JPS63158200A - Dehydration of sludge - Google Patents

Abstract

PURPOSE:To reduce the water content of a dehydrated cake, by adding an amphoteric org. polymer flocculant to org. sludge and dehydrating the resulting mixture. CONSTITUTION:An inorg. flocculant such as caustic soda, caustic potash or slaked lime is added to org. sludge so that a pH value becomes 5-8 after addition. Thereafter, an amphoteric org. polymer flocculant [e.g., dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate] is added to the sludge to form floc. Subsequently, the sludge is dehydrated by a screw press type dehydrator or a filter press type dehydrator. By this method, the filter cloth releasability of a dehydrated cake is enhanced and incineration fuel cost can be conserved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sludge dehydration method for efficiently treating organic sludge generated from sewage, human waste treatment plants, organic industrial wastewater, etc.

[Conventional technology]

Conventionally, organic sludge generated from sewage, human waste treatment plants, organic industrial wastewater, etc. has been treated by adding a polymer flocculant and dewatering it using a screw decanter, a belt press, or the like.

Dehydrated sludge (hereinafter referred to as "dehydrated cake") is sometimes used for landfill, etc., but is mainly disposed of by incineration.

In incineration, most of the fuel is used to evaporate the moisture in the dehydrated cake, and generally, if the moisture in the dehydrated cake decreases by 1%, about 10% of the fuel can be saved.

However, in recent years, due to the advancement of water treatment, changes in the properties of wastewater to be treated, and diversification, etc., sludge has become difficult to dehydrate, resulting in increased fuel costs for incineration. It is requested that the

Organic sludge has a small SS particle size, weak strength, and low specific gravity; it is water-based; it contains a large amount of internally retained water and water attached to the surface; and it contains no putrefying organic matter. Because of its strong adhesion, it is almost impossible to dehydrate it as it is, and it is usually dehydrated by adding an organic polymer flocculant and using a sludge dewatering machine such as a °C screw decanter, belt press, or screw press. .

However, depending on the properties of the sludge, these methods cannot sufficiently reduce the water content of the dehydrated cake.

In addition, recently, there has been an increase in the use of separate flow systems in sewage treatment facilities, which has resulted in an increase in organic matter in sludge, and in particular when using a belt press type dehydrator, peeling of the dewatered cake from the belt is becoming more difficult. Because of this, we are now in a situation where we have to stop dehydration while keeping the moisture content relatively high.

A method of using an inorganic flocculant and an organic polymer flocculant in combination to solve these problems (Japanese Patent Laid-Open No. 58-51998
No. 4, Japanese Unexamined Patent Publication No. RIB59-16599, etc.) have been proposed.

[Problem that the invention seeks to solve]

JP-A No. 58-51998 discloses a method in which polyferric sulfate (an inorganic flocculant) and an organic polymer flocculant are used in combination, and a nonionic, anionic or cationic organic polymer flocculant is used alone. Although this method is described, the particle size of the flocs produced by this method is generally small and has insufficient strength, and the dehydrated cake tends to form lumps, making it difficult to reduce the moisture content of the dehydrated cake.

In addition, JP-A-59-16599 discloses that an inorganic flocculant and an organic polymer flocculant are used in combination, and as the organic polymer flocculant, a Mannich modified product (cationic) of a polyacrylamide polymer and an anionic organic polymer are used. Although a method using a coagulant has been described, in many cases, the removability of the dehydrated cake from the furnace cloth is insufficient, and it is also difficult to reduce the moisture content of the dehydrated cake.

The purpose of the present invention is to solve these problems, to ensure that the generated flocs have sufficient particle size and strength, and that the water content of the dewatered cake is low (and that the dewatering cake of sludge has good removability). The purpose is to provide a method.

[Means for solving problems]

The gist of the present invention resides in a method for dewatering sludge, which comprises adding an amphoteric organic polymer flocculant to organic sludge whose pH value after addition of the inorganic flocculant is 5 to 8, and then dewatering the organic sludge.

In the present invention, organic sludge refers to sludge generated through biological treatment of high BOD wastewater, examples of which include sewage,
Examples include sludge generated in human waste treatment plants, sludge generated in the food industry, chemical industry, etc.

In the present invention, as the inorganic flocculant, sulfuric acid bandate,
Known agents such as ferric chloride, ferrous sulfate, and polyferrous sulfate can be used, but iron-based inorganic flocculants are preferred among these.

The pH value of organic sludge after adding an inorganic flocculant must be in the range of 5 to 8, and if the pi (value is smaller than or exceeds this range, add an amphoteric organic polymer flocculant. When the flocs are generated, the diameter of the flocs is small, and in extreme cases, they do not coagulate at all, and therefore the dewatering efficiency is significantly reduced or dewatering is not possible at all, which is not preferable.

If the p)I value after addition of the inorganic flocculant is in the range of 5 to 8, pH Mir4 adjustment is not particularly required, but in other cases, the pH is adjusted with an alkali or acid.

Caustic soda, caustic potash, slaked lime, ammonia, etc. can be used as the alkali, and among these, caustic soda and slaked lime are preferred.

Further, as the acid, sulfuric acid, hydrochloric acid, acetic acid, sulfamic acid, etc. can be used, and among these, sulfuric acid and hydrochloric acid are preferred.

More preferably, this pH value is 6-7.

Also, the reaction time and pH when an inorganic flocculant is added
There is no need to consider the time required for adjustment, and the addition of an inorganic flocculant and the pH'? A adjustment and addition of the amphoteric organic polymer flocculant may be carried out sequentially.

The amphoteric organic polymer flocculant used in the present invention is:
A polymer flocculant that has a carboxyl group, sulfone group, or a salt thereof as an anionic group in the molecule, and a tertiary amine, its neutralized salt, quaternary salt, etc. as a cationic group. It may contain a nonionic component in addition to the ionic component.

Among these, amphoteric organic polymer flocculants having a carboxyl group or a salt thereof as an anionic group are preferred from the viewpoint of solubility in water, flocculation performance, etc.

Examples of the cationic monomer unit constituting the amphoteric organic polymer flocculant particularly preferably used in the present invention include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminepropyl (meth)acrylamide, and diethylaminopropyl (meth)acrylate. Examples of anionic monomers include acrylic acid, methacrylic acid, and alkali metal salts thereof; As a monomer unit, (meth)acrylamide, N,
Examples include N-dimethyl (meth)acrylamide and N,N-diethyl (meth)acrylamide.

The cation equivalent value Cv and anion equivalent value A of the amphoteric organic polymer flocculant used in the present invention are not particularly limited, but include solubility in water in a dissolution tank before addition to sludge, flocculation performance of sludge, and flocculation Considering dehydration, the cation equivalent value Cv is 1. O~4. Omeq／J
', the anion equivalent value Av is 0.3 to 2. Ome
q/J', Cv/Av ratio is 1.5~
Those in the range of about 8.0 are preferable, and the cation equivalent value Cv is 1.3 to 3.8 meq/J', and the anion equivalent value Av is 0.4 to 1.8 meq7'7, C
It is more preferable that the v/Ay ratio is in the range of 1.8 to 7.0.

In the present invention, the cation equivalent value Cv and anion equivalent value Av of the amphoteric polymer flocculant can be determined by the colloid titration method shown below.

(1) Measurement of cation equivalent value■, Deionized water 9011 in a conical beaker! 1,011 t of a 500 ppm sample solution was added, the pH was adjusted to 3.0 with an aqueous hydrochloric acid solution, and the mixture was stirred for about 1 minute. Next, add 2-3 drops of toluidine blue indicator and titrate with N/400-polyvinyl potassium sulfate reagent (N/4QO-PVSK).

The titration rate was 2g/min, and the sample water changed color from blue to reddish-purple.
The end point is when the sample is held for 10 seconds or more.

■Preparation of sample 500 ppm aqueous solution Precisely weigh samples 0 and 2P (not converted to dry product), transfer to a triangular container with a stopper, and add deionized water at 100 mA! Dissolve with.

Make up 25 ml of this volume with deionized water in a 100 rnl volumetric flask.

1. Calculation method: Cation equivalent value (meq/P) (2) Measurement of anion equivalent value ■: Take 9Qml of deionized water in a conical beaker,
N/1〇- Add 0.5 d of caustic soda aqueous solution, and add N while stirring.
/200-Methyl glycol chitosan test solution 5- is added dropwise and stirred for 1 minute or more. Next, a 500 ppm aqueous solution 101 of the sample was slowly added dropwise, and after being stirred for 5 minutes or more, 2 to 3 m of toluidine blue indicator was added.
N/'400-polyvinyl potassium sulfate reagent (N/40
0-PVSK).

The titration rate is 1 rttl/min, and the end point is when the sample water changes color from blue to reddish-purple and remains for 10 seconds or more.

In addition, in the above operation, the case where no sample is added is considered as a blank test.

■, Preparation sample of 500 ppm aqueous solution of sample 0.171
Weigh accurately (not calculated as dry product), transfer to a triangular kolben with a stopper, and dissolve in deionized water Zoo-. This 50m is 10
Make up to volume with deionized water in a 0M volumetric flask.

(2) Calculation method/Anion equivalent value (meq/J') In the present invention, an amphoteric organic polymer flocculant is added to form flocs, and then dehydrated by a known method.
Examples of dehydrators include screw press type dehydrators,
A filter press type dehydrator, belt press type dehydrator, screw decanter, etc. can be used.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples.

In the examples, the organic polymer flocculants shown in Table 1 were used, and the inorganic flocculants were prepared as a 10% by weight aqueous solution.
The organic polymer flocculant was used as a 0.5% by weight aqueous solution. In addition, the amount of these flocculants added depends on the amount of S in the sludge.
Expressed as weight % of S.

Examples 1 and 2 pH; 6,4, SS; 2,0%, scorching range g, (hereinafter "V
TsJ); 75.1%, M-7# force IJ degree; 6
For human waste surplus sludge with properties of 35 m9/l, the second
After adding the type and amount of inorganic flocculant shown in the table and stirring for about 2 minutes, sodium hydroxide solution was added to adjust the pH to 6.0.

Two minutes after the start of pH adjustment, 1.6% of each amphoteric polymer flocculant R-1 was added to form flocs, and a dehydration test was conducted using a screw decanter. In either case, the floc produced has sufficient thickness and strength, and the dehydrated cake is flaky and has little stickiness, and the moisture content of the cake is low.
Good results were obtained in terms of SS recovery rate.

Comparative Examples 1 and 2 As the organic polymer flocculant, cationic Ni-2 was used in Comparative Example 1, and anionic A-1 was used in Comparative Example 2, and the other conditions were exactly the same as in Example 1. When the test was conducted, as shown in Table 2, the dehydrated cakes of both comparative examples were lumpy and had a high cake moisture content, and exhibited significantly worse performance than Example 1.

Comparative Examples 3 and 4 A dehydration test was conducted in exactly the same manner as in Example 1, except that the pH81M values were set to 4.0, 9, and 0, and sulfuric acid was used as the p)IvA stabilizer in Comparative Example 4. In all cases, the particle size of the flocs was small; in Comparative Example 3, although dehydration was possible, the moisture content of the cake was high; and in Comparative Example 4, dehydration was insufficient.

Examples 3 and 4 pH; 5,1, SS; 2,2%, VTS; 72,8%,
M-alkalinity; 415■/! To the sewage mixed raw sludge with the following properties, inorganic flocculants of the type and amount shown in Table 3 were added, and after stirring for about 20 seconds, sodium hydroxide solution was added to adjust the pH to 6.0. Adjusted to. Approximately 10 minutes after the start of pH adjustment, add 1.0% of each amphoteric polymer flocculant R-1.
A floc was generated by adding the flocs, and a dehydration test using a filter press was conducted. The results are shown in Table 3.
The floc particle size was good, the filter press dehydration method, which was conventionally considered difficult to apply using a polymer flocculant system, could be applied, and both the F prickly releasability of the cake and the cake moisture content were good.

Comparative Example 5 When an inorganic flocculant was added to the sludge of Example 3 in the same manner as in Example 3, the pH value became 4.0.

Therefore, when a polymer flocculant was added to form flocs in the same manner as in Example 3 without adjusting the pH, the flocs were in poor condition and hi dehydration could not be performed using a filter press.

Examples 5 and 6 pH; 5,5, SS; 2,1%, VTS; 78,1%,
To sewage mixed raw sludge with properties of "M-alkalinity" and 750m9/11, an inorganic flocculant was added, the pH was adjusted, and an organic polymer flocculant was added under the conditions shown in Table 3 in the same manner as in Example 3. A dehydration test using a belt press gave good results.

Comparative Examples 6 to 8 A dehydration test was conducted on the same sludge as in Example 5 under the conditions shown in Table 3 in the same manner as in Example 5 except that sulfuric acid was used as the pH adjuster in Comparative Example 7. Ta.

When the cationic organic polymer flocculant of Comparative Example 6 was used, the floc particle size was too small to allow dehydration.

Even when the pH adjustment value of Comparative Example 7 was low, the floc diameter was small and the dehydration state was poor.

When the pH adjustment value of Comparative Example 8 was high, although dehydration was possible, the cake moisture content showed a high value of 74.0%.

Examples 7 and 8 pH; 6.8, SS; 1.8%, v'rs; 6B, 1%
, M-Alkalinity: 3500 ■/l of sewage digested sludge was subjected to the addition of an inorganic flocculant, pH adjustment, addition of an organic polymer flocculant, and a dewatering test using a belt press under the conditions shown in Table 3. When carried out, it was possible to reduce the moisture content of the cake by about 4 to 6% compared to the conventional method.

Comparative Examples 9 to 12 A dehydration test was conducted on the same sludge as in Example 7 under the conditions shown in Table 3 in the same manner as in Example 7 except that sulfuric acid was used as the pH adjuster in Comparative Example 11. Ta.

When the cationic organic polymer flocculant of Comparative Example 9 was used, the floc particle size was too small to allow dehydration.

When the cationic organic polymer flocculant and anionic organic polymer flocculant of Comparative Example 10 were used together, the cake peelability was poor and the cake moisture content was high.

When the pH adjustment value of Comparative Example 11 is low, the floc diameter is small and the P barbed releasability of the cake is poor, and the pH of Comparative Example 12 is low.
When the adjustment value was high, the floc particle size was small and the cake moisture content was high.

[Effects of the Abolition of Ming]

As is clear from the results of Examples, the sludge dewatering method of the present invention has the following excellent effects.

(1) Since the produced floc particle size is large and the floc strength is excellent, the F prickly releasability of the dehydrated cake is excellent.

(2) Compared to the conventional method, the moisture content of the dehydrated cake is approximately 4
Since it is about 6% lower, the fuel cost during sludge incineration can be significantly reduced.

(3) Good dehydration can also be achieved using a filter press type dehydrator, which was not applicable to conventional dehydration methods using organic polymer flocculants.

Claims (2)

[Claims] (1) A method for dewatering sludge, which comprises adding an amphoteric organic polymer flocculant to organic sludge whose pH value after addition of the inorganic flocculant is 5 to 8, and then dewatering the organic sludge. (2) the amphoteric organic polymer flocculant contains a carboxyl group or a salt thereof as an anionic group, and the cation equivalent value Cv of the amphoteric organic polymer flocculant is 1.0 to 4.0 meq/g;
Anion equivalent value Av is 0.3 to 2.0 meq/g, Cv
2. The method according to claim 1, wherein the ratio of /Av is 1.5 to 8.0.