JP3109166B2 - Method for reforming sludge containing aluminum - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reforming aluminum-containing sludge, and in particular, for the purpose of reducing the volume of aluminum-containing sludge, by re-dissolving and re-coagulating and sedimenting aluminum-containing sludge. The present invention relates to a method for reforming sludge having good properties, thickening properties and dewatering properties.

[0002]

2. Description of the Related Art Conventionally, as a method for treating aluminum-containing wastewater, there is a method in which a neutralizing agent is added to wastewater to adjust the pH to about 6 to 8, aluminum is precipitated as aluminum hydroxide, and coagulated and separated.

However, the aluminum-containing sludge obtained by this method has a high solids (SS) concentration of 10%.
g / liter (hereinafter referred to as "lit."), very low concentration, SS concentration is only about 10-20% even if dewatered. is there.

[0004] As an improvement technique in the treatment of such aluminum-containing wastewater, the following method has conventionally been proposed.

A method in which an alkali is added to aluminum hydroxide to obtain an alkali-treated aluminum precipitate, which is mixed and reacted with an acidic aluminum-containing wastewater (JP-B-49)
-36879).

A method in which a part of the sludge that has been coagulated and separated and added to and dissolved in an acid is returned to the coagulation reaction tank (JP-A-2-157005).

[0007]

In the above-mentioned method, at least two reaction tanks are required for forming an alkali-treated aluminum precipitate and a reaction tank for reacting acidic aluminum-containing wastewater. There is a drawback that the equipment is complicated in terms of pH control of the tank and the like. Moreover, the effect of modification by alkali cannot be sufficiently satisfied. Incidentally, according to the results of the examples described in JP-B-49-36879, the SS concentration of the obtained sludge is at most about 40 g / lit.

On the other hand, the above-mentioned method is a method of returning sludge. However, the sludge is dissolved by adding an acid, and is then sent to a reaction tank of a wastewater treatment system. That is, the method is related to the reuse of the flocculant, and the sludge reforming effect cannot be obtained.

As described above, no method has heretofore been proposed which can obtain sludge having a high SS concentration and excellent sedimentation, concentration and dehydration properties, and improvement thereof is desired.

The present invention has been made in view of the above-mentioned conventional circumstances, and it is an object of the present invention to effectively reduce the volume of aluminum-containing sludge to obtain an aluminum sludge having good sedimentation, concentration and dehydration properties. An object of the present invention is to provide a method for reforming contained sludge.

[0011]

According to the method of the present invention for reforming aluminum-containing sludge, a part of the aluminum-containing sludge is dissolved with an acid, and the remainder is dissolved with an alkali. A method for reforming an aluminum-containing sludge in which a liquid and a liquid are mixed in a reaction tank to form an insolubilized substance and then solid-liquid separated, wherein a part of the separated insolubilized substance is returned to the reaction tank. And

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a system diagram showing one embodiment of the method for reforming the aluminum-containing sludge of the present invention, and FIG. 2 is a system diagram showing a coagulation sedimentation treatment method using an aluminum salt.

First, the coagulation precipitation method shown in FIG. 2 will be described. In FIG. 2, 1 is a reaction tank, and 2 and 3 are coagulation tanks, which are provided with stirrers 1A, 2A and 3A, respectively. 4
Is a settling tank. 11 is a pipe for introducing raw water into the reaction tank 1, 12 is a pipe for feeding the liquid in the reaction tank 1 to the coagulation tank, 1
3 is a pipe for discharging the supernatant water separated in the sedimentation tank 4 as treated water, and 14 is a pipe for discharging sludge. Reference numeral 15 denotes a pipe for supplying an aluminum salt to the reaction tank 1. Reference numeral 16 denotes a return pipe for separated water in a later-described sludge reforming step.

In the method shown in the figure, raw water is introduced into the reaction tank 1 through a pipe 11, and separated water in a sludge reforming step described later, which is returned through a pipe 16 in the reaction tank 1, is added thereto. From 15, an aluminum salt is added. Next, the liquid in the reaction tank 1 is fed from the pipe 12 to the coagulation tank 2 and further to the coagulation tank 3, where the liquid is coagulated in the coagulation tanks 2 and 3.
The liquid subjected to the coagulation treatment in the coagulation tanks 2 and 3 is further transferred to the sedimentation tank 4
To be concentrated and precipitated. Thus, the supernatant water of the settling tank 4 is discharged from the pipe 13 as treated water. on the other hand,
The sludge extracted from the sedimentation tank 4 via the pipe 14 is sent to the sludge reforming step shown in FIG.

Next, the sludge reforming method shown in FIG. 1 will be described. In FIG. 1, 21 is an acid dissolving tank, 22 is an alkali dissolving tank, 23 is a neutralization reaction tank, 24 and 25 are coagulation tanks, and they are stirring tanks 21A, 22A, 23A, 24A, respectively.
25A. 26 is a sedimentation tank. 14A, 14B
Are pipes branched from the sludge extraction pipe 14 of FIG. 2 to feed sludge to the acid dissolving tank 21 and the alkali dissolving tank 22, respectively. Reference numeral 31 denotes a neutralization reaction tank 2 for the acid solution in the acid dissolution tank 21.
Reference numeral 32 denotes a pipe for feeding the alkali solution in the alkali dissolution tank 22 to the neutralization reaction tank 23. 33
Are pipes for feeding the liquid in the neutralization reaction tank 23 to the coagulation tank 24,
Reference numeral 6 denotes a pipe for feeding the separated water from the sedimentation tank 26 to the reaction tank 1 shown in FIG. Reference numeral 34 denotes a pipe for extracting sludge from the sedimentation tank 26, and is branched into a pipe 34A having a pump 35 for returning a part of the sludge to the neutralization reaction tank 23, and a pipe 34B for discharging the sludge outside the system. . 36 is an acid dissolving tank 2
1 is a pipe for adding an acid, 37 is a pipe for adding an alkali to the alkali dissolution tank 22, and 38 is a pipe for adding a coagulant to the coagulation tank 24.

In the method shown in FIG. 1, the sludge extracted from the sedimentation tank 4 shown in FIG. 22.

In the acid dissolving tank 21, an acid is added from a pipe 36 to dissolve sludge. On the other hand, in the alkali dissolving tank 22, alkali is added from the pipe 37, and the sludge is dissolved. The acid or alkali used here is not particularly limited as long as it can dissolve aluminum. Usually, acid such as sulfuric acid, nitric acid, hydrochloric acid,
Alternatively, an alkali such as sodium hydroxide, sodium carbonate, calcium hydroxide or the like is used.

The acid dissolving solution in the acid dissolving tank 21 and the alkali dissolving solution in the alkali dissolving tank 22 are respectively connected to a pipe 31,
The mixture is fed to the neutralization reaction tank 23 from 32, and is mixed with the sludge returned from the precipitation tank 26 via the pipe 34A in the neutralization reaction tank 23.

In the present invention, the inflows of the acid solution and the alkali solution are adjusted so that the pH of the solution in the neutralization reaction tank 23 is preferably in the range of 5.8 to 7.2. In addition, since the larger the amount of returned sludge, the more preferable, the solid (SS) concentration in the neutralization reaction tank 23 is preferably 10%.
The amount of returned sludge is adjusted so as to be 0 g / lit. Or more, more preferably 200 g / lit. Or more. Furthermore, neutralization reaction tank 2
The capacity of the neutralization reaction tank 23 is selected with respect to the amount of the inflowing solution and the returned sludge so that the residence time of the liquid flowing into the reactor 3 in the neutralization reaction tank 23 is preferably 10 minutes or more. By adjusting the pH, the SS concentration, and the residence time of the neutralization reaction tank 23 to the above conditions, sludge having more favorable sedimentation, concentration, and dehydration properties can be obtained.

In the method of this embodiment, the neutralization reaction tank 2
Next, the liquid in 3 is fed to the coagulation tank 24 from the pipe 33, and the coagulant is added from the pipe 38 in the coagulation tank 24 to perform coagulation processing. Here, the flocculant used is not particularly limited, but generally a polymeric flocculant is preferred. As the polymer flocculant, any of nonionic, anionic, and cationic types can be applied, but in general, nonionic and anionic types are effective.

The liquid subjected to the coagulation treatment in the coagulation tank 24 is further supplied to the coagulation tank 25 and sufficiently coagulated.
It flows into the sedimentation tank 26 and is concentrated and settled. Then
The separated water in the sedimentation tank 26 is returned to the reaction tank 1 in FIG. 2 from the pipe 16 and is processed together with the raw water. On the other hand, a part of the sludge extracted from the sedimentation tank 26 through the pipe 34 is returned to the neutralization reaction tank 23 from the pipe 34A, and
From 4B, it is discharged out of the system and subjected to dehydration, drying and the like.

The illustrated method is an embodiment of the present invention, and the present invention is not limited to the illustrated method.

For example, the flocculation tanks 24 and 25 are not necessarily required, and the liquid in the neutralization reaction tank 23 may be supplied directly to the precipitation tank 26. However, since the flocculation tanks 24 and 25 are provided and a flocculant is added to perform the flocculation treatment, and then the sedimentation treatment is performed, the sedimentation property of the sludge and the clarification of the separated water are improved. is there.

In the present invention, the sedimentation tank 26 is for separating supernatant water and condensing sludge.
Instead of the sedimentation tank 26, a membrane separation device, for example, an MF (microfiltration) or UF (ultrafiltration) membrane separation device may be used.

The method for reforming the aluminum-containing sludge of the present invention may be any sludge containing aluminum, and is not limited to the coagulation-sedimentation sludge using the aluminum salt shown in FIG. The present invention can be applied to sludge treated by coagulation. That is, when aluminum is contained in raw water, aluminum-containing sludge can be obtained without adding an aluminum salt. Others
The method of the present invention, besides coagulated sedimentation sludge for the purpose of turbidity, for example, aluminum-containing sludge such as a sludge to which fluorine is adsorbed or a food / pharmaceutical factory, and furthermore, aluminum phosphate-containing sludge for removing phosphorus and the like. It is also applicable to volume reduction.

[0026]

In the present invention, aluminum-containing sludge is dissolved by using an acid and an alkali, respectively (the following reaction formula,
), When both dissolving solutions are mixed and neutralized in the reaction tank and subjected to the re-coagulation sedimentation treatment (the following reaction formula), the separated sludge is returned to the reaction tank as seed crystals. Thereby, the sludge is reformed and granulated by returning aluminum sludge generated in the reaction tank to the surface with the returned sludge as a nucleus, and sludge excellent in sedimentation, concentration and dehydration properties is obtained. .

2Al (OH) ₃ + 3H ₂ SO ₄ → Al ₂ (SO ₄ ) ₃ + 6H ₂ O 6Al (OH) ₃ + 6NaOH 6NaAlO ₂ + 12H ₂ O Al ₂ (SO ₄ ) ₃ + 6NaAlO ₂ + 12H ₂ O → 8Al (OH) ₃ + 3Na ₂ SO ₄ By the way, in the method of the present invention, the sludge is divided into two parts,
After dissolving with an acid or an alkali, respectively, the mixture is neutralized, so that the amount of drug used can be reduced.

That is, for example, when the entire amount of sludge is dissolved only with an acid, an acid equivalent to the aluminum contained in the sludge is required (the following reaction formula). Then, in order to neutralize the dissolved sludge, Further, an equivalent amount of alkali is required. Therefore, one equivalent of acid and one alkali is required for each aluminum in the sludge.

On the other hand, when the acid and the alkali are separately dissolved according to the present invention, the alkali (eg, NaOH) may be 1/3 equivalent of aluminum, as shown in the above reaction formula. If the sludge is divided into two equal parts and each is subjected to a dissolution treatment, the chemical cost can be reduced to a quarter of the amount required when the whole amount of the sludge is dissolved with an acid and then neutralized with an alkali. (If the entire amount of sludge is dissolved with an alkali and then neutralized with an acid, the amount is 3/4 of the case where the entire amount of sludge is dissolved with an acid and then neutralized with an alkali.) ADVANTAGE OF THE INVENTION According to this invention, medicine cost is reduced and low cost processing is attained.

[0030]

The following examples, comparative examples and reference examples are given below.
The present invention will be described more specifically.

COMPARATIVE EXAMPLE 1 Aluminum concentration was obtained by adding a sulfuric acid band to Atsugi City water.
Raw water of 05 g / lit. Is supplied to a reaction tank (capacity 0.5 lit.)
Water at 0.1 lit./hr and 50 g / lit.
The pH was adjusted to 6.5 by adding an aqueous NaOH solution. Thereafter, solid-liquid separation was performed in a sedimentation tank (inner diameter / 50 mm).

After the sludge obtained from the settling tank was allowed to stand for 30 minutes, the SS concentration was measured and found to be 8.0 / lit.

Example 1 The sludge obtained in Comparative Example 1 was divided into two parts, to which 15 g / lit. Of H ₂ SO ₄ and 15 g / lit. Of NaOH were added, and dissolved. Next, treatment was performed in the same reaction tank and precipitation tank as used in Comparative Example 1.

That is, the H ₂ SO ₄ solution was added to the reaction tank in an amount of 0.1%.
Water was passed at a constant flow rate of lit./hr and a NaOH solution was automatically injected as a neutralizing agent.
The sludge was returned to the reaction tank at a flow rate of / hr.

After 7 days of continuous operation, the reaction vessel outlet liquid was collected.
When the SS concentration after standing for 30 minutes was measured, 440 g /
lit.

Reference Example 1 Each of the settling tank sludges obtained in Comparative Example 1 and Example 1 was dewatered with a vacuum dehydrator (400 mmHg), and the water content of the obtained dewatered cake was measured. Table 1 shows the results.

[0037]

[Table 1]

From the above results, it is clear that the method for reforming aluminum-containing sludge of the present invention can provide high-concentration sludge having excellent sedimentation, concentration and dehydration properties.

[0039]

As described above in detail, according to the method for reforming aluminum-containing sludge of the present invention, sludge having high concentration and excellent sedimentation, concentration and dewatering properties can be produced at low cost with a small amount of chemicals used. , And efficiently obtained. The sludge obtained by the method of the present invention can be made into a sludge having a lower moisture content than a dewatered cake obtained by subjecting sludge to a dewatering treatment by a conventional method only by a concentration treatment. This makes it possible to eliminate or reduce the dehydrator. In addition, since sludge having a low water content is obtained as described above, the cost of drying when aluminum in the sludge is recovered and reused is greatly reduced. Furthermore, even when disposing as a dewatered cake, since the sludge volume is small, it can be treated at low cost and handling is extremely easy.

[Brief description of the drawings]

FIG. 1 is a system diagram showing one embodiment of a method for reforming an aluminum-containing sludge of the present invention.

FIG. 2 is a system diagram showing a coagulation precipitation treatment method using an aluminum salt.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction tank 2, 3 Coagulation tank 4 Precipitation tank 21 Acid dissolution tank 22 Alkaline dissolution tank 23 Neutralization reaction tank 24, 25 Coagulation tank 26 Precipitation tank

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-52-123977 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 11/00

Claims (1)

(57) [Claims] 1. A part of aluminum-containing sludge is dissolved with an acid, and the remaining part is dissolved with an alkali, and the obtained acid solution and alkali solution are mixed in a reaction vessel to form an insolubilized product. A method for reforming an aluminum-containing sludge to be subjected to post-solid-liquid separation, wherein a part of the separated insolubilized product is returned to the reaction tank.