JPS6350075B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a water treatment method for treating wastewater and clean water by bringing them into contact with activated carbon. Generally, powdered activated carbon used for water treatment such as organic wastewater is regenerated by a wet oxidation regeneration device and used repeatedly. By the way, when activated carbon is regenerated many times, the ash generated during the regeneration and the ash in the inflow water accumulate in the water treatment system. If ash accumulates in the water treatment system, not only will the physical adsorption capacity of activated carbon decrease, but the ash will migrate into the purified water after treatment, causing the purified water to become cloudy or reducing the regeneration capacity of the regeneration equipment. Problems such as For this reason, it is necessary to remove the ash from the activated carbon, but with the technology developed so far, it is not possible to separate and remove the ash, which has a particle size that is approximately equal to or smaller than the finely divided powder activated carbon or granular activated carbon. Currently, activated carbon is recycled and used a predetermined number of times and then disposed of along with the ash. The present invention has been made in view of the above circumstances, and its purpose is to provide water treatment that does not cause ash produced during activated carbon regeneration to migrate into purified water and cause cloudiness, or to eliminate effective activated carbon from being disposed of. The purpose is to provide a method. The present invention will be explained below. In the present invention, the activated carbon discharged from a water treatment device using activated carbon is subjected to wet oxidation treatment to regenerate the activated carbon, and the slurry containing the activated carbon treated by wet oxidation and ash with a relatively small particle size is added with water. In addition, by performing a dilution operation, the interfacial potential of the ash particles is increased to dissociate the activated carbon from the ash particles, and the ash is separated and removed by sedimenting the activated carbon, and the sedimented activated carbon is mixed with the water. and a step of reintroducing it into the processing equipment. Activated carbon generally used for water treatment includes powdered activated carbon with a particle size of 200 mesh or less, and granular activated carbon with a particle size of about 4 to 50 mesh.
In the present invention, any particle size may be used as long as the activated carbon can be applied to the wet oxidation regeneration equipment, but the wet oxidation regeneration equipment naturally has limitations from the equipment standpoint, such as flow due to high pressure and damage to valves that reduce the pressure from high pressure to normal pressure. Powdered activated carbon of 200 mesh or less is most desirable. In addition, the particle size of the ash is approximately the same as or smaller than that of powdered activated carbon or granular activated carbon, and is generated when organic matter adsorbed to organic sludge or activated carbon is oxidized and incinerated by wet oxidation treatment. It is an inorganic substance and falls under the ignition residue specified in JIS K 0102. In addition, the wet oxidation treatment for regenerating activated carbon is a liquid phase oxidation method called the Zimmerman method, in which organic matter adsorbed by activated carbon in water is removed from water containing oxygen such as air under a pressure that maintains water in a liquid phase at a specific temperature. This method uses gaseous oxygen to oxidize, separate, and regenerate organic sludge, and organic sludge is generally burned at the same time at a temperature of 200%.
It is carried out under conditions of ~400℃ and a pressure of 40~60Kg/ ^cm2 , but in recent years, the pressure has been reduced by using catalysts.
The temperature is lowered. In addition, when regenerating with a wet oxidation regeneration device, whether the organic sludge is treated at the same time or only the activated carbon is treated, the treated material that comes out of the wet oxidation regeneration device becomes a solid mixed liquid containing activated carbon and ash. , in the form of a slurry. The mixing amount of the dilution water varies depending on the total hardness of the slurry discharged from the wet oxidation regeneration device and the total hardness of the dilution water. That is, unless the total hardness of the diluted slurry diluted with water is low, activated carbon and ash will not separate sufficiently, and the dilution ratio must be increased. When the total hardness of the diluted slurry is low, for example when the total hardness is less than 100, the activated carbon and ash can be separated by adding 2 to 5 times the dilution water to the slurry. Further, when the total hardness of the diluted slurry is high, for example, when the total hardness is 100 or more, a large amount of water is added to make the dilution ratio higher than the above dilution ratio. In addition, when the total hardness of the diluted slurry is 100 or more, if an ion sequestering agent such as sodium hexametaphosphate or EDTA is added, activated carbon and ash can be separated by adding 2 to 10 times the dilution water to the slurry. This is due to the following reasons. Generally, the interfacial potential ζ of a particle is expressed by the following equation. ζ=4πEd/D Here, E: Particle charge d: Average thickness of the double diffusion tank D: Dielectric constant of the dispersion medium When the total hardness of the diluted slurry is high, the dielectric constant D of the dispersion medium is large. The interfacial potential ζ is low. If the interfacial potential ζ is low, the activated carbon and ash particles will not be sufficiently dissociated. For this reason, adding an ion sequestering agent to act as a dispersant helps dissociate the activated carbon and ash particles. Next, the present invention will be specifically described with reference to the drawings. FIG. 1 is a process diagram showing one embodiment of the present invention, and is an example in which the water treatment method of the present invention is applied to wastewater treatment. First, organic wastewater is sent from pipe 1 to aeration tank 2. Powdered activated carbon is sent to this aeration tank 2 from a pipe 3, and water is sent from a pipe 4 as necessary. In the aeration tank 2, biological treatment using activated sludge and physical adsorption using powdered activated carbon are performed. The organic wastewater treated in the aeration tank 2 is sent to the settling tank 6 through a pipe 5 together with powdered activated carbon and activated sludge.
In the settling tank 6, powdered activated carbon and activated sludge settle at the bottom and are separated from the purified water. The purified water is discharged to the outside through pipe 7. On the other hand, the powdered activated carbon and activated sludge that have settled at the bottom of the settling tank 6 are returned to the aeration tank 1 through a pipe 8, but some of them are sent as surplus sludge to a wet oxidation regeneration device 10 through a pipe 9. In this wet oxidation regeneration device 10, activated sludge is burned at the same time as powdered activated carbon is regenerated. At this time, a part of the powdered activated carbon and activated sludge are oxidized in the air and become inorganic ash. The slurry regenerated and taken out by the wet oxidation regeneration device 10 contains recycled powdered activated carbon and ash. The particle size distribution of powdered activated carbon and ash in this slurry is shown in the following table.

[Table] The sum of the ash content and powdered charcoal content for each particle size is not 100% because it contains some organic matter. As is clear from this table, the powdered charcoal and ash content in the slurry are mostly fine particles of 74μ (200 mesh) or less. Conventionally, the slurry was returned to the aeration tank 1 as it was. However, in this embodiment, the slurry is sent via pipe 11 to an ash separator 12 for separating and removing the ash according to the method of the present invention. Dilution water such as industrial water or well water is sent to the ash separator 12 through a pipe 13 branched from the pipe 4. In the ash separator 12, the slurry is diluted with fresh water to separate powdered activated carbon and ash. Here, the relationship between the total hardness of the diluted slurry diluted with dilution water and the dilution ratio is determined in advance, and the dilution ratio with the dilution water is determined based on the total hardness of the dilution slurry as described above. This is because the total hardness of the diluted slurry differs depending on the type of organic wastewater and dilution water to be treated, and the optimum dilution ratio also differs accordingly. The total hardness of the diluted slurry is
If it is less than 100, dilute it 2 to 5 times. Then,
As shown in the graph in Figure 2, the ash separation and removal rate increases in proportion to the dilution ratio (1x dilution means no dilution), and when diluted 5 times, the ash separation and removal ratio is approximately 46.5. %. If the total hardness of the diluted slurry is 100 or more, as described above, an ion sequestering agent such as sodium hexametaphosphate or EDTA is added to dilute it 2 to 10 times. Then, as shown in the graph of FIG. 3, the ash separation and removal rate increases in proportion to the dilution ratio, and when diluted 10 times, the ash separation and removal rate becomes about 45%. In addition, when adding sodium hexametaphosphate, the approximate addition amount Q is calculated|required by the following formula. Q = (German hardness of dilution water x dilution ratio - 1/dilution ratio + German hardness of slurry x 1/dilution ratio) x 130 (mg/) However, German hardness = total hardness x 0.056 The above formula theoretically Although this is the amount added to reduce the hardness of the diluted slurry to zero, sodium hexametaphosphate is actually consumed by iron ions, barium ions, zinc ions, etc. present in the slurry and dilution water, so the organic Although it varies depending on the type of wastewater and dilution water, approximately the total hardness of the diluted slurry is
It can be used as a guide to keep it below 100. In the ash separator 12, the recycled powdered activated carbon settles to the bottom (see curve A in the graph of Figure 4), and approximately 50% of the absolute amount of ash is dissociated and suspended in the separation water, while the remaining approximately 50% is dissociated and suspended in the separation water. % of ash remains in the recycled powdered activated carbon and settles to the bottom together with the recycled powdered activated carbon. The precipitate of recycled powdered activated carbon containing ash that has settled at the bottom of the ash separator 12 and remains is returned to the aeration tank 2 through the pipe 15 and used again. In addition, the separated water in which the separated and removed ash is suspended is pipe 1.
6 and sent to an ash concentration tank 17. This ash concentration tank 17 is supplied with a cationic flocculant from a pipe 18.
2 ppm is added, and the ash coagulates and settles (see curve B in the graph shown in Figure 4). The coagulated and settled ash becomes a concentrated slurry of about 10%, which is sent from the bottom of the ash concentration tank 17 through a pipe 19 to a dehydrator 20, where it is dehydrated to a water content of about 40% and discharged to the outside. Further, the clarified water after the ash has been separated in the ash concentration tank 17 is sent to the aeration tank 2 through the pipe 22. By separating and removing the ash in this manner, it becomes possible to maintain the ash concentration within the wastewater treatment system at a constant low concentration, allowing the wastewater to be treated in a stable state and improving treatment efficiency. Furthermore, only about 0.5% or less of the recycled powdered activated carbon migrates into the separated water, and more than 99.5% of the recycled powdered activated carbon is recovered and returned to the aeration tank 2 again. . Furthermore, there is no fear that ash will migrate into the purified water and cause it to become cloudy.
Furthermore, there is no fear that the regeneration ability of the wet oxidation regeneration device 10 will be reduced. The embodiment of the process diagram shown in FIG. 5 is an example in which wastewater to be treated is used as dilution water instead of fresh water such as industrial water or well water in FIG. There is no pipe 13, and instead, a pipe 23 branched from pipe 1, through which organic wastewater is sent, is connected to the ash separator 12, and nothing else has changed. Components that are the same as those described above are given the same reference numerals and their explanations will be omitted. In this example, wastewater that should be treated as dilution water is used, so depending on the type of wastewater, the total hardness may be high and it may be necessary to use a slightly larger amount of ion sequestering agent such as sodium hexametaphosphate. However, it has the advantage of not using useful water such as industrial water or well water, and since the concentration of organic wastewater in the ash separator 12 is higher than that in the aeration tank 2, the recycled activated carbon is collected in the ash separator 12. The adsorbed wastewater is sent to the aeration tank 2 together with activated carbon through the pipe 12 or through the ash concentration tank 17 as clear water through the pipe 22, so that the activated carbon adsorption It has the effect that the treatment can be carried out in a place where the substance to be treated is highly concentrated and is efficient. In addition, in the above example, an activated sludge system using activated carbon was shown as a water treatment system using activated carbon, but it is of course possible to use an activated carbon adsorption tower such as a fixed bed or fluidized bed type in place of this. . Furthermore, it is a matter of course that impurities having a faster sedimentation rate than activated carbon may be removed by known gravity separation before or after the dilution sedimentation separation step of the present invention. Furthermore, although the above examples have been described regarding wastewater treatment, it goes without saying that the present invention can also be applied to clean water treatment. As explained above, according to the present invention, ash having a relatively small diameter can be efficiently separated and removed.
In addition, since only water is used to separate and remove the ash, there is no cost involved. By removing ash according to the present invention, it is possible to prevent the deterioration of the adsorption capacity of activated carbon, and there is no need to dispose of activated carbon. Alternatively, it is possible to eliminate inconveniences such as a reduction in the playback ability of the playback device. Furthermore, if an ion sequestering agent is added, the ash can be separated and removed in a more stable state, and there will be no problem even if the total hardness of the slurry or dilution water regenerated by the wet oxidation regeneration device changes. do not have. Next, the present invention will be specifically explained with reference to Examples. Example After regenerating activated carbon using the apparatus shown in FIG. 1, the ash produced was separated and removed. For this, first,
^100m3 /day of organic wastewater and 50Kg/day of powdered activated carbon.
After sending ^780m3 /day of fresh water to aeration tank 2 and treating organic wastewater, powdered activated carbon 12000mg/day and ash content 3000
The treated mixed solution containing 3000 mg/mg of activated sludge was discharged and sent to the settling tank 6, where it was separated by precipitation. Sedimentation tank 6
At a flow rate of 30 m ³ /day, a precipitate containing powdered activated carbon 48000 mg/day, ash content 12000 mg/day, and excess sludge 12000 mg/day was extracted and sent to the wet oxidation regeneration device 10 for regeneration treatment. Ash was produced during this reclamation process. Then, the flow rate 30 from the wet oxidation regeneration device 10
Powdered activated carbon 46570mg/( ^1397m3 /day)
A slurry with an ash content of 13,200 mg/(396 Kg/day) was extracted and sent to the ash separator 12. 120m ³ /day of fresh water is sent to the ash separator 12.
The slurry was diluted with this fresh water, and 1480 mg of ash was separated from the slurry and floated to the surface, while the regenerated material containing the remaining ash settled. Then, from the bottom of the ash separator 12, a precipitate containing powdered activated carbon of 46,330 mg/(1390 Kg/day) and ash content of 7,270 mg/(218 Kg/day) was drawn out at a flow rate of ³⁰ m 3 /day and returned to the aeration tank 2. This precipitate (regenerated powdered activated carbon) contains 7,270 mg of ash, which is about half the ash contained in the slurry (13,200 mg/) recycled by the wet oxidation regeneration device 10. I understand. In addition, ash separator 1
Powdered activated carbon at a flow rate of 120 m ³ /day from the top of 2.
58mg/(7Kg/day), ash 1480mg/(178Kg/
The separated water is extracted and sent to the ash concentration tank 17,
Ash etc. were coagulated and separated using a cationic flocculant (concentration 1 mg/). Flow rate from the bottom of the ash concentration tank 17
Powdered activated carbon 3930 ^mg /(7
Kg/day), a concentrated slurry with an ash content of 10% (178Kg/day) is extracted and sent to the dehydrator 20, where it is dehydrated and then disposed of as a dehydrated cake with powdered activated carbon of 7Kg/day, an ash content of 178Kg/day, and a moisture content of 40%. did. In addition, ash concentration tank 1
118.22 m ³ /day of clear water was drawn out from the upper part of tank 7 and sent to aeration tank 2. The amount of ash generated under this condition is 36 kg/day,
The amount of ash removed by this device is 178Kg/day.
It is clear that by continuously operating this device, the ash concentration in the aeration tank can be kept constant at an extremely low concentration. Incidentally, the ash content was analyzed using the ignition residue heated at 600° C. for 2 hours in accordance with JIS K 0102.

[Brief explanation of the drawing]

Figures 1 and 5 are flow sheets of the apparatus for carrying out the method of the present invention, Figures 2 and 3 are graphs showing the relationship between the dilution ratio of fresh water and the ash separation and removal rate, and Figure 4 is a graph showing the relationship between settling time and settling rate of powdered activated carbon and ash. 10, 35... regenerator, 12, 40... ash separation tank, 13... pipe, 17, 43... ash concentration tank, 23... pipe.

Claims (1)

[Claims] 1. A water treatment method in which wastewater or the like is treated by bringing it into contact with activated carbon, comprising: a step of regenerating activated carbon discharged from a water treatment device using activated carbon by wet oxidation; By adding water to a slurry containing activated carbon and ash with a relatively small particle size and performing a dilution operation, the interfacial potential of the ash particles is increased, the activated carbon and the ash particles are dissociated, and the activated carbon is sedimented. A water treatment method comprising the steps of: separating and removing ash; and reintroducing the precipitated activated carbon into the water treatment device. 2. The water treatment method according to claim 1, wherein an ion sequestering agent is added to the water.