JP2018183755A - Wastewater treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wastewater treatment method capable of performing efficient treatment of wastewater containing COD component such as oil and surfactant, and possible to sufficiently lower the COD of treated water.SOLUTION: There is provided a wastewater treatment method, including: performing pretreatment of adding manganese dioxide and water soluble inorganic salt into wastewater containing COD component to decompose the COD component under acidic condition, adding powdered activated carbon to adsorb residual COD component; adding an alkaline agent to neutralize the wastewater; and adding a polymeric flocculant or an inorganic flocculant in a pH neutral region to coagulate powdered activated carbon on which the COD component etc., is adsorbed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for treating waste water containing a COD component. More specifically, the present invention relates to a wastewater treatment method capable of effectively treating wastewater containing a high concentration of organic matter and reducing the COD concentration.

  Wastewater containing organic matter (oil, surfactant, etc.) discharged from factories and power plants has high COD (chemical oxygen demand), and as a treatment of wastewater with such high COD concentration, An activated carbon adsorption method, an activated sludge method, a method of adding ozone or hydrogen peroxide, and the like are known.

  However, in the activated carbon adsorption method, the adsorption capacity of activated carbon decreases in a short period of time, and the treatment cost increases as the frequency of replacement with new activated carbon increases. In the activated sludge method, the activity of microorganisms is weakened by organic substances contained in the wastewater, so a coagulation separation tank and sludge treatment facility must be installed as pretreatment equipment, and the treatment cost increases as with the activated carbon adsorption method. To do. In the ozone addition method, it is difficult to control the ozone concentration, and the residual ozone treatment is also required. In the method of adding hydrogen peroxide, the treatment efficiency decreases unless the addition amount is increased.

As a method for treating wastewater having a high COD concentration, Patent Document 1 discloses that an oil content is obtained by adding and adsorbing powdered activated carbon to wastewater and then adding an inorganic powder flocculant mainly composed of active silicon dioxide and alumina. And a method for simultaneously processing COD components. In the examples, a wastewater treatment example having an oil content of 386 mg / L and COD of 839 mg / L is disclosed. In this method, after adding 3% by mass of powdered activated carbon to the wastewater in the coagulation sedimentation tank, the inorganic powder coagulant is added in an amount of 3000 ppm (with respect to the wastewater). There is an advantage that the collected supernatant water can be discharged out of the system as treated water.
However, the method described in Patent Document 1 can reduce the COD of wastewater by agglomerating activated carbon that has adsorbed oil and the like to form flocs. However, when applied to wastewater with a high COD concentration, activated carbon is used. There has been a problem that the processing cost increases as the amount increases.

In Patent Document 2, an oxidant (permanganate, hydrogen peroxide, etc.) that exhibits oxidizing power in an acidic state is added to and mixed with wastewater containing persistent COD such as waste landfill leachate, COD is oxidized in the presence of manganese dioxide, this oxidized oxidation solution is aerated in an aeration tank to insolubilize dissolved manganese, and a neutralizing agent and an inorganic flocculant ( Treated with co-precipitated manganese compound in a tank adjusted to pH 5.8 to 8.6 (preferably 7.0 to 8.6) by adding ferric chloride, ferric sulfate, etc. A method of separating the sludge into sludge has been proposed.
However, in the method described in Patent Document 2, since the pH in the tank to which the inorganic flocculant is added is adjusted to the alkali side, the pH adjusting function of the inorganic flocculant is not used.

Japanese Patent No. 4169614 (claims, paragraphs [0023] to [0024], [0035], etc.) Japanese Examined Patent Publication No. 6-96150 (Claims, Tables 1 and 2, FIG. 1, FIG. 2, etc.)

  The present invention has been made in view of the above problems, and can efficiently treat wastewater containing COD components such as oil and surfactant, and can treat the COD of treated water even for wastewater having a high COD concentration. It aims at providing the waste water treatment method which can fully be reduced.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research. As a result, after pre-treating the wastewater containing the COD component, treatment with activated carbon and a flocculant results in good treatment results with a small amount of activated carbon. And the present invention has been achieved.

That is, the wastewater treatment method of the present invention is
After performing pre-treatment to decompose the COD component under acidity by adding manganese dioxide and water-soluble inorganic salt to the wastewater containing the COD component,
Add powdered activated carbon to adsorb residual COD components,
An alkaline agent is added for neutralization, and the powdered activated carbon is agglomerated by adding a polymer flocculant or an inorganic flocculant in a neutral pH range.

  In the wastewater treatment method according to the present invention, before performing the activated carbon adsorption treatment, manganese dioxide and a water-soluble inorganic salt are added to the wastewater, and if necessary, an acidic agent such as an acidic agglomeration aid is added and pretreated under acidity. In addition, COD components such as oil and surfactant in the waste water can be efficiently removed, and the subsequent activated carbon adsorption treatment becomes easy.

  In the wastewater treatment method according to the present invention, when the COD concentration of the wastewater is 500 mg / L or more, it can be applied more suitably and the effect is high.

  Moreover, in the waste water treatment method according to the present invention, the preferable total addition amount of the manganese dioxide and the water-soluble inorganic salt to the waste water is in the range of 0.05 to 5.0% by mass. When the addition amount is too small, the pretreatment effect is insufficient. On the other hand, when the addition amount is too large, the pretreatment effect is not improved, and the processing cost may be increased.

  In the wastewater treatment method according to the present invention, the acid agent is preferably an iron-based agglomeration aid or an aluminum-based agglomeration aid, but inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid can also be used. By adding manganese dioxide and water-soluble inorganic salt under acidic conditions, a part of COD in the wastewater is decomposed, and the COD component in the wastewater whose concentration has decreased is adsorbed, so a small amount of powdered activated carbon can be added. The COD concentration of waste water containing high concentration organic matter can be reduced. The pH of the waste water before or after the addition of manganese dioxide and the water-soluble inorganic salt is preferably 3.0 to 5.5, and the temperature of the waste water during the pretreatment is preferably 35 ° C. or higher. The reason for this is not clear, but it is presumed that increasing the drainage temperature has the effect of promoting the decomposition of the COD component.

  In the wastewater treatment method according to the present invention, an inorganic powder flocculant mainly composed of active silicon dioxide and alumina is preferably used. Such an inorganic powder flocculant is less susceptible to the influence of the pH of the wastewater, and thus can be more suitably applied and has a high effect.

  As described above, according to the wastewater treatment method of the present invention, wastewater containing high-concentration COD components can be efficiently treated, and the COD of treated water can be reduced to a predetermined target value or less. Supernatant water and sludge can be treated with existing wastewater treatment equipment.

It is a schematic process drawing which shows one Embodiment of the waste water treatment method which concerns on this invention.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic process diagram showing an embodiment of the waste water treatment method of the present invention. The waste water treatment method shown in FIG. 1 includes a primary pretreatment tank 10 to which manganese dioxide and a water-soluble inorganic salt are added, a secondary pretreatment tank 20 to which an acid agent is added and mixed, and a COD adsorption tank that performs adsorption treatment with activated carbon. 30, a pH adjusting tank 40, and an aggregating treatment tank 50 for performing an aggregating treatment with an aggregating agent.

  First, waste water (normally pH 6-8) is accommodated in the primary pretreatment tank 10. Subsequently, manganese dioxide and a water-soluble inorganic salt are added to the accommodated waste water and stirred. The order of adding manganese dioxide and water-soluble inorganic salt is arbitrary, and is not particularly limited.

  As wastewater, wastewater containing organic matter such as oil discharged from factories, power plants, surfactants, dyeing wastewater, leather manufacturing wastewater, paint wastewater is mainly used. Examples of the oil component include crude oil-derived components such as crude oil, heavy oil, and sludge accumulated in a heavy oil storage tank, animal and vegetable oils, insulating oil, lubricating oil, release oil, cutting oil, mineral oil, paint, and tannin. The COD concentration of the wastewater in the wastewater treatment method of the present invention is not particularly limited, but can be more suitably applied when the COD concentration of the wastewater is 500 mg / L or more.

  In the present invention, manganese dioxide has the effect of oxidatively decomposing COD components and reducing COD. Although manganese dioxide varies depending on the quality of the wastewater, it is preferably added in an amount of 0.025 to 2.5% by mass, more preferably 0.025 to 2.0% by mass, and still more preferably 0.025 to 2.5%. 1.0% by mass. If the added amount is 0.025% by mass or more, the organic matter in the waste water can be oxidatively decomposed. If the added amount is 2.5% by mass or less, it is necessary to separately provide equipment for treating the remaining manganese. There is no.

  In the present invention, the water-soluble inorganic salt is presumed to have an action of assisting oxidative decomposition of manganese dioxide with respect to organic substances (oil, surfactant, etc.) in waste water. Although the amount of addition varies depending on the quality of the wastewater, it is preferably added in an amount of 0.025 to 2.5% by mass, more preferably 0.025 to 2.0% by mass, and still more preferably, in the same manner as manganese dioxide. It is 0.025-1.0 mass%. If the added amount is 0.025% by mass or more, the oxidative decomposition of manganese dioxide with respect to the COD component in the wastewater can be decomposed, and if it is 2.5% by mass or less, the subsequent treatment is adversely affected. There is no fear of affecting.

  As the water-soluble inorganic salt, a compound having high solubility in waste water such as sodium salt and potassium salt is preferable. For example, sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, potassium nitrate, sodium nitrate, potassium iodide, sodium iodide, etc. Is mentioned.

  The ratio of manganese dioxide and water-soluble inorganic salt added to the wastewater is preferably in the range of 8: 2 to 2: 8, more preferably in the range of 6: 4 to 4: 6, by mass ratio. The mass ratio can be selected depending on the type and amount of organic matter in the waste water.

  During the pre-aggregation treatment, the temperature of the waste water is not particularly limited, but the higher the temperature of the waste water stored in the primary pretreatment tank 10, the lower the COD concentration of the waste water. The temperature of the waste water is preferably about 35 to 60 ° C. in consideration of an increase in processing cost due to introduction of heat treatment. During the pre-aggregation treatment, the waste water having the above temperature may be used as it is, or the waste water may be heated and used.

  The drainage temperature is preferably determined in consideration of the hydrophile-lipophile balance (HLB) of the surfactant contained. For example, a release agent is mixed in waste water discharged from a rubber factory, and examples of the release agent include nonionic surfactants such as adducts of ethylene oxide (EO) and propylene oxide (PO). Sometimes used. Nonionic surfactants are known to have an inherent cloud point and are well soluble in water at temperatures below the cloud point, but become sparingly soluble at temperatures above the cloud point. As the temperature of water increases, the degree of hydration decreases, and the balance between hydrophilic and hydrophobic groups tends to be hydrophobic. Therefore, it is presumed that by adding the water-soluble inorganic salt in the primary pretreatment tank 10, the cloud point is lowered and the COD component in the wastewater is more easily decomposed.

  The wastewater accommodated in the primary pretreatment tank 10 to which manganese dioxide and water-soluble inorganic salt are added is transferred to the downstream secondary pretreatment tank 20, and an acid agent is added and mixed in the secondary pretreatment tank. . Examples of the acidic agent include inorganic acid acids such as sulfuric acid, hydrochloric acid, and nitric acid in addition to general acidic agglomeration aids such as iron-based agglomeration aids and aluminum-based agglomeration aids. In view of the ability to agglomerate, an acidic agglomeration aid is preferably used. Examples of the acidic agglomeration aid include polyaluminum sulfate (PAC), polyaluminum chloride, aluminum sulfate (common name: vanous sulfate), polyferric sulfate (common name: polyiron), polysilica iron, ferrous chloride, A solution such as ferric chloride or ferric sulfate, a solution containing these as a main component, or a mixture thereof can be used. Among these acidic agglomeration aids, trivalent iron-based agglomeration aids such as ferric chloride and ferric sulfate are preferable because they have a high effect of precipitating manganese compounds. The acid flocculation aid may be used at a general use concentration, and is usually added in an amount of 0.05 to 0.5% by mass with respect to the waste water.

  It is preferable that the pH of the waste water accommodated in the secondary pretreatment tank 20 is in the range of 3.0 to 5.5 (acidic). Therefore, when the pH of the waste water is within the above range, addition of an acid agent is unnecessary.

  Pretreated water in the secondary pretreatment tank 20 is transferred to the COD adsorption tank 30, and powdered activated carbon is added to the COD adsorption tank 30. Although pH adjustment with respect to the pretreatment water accommodated in the COD adsorption tank 30 is not essential, it is preferably in the range of pH 5.0 to 6.5.

  The powdered activated carbon is added to the acidic pretreated water and stirred for a predetermined time, whereby the residual COD component in the pretreated water is adsorbed on the powdered activated carbon. The kind of powder activated carbon is not specifically limited. The powdered activated carbon is preferably powdered activated carbon having an average particle size of 200 μm or less, more preferably an average particle size of 1 to 150 μm, and still more preferably an average particle size of 1 to 100 μm. If the average particle size is less than 1 μm, it tends to be scattered and difficult to handle, and the cost of micronization tends to increase. If it exceeds 150 μm, the specific surface area becomes small and a large amount is required to maintain a constant adsorption capacity. Tend to require powdered activated carbon. As a method for measuring the average particle diameter of the powdered activated carbon, a known method such as a laser diffraction scattering method can be used.

The amount of powdered activated carbon added varies depending on the type of activated carbon and the wastewater to be treated, but is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, particularly with respect to the wastewater (treated water). Preferably it is 1-3 mass%. If it is 0.1 mass% or more, the adsorption capacity of the powdered activated carbon will not be insufficient, and if it is 10 mass% or less, the processing cost will not be remarkably increased.
The time required for adsorbing the COD component remaining in the waste water after the pretreatment to the powdered activated carbon is not particularly limited, but it is usually preferable to stir for 5 minutes or more.

  Next, the treated water to which the powdered activated carbon is added is transferred to the pH adjusting tank 40, and the transferred pretreated water is adjusted to pH 6.0 to 8.0 using an alkali agent as a neutralizing agent. By adjusting the pH within this range, aggregation with an inorganic flocculant or a polymer flocculant added in the downstream is smoothly performed. Examples of the alkaline agent include slaked lime, quicklime, lime, caustic soda, soda ash, etc. Caustic soda is preferable from the viewpoint of reducing the amount of sludge.

  Next, neutral pretreatment water containing powdered activated carbon is transferred to the agglomeration treatment tank 50, and a flocculant is added to the waste water (treated water) in the aggregation treatment tank 50. By adding a flocculant, the oil and COD components adsorbed on the powdered activated carbon are coagulated and precipitated together with the powdered activated carbon to form sludge, and the oil and COD components in the waste water are contained in the sludge and processed. Become. On the other hand, in the upper layer of the flocculation treatment tank 50, supernatant water from which oil and COD components have been removed is formed.

  What is necessary is just to use a flocculant by a general use density | concentration, It is preferable to add 0.01-1.0 mass% with respect to treated water, More preferably, it is 0.02-0.5 mass%.

  As the flocculant, a general polymer flocculant or an inorganic flocculant can be used. The polymer flocculant is selected from, for example, polyacrylamide flocculants such as acrylic amide (co) polymer, styrene flocculants such as polystyrene sulfonic acid, acrylic flocculants such as polyacrylic acid, and the like. Nonionic, cationic, anionic and amphoteric ones can be used. In addition, chitosan-based polymer flocculants and alginic acid-based polymer flocculants can also be used. Among them, polyacrylamide polymer flocculants are preferable from the viewpoint of performance and cost.

  As the inorganic flocculant, an inorganic powder flocculant mainly composed of active silicon dioxide and alumina is preferable. Since the flocculant exhibits excellent flocculation performance in a wide pH range, it has an advantage that pH adjustment of treated water is easy.

  After the settled sludge is discharged out of the flocculation treatment tank 50, filtration and / or dehydration treatment is performed to obtain a dehydrated cake. As the dehydrating device, a conventionally known dehydrating device can be used, and examples thereof include a filter using a woven fabric or a non-woven fabric, a centrifuge, a rotary press filter, a bag filter, a filter press, a belt press and the like. Since sludge has extremely good dewaterability, it can be easily recovered. Since the dehydrating apparatus may have a simple configuration, the filtration system and the dehydrating system can be simplified.

  On the other hand, the supernatant water can be treated using a conventionally known treatment device and discharged as treated water. For example, a method in which the supernatant water is sequentially passed through a sand filtration tower and an activated carbon adsorption tower.

  The supernatant water is used for water quality inspection. In the water quality test, the pH, SS, and COD of the water are measured to check whether or not a predetermined reference value is cleared. The treated water can be discharged as treated water with reference to a predetermined pH standard value (for example, 6 to 8), SS standard value (for example, 25 mg / L or less), and COD standard value (for example, 160 mg / L or less). it can. If the treated water does not clear a predetermined reference value (particularly the COD reference value), pretreatment, activated carbon adsorption, neutralization / coagulation treatment may be performed again. Thereby, COD of treated water can be reliably made below a predetermined standard value.

  In the wastewater treatment method according to the present invention, the preferred pH of the pretreatment water in the activated carbon adsorption step (COD adsorption tank 30) is in the range of 5.0 to 6.5, and the treatment in the aggregation treatment step (aggregation treatment tank 50). The preferred pH of water is in the range of 6.0 to 8.0. By adjusting the pH of the pretreated water in the activated carbon adsorption step to the above range, it is presumed that the COD component in the wastewater is easily adsorbed on the activated carbon by being positively charged. Thereafter, the pH of the treated water is neutralized by using a neutralizing agent, so that the charge is neutralized, and suspended matters and dissolved matters in the waste water form flocs and quickly aggregate and precipitate. Furthermore, since a large floc is formed by adding an inorganic or polymer flocculant, an excellent sedimentation and separation effect can be obtained.

  By carrying out the above treatment steps, it is possible to treat high-concentration COD-containing wastewater until it can be treated with existing wastewater treatment facilities.

  The waste water treatment method of the present invention may be applied to batch treatment or continuous treatment. In addition, the processing order of the primary pretreatment tank 10 and the secondary pretreatment tank 20 is switched, and the secondary pretreatment tank 20 is configured as a primary pretreatment tank and the primary pretreatment tank 10 is configured as a secondary pretreatment tank. It comes out. Furthermore, the primary pretreatment tank 10 and the secondary pretreatment tank 20 can be configured as a single treatment tank. Thus, when performing a pre-processing in one processing tank, the addition order of manganese dioxide, a water-soluble inorganic salt, and an acidic agent is arbitrary, and is not specifically limited.

  Furthermore, the COD adsorption tank 30, the pH adjustment tank 40, and the coagulation treatment tank 50 can be constituted by one treatment tank, and the primary pretreatment tank 10 to the coagulation treatment tank 50 can be constituted by one treatment tank. You can also. Even when the primary treatment tank 10 to the coagulation treatment tank 50 are constituted by one treatment tank, the order of addition of manganese dioxide, water-soluble inorganic salt, and acid agent is not particularly limited, and the COD component is acidic. The pre-processing for decomposing | disassembling should just be performed.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to those Examples.

Example 1
Waste water containing mineral oil and a rubber release agent (nonionic surfactant) was treated with a waste water treatment apparatus as shown in FIG. The drainage properties were pH: 7.9, SS: 36 mg / L, COD: 3500 mg / L.

The waste water having a liquid temperature of 40 ° C. is introduced into the primary pretreatment tank 10, and 0.1% by mass (1 kg / m ³ ) of manganese dioxide and 0.1% by mass (1 kg / m ³ ) of the waste water. After the potassium sulfate powder is added and mixed, this waste water is transferred to the secondary pretreatment tank 20, and 0.1 mass% (1 L / m ³ ) aqueous ferric chloride solution is added to the waste water and mixed for about 20 minutes. did. The pH of the water (treated water) at this time was 3.5.
After introducing the treated water into the COD adsorption tank 30 and adding 2% by mass (20 kg / m ³ ) of powdered activated carbon (trade name: “NAC-TJ” manufactured by Noatec Co., Ltd.) to the waste water, The powdered activated carbon was dispersed in the treated water by stirring with a stirrer for about 10 minutes. This treated water was transferred to the pH adjusting tank 40, and caustic soda was added to adjust the pH of the treated water to 6.2.
After introducing the neutralized treated water into the agglomeration treatment tank 50, 0.05% by mass (500 g / m ³ ) of inorganic powder flocculant (trade name: “Superna” manufactured by Noatec Co., Ltd.) with respect to the treated water. Mitt TN315NY-T3 ”(average particle size 150 μm) was added and agitated to agglomerate the powdered activated carbon, and then the agitation was stopped to allow the powdered activated carbon and the inorganic powder aggregating agent to settle.

  After confirming that transparent supernatant water was obtained in the upper layer, the supernatant water of the flocculation tank 50 was collected and analyzed for water quality. As a result, the water quality of the treated water was pH 6.5, SS 10 mg / L or less, and COD 70 mg / L.

  The COD removal rate of the treated water after the water treatment was 98%, which cleared the emission standard value (160 mg / L). For this reason, it could be discharged out of the system as treated water.

Here, the main components of “Super Namit TN315NY-T3” used as the flocculant are as follows.
SiO ₂ approx. 70%
Al ₂ O ₃ about 15%
K ₂ O about 5%
Na ₂ O about 2%
SO ₃ approx. 1%
CaO about 1%
C About 2%

(Measuring method)
pH: JIS K0102 12.1 Glass electrode method SS: JIS K0102 14.1 Suspended matter COD: JIS K0102 17 Oxygen consumption by potassium permanganate at 100 ° C

(Example 2)
In Example 1, the wastewater was treated in the same manner as in Example 1 except that the wastewater having a liquid temperature of 25 ° C. was used. As a result, the water quality of the treated water was pH 6.5, SS 10 mg / L or less, and COD 147 mg / L.

(Comparative Example 1)
In Example 1, waste water was treated in the same manner as in Example 1 except that potassium sulfate was not added. As a result, the water quality of the treated water was pH 6.5, SS 10 mg / L or less, and COD 185 mg / L, and the treatment effect was remarkably deteriorated.

(Comparative Example 2)
In Example 1, the waste water was treated in the same manner as in Example 1 except that manganese dioxide was not added. As a result, the water quality of the treated water was pH 6.5, SS 10 mg / L or less, and COD 320 mg / L, and the treatment effect was remarkably deteriorated.

(Example 3)
In Example 1, the wastewater was treated in the same manner as in Example 1 except that dilute hydrochloric acid was added to adjust the pH of the wastewater to 3.5 instead of adding the ferric chloride aqueous solution. As a result, the water quality of the treated water was pH 6.7, SS 10 mg / L or less, and COD 75 mg / L.

  According to the present invention, high-concentration COD wastewater can be treated at a lower cost than in the past.

10 Primary pretreatment tank 20 Secondary pretreatment tank 30 COD adsorption tank 40 pH adjustment tank 50 Aggregation treatment tank

That is, the wastewater treatment method of the present invention is
After pretreatment that decomposes the COD component under acidity by adding manganese dioxide, water-soluble inorganic salt (but does not include acidic flocculation aid) and acidic flocculation aid to wastewater containing COD component ,
Add powdered activated carbon to adsorb residual COD components,
An alkaline agent is added for neutralization, and the powdered activated carbon is agglomerated by adding a polymer flocculant or an inorganic flocculant in a neutral pH range.

Claims (7)

After performing pre-treatment to decompose the COD component under acidity by adding manganese dioxide and water-soluble inorganic salt to the wastewater containing the COD component,
Add powdered activated carbon to adsorb residual COD components,
A wastewater treatment method characterized by neutralizing by adding an alkali agent and coagulating the powdered activated carbon by adding a polymer flocculant or an inorganic flocculant in a neutral pH range.   The wastewater treatment method according to claim 1, wherein the COD concentration of the wastewater is 500 mg / L or more.   The wastewater treatment method according to claim 1 or 2, wherein the water-soluble inorganic salt is potassium sulfate.   The wastewater treatment method according to any one of claims 1 to 3, wherein the pH is 3.0 to 5.5 before or after adding manganese dioxide and a water-soluble inorganic salt.   The wastewater treatment method according to any one of claims 1 to 4, wherein an acidic aggregation assistant selected from iron-based aggregation assistant or aluminum-based aggregation assistant is added as an acidic agent during pretreatment.   The wastewater treatment method according to any one of claims 1 to 5, wherein the temperature of the wastewater during the pretreatment is 35 ° C or higher.   The wastewater treatment method according to any one of claims 1 to 6, wherein the inorganic flocculant is an inorganic powder flocculant mainly composed of active silicon dioxide and alumina.

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