JP2991588B2 - Method for dewatering sludge containing calcium compound - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a fluorine-containing wastewater such as a hydrofluoric acid wastewater from a semiconductor plant or a flue gas desulfurization wastewater from a thermal power plant, which is added with a calcium compound such as slaked lime or calcium chloride to fluorinate fluorine. Such as sludge mainly containing calcium fluoride generated from a wastewater treatment step of precipitation and removal as calcium, or sludge mainly containing calcium compounds generated from the cement industry, lime manufacturing industry, etc.
The present invention relates to a method for dehydrating a sludge mainly containing a calcium compound (hereinafter sometimes simply referred to as a sludge containing a calcium compound).

[0002]

2. Description of the Related Art In a sludge mainly containing the above-mentioned calcium compound, a calcium compound which is insoluble or hardly soluble in water such as slaked lime, calcium carbonate, calcium fluoride, calcium sulfate, calcium phosphate, etc. It often contains chemicals such as activators or organic matter from biological treatment processes of general wastewater.

[0003] Conventionally, sludge containing mainly calcium compounds is dehydrated without chemical injection.
A method of adding and flocculating and dehydrating an anionic polymer flocculant or a cationic polymer flocculant, and a method of flocculating and dehydrating using an anionic polymer flocculant and a cationic polymer flocculant in combination are known. .

[0004] However, in the method of dehydrating without chemical injection, a dehydrator such as a belt press dehydrator or a screw press dehydrator that needs to coagulate sludge during dehydration cannot be used. It is limited to a filter press type dehydrator, and has a disadvantage that the dehydration efficiency is poor.

In the method using either an anionic polymer flocculant or a cationic polymer flocculant, a change in the calcium compound content in the sludge, a change in the composition and content of other components other than the calcium compound, and the like. It is difficult to perform stable dehydration treatment, and there is a drawback that efficient dehydration treatment cannot be performed because the strength of generated flocs is weak.

In the method using both an anionic polymer flocculant and a cationic polymer flocculant, it is easier to cope with the property change of the calcium compound-containing sludge than in the case of using each of them alone, but a stable treatment is performed. Is still not enough. Also, to perform efficient dehydration processing,
The strength of the flocs generated was not sufficient.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art, and is not affected by the change in the properties of the calcium fluoride- containing sludge, so that the calcium fluoride- containing sludge can be efficiently produced. Solid-liquid separation and dehydration of suspended solids
It is an object of the present invention to provide a method for dehydrating a sludge containing lucium .

[0008]

Means for Solving the Problems In order to achieve the above object, the present inventors have studied various methods, and as a result, have found a method for stably and efficiently dewatering a sludge containing a calcium compound, and have achieved the present invention. It was completed.

That is, the present invention is characterized in that an amphoteric polymer coagulant having a cationic group and an anionic group in one molecule is added to sludge mainly containing calcium fluoride to coagulate a suspended substance and dehydrate it. And a method for dewatering sludge containing calcium compounds.

[0010] The sludge containing mainly calcium fluoride in the present invention, the fluorine-containing waste water, such as waste water of flue gas desulfurization of hydrofluoric acid wastewater and thermal power plants of the semiconductor factory if example embodiment, with the addition of slaked lime and calcium chloride precipitate fluorine as calcium fluoride, and a sludge containing mainly calcium fluoride discharged from removing.

The amphoteric polymer flocculant used in the present invention is not particularly limited as long as it is a polymer compound having a cationic group and an anionic group in one molecule. For example, a tertiary salt of dimethylaminoethyl (meth) acrylate and Copolymer of one or more cationic monomers selected from quaternary salts and the like and one or more anionic monomers selected from acrylates, 2-acrylamido-2-methylpropanesulfonate and the like Alternatively, a ternary copolymer of the above cationic monomer and anionic monomer with a nonionic monomer such as acrylamide may be used.

The monomer composition ratio of the amphoteric polymer flocculant used in the present invention is not particularly limited, but is 8 to 95 mol% of a cationic monomer, 4 to 30 mol% of an anionic monomer and a nonionic It is preferable that the monomer content is 85 mol% or less.

[0013] In the second invention, an amphoteric polymer flocculant having a cationic group and an anionic group in one molecule is added to a sludge mainly containing a calcium compound, and then an anionic polymer flocculant is further added. The present invention relates to a method for dewatering calcium compound-containing sludge, which comprises coagulating and dewatering a suspended substance.

The second invention in which an anionic polymer flocculant is added after an amphoteric polymer flocculant is added, is to further increase the floc strength by the anionic polymer flocculant, and to obtain a water content, SS More favorable results are obtained in terms of recovery.

The anionic polymer coagulant used in the second invention is, for example, a copolymer of acrylate and acrylamide, acrylamide and acrylate
Tertiary copolymer of acrylamide-2-methylpropanesulfonate, polyacrylate and the like.

The dehydrator used for dehydration in the present invention is not particularly limited. For example, a screw press type dehydrator,
Examples thereof include a belt press type dehydrator and a centrifugal dehydrator, and a screw press type dehydrator is particularly preferable.

The present invention relates to a method of adding an amphoteric polymer coagulant having both a cationic group and an anionic group in one molecule to a sludge mainly containing a calcium compound, coagulating a suspended substance in the sludge, and then dehydrating the sludge. Thus, a more stable dewatering effect can be obtained as compared with the conventional method. The mechanism by which this effect is obtained by the present invention is not clear, but calcium compound-containing sludge often aggregates with any of anionic polymer flocculants and cationic polymer flocculants. Is thought to have a site where each of the anion group and the cation group acts, and the amphoteric polymer flocculant having both the anion group and the cation group in one molecule is strong by acting on both sites. It is presumed that a large floc is generated.

As described above, according to the present invention, a stable coagulation and dewatering effect can be obtained even if the properties of sludge mainly containing a calcium compound are largely changed.

An embodiment of the present invention will be described below, but the present invention is not limited to the following embodiment.

[0020]

EXAMPLES Table 1 shows the amphoteric polymer flocculants, anionic polymer flocculants and cationic polymer flocculants used in Examples and Comparative Examples, and the properties of the sludge used in Examples and Comparative Examples. Table 2 shows the main components of the suspended substance. The sludge used was sludge containing calcium fluoride, which was generated from a hydrofluoric acid wastewater treatment process in a semiconductor factory.

[0021]

[Table 1]

[0022]

[Table 2]

As is clear from Table 2, the suspended solids contained in the used sludge contain a large amount of fluorine and calcium. Therefore, these sludges contain calcium fluoride as a calcium compound. It is clear that a lot is included. In each of the sludges, the sludges B and C contain a large amount of aluminum, and the sludge B also contains a large amount of silicon.

Examples 1 to 3 and Comparative Examples 1 to 3 Polymer flocculants were added to the test sludges A to C shown in Table 2 at the ratios shown in Table 3, and the suspension was agglomerated by stirring. The flocculated floc thus formed was dehydrated by a screw press type dehydrator (trade name “SPS-305CPHS”, manufactured by Organo Corporation).

In the case of the combined system of Example 3 and Comparative Example 3, the first polymer flocculant was added to the test sludge and stirred, and then the second polymer flocculant was added and stirred to produce sludge. The coagulation floc was similarly dehydrated by performing a dehydration treatment.

Table 4 shows the results of the dehydration test. The floc strength in Table 4 indicates that ◎ is the strongest and weakens in the order of Δ, Δ, and × below.

[0027]

[Table 3]

[0028]

[Table 4]

As is evident from the results in Table 4, Examples 1 and 2 in which the amphoteric polymer flocculant of the present invention was used alone had flocs having a size and strength sufficient for dehydration treatment. Good results were obtained in both the SS recovery rate and the water content of the dehydrated cake. Example 3 using an amphoteric polymer flocculant and an anionic polymer flocculant in combination
For both sludges, the SS recovery rate and the water content of the dewatered cake were even better, and a stable dewatering treatment could be performed.

On the other hand, Comparative Example 1 in which each of the anionic polymer flocculant and the cationic polymer flocculant was used alone,
In Comparative Example 2, all of the floc strength, the SS recovery rate, and the water content of the dewatered cake were worse than those of the present invention, and there were cases where dewatering was impossible depending on the sludge.

Comparative Example 3 in which a cationic polymer flocculant and an anionic polymer flocculant were used in combination was compared with Comparative Example 1 and Comparative Example 2 in any of floc strength, SS recovery rate and dehydrated cake water content. However, it was inferior to that of the present invention, and was not sufficient for efficient dehydration.

In the method of the present invention, the SS recovery rate and the water content of the dewatered cake were better than those of the conventional method for any of the calcium compound-containing sludges, and efficient dehydration treatment was performed.

[0033]

According to the method of the present invention , calcium fluoride
In the dehydration treatment of sludge mainly containing water, the generated flocs have sufficient strength, and it is possible to improve the SS recovery rate, reduce the water content of the dewatered cake, and the like. In addition, fluoride
It is easy to respond to changes in properties, components, and the like of sludge mainly containing calcium chloride, and enables efficient dehydration treatment.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-90098 (JP, A) JP-A-64-4207 (JP, A) JP-A-2-14799 (JP, A) JP-A-4- 193308 (JP, A) JP-A-62-238000 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C02F 11/00-11/20 B01D 21/01

Claims (3)

(57) [Claims] 1. Calcium characterized in that a suspended substance is flocculated by adding an amphoteric polymer flocculant having a cationic group and an anionic group in one molecule to sludge mainly containing calcium fluoride to dehydrate the sludge. A method for dewatering compound-containing sludge. 2. A sludge containing mainly calcium fluoride, to which an amphoteric polymer flocculant having a cationic group and an anionic group in one molecule is added, and further an anionic polymer flocculant is added to the sludge. A method for dewatering calcium compound-containing sludge, comprising coagulating and dewatering. 3. Dehydration using a screw press type dehydrator.
The method according to claim 1 or 2, wherein
Dehydration method.