JPH03278900A - Treatment of sewage sludge - Google Patents

Abstract

PURPOSE:To perform economical melting treatment, in conditioning sludge, by electrolyzing the sludge using an iron material electrode or an insoluble metal electrode as an anode. CONSTITUTION:In a sludge treatment method conditioning and dehydrating sludge generated in a sewage treatment plant and incinerating the dehydrated sludge to subject the same to melting treatment or immediately subjecting the dehydrated sludge to melting treatment, the sludge is electrolized using an iron material electrode or an insoluble metal electrode as an anode or subjected to electrolytic treatment by using the insoluble electrode in the first half and by using the iron material electrode in the latter half. Or, iron chloride, aluminum chloride, iron sulfate and aluminum sulfate are added to the sludge after conditioning as metal salts to electrolize the sludge under a condition of pH 2-7.

Description

[Detailed Description of the Invention] [Industrial Application] This invention relates to an improvement in a method for treating sludge generated in sewage treatment plants, etc. In particular, when melting and disposing of dehydrated sludge, it is possible to This paper proposes a method for treating sewage sludge, etc., which can yield dehydrated sludge that is easier to melt than dehydrated sludge tempered using slaked lime.

[Prior art and its problems]

In recent years, the amount of sludge generated from treatment plants has tended to increase as the amount of inflowing sewage increases and water treatment becomes more sophisticated. Establishing a proper treatment and disposal method for this increasing amount of sludge is one of the necessary and urgent issues for sewage treatment.

Currently, sludge is mainly treated by a combination of processes such as concentration, digestion, dewatering, and incineration, and after being reduced in volume and volume, it is disposed of in a landfill.

However, due to the recent occurrence of new problems related to secondary pollution at landfill sites and the difficulty in securing disposal sites, there are fewer concerns about secondary pollution, and the effective use of generated slabs has become more difficult than expected. Melting treatment methods for sludge produced in Japan are attracting attention and are being put into practice.

This sludge melting treatment method requires a higher treatment temperature than the conventional sludge incineration method, so it depends on the amount of material to be melted and the melting characteristic temperature, etc., operating conditions, required amount of heat, furnace wall, etc. The operational stability will be greatly influenced by fire resistance, etc.

The preferred conditions for the material to be melted in the melting process are (υ) The mass and volume of the material to be melted should be based on the raw sludge as much as possible, that is, it should contain few additives such as slaked lime, which are difficult to melt.

(2) Dehydrated sludge has a large amount of heat.

(3) Melt characteristic temperatures such as softening point, melting point, and melting point should be as low as possible.

(4) The generated slab must have physical properties that allow it to be used effectively as a resource, and be generated stably.

etc.

On the other hand, in the conventional method of using ferric chloride and slaked lime as conditioning agents during sludge conditioning before dewatering, slaked lime I is added in an amount of 30 to 60% based on the sludge solids. The following phenomena occur. That is, (1) Addition of slaked lime increases the weight and volume of dehydrated sludge.

(2) Dilute the organic content in the sludge to reduce the calorific value per unit mass of dehydrated sludge.

(3) Additives increase basicity and raise the melting characteristic temperature.

In this way, the conventional method uses 30 to 60 slaked lime per solid matter.
% was added, making the dewatered sludge unfavorable for melt processing.

[Means for solving problems]

The present invention was made in order to improve the problems of the dehydrated sludge that has been tempered using ferric chloride and slaked lime. 0 (11) In a sludge treatment method in which sludge generated in sewage treatment plants, etc. is tempered and dehydrated, incinerated, and then melted or immediately melted, In this case, this was electrolyzed using an iron electrode or an insoluble metal electrode as an anode, or the first half was electrolytically treated with an insoluble metal electrode and the second half was an iron electrode.

(21) At least one of iron chloride, aluminum chloride, iron sulfate, and aluminum sulfate is added as a metal salt to the sludge liquid to be tempered as described in (11) above, and the PH2
90(3) Furthermore, after electrolyzing the sludge by the method described in item 11 above, the basicity (Ca o / S
io.

1 slaked lime was added and mixed so that the weight ratio (weight ratio) was in the range of 0.5 to 1.5.

That is, in the present invention, an electrolytic treatment method is adopted in place of the treatment method of adding slaked lime, which was used in large quantities in the conventional treatment method, to reduce the volume and volume of dehydrated sludge, and to reduce the volume of dehydrated sludge. This method suppresses the increase in inorganic substances and suppresses the decrease in calorific value of dehydrated sludge, making it easier to melt.Also, by adding metal salts during electrolysis and adjusting the pH of the sludge solution to 2 to 7, The agglomeration and oxidation of sludge during electrolysis is promoted to improve subsequent dewatering performance, and slaked lime is added to the sludge after dewatering to improve its basicity ICa.

/S i 02 ) is adjusted to be in the range of 0.5 to 1.5, thereby reducing the softening point temperature, melting point, melting point temperature, etc. during melting treatment.

In addition, the above melting characteristic temperature is adjusted as described above because the basicity of sludge treated by conventional methods is 3.0 or more, and slaked lime is not used in the present invention. At the very least, the above-mentioned temperature characteristics are much lower than conventional ones.

The present invention will be explained in detail below.

The sludge to be treated in the present invention is sludge generated in sewage treatment plants, etc., and is treated after being concentrated by gravity sedimentation, pressure flotation, etc., and inorganic substances such as lime are added to this concentrated sludge. The main feature is that the material is tempered by electrolysis, dehydrated, and then melted.In the above-mentioned electrolysis, an iron material or insoluble metal connected to a DC power source is used as an anode. An appropriate metal material such as stainless steel is used for the cathode. Then, a metal salt such as iron chloride is added to the sludge introduced into the electrolytic cell in which these electrode plates are installed, and electricity is applied thereto. To explain this in more detail, the metal salts added are mainly for acting on sludge to form flocs, and iron chloride (Fecll, FeCl) is used to form flocs.
13)-Aluminum chloride A (A Ic Is
) ・Iron sulfate (F e SO4, Few(So= )i
) etc. are suitable. These metal salts are hydrolyzed in the sludge to form metal hydroxides, which promote coagulation and flocculation of the sludge, make the sludge acidic, and facilitate the oxidation of the sludge. Then, by further supplying electricity, oxygen, chlorine, and hypochlorite are generated, and the sludge is oxidized and becomes a sludge that can be easily filtered and dehydrated. During this electrolysis, it is preferable to adjust the pH of the sludge to 2 to 7.

Next, an iron material or an insoluble metal electrode is used as the electrode material for the anode, and although the iron material is eluted and consumed, it is inexpensive. Various types of insoluble metal electrodes with excellent conductivity and corrosion resistance can be used. Preferably.

Since the cathode facing the anode is not electrolytically corroded, materials such as Tekken Stainless Q nickel and titanium can be used.

These anodes and cathodes are arranged to face each other in the electrolytic cell container, and in order to obtain a sufficient current-carrying area, it is usually desirable to arrange an appropriate number of plate-shaped bodies in parallel and alternately.

Regarding the voltage in electrolytic treatment, a low voltage is advantageous from the standpoint of equipment and safety, but in reality it is 1.5 to 35 Vii!
Preferably. In addition, the current value varies depending on the type and composition of sludge, but it is 0.5 to 5 All for raw sludge.
The electrolytic treatment time is approximately 30 to 120 minutes, and approximately 100% of the effect can be obtained.

For example, sludge with ferric chloride added and mixed in advance and adjusted to a pH of 5 to 6 is supplied to an electrolytic treatment tank placed facing a stainless steel cathode using an iron material or an insoluble metal electrode as an anode. When a direct current is applied to the sludge while stirring and circulating it, the added ferric chloride is hydrolyzed and causes the sludge to coagulate, producing a sludge floc.

Furthermore, the produced sludge floc is oxidized and dehydrated by chlorine or oxygen generated at the anode and hypochlorite produced, and is reformed into hydrophobic sludge with good filtration and dewatering properties.

The sludge modified by K in this way can be easily dehydrated without adding a large amount of slaked lime as in the conventional method, but the dehydrated cake treated in this way contains some talc and sludge. The suitability for melting can also be further increased by adding ash.

In other words, the composition of dehydrated sludge that lowers the softening point temperature, melting point, melting point temperature, etc. during melting treatment is silica (Si
02) The content is nearly 30%, and at the same time,
It has been reported that the basicity (weight ratio of Ca o /S i cH) is as close to 1 as possible. In this regard, in the method according to the present invention, it has been confirmed that adding a small amount (approximately 15%) of slaked lime to the sludge after dewatering is advantageous in melting the sludge.

In other words, when iron material is used as the anode material in the electrolytic treatment of sludge, the filtration and dewatering properties of the treated sludge are high, but the Sio2 content in the sludge is diluted by the iron eluted from the anode material, resulting in a relatively high Sio2 content. Iron oxide (Feoj) is a melting point substance.
, Feo), etc., and the melting point lowering effect will not be sufficient. In such cases, as mentioned above, by adding a small amount of slaked lime, the temperature during the melting process can be lowered. It can be lowered.

Furthermore, the processing temperature during melting treatment, such as the melting point, of the dehydrated sludge treated by the method according to the present invention is 300°C lower than that of 40% limestone (dry cake weight ratio) by the conventional treatment method. be. (See Table 1 and Examples) In addition, when using an insoluble metal electrode as an anode material during electrolytic treatment, if the insoluble metal electrode conventionally used as an electrode for chlorine production is used, chlorine will be generated. The pH of the sludge after electrolytic treatment is 3 to 4, which requires neutralization with slaked lime, but the amount of slaked lime required for neutralization is smaller than that of the conventional method (iron salt - addition of slaked lime). then 1
/3 to 1/4, and there is no adverse effect on the melting characteristic temperature of dehydrated sludge.

From the above-mentioned points, this thermal conditioning method has better dewatering performance than the conventional salt iron-slaked lime method, suppresses the decrease in the Sio2 content in the sludge composition, and keeps the basicity of dehydrated sludge within an appropriate range. In the first half of the electrolytic treatment, insoluble metal electrolysis is used to mainly oxidize the sludge to make it hydrophobic sludge, and in the second half, the electrolytic treatment is performed using iron material as the anode material to prevent flocculation of the sludge liquid due to eluted iron. The dehydrated sludge produced by neutralization and tempered sludge with good dewatering properties, the addition of slaked lime to an extent that the basicity falls within the range of 0.5 to 1.5, and dewatering treatment, can be produced using conventional methods. By performing electrolytic refining, the melt point temperature can be much lower than the melt point temperature of dehydrated sludge, such as 0 or higher, and it is possible to refine sludge that can exhibit dewatering performance equivalent to or higher than conventional methods. At the same time, it is possible to obtain dehydrated sludge that is highly suitable for melt treatment.

〔Example〕

Table 1 shows that by the method of the present invention and the conventional salt iron-slaked lime method,
Electrolytically treated mixed raw sludge 2501 with a sludge concentration of 2.0%,
The results of Examples in which the characteristic melting temperature was measured after filtration and dehydration using a filter press dehydrator are summarized below.

Table 1 Examples) As an insoluble metal electrode, No. 3 used an insoluble metal electrode in which a coating containing a platinum group metal oxide as a main component was provided on titanium.

) The filtration conditions were press-in pressure 5 kfl/ej, press-in time 5 minutes, squeezing pressure 15&IF/e4, and squeezing time 15 minutes.

(Note 3) The addition rate of Fecl+Ca(0H)2 is the weight ratio of dry solids.

As shown in Example 1, an iron material was used for the anode (Note 2 (Note 1) The table shows the dewatering performance of tempered sludge electrolytically treated using an insoluble metal electrode in the first half and an iron electrode in the second half. The results showed that the filtration rate was equal to or higher than that of the conventional method.

Furthermore, the characteristic melting temperature of dehydrated sludge after electrolytic treatment was lower than that of conventional methods.

〔Effect of the invention〕

When dehydrated sludge generated at sewage treatment plants is incinerated and then melted, or when the dehydrated sludge is immediately melted, the dehydrated sludge tempered using the conventional method (adding metal salts and slaked lime) is Due to the large amount of slaked lime added (approximately 30 to 60% based on solids), the amount of dehydrated sludge generated increases and the amount of materials to be melted increases. Furthermore, since the added slaked lime is nonflammable, it dilutes the organic content in the sludge, lowers the calorific value of the sludge, and increases the basicity, thereby increasing the melting characteristic temperature.

In this way, slaked lime added in large quantities for dehydration and tempering causes various problems in melt processing.

On the other hand, the dehydrated sludge produced by the treatment method according to the present invention makes it possible to reduce the amount of slaked lime that causes the above problem, produces a small amount of melted material, has a high calorific value, and Dehydrated sludge with a low melting characteristic temperature is produced, which facilitates the operating conditions for melting treatment, reduces the amount of fuel used, and extends the life of heavy reactor wall materials, allowing for economical melting treatment.

Claims (3)

[Claims] (1) In a sludge treatment method in which sludge generated in a sewage treatment plant, etc. is tempered, dehydrated, incinerated, and then melted or immediately melted, the sludge is heated as an anode when tempering the sludge. A method for treating sewage sludge, etc., characterized by electrolyzing using a ferrous electrode or an insoluble metal electrode, or electrolytically treating the first half with an insoluble electrode and the second half with a ferrous electrode. (2) In claim (1), at least one of iron chloride, aluminum chloride, iron sulfate, and aluminum sulfate is added as a metal salt to the sludge to be tempered, and the PH2
A method for treating sewage sludge, etc., characterized by carrying out electrolytic treatment under the conditions of ~7. (3) After the electrolytic treatment according to the method described in claim (1), slaked lime is added to the dewatered sludge so that its basicity (weight ratio of Cao/Sio_2) is in the range of 0.5 to 1.5. A method for treating sewage sludge, etc., characterized by addition and mixing and dewatering.