JPH08173999A - Method for dewatering sludge - Google Patents

Abstract

PURPOSE: To dewater effectively and efficiently sludge produced in sewage treatment by adding a polyferric sulfate coagulant and, after pH being adjusted, a cationic polymer coagulant in a coagulation process of sludge. CONSTITUTION: A first coagulant is added into sludge produced in sewage treatment, and the sludge, after being adjusted of its pH appropriately, is added with a second coagulant and mixed by agitation. The obtained coagulated sludge is supplied to a dewaterer to be dewatered. In such a sludge dewatering method, a polyferric sulfate coagulant is used as the first coagulant. The appropriate pH is 4.0-7.0. A cationic polymer coagulant in which the cationic equivalent is adjusted at 5.0meq/g or more by mixing polyamidine with cationic equivalent of 5.5-6.5meq/g which comprises a repeating unit indicated by the formula (where, X is an amide group, a nitrile group, an amino-HCl base, a formyl group, etc.) is used as the second coagulant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dehydrating sludge produced in sewage treatment.

[0002]

2. Description of the Related Art Generally, sludge produced in sewage treatment is an aggregate of organic matter and inorganic matter having a complicated structure, and it is difficult to separate water by dehydration operation without appropriate pretreatment. Therefore, dehydration is performed after improving the dehydration characteristics of sludge by adding a coagulant or the like.

[0003] For example, when the digested sludge obtained by digesting the first settling sludge with high temperature and the surplus activated sludge are dehydrated in a single treatment plant, the digested sludge and the surplus activated sludge are mixed, and the mixed sludge is mixed with polysulfate second After adding iron and stirring and mixing, and further adding and stirring and mixing a cationic polymer flocculant having a cation equivalent of about 4.8 meq / g such as polyacryloyloxyethylene trimethyl ammonium chloride and stirring and mixing, the obtained flocculated sludge was Dehydrated.

[0004]

However, the above-described conventional dewatering method has a problem in that strong flocs are not formed in the flocculation step and sludge is not sufficiently dewatered.

The present invention solves the above problems, and an object of the present invention is to provide a sludge dewatering method capable of effectively and efficiently dewatering sludge generated in sewage treatment.

[0006]

In order to solve the above problems, in the sludge dewatering method of the present invention, the first flocculant is added to the sludge produced in the sewage treatment to adjust the pH of the sludge to an appropriate pH. Then, in the sludge dewatering method, in which a second flocculant is added to this sludge, and the mixture is stirred and mixed, and the obtained flocculated sludge is supplied to a dehydrator to dehydrate, the first flocculant is a polyferric sulfate ferric flocculant And the suitable pH is 4.0 to 7.0,
The second flocculant has the general formula:

[0007]

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By adding a polyamidine having a cation equivalent of 5.5 to 6.5 meq / g consisting of repeating units represented by the formula (wherein X is an amide group, a nitrile group, an aminohydrochloride group, a formyl group, etc.) , Cation equivalent 5.
It is characterized by being a cationic polymer flocculant prepared at 0 meq / g or more.

[0009]

According to the above construction, by adding the poly (ferric sulfate) coagulant to the sludge and adjusting the pH to 4.0 to 7.0, the alkaline component in the sludge is consumed and the sludge in the sludge is Therefore, the hydrophilic colloid particles are charged negatively, and the negatively charged hydrophilic colloid particles are reacted with the cationic group of the cationic polymer flocculant. At this time, since the above-mentioned cationic polymer flocculant has a strong reactivity to neutralize the negative charge, the negative charge on the surface of the hydrophilic colloid particles is effectively neutralized, and flocculation and dehydration are prevented. The property is improved.

[0010]

EXAMPLES The present invention will be described below with reference to examples. Digested sludge obtained by high-temperature digestion of primary sludge generated in sewage treatment and excess activated sludge were mixed in a volume ratio of 6: 4, and the ferric polysulfate coagulant was added to the mixed sludge in an amount of iron per dry sludge weight. The pH of the mixed sludge was adjusted to 6.9 while adding and mixing with stirring so that the ratio was about 0, 3, 4%, respectively. Then, the mixed sludge was added to the general formula:

[0011]

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(In the formula, X is an amide group, a nitrile group, an amino-hydrochloric acid group or a formyl group.) A polyamidine-cationic polymer flocculant (cation equivalent of 5.5 to 6.5 meq / g, molecular weight about 3,000,000, intrinsic viscosity of 0.2% aqueous solution 50c
(p, pH 4.0-5.0) 1-2% based on the weight of dry sludge
Was added and mixed with stirring. The obtained coagulated sludge was supplied to a belt press type dehydrator for dehydration.

For comparison, the sludge was dehydrated in the same manner as above except that polyacryloyloxyethylenemethylammonium chloride quaternary salt was added instead of polyamidine.

The results are shown in the graph of FIG. In FIG. 1, the horizontal axis represents the polymer addition rate (%) (vs. TS), the vertical axis represents the cake water content (%), and polymer A is polyamidine.
The cationic polymer flocculant, Polymer B, is a quaternary salt of polyacryloyloxyethylene methyl ammonium chloride.

As can be seen from FIG. 1, in the method of the present invention in which the polymer A is added, the water content of the cake is lower than in the conventional method in which the polymer B is added, and the method of the present invention is an excellent sludge dewatering method. I can say. This is because the polymer A has a strong reactivity to neutralize the negative charge, effectively neutralizes the negative charge on the surface of the hydrophilic colloid particles of sludge, and improves the flocculation property and dehydration property. by.

In the above examples, polyamidine was used alone as the cationic polymer flocculant, but the above cation such as a mixture of polyamidine mixed with dialkylaminoethyl acrylate at a mixing ratio of 100 to 50% was used. Any mixture may be used as long as it is compatible with the conditions as the hydrophilic polymer flocculant, and the polyamidine itself can be used without being limited to the above.
Cationic polymer flocculant is 1-2 per dry sludge weight.
%, Preferably 0.6 to 1.5%.

The ferric polysulfate flocculant may be added in an amount of usually 5 to 25%, preferably 9 to 15% (corresponding to an iron content of 3 to 5% based on the weight of dry sludge) per dry sludge weight. The pH may be adjusted to 4.0 to 7.0.

The dewatering method of the present invention can be applied to digested sludge, excess activated sludge, or mixed sludge of digested sludge and excess activated sludge. In the case of mixed sludge, digested sludge and excess activated sludge are mixed. Usually, they are mixed in a ratio of 9: 1 to 1: 9, preferably 8: 2 to 2: 8.

[0019]

As described above, according to the present invention, when the sludge produced in the sewage treatment is coagulated and dehydrated, in the coagulation step, a ferric polysulfate coagulant is added to adjust the pH, and then the cation is added. Cation equivalent 5.0 meq prepared by blending 5.5 to 6.5 meq / g of polyamidine
/ G or more of the cationic polymer flocculant was added. As a result, flocculation properties can be improved more than in the past, the filterability by gravity dehydration can be enhanced, the sludge treatment amount and filtration rate can be increased, and the SS recovery rate can be increased. Also, as a solid flock,
The water content of the dehydrated cake can be reduced and the cake peeling property from the filter cloth can be improved.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a polymer addition rate (%) and a cake water content (%) in a sludge dewatering method of the present invention by comparison with a conventional sludge dewatering method.

Claims (1)

[Claims] 1. A coagulant obtained by adding a first flocculant to sludge produced in sewage treatment to adjust the pH of the sludge to an appropriate pH, and then adding a second flocculant to this sludge and mixing with stirring. In the sludge dewatering method of supplying sludge to a dewatering machine for dehydration, the first flocculating agent is a polyferric sulfate sulfate flocculant, the suitable pH is 4.0 to 7.0, and the second flocculating agent is The agent has the general formula: (In the formula, X is an amide group, a nitrile group, an amino hydrochloride group,
A cation equivalent of 5.0 meq / g by blending a polyamidine having a cation equivalent of 5.5 to 6.5 meq / g composed of a repeating unit represented by a formyl group).
A method for dewatering sludge, which is the cationic polymer flocculant prepared above.