JPH0749120B2 - Sludge treatment method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to treatment and disposal of sludge generated by treatment of tap water, sewage and various industrial wastewater.

[0002]

2. Description of the Related Art Conventionally, a large amount of sludge is generated in the treatment of tap water, sewage and various industrial wastewater, and particularly when treating sewage such as sewage by an activated sludge method, a large amount of sludge is generated.
These sludges are usually reduced in volume through processes such as concentration, dehydration, drying, incineration, etc., and then disposed of in landfill.
Since these sludges have a high water content and are difficult to dehydrate, they consume a great deal of expense and energy for their treatment and disposal, and those that are incinerated can be reused as they are. Since it is not something that can be done and there is no choice but to reclaim it, there is no room at the disposal site, and we are struggling to deal with it.

Regarding the treatment of sludge using clay minerals, the present applicant has been conducting research for some time, and in Japanese Patent Publication No. 52-18668, the amount of 3 to 50 kg per ton of suspended solids was previously mentioned. A method for treating a suspension is proposed in which bentonite and a polymer flocculant are added, and the mixture is supplied to one end of a horizontal cylindrical rotary container to give a rolling motion to separate a solid from a liquid.

Further, regarding the same treatment of a suspension, the applicant of the present invention discloses in Japanese Patent Publication No. 53-13059 that a polymer flocculant and bentonite are added to a suspension containing suspended solids, and a treatment tank is added. The concentration of suspended solids in the vessel is 5 to 300 g /
While maintaining the liter, the liquid is given a swirling flow by a rotary blade in the processing tank, and the suspended solid in the liquid is granulated into a pellet-like solid by using a processing tank in which the swirling flow is not disturbed. A solid-liquid separation method for separating is proposed.

Further, in Japanese Patent Laid-Open No. 54-16845, clay minerals are used for treating organic wastewater sludge, and the first settling tank sludge and surplus generated from organic wastewater treatment plants such as sewage treatment plants. After adding bentonite to activated sludge or organic waste sludge of these mixed sludges, add anionic polymer coagulant or nonionic polymer coagulant, or mixed polymer coagulant of these sludges to coagulate sludge Suggesting a way to do it.

[0006]

In any of the above-mentioned methods, the expansiveness of bentonite is used to enhance the effect of the organic polymer flocculant, to form a relatively strong agglomerate, and to enhance the dehydration efficiency. To do. However, even with these methods, the water content cannot be significantly lowered, the contribution to the total cost of sludge treatment is small, and no significant improvement is made, so further efficiency improvement is required. .

According to the present invention, when treating sludge or its dehydrated cake, the clay mineral is replaced with divalent metal ions.
By adding this and leaving it for a certain period of time, a self-shrinking action is caused in the clay mineral, and by this action dehydration and solidification proceed, and a sludge treatment method that leads to a dry solidification state with less energy is provided. The purpose is to do.

[0008]

The object of the present invention can achieve the above object by the following means. (1) Substitution of a cation-exchangeable clay mineral containing silicon oxide and aluminum oxide as main components with divalent metal ions
After adding it to the sludge to dehydrate it, the dehydration case
A sludge treatment method characterized by dehydration and solidification by leaving ki for a certain period of time.

(2) A cation-exchangeable clay mineral containing silicon oxide and aluminum oxide as main components is replaced with a divalent metal ion, and this is added to and mixed with a dehydrated cake of sludge.
Then , the sludge treatment method is characterized in that it is dehydrated and solidified by leaving it for a certain period of time. Examples of the clay mineral having cation exchange properties containing silicon oxide and aluminum oxide as main components used in the present invention include, for example, bentonite, sauconite, nontronite, saponite, hectorite, vermiculite, and the like. The composition is such that the ratio of silicon oxide: aluminum oxide is approximately 4: 1 to 2: 1 and other oxides such as iron, calcium, sodium, magnesium and titanium are included.

The clay mineral basically has a sandwich structure in which silicon oxide sandwiches aluminum oxide in terms of a mineral structure, and the main constituent is a multilayer structure in which this is a unit layer. Since the silicon oxide side of this unit layer has a large amount of anion charge, when the unit layers overlap, they electrically repel each other, and as a result, the interlayer portion becomes elastic and at the same time the permanent anion charge is Since it has a cation exchange ability, it usually has a monovalent metal ion as the cation.

In the present invention, a clay mineral modified by substituting it with a divalent metal ion is used. This metamorphic clay mineral is hereinafter referred to as "metamorphic clay mineral". The modification is performed by immersing the clay mineral in a solution of a divalent metal compound that releases a divalent metal ion, and replacing the monovalent metal ion in the clay mineral with the divalent metal ion or adding the divalent metal compound to the clay mineral. It is good to add and mix. Two
As the valent metal compound, it is preferable to use a water-soluble salt such as calcium, magnesium or barium. Among these, it is preferable to use a calcium salt, for example, calcium chloride.

For reference, the case where the clay mineral and the divalent metal compound are added to the sludge or the dehydrated cake thereof is shown for reference. Both of them may be added simultaneously or separately. The mineral may be added first, or vice versa, the divalent metal compound may be added first. Further, when the clay mineral and the divalent metal compound are added, the clay mineral 1
It is preferable to use 5 to 30 parts by weight of the divalent metal compound with respect to 00 parts by weight, but the addition ratio is clay mineral or 2 parts by weight.
It also depends on the type of valent metal compound.

The amount of the above-mentioned modified clay mineral added to the sludge varies depending on the properties of the sludge or the modified clay mineral, particularly the properties of the sludge, but in the case of the inorganic sludge, it is relatively small,
As the amount of organic substances increases, the amount of the modified clay mineral to be added is preferably 5 to 100% by weight, and more preferably 10 to 50% by weight, based on the solid content of sludge.
Generally, the larger the number, the more preferable. The amount of the divalent metal compound used may be basically the amount required for cation exchange, but some sludges have an acidic pH, and preferably the pH is neutral or higher. It is better to add 5 to 30% by weight to clay minerals, especially 10 to 20
% By weight is preferred, and 2 to 5 for sludge solids
0% is suitable. In these cases, a polymer coagulant may be used in combination, and any polymer coagulant that is already known may be used.

As described above, the above-mentioned modified clay mineral is added to sludge and then dehydrated. As the dehydrating means, known separating means such as filtration, centrifugal separation, belt press, filter press and the like can be used. Then, the dehydrated cake generated by the dehydration operation is left for a certain period of time. The leaving time is sufficient for increasing the degree of solidification of the dehydrated cake. Incidentally, the metamorphic clay mineral in dehydrated cake or clay mineral and may be added a divalent metal compound.

When the above-mentioned modified clay mineral is added to sludge,
In order to improve dispersibility in sludge, it is better to add a slurry . Furthermore, when the modified clay mineral or the like is added, it may be added not to the sludge but to the dehydrated cake of the sludge. In that case, it is usually added in powder form, but it is necessary to sufficiently mix it with the dehydrated cake with a kneader or the like. There is.

[0016]

The clay mineral used in the present invention has a structure in which the layers are stretchable and contractible, and the present invention utilizes this property. However, in the clay mineral used here, the cation is usually 1 Since it is a valent metal, it is necessary to add a divalent metal compound having a cation of a divalent metal to perform cation exchange. However, if the clay mineral originally contains a divalent metal ion, a cation is particularly preferable. There is no need for replacement (such clay minerals are also included in the above “metamorphic clay mineral”).

The difference between the monovalent type and the divalent type is that the monovalent type is very hydrophilic and swells significantly when water is added, but the divalent type reduces the hydrophilicity and swells. The degree is significantly reduced. For this reason, in the present invention, it is important that the cation to be contained is a divalent metal, and the divalent metal compound used for the cation exchange may be any kind as long as it contains a divalent metal ion. It does not matter whether it is an organic substance or an inorganic substance, but it is preferable to use a compound such as calcium or magnesium.

In the present invention, by adding the above-mentioned modified clay mineral and the like to sludge, the action of self-dehydration occurs after the dehydration operation. The mechanism of this self-dehydration will be described. When it is added to sludge and dehydrated, the sludge particles are cross-linked with the clay mineral by the divalent metal ions. This cross-linking action causes an electrical displacement in the stretchable part of the clay mineral, causing a deformation in the inter-layer lattice, and also changes the coordination state of the adsorbed water to reduce the hydrophilicity, resulting in adsorption. The water that had been released is released, and the interlayer portion self-contracts. The sludge particles trapped between the clay mineral lattices are dehydrated as the clay mineral shrinks, and as the dehydration progresses, the crosslinking is strengthened and solidification proceeds.

Therefore, when treating sludge, it is necessary to bring the clay mineral into good contact with the sludge by a dehydration operation, but there is no restriction on the dehydrator used for it, and a belt press is used in the following examples. Therefore, the organic polymer coagulant is used for coagulation, but the organic polymer coagulant is not always necessary depending on the model and the type of sludge. Further, the action of self-dehydration occurs by adding and mixing the above-mentioned modified clay mineral to the dehydrated cake.

To complete self-dehydration and solidification, it must be left for a certain period of time, but it is necessary to chemically promote the crosslinking action of the divalent metal, physically blow hot air, or dehumidify the environment. By doing so, the action can be promoted and the dehydration and solidification can be completed in a short time. Further, the solidified material has a considerable breaking strength, at the same time it is not re-dispersed or broken even when it comes into contact with water, and since water absorption and water retention are high, various effective utilization methods are conceivable.
One of the methods is to mold it into a shape suitable for the purpose and then solidify it, and it can also be used as a means for containing harmful substances.

[0021]

EXAMPLES The present invention will be specifically described below with reference to examples. However, the present invention is not limited to this embodiment. Example 1 Sewage mixed raw sludge was used as the sludge to be solidified, and the sludge concentration was 17.2 g / liter. Bentonite (mainly montmorillonite) was used as the clay mineral to be added, and its addition rate was 20% with respect to the solid matter of sludge, and slaked lime was used as the divalent metal compound added with it, and the addition rate was sludge. To 4% of solids. Since a belt press was used as a dehydrator for dewatering sludge, bentonite and slaked lime were added and mixed, and then an organic polymer compound flocculant (addition rate 0.7%) was added for dewatering.

For comparison, when only the organic polymer compound flocculant was added (addition rate 0.7%) (Comparative Example 1),
Dehydration was also performed in the case where bentonite (addition rate 20%) and an organic polymer coagulant (addition rate 0.7%) were added (Comparative Example 2). As for the water content of the dehydrated cake obtained by the dehydration, as a result of adjusting the dehydration conditions so that the water content of each cake was almost the same, 78.5 in Comparative Examples 1 and 2.
%, 79.1%, and in the case of the present invention, it was 78.2%.

Next, 20 g of each dehydrated cake was allowed to stand for about 18 hours, and changes in the solidified state and cake water content (weight) over time were measured. The results are shown in Table 1,
The environment that was left was a humidity of 54% and a temperature of 22 ° C.

[0024]

[Table 1] In this measurement, since the sample was left in the air, there was evaporation of water due to drying, and in the case of Comparative Example 1 in which only the organic polymer coagulant was added, the decrease in water content was solely due to drying. On the other hand, in the case of Comparative Example 2 in which the clay mineral was added but the divalent metal compound was not added, the decrease in water content was the same as in the case of adding only the organic polymer coagulant, and the self-shrinking phenomenon was recognized. There wasn't. However, in the case of the present invention, as is clear from Table 1, the decrease rate of the water content is comparative example 1.
It is significantly higher than in the cases of 2 and 2, and the dehydration action by the self-shrinkage of the clay mineral is exerted in addition to the drying.

[0025]

EFFECTS OF THE INVENTION According to the present invention, when treating sludge or its dehydrated cake, the clay mineral and the divalent metal compound are used and the dehydration is carried out by the self-shrinking action of the clay mineral, simply by allowing it to stand for a certain period of time. Solidification progresses at the same time, and it is possible to lead to a dry solidification state at once with a small amount of energy. This solidified product is not redispersed or destroyed even when it comes into contact with water, and since it has high water absorption and water retention, it can be effectively used in various fields, and the amount sent to landfill is reduced. , Will help the disposal site measures. Moreover, since the sludge treated by the present invention is in a solidified state, it is very easy to handle.

Claims (2)

[Claims] 1. A clay mineral having silicon oxide and aluminum oxide as main components and having a cation exchange property is replaced with a divalent metal ion, and this is added to sludge for dehydration, followed by removal thereof.
Dehydrate and solidify by leaving the water cake for a certain period of time
Processing method of sludge, characterized in that. 2. A clay mineral having silicon oxide and aluminum oxide as main components and having a cation exchange property is replaced with a divalent metal ion, and this is added to and mixed with a dehydrated cake of sludge,
A sludge treatment method characterized by being dehydrated and solidified by leaving it for a certain period of time.