 .011 .100 70 125 170 183 41.2 6 200 9.6 .017 .047 83 123 147 158 45.7 7 200 2.0 .025 .100 85 125 172 14.3 x 200 9.5 .025 .092 137 163 55.9 (Average) 9 200 5.0 v015 .100 112 158 172 177 43.5 10 200 5.2 .029 .096 150 178 178 44.3 (Average) 11 200 9.9 .025 .101 115 130 135 137 31.4 12 200 5.2 .012 .096 115 160 172 175 41.6 13 200 5.2 .024 .096 123 168 174 176 43.3 14 200 3.6 .024 .097 92 137 158 170 24.0 15 200 9.4 .027 .098 73 100 114 123 24.4 16 200 6.0 .025 .100 102 140 153 160 30.0  
 Notes: Based on dry weight of sludge.  
 In all tests, the minimal quantities of polyelectrolytes that was used in Example No. 2. This is due primarily required to increase solids to approximately 30% in to the small percentage polyelectrolyte (dry basis) by 120 seconds was used as criteria for adequate flocculaweight used based on the dry weight of the sludge. In tion and dewatering. The 30% solids level after filtra- 20 all tests, approximately 30% solids after 4 minutes vact iS an adequate Solids Content for Sustaining uum filtration on a filter leaf was used as criteria for adbustion when the filter cake is later incinerated. equate flocculation and dewatering.  
  EXAMPLE 3 EXAMPLE NO. 4 A predetermined amount (based on the dry weight of 25 F u l t d t the sludge) of a 0.05% by weight aqueous solution of i ls i li gg :1 an anionic polyelectrolyte (Purifloc A-23) is added to S are e g? 3: X1 t as 2000 ml. of raw primary sludge and mixed. Then a spea i fi Su 5 1 O l :5 e amme cific amount of a 0.5% by weight aqueous solution of e sewage rea men p a cqmmercla op- 3 eration and the sludge had an initial SOlldS content of cationic polyelectrolyte (based on the dry weight of the 10.8% by weight. The starch is added to the sewage as sludge) prepared according to Example No. 1 15 added a 0.5% by weight solutlon at a 0.04875% by weight and mixed, being sure not to deflocculate the sludge basis (based on the dry weight of the sewage). with the agitation. A filter leaf with a reduced pressure The amine 0] e1 ctrol te (Purifloc A 23) is added of 13 inches Hg is then lowered into the conditioned as a 0 057 b i i Solution at a O 0275,? b sludge. Filtrate is collected for 60 seconds and the filter 35 y g que 0 y werght basis (based on-the dry weight of the sludge). leaf 1S removed and allowed to dry under reduced pres- The treated sludge 1S filtered on a rotary filter at a rate sure for another seconds. The filter cake is then reof 277.5 wet pounds per minute. The treated sludge has moved and percent SOlldS and total dry solids are detera SOlldS content of 31.95%. On a dry solids basis, 0.975 mined. Results are as follows.  
  40 pounds of starch reactant 18 added per ton of dry sludge recovered. This is a very satisfactory performance both Amount of from a cost and a technical viewpoint.  
  Cationic Amount of Oxidized Anionic Solids EXAMPLE NO. 5 Sludge Starch Polymer After c Run (mi) S lids Added We) Added Filtration 45 The following is a 15 day plant size run using oxidized l 2000 65 m5 m2 2&amp;8 dent cationic starch in which the starch is 2.2% 0x1- 2 2000 945 932 218 dized and has a degree of substitution of 0.25 of an 2 388g 32 -82; gig amine butene halide (particularly l-chloro-4-butenyltrimethylammonium chloride). The cationic starch is Notes: Based on dry weight of sludge. 50 added as a l 1 solution weight. The anionic polyelectrolyte (Purifloc A-23) is added as a 0.05% soluln this Example, the test procedure for determining adtion by weight. The sewage treatment plant is a comequate flocculation and dewatering by the polyelecmercial operation and the results obtained are as foltrolyte has been changed from the Buchner funnel test lows:  
 (untinuctl i Amount of Amount of Solids Dry Pounds Pounds Cationic Anionic After Tons Oxidized Anionic Oxidized Polyelectrolyte Filtration Filtered Cationic Polyelectrolyte Starch Added(%) Starch Added Per Run Solids Added(%)&#39; Per Dry Dry Ton Ton Sludge Sludge (ominucnl Amount of Amount of 7! Solids Dry Pounds Pounds Cationic Anionic After l&#39;ons Oxidized Anionic Oxidized Polyclectrolytc Filtration Filtered Cationic Polyelectrolyte Starch Added(%)&#39; Starch Added Per Run 7: Solids AddedU/r Per Dry Dry Tori Ton Sludge Sludge Based on dry weight of the sludge.  
  In all the daily runs the criteria for adequate flocculation and dewatering was 30% solids level after filtration. The average percent solids for the entire 15 day run was 32.2%. On a dry solids basis, an average of 1.63 pounds cationic starch (0.0815% based on dry weight of the sludge) was added per dry ton sludge recovered. This was a very satisfactory performance both from a cost and technical viewpoint.  
 What is claimed is:  
  1. A method of treating raw primary sedimented sewage sludge including the steps of adding from 0.016% to O. 1875% by weight (based on the dry weight of the sludge) of gelatinized oxidized cationic starch ether of amine butene halide to raw primary sedimented sludge, said starch ether having a carboxyl content equivalent to a degree of substitution of about 0.0036 to about is gelatinized prior to reaction with the amine butene.  
 reagent.  
  3. The method of claim 1 wherein the starch ether is 1-chloro-4-butenyltrimethylammonium chloride.  
 4. The method of claim 1 wherein the starch is dent corn starch.  
  5. The method of claim 4 wherein the starch is dent corn starch and the amine butene halide is l-chloro-4- butenyltrimethylammonium chloride.