JP2004275884A - Waste water treating method, waste water treating apparatus and treating system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a waste water treating method, a waste water treating apparatus and a treating system by which oil can be removed from waste water containing the oil such as heavy oil and sludge without producing industrial waste, by which chemical oxygen demand and nitrogen components of the waste water can be reduced at the same time, and further, which is applicable to various kinds of waste water treatments from a small size to large size with simple apparatus constitution and is excellent in separation efficiency. <P>SOLUTION: In the waste water treating method in which suspensoid in the waste water is subjected to flocculation precipitation and then supernatant water is discharged out of the system, the waste water is treated by addition of active carbon and then an inorganic flocculant is added thereto. The waste water treating apparatus is provided with a flocculation precipitation tank in which the waste water is separated into the supernatant water and flocculation precipitation slurry, an active carbon adding means for adding the active carbon to the waste water, a flocculant adding means for adding the inorganic flocculant and an agitation means for agitating the waste water in the flocculation precipitation tank. The waste water treating system is provided with the waste water treating apparatus, a dehydration device and a returning means for returning separated water of the dehydration device to the flocculation precipitation tank as raw water. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wastewater treatment method, a wastewater treatment apparatus and a treatment system for treating various wastewaters using a coagulant, and particularly to a wastewater containing oil such as heavy crude oil and sludge, a COD component, and a nitrogen component. The present invention relates to a wastewater treatment method, a wastewater treatment device, and a wastewater treatment system to be treated.
[0002]
[Prior art]
Wastewater from power plants and factories, and wastewater such as sewage and leachate from landfills contain various oils and organic pollutants. Therefore, these oils, COD components, and nitrogen components are removed. ing. Conventionally, methods for treating wastewater containing oil include floating oil separation processing using a floating oil separation device such as an API oil separation tank and a CPI oil separation tank, oil adsorption by a sand filtration tank, and COD component adsorption by an activated carbon tank. And flotation separation under pressure.
[0003]
FIG. 2 is a schematic view showing a conventional floating oil separation processing apparatus. In the floating oil separation process, after the floating oil 31 contained in the raw water 11 is recovered in the oil separation tank 21, the remaining raw water is subjected to hydrogen peroxide treatment, ultraviolet treatment, activated carbon treatment or ozone treatment in the COD treatment device 22. After the COD of the wastewater stored in the water test tank 23 is measured and confirmed to be equal to or less than a predetermined discharge reference value, the wastewater is discharged as treated water 18.
[0004]
FIG. 3 is a schematic diagram showing an adsorption treatment apparatus in which a sand filtration tank and an activated carbon tank are combined. In this adsorption treatment, after the oil content in the raw water is adsorbed by the sand 32 in the sand filtration tank 24, the COD component contained in the remaining water is adsorbed by the granular activated carbon 33 in the activated carbon tank 25. The water is discharged as treated water 18 through a water detection tank 23.
[0005]
Therefore, in these treatment methods, it is necessary to increase the size of the separation tank for securing the treatment capacity and to install a separate COD treatment device, and there is a problem that activated carbon for treatment becomes industrial waste.
[0006]
On the other hand, in the pressure flotation treatment shown in FIG. 4, first, a pH adjusting agent 34 and an inorganic powder coagulant 35 are added in a neutralization reaction tank 26 to perform a drainage treatment. A pressurized water 38 pressurized by the compressed air 37 sent into the gas-liquid separation tank 29 is supplied to a floating tank 28 provided downstream of the agent 36 by coagulation treatment by adding the agent 36 to forcibly float the flocs. After being removed by the scum schema 30, the treated water 18 is discharged. Therefore, there is a problem that the device becomes heavy and the recovered floc becomes an industrial waste.
[0007]
Therefore, in order to eliminate the generation of secondary waste, there has been proposed a method of incinerating waste activated carbon generated using powdered activated carbon. For example, Japanese Patent Application Laid-Open No. 9-75910 discloses an immersion type membrane separation device using a microfiltration membrane or an ultrafiltration membrane by adding powdered activated carbon to activated sludge treatment water obtained by treating wastewater with activated sludge. Further, a method is disclosed in which water is passed through a reverse osmosis membrane separation device as necessary to recover permeated water as regenerated water (see Patent Document 1). However, the activated carbon treated wastewater is further permeated through a membrane separation device, which leads to complication of the device and an increase in treatment cost, and when used for wastewater treatment containing oil such as sludge, oil adheres to the membrane surface. Therefore, there is a problem that the life of the device becomes extremely short and cannot be used practically.
[0008]
Japanese Patent Application Laid-Open No. 9-248572 discloses a membrane filtration method for removing suspended substances by combining a membrane filtration treatment and an activated carbon treatment (see Patent Document 2). However, in order to improve the adsorption efficiency by activated carbon, a method is employed in which activated carbon adhering to the membrane surface of the membrane module is removed with washing water and returned to a raw water tank for recirculation.
[0009]
Japanese Patent Application Laid-Open No. 2001-276892 discloses that raw water to which a coagulant is added is passed through a perforated plate to perform solid-liquid separation, and a membrane separation unit is provided downstream of the raw water and introduced into the membrane separation unit. A wastewater treatment apparatus provided with a means for adding powdered activated carbon to raw water is disclosed (see Patent Document 3). However, since the membrane separation unit is provided, it is not suitable for treating wastewater containing oil as described above.
[0010]
[Patent Document 1]
JP-A-9-75910 (Claim 1, paragraph numbers 0031, 0040, 0048, etc.)
[Patent Document 2]
JP-A-9-248572 (Claim 1, paragraph number 0004, etc.)
[Patent Document 3]
JP 2001-276892 A (Claim 1 etc.)
[0011]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described conventional problems, and removes oil from wastewater containing oil such as heavy oil and sludge without generating industrial waste, and at the same time, reduces COD component and nitrogen component of wastewater. An object of the present invention is to provide a wastewater treatment method, a wastewater treatment device, and a treatment system with excellent separation efficiency, which can be reduced and can be applied to various wastewater treatments from small to large with a simple device configuration. I do.
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have conducted intensive studies. As a result, when the inorganic coagulant is added after the suspension in the waste water is adsorbed with activated carbon, a good coagulation promoting effect is exhibited, and the oil content and COD It has been found that activated carbon adsorbing the components, nitrogen components, etc., forms flocs and shows great sedimentation, and that the dewatering properties of the flocs are extremely good, thus completing the present invention.
[0013]
That is, the wastewater treatment method of the present invention is a wastewater treatment method in which the suspended solids in the wastewater are coagulated and precipitated, and then the supernatant water is discharged out of the system. It is characterized by adding an inorganic coagulant. According to this configuration, even wastewater containing oil such as sludge, a COD component and a nitrogen component can be simultaneously treated, and the oil adsorption treatment and the activated carbon coagulation treatment can be performed in the same reaction tank. Can be performed. Further, since the coagulation property of activated carbon and the sedimentation property of coagulated activated carbon are very good, it is possible to discharge the treated water only by collecting the supernatant water. Furthermore, wastewater treatment can be performed by a simple operation, so that the entire apparatus can be reduced in size. In addition, since there is no need to perform expensive membrane treatment or the like, treatment can be performed in a single operation, and wastewater treatment can be performed at low cost. .
[0014]
In the wastewater treatment method of the present invention, it is preferable that the coagulated sediment slurry is dewatered and the separated water after dehydration is returned to the wastewater as raw water. According to this configuration, the circulating use of wastewater and the reduction of industrial waste are achieved, and the generated agglomerates can be effectively used as auxiliary fuel for cement kiln furnaces and the like.
[0015]
In the wastewater treatment method of the present invention, it is preferable that the activated carbon is powdered activated carbon. By using powdered activated carbon, the specific surface area is increased, so that the adsorption efficiency is improved, and the wastewater can be treated with a small amount of addition. The particle size of the activated carbon is preferably 200 μm or less, more preferably 100 μm or less.
[0016]
In the wastewater treatment method of the present invention, it is preferable that the inorganic coagulant is an inorganic powder coagulant. The use of the inorganic powder coagulant eliminates the need to adjust the pH of raw water, thereby improving the processing efficiency.
[0017]
Further, in the wastewater treatment method of the present invention, it is preferable that the addition amount of the activated carbon is 0.1% to 10% and the addition amount of the inorganic coagulant is 50 ppm to 10,000 ppm. The wastewater treatment method of the present invention can be applied to various wastewater treatments, and is particularly suitable for treatment of wastewater containing an oil component and / or a COD component and / or a nitrogen component.
[0018]
Next, the wastewater treatment apparatus of the present invention includes a coagulation sedimentation tank for separating wastewater into supernatant water and a coagulation sediment slurry, activated carbon addition means for adding activated carbon to the wastewater, and adding an inorganic coagulant to the wastewater. It is characterized by comprising a flocculant adding means, and a stirring means for stirring the wastewater in the flocculation settling tank. According to this wastewater treatment apparatus, the above wastewater treatment method can be effectively implemented.
[0019]
Further, a wastewater treatment system of the present invention includes the wastewater treatment device described above, a dewatering device, and a return means for returning separated water from the dewatering device as raw water to a coagulation settling tank. According to this wastewater treatment system, the above wastewater treatment method can be effectively implemented.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a flow sheet showing a preferred embodiment of the wastewater treatment device and treatment system of the present invention. The present invention can be applied to wastewater treatment including at least one of an oil component, a COD component, and a nitrogen component. The concentration of oil, COD component, nitrogen component and the like in wastewater to which the present invention can be applied is not particularly limited, and the present invention can be applied to sewage and industrial wastewater containing no oil, underground leachate, and the like. It is suitable for treating wastewater containing a COD component and / or a nitrogen component.
[0021]
The wastewater treatment device shown in FIG. 1 is an example of a device that removes oil and / or COD components and / or nitrogen components from raw water (drainage) such as heavy oil tank cleaning wastewater. As the oil component, for example, crude oil, heavy oil, crude oil-derived components such as sludge deposited in a heavy oil storage tank, and animal and vegetable oils, insulating oil, lubricating oil, release oil, cutting oil, oils containing organochlorine-based compounds, etc. No. This wastewater may contain a cleaning solvent (hydrocarbons such as dodecane, alcohols) used for removing oil from a heavy oil storage tank, a transformer, a condenser, and the like, a surfactant, trihalomethane, and the like.
[0022]
As shown in FIG. 1, the wastewater treatment apparatus includes an agglomeration settling tank 1 for separating an inflowed wastewater 11 into a supernatant water 17 and an agglomeration settling slurry 14, an activated carbon adding unit 12 for adding activated carbon to the wastewater, A coagulant adding means 13 for adding an inorganic coagulant to the wastewater and a stirring means 2 for stirring the wastewater in the coagulation settling tank are provided.
[0023]
In the present invention, a known inorganic coagulant can be appropriately used as the inorganic coagulant. However, an inorganic powder coagulant is preferably used because it is not particularly necessary to adjust the pH of wastewater.
[0024]
Activated carbon is first added to the coagulation sedimentation tank 1, and oil and / or COD components and / or nitrogen components in raw water are adsorbed on the activated carbon. If necessary, the quality of the raw water is adjusted to a pH suitable for coagulation, but according to the method using the inorganic powder coagulant of the present invention, pH adjustment of the raw water is basically unnecessary. The activated carbon is not particularly limited as long as it has an adsorption ability, and for example, powdered activated carbon, granular activated carbon, and the like are used. Among these, powdered activated carbon is preferred because of its large specific surface area, excellent dispersibility, and high ability to adsorb suspended solids in wastewater. The particle size of the powdered activated carbon is preferably 200 μm or less. The average particle size of the powdered activated carbon is usually 1 to 150 μm, more preferably 1 μm to 100 μm. If it is less than 1 μm, it tends to be scattered and the like, making it difficult to handle, and the cost of micronization tends to be high. If it exceeds 150 μm, the specific surface area becomes small and a large amount of powdered activated carbon is required to maintain a constant adsorption capacity This is because it tends to be necessary. The average particle size of the powdered activated carbon is more preferably 5 to 80 μm.
[0025]
The amount of activated carbon to be added varies depending on the type of activated carbon and the wastewater to be treated, but it is preferable to add 0.1% to 10% to raw water, more preferably 0.5% to 5% to raw water. Good to do. If the amount is less than 0.1%, the adsorption capacity of the activated carbon tends to be insufficient as a whole, and if it exceeds 10%, the activated carbon tends to be wasted. The activated carbon is preferably dispersed in the waste water using a stirring device such as a mixer as appropriate, and the stirring conditions are preferably such that low-speed stirring is performed rather than rapid stirring from the viewpoint of preventing collapse of flocculated flocs. The time required for dispersion is not particularly limited, but the stirring is usually performed for 5 minutes or more.
[0026]
After the activated carbon is uniformly dispersed in the raw water, an inorganic coagulant is added to the coagulation treatment layer 1. At this time, the oil component and / or COD component and / or nitrogen component adsorbed on the activated carbon is subjected to coagulation sedimentation treatment to form coagulated sediment sludge, and the oil component and / or COD component and / or nitrogen component in raw water is converted into coagulated sediment sludge. Included and fully removed.
[0027]
Here, examples of the inorganic powder coagulant include iron-based coagulants such as ferric chloride, ferric polysulfate, aluminum sulfate, polyaluminum sulfate, and polyaluminum chloride, and aluminum-based inorganic metal salt-based coagulants. A mixture mainly composed of pulverized common flocculant, fly ash, artificial zeolite, etc. can be used, but in particular, it is mainly composed of activated silicon dioxide and alumina, and its absolute value is the maximum value of zeta potential. Is preferred from the viewpoints of cohesiveness and post-use of aggregates.
[0028]
Although the particle size of the inorganic powder flocculant is not particularly limited, the average particle size is preferably from 50 μm to 350 μm, and more preferably from 75 μm to 150 μm. If it is less than 50 μm, the cost of fine particles required for pulverization tends to be high, and if it exceeds 350 μm, a large amount of inorganic powder coagulant tends to be required to maintain a certain coagulation ability. Further, from the viewpoint of shortening the treatment time by increasing the sedimentation speed of the aggregates, the main component of the inorganic powder coagulant preferably has a large specific gravity to some extent, and preferably has an average specific gravity of 1.5 or more.
[0029]
The amount of the inorganic coagulant added depends on the type of the inorganic coagulant and the type of the wastewater to be treated, but it is preferable to add 50 ppm to 10,000 ppm to the raw water, and more preferably 100 ppm to 100 ppm to the raw water. It is better to add 5,000 ppm. The added inorganic powder flocculant is preferably dispersed in the wastewater using a stirring device such as a mixer as appropriate, but after the flocculant is formed, the flocculation floc is settled. Good to do. In the coagulation sedimentation tank 1, an activated carbon floc adsorbing oil and / or COD component and / or nitrogen component and an inorganic powder coagulant are precipitated, and the upper layer is sufficiently filled with oil, COD component and nitrogen component in raw water. The removed clear supernatant water 17 is formed. Therefore, oil removal and COD removal or nitrogen component removal conventionally performed by separate apparatuses can be simultaneously performed by the same processing apparatus.
[0030]
The size of the coagulating sedimentation tank 1 may be selected according to the amount of wastewater to be treated. Therefore, the size of the equipment can be reduced.
[0031]
The supernatant water 17 in the coagulation / sedimentation tank 1 is discharged out of the tank by the liquid feed pump 5 and guided to the water test tank 7 for storing the supernatant water 17. In the water test tank 7, whether or not the treated water 18 has a COD equal to or less than a predetermined discharge reference value is inspected. The oil content and the nitrogen content of the treated water stored in the water test tank are inspected. When dust, activated carbon, fine powder of a coagulant, etc. remain in the supernatant water 17 discharged from the coagulation / sedimentation tank 1, a filtration treatment by the filter 6 is performed. However, the filter 6 need not always be provided. According to the method of the present invention, since the supernatant water 17 introduced into the water test tank is sufficiently lower than the standard COD value of the wastewater treatment, the supernatant water is further subjected to a coagulation treatment using a polymer coagulant or a water permeation treatment using a membrane. It is not necessary and is discharged out of the system as treated water 18. For this reason, the wastewater treatment cost can be reduced.
[0032]
The slurry 14 of the coagulated sediment containing oil and / or COD component and / or nitrogen component remains as a residue in the coagulated sedimentation tank 1 after discharging the supernatant water. After the slurry residue 14 is discharged out of the coagulation / sedimentation tank 1, the dewatering device 3 performs a dehydration treatment. As the dehydrating device, a conventionally known dehydrating device can be appropriately used, and examples thereof include a filter using a woven or nonwoven fabric, a centrifuge, a rotary press filter, a bag filter, a filter press, and a belt press. Since the aggregate has extremely good dehydration properties, the aggregate can be easily collected. Since the dehydrator may have a simple configuration, the filtration system and the dehydration system can be simplified. Separated water 15 (for example, filtrate) separated from the slurry is returned to the flocculation / sedimentation tank 1 by the circulating pump 4. For this reason, wastewater is not discharged out of the system.
[0033]
On the other hand, the aggregate 16 subjected to solid-liquid separation in the dehydrator 3 has excellent dehydration properties and low adhesiveness, and thus has excellent handling properties. Therefore, it can be effectively used as an auxiliary fuel for a cement kiln furnace or the like.
[0034]
【Example】
Next, the present invention will be specifically described with reference to examples, but the present invention is not limited to only the following examples. In the following examples and the like, “% by mass” is abbreviated as “%” unless otherwise specified.
[0035]
(Example 1)
Wastewater containing insulating oil was treated with a wastewater treatment device as shown in FIG. Wastewater containing 386 ppm of oil, 839 ppm of COD, and 118 ppm of nitrogen was used. 3 m ³ of the waste water was introduced into the coagulation sedimentation tank 1, and 90 kg (with respect to the waste water: 3%) of powdered activated carbon (manufactured by Noatech Co., Ltd., trade name: “NAC-01”, average particle size: 75 μm) was added. The mixture was stirred with a stirrer for about 10 minutes to disperse the activated carbon powder in the waste water. Next, 9 kg of an inorganic powder coagulant (manufactured by Noatech Co., Ltd., trade name: “Super Namit TN315NY-T3”, average particle size: 150 μm) (with respect to drainage: 3,000 ppm) was added thereto, followed by stirring to remove powdered activated carbon. After the coagulation, the stirring was stopped and the powdered activated carbon and the inorganic powder coagulant were settled. Then, after confirming that clear supernatant water was obtained in the upper layer, the supernatant water 17 of the flocculation settling tank 1 was discharged by the pump 5, and the supernatant water 2. the introduction of 5m ^3.
[0036]
As a result of water quality analysis of the water stored in the water test tank, the oil content was below the detection limit, the COD was 13.1 ppm, and the nitrogen was 4.69 ppm. The COD removal rate of the treated water after the wastewater treatment was 98.4%, sufficiently clearing the discharge standard value (20 ppm). For this reason, the treatment with the polymer flocculant was unnecessary, and it was possible to discharge the treated water 18 out of the system as it was.
[0037]
From the results of Example 1, it was found that the oil component and the COD component could be simultaneously removed from raw water by adding the powdered activated carbon and the inorganic powder coagulant.
[0038]
(Measuring method)
pH: JIS K0102 12.1 Glass electrode method Oil content: JIS K0102 Announcement No. 59 of 1976, Table 8 Extraction separation weight method COD: JIS K0102 17 Titration method Total nitrogen: JIS K0102 45.2 Ultraviolet absorption spectrophotometry
(Comparative Example 1)
The wastewater was treated using a wastewater treatment device as shown in FIG. The wastewater used contained 400 ppm of oil, 1,090 ppm of COD, and 230 ppm of nitrogen. 3 m ³ of the waste water is introduced into the neutralization reaction tank 26, and 1400 ppm of an inorganic coagulant is added thereto, followed by drainage treatment. Then, 1 ppm of a polymer coagulant is added in a slow stirring tank 27 to perform coagulation treatment. The flock was forcibly floated in a floating tank 28 installed downstream, and removed by a scum schema 30, and then discharged as treated water.
[0040]
As a result of water analysis of the treated water, the oil content was 3 ppm, the COD was 650 ppm, and the nitrogen was 170 ppm. In this treated water, the oil content cleared the emission standard value, but the COD removal rate was 40.4%, and the COD component was reduced by only about half.
[0041]
(Comparative Example 2)
The wastewater was treated using the same wastewater as in Example 1 using a wastewater treatment apparatus as shown in FIG. 3 m ³ of waste water was introduced into the coagulation sedimentation tank 1, and 90 kg of powdered activated carbon (based on waste water: 3%) was added in the same manner as in Example 1 to sufficiently disperse the activated carbon in the waste water, and then stirring was stopped. After standing overnight, most of the powdered activated carbon was floating above the coagulation sedimentation tank.
[0042]
(Example 2)
The wastewater was treated by a wastewater treatment device as shown in FIG. The same drainage as in Example 1 was used. 2.9 m ^{3 of the} raw water and 0.1 m ³ of the return water from the dehydrator 3 were introduced into the coagulation sedimentation tank 1, and 90 kg of powdered activated carbon similar to that in Example 1 (with respect to drainage: 3%) was added. The powdered activated carbon was dispersed in the waste water by stirring for about 10 minutes. Next, 9 kg of the same inorganic powder coagulant (with respect to effluent: 3,000 ppm) as in Example 1 was added and stirred to coagulate the powdered activated carbon. Then, the stirring was stopped and the powdered activated carbon and the inorganic powdered coagulant were added. Settled. Then, after confirming that clear supernatant water was obtained in the upper layer, the supernatant water 17 of the coagulation settling tank 1 was discharged by the pump 5, and the supernatant water 2. the introduction of 5m ^3.
[0043]
As a result of water quality analysis of the water stored in the water test tank, the oil content was below the detection limit, the COD was 11.6 ppm, and the nitrogen was 4.86 ppm. The COD removal rate of the treated water after the wastewater treatment was 98.6%, which sufficiently cleared the discharge standard value (20 ppm). For this reason, the treatment with the polymer flocculant was unnecessary, and it was possible to discharge the treated water 18 out of the system as it was.
[0044]
From the results of Example 2, it can be seen that the oil, COD and nitrogen components can be simultaneously removed from raw water by adding powdered activated carbon and an inorganic powder coagulant. Was further reduced.
[0045]
【The invention's effect】
As described above, according to the present invention, even wastewater containing oil such as insulating oil or sludge, COD component or nitrogen component can be treated simultaneously, and furthermore, the oil adsorption treatment and activated carbon Can be performed in the same reaction tank, so that the equipment can be downsized, the system can be simplified, and the amount of drug used can be reduced. In addition, since the coagulability of activated carbon and the sedimentation and dehydration properties of the coagulated activated carbon are very good, it can be discharged as treated water only by collecting the supernatant water.
[0046]
Since the aggregates have good sedimentation and dehydration properties, they can be easily collected, so that the filtration system and the dehydration system can be simplified. Furthermore, since the aggregate has good dehydration properties and low adhesiveness, it has excellent handling properties and can be effectively used as fuel.
[0047]
Further, by using an inorganic powder coagulant, complicated pH adjustment of raw water (drainage) is basically unnecessary.
[0048]
As described above, according to the present invention, wastewater treatment can be performed at lower cost than in the past.
[Brief description of the drawings]
FIG. 1 is a schematic view showing one embodiment of a wastewater treatment device according to the present invention.
FIG. 2 is a schematic view showing a conventional wastewater treatment apparatus.
FIG. 3 is a schematic view showing a conventional wastewater treatment apparatus.
FIG. 4 is a schematic view showing a conventional wastewater treatment apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Coagulation sedimentation tank 2 Stirrer 3 Dehydrator 4 Pump 5 Pump 6 Filter 7 Test tank 11 Raw water (drainage)
12 Activated carbon 13 Inorganic powder coagulant 14 Coagulated sediment slurry 15 Separated water (return water)
16 Aggregate 17 Supernatant water 18 Treated water 21 API oil separation tank 22 COD treatment device 23 Water detection tank 24 Sand filtration tank 25 Activated carbon tank 26 Neutralization reaction tank 27 Slow stirring tank 28 Floating tank 29 Gas-liquid separation tank

Claims (9)

This is a wastewater treatment method in which the suspended solids in the wastewater are coagulated and precipitated, and the supernatant water is discharged out of the system. The method comprises adding activated carbon to the wastewater, treating the wastewater, and then adding an inorganic coagulant. And wastewater treatment method. The wastewater treatment method according to claim 1, wherein the coagulated sediment slurry is dehydrated, and the separated water after dehydration is returned to the wastewater as raw water. The wastewater treatment method according to claim 1 or 2, wherein the activated carbon is powdered activated carbon. The wastewater treatment method according to any one of claims 1 to 3, wherein a particle size of the activated carbon is 200 µm or less. The wastewater treatment method according to any one of claims 1 to 4, wherein the inorganic coagulant is an inorganic powder coagulant. The wastewater treatment method according to any one of claims 1 to 5, wherein an addition amount of the activated carbon is 0.1% to 10%, and an addition amount of the inorganic coagulant is 50 ppm to 10,000 ppm. The wastewater treatment method according to any one of claims 1 to 6, wherein the wastewater contains an oil component and / or a COD component and / or a nitrogen component. A coagulating sedimentation tank for separating wastewater into supernatant water and a coagulated sediment slurry; activated carbon adding means for adding activated carbon to the wastewater; a coagulant adding means for adding an inorganic coagulant to the wastewater; And a stirring means for stirring the wastewater. A wastewater treatment system, comprising: the wastewater treatment device according to claim 8, a dewatering device, and a return unit that returns separated water from the dewatering device as raw water to the coagulation settling tank.

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