JP2012196614A - Method and system for wastewater treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and system for wastewater treatment, capable of efficiently removing various components in an original wastewater in the treatment using a reverse osmosis membrane, and capable of effectively utilizing the cleaning waste liquid of the reverse osmosis membrane.SOLUTION: An original wastewater 1 is subjected to alkali aggregation and precipitation in an alkali aggregation/precipitation tank 12, and the generated precipitate 4 is separated. The water 3 treated by alkali aggregation and precipitation is treated by a reverse osmosis membrane treatment unit 14 to obtain a permeated water 7. The reverse osmosis membrane provided to the treatment unit 14 is cleaned by an alkaline chemical liquid 6, and a cleaning waste liquid 9 generated at that time is returned to the alkali aggregation/precipitation tank 12 or an original wastewater storage tank 11 in the previous stage thereof.

Description

  The present invention relates to a wastewater treatment method having alkali coagulation sedimentation treatment and reverse osmosis membrane treatment, and a treatment system thereof.

  Conventionally, a method for treating waste water using a reverse osmosis membrane is known, and in reverse osmosis membrane treatment, it is common to periodically wash the reverse osmosis membrane with a cleaning chemical. For example, Patent Document 1 discloses a method for cleaning a reverse osmosis membrane using a cleaning liquid containing an enzyme agent or an alkali.

JP 2010-22896 A

  Since the reverse osmosis membrane treatment is a very advanced treatment, it is basically preferable to reduce the treatment load in the reverse osmosis membrane treatment by pretreatment and increase the treatment amount. At the same time, it is preferable to reduce the frequency of washing the reverse osmosis membrane and reduce the amount of drainage generated with the washing of the reverse osmosis membrane.

  The present invention has been made in view of the above circumstances. The purpose of the present invention is to efficiently remove various components in the raw effluent in the treatment using the reverse osmosis membrane, and to effectively use the cleaning effluent of the reverse osmosis membrane. An object of the present invention is to provide a wastewater treatment method and wastewater treatment system that can be used.

  The wastewater treatment method of the present invention that has been able to solve the above-mentioned problems includes an alkali agglomeration precipitation step in which raw wastewater is agglomerated and precipitated under alkaline conditions, and the generated precipitate is separated; A reverse osmosis membrane treatment step of obtaining permeated water by treating the alkali agglomerated precipitation treated water obtained by separating the water; an alkali washing step of washing the reverse osmosis membrane with an alkaline cleaning chemical; and alkali washing It has a feature in that it has a washing drainage return process in which the washing drainage discharged from the process is returned to the alkali coagulation sedimentation process or the preceding stage. Since the wastewater treatment method of the present invention includes an alkali coagulation precipitation step and a reverse osmosis membrane treatment step, various components, particularly soluble inorganic components, in the raw wastewater can be efficiently removed. In addition, since it has an alkali cleaning step and a cleaning drainage return step, it is not necessary to process the cleaning drainage of the reverse osmosis membrane, and the amount of alkaline coagulant used in the alkali coagulation sedimentation step can be reduced. In some cases, the use of alkaline flocculating agents can be completely replaced.

  The washing effluent may be returned directly to the alkali coagulation precipitation step, or may be returned to the alkali coagulation precipitation step via another step. In the latter case, a method of returning the raw wastewater to the raw wastewater storage step by providing a raw wastewater storage step for storing the raw wastewater in the raw wastewater storage tank before the alkali coagulation sedimentation step; A cleaning drainage storage process stored in the storage tank may be provided, and a method of returning the cleaning drainage from the cleaning drainage storage tank to the alkali coagulation sedimentation process or the preceding stage may be employed.

  The present invention also provides, as a waste water treatment system for suitably carrying out the waste water treatment method of the present invention, an alkali coagulation sedimentation tank for coagulating and precipitating raw waste water under alkaline conditions; A reverse osmosis membrane device having a reverse osmosis membrane for treating the precipitated treated water; a cleaning chemical solution supply means for supplying an alkaline cleaning chemical solution to the reverse osmosis membrane device; and a cleaning discharge of the cleaning chemical solution discharged from the reverse osmosis membrane device There is provided a wastewater treatment system having a washing waste liquid returning means for returning the liquid to the alkali coagulation sedimentation tank or the preceding stage.

  The wastewater treatment system of the present invention may further include a raw drainage storage tank that stores the raw wastewater, and the cleaning drainage return means may return the cleaning drainage to the raw drainage storage tank. Alternatively, the wastewater treatment system of the present invention further includes a cleaning drainage storage tank for storing cleaning drainage, and the cleaning drainage return means returns the cleaning drainage from the cleaning drainage storage tank. Good.

  The wastewater treatment method and wastewater treatment system of the present invention can efficiently remove various components in raw wastewater, particularly soluble inorganic components. In addition, the treatment of the drainage solution of the reverse osmosis membrane is not necessary, and the amount of the alkaline flocculating agent used in the alkali flocculating precipitation treatment can be reduced. In some cases, the use of the alkaline flocculating agent can be completely replaced.

An example of the waste water treatment system used suitably for the waste water treatment method of this invention is represented. The other example of the waste water treatment system used suitably for the waste water treatment method of this invention is represented.

  The wastewater treatment method of the present invention is to obtain treated water (permeated water) by subjecting raw wastewater to alkali coagulation sedimentation treatment and reverse osmosis membrane treatment. That is, the wastewater treatment method of the present invention comprises an alkali agglomeration precipitation step in which raw wastewater is agglomerated and precipitated under alkaline conditions and the generated precipitate is separated, and an alkali obtained by separating the precipitates in the alkali agglomeration precipitation step. A reverse osmosis membrane treatment step of treating the coagulation sedimentation treated water with a reverse osmosis membrane to obtain permeated water. In the present invention, the treatment in the alkali agglomeration precipitation process may be referred to as “alkali agglomeration precipitation treatment”, and the treatment in the reverse osmosis membrane treatment process may be referred to as “reverse osmosis membrane treatment”.

  Although the raw waste water used as the process target in the processing method of this invention is not specifically limited, It is preferable to use the raw waste water containing a metal ion as a raw waste water suitable for an alkali coagulation precipitation process and a reverse osmosis membrane process. If metal ions are contained in the raw wastewater, the metal ions are suitably removed from the raw wastewater by alkali coagulation precipitation treatment and / or reverse osmosis membrane treatment. From the point of removing metal ions by alkali coagulation sedimentation treatment, it is preferable that at least one of the elements of Groups 2 to 13 of the periodic table is contained in the raw waste water in an ionic form. From the viewpoint of enhancing the metal ion removal efficiency in the alkali coagulation sedimentation treatment, it is preferable that metal ions are present in the raw wastewater at a certain concentration. Therefore, from this point of view, the raw wastewater includes magnesium and calcium. And at least one element selected from the group consisting of barium, titanium, zirconium, vanadium, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel, lead, copper, zinc, cadmium, and aluminum in an ionic form Is preferred.

  The raw waste water may also contain organic components and inorganic components other than those described above. For example, if the raw wastewater contains an organic component, as will be described later, it is easy to obtain a cleaning effect such as recovery of the membrane permeation flow rate by cleaning the reverse osmosis membrane with an alkaline cleaning chemical.

  Examples of the raw wastewater to be treated by the treatment method of the present invention include wastewater from factories such as iron making, steel, non-ferrous metals, machinery, metal processing, plating, painting, cement, and landfill leachate.

  In the alkali coagulation precipitation step, the raw waste water is coagulated and precipitated under alkaline conditions, and the generated precipitate is separated. If metal ions are contained in the raw waste water, the metal ions are precipitated as hydroxides by making the raw waste water alkaline. Therefore, the metal component can be removed to some extent from the raw waste water by separating the generated precipitate such as metal hydroxide.

  What is necessary is just to make pH larger than 7 at the time of carrying out alkali coagulation precipitation processing, and what is necessary is just to adjust pH according to the kind of metal ion contained in raw | natural waste water. For example, when targeting calcium ions and magnesium ions, it is preferable to adjust the pH to 10 or more and 14 or less, and when targeting zinc ions, it is preferable to adjust the pH to greater than 7 and 11 or less.

  In the alkali coagulation precipitation step, it is preferable to make the raw waste water alkaline by adding an alkaline coagulant. The alkaline aggregating agent is not particularly limited as long as it shows alkalinity, and alkali metal hydroxides, alkali metal salts, alkaline earth metal hydroxides, alkaline earth metal salts, ammonia and the like can be used. In addition, since ammonia may produce | generate a soluble salt, it may be inferior to versatility. In addition, alkaline earth metal hydroxides and alkaline earth metal salts may be undesirable because they themselves precipitate and increase the amount of precipitate generated in the alkali coagulation precipitation treatment. Therefore, it is preferable to use an alkali metal hydroxide or an alkali metal salt as the alkaline aggregating agent, and it is preferable to use sodium hydroxide, sodium carbonate, or sodium hydrogen carbonate from the viewpoint of availability at low cost.

  In the alkali agglomeration precipitation step, a precipitate having good solid-liquid separation may not be obtained only by adding an alkaline aggregating agent. In such a case, it is preferable to add an agglomeration aid in addition to the alkaline aggregating agent in order to improve the agglomeration property and sedimentation property of the generated precipitate. Examples of the agglomeration aid include inorganic aggregating agents such as polyaluminum chloride, aluminum chloride, aluminum sulfate, ferric chloride, ferrous sulfate, ferric sulfate, and polyferric sulfate, and anionic polymers (for example, Polyacrylamide partially hydrolyzed salts, polyacrylic acid, etc.), cationic polymers (eg, polyethyleneimine, quaternary ammonium salts, etc.), nonionic polymers (eg, polyacrylamide, polyoxyethylene, etc.), etc. Molecular flocculants can be used.

  What is necessary is just to isolate | separate the deposit produced | generated by the alkali aggregation precipitation process by a well-known solid-liquid separation means. For example, the alkali coagulation sedimentation treatment is performed in the alkali coagulation sedimentation tank, the precipitate is drawn out from the lower part of the precipitation tank, and the supernatant is obtained as the alkali coagulation precipitation treated water from the upper part of the precipitation tank.

  Alkali coagulation precipitation treated water obtained by separating the precipitate in the alkali coagulation precipitation treatment step is treated with a reverse osmosis membrane to obtain permeated water. By treating the alkali coagulation precipitation treated water with a reverse osmosis membrane, various components such as metal ions that could not be removed by the alkali coagulation precipitation treatment can be removed. Reverse osmosis membrane treatment can remove any soluble, insoluble, inorganic, or organic components contained in alkali coagulation sedimentation treated water. Drinking is possible by increasing the removal rate of these components. High purity water can be obtained as permeate. In addition, what is necessary is just to set the said removal rate suitably according to the permeate quality calculated | required.

  A reverse osmosis membrane can use a well-known thing, and the format and raw material are not specifically limited. As the reverse osmosis membrane, for example, a membrane such as a hollow fiber membrane, a spiral membrane, or a tubular membrane may be used. As the membrane material (constituent material), cellulose acetate, aromatic polyamide, polyvinyl alcohol, polysulfone Etc.

  Prior to the treatment with the reverse osmosis membrane, the alkali agglomeration treatment water obtained in the alkali agglomeration treatment process is preferably neutralized with an acidic agent. By neutralizing the alkali coagulation precipitation treated water with an acidic agent, it becomes difficult for metal hydroxides and the like to generate scale on the surface of the reverse osmosis membrane and the like, and the reverse osmosis membrane treatment can be suitably performed. When neutralizing the alkali coagulation precipitation treated water with an acidic agent, the pH of the alkali coagulation precipitation treated water after neutralization is not particularly limited as long as the pH is lower than that before neutralization. As the acidic agent, inorganic acids such as sulfuric acid, hydrochloric acid, carbonic acid (carbon dioxide) are preferably used. When a precipitate is generated by neutralizing the alkali coagulation precipitation treated water with an acidic agent, it is preferable to separate the generated precipitate by a known solid-liquid separation means (for example, precipitation separation).

  Alkaline coagulation sedimentation treated water is treated with a microfiltration membrane (hereinafter referred to as “MF membrane”) and / or an ultrafiltration membrane (hereinafter referred to as “UF membrane”) prior to treatment with a reverse osmosis membrane. It is also preferable to do. As a pretreatment for the reverse osmosis membrane treatment, by treating the alkali coagulation precipitation treated water with an MF membrane or a UF membrane, the precipitate that could not be removed by the alkali coagulation precipitation treatment can be solid-liquid separated. Clogging of the film during processing can be made difficult to occur.

  What is necessary is just to use a well-known thing as a MF film | membrane and a UF film | membrane, The form and raw material are not specifically limited. As the MF membrane or UF membrane, for example, a membrane of a hollow fiber membrane, a tubular membrane, a flat membrane, a monolith membrane or the like may be used, and as materials for these membranes, cellulose acetate, polysulfone, polyethylene, Examples thereof include organic films such as chlorinated polyethylene, polypropylene, and polyacrylonitrile; inorganic films such as alumina and zirconia.

  When alkali coagulation sedimentation treated water is treated with an MF membrane or UF membrane, it is preferable to perform membrane cleaning with an oxidizing agent such as sodium hypochlorite when clogging of the membrane occurs or the membrane permeation flow rate decreases. . When an oxidizing agent is added to the alkali coagulation precipitation treated water, a reducing agent (for example, sodium thiosulfate, sodium bisulfite, etc.) is added to the alkali coagulation precipitation treated water containing the oxidizing agent after membrane washing to prevent deterioration of the reverse osmosis membrane. Etc.) is preferably added.

  It is preferable that a scale dispersant is added to the alkali coagulation precipitation treated water during the reverse osmosis membrane treatment or prior to the reverse osmosis membrane treatment. By adding a scale dispersant to the alkali coagulation precipitation treated water, it becomes easy to prevent clogging of the reverse osmosis membrane and a decrease in the membrane permeation flow rate. The scale dispersant may be added when processing with an MF membrane or a UF membrane. As the scale dispersant, a known one may be used. For example, a phosphonic acid group-containing compound, a carboxyl group-containing polymer, a sulfone group-containing polymer, a water-soluble salt of the polymer, and the like can be used.

  The alkali coagulation precipitation treated water is also preferably treated with activated carbon prior to treatment with the reverse osmosis membrane. Specifically, for example, alkali coagulation precipitation treated water may be passed through a column filled with activated carbon. By treating the alkali coagulation precipitation treated water with activated carbon, a part of the soluble component in the alkali coagulation precipitation treated water is adsorbed and removed, and the load of the reverse osmosis membrane treatment can be reduced.

  The above-described neutralization with an acidic agent, treatment with an MF membrane or UF membrane, and treatment with activated carbon may be performed in combination. Furthermore, you may apply well-known water treatment operation (for example, chelate treatment etc.) to alkali coagulation precipitation treated water.

  By the way, in the reverse osmosis membrane treatment step, as the reverse osmosis membrane treatment is continued, organic substances adhere to the surface of the reverse osmosis membrane, and the membrane clogs and the membrane permeation flow rate decreases. Organic substances that cause clogging of the membrane include organic substances that can be contained in the raw waste water, organic polymer flocculants used in alkali coagulation precipitation treatment, scale dispersants added to alkali coagulation precipitation treatment water, and other organic substances used as appropriate It is considered to be derived from a drug (for example, a surfactant). Even if the organic waste is not contained in the raw waste water, some organic chemical is generally added in the alkali coagulation precipitation treatment or reverse osmosis membrane treatment. In addition, microorganisms may propagate on the surface of the reverse osmosis membrane, and in such a case, microorganisms and metabolites thereof (for example, proteins, polysaccharides, humic substances, etc.) adhere to the surface of the membrane.

  Therefore, in the wastewater treatment method of the present invention, an alkaline cleaning process is provided for cleaning the reverse osmosis membrane with an alkaline cleaning chemical. By washing the reverse osmosis membrane with an alkaline agent, organic substances adhering to the surface of the reverse osmosis membrane can be removed, and as a result, the membrane permeation flow rate reduced in the reverse osmosis membrane treatment can be recovered. The alkali cleaning step is not always performed, and may be performed periodically, for example, once a day or when the membrane permeation flow rate is lowered to a predetermined level or less while measuring the membrane permeation flow rate. While performing the alkali cleaning process, it is preferable not to perform (discontinue) the reverse osmosis membrane treatment process. The amount of the cleaning chemical to be used is appropriately adjusted according to the cleaning effect. For example, about 3% to 15% of the amount of water used for the reverse osmosis membrane treatment is preferable.

  The cleaning chemical used in the alkali cleaning step is not particularly limited as long as it is an alkaline chemical, but an alkali metal hydroxide is used from the viewpoint of making it difficult to generate scale derived from the cleaning chemical on the surface of the reverse osmosis membrane. It is preferable to use sodium hydroxide from the viewpoint of availability at low cost. The pH of the cleaning chemical is preferably 10 or more and 13 or less from the viewpoint of efficient cleaning and prevention of corrosion of equipment.

  In the alkali cleaning step, a surfactant (for example, sodium dodecyl sulfate), a chelating agent (for example, sodium ethylenediaminetetraacetate) and the like may be used in combination with the alkaline cleaning chemical. By using such a drug in combination, the cleaning effect of the reverse osmosis membrane may be enhanced.

  From the alkaline cleaning step, the cleaning drainage generated by cleaning the reverse osmosis membrane with the cleaning chemical solution, that is, the cleaning wastewater of the cleaning chemical solution is discharged. The cleaning drainage liquid is generated when an alkaline cleaning chemical solution comes into contact with the reverse osmosis membrane. The cleaning waste liquid may be one in which the cleaning chemical solution is in direct contact with the reverse osmosis membrane, or the cleaning chemical solution is in indirect contact with the reverse osmosis membrane through an organic substance attached to the reverse osmosis membrane. Included in washing drainage.

  In the wastewater treatment method of the present invention, there is provided a cleaning drainage return step for returning the cleaning drainage discharged from the alkali cleaning step to the alkali coagulation precipitation step or the preceding step. By returning the cleaning effluent discharged from the alkali cleaning process to the alkali coagulation sedimentation process or the previous stage, it becomes unnecessary to treat the cleaning effluent, and the alkaline coagulant used in the alkali coagulation precipitation process Can be reduced, and in some cases, the use of alkaline aggregating agents can be completely replaced. The washing effluent is preferably alkaline, and specifically, the pH is preferably greater than 7.

  The washing effluent may be returned directly to the alkali coagulation precipitation step, or may be returned to the alkali coagulation precipitation step via another step. The latter case will be described with two examples.

  As a first example, there is a method in which an original drainage storage step for storing raw wastewater in an original drainage storage tank is provided before the alkali coagulation precipitation step, and the washing waste liquid is returned to the original drainage storage step. By returning the washing effluent to the raw drainage storage tank, the raw drainage storage tank has a buffer function for the alkali coagulation precipitation process, and it becomes easy to perform the alkali coagulation precipitation process stably.

  As a second example, there is a method of providing a cleaning drainage storage step of storing the cleaning drainage in the cleaning drainage storage tank, and returning the cleaning drainage from the cleaning drainage storage tank to the alkali coagulation precipitation step. Since the cleaning drainage is not always discharged, a cleaning drainage storage tank that stores the cleaning drainage is provided, so that the cleaning drainage is temporarily stored in the cleaning drainage storage tank and the cleaning drainage is cleaned. By returning to the alkali coagulation sedimentation process little by little from the drainage storage tank, it becomes easy to perform the alkali coagulation sedimentation process stably.

  Next, an example of the waste water treatment system suitably used for the waste water treatment method of the present invention will be described with reference to FIG. The scope of the present invention is not limited to the following embodiments.

  The wastewater treatment system of the present invention includes an alkali coagulation sedimentation tank 12 that coagulates and precipitates the raw wastewater 1 under alkaline conditions, and a reverse osmosis membrane that treats the alkali coagulation precipitation treated water 3 that is a supernatant from the alkali coagulation sedimentation tank 12. And reverse osmosis membrane device 14.

  In the wastewater treatment system shown in FIG. 1, the raw wastewater is first stored in the raw wastewater storage tank 11. The raw waste water storage tank 11 is provided as necessary, and has a buffer function for alkali coagulation sedimentation treatment.

  The raw wastewater 1 stored in the raw wastewater storage tank 11 is supplied to the alkali coagulation sedimentation tank 12. In the alkali coagulation sedimentation tank 12, the precipitate 4 is produced by coagulating and precipitating the raw waste water 1 under alkaline conditions. At this time, it is preferable to add the alkaline flocculating agent 2 to the alkali flocculation settling tank 12 to make the raw waste water 1 alkaline. As a means for supplying the aggregating drug 2, an aggregating drug supply means communicating with the alkali agglomeration sedimentation tank 12 is preferably provided. In FIG. 1, a pump 21 is provided as the aggregating drug addition means.

  The precipitate 4 generated in the alkali coagulation sedimentation tank 12 is drawn out from the lower part of the precipitation tank 12, and the alkali coagulation precipitation treated water 3 is obtained as a supernatant from the upper part of the precipitation tank 12. The alkali coagulation precipitation treated water 3 is sent to the neutralization tank 13, and is neutralized with the acidic chemical 5 in the neutralization tank 13. In addition, the neutralization tank 13 is provided as needed. In FIG. 1, as a means for supplying the acidic drug 5 to the neutralization tank 13, an acidic drug supply means (pump 22 in FIG. 1) communicating with the neutralization tank 13 is provided.

  The alkali coagulation sedimentation treated water 3 is neutralized in the neutralization tank 13 and then sent to the reverse osmosis membrane device 14 by the pump 23. The reverse osmosis membrane device 14 includes a reverse osmosis membrane, and the alkali coagulation precipitation treated water 3 is treated with the reverse osmosis membrane to obtain the permeated water 7 and the concentrated water 8. The permeated water 7 is obtained by removing various components from the alkali coagulation sedimentation treated water 3, and the concentrated water 8 is obtained by concentrating the various components.

  The wastewater treatment system is provided with cleaning chemical supply means (pump 24 in FIG. 1) for supplying the alkaline cleaning chemical 6 to the reverse osmosis membrane device 14. The cleaning chemical solution supply means communicates with the reverse osmosis membrane device 14, and the reverse osmosis membrane is cleaned with the alkaline cleaning chemical solution 6. The alkaline cleaning chemical 6 supplied to the reverse osmosis membrane device 14 comes into contact with the reverse osmosis membrane and is discharged from the reverse osmosis membrane device 14 as a cleaning drainage 9.

  The waste water treatment system has a cleaning waste liquid returning means (pump 25 in FIG. 1) for returning the cleaning waste liquid 9 of the cleaning chemical liquid 6 discharged from the reverse osmosis membrane device 14 to the alkali coagulation sedimentation tank 12. The cleaning drainage return means communicates with the reverse osmosis membrane device 14, and the cleaning drainage return means returns the cleaning drainage liquid 9 to the alkali coagulation sedimentation tank 12 or earlier. In FIG. 1, the cleaning waste liquid 9 is first returned to the raw drainage storage tank 11 and then returned to the alkali coagulation sedimentation tank 12 through the raw drainage storage tank 11.

  In FIG. 1, the pump is shown as the aggregating drug addition means, the acidic drug addition means, the cleaning chemical liquid supply means, and the cleaning waste liquid return means, but it is not essential that these means be equipped with a pump. For example, in the case where each fluid such as a medicine can be transferred under natural flow, the pump does not have to be provided, and it is sufficient that each means is provided with a pipe line, an opening or the like.

  Another example of the wastewater treatment system of the present invention will be described with reference to FIG. In the description of FIG. 2, the description overlapping with that of FIG. 1 is omitted.

  The waste water treatment system shown in FIG. 2 is not provided with the original waste water storage tank 11 of the waste water treatment system shown in FIG. 1, but is provided with a cleaning waste liquid storage tank 15 for storing the cleaning waste liquid 9 instead. Yes. The cleaning drainage 9 is returned from the reverse osmosis membrane device 14 to the cleaning drainage storage tank 15 by the cleaning drainage returning means (pumps 25 and 26 in FIG. 2), and the alkali coagulation sedimentation from the cleaning drainage storage tank 15. It is returned to the tank 12.

  In FIGS. 1 and 2, the cleaning waste liquid 9 is returned to the alkali coagulation sedimentation tank 12 via the raw drainage storage tank 11 or the cleaning drainage storage tank 15. The tank 15 should just be provided as needed. That is, the cleaning waste liquid 9 may be returned directly to the alkali coagulation sedimentation tank 12 by the cleaning drain liquid returning means.

  INDUSTRIAL APPLICABILITY The present invention can be used for treatment of waste water from factories such as iron making, steel, non-ferrous metals, machinery, metal processing, plating, painting, cement, and landfill leachate.

1: Raw drainage 2: Alkaline flocculating agent 3: Alkaline flocculation treatment water 6: Alkaline cleaning chemical solution 7: Permeated water 8: Concentrated water 9: Wash drainage 11: Raw drainage storage tank 12: Alkaline flocculation precipitation tank 13: Neutralization tank 14: Reverse osmosis membrane device 15: Wash drainage storage tank

Claims (6)

An alkali agglomeration precipitation step of aggregating and precipitating the raw wastewater under alkaline conditions to separate the generated precipitate;
A reverse osmosis membrane treatment step of obtaining permeated water by treating the alkali agglomeration precipitation treated water obtained by separating the precipitate in the alkali agglomeration precipitation step with a reverse osmosis membrane;
An alkaline washing step of washing the reverse osmosis membrane with an alkaline detergent solution;
A wastewater treatment method, comprising: a washing waste liquid returning process in which the washing waste liquid discharged from the alkali washing process is returned to the alkali coagulation sedimentation process or the preceding process. Furthermore, in the previous stage of the alkali coagulation sedimentation step, the raw wastewater storage step of storing the raw wastewater in the raw wastewater storage tank,
The waste water treatment method according to claim 1, wherein the cleaning waste liquid is returned to the raw waste water storage step. Furthermore, it has a cleaning drainage storage step of storing the cleaning drainage in a cleaning drainage storage tank,
The waste water treatment method according to claim 1, wherein the cleaning waste liquid is returned from the cleaning waste liquid storage tank to the alkali coagulation precipitation step or a step preceding it. An alkali coagulation sedimentation tank for coagulating and precipitating raw wastewater under alkaline conditions;
A reverse osmosis membrane device comprising a reverse osmosis membrane for treating alkali coagulation precipitation treated water which is a supernatant from the alkali coagulation sedimentation tank;
Cleaning chemical supply means for supplying an alkaline cleaning chemical to the reverse osmosis membrane device;
A waste water treatment system comprising: a cleaning waste liquid returning means for returning the cleaning waste liquid discharged from the reverse osmosis membrane device to the alkali coagulation sedimentation tank or the preceding stage. Furthermore, it has a raw wastewater storage tank for storing the raw wastewater,
The wastewater treatment system according to claim 4, wherein the cleaning drainage return means returns the cleaning drainage to the raw drainage storage tank. And a cleaning drainage tank for storing the cleaning drainage,
The wastewater treatment system according to claim 4, wherein the cleaning drainage return means returns the cleaning drainage from the cleaning drainage storage tank.

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