JPS5933440B2 - Sludge dewatering method - Google Patents

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 a synthetic cationic polymer flocculant such as a quaternized dimethylamine ethyl methacrylate polymer or a Mannich modified polyacrylamide polymer, or these combined with an inorganic flocculant or a synthetic anion. Treatment is carried out by adding a polymer flocculant, but these treatments do not reduce the moisture content of the cake sufficiently and the cake is lumpy, requiring a large amount of fuel for drying and incineration. Workability such as spreading was poor, and it was necessary to add a large amount of sawdust to adjust the moisture content in the sludge composting process.

Furthermore, in the conventional method as described above, the amount of sludge treated is not sufficient, and as a result, the operating time of the dehydrator becomes long 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 carried out. , 2/3 to 415 from the lowest water level in the area between the highest and lowest water levels
This invention is intended to improve the drawbacks of these conventional methods, and it is not possible to reduce the moisture content of the dehydrated cake, improve the appearance of the cake, or increase the throughput. By combining agents and performing flocculation under specific stirring conditions, sludge flocs with strong floc strength are generated.
By lowering the water level in the centrifugal dehydrator and centrifugally dewatering the resulting flocs, the flocs are scraped up onto the water surface and dehydrated while being squeezed, thereby reducing the moisture content of the cake, improving the appearance of the cake, and improving the process. The purpose is to provide a sludge dewatering method that can increase the amount of sludge.

In this invention, chitosan is added to organic sludge and the first agitation is performed, the first agitation is strong agitation such that no flocs are generated or the diameter of the generated flocs is 2 mm or less, and then the acrylic sludge is 5 with sodium chloride as a constituent unit
Adding an anionic polymer containing 0 mol% or more and performing a second stirring, supplying the generated floc to a centrifugal dehydrator,
This sludge dewatering method is characterized by centrifugal dewatering with the water level in the dehydrator set to 1/2 or less of the middle range between the highest and lowest water levels, and the flocs are scraped up onto the water surface and dehydrated while being squeezed.

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, human waste in the treatment of sewage, human waste, industrial wastewater (e.g. food factory wastewater, fishery processing wastewater, aquifer wastewater, water pulp wastewater), etc. Examples include, but are not limited to, septic tank sludge and mixed sludge thereof, and sludge containing relatively large amounts of organic matter is the target of treatment.

Chitosan as the first flocculant is obtained by deacetylating the chitin of crustaceans such as crabs and shrimp, and chitosan itself is insoluble in water, but organic or inorganic acid salts (
Sulfates are excluded (.

), it is soluble in water.

Therefore, in the present invention, chitosan is added in the form of a water-soluble organic or inorganic acid salt.

Examples of water-soluble salts of chitosan include formates, acetates, hydrochlorides, and nitrates.

As for the addition method, the water-soluble salt of chitosan may be added as it is, but it is easier to handle and add it as an aqueous solution.
It is also preferable because it is dispersed throughout the sludge to be treated.

The anionic polymer as the second flocculant is a water-soluble linear polymer containing 50 mol% or more of sodium acrylate as a structural unit, and includes sodium polyacrylate,
These include partial hydrolysates of polyacrylamide, copolymers of acrylamide and acrylic acid (including multicomponent copolymers with other structural units), 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 30° C. using a 2N aqueous sodium hydroxide solution as a solvent.

This anionic polymer is also preferably used as an aqueous solution.

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

The flocculation method is to add chitosan to the sludge, perform a first agitation to neutralize the charge, then add an anionic polymer,
A second agitation is performed to form flocs.

In this case, if the first agitation is stronger than normal agitation (agitation that produces large flocs) to reduce the diameter of the flocs that are generated, the strength of the flocs that are generated after the second agitation will increase. , the dewatering properties of the floc are improved and the moisture content of the dehydrated cake is also reduced.

The second stirring may be normal stirring.

Strong stirring in the first stirring does not generate flocs.
Alternatively, strong stirring is performed so that the diameter of the generated flocs is less than 2 mmJJ, thereby neutralizing the electric charge of the sludge.

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 a large amount of water, so 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 small flocs of 2 or less.

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 ordinary stirring for generating flocs.

By performing such agitation and mixing, the sludge particles whose charge has been neutralized by reacting with chitosan coagulate to form flocs, producing strong and large flocs, resulting in extremely good dewatering performance. .

The stirring method in the above-mentioned 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.

Regarding the degree of stirring, when using a stirring tank equipped with a stirrer, as a guideline, strong stirring can be performed at a circumferential speed of the stirring blade of 1 to 5 m/sec, and normal stirring can be set to 0.1 to 0.5 m/sec.

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 add the chitosan to the reaction tank installed in the sludge pipe, and then inject the anionic polymer immediately before or into the dehydrator, and add the chitosan to the reaction tank installed in the sludge pipe. 2. 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 flocculation is carried out by adding an alkaline earth metal compound such as hydroxide or other alkaline earth metal compounds, the flocculation effect will be good.

In this case, the amount of the alkaline earth metal compound added to the sludge is about 200 to 100011Q/1.

The flocs generated as described above are supplied to a centrifugal dehydrator for centrifugal dehydration, either as they are or after removing the separated water.

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, 3 is a sludge pump, and 4 is a dehydrator.

The treatment method is to take out the sludge from the sludge tank 1 into the sludge supply pipe 5,
Here, chitosan is injected from the chemical injection pipe 6, passed through the line mixer 2 for first strong stirring, further stirred by the slurry feed pump 3, and anionic polymer is injected from the chemical injection pipe 7. While performing the stirring described in step 2, the water is supplied 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 from the mud supply pipe 12 through the mud supply port 14 of the inner screw 13. The sludge flocs are centrifuged by the centrifugal force caused by the rotation of the inner screw 13.

In this case, the inner barrel screw 13 advances due to the differential speed between the outer barrel bowl 11 and the inner barrel screw 13, and the sludge flocs concentrated on the peripheral wall side are scraped up to the cone part 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 chute 19.

20 is a V-pulley for rotating the outer barrel bowl 11, 21 is a bearing, and 22 is a gear box for giving a differential speed to the inner barrel screw 13.

The overflow port 18 is composed of an orifice plate, and by changing the position of the orifice, the water level in the outer body bowl 11 is changed and the length of the drain section (the portion above the water surface of the cone portion 15) is adjusted.

In the present invention, the orifice is adjusted so that the water level is 1/2 or less between the highest water level and the lowest water level, and centrifugation is performed at a water level in the dehydrator that is 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 floc is scraped up by the inner body screw 13. By moving the flocs on the inclined surface 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 making it possible to lower the moisture content of the cake.

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 rake-up speed is determined by the outer barrel bowl 11 and inner barrel screw 13.
It is determined by the differential speed of

Similarly, what is the amount of mud supplied (processing amount)? When the temperature is increased, compaction of the cake (SS) is achieved, and the moisture content is lower than when it is not used.

In the present invention, chitosan, which is a natural product, is used as a cationic flocculant as the first flocculant to neutralize the electric charge,
Since the flocs are formed using an anionic polymer based on sodium polyacrylic acid, which is compatible with this, the flocs are less sticky, strong, and highly compressible than those using synthetic cationic polymer ageing agents. The cake is produced and fed to a centrifugal dehydrator, which lowers the water level and scrapes up the floc above the water surface and dehydrates it while squeezing it. This allows the cake to be squeezed and dehydrated on the water surface. , the moisture content of the cake can be lowered, the outer shape of the cake can be reduced, and the stickiness of the cake can be reduced.

For this reason, the drying efficiency of the dehydrated cake is good, the amount of auxiliary fuel for drying and incineration can be reduced, and in the case of composting, the amount of mixed sawdust etc. can be reduced.

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 properties as a whole.

Example 1 Aerobic digestion sludge, excess activated sludge, in human waste oxidation treatment
and a mixture of flocculated sludge in the tertiary treatment with sulfuric acid band of treated water (pH 6.8-6.9, SS: 1.4
~1.8%, vSS: 68-72% [vs. 5S])
Processed according to the processing flow shown in the figure.

Since sludge contains sulfate ions, 300 μ/l of calcium chloride was added to sludge tank 1 to reduce the amount of sludge treated.
At 0 kg5S/Hr, an aqueous solution of chitosan acetate (0.5% aqueous solution viscosity 150 cP (30 rpm, B-type viscometer), colloid equivalent @ = 4.5 meq/f) was added from the chemical injection tube 6, and the first stirring was performed. Strong stirring was performed at a circumferential speed of 3 rn/sec and a floc diameter of 1.5 m, and the chemical injection pipe 7 was
An aqueous solution of 30°G sodium polyacrylate ([η] 2N-NaoH = 6.5 [dl/fI], colloid equivalent value = IO, 6meq/S') was added from the mixture and dehydrated by stirring normally. did.

The dehydrator 4 is a screw decanter of the type shown in Fig. 2 (H840L manufactured by Ishikawajima Harima Heavy Industries KK).
The radius of 1 is 20cfrL, and the centrifugal force due to rotation is 3000G.
Table 1 shows the results of a dehydration test by changing the water level of the overflow port 18.

In Table 1, the water level is expressed as a ratio from the lowest water level in the middle region, with the highest water level being 1 and the lowest water level being 0, and the addition rate is listed in the order of chitosan/sodium polyacrylate.

As a comparative example, when the water level was raised to more than 1/2, a copolymer of methyl chloride quaternary product of dimethylaminoethyl methacrylate and acrylamide (hereinafter referred to as DAM copolymer) was produced from the chemical injection pipe 6 at 30°C. -°-E/L/ratio-1: 1. [η]lN-
NaCl-7, 0 (dl/S'), colloid equivalent value =
3.6 meq/? ) and reduce the circumferential speed to 0.
．． The results are also shown when normal stirring was performed at 5 mw/sec and the diameter of the generated flocs was 4.5 mm, and no drug was injected from the drug injection tube 7.

From the above results, it can be seen that the cake moisture content, SS recovery rate, and cake appearance of the examples are superior to those of the comparative examples.

Example 2 In the treatment of Example 1, 85% of sodium acrylate and acrylamide were used instead of sodium polyacrylate.
:15 (molar ratio) copolymer (hereinafter referred to as AA copolymer) and a DAM copolymer with a molar ratio of 7:3 were used, and the results of a dewatering test were conducted by varying the amount of sludge treated. are shown in Table 2.

From the above results, it can be seen that the processing amount of the example can be larger than that of the comparative example, and that the processing result becomes better as the processing amount increases.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing one embodiment of the present invention, and FIG. 2 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, and 10 11 is a casing, 11 is an outer shell bowl, 12 is a mud supply pipe, 13 is an inner shell screw, 14 is a mud supply port, and 18 is an overflow port.

Claims (1)

[Scope of Claims] 1. Chitosan is added to organic sludge and first agitation is performed, and the first agitation is such strong agitation that no flocs are generated or the diameter of the generated flocs is 2u or less. ,
Next, an anionic polymer containing 50 mol% or more of sodium acrylate as a constituent unit is added and a second stirring is performed, and the generated flocs are fed to a centrifugal dehydrator, and the water level of the dehydrator is adjusted to a level between the highest and lowest water levels. A sludge dewatering method characterized by centrifugally dewatering the flocs to 1/2 or less of the water surface, and dewatering the flocs while scraping them up onto the water surface and squeezing them. 2. The sludge dewatering method according to claim 1, wherein the anionic polymer is one or more selected from polyacrylic acid, a partial hydrolyzate of acrylamide, and a copolymer of acrylamide and acrylic acid. 3. The sludge dewatering method according to claim 1 or 2, wherein the dehydrator is of a structure that scrapes up the cake onto an inclined surface formed on the water surface.