JP2683225B2 - Method for producing activated carbon and method for using the activated carbon for water treatment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-value-added activated carbon obtained from activated sludge generated in large quantities during biological treatment of sewage, a method for producing the activated carbon, and a method for using the activated carbon for water treatment. It is a thing.

[0002]

2. Description of the Related Art Conventionally, dehydrated sludge, which is produced in large quantities during sewage treatment, is mainly incinerated, and useful substances are not recovered and resources are not utilized. In addition, landfill disposal of incinerated ash has many problems such as enormous cost and it becomes more and more difficult to secure a disposal site. In addition, sludge is slagged and melted as a recent sludge treatment method, but it is difficult to say that the materials obtained from these are effectively utilized.

Further, various methods for carbonizing and activating sewage sludge to obtain an adsorbent have been proposed, but these attempts are technically established because they contain a large amount of inorganic substances. That is not the case at present. As mentioned above, it is required to establish technologies for volume reduction and reuse of sewage sludge at an early stage.

By the way, when producing activated carbon in Japan, wood, sawdust, coconut shell, coal,
There is a background that most of the carbonaceous materials such as lignite are dependent on imports. On the other hand, from the viewpoint of securing water resources, there is a demand for inexpensive activated carbon with excellent purification capacity in order to purify and reuse water.

In this respect, sewage sludge contains many inorganic substances containing calcium, iron, aluminum, phosphorus, silicon and magnesium as main components, and gas activation method using steam and carbon dioxide, zinc chloride, phosphoric acid and alkali metal salts are used. It was difficult to obtain activated carbon by the chemical activation method used. For example, attempts have been made to obtain activated carbon (decoloring agent) by directly carbonizing and activating the sewage sludge after dewatering it, but activated carbon (decoloring agent) with high performance has not been obtained because of many inorganic substances. Also, it is known that sewage sludge is activated by carbonization and steam in a nitrogen atmosphere, but in this case, no inorganic substance is added as a coagulant,
Even when using raw sludge that has been flocculated with a polymer flocculant and centrifuged,
Specific surface area 54 to 69 m ² / g, pore volume 0.06 to 0.
10 ml / g, iodine adsorption amount 93-151 mg / mg,
Only about 1/10 the performance of commercial activated carbon has been obtained.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to use inexpensive and high-performance activated carbon, a method for producing the activated carbon, and the activated carbon for water treatment. To provide a way to do.

[0007]

In order to achieve the above object, the gist of the present invention is to carbonize sewage sludge, extract inorganic substances with an acid, and subsequently perform activation treatment to obtain a specific surface area of 1300 m ^2. / G or more, the pore volume is 3.00
A method for producing activated carbon having an amount of ml / g or more is a first invention, and in the above-mentioned first invention, an alkali metal silicate is added as a foaming agent and activator when carbonizing sewage sludge. A second invention is a method for producing activated carbon,
After sewage was subjected to circulation nitrification denitrification and then sand filtered, the specific surface area was 1300 m ² / g or more and the pore volume was 3.00 ml /
A third invention is a method of using activated carbon for water treatment, which is characterized in that it is passed through a container filled with activated carbon of g or more.

In the above-mentioned first invention, a method for producing activated carbon characterized in that sodium hydroxide is used as an activating agent is referred to as a fourth invention. In the above-mentioned first invention, the activation temperature is 350 to 450 ° C. After heating for a certain time,
A method for producing activated carbon, which comprises heating at 450 to 900 ° C. for a certain period of time, is a fifth invention, and in the above first invention, sodium hydroxide is used as an activator and an activation temperature is 350 to 450 ° C. After heating for a certain time,
A method for producing activated carbon, which comprises heating at 450 to 900 ° C. for a certain period of time, is defined as a sixth invention, and in the second invention, the amount of alkali metal silicate added is increased to produce activated carbon. The method is the seventh invention.

Sewage sludge is molded directly or after adjusting the water content. To 1000 parts by weight of dried solid matter in sewage sludge, 1 to 250 parts by weight of an alkali metal silicate is added as a molding agent, a foaming agent and an activator, When the mixture is kneaded and then molded, it reacts with the inorganic substances in the sludge to gel, and a molded product that is easy to handle can be obtained.

When this molded product is dried and then heat-treated at 300 to 800 ° C., a carbide containing 20 to 75% by weight of an inorganic substance can be obtained.

Crushed charcoal can be obtained by crushing this charcoal, and pulverized charcoal can be obtained, but in order to efficiently obtain a charcoal having a certain shape by using a sieve or the like, 1000 parts by weight of sewage sludge solid matter is required. In addition, by adding 1 to 250 parts by weight, preferably 5 to 100 parts by weight of an alkali metal silicate, and heat-treating after molding, an appropriate strength can be obtained and it is not pulverized,
A constant shape can be maintained in the subsequent steps.

Hydrochloric acid, perchloric acid, chloric acid, chlorous acid, hypochlorous acid, sulfuric acid, nitric acid, acetic acid, formic acid and their mixed acids are added to the above-mentioned carbides in an amount equal to or more than the equivalent of the metals in the inorganic material, preferably 1 equivalent. Most of the metals are eluted in the acid solution when the mixture is added at least 5 times and heated and stirred. The inorganic substance eluted in the acid solution is reused as a useful industrial raw material after the precipitation and separation of iron phosphate and calcium phosphate using the PH / solubility product and the recovery of phosphorus by selective adsorption. The above acid solution is filtered and washed with water several times, but the first 2 to 5 times is 0.001 to 1 times.
It is preferable to wash with water with N / l acid, and in this way, metal hydroxide precipitates that hinder activation are not formed in the carbide pores.

After pickling, the washed carbonaceous product is dried to obtain 1
While having a specific surface area of 00 to 300 m ² / g,
A porous carbide with a pore volume of 0.5-1.5 ml / g is obtained. The above values are close to those of charcoal, which is good quality activated carbon. When observed with a scanning electron microscope at a magnification of 1,000 to 5,000 times, this carbide does not show a large honeycomb structure formed of a temporary charcoal conduit or cell membrane. ~
Over a wide range of up to 2 × 10 ⁶ Å, macropores, mesopores and micropores having a diameter smaller than that of the carbide particles were evenly distributed in the traces of the inorganic substances eluted by the acid.
It exhibits porosity as a good quality activated carbon raw material. In addition, in the porous carbide, an inorganic substance whose main component is acid-insoluble silicon,
5-40% by weight remains.

In order to activate the above-mentioned porous carbide to obtain high-performance activated carbon, a chemical activation method using an alkaline chemical is preferable, in which an inorganic substance containing silicon as a main component is eluted to form macropores, which is further peculiar to chemical activation. Micropores and mesopores are generated.

A known method may be used for the activation with the above-mentioned alkaline chemicals. For example, it is mixed with an alkaline chemical and heat-treated at 350 to 900 ° C. in an inert gas atmosphere,
A method of activating after elution of an inorganic substance containing silicon as a main component is preferable, and the temperature is kept at a temperature of 350 to 450 ° C., which is a temperature above the melting point of the alkaline chemical and the activation reaction rate of the carbide is slow, for 0.5 to 5 hours. After that, raise the temperature to 450-9
0.25-5 hours at 00 ° C, more preferably 650-8
When activated at 50 ° C. for 0.5 to 3 hours, the yield and adsorption performance are improved, which is economical.

After activating the alkali, it is dissolved, filtered and washed with water.
After repeated washing with water, 0.001 to 3 N / l hydrochloric acid, nitric acid, sulfuric acid and mixed acid thereof are added to acidify, decalcify, neutralize and wash. When silicic acid remains in the solution, it turns into silicic acid gel. Although the performance of activated carbon is reduced, the silicic acid gel has a slower sedimentation rate than activated carbon, and can be separated together with the supernatant liquid by repeated stirring and decantation. The dissolution is 2 to 50 times the volume of the added alkaline drug, preferably 2 times.
If you add 10 times the volume of water, the alkali concentration will be high,
It does not precipitate silicic acid gel, has a high filtration rate and is efficient.
High-performance activated carbon can be obtained by drying after the above operation.

In order to obtain granular activated carbon from the activated carbon obtained by the above-mentioned method, a known method may be used. Phenolic resin, urea resin, pitch, which can obtain strength of the molded product,
1 to 1 of tar, sodium alginate, formalin condensate of naphthalene sulfonate, or resin of lignin main material
Granular activated carbon can be obtained by adding 30% by weight as a binder, kneading, granulating and heating in an inert gas atmosphere at 150 to 850 ° C. for 30 minutes to 5 hours.

[0018]

[Function] By treating the carbonized sewage sludge with an acid to elute the inorganic substances in the carbide to obtain a porous carbide, and further activating the carbide, the specific surface area / pore volume is large,
It is possible to obtain activated carbon having excellent adsorption performance.

If sodium hydroxide is used as the activator, activated carbon having particularly developed mesopores (pore radius of 10 to 250 Å) can be obtained. Also, when activating this,
As the activation temperature, by adopting the two-stage heating of heating at 350 to 450 ° C. for a certain period of time to elute the inorganic substance, and then heating at 450 to 900 ° C. for a certain period of time, the yield and the adsorption performance are improved and the mesoscopic property is improved. The holes can be increased. The temperature of the second stage heating in this second stage heating is 90
If it exceeds 0 ° C, the yield with respect to the carbide obtained by extracting the inorganic substance with an acid will be extremely reduced, and if it is less than 450 ° C, the adsorption performance will be low.

When the sludge is carbonized, it is molded directly or after adjusting the water content, but if an alkali metal silicate is added, a molded product that is easy to handle can be obtained without adjusting the water content. Furthermore, by increasing the addition amount of this alkali metal silicate, activated carbon with a high ratio of micropores and mesopores can be obtained.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. [Example 1] Excess sludge of a split-type urban sewage treatment plant as sewage sludge was dehydrated with a belt press using ferric chloride as a coagulant. Dehydration of water content 77.49% by weight and ignition loss 14.41% by weight. Using sludge as a raw material, molded into a cylindrical shape with a diameter of 40 mm and a length of 80 mm, and the cylindrical shape has a water content of 20% by weight.
And dried in a dryer to maintain the temperature at 650 ° C. or lower to obtain a carbide. This carbide was crushed to a diameter of 2 mm or less using a crusher, and hydrochloric acid with a concentration of 7% by weight was used in a weight ratio of 1
A 0-fold amount was added, and the mixture was boiled while stirring for 20 minutes. afterwards,
Suction filtration is carried out, the acid solution is separated, and the mixture is taken up with 0.01 N / l hydrochloric acid
After washing twice, the filtrate was repeatedly washed with water until PH of 5 or more, and dried at 110 ° C. for 2 hours with a drier to obtain a charcoal-based material. Further, the obtained carbide was put into a nickel crucible, potassium hydroxide was added in an amount of 3 times by weight, and the temperature was kept at 450 ° C. in a nitrogen gas atmosphere for 1.5 hours, then at 650 ° C.
The temperature was raised to 2 and heated for 2 hours for activation. After cooling, it was dissolved in 10 times volume of potassium hydroxide, suction filtered, and the activated charcoal obtained by separating the alkaline solution was transferred to a vessel for washing with water and stirred until the pH of the washing solution reached 10. The sedimentation (decantation) was repeatedly washed with water. After that, 0.1
The mixture was stirred in a N / l hydrochloric acid solution for 10 minutes and decalcified. After deashing, suction filtration was performed, and the filtrate was repeatedly washed with water until the pH became 5, and then dried at 110 ° C. for 2 hours to obtain activated carbon.

Example 2 The same dehydrated sludge as in Example 1 was used as a raw material, and sludge 100 was used as a molding agent / foaming agent / activator.
In 0 part by weight, JIS No. 3 sodium silicate aqueous solution (composition:
Na ₂ O = 9.26% by weight, SiO ₂ = 28.26% by weight) 12.6 parts by weight mixed with 50 parts by weight of water was added and kneaded. The same treatment as in Example 1 was carried out to obtain activated carbon.

[Embodiment 3] In Embodiment 2, according to JIS3
Activated carbon was obtained by the same treatment as in Example 2 except that the amount of the No. sodium silicate aqueous solution added was changed to 25.2 parts by weight.

The compositions (parts by weight) of the carbides obtained from the dehydrated sludge moldings in Examples 1 to 3 are shown in Table 1 below.

[0025]

[Table 1]

The physical properties of the activated carbons obtained in Examples 1 to 3 are shown in Table 2 below, and the physical properties of commercially available activated carbons are shown in Table 3 for comparison.

In Tables 2 to 5, Table 7 and Table 8, the gas adsorption method (BET method), the nitrogen gas adsorption method and the mercury injection method are the test methods having the following contents. Gas adsorption method (BET method) = a method of adsorbing gas molecules on a solid surface, measuring the amount of adsorption at a certain adsorption equilibrium pressure, and calculating by the BET formula.

Nitrogen gas adsorption method: A method of determining the pore distribution and pore volume from the adsorption isotherm by changing the relative pressure of nitrogen gas stepwise. Mercury injection method = A measurement method that utilizes the fact that mercury is pressed into the pores sequentially by applying pressure. The pore diameter is obtained from the required pressure, and the pore volume is obtained from the press-fitted amount.

[0029]

[Table 2]

[0030]

[Table 3]

As is clear from Tables 2 and 3, this Example 1
Those of Nos. 3 to 3 have a larger specific surface area and pore volume than commercial activated carbon and are excellent in methylene blue adsorption performance.

In Examples 1 to 3 described above, the amount of JIS No. 3 sodium silicate aqueous solution (alkali metal silicate) added was changed with respect to 1000 parts by weight of sewage sludge when carbonizing the sewage sludge. A comparison of pore volumes is shown in FIG. 1, a comparison of cumulative pore volumes is shown in FIG. 2, and a comparison of differential pore volumes is shown in FIG.

In Example 1, JIS No. 3 sodium silicate aqueous solution was not added, and in Examples 2 and 3, JIS No. 3 sodium silicate aqueous solution was added in an amount of 12.6 parts by weight and 25.
2 parts by weight, and as is clear from FIGS. 1 to 3, when carbonizing the sewage sludge, the addition of the alkali metal silicate as in Example 2 or 3 increases the micropores and mesopores. By further increasing the addition amount (Example 3), activated carbon having a higher ratio of micropores and mesopores can be obtained.

In FIG. 1, micropores, mesopores,
The radius of each macropore is 5-10Å, 10-
250Å, 250-1500Å.

Example 4 Agglomerated and dehydrated in the same manner as in Examples 1 to 3, the water content was 75.40% by weight, and the loss on ignition was 16.
Using 40% by weight of dehydrated sludge as a raw material, the same treatment as in Example 1 was performed to obtain activated carbon. And 200 to this activated carbon
After adding water by weight% and moistening, add 20% by weight of formalin condensate of naphthalene sulfonate as a binder, knead with a kneader, and use a desk pelleter to obtain a diameter of 3 mm.
・ Granulate to a length of 3 mm, dry at 110 ° C for 4 hours in a drier, and then in a nitrogen gas atmosphere at a rate of 7 ° C / min.
After the temperature was raised to 0 ° C., the temperature was maintained for 2 hours for heat treatment to obtain granular activated carbon.

[Embodiment 5] The same dehydrated sludge 10 as in Embodiment 4
To 00 parts by weight, a mixture of 5 parts by weight of JIS No. 3 sodium silicate aqueous solution and 50 parts by weight of water was added and kneaded.
Thereafter, the activated carbon obtained by the same treatment as in Example 2 was further treated in the same manner as in Example 4 to obtain granular activated carbon.

The physical properties of the granular activated carbon obtained in Examples 4 and 5 are shown in Table 4 below, and for comparison, the physical properties of commercially available activated carbon for water treatment are shown in Table 5.

[0038]

[Table 4]

[0039]

[Table 5]

As is clear from Tables 4 and 5, those according to Examples 4 and 5 have pores over a wide range of micropores, mesopores, and macropores, and are higher than those of commercial activated carbon for water treatment. It has a large specific surface area and pore volume, and is superior to commercially available products in both methylene blue adsorption performance and iodine adsorption performance.

Example 6 An experiment was conducted to evaluate the adaptability of the granular activated carbon obtained in Examples 4 and 5 to water treatment. The method is as follows: Circulating nitrification denitrification of the first settling basin of the middle-scale diversion type urban sewer system, and sand filtering, and this raw water is used as piping 1, 2 or 3 as shown in FIG.
Diameter 1 filled with activated carbon C ₁ , C ₂ or C ₃ via
It is a method of passing water through gravity downflow through a column X, Y or Z of 30 mm and height of 750 mm. 4 is the water flow direction during backwashing. The experimental specifications are shown in Table 6 below.

[0042]

[Table 6]

FIG. 5 shows the changes in the COD removal rate and TOC removal rate with respect to the cumulative water flow rate obtained in Example 6. As is clear from FIG. 5, the samples according to Examples 4 and 5 are superior to the standard product in both the COD removal rate and the TOC removal rate.

[Embodiment 7] Aggregation in the same manner as in Embodiment 1,
To 1000 parts by weight of dehydrated sludge having a dehydrated water content of 74.50% by weight and a loss on ignition of 17.8% by weight, a mixture of 5.1 parts by weight of JIS No. 3 sodium silicate aqueous solution with 50 parts by weight of water was added. After kneading and molding in the same manner as in Example 1, the same treatment as in Example 1 was carried out to obtain activated carbon.

Example 8 Activated carbon was obtained in the same manner as in Example 7, except that sodium hydroxide was used instead of potassium hydroxide as the activator.

Example 9 In activating the obtained carbide in Example 7, the carbide was put into a nickel crucible, potassium hydroxide was added in an amount of 3 times by weight, and the temperature was maintained at 450 ° C. in a nitrogen gas atmosphere. Heat for 1.5 hours, then 8 more
Activated carbon was obtained by the same treatment as in Example 7, except that activation was performed by heating to 30 ° C. and heating for 2 hours.

[Example 10] In Example 7, when activating the obtained carbide, sodium hydroxide was used as the activator instead of potassium hydroxide, the carbide was put in a nickel crucible, and sodium hydroxide was used in a weight ratio. The same treatment as in Example 7 was carried out except that activation was carried out by a method of adding 3 times the amount, heating at 450 ° C. for 1.5 hours in a nitrogen gas atmosphere, heating to 830 ° C. and heating for 2 hours. To obtain activated carbon.

The methylene blue adsorption performance, iodine adsorption performance and specific surface area of the activated carbons obtained in Examples 7 to 10 are shown in Table 7 below, and a comparison of the pore volumes by the nitrogen gas adsorption method is shown in FIG. A comparison of pore volumes is shown in FIG. 7, a comparison of differential pore volumes is shown in FIG. 8, and a distribution of pore volumes is shown in Table 8 below.

[0049]

[Table 7]

[0050]

[Table 8]

As is apparent from FIGS. 6 to 8 and Table 8, by raising the temperature during activation (Example 9) or by using sodium hydroxide as an activator (Example 8),
The proportion of mesopores can be increased. The ratio of mesopores can be further increased by increasing the activation temperature and using sodium hydroxide as the activator (Example 10). Further, as is clear from Table 7, the materials according to Examples 8 to 10 are superior in methylene blue adsorption performance as compared with Example 7. The meanings of the pore radii of the micropores, mesopores and macropores are the same as in FIG.

[0052]

Since the present invention is configured as described above, the following effects can be obtained. According to the invention of claim 1 or 2, by utilizing the sewage sludge that has not been utilized as a useful resource,
It is possible to provide an inexpensive activated carbon manufacturing method with excellent performance. According to the invention of claim 1 or 2, it has a large specific surface area and pore volume as compared with a commercially available product, and has micropores (pore radius 10 Å or less), mesopores (pore radius 10 to 250 Å)
Also, it has pores over a wide range of macropores (pore radius 250 to 50000Å), and by utilizing this feature, it is possible to produce activated carbon that exhibits excellent performance even when used for water treatment. Furthermore, according to the invention described in claim 1 or 2, it is possible to produce activated carbon that can be used as biological activated carbon that takes advantage of macropores and the pore volume having a large pore radius exceeding 50,000 Å. According to the invention described in claim 3, water treatment can be efficiently performed. According to the inventions of claims 4 to 6, activated carbon having a high mesopore ratio can be produced. The activated carbon having many mesopores has excellent dye adsorption performance and can be suitably used for liquid phase adsorption having a large adsorption molecule diameter. According to the invention of claim 7, activated carbon having a high ratio of micropores and mesopores can be produced.

[Brief description of the drawings]

FIG. 1 is a view showing a distribution of pore volumes of activated carbon produced by the method of the present invention.

FIG. 2 is a diagram showing FIG. 1 in terms of cumulative pore volume.

FIG. 3 is a diagram showing FIG. 1 in terms of differential pore volume.

FIG. 4 is a diagram illustrating a water treatment experiment method.

FIG. 5 is a diagram showing changes in COD and TOC with respect to the cumulative water flow rate in a water treatment experiment.

FIG. 6 is a diagram showing another distribution of the pore volume of activated carbon produced by the method of the present invention.

FIG. 7 is a diagram showing FIG. 6 in terms of cumulative pore volume.

FIG. 8 is a diagram showing FIG. 6 in terms of differential pore volume.

Claims (7)

(57) [Claims] 1. A method of carbonizing sewage sludge and then removing an inorganic substance with an acid
The specific surface can be obtained by extraction and subsequent activation.
Product volume is more than 1300 m ² / g and pore volume is 3.00 ml
A method for producing activated carbon having an amount of not less than / g . 2. The method for producing activated carbon according to claim 1, wherein an alkali metal silicate is added as a foaming agent and activator when carbonizing the sewage sludge. 3. Sewage obtained by circulating nitrification denitrification and then sand filtration has a specific surface area of 1300 m ² / g or more and a pore volume of
A method of using activated carbon for water treatment, which comprises passing through a container filled with 3.00 ml / g or more of activated carbon . 4. The method for producing activated carbon according to claim 1, wherein sodium hydroxide is used as the activator. 5. The activation temperature according to claim 1 , which is 3
After heating at 50-450 ° C for a certain time, 450-900
A method for producing activated carbon, which comprises heating at ℃ for a certain period of time. 6. The method according to claim 1, wherein sodium hydroxide is used as the activator and the activation temperature is 350 to 450.
A method for producing activated carbon, which comprises heating at 450 ° C. for a certain period of time and then heating at 450 to 900 ° C. for a certain period of time. 7. The method for producing activated carbon according to claim 2, wherein the amount of alkali metal silicate added is increased.