CA1067221A - Method for treating liquid wastes - Google Patents

Abstract

A B S T R A C T
A method for treating a waste liquid which comprises adding to a solution or suspension to be clarified a water-soluble melamine resin con-taining in the molecule a unit expressed by the following formula

Description

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Thi5 invention relates to a method for treating waste waters which can exhibit an excellent treating effect on the clarification of not only solid-containing ~spended waste liquids such as pulp spent liquors from paper mills or waste waters discharged from sand and gravel extracting places, but also waste effluents in the form of solutions or emulsions such as emulsion wastes and rubber latices discharged from textile finishing plants, aqueous solutions of acid dyes discharged from dyeing factories, or oil-containing emulsion wastes from machine-building factories.
More specifically, this invention relates to a method for treating waste liquids, which comprises adding to a solution or suspension to be clari-fied a water-soluble melamine resin containing in the molecule a unit ex-pressed by the following formula NH+2X-N l (I) N - C~ /C-N~ICH2 OH
wherein X represents an anion derived from an inorganic or organic acid, wherein the amino group to which a methylol group is not attached is cationic.
Clarification of waste liquids discharged in various chemical and other industries has been an i~lportant problem in controlling environmental pollution.
It has already been proposed (Japanese Patent Publication No.
12517/63 published on July 18, 1963) to clarify waste liquids by removing hydrophobic or nearly hydrophobic inorganic or organic fine solid particles suspended therein. This Japanese Patent discloses a wide variety of chemicals for use in such a method, which include:
(A) Polycondensates formed between urea, thiourea or melamine and formaldehyde;
(B) Copolycondensates prepared from a combination of urea, thiourea and formaldehyde, a combination of urea, melamine and formaldehyde, and a combination of thiourea, melamine and formaldehyde;

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(C) Copolycondensates prepared from the polymers (A) or (B) above and other compounds copolymerizable with them to an extent that their properties as a flocculating agent are not lost; and (D) Neutral, anionic, cationic or amphoteric modified products ob-tained by reacting the methylol group of the above polymers (A), (B) or (C) with an alcohol such as methyl alcohol, ethyl alcohol, ethylene glycol, glycerine or sucrose, an acid such as acetic acid, succinic acid, malic acid, tartaric acid, maleic acid or glutamic acid, or an amine such as ethanolamine, ethylene diamine or lysine capable of reacting with the methylol group; or salts of these modified products.
It is described in this Patent that the base of the condensation polymers (A) to (D) consists of a combination of a urea, thiourea or melamine group shown below ~1) Il 11 l / \ / C // \ N (1) =N-C C-N=
~N
urea groupthiourea group melamine group with a monovalent or divalent hydrocarbon group or other group having a re-latively low molecular weight shown below (2-1) and (2-2).
~2-1) In the case of the polymers (A), (B) and (C):--H, -CH20H, -CH2-, -CH20CH2-(2-2) In the case or the polymer (D):--H, -CH20H, -CH2-, -CH20CH2-; -CH20CH3, -CH20CH2-CH20H

(when the methylol group is reacted with an alcohol);

-CH200CCH3, -CH200C CH2-CH2-COOH

(when the methylol group is reacted with an acid);

2 2 CH2 NH3-Cl , -CH20-CH2-CH~-NH+-Cl-(when the methylol group is reacted with an amine).
We made extensive investigations with a view to developing a treating agent which would be able to flocculate and sediment not only solid rr~ - 2 -10672~1 particles suspended in waste liquors but also solutes in waste liquors in the form of solutions or emulsions. These investigations finally led to the discovery that a water-soluble melamine resin containing in the molecule a unit expressed by the following formula (I) NH X
/c \
HN N

CH ~N / (I) 0}1 wherein X represents an anion derived from an inorganic or organic acidJ
which can be distinguished from the melamine resins disclosed in the above patent in that the amino group to which a methylol group is not attached is cationic, can be used as a very effective treating agent for waste liquids.
The above water-soluble melamine resin may contain minor amounts, for e~ample, less than 1 mol, preferably less than 0.7 mol, more preferably less than 0.5 mol, per mol of the triazine nucleus of the above formula, of another unit derived from an amino compound such as urea, dicyandiamide or acetoguanamine.
The above water-soluble melamine resins which contains the above unit in the molecule and in which the amino group to which a methylol is not attached is cationic are known (H.P. Wohnsiedler: I.E.C., 44, 2679, 1952), and it is known to use resins of this type for improving the wet strength of paper (United States Patent specification No. 2,345,543). However, it has been completely unknown that these resins would exhibit superior activities in the clarification of waste liquids in the form of solutions or emulsions as well as suspensions. According to this invention, it was unexpectedly found that these melamine resins exhibit superior clarifying activities in fields where the effect and the time of addition are quite different from those for incrcasing the wet strength of paper, especially in the field of waste water treatment.
This invention seeks to provide a met~od _ 3 _ ~J

7ZZl for treating waste liquids in the form of solutions or e~ulsions as well as suspensions with a superior clarifying effect.
m us, this invention provides for a method for treating a waste aqueous liquid which comprises adding to an aqeuous solution or suspension to be clarified an effective amount of a water-soluble melamine-based resin containing in the lecule from about 5 to about 20 units of the formula I

N ~3 H2X ~3 C \ (I) HN ~NH

wherein X ~3 represents an anion derived from an organic or inorganic acid, which resin has been prepared by reacting 1 mol of melamine with from 2 to 3 mols of formaldehyde, and adding to the resulting methylol melamine solution an organic or inorganic acid in an amount of from about 0.5 to about 3.5 mols per mol of melamine present.
m e solutions or suspensions which are to be treated in accordance with the method of this invention include, for example, pulp spent liquors from paper mills, waste waters from sand and gravel extracting places, emul-sions and rubber latices from textile finishing plants, aqueous solutions of acid dyes discharged from dyeing factories, and oil-containing emulsions from machine-building factories. m e resins used in this invention are especially useful for removing the matter dissolved or suspended in wastes of the solu-tion or emulsion type.
Melamine resins containing about 5 to 20, preferably 10 to 20,units of the above formula (I) are preferably used. Examples of anion ex-pressed by X in the formula (I) are those derived from inorganic acids such as hydrochloric acid or phosphoric acid, or those derived from organic acids such as formic acid or acetic acid.
The water-soluble melamine resin containing the unit of formula (I) can be prepared, for example, by reacting 1 mol of melamine with about 2 to 3 ~ _ 4 _ .....
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` 1(~67Z21 mole of formaldehyde in a custo~ary manner, cldding a relatively large amount of an acid to the resulting methylol melamine solution to adjust the resin concentration properly, for example, to an extent of providing about 6-20%
aqueous solution, and aging the solution at room temperature for more than about one day. The amount of the acid can be varied properly according to the type of the acid used, and the preferred amount is, for example, 0.7 to 1.3 mols for hydrochloric acid, 2 to 3 mols for phosphoric acid, and about 1.6 to 2~5 mols for formic acid, all per mol of the melamine. ~enerally, the amount of the acid is about 0.5 to 3.5 mols per mole of the melamine.
In the method of this invention, the above melamine resin can be used conjointly with an inorganic metal salt such as aluminum s~lfate, ferrous chloride or poly(aluminum chloride) or an organic polymeric flocculant such as polyacrylamide. The amount of the ir.organic salt and/or the organic poly-- 4a -,~
~: `

~0~7ZZl meric flocculant can be varied properly according to such ~actors as the type of the ~aste liquid to be treated, or the type of the suspended, dissolved or dispersed matter to be flocculated and removed. For example, the amount of the inorganic metal salt is not more than about 500% by weight of the matter to be removed, and the amount of the organic polymeric flocculant is equal to, or lower than, the amount of the water-soluble melamine resin used in accord-ance with this method.
The amount of the water-soluble melamine resin to be used in this invention can be varied properly according to the characteristics of the solu-tion, emulsion or suspension to be treated, or the type or characteristics of the matter contained therein. ~sually, the amount of the melamine resin used is about 1/1000 to 2 parts by weight, and in most cases, about 1/500 to 1.5 parts by weight, per part by weight of the total amount of the matter in the waste solution, emulsion or suspension. For example, in the case of an acid dye solution, the melamine resin is used in an amount of about 200 to about 1500 g per kilogram of the solute; in the case of an emulsified solution, the melamine resin is used in an amount of about 50 to about 200 g per kilogram of the solute; and in the case of a suspension such as a pulp spent liquor, the amount of the melamine resin is about 2 to about 300 g per kilogram of the suspended matter.
When other chemicals are conjointly used, the amount of the melamine resin used can be properly increased or decreased according to the types and amounts of the other chemicals.
; In the practice of the method of this invention, the pH of the waste liquid to be clarified can be easily determined experimentally accord-ing to the type of the matter to be removed from the waste liquid and other conditions. Specific examples of pH adjustment are shown in the Examples to be given hereinbelow.
One specific procedure of performing the method of this invention comprises adding the water-soluble melamine resin having the unit of formula (I) in the molecule, to a liquid to be treated which has been adjusted to the desired pH during its transfer to a precipitating or filtering device, stir-ring the mixture rapidly so as not to cause non-uniformity in concentration, and to form a flocculated mass, and if desired, rather slowly stirring the liquid using the abovementioned other chemicals to grow the resulting floc-culated mass to coarser particles to facilitate precipitation or filtration, and then precipitating or filtering the solute or suspended matter in the waste liquid.
The sequence of adding the water-soluble melamine resin and the chemicals can be chosen as desired.
According to this invention, it is possible to rapidly precipitate and flocculate not only the suspended matter in suspensions, but also in particular the solute in a solution of an acid dye having a hydrophilic group thereby rendering it extremely easy to clarify the waste water to be treated.
The following Examples and Comparative Examples illustrate the present invention specifically. In these Examples, the following resins were used.
Resin A
A reactor equipped with a condenser tube and a stirrer was charged with 126 g ~1 mol) of melamine and 240 g (3 mols) of 37% formaldehyde whose pH had been adjusted to 8 with sodium hydroxide, and at a reaction temperature 85 to 90C., the reaction mixture was stirred. After the melamine dissolved, the reaction was further performed at this temperature for about 30 minutes.
The reaction product was cooled to room temperature to form a transparent resin solution.
Resin B (invention) 2 Mols of formic acid, per 126 g (1 mol) of melamine in the resin solution, of formic acid and water were added to the same resin solution as resin solution A to adjust the solids content to 10%. The solution was aged at room temperature for more than one day to form a slightly bluish resin solution.
Re _ n C (invention) A resin solution prepared in accordance with the same recipe as resin A was dried by means of a spray dryer to form a dry solid powdery resin.

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216 G of this powdery resin was added to dilute hydrochloric acid obtained by mixing 100 g of HCQ having a concentration of 36.3% and 3300 g of water. The mixture was stirred to form a resin solution having a concentration of about 6%. Prior to use, the solution was aged at room temperature for more than 24 hours.
For comparison, the following resins D tc I were prepared.
Comparison Resin D (melamine resin) A reactor equipped with a condenser tube and a stirrer was charged with 126 g (1 mol) of melamine, 240 g (3 mols) of 37% formaldehyde whose pH
had been adjusted to 8 with sodium hydroxide, and 60 g of water, and they were reacted at a reaction temperature of 85 to 90C. After the melamine dissolved, the pH of the solution was reduced to about 7 with hydrochloric acid, and the condensation reaction was performed until the turbidity point (the temperature at which the resin solution becomes turbid when the resin concentration is

3% - Koeda, Kogyo Kagaku Zasshi 60, 1567, 1957) became 15C. The product was then cooled to room temperature to form a resin solution.
Comparison Resin E (urea resin) 60 G of urea was reacted with 240 g of 37% formaldehyde whose pH
had been adjusted to 8 with sodium hydroxide at a temperature of 85 to 90C.
for 30 minutes. The pH of the solution was reduced to 4.2 with formic acid, and the reaction was continued at 80C. for about 3 hours. Then, the reaction product was rapidly cooled to room temperature to form a resin solution.
Comparison Resin F (melamine-urea cocondensed resin) 180 G of urea, 13 g of melamine, 450 g of 37% formaldehyde and 100 g of water were mixed, and the pH of the mixture was adjusted to 8 with sodium carbonate. The mixture was reacted at 80C. for 3 hours to form a resin solu-tion.
Comparison Resin G (alcohol-modified melamine resin) 50 G of melamine and 114 g of 37% formaldehyde whose pH had been adjusted to 8.5 were mixed, and stirred at 85C. After the melamine dissolved, 240 g of methanol containing 1.6 mQ. of formic acid (2N) was added, and the mixture was reacted under reflux for about 2 hours. The pH of the solution ~' 1()67221 was returned to 8, and the reaction mixture l~as concentrated at reduced pres-sure to form a resin solution having a concentration of about 80%.
Comparison Xesin H (acid-modified melamine resin) 126 G of melamine, 240 g of 37% formaldehyde whose pH had been ad-justed to 8.0, and 140 g of water were reacted at 80C. for 30 minutes with stirring, and then, 75 g of tartaric acid was gradually added dropwise. Dur-ing this time, the pH of the reaction mixture was adjusted to 7-8 with sodium hydroxide. The reaction was continued for 30 minutes, and the temperature was lowered to room temperature to form a resin solution.
Comparison Resin I (amine-modified melamine resin) 126 G of melamine, 240 g of 37% formaldehyde whose pH had been ad-justed to 8 and 80 g of water were mixed, and reacted at 80C. for 30 minutes with stirring. Then, 75 g of triethanolamine neutralized with 6N HCQ was added, and the mixture was further reacted for 60 minutes. The reaction pro-duct was cooled to room temperature to form a resin solution.
Tests for flocculation wers performed as follows:
1) Sedimentation Test (a) PLace lO0 mQ. of a waste water in a 100 mQ. Nessler's tube.
(b) Add a predetermined amount of the test resins of a suitable concen-tration.
(c) Seal the tube with a stopcock, and tumble it 10 times.
(d) Allow the tube to stand, and measure the speed (cm/min.) of move-ment of the interface between the supernatant liquid and the flocculated mass.
(e) Where there is no distinct interface between the supernatant liquid and the flocculated mass, measure the time required for the flocculated mass to deposit to a height of 2 cm from the bottom of the tube.
2) Jar Test (a) Place 300 mQ. of a waste water in a 500 mQ. beaker.
~b) Add a predetermined amount of the test resin of a suitable concen-tration (or other chemical).
(c) Stir the mixture for 5 minutes at 150 revolutions per minute using a jar tester. (In the case of an oil-containing waste water, the speed of ~,., .. .

~)67ZZl rotation is adjusted to 100 rpm.) (d) Add a predetermined amount of other chemical (or a resin of suitable concentration), if desiredJ and further stir the mixture for 5 minutes at 50 revolutions per minute.
(e) Suction filter the mixture using a filter paper (No. 5C~.
(f) Measure the percent transmission of the filtrate at a suitable wavelength.
Example 1 and Comparative Example 1 The jar test was conducted using a solution of a dye (Milling Brilliant Red B: C.I. Acid Red 249) in a concentration of 100 ppm as the waste water and the resin C.
The test results are shown in Table l. It was found that the dye dissolved was removed by the resin C almost completely, and the filtrate was much the same as water.
A similar effect was obtained with the case of using the resin C
and an inorganic salt, but when the inorganic salt was used alone, no effect was obtained.
Table l Flocculating effect on dye solutions Amount of Chemicals used conjointly Percent resin C transmission Runs Nos. as solids A12(SO4) FeCQ FeS0 (%) (ppm) 3 3 4(~ = 520 nm) .
Example 11 80 0 0 0 97.5 2100 0 0 0 98.5 380 100 0 0 95.0 4100 0 100 0 92.5 5100 0 0 100 96.3 _ _. .
Comparative Example 16 0 100 0 0 1.5 200 0 0 1.2 0 100 0 3.0 0 0 10~ 11.3 _ g _ ? '~ ' 1~6~2Zl Example 2 The same test as in Example 1 was repeated except that resin B was used instead of the resin C. It was found that the percent transmission of the filtrate was 96 to 98% when the amount of the resin added was 80 to 100 ppm. This means that the dye dissolved was almost completely removed.
Example 3 and Comparative Example 2 The jar test was performed using a light brown kraft pulp spent liquor (involatile content 500 ppm) as the waste water and the resin C. The pH of the spent liquor had been adjusted to about 5 with hydrochloric acid.
The test results are shown in Table 2. It can be seen from thé table that both the resin alone or the combination of the resin and aluminum sul-fate exhibited marked flocculating actions on the waste water. The filtrate after separation of the flocculated mass by filtration was trasparent.
The use of aluminum sulfate alone led to a percent transmission of less than 86%.
Table 2 Flocculating effect on pulp spent liquors Amount ofAmount of Percent resin CA12~S04)3 transmission Runs Nos. as solids (%) at (ppm) (ppm) ~ = 380 nm ~ __ I
Example 3 1 90 0 97.0 2 100 0 98.0 3 120 0 98.8

4 5 300 94.0 300 98.0 Comparative _ - -Example 2 6 0 50 79.8 7 0 100 79.2 8 0 200 82.2 9 1 0 300 85.1 Example 4 The jar test was performed using two types of commercially available acrylic emulsion (1000 ppm, pH 7-8) and the resin C. It was found that when the amount of the resin C was 110 to 130 ppm, the emulsion flocculated con-~ -- 10 ~,; .

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siderably. The filtrate was very much clarified with a percent transmissionof 96 to 100%.
Example 5 The jar test was performed using two types of commercially available machine oils [JIS W-ll type (1000 ppm, pH 10) and JIS W-31 type (10000 ppm, pH 9.6)] as waste water and resin C.
When the amount of the resin C was 300 to 350 ppm, the emulsion of the JIS W-ll type machine oil was flocculated and the flocculated mass got afloat. The filtrate became transparent. The starting waste water and the filtrate were treated respectively with n-hexane to extract the oil, and the rate of oil removal was measured. On the other hand, COD of both the starting waste water and the filtrate was measured using potassium permanganate, and the rate of COD reduction was determined. Both of these tests were performed in accordance with JIS KO102, and the rate of oil removal and the rate of COD
reduction were both more than 90%.
In the case of JIS W-31 type machine oil, the filtrate became trans-parent when the amount of the resin C was 1000 to 3000 ppm. The rate of oil removal determined by the same method was more than 98%.
Example 6 and Comparative Example 3 The sedimentation test was performed to compare the flocculating effect of the resin C of this invention with those of the resins D to I.
The results are shown in Table 3, from which it can be seen that the comparison resins had extremely poor effects.

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Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for treating a waste aqueous liquid which comprises adding to an aqueous solution or suspension to be clarified an effective amount of a water-soluble melamine-based resin containing in the molecule from about 5 to about 20 units of the formula I
(I) wherein X ? represents an anion derived from an organic or inorganic acid, which resin has been prepared by reacting 1 mol of melamine with from 2 to 3 mols of formaldehyde, and adding to the resulting methylol melamine solution an organic or inorganic acid in an amount of from about 0.5 to about 3.5 mols per mol of melamine present.

2. The method of claim 1 wherein X ? in the formula represents an anion derived from an inorganic or organic acid selected from the group consisting of hydrochloric acid, phosphoric acid, acetic acid, and formic acid.

3. The method of claim 1 wherein the amount of said water-soluble melamine resin is about 1/1000 to about 2 parts by weight per part of weight of the solute or suspended matter in said waste liquid.

4. The method of claim 1 wherein the water-soluble melamine resin contains from about 10 to about 20 units of formula I.