JPH06343998A - Dehydration process for calcium compound containing sludge - Google Patents

Abstract

PURPOSE:To provide a hydration process for sludge containing mainly a calcium compound in which solid-liquid separation and dehydration of a suspended material in the calcium compound containing sludge are carried out efficiently without being affected by the variation of properties of sludge containing mainly the calcium compound. CONSTITUTION:An amphoteric polymeric coagulant having cation and anion in one molecule is added to sludge containing mainly a calcium compound to caogulate and dekydrate a suspended material in the dehydration process for sludge containing mainly the calcium compound.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the addition of calcium compounds such as slaked lime and calcium chloride to fluorine-containing wastewater such as hydrofluoric acid wastewater of semiconductor factories and flue gas desulfurization wastewater of thermal power plants. Sludge mainly containing calcium fluoride generated from the wastewater treatment step of removing the precipitate 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 sludge mainly containing a calcium compound (hereinafter, also simply referred to as calcium compound-containing sludge).

[0002]

2. Description of the Related Art In a sludge containing mainly the above-mentioned calcium compounds, water-insoluble or sparingly soluble calcium compounds such as slaked lime, calcium carbonate, calcium fluoride, calcium sulfate, calcium phosphate, etc. It often contains chemical substances such as activators, or organic substances from the biological treatment process of general wastewater.

[0003] Conventionally, as a method of dehydrating sludge mainly containing calcium compounds, a method of dehydrating without chemicals,
Known methods include a method of adding an anionic polymer coagulant or a cationic polymer coagulant to coagulate / dehydrate, and a method of combining an anionic polymer coagulant and a cationic polymer coagulant to coagulate / dehydrate. .

However, in the method of dehydrating without chemicals, it is not possible to use a dehydrator such as a belt press type dehydrator or a screw press type dehydrator which needs to agglomerate sludge during dehydration. It was limited to a filter press type dehydrator, and had the drawback of poor dehydration efficiency.

Further, in the method using either the anionic polymer flocculant or the cationic polymer flocculant, the change of the calcium compound content in the sludge, the change of the composition and the content of the components other than the calcium compound are changed. However, it is difficult to perform stable dehydration treatment, and the strength of the flocs to be generated is weak, so that efficient dehydration treatment cannot be performed.

The method of using both an anionic polymer flocculant and a cationic polymer flocculant is easier to deal with changes in the properties of the calcium compound-containing sludge than in the case of using each of them alone, but a stable treatment is carried out. Is not enough for me. In addition, in order to perform efficient dehydration treatment,
The strength of the generated flock was not sufficient.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art, is not affected by changes in the properties of calcium compound-containing sludge, and efficiently fixes suspended substances in calcium compound-containing sludge. It is an object of the present invention to provide a method for dehydrating calcium compound-containing sludge, which comprises liquid separation and dehydration.

[0008]

In order to achieve the above object, the present inventors have devoted themselves to various methods, and as a result, found a method for dehydrating calcium compound-containing sludge in a stable and efficient manner. It came to completion.

That is, the present invention is characterized in that an amphoteric polymer flocculant having a cation group and an anion group in one molecule is added to sludge mainly containing a calcium compound to flocculate a suspended substance and dehydrate it. The present invention relates to a method for dehydrating sludge containing calcium compounds.

The sludge mainly containing a calcium compound in the present invention is, for example, slaked lime, calcium carbonate,
It is a sludge that mainly contains solid calcium compounds such as calcium fluoride, calcium sulfate, and calcium phosphate, and its representative is, for example, fluorine-containing wastewater such as hydrofluoric acid wastewater of semiconductor factories and flue gas desulfurization wastewater of thermal power plants. , Calcium compounds are added to sludge mainly containing calcium fluoride discharged from the step of precipitating and removing fluorine as calcium fluoride by adding slaked lime, calcium chloride or the like, or drainage containing phosphorus (P), Examples thereof include sludge containing mainly calcium phosphate discharged from the step of precipitating and removing phosphorus as calcium phosphate.

The amphoteric polymer flocculant used in the present invention is not particularly limited as long as it is a polymer compound having a cation group and an anion 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 one or more anionic monomers selected from acrylic acid salts, 2-acrylamido-2-methylpropane sulfonate, etc. Alternatively, a terpolymer of the above-mentioned cationic monomer or anionic monomer and a nonionic monomer such as acrylamide may be used.

The proportion of the monomer of the amphoteric polymer flocculant used in the present invention is not particularly limited, but it is 8 to 95 mol% of cationic monomer, 4 to 30 mol% of anionic monomer and nonionic. It is preferably 85 mol% or less of the monomer.

In a second aspect of the present invention, an amphoteric polymer flocculant having a cation group and an anion group in one molecule is added to sludge mainly containing a calcium compound, and then an anionic polymer flocculant is further added. The present invention relates to a method for dehydrating sludge containing a calcium compound, which comprises aggregating and suspending suspended matter.

A second aspect of the present invention, in which the anionic polymer flocculant is added after the amphoteric polymer flocculant is added, the floc strength is further increased by the anionic polymer flocculant, and the water content of the obtained dehydrated cake, SS More favorable results are obtained in terms of recovery rate.

The anionic polymer flocculant used in the second invention is, for example, a copolymer of acrylate and acrylamide, or acrylamide and acrylate.
Examples include terpolymers of acrylamide-2-methylpropane sulfonate, polyacrylates, 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.

In the present invention, a sludge mainly containing a calcium compound is added with an amphoteric polymer flocculant having both a cation group and an anion group in one molecule to coagulate suspended matter in the sludge and then dehydrated. Therefore, the dehydration effect more stable than that of the conventional method can be obtained. Although the mechanism by which such an effect is obtained by the present invention is not clear, calcium compound-containing sludge often aggregates with both anionic polymer aggregating agents and cationic polymer aggregating agents, sludge particles in calcium compound-containing sludge. It is considered that there is a site on which both an anion group and a cation group act, and an amphoteric polymer flocculant having both an anion group and a cation group in one molecule is strong by acting on both sites. It is presumed that some flock is generated.

As described above, according to the present invention, stable flocculation and dehydration effects can be obtained even if the properties of sludge mainly containing calcium compounds are largely changed.

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

[0020]

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

[0021]

[Table 1]

[0022]

[Table 2]

As is clear from Table 2, both the constituents of the suspended substances contained in the sludge used were fluorine and calcium, and therefore, in these sludges, calcium fluoride was used as a calcium compound. It is clear that a lot of is included. Regarding each sludge, the sludges B and C also 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 in the proportions shown in Table 3, and the suspension substances were flocculated by stirring. Then, the produced floc flocs were dehydrated by a screw press type dehydrator (trade name "SPS-305CPHS", manufactured by Organo Co., Ltd.).

In the case of the combined system of Example 3 and Comparative Example 3, the first polymeric flocculant was added and stirred to the sample sludge, and then the second polymeric flocculant was added and stirred to generate the sludge. The flocculation flocs were similarly dehydrated.

The results of the dehydration test are shown in Table 4. Regarding the floc strength in Table 4, ⊚ is the strongest, and ◯, Δ, and × are weaker in this order.

[0027]

[Table 3]

[0028]

[Table 4]

As is clear from the results shown in Table 4, in Examples 1 and 2 in which the amphoteric polymer flocculant of the present invention was used alone, a floc having a size and strength sufficient for dehydration treatment was used. Good results were obtained in all of SS recovery rate and dehydrated cake water content. Example 3 in which an amphoteric polymer flocculant and an anionic polymer flocculant are used in combination
The SS recovery rate and the water content of the dehydrated cake were even better for any of the sludges, and stable dehydration treatment could be performed.

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

In Comparative Example 3 in which the cationic polymer coagulant and the anionic polymer coagulant were used in combination, the floc strength, SS recovery rate and dehydrated cake water content were higher than those of Comparative Example 1 and Comparative Example 2. However, it was inferior to that of the present invention and was not sufficient for efficient dehydration.

The method of the present invention has a better SS recovery rate and dehydrated cake water content than any conventional method with respect to any calcium compound-containing sludge, and an efficient dehydration treatment can be performed.

[0033]

EFFECTS OF THE INVENTION According to the method of the present invention, the flocs produced have a sufficient strength in the dehydration treatment of sludge mainly containing calcium compounds, the SS recovery rate is improved, and the dehydrated cake water content is reduced. It will be possible. Further, it is possible to easily cope with changes in properties, components, etc. of sludge mainly containing calcium compounds, and to enable efficient dehydration treatment.

Claims (4)

[Claims] 1. A calcium compound characterized by adding an amphoteric polymer flocculant having a cation group and an anion group in one molecule to a sludge mainly containing a calcium compound to flocculate a suspended substance and dehydrate it. Dewatering method of contained sludge. 2. A sludge mainly containing a calcium compound is added with an amphoteric polymer flocculant having a cation group and an anion group in one molecule, and then an anionic polymer flocculant is added to form a suspended substance. A method for dehydrating sludge containing a calcium compound, which comprises aggregating and dehydrating. 3. The dehydration method according to claim 1, wherein the calcium compound is a calcium compound containing calcium fluoride. 4. The dehydration method according to claim 1, wherein the dehydration is performed using a screw press type dehydrator.