JP5593786B2 - Electroosmotic dehydration method - Google Patents

Description

  The present invention relates to a method for performing electroosmotic dehydration treatment of sludge generated in various industrial wastewater treatment processes, and in particular, by adding a dispersant to sludge before electroosmosis dehydration, the power consumption of electroosmosis dehydration equipment. The present invention relates to a method for obtaining a dehydrated cake having a low water content while suppressing the above.

  Sludge generated in the process of treating various industrial wastewater contains a lot of water, so it is disposed of as waste after being dehydrated. Conventionally, mechanical dehydration devices such as pressure dehydrators such as belt presses and filter presses and centrifugal dehydrators have been used for sludge dewatering. However, some of these sludges (fibers and Except for sludge containing a lot of easily dehydrated components such as sand, the water content cannot be lowered sufficiently, and the water content of the obtained dehydrated sludge is limited to about 80%.

  On the other hand, in the case of electroosmotic dehydration treatment in which a direct current is applied to sludge and dewatered by electroosmosis, the sludge to be treated is energized and the negatively charged sludge is drawn to the anode side, while the sludge gap Since dehydration is performed by applying pressure while water is moved to the cathode side and separated, dehydration efficiency is higher than in the case of mechanical dehydration, and the moisture content of sludge can be further reduced.

Conventionally, in order to increase the dewatering efficiency in the electroosmotic dewatering treatment of sludge, it has been proposed to increase the electrical conductivity of the sludge as follows.
(1) A method of adding an electrolyte such as sodium sulfate or sodium carbonate to sludge to be dehydrated (Patent Document 1, Patent Document 2)
(2) Method of heating sludge to be dehydrated (Patent Document 3)

JP-A-3-262818 Japanese Patent Publication No.7-73646 Japanese Patent No. 3576269

However, the above prior art has the following problems.
(1) In a method in which an electrolyte such as sodium sulfate or sodium carbonate is added to sludge, the electric conductivity of the sludge increases, so that an excessive current flows and the power consumption required for dehydration increases.
(2) In the method of heating sludge, it is necessary to add heat to the sludge, so that a heating facility is required and an energy cost for heating is required.

  The present invention solves the above-described conventional problems, and prevents an increase in power consumption due to excessive application of current, and in an electroosmotic dehydrator without performing external energy input such as heating. It is an object of the present invention to provide an electroosmotic dehydration method for obtaining a dehydrated cake having a low water content while suppressing power consumption.

  As a result of intensive studies to solve the above problems, the present inventors have added a dispersant to sludge to be subjected to electroosmosis dehydration treatment, thereby improving the dehydration efficiency of the electroosmosis dehydrator and suppressing power consumption. And found that a dehydrated cake having a low water content can be obtained.

  The present invention has been achieved on the basis of such findings, and the gist thereof is as follows.

[1] In the method for electroosmotic dehydration treatment of sludge, one or two selected from the group consisting of lignin sulfonate, melamine sulfonate, naphthalene sulfonate, and gluconate is used as the sludge to be subjected to the dehydration treatment. An electroosmotic dehydration method comprising adding a dispersant that is a seed or more .

[2] Oite to [1], the addition amount of the dispersant, electroosmotic dehydration process, wherein the 0.1 to 10 wt% absolute dry sludge weight per sludge subjected to dehydration treatment.

[3] [1] or Oite in [2], the sludge to be subjected to the dehydration treatment, flocculation, electroosmotic dehydration process which is a sludge which has undergone the dehydration process.

According to the present invention, by adding a dispersant to the sludge to be subjected to electroosmosis dehydration treatment, it is possible to disperse the sludge particles and increase the dewaterability of pore water between the sludge particles. It is possible to obtain a dehydrated cake having a low water content while suppressing power consumption in the apparatus.
This method does not require external energy such as heating, and can reduce power consumption, and thus is effective in reducing dehydration costs.

It is a schematic diagram which shows the structure of the electroosmosis dehydration tester used in the Example. It is a graph which shows the results of Examples 1 and 2 and Comparative Examples 1 and 2.

  Hereinafter, embodiments of the electroosmotic dehydration method of the present invention will be described in detail.

  The electroosmotic dehydration method of the present invention is characterized in that a dispersant is added to sludge to be subjected to electroosmosis dehydration treatment.

The dispersant used in the present invention is not particularly limited as long as it is an effective dispersant for improving the sludge dewatering efficiency, and examples thereof include the following.
(1) Dispersant having a negatively charged functional group Such a dispersant absorbs sludge and increases the zeta potential of the sludge particles to the negative side to disperse the sludge particles. By making the pore water move to the cathode side for easy separation, dewatering efficiency can be increased.
(2) Dispersant exhibiting steric hindrance action This dispersant does not adsorb on sludge particles, but exists between sludge particles and exerts steric hindrance repulsive force. Dewatering efficiency can be improved by improving the separation and dewatering properties of pore water.
(3) Dispersant with adsorption or affinity to sludge This dispersant also adsorbs to sludge and improves the dewaterability in the same manner as the dispersant of (1).

As the dispersant of the above (1) and (3), those having a functional group having a negative electric repulsive force such as a hydroxyl group, a sulfone group, a phosphone group, and a carboxyl group are preferable. Specifically, lignin sulfonic acid Examples thereof include a dispersant mainly composed of a salt, melamine sulfonate, naphthalene sulfonate, gluconate and the like. In addition, alkali metal salts, such as a sodium salt and potassium salt, are mentioned as a form of a salt of lignin sulfonate, melamine sulfonate, naphthalene sulfonate, and gluconate. Also, the following can be used.
Higher Fatty Acid Salts Secondary Higher Fatty Acid Salts Higher Alkyl Dicarboxylates Primary Higher Alcohol Sulfate Salts Secondary Higher Alcohol Sulfate Salts Primary Alkyl Sulfonate Secondary Alkyl Sulfonate Higher Alkyl ・Disulfonates Sulfated fats and fatty acid salts Sulfonated higher fatty acid salts Higher alkyl phosphoric acid ester salts Higher fatty acid ester sulfates Higher fatty acid ester sulfonates Higher alcohol ether ether sulfates Higher alcohol ether ether sulfonates Higher Fatty acid and proteolytic amino acid condensate Higher fatty acid and amino acid condensate Higher fatty acid amide alkylol sulfate Higher fatty acid amide alkyl sulfonate Higher alkyl sulfonamide alkyl carboxylate Sulfon Acid ester salt Alkyl benzene sulfonate Alkyl phenol sulfonate Alkyl naphthalene sulfonate Formalin condensate of alkyl naphthalene sulfonate Alkyl diphenyl and many other sulfonates Alkyl・ Ketyl compounds of allyl sulfonates Petroleum sulfonates

  On the other hand, as the dispersant of (2), those having a functional group having steric hindrance repulsive force such as polycarboxylic acid are preferable, and specifically, polycarboxylic acid ether compounds, carboxyl group-containing polyether compounds, polycarboxylic acids, and the like. Examples include acid compounds.

  These dispersing agents may use only 1 type and may use 2 or more types together.

  The amount of such dispersant added varies depending on the sludge properties, applied voltage during electroosmotic dehydration, dehydration time, etc., but is 0.1 to 0.1 per dry absolute sludge weight (DS) of the sludge used for electroosmosis dehydration. 10 wt% (hereinafter, this ratio is described as “wt% / DS”), particularly 0.1 to 5 wt% / DS is preferable. If the amount of the dispersant added to the sludge is too small, the effect of improving the dewatering efficiency by adding the dispersant cannot be sufficiently obtained. However, if the amount of the dispersant added is too large, the cost of the drug is high, and in the case of a dispersant containing ions such as Na, the electrical conductivity of the sludge increases too much and there is a risk of excessive energization.

  In addition, there is no restriction | limiting in particular as the addition method of the dispersing agent to sludge, What is necessary is just a method which can add a dispersing agent to the sludge introduce | transduced into an electroosmosis dehydrator, and can disperse | distribute it uniformly. Examples thereof include a method in which a dispersant is added and mixed with a mixer, a method in which a dispersant is sprayed on sludge to be transported by piping and mixed during transport, and a method in which the sludge is sprayed on sludge immediately before electroosmotic dehydration.

  The form of addition of the dispersant is not particularly limited, and the solid dispersant may be added as a powder, or may be added as an aqueous solution, but it is 10 to 50 weights in terms of uniform dispersion and mixing property to sludge. It is preferable to add as an aqueous solution of about%.

  In the present invention, the sludge to be subjected to electroosmosis dehydration treatment is not particularly limited, but is concentrated sludge generated in the treatment process of various industrial wastewater, for example, concentrated sludge generated in the biological treatment process (biological treatment liquid is settled in a settling tank, Agglomeration by adding a suitable flocculant to 95 to 99 wt% (sludge with a water content unit of "%" hereinafter) obtained by solid-liquid separation in a flotation tank, membrane separator, etc. The sludge having a water content of about 70 to 90% obtained by treatment and dehydration treatment with a mechanical dehydrator such as a gravity dehydrator, a centrifugal dehydrator, a belt press, a screw press, or a filter press is preferable. If the sludge to be subjected to the electroosmotic dehydration treatment is not sludge that has undergone agglomeration and dehydration treatment, the dehydration efficiency by the electroosmosis dehydration treatment may be poor, and dehydrated sludge having a low water content may not be obtained.

The flocculant used for the coagulation treatment of the concentrated sludge is not particularly limited, and those having an excellent coagulation effect are used depending on the sludge properties, etc., but in general, aluminum chloride (AlCl ₃ ), polyaluminum chloride, Sulfuric acid band (Al ₂ (SO ₄ ) ₃ ), aluminum hydroxide (Al (OH) ₃ ) or aluminum oxide (Al ₂ O ₃ ) dissolved with hydrochloric acid (HCl) or sulfuric acid (H ₂ SO ₄ ) Iron-based flocculants such as aluminum salts such as ferric chloride (FeCl ₃ ), ferric sulfate (Fe ₂ (SO ₄ ) ₃ ), iron salts such as ferrous sulfate (FeSO ₄ ) One type or two or more types of various inorganic flocculants such as silica flocculants and silica flocculants can be used. Preferably, polyferric sulfate is used because the dehydrating performance of electroosmotic dehydration can be improved.

  These inorganic flocculants and polymer flocculants may be used in combination. As the polymer flocculant to be used in combination, various polymer flocculants such as an anionic polymer flocculant, a cationic polymer flocculant, a nonionic polymer flocculant, and an amphoteric polymer flocculant can be used. It is preferable to use an amphoteric polymer flocculant (amphoteric polymer). As the amphoteric polymer flocculant, a monomer having an amino group or an ammonium base, a copolymer of (meth) acrylamide and (meth) acrylic acid or a salt thereof is preferable, and as a monomer having an amino group or an ammonium base, for example, (Meth) acryloyloxyethyltrimethylammonium chloride, (meth) acryloyloxyethyldimethylbenzylammonium chloride, (meth) acryloyloxy-2-hydroxypropyltrimethylammonium chloride and other (meth) acryloyloxyalkyl quaternary ammonium salts, (meth) (Meth) acryloyloxyalkyl tertiary amine salts such as acryloyloxyethyldimethylamine sulfate or hydrochloride, (meth) acryloyloxypropyldimethylamine hydrochloride, (meth) acryloyl (Meth) acryloylaminoalkyl quaternary ammonium salts such as nopropyltrimethylammonium chloride and (meth) acryloylaminopropyltrimethylammonium methyl sulfate can be mentioned (here, “(meth) acryl” means “acrylic and / or Or “methacryl”, and the same applies to “(meth) acryloyl”. These monomers can be used individually by 1 type, or can also be used in combination of 2 or more type. Among these, (meth) acryloyloxyalkyl quaternary ammonium salts are excellent in the dehydration effect and can be preferably used, and acryloyloxyethyltrimethylammonium chloride and methacryloyloxyethyltrimethylammonium chloride can be particularly preferably used. .

  Examples of (meth) acrylic acid or a salt thereof include (meth) acrylic acid, sodium (meth) acrylate, ammonium (meth) acrylate, calcium (meth) acrylate, and the like. Among these, acrylic acid and sodium acrylate can be particularly preferably used.

  The amphoteric polymer flocculant can be copolymerized with another comonomer. Examples of other comonomers include vinyl pyrrolidone, maleic acid, and methyl acrylate. The copolymerization amount of these comonomers is usually preferably 20 mol% or less, and more preferably 10 mol% or less.

  These polymer flocculants may be used individually by 1 type, and may use 2 or more types together.

  The amount of these flocculants added is appropriately determined so that a dehydrated sludge having a desired water content can be obtained. Usually, when the flocculant is treated using only an inorganic flocculant, the absolute dry sludge weight of the sludge ( When the inorganic flocculant and the polymer flocculant are used in combination in an amount of about 1 to 20% by weight (hereinafter referred to as “% / DS”) with respect to DS), the inorganic flocculant is 1 to 10% / The DS is preferably about 1 to 10% by weight / DS of the polymer flocculant.

As described above, there is no particular limitation on the electroosmotic dehydration apparatus used for electroosmotic dehydration treatment of sludge obtained by preferably coagulating and dehydrating biologically treated sludge, and generally available electroosmosis dehydration apparatus. Can be used.
The electroosmotic dehydration treatment conditions are not particularly limited. For example, the following conditions can be adopted. By such electroosmosis dehydration treatment, the water content is 70% or less, for example, about 60 to 65%. It is preferable to obtain a low water content sludge.
Applied pressure: 0.1 to 200 kPa
Applied voltage amount: 20-100V
Dehydration time: 5-60 minutes

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[Examples 1 and 2, Comparative Examples 1 and 2]
Using the column type electroosmosis dehydration tester shown in Fig. 1, belt press dehydration by adding 5 wt% / DS of polyferric sulfate and 3 wt% / DS of amphoteric polymer to the aerobic biological treatment sludge of food wastewater An electroosmotic dehydration treatment of the dehydrated sludge having a moisture content of 79% was performed.

  In this electroosmosis dehydration tester, sludge 3 is introduced into a sludge column (diameter 100 mm) 2 provided with a cathode 1 made of stainless mesh at the bottom, a load F is applied by a piston-type anode 4 and an anode is supplied by a power source 5. The electroosmotic dehydration process is performed under pressure by applying a voltage between 4 and the cathode 1.

The electroosmotic dehydration treatment conditions are as follows.
<Dehydration conditions>
Sludge amount: 170g
Dehydration time: 10 minutes Applied voltage: 60V
Applied pressure: 0.3 kgf / cm ²

  The chemicals shown in Table 1 were added to the sludge to be subjected to electroosmotic dehydration treatment and mixed using a chemical spoon (however, no chemicals were added in Comparative Example 1. Also, the lignin of Example 1) The sulfonate is a sodium salt of lignin sulfonic acid, and the melamine sulfonate of Example 2 is a sodium salt of melamine sulfonic acid.)

In addition, each chemical | medical agent was added to sludge as about 10-50 weight% aqueous solution, and the water addition amount to each sludge was adjusted so that it might become the same.
The power consumption in each example and the water content (reached water content) of the obtained dehydrated cake were as shown in Table 1 and FIG.
Note that the direction of the arrow in FIG. 2 indicates the magnitude of the amount of drug added in Examples 1 and 2 and Comparative Example 2. The steep slope is more effective, that is, the dehydration efficiency per power consumption is higher. Indicates high.

These results show the following.
In Examples 1 and 2 to which lignin sulfonate and melamine sulfonate were added, the water content reduction effect per power consumption was large, and the water content of the dehydrated cake obtained by suppressing power consumption was effectively reduced. be able to.
In Comparative Example 2 in which the bow glass as an electrolyte is added, the moisture content of the dehydrated cake obtained can be reduced to some extent, but the power consumption is greatly increased, which is not preferable in terms of energy cost.

1 mesh cathode 2 column 3 sludge 4 anode 5 power supply

Claims (3)

In the method of electroosmotic dehydration treatment of sludge, the sludge to be subjected to the dehydration treatment is one or more selected from the group consisting of lignin sulfonate, melamine sulfonate, naphthalene sulfonate, and gluconate. An electroosmotic dehydration method comprising adding a dispersant. Oite to claim 1, the added amount of the dispersing agent, electroosmotic dehydration process, wherein the 0.1 to 10 wt% absolute dry sludge weight per sludge subjected to dehydration treatment. The electroosmotic dehydration method according to claim 1 or 2 , wherein the sludge to be subjected to the dehydration treatment is sludge that has undergone agglomeration and dehydration treatment.

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