JPS5858200A - Method of dehydrating sludge - Google Patents

Abstract

PURPOSE:To lower the moisture content ratio of cake, by successively adding chitosan and an anionic polymer containing a specified amount of sodium acrylate to organic sludge, and dehydrating the formed flocks to a specified water level by a dehydrator. CONSTITUTION:Organic sludge is mixed with 0.5-4wt% chitosan and primarily agitated, to neutralize the electrical charge of the sludge and to improve the dehydrating property of flocks. Said chitosan is added in the form of a water-soluble organic or inorganic salt. Thereafter, 0.2-3wt% an anionic polymer containing 50mol% or more sodium acrylate as a constitutional unit is added, and the secondary agitation is carried out to form flocks. The anionic polymer is polyacrylic acid, etc. The formed flocks are controlled below about 2mm., supplied to a centrifugal dehydrator and centrifugally dehydrated thereby. The dehydration is hence performed by controlling the water level of the dehydrator below a half of an intermediate zone between the maximum and minimum water levels.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for centrifugal dewatering of organic sludge, and particularly to a method for coagulating organic sludge and dewatering it in a centrifugal dewaterer.

Conventionally, centrifugal dewatering of organic sludge has been carried out using synthetic cationic polymer flocculants such as quaternized dimethylaminoether methacrylate polymers or Mannich modified polyacrylamide polymers, or synthetic cationic polymer flocculants combined with these inorganic flocculants or synthetic polymers. Treatment is performed by adding anionic polymer flocculants, but these treatments do not reduce the moisture content of the cake sufficiently and the cake is lumpy and bulky.For this reason, a large amount of fuel is required for drying and incineration, which makes it difficult to restore agricultural land. Workability such as spraying on the site was poor, and in the sludge composting process, it was necessary to add a large amount of sawdust to adjust the moisture content. Furthermore, in the conventional method as described above, the amount of sludge treated is not sufficient, resulting in a disadvantage that the operating time of the dehydrator becomes longer and the number of dehydrators installed increases.

Generally, centrifugal dehydrators are equipped with an orifice plate to adjust the water level inside the dehydrator, but the sludge flocs produced by conventional methods have weak floc strength, so if the water level is lowered, the cake will not be discharged. , Minimum water level force in the intermediate area between the highest water level and the lowest water level v3 ~ 415
It is not possible to reduce the moisture content of the dehydrated cake, improve the appearance of the cake, or increase the throughput.

This invention is intended to improve the drawbacks of such conventional methods.By performing flocculation using a combination of specific flocculants, lowering the water level of the centrifugal dehydrator and centrifugally dehydrating the resulting flocs, the water content of the cake can be reduced. The purpose of the present invention is to provide a sludge dewatering method that can reduce the amount of sludge, improve the appearance of the cake, and increase the throughput.

In this invention, chitosan is added to organic sludge, the first stirring is performed, and then an anionic floc containing 50 mole or more of sulfur acrylate as a constituent unit is supplied to a centrifugal dehydrator, and the water level of the dehydrator is This is a sludge dewatering method characterized by performing centrifugal dewatering by reducing the water level to 1/2 or less of the intermediate range between the highest water level and the lowest water level.

The sludge that can be treated in the present invention is organic sludge,
For example, initial settling sludge, excess activated sludge, anaerobic or aerobic digested sludge, coagulated sedimentation sludge, Examples include, but are not limited to, primary sludge and mixed sludge, and sludge containing a relatively large amount of organic matter is the target of treatment.

Chitosan as the first flocculant is obtained by deacetylating the chitin of crustaceans such as shrimp, and chitosan itself is not bathable in water, but organic acid salts or inorganic acid salts (7. excluding 4 arate salts), it is soluble in water. Therefore, in the present invention, chitosan is added in the form of a water-bathable organic or inorganic acid salt. Examples of water-bathable salts of chitosan include formates, acetates, hydrochlorides, and nitrates. Regarding the addition method, the water-soluble salt of chitosan may be added as it is, but it is preferable to add it as a water bath liquid because it is easier to handle and is dispersed throughout the sludge to be treated.1. .

The anionic polymer as the second flocculant is a water-bathable linear polymer containing 50 moles or more of sodium acrylate as a structural unit, sodium polyacrylate,
Partial hydrolysates of polyacrylamide, copolymers of acrylamide and acrylic acid (including multicomponent copolymers with other structural units), and the like can be used, and one or more of these can be used. Although the degree of polymerization is not particularly limited, it is usually preferable that the intrinsic viscosity is about 1 to 15 as determined at 60° C. using a 2N aqueous sodium hydroxide solution as a solvent. This anionic polymer is also desirably used as a water bath liquid.

The amount of these flocculants added depends on the properties of the sludge (e.g. pH, S
Generally speaking, the amount of chitosan is 0.4 to 5'wt% (vs. SS) and the anionic polymer is approximately 0.2-3 wt% (vs. Ss). .

The flocculation method involves adding chitosan to sludge, performing a first stirring to neutralize the charge, then adding an anionic polymer, and performing a second stirring to form flocs. In this case, the first agitation may be normal agitation (stirring to the extent that large flocs are generated), but if the diameter of the flocs generated is reduced by agitation stronger than normal agitation, the dehydration of the flocs will be improved. As a result, the moisture content of the dehydrated cake also decreases. The second stirring may be normal stirring.

The strong stirring in the first stirring is done with enough force to prevent flocs from forming.
Alternatively, the electric charge of the sludge is neutralized by strong stirring such that the diameter of the flocs produced is 2 mm or less.

In the conventional two-stage flocculation method, the objective is to generate as large a floc as possible, so the first flocculant is added to generate a large floc, and the second flocculant is added to generate an even larger floc. Although the flocs produced in this way were large and had good sedimentation properties, they were not suitable for centrifugal dehydration. That is, the inside of the floc is unreacted, the electric charge is not neutralized, and it contains water for a long time, and even if centrifugal dehydration is performed, the moisture inside the floc cannot be removed. Therefore, there was not much difference in dewatering performance between the sludge and the one-stage flocculated sludge.

In the present invention, the entire sludge is reacted by strong stirring after the addition of chitosan, and the electric charge of the sludge is neutralized, thereby improving the dewaterability of the floc produced by adding an anionic polymer. In order to neutralize the electric charge of the sludge, it is better not to generate flocs during stirring and mixing, and even if flocs are generated, it is necessary to limit the generation to two or less small flocs. For this reason, as described above, the first stirring is performed with stronger stirring than the normal stirring for generating flocs.

After neutralizing the charges as described above, an anionic polymer is added and mixed with stirring to form flocs.

The stirring in this case may be normal stirring for generating all the flocs. By carrying out such agitation and mixing, the sludge particles whose charges have been neutralized by reacting with chitosan coagulate, and the total aqueous properties of the flocs are extremely improved.

The stirring method in the above stirring and mixing is not particularly limited, and may include stirring using a stirring blade in a stirring tank, stirring by a flow in a line mixer or piping, stirring by passing through a pump such as a centrifugal pump, etc. As for the degree of stirring, when using a stirring tank equipped with a stirrer, as a guide, strong stirring is performed at a circumferential speed of the stirring blade of 1 to 5 m/see,
Normal stirring can be 01-0.5 rn/see. A preferred flocculation method is to add chitosan immediately before the line mixer installed in the sludge piping or to the reaction tank and react with the first stirring, then inject the anionic polymer immediately before or into the dehydrator, and then in the machine. A second agitation is performed to generate flocs. If the sludge to be treated contains sulfate ions, the generated flocs will become smaller and the flocculation effect will deteriorate. If the entire flocculation is carried out by adding an alkaline earth metal compound such as a hydroxide or an alkaline earth metal compound such as a hydroxide, the flocculation effect will be good. In this case, the amount of alkaline earth metal compound added to the sludge is 200 to 1000 m9/l! degree.

The flocs generated as above are as they are! After removing the water or separated water, supply it to a centrifugal dehydrator and perform centrifugal dehydration. In this case, the dehydration process is performed by setting the water level in the dehydrator to 1/2 or less of the intermediate range between the highest water level and the lowest water level.

This will be explained below with reference to the drawings. FIG. 1 is a system diagram showing one embodiment of the present invention, and FIG. 2 is a vertical sectional view of the dehydrator.

In FIG. 1, 1 is a sludge tank, 2 is a line mixer, 6 is a sludge pump, and 4 is a dehydrator. The treatment method is to take out the sludge from the sludge tank 1 to the supply pipe 5, inject chitosan from the chemical injection pipe 6, pass it through the line mixer 2 for first strong stirring, and further stir it at the hot water supply Bonzoro.・At the same time, inject the anionic polymer from the drug injection pipe 7,
While performing the second stirring, the mixture is fed to the dehydrator 4 and subjected to centrifugal dehydration.

The dehydrator 4 is shown in FIG. 2, and feeds mud into the outer bowl 11 rotating inside the casing 10 through the mud supply pipe 12 and the inner barrel screw 16. ,
The sludge flow and ivy are centrifuged by the centrifugal force generated by the outer bowl 11 and the inner barrel screw 160 rotations. In this case, the inner barrel screw 16 advances due to the differential speed between the outer barrel bowl 11 and the inner barrel screw 16, and the sludge flocs concentrated on the peripheral wall side are scraped up to the cone portion 15 by the centrifugal force, and the solid chute is sent from the cake outlet 16. It is discharged on 17th.

On the other hand, the separated water is discharged from the overflow port 18 to the liquid unit 19. 20 is a V pulley for rotating the outer bowl 11 times, 2
1 is a bearing, and 22 is a gear box for applying a differential speed to the inner barrel screw 16.

The overflow port 18 consists of an orifice plate, and by changing the position of the orifice, the water level in the outer body bowl 11 is changed to adjust the length of the draining section (the portion above the water surface of the cone portion 15. 1/2 of the middle area between the lowest water level and the water level
Adjust the orifice so that the water level is as shown below, and perform centrifugation with the water level in the dehydrator shallower than in the conventional method.

In centrifugation, the solid content is concentrated on the periphery and the liquid part is separated on the inside, so it is better to separate the solid solution from both ends by raising the water level. On the other hand, in the present invention, since strong and highly compacted flocs are generated, the water level of the dehydrator is lowered to expose the cone portion 15 above the water surface, and the flocs are scraped up by the inner screw 16 to form the cone portion. By moving the flocs on the inclined surface of No. 15, the free water adhering to the flocs can be drained, and the internal moisture can also be squeezed out by squeezing with a screw, thereby lowering the di-cake moisture content. .

. If the scraping speed by the inner barrel screw 13 is as small as possible without deteriorating the SS recovery rate, the residence time in the cone portion 15 will be longer and the cake will be compacted, resulting in a lower cake moisture content. This raking speed is determined by the differential speed between the outer bowl 11 and the inner screw 13, and as the differential speed decreases, the raking speed decreases. Similarly, if the amount of mud supplied (processing amount) is increased, consolidation of the cake (SS) will be achieved,
In the present invention, chitosan, a natural product, is used as the cationic flocculant as the first flocculant to neutralize the charge, and an anionic polymer based on boria sodium acrylate, which is compatible with chitosan, is used. This creates flocs that are less sticky, stronger, and more compact than those using synthetic cationic polymer flocculants, and are fed to a centrifugal dehydrator to lower the water level. By dehydrating, the cake can be squeezed on the water surface to dehydrate the cake, thereby reducing the moisture content of the cake, reducing the outer shape of the cake, and reducing the stickiness of the cake. Therefore, the drying efficiency of the dehydrated cake is high, and the drying and
Not only does it require less auxiliary fuel for incineration, but in the case of composting, it is possible to reduce the amount of Jl mixed in with sawdust and the like. In addition, the amount of treatment in the dehydrator can be increased, and by increasing the amount of treatment, the moisture content of the cake is further reduced, resulting in stable treatment performance as a whole.

Example 1 Aerobic digested sludge, excess activated sludge, in human waste oxidation treatment
and a mixture of flocculated sludge in the tertiary treatment with sulfuric acid band (pH 6,8-6.9. SS: 1.4-1
．． 8%, vSS: 68-72% [vs. 5S]) was treated according to the processing flow shown in FIG. Since sludge contains sulfate ions, calcium chloride 'i 300 is added to sludge tank 1.
m9/l was added to reduce the amount of sludge treated to 70kg5 S/l.
As Hr, the entire aqueous solution of chitosan acetate (05 water bath liquid viscosity 150 cPr 30 rpm, B-type viscometer], colloid equivalent value -4.5 meq/g) was added from the chemical injection pipe 6, and the entire aqueous solution was added from the chemical injection pipe 7. A water bath solution of sodium polyacrylate ([η] 2N-NaoH = 6.5 [dl/g], colloid equivalent value = 10.6 meq/g) was added and dehydrated.

The dehydrator 4 is a screw decanter of the type shown in Fig. 2 (H840L manufactured by Ishikawajima Harima Heavy Industries KK),
The radius is 20CTL, the centrifugal force due to rotation is 3000G, and the results of a dehydration test by changing the water level of the overflow port 18 are
Shown below. In Table 1, the water level is determined by the ratio from the lowest water level in the middle area, where the highest water level is 1 and the lowest water level is 0.
The addition rate is listed in the order of chitosan/sodium polyacrylate.

As a comparative example, when the water level is raised to more than 1/2 of the total, and when a copolymer of methyl chloride quaternized dimethylaminoethyl methacrylate and acrylamide (hereinafter referred to as DAM copolymer) is added from the chemical injection pipe 6 at 60°C ...Molar ratio=1:1, [η]1N-Nac4=
ZOCdI14i], colloid equivalent value = 3.6 me
The results obtained when an aqueous solution of >q/g was injected and no drug was injected from the drug injection tube 7 are also shown.

It can be seen that the cookie moisture content, S/S recovery rate, and cake appearance are superior compared to the above.

Example 2 In the treatment of Example 1, 85% of sodium acrylate and acrylamide were used instead of sodium polyacrylate.
: Results of dewatering tests using a 15 (mole ratio) copolymer (hereinafter referred to as AA copolymer) and a DAMAA copolymer with a molar ratio of 7:B, and varying the amount of sludge treated. From the results of 1 or more shown in Table 2, it can be seen that the example can increase the processing ambiguity more than the comparative example, and the processing results become better as the processing amount increases.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing one embodiment of the present invention, and FIG. 12 is a vertical sectional view of a dehydrator, in which 1 is a sludge tank, 2 is a line mixer, -3 is a sludge pump, 4 is a dehydrator, 10 11 is a casing, 11 is an outer shell bowl, 12 is a mud supply pipe, 16 is an inner shell screw, 14 is a mud supply port, and 18 is an overflow port. Representative Patent Attorney Yanagihara Inari

Claims (1)

[Claims] First stirring is performed by adding chitosan to CI+organic sludge, then acrylic acid is added, and second stirring is performed by adding an anionic polymer containing 50 mol or more of IJium as a constituent unit. The generated flocs are fed to a centrifugal dehydrator, and the water level of the dehydrator is set to 1, which is between the highest water level and the lowest water level.
．． A sludge deicing method characterized by centrifugal dehydration at a temperature of /2 or less (2) Anionic polymer is maryacrylic acid, ac+)
/l/7 Sludge dewatering method (3) according to claim 1, wherein the first stirring is one or more selected from a partial hydrolyzate of amide and a copolymer of acrylamide and acrylic acid. The sludge dewatering method according to claim 1 or 2, in which the agitation is so strong that no flocs are generated or the diameter of the generated flocs is 2 m1R or less 14) The dehydrator is formed on the water surface. The sludge dewatering method according to any one of claims 1 to 3, which has a structure of scooping up a cake on an inclined surface.