JP4287730B2 - Sludge dewatering method - Google Patents

Description

Detailed Description of the Invention

  The present invention relates to a method for dewatering sludge, and more particularly to a method for dewatering sludge by using a dicyandiamide-based flocculant and an organic polymer flocculant in combination, and in particular, a dewatering method effective for hardly dewaterable organic sludge.

Organic polymer flocculants exhibit high cohesiveness with a small amount of addition, and since their development, they are frequently used for flocculation of pollutants in sludge, concentration of sludge, and dehydration instead of the conventional inorganic flocculants. In particular, cationic polymer flocculants have been frequently used alone. However, in recent years, sludge has become difficult to dehydrate due to an increase in sludge generation and changes in sludge properties, and in terms of sludge treatment, dehydrated cake moisture content, SS recovery rate, cake peelability from filter cloth, etc. Further improvement is required, and it is difficult to cope with the cationic polymer flocculant alone.

In order to cope with such a situation, various methods of using organic polymer flocculants having different physical properties and structures in combination have been proposed. For example, a cationic polymer flocculant, an anionic polymer flocculant, and a sludge dewatering agent containing an acidic substance (Japanese Patent Publication No. Sho 63-52527), an amphoteric polymer flocculant and an acrylate cationic polymer flocculant are used in combination. Method (JP-A-2-31899), a method using a polyamidine-based flocculant and an amphoteric polymer flocculant (JP-A-7-223000), a combined polyamine cationic polymer flocculant and an amphoteric polymer flocculant Many dehydrating agents and treatment methods have been disclosed, such as a method for conducting an anionic polymer flocculant and an amphoteric polymer flocculant (Japanese Patent Laid-Open No. 2003-117600).

While many methods for using two or more organic polymer flocculants in combination have been proposed in this manner, many methods for using an inorganic flocculant and an organic polymer flocculant in combination have also been proposed. This is presumably because inorganic flocculants can increase the neutralization rate of sludge more often than cationic polymer flocculants, and are particularly effective in treating hardly dewaterable sludge. For example, a method in which an inorganic flocculant and an amphoteric polymer flocculant are used in combination (Japanese Patent Laid-Open Nos. 63-158200, 2-180700, 4-59100, 7-256300, etc.) Of using an agent, an anionic polymer flocculant, and an amphoteric polymer flocculant (JP-A-6-134213, JP-A-2003-251399), a method of using an inorganic flocculant and an anionic polymer flocculant in combination (JP-A-10-57967, JP-A-2000-185204), a method of using a cationic polymer flocculant and an inorganic flocculant in combination (JP-A-9-24400, JP-A-2002-166300) and the like are disclosed. ing.

However, although the method using an inorganic flocculant improves the dewaterability of the hardly dewaterable sludge, it has the following various problems.
(1) The inorganic flocculant component is highly acidic and corrodes equipment.
(2) Depending on the sludge, the pH is excessively lowered and the performance of the polymer flocculant to be added next is lowered, so that neutralization may be required, and the operation becomes complicated.
(3) Since the inorganic flocculant is added in a large amount, and the amount of dehydrated cake increases accordingly, the disposal cost increases.
(4) When sludge is fertilized, the metal component derived from the inorganic flocculant becomes a problem.

Problems to be solved by the invention

A method using a combination of an inorganic flocculant and an organic polymer flocculant, particularly an amphoteric polymer flocculant, is effective for the treatment of highly organic and hardly dewatering sludge. It has many problems. An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for efficiently dewatering various sludges, particularly hardly dewatering organic sludge.

Means for solving the problem

As long as the inorganic flocculant is used, it is difficult to eliminate the above-mentioned problems, and various investigations of treatment agents in place of the inorganic flocculant were conducted. As a result, focusing on the effect of dicyandiamide type flocculant among many treatment agents, as a result of investigation, it was found that the object of the present invention can be achieved by using dicyandiamide type flocculant and organic polymer flocculant in combination. The present invention has been completed.

That is, the present invention is to add a dicyandiamide-based flocculant and an amphoteric polymer flocculant or an amphoteric polymer flocculant to a sludge and add and mix sequentially or simultaneously to dehydrate the sludge. It is about how to do. Regarding the dewatering of sludge using a dicyandiamide-based flocculant, JP-A-54-92572 discloses a method in which a dicyandiamide-formaldehyde condensation polymer flocculant and a chitosan-based cationic polymer flocculant are used in combination. However, there are no other examples of use, and the method of the present invention can be said to be a novel method.

The dicyandiamide flocculant used in the present invention is a water-soluble dicyandiamide / formaldehyde condensate or dicyandiamide / formaldehyde / ammonium chloride condensate. Basically, a product obtained by adding formaldehyde to dicyandiamide and condensing it in the presence of an acid or an ammonium salt thereof and commercially available as an aqueous solution can be used.

As the amphoteric polymer flocculant used in the present invention, a copolymer of an anionic monomer and a cationic monomer, a copolymer of an anionic monomer, a cationic monomer and a nonionic monomer, or an anionic monomer and a cationic monomer are used. Mennich modified products or Hoffmann degradation products of the copolymer can be mentioned. Specific examples of the cationic monomer include tertiary or quaternized products such as dialkylaminoalkyl acrylate, dialkylaminoalkyl methacrylate, and dialkylaminoalkyl acrylamide. For example, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethyl Specific examples include tertiary or quaternized aminopropylacrylamide, but are not limited thereto. Examples of the anionic vinyl monomer include, but are not limited to, acrylic acid, methacrylic acid, vinyl sulfonic acid, 3-methacryloyloxypropane sulfonic acid, and alkali metal salts and ammonium salts thereof. Examples of nonionic vinyl monomers include, but are not limited to, vinyl group-containing amides such as acrylamide and methacrylamide, vinyl group-containing nitriles, and alkyl esters of (meth) acrylic acid.

Examples of the cationic polymer flocculant used in the present invention include dimethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, a quaternary salt or a homopolymer of the quaternary salt thereof, and acrylamide or methacrylic acid thereof. Examples thereof include a copolymer with amide, a Hoffman degradation product of polyacrylamide or polymethacrylamide, and polyamidine.

Examples of the anionic polymer flocculant used in the present invention include sodium acrylate polymer, copolymer of sodium acrylate or sodium methacrylate and acrylamide or methacrylamide, partial hydrolysis of acrylamide polymer or methacrylamide polymer. And terpolymers of acrylamide or methacrylamide and sodium acrylate or sodium methacrylate and sodium 2-acrylamido-2-methylpropanesulfonate.

In the present invention, when each flocculant is added to sludge, the optimum method varies depending on the sludge properties, but in general, a dicyandiamide type flocculant is added first, followed by an organic polymer flocculant. Is preferred. However, it is also possible to add each coagulant simultaneously. Regarding the addition amount, the dicyandiamide-based flocculant exhibits an effect by adding 50 to 1000 ppm to the sludge, but a more preferable addition amount is 100 to 600 ppm. Moreover, when using a dicyandiamide type | system | group flocculant and an amphoteric polymer flocculant, the addition amount has the preferable range of 1: 0.1-1: 2 by weight ratio. When a dicyandiamide type flocculant, a cationic polymer flocculant, and an anionic polymer flocculant are used, the weight ratio is preferably in the range of 1: 0.1: 0.1 to 1: 2: 2. As long as the effect of the present invention is not affected, sulfamic acid and other additives can be added to the flocculant as necessary.

By applying the method of the present invention described above to various sludges, it was confirmed that a dehydrated cake having a large floc diameter, a low water content and excellent peelability was obtained. The method of the present invention is particularly effective for the dehydration treatment of hardly dewatering organic sludge such as surplus sludge, mixed sludge, digested sludge, etc. generated in the treatment of sewage and wastewater. In comparison, the same or higher effects can be obtained, and the addition amount is small and the operation is easy.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

The following flocculants were used in the following comparative examples and examples.
Dicyandiamide flocculant: 55% aqueous solution of dicyandiamide-formaldehyde-ammonium chloride condensate (trade name: Zetag 7103, manufactured by Ciba Specialty Chemicals)
Amphoteric polymer flocculant: methacrylate sulfate (45) -acrylamide (46) -acrylic acid (9) copolymer (trade name D-330E, Kayafloc Co., Ltd.)
Cationic polymer flocculant: acrylate medium cation (Kayafloc Co., Ltd. trade name C-599-1RM)
Anionic polymer flocculant: Acrylamide-based moderately weak anion (Kayaflock Co., Ltd. trade name A-200)
Inorganic flocculants: polyferric sulfate (trade name Polytetsu, Nippon Steel Mining Co., Ltd.), polyaluminum chloride (trade name PAC260A, Taki Chemical Co., Ltd.)

As the test sludge, the hardly dewaterable surplus sludge from the slaughterhouse was used. The sludge properties are as follows.
pH: 6.25
TS: 1.50%
SS: 1.41%
VTS: 80.7%
M alkalinity: 440ppm
Coarse fiber: 5.0%

Example 1
100 ml of sludge was taken in a 300 ml beaker, and a predetermined amount of dicyandiamide-based flocculant (DD) and amphoteric flocculant (D-330E) were sequentially added with stirring, followed by stirring at 350 rpm for 60 seconds. After measuring the aggregation state and the floc diameter, the relationship between the filtration time and the filtrate amount was measured with a Nutsche funnel (filtration area 20 cm ² ) covered with a 60 mesh nylon filter cloth, and the filterability was observed. The obtained cake was sandwiched between 60 mesh nylon filter cloths and squeezed with a pressure dehydration tester at a surface pressure of 0.5 kg / cm 2 for 1 minute, and then the peelability of the cake from the filter cloth and the cake moisture content were determined. The DD addition amount was changed from 300 ppm to 500 ppm, and D-330E was kept constant at 100 ppm. The results are shown in Table 1. The flock diameter, filtration rate, cake moisture content, and peelability all showed very good results.

Comparative Example 1
In Example 1, a test was conducted with the DD addition amount set to zero. The results are shown in Table 1. Compared with the case where DD was added, both dehydration and peelability were greatly reduced.

Example 2
In Example 1, the same test was conducted except that the amount of D-330E added was kept constant at 120 ppm. The results are shown in Table 1.

Comparative Example 2
In Example 2, a test was conducted with the DD addition amount set to zero. The results are shown in Table 1.

Example 3
In Example 1, the same test was conducted except that the amount of D-330E added was constant at 140 ppm. The results are shown in Table 1. Increasing the amount of amphoteric flocculant tended to increase the effect.

Comparative Example 3
In Example 3, a test was performed with the DD addition amount set to zero. The results are shown in Table 1.

Comparative Example 4
In Example 1, the same test was performed using polyaluminum chloride (PAC) instead of the dicyandiamide type flocculant. The PAC addition amount was changed from 300 to 3000 ppm, and the addition amount of the amphoteric flocculant D-330E was kept constant at 100 ppm. The results are shown in Table 2.

Comparative Example 5
In Comparative Example 1, the same test was performed using polyferric sulfate (polyiron) instead of polyaluminum chloride. About what the pH fell by polyiron addition, caustic soda was added and it adjusted to pH 6.0. The results are shown in Table 2.

Example 4
In Example 1, instead of the amphoteric flocculant (D-330E), the cationic flocculant (C-599-1RM), the anionic flocculant (A-200), and sulfamic acid were used in a weight ratio of 7: 2: The same test was performed except that the aqueous solution (CA) mixed and dissolved in No. 1 was added. The results are shown in Table 4. The effect was almost the same as when using the amphoteric flocculant.

The invention's effect

The method of the present invention has a large floc diameter compared to conventional sludge dehydrating agents and sludge treatment methods, various filtration sludges, especially organic difficult-to-dehydrate sludges that are difficult to treat with sludge, filtration rate, cake water content. The rate and the peelability of the dehydrated cake were both very good. This is a useful method that exhibits an effect equal to or higher than that of a conventional method of using an inorganic flocculant and an organic polymer flocculant without using an inorganic flocculant.

Claims (1)

  Sludge characterized by adding a dicyandiamide-based flocculant and an amphoteric polymer flocculant or an amphoteric polymer flocculant sequentially or simultaneously to the sludge for dehydration. Dehydration method.