JPH1028995A - Treatment of waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the floor space and equipment cost by miniturizing the equipment and to provide a method for treating waste water reducing the cost of operation and control and disposing of the org. matter and nitrogen compds. in the waste water. SOLUTION: The waste water contg. org. matter or nitrogen compds. is introduced into a biological treating device 1 to decompose the nitrogen compds. and org. matter, and a part of the biologically treated water 22 is treated in a flocculating and settling device 4. Further, the remainder of the water 22 biologically treated in the device 1 is introduced into a solid-liq. separator 10 through a flocculation device 8 and then into a desalter 12. The concd. water 36 discharged from the desalter 12 is returned to the biological treating device 1 and mixed with the untreated waste water, and the org. matter and nitrogen compds. remaining in the concd. water 36 are decomposed in the device 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating wastewater, and more particularly to a method for treating wastewater for treating organic matter and nitrogen compounds among components contained in wastewater such as flue gas desulfurization wastewater and domestic wastewater.

[0002]

2. Description of the Related Art As an advanced treatment method of wastewater containing organic substances and nitrogen compounds, most of nitrogen components are removed by a biological nitrification denitrification method, and then a coagulant is added to the biological treatment water to carry out coagulation treatment. Then, a method of membrane-separating the coagulated water has been conventionally known.

Referring to FIG. 4, wastewater containing the above-mentioned components is led to a biological treatment device (biological nitrification and denitrification treatment device) 41, and nitrogen in the wastewater is subjected to biochemical oxidation using aerobic microorganisms. The compound is changed to nitrate or nitrite, and the nitrate or nitrite is changed to nitrogen gas by biochemical reduction using an anaerobic microorganism, thereby decomposing most of nitrogen compounds and organic substances.

[0004] The biologically treated water 52 is led to a coagulation and sedimentation device 43 via a drainage storage tank 42, and as a coagulant C 53, ferric salts such as ferric chloride and ferric nitrate, aluminum chloride and aluminum nitrate , An inorganic coagulant found in aluminum salts such as PAC (polyaluminum chloride) is added, and the pH is adjusted to 6 to 8 with a pH adjuster 54 such as sodium hydroxide and calcium hydroxide. The addition forms coarse flocs with the suspension in the wastewater and precipitates.

[0005] The settled coagulated sediment sludge 56 is condensed by the concentration device 44.
And then dehydrated in a dehydrator 45, and then dehydrated cake 5
Discharge as 7. Further, the desorbed liquid 58 generated at that time is returned to the drainage storage tank 42 to be circulated. The supernatant water 55 after coagulation and sedimentation in the coagulation and sedimentation device 43 is
To remove suspended particles and fine particles remaining in the liquid.

The separated liquid 59 discharged from the filtration device 46 is guided to an RO (reverse osmosis) desalination device 47, and salts dissolved in the liquid are removed by a reverse osmosis membrane. Then, the permeated water that has passed through the membrane is reused or discharged as desalted water 60.

[0007] The concentrated water 61 generated by the RO desalination process contains concentrated organic substances and nitrogen compounds removed from the wastewater and cannot be discharged as it is, so it passes through the adsorption device 48 filled with activated carbon or the like. After removing these components, the water is discharged as adsorption treated water 62.

[0008]

However, the above-mentioned prior art has the following problems.

(1) In order to treat the entire amount of the wastewater to a high degree, large-scale equipment is required for each of the filtration device 46 and the RO desalination device 47 which are the processes after the coagulation and sedimentation.

(2) A large amount of sludge flowing into the filtration device 46 tends to increase the load on the device, and maintenance is troublesome.

(3) It is necessary to separately install a new activated carbon adsorption device 48 for treating the concentrated water 61 discharged from the RO desalination treatment device 47. Moreover, the concentrated water 6
1 has a large amount and a high salt concentration, so that a large-sized adsorption device 48 is required.

As described above, the conventional technology tends to increase the size of the equipment, which increases the equipment cost, operation and management costs, and requires a large installation area.

An object of the present invention is to provide a wastewater treatment method for treating organic matter and nitrogen compounds in wastewater, which makes it possible to reduce the installation area and equipment cost by reducing the size of the equipment and to reduce the operation and management costs. And

[0014]

SUMMARY OF THE INVENTION The present invention provides the following wastewater treatment method for solving the above-mentioned problems.

In a method for treating wastewater containing an organic substance or a nitrogen compound, a biological treatment step of biologically treating the wastewater to decompose a nitrogen compound and an organic substance, and a part of biologically treated water obtained from the biological treatment step Coagulation sedimentation process, coagulation sedimentation process, solid-liquid separation process of solid-liquid separation of the remaining biologically treated water obtained from the biological treatment process, and desalination process subsequent to the solid-liquid separation process The concentrated water discharged from the desalting step is returned to the biological treatment step and mixed with untreated wastewater, and the organic substances and nitrogen compounds remaining in the concentrated water are decomposed in the biological treatment step. I do.

In this wastewater treatment method according to the present invention, as described above, advanced treatment including desalination treatment is performed only on the amount of water to be reused among wastewater to be treated, and wastewater discharged is aggregated. Since only treatment required for discharge such as settling treatment is performed, a solid-liquid separation device using an MF (microfiltration) membrane or a UF (ultrafiltration) membrane and RO (reverse osmosis) necessary for obtaining reused water ) Each of the desalination devices can be downsized.

In the wastewater treatment method according to the present invention, R
Since the concentrated water generated by the O desalination treatment is returned to the biological treatment step, which is the first step, for treatment, the treatment equipment such as an adsorption device required in the conventional wastewater treatment method is not required. Thus, according to the wastewater treatment method of the present invention, the equipment can be reduced in size or omitted, and the equipment cost and operation cost can be greatly reduced.

In the wastewater treatment method according to the present invention, in addition to the above-described steps, the concentrated sludge discharged from the solid-liquid separation step includes:
The biologically treated water is mixed with the coagulation liquid obtained by coagulation treatment, a part of the mixed liquid is circulated to the solid-liquid separation step to perform solid-liquid separation again, and the remainder of the mixed liquid is subjected to the coagulation sedimentation step. It is desirable to mix with sludge discharged from, and concentrate and dewater.

As described above, when the concentrated sludge discharged from the solid-liquid separation step and the sludge discharged from the coagulation sedimentation step are mixed and treated collectively, no large-scale equipment is required, and the maintenance work can be omitted. .

Further, in the wastewater treatment method of the present invention, after the concentrated sludge discharged from the solid-liquid separation step is mixed with biologically treated water, the mixture is led to the coagulation / sedimentation step to perform the coagulation / sedimentation treatment. It is desirable.

When the concentrated sludge discharged from the solid-liquid separation step is mixed with the biologically treated water, coarse flocs can be formed with the suspended particles in the concentrated sludge as nuclei, and the sedimentation and sedimentation in the coagulation sedimentation step Can be improved.

In order to solve the above-mentioned problems, the present invention provides a biological treatment step of subjecting wastewater containing an organic substance or a nitrogen compound to biological treatment to decompose the nitrogen compound and the organic substance, and then sedimenting and separating the suspended matter. It consists of a solid-liquid separation step for solid-liquid separation of biologically treated water obtained from the biological treatment step, and a desalination treatment step for desalination processing following the solid-liquid separation step, and is discharged from the desalination processing step. The present invention provides a method for treating wastewater in which concentrated water is returned to the biological treatment step and mixed with untreated wastewater, and organic substances and nitrogen compounds remaining in the concentrated water are decomposed in the biological treatment step.

When the concentrated water generated in the desalination process is returned to the biological treatment process at the forefront for treatment, there is no need to separately provide a treatment facility such as an adsorption device, and the facility can be reduced in size or omitted. Advantageously, the facility and operating costs can be significantly reduced and the footprint can be reduced. In this wastewater treatment method, the entire amount of biologically treated water is desalted, so that it can be applied to the case where the ratio of the amount of water reused to the amount of wastewater is large.

In the wastewater treatment method of the present invention described above, a biological nitrification denitrification treatment can be employed as the biological treatment step, and a high-speed coagulation / sedimentation treatment may be employed in the coagulation / sedimentation treatment step.

In the wastewater treatment method of the present invention described above, the solid-liquid separation step may include a microfiltration treatment or an ultrafiltration treatment, and the desalination treatment step may include a reverse osmosis treatment.

[0026]

Next, a wastewater treatment method according to the present invention will be described in detail with reference to the embodiments shown in FIGS. In the first embodiment shown in FIG. 1 and the second embodiment shown in FIG. 2, the wastewater is biologically treated in a previous step to remove organic substances and nitrogen compounds in the wastewater, and then the biologically treated water is placed in a subsequent step. In this step, the system is branched into two systems, one of which is subjected to coagulation treatment in the coagulation sedimentation treatment step and discharged as water quality below the regulation value, and the other is subjected to desalination treatment in the desalination treatment step for reuse.

As described above, by performing the parallel treatment according to the purpose, for example, it is possible to perform an advanced treatment only for a necessary amount as domestic water for industrial use, raw water for industrial water or pure water, etc. Can be omitted.

On the other hand, in the third embodiment shown in FIG. 3, after the wastewater is biologically treated as described above, the entire amount of the biologically treated water is subjected to desalination treatment. Applies when there are many.

(First Embodiment) First, a first embodiment will be described with reference to FIG. Wastewater 21 containing organic matter, nitrogen compounds, and the like, such as power plant wastewater and general wastewater, is introduced into a biological treatment device (biological nitrification and denitrification treatment device) 1. The biological treatment apparatus 1 may be a known apparatus similar to that described in the section of the related art, and includes a nitrification tank 1a, a denitrification tank 1b, an oxidation tank 1c, a sedimentation tank 1d, and the like. In the nitrification tank 1a, nitrogen compounds in the wastewater are oxidized by the action of the aerobic microorganisms, and change into nitrite and nitrate as shown in the following chemical formula 1 through the state of ammonia nitrogen.

[0030]

Embedded image

In the denitrification tank 1b, nitrite and nitrate generated in the nitrification tank 1a are reduced by the action of an anaerobic microorganism, and as shown in the following chemical formula 2, nitrogen oxide gas (N ₂ O) or nitrogen gas (N ₂ ) Dissipate into the atmosphere. In this process, anaerobic microorganisms, that is, denitrifying bacteria, are added with methanol as a nutrient source. This biological nitrification and denitrification degrades most of the nitrogen compounds and organic matter.

[0032]

Embedded image

Next, in the oxidation tank 1c, untreated organic matter contained in the wastewater and organic matter such as methanol, which is usually added as a nutrient to denitrifying bacteria, are oxidized by the action of aerobic microorganisms to produce carbon dioxide gas ( (CO ₂ ) and water (H ₂ O).
The nitrification-denitrification-treated water from which organic substances and nitrogen compounds have been removed in this way is transferred to a sedimentation tank 1d to remove suspended substances (SS) composed of living organisms and the like that have contributed to the treatment by precipitation treatment.

Thereafter, a part of the biologically treated water 22 is led to the coagulation / sedimentation treatment step via the relay tank 3, and the remaining part is led to the desalination treatment step. The distribution ratio to both processes is determined by the processing capacity of each device and the required amount of recovered water, and, for example, 3/4 is discharged, 1/4 is recovered and reused.
In addition, the relay tank 3 may be used also as the drainage storage tank 2,
In that case, it can be omitted.

One of the branches of the biologically treated water 22 is introduced into the coagulation sedimentation apparatus 4, and the coagulant A23 is added and mixed. The coagulant A 23 may be added to the biological treatment liquid 22 in the pipe just before flowing into the coagulation / sedimentation apparatus 4 or in the same apparatus 4.

Examples of the flocculant A23 include ferric salts such as ferric chloride and ferric sulfate; inorganic flocculants found in aluminum salts such as aluminum chloride, bansulfate and PAC; and organic polymer flocculants. One or more types are appropriately selected from the above. After adding the flocculant A23, the pH is adjusted to 6 to 8 with a pH adjuster 24 such as sodium hydroxide and calcium hydroxide.
To form coarse flocs with the suspension in the liquid.

As the coagulating sedimentation device 4, a high-speed coagulating sedimentation device (granulation sedimentation device) may be used instead of a normal coagulation sedimentation device. In this case, pellets having better sedimentation properties are formed as compared with ordinary flocks. For example, LV = about 0.8 m / h for flocs, whereas LV = about 8 to 15 m / h for pellets. Becomes

The supernatant water 25 obtained in the coagulating sedimentation apparatus 4 is
If necessary, a trace amount of suspended matter is removed by a filtration device 5 such as sand filtration, and then discharged as treated water 26. Coagulation sedimentation device 4
The coagulated sediment (floc or pellet) 27 settled at the bottom of is concentrated by the concentrator 6, further dewatered by the dehydrator 7, and then discharged out of the system as a dewatered cake 28.

When the coagulated sediment sludge 27 is in the form of pellets, the concentration and dewatering properties are improved as compared with ordinary flocs, and a cake having a low water content is obtained. The separated water separated by the concentrating device 6 is returned to the drainage storage tank 2 and circulated.

The other of the biologically treated water 22 is introduced into the coagulation device 8 and is converted into a coagulant B30.
One or a plurality of inorganic coagulants are selected from ferric salts such as iron and ferric sulfate, aluminum chloride, bansulfate, and aluminum salts such as PAC. By adjusting the pH to 6 to 8 with a pH adjuster 24 such as sodium or calcium hydroxide, a floc is formed together with the suspension in the liquid.

When the organic polymer flocculant is added here, the solid-liquid separator 10 using a MF (microfiltration) membrane or a UF (ultrafiltration) membrane installed in the subsequent stage, and the desalination using an RO membrane It should not be added because it will obstruct the pores in each membrane of the device 12 and so on.

The floc-formed flocculant 31 is supplied to the circulation tank 9.
To the concentrated sludge 33 returned from the subsequent solid-liquid separation device 10 and circulated between the solid-liquid separation device 10 and the sludge is brought into a high concentration state, and new flocs grow sequentially. To go.

When the sludge concentration exceeds a certain level, for example, when the sludge concentration reaches 10,000 mg / liter, a part of the sludge is withdrawn from the tank, transferred to the concentrating device 6 and discharged from the coagulating sedimentation device 4. After being mixed with the coagulated sedimentation sludge 27, it is concentrated and dehydrated in the same manner as described above.

As described above, the concentrated sludge 33 remaining in the circulation tank 9 is circulated to the solid-liquid separator 10, and is filtered by the MF membrane or the UF membrane. The MF membrane has a pore diameter of 0.1 to 10 μm and removes fine particles having a larger diameter, and the UF membrane has a pore diameter of 0.001 to 0.1 μm to remove colloid particles and polymer substances. Remove.

The separated liquid 32 that has passed through the MF or UF membrane of the solid-liquid separator 10 is supplied to the desalter 12 via the relay tank 11 to remove fine particles and colloidal particles.
Further, dissolved salts are removed by an RO (reverse osmosis) membrane.

In order to prevent microorganisms and scale from adhering to the RO membrane, a bactericide or an inhibitor, such as that found in a chlorine-based oxidizing agent such as sodium hypochlorite, may be added to the RO membrane immediately before flowing into the apparatus. It may be injected through a pipe or the like.

The permeated liquid 3 that has passed through the RO membrane in the desalination device 12
4 is transferred to a recovery water tank 13 and supplied to a required location as recovered water 35 for reuse. Further, the concentrated water 36 is returned to the inlet of the biological treatment apparatus 1 which is the previous step, and is circulated together with newly flowing wastewater in the same manner as described above.

(Second Embodiment) Next, a second embodiment shown in FIG. 2 will be described. In this case as well, wastewater containing organic matter, nitrogen compounds, and the like, such as power plant wastewater and general wastewater, is introduced into the biological treatment apparatus 1, and most of organic matter and nitrogen compounds are decomposed by the action of microorganisms. Then, the obtained biologically treated water is branched, a part of the water is treated in the coagulation sedimentation treatment step and discharged as described above, and the remaining water obtained by treating the remaining part in the desalination treatment step is reused. Offer.

The difference between the process of FIG. 2 and FIG. 1 is that the biologically treated water supplied to the desalination process is completely filtered by a solid-liquid separation device 10 through an MF membrane or a UF membrane. Without providing the circulation tank 9, the concentrated sludge 33 discharged from the solid-liquid separation device 10 is supplied to the relay tank 3 in the coagulation / sedimentation treatment step, and mixed with fresh biological treatment water 22. Other configurations are substantially the same as those described with reference to FIG.

With such a configuration, when the biologically treated water 22 is subjected to coagulation and sedimentation treatment, it has an effect of forming coarse flocs using suspended particles in the concentrated sludge 33 supplied from the solid-liquid separator 10 as nuclei. This has the effect of improving the sedimentation and separability in the coagulation and sedimentation device 4.

Third Embodiment Next, a third embodiment will be described with reference to FIG. Wastewater 21 containing organic substances, nitrogen compounds, and the like, such as power station wastewater and general wastewater, is introduced into the biological treatment apparatus 1, and most of organic substances and nitrogen compounds are decomposed by the action of microorganisms. Then, the obtained biologically treated water 22 is processed in the desalination process without branching, and the recovered water 35 is reused. That is, in the third embodiment shown in FIG. 3, the aggregation treatment step in FIG. 1 is omitted, and other configurations are substantially the same as those described in FIG. The third embodiment is suitable when the ratio of the amount of water that needs to be reused to the amount of discharged wastewater is large.

(Example 1) A treatment experiment was conducted on the comprehensive wastewater discharged from the A business in the process shown in FIG. The properties of the wastewater (raw water), coagulated sedimentation water obtained by treating it, and recovered water after desalination treatment are summarized in Table 1. Table 2 shows the amounts of coagulated sediment sludge and MF treated sludge generated at that time.

Although the respective processing conditions during the process are shown in Tables 3 to 5, in this example, the sand filtration treatment was omitted in order to grasp the effect of the coagulation sedimentation treatment. As a result, it was confirmed that all the coagulated sedimentation treated water sufficiently satisfies the standard values of the ordinance of the Prime Minister's Ordinance that sets the drainage standards, and has a value that does not cause any problem.

It was also confirmed that the recovered water from the desalination treatment also had dissolved salts effectively removed, and was connected to, for example, subjected to ion exchange treatment to have a value that would not cause any trouble. Furthermore, since the MF-treated sludge was sufficiently circulated and concentrated by the cross flow, the amount of generated sludge was small, and it was found that the concentration tank could be downsized when mixed with coagulated sediment sludge.

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

[Table 3]

[0058]

[Table 4]

[0059]

[Table 5]

(Example 2) The same wastewater as in Example 1 was subjected to a treatment experiment in the steps shown in FIG. Table 6 summarizes the properties of the wastewater (raw water), the coagulated sedimentation treated water obtained by treating it, and the recovered water after desalination treatment. In addition,
The treatment conditions during the process are exactly the same as those shown in Tables 3 to 5, but in this example, the sand filtration treatment was omitted in order to grasp the effect of the coagulation sedimentation treatment.

As a result, substantially the same value as in Example 1 was obtained for both the coagulated sedimentation treated water and the desalted treated recovered water. During the coagulation and sedimentation treatment, it is considered that the concentrated sludge generated during the MF treatment acts as a seed crystal nucleus to promote the coagulation reaction. Obtained.

[0062]

[Table 6]

(Example 3) The same wastewater as in Example 1 was subjected to a treatment experiment in the process shown in FIG. The properties of the wastewater (raw water) and the recovered water after desalination obtained by treating it are summarized in Table 7. The processing conditions during the process are exactly the same as those shown in Tables 3 to 5.
As a result, the value of the desalinated water recovered was almost the same as that of Example 1.

[0064]

[Table 7]

[0065]

As described above, in the wastewater treatment method according to the present invention, the concentrated water generated by the desalination treatment is returned to the foremost biological nitrification and denitrification treatment step for treatment. There is no need to separately provide processing equipment such as an adsorption device required for the processing, and the equipment can be reduced in size or omitted. For this reason, the equipment cost and the operating cost can be significantly reduced, and the installation area can be reduced.

In the wastewater treatment method of the present invention, a part of the biologically treated water obtained from the biological treatment step is sent to the coagulation and sedimentation treatment step for coagulating and sedimentation treatment, and the remaining part of the biologically treated water obtained from the biological treatment step is removed. In a solid-liquid separation step of solid-liquid separation, and a desalination treatment step of desalination treatment subsequent to the solid-liquid separation step. Since only advanced treatment is performed, it is possible to reduce the size of each of the solid-liquid separation device and the RO desalination device using MF or UF.

Further, in the wastewater treatment method of the present invention, the concentrated sludge discharged from the solid-liquid separation device is mixed with the sludge discharged from the coagulation sedimentation device in a concentrated state and is treated collectively. No large-scale equipment is required, and maintenance work can be omitted.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a wastewater treatment step according to a first embodiment of the present invention.

FIG. 2 is an explanatory view of a wastewater treatment step according to a second embodiment of the present invention.

FIG. 3 is an explanatory view of a wastewater treatment step according to a third embodiment of the present invention.

FIG. 4 is an explanatory diagram of a wastewater treatment process in the conventional technology.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Biological treatment apparatus 1a Nitrification tank 1b Denitrification tank 1c Oxidation tank 1d Precipitation tank 2 Drainage storage tank 3 Relay tank 4 Coagulation sedimentation apparatus 5 Filtration apparatus 6 Concentration apparatus 7 Dehydration apparatus 8 Coagulation apparatus 9 Circulation tank 10 Solid-liquid separation apparatus 11 Relay tank 12 Desalination device 13 Recovery water tank 21 Wastewater 22 Biologically treated water 23 Coagulant A 24 pH adjuster 25 Supernatant water 26 Treated water 27 Coagulated sediment sludge 28 Dehydration cake 29 Desorbed liquid 30 Coagulant B 31 Coagulated liquid 32 Separated liquid 33 Concentrated sludge 34 Permeate 35 Collected water 36 Concentrated water

Continued on the front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical display location C02F 9/00 502 C02F 9/00 502P B01D 61/02 500 B01D 61/02 500 61/14 500 61/14 500 C02F 1/44 C02F 1/44 K 1/52 1/52 Z 3/30 3/30 Z 3/34 101 3/34 101A (72) Inventor Heian Nakagawa 5-1-1, Komatsudori, Hyogo-ku, Kobe-shi Shinryo High-Tech Co., Ltd.

Claims (7)

[Claims] 1. A method for treating wastewater containing an organic substance or a nitrogen compound, comprising: a biological treatment step of biologically treating the wastewater to decompose a nitrogen compound and an organic substance; and a biologically treated water obtained from the biological treatment step. A coagulation sedimentation step of partially coagulating and sedimentation processing, a solid-liquid separation step of solid-liquid separation of the remaining biologically treated water obtained from the biological treatment step, and a desalination treatment step of desalination subsequent to the solid-liquid separation step The concentrated water discharged from the desalting step is returned to the biological treatment step and mixed with untreated wastewater, and the organic substances and nitrogen compounds remaining in the concentrated water are decomposed in the biological treatment step. A method for treating wastewater, comprising treating. 2. The concentrated sludge discharged from the solid-liquid separation step is mixed with the coagulated liquid obtained by coagulating the biologically treated water, and a part of the mixed liquid is circulated to the solid-liquid separation step. The method for treating wastewater according to claim 1, wherein the remaining portion of the mixed solution is mixed with sludge discharged from the coagulation sedimentation process, and the mixture is concentrated and dehydrated. 3. A coagulation liquid obtained by coagulating a part of the biologically treated water is subjected to solid-liquid separation, and the concentrated sludge discharged is mixed with the biologically treated water, followed by leading to the coagulation and sedimentation treatment step. The method for treating wastewater according to claim 1 or 2, wherein: 4. A method for treating wastewater containing an organic substance or a nitrogen compound, comprising: a biological treatment step of biologically treating the wastewater to decompose the nitrogen compound and the organic substance; Solid-liquid separation step of solid-liquid separation of the biologically treated water obtained, and desalination treatment step of desalination treatment following the solid-liquid separation step, and the concentrated water discharged from the desalination treatment step A method for treating wastewater, comprising returning to the biological treatment step, mixing with untreated wastewater, and decomposing organic substances and nitrogen compounds remaining in the concentrated water in the biological treatment step. 5. The method according to claim 1, wherein the biological treatment step is a biological nitrification and denitrification treatment. 6. The method for treating wastewater according to claim 1, wherein the coagulation-sedimentation process is a high-speed coagulation-sedimentation process. 7. The method according to claim 1, wherein the solid-liquid separation step includes a microfiltration treatment or an ultrafiltration treatment, and the desalination treatment step includes a reverse osmosis treatment. Wastewater treatment method.