JPS6142394A - Treatment of water - Google Patents

Abstract

PURPOSE:To facilitate regeneration by increasing the spatial speed of the amount of treating water, by contacting fibrous activated carbon having fine pores with a specific radius with raw water to remove a noxious substance by adsorption before excluding the greater part of water held by said fibrous activated carbon. CONSTITUTION:Fibrous activated carbon, wherein the fine pore volume occupied by fine pores with a pore radius of 15Angstrom or less is 0.3cc/g or more, is prepared. This fibrous activated carbon is brought into contact with raw water containing a noxious substance such as a malodorous substance or a lower organohalogen compound and the noxious substance is adsorbed with the fibrous activated carbon to be removed from raw water. Air over-saturated water is passed through this fibrous activated carbon bed having the noxious substance adsorbed therewith to substitute the greater part of water held by the activated carbon bed by air bubbles to remove said water. Subsequently, fibrous activated carbon is regenerated by pressurized or over-heated steam with temp. of 100-200 deg.C. Said fibrous activated carbon is prepared, for example, by carbonizing a cellulosic fiber at 200-300 deg.C before activation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a water treatment method, and particularly to a water treatment method for adsorbing and removing harmful substances such as odor substances and organic halogen compounds dissolved in water.

Recently, rivers, lakes, etc., which are water sources for tap water and industrial water, have become increasingly polluted due to the influx of various types of wastewater, and in order to utilize these water sources, advanced treatment is required in addition to conventional water treatment methods. It has become required. In particular, moldiness in drinking water resulting from the proliferation of microorganisms due to eutrophication of lakes and marshes.
In addition, there are problems such as contamination of underground water sources due to the contamination of industrial solvents and dry cleaning detergents, and the latter in particular has odor and health problems such as carcinogenicity, and it is difficult to remove organic halogen compounds. This is an urgent issue in water treatment.

The purpose of the present invention is to efficiently remove these harmful substances that cannot be removed by normal purification treatment, and to provide highly treated water that is suitable for drinking water, has no unpleasant odor, and is free from health problems. It's about doing.

[Conventional technology]

Adsorption using activated carbon is used for such advanced treatment of water, particularly for raw water containing odor components and organic components. The activated carbon used is in the form of granules or powder, and the granular activated carbon is used in a fixed bed or fluidized bed format, and the powdered activated carbon is mixed and stirred in raw water and then sedimented and separated.

[Problem to be solved by the invention]

In the above-mentioned advanced processing, the use of powdered activated carbon requires special equipment for sedimentation and separation of the powdered activated carbon in the treatment water, and the processing speed is slow due to the sedimentation and separation of fine powder, and the separated activated carbon powder Since recycling is not actually carried out, it is extremely disadvantageous from both an efficiency and cost perspective.

On the other hand, granular activated carbon is used to recycle used activated carbon, and is actually used in advanced treatment for deodorizing tap water. However, the method using granular activated carbon has a large flow resistance when used in a fixed bed, and the flow resistance increases with use due to the disintegration of activated carbon particles and the deposition of solids in the water, so backwashing is required frequently. There is a need to do. Although the method using a fluidized bed is advantageous in terms of flow resistance, there is a problem in removing fine carbon particles caused by friction between particles. The fundamental problem with methods using granular activated carbon, whether fixed bed or fluidized bed, is that the adsorption rate is slow. That is, since adsorption in granular activated carbon is carried out through the pores inside the particles, the rate-determining step is the diffusion of adsorbate into the inside of the particles. For this reason, for example, when the purpose is to deodorize raw water, the space velocity (S V) of the amount of water to be treated is about 5 to 10 in a fixed bed and 10 to 15 in a fluidized bed (based on the height of the static bed), which is quite large. It requires a large amount of processing equipment and a large site area.

In addition, the granular activated carbon that has been used in a fixed bed or fluidized bed and whose adsorption capacity has decreased is separated and taken out and sent to a separate regeneration processing device, where it is heated at a high temperature of 700 to 800°C to remove water vapor and carbon dioxide. Processed in an oxidizing atmosphere. Therefore, special high temperature treatment equipment is required for regeneration treatment.

In addition, in the regeneration process, a loss of activated carbon occurs due to the reaction at high temperature, and the weight loss of activated carbon due to this loss is generally about 5
% by weight, and a loss of about 3% by weight is unavoidable even when the sole purpose is to restore the deodorizing power.

[Means for solving problems]

Recently, fibrous activated carbon has been developed by carbonizing synthetic polymer fibers such as polyacrylonitrile, phenolic resin, and polyvinyl alcohol. diameter is 5
Because it is extremely thin at ~20 μm and smaller than the particle size of powdered activated carbon, its outer surface area is extremely large, and the adsorbate has direct access to the pores during adsorption, so it is difficult to diffuse into the inside of the particles like in granular activated carbon. There is no rate-limiting step and the adsorption rate is extremely high. The present invention focused on the characteristics of fibrous activated carbon and used it to adsorb and remove harmful substances from water.
It has been found that the used fibrous activated carbon can be regenerated very easily at a temperature significantly lower than that of granular activated carbon.

That is, the present invention includes a step of adsorbing and removing harmful substances in raw water by bringing raw water into contact with fibrous activated carbon in which pores with a pore radius of 15 square meters or less occupy a pore volume of 0,+tc;/g or more;
The method is characterized by including a step of removing most of the water held between the fibers from the fibrous activated carbon that has adsorbed the harmful substances, and a step of regenerating the fibrous activated carbon from which the retained water has been removed using heated gas. It is a water treatment method.

The fibrous activated carbon used in the present invention includes, for example, cellulose fibers, phenolic resin fibers, polyacrylonitrile fibers, polyvinyl alcohol fibers, etc.
It is carbonized at 0''C and further activated with an activation gas such as high temperature steam.

However, the fibrous activated carbon used in the present invention is not limited to the above-mentioned manufacturing method; for example, fibrous activated carbon made from pitch coke or the like can be used as long as it has the necessary adsorption capacity.

The harmful substances to be adsorbed and removed from raw water in the present invention are, for example, odorous substances typified by musty odor or dissolved organic solvents such as trichlorethylene, which have a relatively low molecular weight in the total organic carbon (TOC) in water. Therefore, it is more effective to have a smaller pore radius for the pore distribution of fibrous activated carbon that adsorbs and removes these substances. used.

The total pore volume is also 0.5 CC/g or more, preferably 0.5 CC/g or more.
6cc/g or more is used. If the pore volume is smaller than the above, the amount of water treated per unit weight of fibrous activated carbon is small, and frequent regeneration treatments are required, which is not practical.

Fibrous activated carbon can be found in the form of yarn, but it is usually formed into felt or woven fabrics, and the adsorption layer for raw water treatment is used in the form of stacking these felts or woven fabrics, and the packing density varies depending on the degree of compression. It depends, but it's usually 0. Ig/. . Before and after.

The type of adsorption layer in the water treatment method of the present invention is arbitrary. Cut the fibrous activated carbon felt or woven cloth to match the cross section of the adsorption tower, overlap the cut pieces to the desired layer height to form an adsorption layer, and pass raw water through it in a countercurrent or downward flow. Alternatively, if the adsorption tower has a square cross section, fibrous activated carbon felt or woven cloth may be folded and filled. The water-permeable cylinder may also be filled with felt or woven fabric of fibrous activated carbon.

Adsorption process The raw water treated in the present invention contains low molecular weight harmful substances, especially substances that cause musty odors caused by microorganisms that occur in lakes and marshes (typified by 2-methylisoborneol and diosmin), and substances used for industrial and dry cleaning purposes. This is water in which the low-molecular-weight organic halogen compounds used (trichloromethane, trichloroethylene, etc.) are dissolved. The purpose of the present invention is to
Since this is an advanced treatment that removes these harmful substances that cannot be removed by normal purification treatment, the raw water must have been pretreated with other substances that require treatment, such as SS, , BOD, etc., or be free from these substances. It is preferable to use underground water or the like with a small amount of water.

When the water flow rate for raw water treatment is for the purpose of deodorization, a space velocity (SV) relative to the adsorption layer volume of 40 to 200 can be adopted depending on the degree of water quality, and for the purpose of removing lower organic halogen compounds. For example, in the case of removing trichlorethylene, high-speed processing of 8200 or more is also possible.

In the case of deodorizing treatment, the odor concentration (To) of sampled water sampled from the treated water that has passed through the adsorption layer is measured using, for example, the Japan Water Works Association drinking water test method, and if TO exceeds a certain standard, for example 7, the water flow is stopped. The adsorption layer is then regenerated. In the case of removing lower organic halogen compounds, gas chromatograph,
Alternatively, the concentration is measured by absorbance using a spectrophotometer.

An adsorption tower whose adsorption capacity has decreased due to raw water treatment is regenerated, but at that time, the retained water remaining between the fibers of the fibrous activated carbon is dehydrated from the adsorption layer in advance.

Dehydration process During the regeneration process, the water in the adsorption tower is removed, but even after the water is removed, a large amount of water is still retained between the fibers of the adsorption layer, and this water is used to absorb the energy of hot steam during regeneration. It takes time to absorb and raise the crystallinity to the level required for regeneration, and a large amount of energy is consumed. By air blowing, the water between the fibers is pushed out to a large extent, but the flow resistance in the part where the air passes through first becomes small, so air channels are formed, and the water retained between the fibers in the adsorption layer (after the channels) is There is a risk that the particles may not be removed easily, resulting in uneven reproduction.

In the method of the present invention, air blowing may also be employed, but preferably a method is employed in which water in which air is supersaturated is substituted for the water held between the fibers of the adsorption layer. Air supersaturated water can be obtained, for example, by dissolving air in water under a pressure of about 3 kg/ci at normal pressure, or by using water in which air has been saturated dissolved at low temperature at room temperature or under heating. It will be done. Air-supersaturated water already contains fine bubbles, and further generates fine bubbles when flowing between the fibers. These bubbles are trapped between the fibers and the retained water is removed accordingly. Due to the accumulation of microbubbles, the flow resistance in that area increases, so the air-supersaturated water flows to the area where there are fewer trapped air bubbles, and air bubbles are collected in that area. As a result, the entire adsorption layer is uniformly filled with bubbles, and retained water is effectively removed. The flow resistance of air-supersaturated water in the adsorption layer increases as the collection of air bubbles progresses, and reaches 1 kg /
It reaches about cJ. Next, the flow of air-supersaturated water is stopped, the water is drained, and air blowing is performed if necessary.

Table 1 shows the amount of residual water by various dehydration methods.
Air supersaturated water (also called bubble water) has an excellent retained water removal effect.

The fibrous activated carbon adsorption layer from which retained water has been removed is regenerated by hot steam.

Regeneration Process Regeneration is carried out by passing water vapor at 100-200°C through the adsorption bed. As the steam, low-pressure steam or medium-pressure steam from a boiler may be used as is, but preferably superheated steam obtained by heating low-pressure steam is used. Further, an inert gas such as nitrogen gas or combustion gas can be used as the regeneration gas, and in this case, depending on the heat capacity of the gas, a high temperature heating gas of approximately 300''C is preferably used.

In the raw water treatment process, the adsorption layer adsorbs not only harmful substances but also TOC in the raw water, and this adsorbed TO
Although water vapor at 100 to 200'C is not sufficient for desorption of C, when the retained water remaining in the dehydration step is evaporated by the introduction of water vapor, the effect of steam distillation causes the desorption of T○C. Since the TOC is distilled out from the adsorption layer, about 70 to 80% of the adsorbed TOC is removed by desorption.

Water vapor containing desorbed substances is condensed and treated separately as wastewater.

The regenerated adsorption tower is used again in the raw water treatment process.

Reactivation When raw water treatment and regeneration are repeated according to the method of the present invention, a decrease in adsorption capacity is observed. This is TO in raw water
This is because C has been adsorbed and accumulated, and in this case, the adsorption capacity can be recovered by reactivating the fibrous activated carbon in the adsorption layer.

In general, when organic halogen compounds are adsorbed and removed from groundwater, the amount of TOC in the raw water is small, so reactivation is infrequent; however, when removing musty odors, the water source is lake water, so TOC in the raw water is The larger the amount, the more frequent the reactivation will be.

Reactivation can be performed in the same way as normal activated carbon activation,
For example, this is carried out by a method of treating with LPG combustion gas of 800'C or more for 1 to 20 minutes.

[Action and effect]

By using fibrous activated carbon as an adsorbent, the water treatment method of the present invention can treat harmful substances such as odor substances and lower organic halogen compounds at a high flow rate through advanced treatment of raw water. Compared to treatment using granular activated carbon, the equipment is smaller. Regeneration of the adsorption bed is easily carried out using low-pressure steam or combustion gas while the adsorption tower is still filled, and the adsorption tower is sterilized with heated gas each time it is regenerated, so there are no hygiene issues. Does not occur.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 Deodorization treatment of outlet water of a rapid filtration basin in a water purification plant was carried out using activated carbon fibers based on polyacrylon (Fine Guard Special Sample, manufactured by Toho Bethlon Co., Ltd.). The pore characteristics of the sample used were as follows.

(1) BIT surface area 1200m/g (2) Pore volume (water vapor adsorption method) Radius 15% or less 0.3580C/g15~3oX
o, 344cc/g30X or more 0.0
41 cc/g Total pore volume J743 cc/g A felt sheet of activated carbon fiber was cut out into a disc shape with a diameter of 100 mm and packed in a stacked state in a stainless steel column with an inner diameter of 100 mm. The filling amount is 109g, and the height of the filling bed is 16
It was 5 mm.

Raw water was passed through at 5V58. The TO (odor concentration) of the raw water varied between 30 and 65, but the amount of treated water until the TO of the treated water exceeded 7 was 64,001.

Next, raw water in which air was saturated and dissolved at room temperature under a pressure of 3 kg/cJ a was supplied directly from the pressurized tank to the adsorption column in a downward flow while being controlled by a valve, until the adsorption layer was filled with air bubbles. When the pressurized water substantially stopped flowing, the supply of pressurized water was stopped, and after the water was drained, air was blown.

Superheated steam at 150°C at a flow rate of 2.5 kp/hr
Regeneration processing was performed over time.

After the regeneration process was completed, the raw water was deodorized again under the same conditions as before, and the amount of water passed until To exceeded 7 was 650.
It was 0j.

Example 2 Groundwater containing 500 ppb of trichlorethylene was treated with phenolic activated carbon fiber (manufactured by Kuraray Chemical Co., Ltd., FT
15)1. Water was passed through a column packed with OOg. FT1
The total pore volume of No. 5 was 0.583 cc/g, and the pore volume of 15% or less of the radius was 573 cc/g.

The packed bed in the column had a diameter of 15 mm, a bed height of 66 mm, and a packing density of 0.085 g/cc. Water flow rate 2.5z
/hr (S V : 210), and the ultraviolet absorbance of a sample of the treated water at a wavelength of 210 mμ was measured using a spectrophotometer to calculate the trichlorethylene concentration in the treated water. The trichlorethylene concentration in the treated water remained below 50 ppb until the water flow time was 30 hours, and after that, the concentration rose rapidly and reached almost the same level as the raw water after 40 hours.

Then, air-supersaturated water was applied to the column in an upward flow,
Bubbles were generated in the packed column, and after most of the water was expelled by the bubbles, excess water was removed by air blowing in a downward direction.

The outside of the column was kept at 140°C using a ribbon heater.
1. Superheated steam at 140°C at a flow rate of 200 g/hr.
Desorption and regeneration treatment was performed for 5 hours. When the effluent steam was condensed in a condenser and the amount of trichlorethylene in the condensed water was measured, the total amount of distilled trichlorethylene was 72% of the amount of adsorbed trichlorethylene, but since the absolute amount was small, it is thought that there was evaporation loss, etc. . On the other hand, when the recycled activated carbon fibers were dried by blowing air at 100''C and weighed, no residual trichlorethylene was found. As in the previous case, the trichlorethylene concentration in the treated water was below 50 ppb up to a flow rate of 70 tons, and no change in the removal ability was observed even after repeated regeneration and adsorption.

Applicant: Water Desalination Promotion Center Kunitaro Kawazoe

Claims (6)

[Claims] (1) The pore volume occupied by pores with a pore radius of 15 Å or less is 0
．． A process of adsorbing and removing harmful substances in the raw water by bringing raw water into contact with fibrous activated carbon having a concentration of 3 cc/g or more, and removing most of the water held between the fibers from the fibrous activated carbon that has adsorbed the harmful substances. and a step of regenerating fibrous activated carbon from which retained water has been removed using heated gas. (2) Claim No. 1, in which the harmful substance is an odorous substance (
The method described in section 1). (3) The method according to claim (1), wherein the harmful substance is a lower organic halogen compound. (4) The method according to claim (1), wherein the retained water is removed by passing air-supersaturated water through the fibrous activated carbon layer and replacing the retained water with air bubbles. (5) The heating gas is pressurized or superheated steam at 100 to 200°C.
4) The method described in any of the above. (6) The method according to any one of claims (1) to (4), wherein the heating gas is an inert gas at a temperature of 100 to 300°C.