JP7600737B2 - Wastewater treatment method and wastewater treatment device - Google Patents

Description

This disclosure relates to a wastewater treatment method and wastewater treatment device for wastewater containing organic matter, oil, and surfactants.

In cardboard manufacturing factories, wastewater is generated from glue washing water from laminating machines and ink washing water from box making machines. This wastewater contains organic matter such as glue, as well as oil and surfactants, and the oil and surfactants contained in the wastewater may emulsify to form an emulsion.

As a method for removing oil that has formed an emulsion from oil-containing wastewater, a method for treating oil-containing wastewater has been disclosed that includes a pretreatment step in which salt is added to the water to be treated, and a flocculation treatment step in which a flocculant is added (see Patent Document 1).

In addition, as a method for recovering oil from oil-containing wastewater that has formed an emulsion, a method for treating oil-containing wastewater has been disclosed that includes a pretreatment step of adding salt to the water to be treated, and a separation step of separating the oil from the water to be treated that has been separated into oil and water in the pretreatment step (see Patent Document 2).

JP 2017-39088 A JP 2017-94260 A

However, in Patent Document 1, the wastewater does not contain a surfactant, and in the addition of the flocculant, an inorganic flocculant and a polymer flocculant are used in combination, which causes problems such as an increase in the amount of sludge, which places a burden on subsequent treatment, and an increase in the viscosity of the treated water.
Furthermore, in Patent Document 2, since the oil in the wastewater is recovered, no coagulant is used, and therefore, one must say that the method is insufficient from the viewpoint of treating wastewater containing organic matter, oil, and surfactants.
An object of the present invention is to provide a new method for treating wastewater containing organic matter, oil, and a surfactant.

The present inventors have conducted research to solve the above problems, and have found that the above problems can be solved by adding salt and an inorganic flocculant in the same process to wastewater containing organic matter, oil, and a surfactant, and have completed the present invention. The present invention includes the following.
[1] A method for treating wastewater containing organic matter, oil, and a surfactant, comprising:
a flocculation treatment step of adding salt and an inorganic flocculant to the wastewater; and a flocculation removal step of removing flocs formed in the wastewater by the flocculation treatment.
[2] The wastewater treatment method according to [1], wherein the organic matter concentration (CODMn) is 10 mg/L or more and 1000 mg/L or less.
[3] The wastewater treatment method according to [1] or [2], wherein the oil concentration is 10 mg/L or more and 1000 mg/L or less.
[4] The wastewater treatment method according to any one of [1] to [3], wherein a polymer flocculant is not substantially used in the flocculation treatment step.
[5] The wastewater treatment method according to any one of [1] to [4], further comprising a high-stage treatment step in which high-stage treatment is performed on the treated water from which flocs have been removed in the floc removing step.
[6] The wastewater is stored in a wastewater storage tank equipped with an organic matter concentration measuring device, and a transfer step is included in which the wastewater is transferred from the wastewater storage tank to a coagulation treatment tank in which the coagulation treatment step is performed;
The wastewater treatment method according to any one of [1] to [5], wherein, in the flocculation treatment step, the amount of the inorganic flocculant added is adjusted based on organic matter concentration information obtained from the organic matter concentration meter.
[7] A wastewater storage tank for storing wastewater containing organic matter, oil, and a surfactant;
a coagulation treatment tank for adding salt and an inorganic coagulant to the wastewater to perform coagulation treatment;
a solid-liquid separation tank for removing wastewater flocs formed during the coagulation treatment;
A wastewater treatment device comprising:
[8] The wastewater treatment device according to [7], wherein the organic matter concentration (CODMn) is 10 mg/L or more and 1000 mg/L or less.
[9] The wastewater treatment device according to [7] or [8], wherein the oil concentration is 10 mg/L or more and 1000 mg/L or less.
[10] The wastewater treatment device according to any one of [7] to [9], wherein substantially no polymer flocculant is used in the flocculation treatment tank.
[11] The wastewater treatment device according to any one of [7] to [10], further comprising a high-stage treatment tank for performing high-stage treatment on the treated water obtained in the solid-liquid separation tank.
[12] The wastewater storage tank is equipped with an organic matter concentration meter,
The wastewater treatment device according to any one of [7] to [11], further comprising an additive amount control mechanism for adjusting the additive amount of the inorganic flocculant and/or salt in the flocculation treatment tank based on the organic matter concentration information obtained from the organic matter concentration measuring device.

This disclosure provides a wastewater treatment method and wastewater treatment device that effectively treats wastewater containing organic matter, oil, and surfactants.

FIG. 1 is a flow diagram showing steps of a wastewater treatment method according to one embodiment of the present invention. 1 is a schematic diagram showing a wastewater treatment device according to one embodiment of the present invention. FIG. 1 is a flow chart showing steps of a wastewater treatment method according to one embodiment of the present invention. 1 is a schematic diagram showing a wastewater treatment device according to one embodiment of the present invention. 1 is a schematic diagram showing a wastewater treatment device according to one embodiment of the present invention.

One embodiment of the present invention is a method for treating wastewater containing organic matter, oil, and a surfactant, the method comprising: a flocculation treatment step of adding salt and an inorganic flocculant to the wastewater; and a flocculation removal step of removing flocs formed in the wastewater by the flocculation treatment.
Another embodiment of the present invention is a wastewater treatment device comprising a wastewater storage tank for storing wastewater containing organic matter, oil, and a surfactant, a coagulation treatment tank for performing coagulation treatment by adding salt and an inorganic coagulant to the wastewater, and a solid-liquid separation tank for separating and removing flocs of the wastewater formed by the coagulation treatment. Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In this specification, the organic matter refers to organic substances other than oil and fat, such as mud, metabolites of animals and plants, polymers including chemicals, etc. Therefore, the organic components that cause water pollution are composed of "oil" and "organic matter (organic substances other than oil)."
The oil content and the organic matter can be measured by different analytical methods.
and the oil content can be measured using normal hexane extractable substances (animal and vegetable oils or mineral oils).

FIG. 1 is a flow diagram showing the steps of a wastewater treatment method according to one embodiment of the present invention.
The wastewater treatment method of this embodiment may include a wastewater storage step, a wastewater transfer step, a flocculation treatment step, a floc removal step, and a high-level treatment step. Among these steps, steps other than the flocculation treatment step and the floc removal step may be omitted or replaced with other steps as appropriate. Furthermore, steps not shown in this flow chart may be added as appropriate.

2 is a schematic diagram showing a wastewater treatment device 10 for carrying out the wastewater treatment method. The wastewater treatment device 10 includes a wastewater storage tank 11, a flocculation treatment tank 12, and a solid-liquid separation tank 13. The arrows connecting the tanks in the figure indicate the flow of wastewater (water to be treated, treated water) or flocs (sludge) through a water supply line or the like. In addition, the wastewater (water to be treated, treated water) or sludge can be transferred to the next tank by opening and closing a valve 14 on the arrow.
The wastewater in the wastewater storage tank 11 is, for example, cleaning wastewater from a cardboard factory, and may be glue washing water from a laminating machine and ink washing water from a box making machine. Such wastewater contains organic matter, oil, and surfactant, but may also contain other substances. In addition, the oil and surfactant contained may or may not form an emulsion. The types of organic matter, oil, and surfactant in the wastewater are not particularly limited, and may be any that can be mixed into the wastewater.

The concentration of organic matter in the wastewater (CODMn) is not particularly limited, but is preferably 10 mg/L or more and 1000 mg/L or less, and more preferably 100 mg/L or more and 500 mg/L or less.
The oil concentration in the wastewater is not particularly limited, but is preferably 10 mg/L to 1000 mg/L, and more preferably 30 mg/L to 500 mg/L. The oil concentration is measured as a normal hexane extractable substance.
The concentration of the surfactant in the wastewater is not particularly limited, but is preferably 10 mg/L or more and 3000 mg/L or less, and more preferably 100 mg/L or more and 2000 mg/L or less.

The coagulation treatment tank 12 is a tank in which fine particles contained in the wastewater are coagulated and flocculated by adding salt and an inorganic coagulant to the wastewater transferred from the wastewater storage tank 11. The coagulation treatment tank 12 is usually equipped with an agitator that agitates the wastewater to improve the coagulation efficiency, but it is not necessarily required to be equipped with such an agitator.
In this embodiment, salt and an inorganic flocculant are added to the wastewater in the same process, i.e., the flocculation treatment process. By adding salt in addition to the inorganic flocculant, it is possible to promote the separation of the emulsion formed in the wastewater by the oil and surfactant, and the flocculation effect of the inorganic flocculant is improved. Furthermore, by adding salt and an inorganic flocculant in the same process, the separation of the emulsion and the flocculation of organic matter proceed simultaneously, improving the efficiency of the wastewater treatment.
When salt and an inorganic flocculant are added to wastewater in the flocculation treatment step, they may be added simultaneously if they can be added in the same step, or the salt may be added first. From the viewpoint of simultaneously proceeding with the separation of emulsion and the flocculation of organic matter to improve the efficiency of wastewater treatment, it is preferable to add them simultaneously.

The type of salt to be added is not particularly limited as long as it is a salt that can exist as an ion in the wastewater, and a salt that dissolves in the wastewater and easily ionizes is preferred. Specific examples include sodium chloride, calcium chloride, magnesium chloride, potassium chloride, etc.
The amount of salt added to the wastewater is not particularly limited, but is preferably 50,000 mg/L or less, more preferably 30,000 mg/L or less, and most preferably 20,000 mg/L or less. There is no lower limit to the amount of salt added, but it is preferably more than 0 mg/L, and more preferably 500 mg/L or more.

The type of inorganic additive to be added is not particularly limited, and any known inorganic flocculant can be used, such as aluminum sulfate, polyaluminum chloride, ferric chloride, ferrous sulfate, and polyferric sulfate.
The amount of inorganic flocculant added to the wastewater is preferably 5 ppm by mass to 1000 ppm by mass, more preferably 10 ppm by mass to 500 ppm by mass, and even more preferably 20 ppm by mass to 200 ppm by mass, calculated as the solid amount of the inorganic flocculant.

In the coagulation treatment step, the pH may be adjusted by adding a pH adjuster to the coagulation treatment tank 12. Known acids or alkalis can be used as the pH adjuster. The pH of the wastewater in the coagulation treatment tank 12 is set appropriately depending on the type of inorganic coagulant, and in the case of an aluminum-based coagulant, the pH is preferably controlled to about 5.0 to 8.0, more preferably about 6.0 to 7.5, and even more preferably about 6.5 to 7.0. In the case of an iron-based coagulant, the pH is preferably controlled to 4.0 or higher, and more preferably about 6.5 to 7.0.

In the coagulation treatment step, it is preferable to add substantially no other substances to the coagulation treatment tank 12 other than salt, inorganic coagulant, and pH adjuster, and it is particularly preferable to add substantially no polymer coagulant. By substantially not adding a polymer coagulant, the increase in viscosity of the coagulated material is suppressed, and therefore adhesion of the coagulant to the tank and transfer piping can be suppressed. In addition, the increase in viscosity of the wastewater can be suppressed, and therefore poor separation of the wastewater and sludge can be suppressed. Furthermore, the water content of the sludge is reduced, so the amount (bulk) of sludge is suppressed, and sludge treatment costs are reduced.

In this specification, "substantially not added" means that a small amount of polymer flocculant may be added within a range in which the effect of not adding the polymer flocculant described above can be obtained. If a polymer flocculant is added, the amount is preferably 0.01 mg/L or less, more preferably 0.001 mg/L or less, and even more preferably not added at all.
The polymer flocculant is not particularly limited, and examples thereof include polyacrylamide, 2-acryloylamino-2-methylpropanesulfonic acid (AMPS), etc. Examples of the polymer flocculant include anionic polymer flocculants, cationic polymer flocculants, nonionic polymer flocculants, etc.

In the solid-liquid separation tank 13, solid-liquid separation is performed on the wastewater containing flocs transferred from the coagulation treatment tank 12, separating it into treated water 18 and sludge 17, which is an aggregate of flocs, and then removing the sludge 17. There are no particular limitations on this floc removal process, and any known removal method may be used. In one example, the sludge 17 can be made to float in the wastewater by applying pressure, and separated into treated water 18 and sludge 17. In another example, the wastewater can be left to stand for a predetermined time by sedimentation separation, and separated into the supernatant liquid (treated water) and precipitate (sludge).

The separated sludge 17 is treated by a known sludge treatment method. In this embodiment, since a polymer flocculant is not substantially added and the moisture content of the separated sludge is reduced, the amount (bulk) of the sludge is suppressed, and the sludge treatment cost can be reduced.
The treated water 18 may also be subjected to advanced treatment steps, as described in a preferred embodiment below.

3 is a flow diagram showing the steps of a wastewater treatment method according to another embodiment of the present invention. The wastewater treatment method of this embodiment may include a wastewater storage step, a wastewater transfer step, a coagulation treatment step, a floc removal step, and a high-level treatment step. The organic matter concentration and/or salt concentration in the wastewater stored in the wastewater storage step are measured, and the concentration of the inorganic coagulant and/or salt added in the coagulation treatment step is controlled by an inorganic coagulant and/or salt concentration control means based on the information.

Fig. 4 is a schematic diagram showing a wastewater treatment device 20 for carrying out the wastewater treatment method according to another embodiment of the present invention. Similar to the wastewater treatment device 10 shown in Fig. 2, the wastewater treatment device 20 includes a wastewater storage tank 21, a flocculation treatment tank 22, and a solid-liquid separation tank 23, and a salt 25 and an inorganic flocculant 26 are added to the flocculation treatment tank 22.
In this embodiment, the wastewater storage tank 21 is provided with an organic matter concentration meter 29. Information on the organic matter concentration measured by the organic matter concentration meter 29 is fed forward to an inorganic flocculant concentration control mechanism and/or a salt concentration control mechanism (not shown), so that the amount of salt 25 added by the salt concentration control mechanism to the flocculation treatment tank and the amount of inorganic flocculant 26 added by the inorganic flocculant concentration control mechanism to the flocculation treatment tank can be adjusted (indicated by dashed arrows in the figure). That is, when the organic matter concentration obtained by the organic matter concentration meter 29 is high, control is performed to increase the amount of inorganic flocculant and/or salt to be added, and when the organic matter concentration obtained by the organic matter concentration meter 29 is low, control is performed to decrease the amount of inorganic flocculant and/or salt to be added.

The amount of inorganic coagulant and/or salt may be controlled, for example, by inputting a relationship equation between the organic matter concentration in the wastewater and the inorganic coagulant and/or salt to be added into a known control program in advance, and using an inorganic coagulant concentration control mechanism and/or a salt concentration control mechanism equipped with the control program. Alternatively, the manager of the wastewater treatment device may grasp information on the organic matter concentration in the wastewater and control the inorganic coagulant concentration and/or the amount of salt according to that concentration.
In this way, by feeding forward information on the organic matter concentration in the wastewater measured by the organic matter concentration meter 29 provided in the wastewater storage tank 21 and controlling the amount of salt 25 and/or inorganic coagulant 26 added to the coagulation treatment tank 22, the waste of adding more salt and/or inorganic coagulant than necessary can be reduced, and wastewater treatment can be carried out efficiently.

5 is a schematic diagram showing a wastewater treatment apparatus according to still another embodiment of the present invention, which shows a wastewater treatment apparatus 30 including an advanced treatment tank 39 for performing an advanced treatment process. In the wastewater treatment apparatus 30, the treated water after the sludge 37 is separated in the solid-liquid separation tank 33 is transferred to the advanced treatment tank 39. The advanced treatment tank 39 is a treatment tank for treating the treated water at an even higher level. The advanced treatment tank 39 is provided with activated carbon 39a, and is capable of removing organic matter and impurities from the treated water by the adsorption action of the pores of the activated carbon 39a.
Therefore, the highly treated water 38 that has been subjected to high-level treatment in the high-level treatment tank 39 becomes treated water that has been treated at a high level.

In the advanced treatment tank 39, advanced treatment means other than activated carbon may be used as long as they can perform advanced treatment of the treated water. Examples of advanced treatment means other than activated carbon include sand filtration.

All of the wastewater treatment devices 10, 20, and 30 according to this embodiment have valves, and the transfer of wastewater (treated water) can be adjusted by opening and closing the valves. Therefore, by opening and closing the valves at regular intervals, wastewater treatment can be performed in a batch (intermittent) manner. On the other hand, by keeping the valves basically open, wastewater treatment can also be performed in a continuous manner.

The effects of the present invention will be described below with reference to specific experimental data.
Normal hexane mineral oil (normal hexane extract concentration 110 mg/L) was prepared as the oil component, commercial laundry detergent (250 mg/L) was prepared as the surfactant, and washing wastewater containing animal and plant organic matter was prepared.
To this washing wastewater, aluminum sulfate (inorganic flocculant) and sodium chloride (salt) were added at the same time in the amounts shown in Table 1, and the washing wastewater was subjected to a pressure flotation treatment (pressure 0.6 Pa). Thereafter, the oil content in the washing wastewater was measured. The results are shown in Table 1.

As shown in Table 1, the oil content in the washing wastewater is lower when both salt and an inorganic coagulant are added (corresponding to the Example) than when aluminum sulfate or sodium chloride, or both are not added (addition amount 0) (corresponding to the Comparative Example).

10, 20, 30 Wastewater treatment device 11, 21, 31 Wastewater storage tank 12, 22, 32 Coagulation treatment tank 13, 23, 33 Solid-liquid separation tank 14, 24, 34 Valve 15, 25, 35 Salt 16, 26, 36 Inorganic coagulant 17, 27, 37 Sludge 18, 28 Treated water 29 Organic matter concentration meter 38 Highly treated water 39 Highly treated wastewater 39a Activated carbon

Claims (8)

A method for treating wastewater containing organic matter, oil, and a surfactant, comprising the steps of:
A wastewater treatment method comprising: a flocculation treatment step of adding salt and an inorganic flocculant to the wastewater; and a flocculation removal step of removing flocs formed in the wastewater by the flocculation treatment,
The concentration of the oil is 10 mg/L or more and 1000 mg/L or less,
the salt is sodium chloride, calcium chloride, magnesium chloride, or potassium chloride;
The inorganic flocculant is aluminum sulfate, polyaluminum chloride, ferric chloride, ferrous sulfate, or polyferric sulfate;
The wastewater treatment method, wherein in the flocculation treatment step, a polymer flocculant is added in an amount of 0.01 mg/L or less, or no polymer flocculant is added at all . The wastewater treatment method according to claim 1, wherein the organic matter concentration (CODMn) is 10 mg/L or more and 1000 mg/L or less. 3. The wastewater treatment method according to claim 1, further comprising a high-stage treatment step for subjecting the treated water from which flocs have been removed in the floc removing step to a high-stage treatment. The wastewater is stored in a wastewater storage tank equipped with an organic matter concentration measuring device, and a wastewater transfer step is included in which the wastewater is transferred from the wastewater storage tank to a coagulation treatment tank in which the coagulation treatment step is performed;
The wastewater treatment method according to any one of claims 1 to 3 , wherein in the flocculation treatment step, an amount of the inorganic flocculant added is adjusted based on organic matter concentration information obtained from the organic matter concentration measuring device. A wastewater storage tank for storing wastewater containing organic matter, oil, and a surfactant;
a coagulation treatment tank for adding salt and an inorganic coagulant to the wastewater to perform coagulation treatment;
a solid-liquid separation tank for removing wastewater flocs formed during the coagulation treatment;
A wastewater treatment device comprising:
The concentration of the oil is 10 mg/L or more and 1000 mg/L or less,
the salt is sodium chloride, calcium chloride, magnesium chloride, or potassium chloride;
The inorganic flocculant is aluminum sulfate, polyaluminum chloride, ferric chloride, ferrous sulfate, or polyferric sulfate;
In the coagulation treatment, a polymer coagulant is added in an amount of 0.01 mg/L or less, or no polymer coagulant is added at all . The wastewater treatment device according to claim 5 , wherein the concentration of the organic matter (CODMn) is 10 mg/L or more and 1000 mg/L or less. The wastewater treatment equipment according to claim 5 or 6 , further comprising a high-stage treatment tank for performing high-stage treatment on the treated water obtained in the solid-liquid separation tank. The wastewater storage tank is equipped with an organic matter concentration measuring device,
The wastewater treatment device according to any one of claims 5 to 7 , wherein the flocculation treatment tank has an addition amount control mechanism that adjusts the amount of the inorganic flocculant and/or salt added based on the organic matter concentration information obtained from the organic matter concentration measuring device.

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