JPH0929288A - Method for removing heavy metal in sewage sludge or the like - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively remove a heavy metal and to convert sewage sludge or the like into manure high in safety by decompressing the inside of a cooker while bringing sewage sludge and factory effluent or the like into contact with heating oil heated in the cooker and performing dewatering treatment and also decomposing the molecules of heavy metals by a free fatty acid produced by oxidation of oil. SOLUTION: Single oil such as animal oil, fish oil or vegetable oil or mixed oil thereof is held in a cooker and heated at 50-230 deg.C. In this case, sewage sludge is charged into the cooker 1 and immersed in the heated oil and agitated by many blades 4 and also the inside of the cooker 1 is kept in a decompression state. Thereby, oxidation of oil is promoted and the acid value of the oil is increased and a free fatty acid is produced. Molecules of heavy metals are decomposed by bringing the free fatty acid into contact with the heavy metals contained in sewage sludge and factory effluent and the heavy metals are removed. Then, treated substance applied to dehydration treatment is taken out from the cooker 1 and deoiled until about 1-20% by a compressor and thereafter finely crushed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for removing heavy metals from sewage sludge and the like.

[0002]

2. Description of the Related Art Conventionally, sewage sludge treated at a sewage treatment plant or the like, factory effluent or the like is used at 75% to 8% by utilizing, for example, a belt press, a screw press or a centrifuge.
It was dehydrated by 5%, and thereafter, the treated product was incinerated or buried in a landfill.

However, since this sewage sludge contains active ingredients such as nitrogen, ammoniacal nitrogen, phosphoric acid and potassium, it has recently been used as a fertilizer in fields and the like.

[0004]

However, the sewage sludge and factory effluent treated by the above method have the following drawbacks.

That is, such sewage sludge and factory effluent contain heavy metals such as mercury, cadmium and arsenic in addition to the active ingredients, and these heavy metals adversely affect crops,
I could not use it with confidence.

It is an object of the present invention to provide a method for removing heavy metals such as sewage sludge and factory effluent which can solve the above problems.

[0007]

According to the present invention, sewage sludge, factory effluent, and the like are brought into contact with heated oil such as animal oil, fish oil, or vegetable oil heated in the cooker while the inside of the cooker is kept under a constant decompression condition. Decompress and stir and heat sewage sludge and factory effluent using heating oil as a heat medium to dehydrate sewage sludge and factory effluent, and at the same time oxidize oil by heat treatment of oil to generate by oxidation of oil. Molecules of heavy metals contained in the sewage sludge and factory effluent are decomposed by the free fatty acids that have been generated, and then the sewage sludge and the like is taken out from the cooker and deoiled to remove the heating oil from the sewage sludge and factory effluent. An object of the present invention is to provide a method for removing heavy metals such as sewage sludge, which is characterized by oiling.

Further, in the present invention, the pressure reduction in the cooker is
It is intended to provide a method for removing heavy metals such as sewage sludge, which is characterized by performing a combination of a small initial decompression and a large late decompression.

[0009]

The embodiments of the present invention will be described in detail with reference to the drawings. First, a single oil or a mixed oil such as animal oil, fish oil or vegetable oil is stored in a cooker 1 of 10 m ² , and 50
Heat to a temperature in the range of ℃ to 230 ℃.

In this embodiment, the cooker 1 contains 2000 liters of heating oil as a heating medium.

Then, the sewage sludge is put into the cooker 1 described above, and the sewage sludge and factory effluent are immersed in heating oil to close the cooker.

In this embodiment, the heating oil is heated to 130 ° C.
While stirring, heat and stir the sewage sludge in the cooker 1,
Although the inside of the cooker is depressurized, the heating temperature is raised to about 180 ° C in the early stage of heating the heating oil to accelerate the oxidation of the oil and increase the acid value of the oil to produce free fatty acids. I'm trying to make a difference.

Here, in the first embodiment, in the cooker 1,
Sewage sludge, factory effluent, etc. are continuously added and treated, and the configuration will be described in detail below.

That is, the cooker 1 is a cylindrical horizontal type capable of accommodating heating oil. A jacket 2 is provided on the peripheral wall of the cooker 1, and an exhaust gas for removing steam inside the cooker 1 is provided above the jacket 2. A mouth 3 is provided.

Further, in the cooker 1, a rotary shaft 4a is axially supported in the axial direction, and a large number of stirring blades 4 for stirring the heating oil and the sewage sludge are attached to the rotary shaft 4a.

Further, a supply pipe 5 is connected to one side of the cooker 1 and the connecting portion of the pipe 5 is located below the oil level L of the heating oil.

A hopper 6 for containing sewage sludge is connected to the tip of the supply pipe 5, and the hopper 6 is connected to the hopper 6.
More into cooker 1.

In this embodiment, in the middle of the supply pipe 5,
A plurality of supply valves 7 and a pump P are provided, and the pump P
The sewage sludge is forcibly sent to the cooker 1 for processing.

Further, the supply valve 7 is used to maintain the reduced pressure condition in the cooker 1.

Further, a processed material outlet 8 is provided on the other side of the cooker 1, and a predetermined amount of processed material processed by the cooker 1 is taken out from the same outlet 8.

Further, the dehydrated product is taken out from the cooker 1 and deoiled by a press, a centrifuge, normal hexane or the like until it becomes about 1 to 20%. The deoiled processed product is in a dried state and then finely pulverized.

This treated product contains active ingredients such as nitrogen, ammoniacal nitrogen, phosphoric acid and potassium, and is used for fertilizers and the like.

In such a treatment process, the heating oil is oxidized by the initial high temperature heating, the acid value is increased, and free fatty acid is produced, and the free fatty acid is a heavy metal contained in sewage sludge or factory effluent. When it comes into contact with, it decomposes molecules of heavy metals to remove heavy metals contained in sludge, drainage and the like.

In order to convert the oxidized oil into an oil having a low acid value, it is necessary to carry out deoxidation refining. For that purpose, it is necessary to neutralize the acid by adding an alkali for deoxidation. it can.

Therefore, when the oil obtained by producing free fatty acids and decomposing heavy metals is used for treating other raw materials, it is used after being deoxidized and refined with an alkali.

Further, the heating oil in the cooker after the dehydration treatment and the oil deoiled from the processing raw material may contain a part of heavy metal which is not decomposed. In this case, 1
After adding 0% water or alkali and washing with water and stirring, it is possible to remove a heavy metal as a solid content from water or oil by applying a centrifugal separator and utilizing the difference in specific gravity between oil and water and heavy metal.

In the second embodiment, when the depressurizing process is performed, the sewage sludge and the factory effluent are immersed in heating oil, and then treated under a small depressurizing condition, and then under a large depressurizing condition. Perform dehydration treatment and continue oil temperature dehydration for about 1 hour.

That is, in this embodiment, the initial value is 20
About 10 minutes to 20 mmHg decompression from normal pressure,
In the latter half of the period, about 740 to 40 minutes from normal pressure for about 40 minutes.
The pressure is reduced to 750 mmHg and treated until the water content becomes 5 to 6%.

By such a two-stage depressurization process, the active ingredients in the sewage sludge are first solidified and stabilized in the initial stage to prevent the active ingredients contained therein from flowing out.

In the latter stage, the water contained in the sewage sludge is evaporated, and the heating oil is allowed to penetrate into the sludge after the evaporation of water to replace the water with the heating oil.
By such replacement, a reliable dehydration treatment is performed.

Further, the dehydrated product is taken out from the cooker and deoiled by a press, a centrifuge, normal hexane or the like until the content becomes about 1 to 20%.

The deoiled sewage sludge is in a dried state and then finely pulverized, and the treated product contains active ingredients such as nitrogen, ammoniacal nitrogen, phosphoric acid and potassium. Used for raw materials such as fertilizer.

In such a treatment process, the heating oil is oxidized by the initial high-temperature heating, the acid value is increased, and free fatty acids are produced, and the free fatty acids are the heavy metals contained in the sewage sludge and factory effluent. When it comes into contact with, it decomposes molecules of heavy metals to remove heavy metals contained in sludge, drainage and the like.

In order to convert the oxidized oil into an oil having a low acid value, it is necessary to carry out deoxidation refining. For that purpose, it is necessary to neutralize the acid by adding an alkali for deoxidation. it can.

Therefore, when the oil obtained by producing free fatty acids and decomposing heavy metals is used for treating other raw materials, it is used after being deoxidized and refined with an alkali.

Further, the heating oil in the cooker after the dehydration treatment and the oil deoiled from the processing raw material may contain a part of heavy metal which is not decomposed. In this case, 1
After adding 0% water or alkali and washing with water and stirring, it is possible to remove a heavy metal as a solid content from water or oil by applying a centrifugal separator and utilizing the difference in specific gravity between oil and water and heavy metal.

In this embodiment, the cooker has about 4000
When adding kg of sewage sludge, approximately 200
It is possible to collect kg of processed material.

Here, the analysis results of the sewage sludge before treatment and the sewage sludge after treatment by the above-mentioned removal method will be described in detail.

That is, Table 1 shows the analysis results of the sewage sludge before treatment, and when treated by the above method, the results shown in Table 2 are obtained.

[0040]

[Table 1]

[0041]

[Table 2]

Thus, from Tables 1 and 2, according to the above method, effective heavy metals can be removed from sewage sludge.

The dewatered water from the sewage sludge was collected by the above method, and the analysis results are shown in Table 3.

[0044]

[Table 3]

According to Table 3, heavy metals such as mercury, cadmium, and arsenic in the sewage sludge were not detected in the water dewatered from the sewage sludge because they were all below the detection limit value. It was decomposed and removed from the sewage sludge.

As described above, the sewage sludge can be easily used as a soil conditioner or the like without removing the heavy metals by the above method and incinerated, and the recovered water can be directly used in rivers and the like. Can be flushed.

[0047]

According to the present invention, the sewage sludge or the factory effluent is dehydrated under constant depressurization conditions while continuously feeding the sewage sludge or the factory effluent into the cooker containing the heated oil by a pump. Stabilize the active ingredients in the solidification, prevent the outflow of the active ingredients contained in these, and evaporate the water contained in the sewage sludge, and permeate the heating oil into the sludge after the water evaporation to remove the sludge. In this, water is replaced with heating oil, and a reliable dehydration treatment is performed by such replacement.

Further, in the present invention, sewage sludge and factory effluent are put into a cooker containing heated oil and treated under a small reduced pressure condition, and thereafter, the sludge is dehydrated under a large reduced pressure condition. In the initial stage, the active ingredients in the sewage sludge are solidified and stabilized to prevent the active ingredients contained therein from flowing out.

Further, in the latter stage, the water contained in the sewage sludge and factory effluent is evaporated, and the heating oil is allowed to penetrate into the sludge after the water evaporation to replace the water with the heating oil. By such replacement, a reliable dehydration treatment is performed.

That is, when the heating oil is permeated into the sewage sludge after water evaporation and the factory effluent to replace the water with the heating oil in the sludge, the free fatty acid generated by the oxidation of the heating oil is sewage. Molecules of heavy metals contained in sludge and factory effluent can be divided to easily remove heavy metals from sewage sludge and factory effluent.

Then, the dehydrated product is taken out from the cooker and deoiled by a press, a centrifuge, normal hexane or the like until the content becomes about 1 to 20%.

Further, the deoiled sewage sludge and factory effluent are in a dried state and then finely crushed,
This treated product contains active ingredients such as nitrogen, ammoniacal nitrogen, phosphoric acid and potassium, and can be used as a raw material for fertilizers and the like.

As described above, by removing heavy metals from sewage sludge and factory effluent by the above method, it is possible to obtain a fertilizer that can be used safely without affecting crops.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of a treatment apparatus for sewage sludge, factory effluent, etc. according to the present invention.

[Explanation of symbols]

 1 Cooker 2 Jacket 5 Supply pipe 6 Hopper 7 Supply valve P Pump

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] July 25, 1995

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0043

[Correction method] Change

[Correction contents]

The dewatered water from the sewage sludge was collected by the above method, and the analysis results are shown in Table 3. In addition, each numerical unit of the test result of Table 1, Table 2, and Table 3 is P. P. M.

Claims (2)

[Claims] 1. The sewage sludge, factory effluent, etc. are brought into contact with heating oil heated in the cooker, such as animal oil, fish oil or vegetable oil, and the inside of the cooker is depressurized under a constant depressurized condition to heat the heating medium As a result, the sewage sludge and factory effluent are stirred and heated to dehydrate the sewage sludge and factory effluent, and the oil is oxidized by the heat treatment of the oil. Sewage characterized by decomposing heavy metal molecules contained in effluent, etc., then removing sewage sludge etc. from the cooker and deoiling heating oil from sewage sludge and factory effluent etc. by deoiling treatment Method for removing heavy metals such as sludge. 2. The method for removing heavy metals such as sewage sludge according to claim 1, wherein decompression in the cooker is performed by a combination of a small initial decompression and a large late decompression.