Method for treating wastewater containing organic matter

Abstract

To stabilize a treatment in a membrane separation step in a method for treating organic material-containing waste water wherein an organic material-containing waste water is subjected to an aerobic biological treatment using a fluidized bed carrier, followed by a coagulation treatment then a membrane separation.SOLUTION: In a method for treating organic material-containing waste water including a biological treatment step of an aerobic biological treatment of organic material-containing waste water using a fluidized bed carrier, a coagulation treatment step of a coagulation treatment by adding a coagulant to biological treatment water from the biological treatment step, and a solid-liquid separation step of solid-liquid separation of coagulation treatment water from the coagulation treatment step by membrane separation, the number of animalcule including Metazoa deposited on the fluidized bed carrier is maintained at 20000 or under per 1 mL of a tank volume.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for treating wastewater containing organic matter, and more particularly to a method for treating wastewater containing organic matter by biological treatment, followed by coagulation treatment and solid-liquid separation. [Background technology]

[0002] In recent years, methods for treating wastewater containing organic matter, in which wastewater containing organic matter is subjected to aerobic biological treatment in an aeration tank followed by coagulation treatment or membrane separation treatment, have been used in a wide range of fields.By subjecting the biologically treated water to solid-liquid separation using ultrafiltration (UF) membranes or advanced treatment mainly using reverse osmosis (RO) membranes, organic and inorganic substances in the biologically treated water can be removed and reused, but if substances that clog the membranes enter the system, it becomes difficult for water to pass through, and cleaning is required.

[0003] Fluctuations in the quality of the biologically treated water will also cause fluctuations in the quality of the water that flows into the membrane separation treatment process at the subsequent stage, leading to membrane blockages. To prevent this from happening, the raw water quality of the biological treatment, the treated water quality, the inflow load, and operating conditions (water temperature, pH, DO, etc.) are carefully managed, but changes in the biota that cannot be fully understood by these parameters can cause the membrane treatment situation to deteriorate, making it necessary to quickly clean the membrane or reduce the amount of water passing through.

[0004] Biological treatment includes activated sludge (biological sedimentation type) which uses suspended microorganisms (sludge), membrane activated sludge, and biofilm method which uses sludge attached to carriers. Among the biofilm methods, the fluidized bed method using fluidized carriers is capable of high load operation and requires a small installation area, so it has been widely adopted in biological treatment for wastewater recovery in recent years.

[0005] Because the fluidized bed method is easier to operate than the suspended sludge method, there has been little attention paid to the management and control of biota, and the impact of inadequate management of biota on downstream advanced treatment has been overlooked. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-121558 Summary of the Invention [Problem to be solved by the invention]

[0007] When biologically treating wastewater containing organic matter and then subjecting it to membrane separation to recover treated water, membrane separation devices with fine pores, such as reverse osmosis (RO) membranes, are widely used because they can remove even high-molecular-weight organic matter and produce high-quality treated water. However, because the pore size of these membrane separation devices is small, if the concentration of organic matter entering the device is high, the organic matter tends to accumulate on the membrane surface, causing a significant increase in filtration resistance and making it difficult for water to pass through.

[0008] The present invention aims to stabilize the treatment in the membrane separation step in a method for treating organic matter-containing wastewater, which involves aerobic biological treatment using a fluidized bed carrier, followed by coagulation treatment and then membrane separation. [Means for solving the problem]

[0009] The present invention has the following gist.

[0010] [1] A biological treatment process in which organic matter-containing wastewater is subjected to aerobic biological treatment using a fluidized bed carrier; a flocculation treatment step in which a flocculant is added to the biological treatment water from the biological treatment step to perform flocculation treatment; a solid-liquid separation step of separating the coagulated water from the coagulation treatment step into solid and liquid form by membrane separation; A method for treating wastewater containing organic matter, comprising: A method for treating wastewater containing organic matter, characterized in that the number of microscopic animals, including metazoans, attached to the fluidized bed carrier is maintained at 20,000 or less per mL of tank volume.

[0011] [2] The method for treating wastewater containing organic matter according to [1], further comprising an advanced treatment step downstream of the solid-liquid separation step, in which dissolved substances contained in the water are removed by membrane separation.

[0012] [3] The method for treating organic matter-containing wastewater according to [1], wherein the fluidized bed carrier is a sponge carrier.

[0013] [4] The method for treating wastewater containing organic matter according to [1], wherein the number of microscopic animals is the sum of the number of metazoans and the number of protozoans multiplied by a predetermined coefficient (a value selected from the range of 0.01 to 0.5).

[0014] [5] A method for treating wastewater containing organic matter according to [1], wherein when the number of microscopic animals per 1 mL of the tank volume exceeds 20,000, the amount of flocculant added in the flocculation step is increased to 1.2 to 3.0 times the average amount added up to that point.

[0015] [6] The method for treating wastewater containing organic matter according to [1], wherein when the number of microscopic animals per 1 mL of the tank volume exceeds 20,000, the aeration volume in the biological treatment process is increased to 1.2 to 2.5 times the average aeration volume up to that point.

[0016] [7] A method for treating wastewater containing organic matter according to [1], wherein when the number of microscopic animals per 1 mL of the tank volume exceeds 20,000, the aeration volume in the biological treatment process is increased to 0.7 to 0.9 times the average aeration volume up to that point, and measures are taken to maintain the dissolved oxygen concentration at 2 mg / L or higher.

[0017] [8] The method for treating wastewater containing organic matter according to [1], wherein, when the number of microscopic animals per 1 mL of the tank volume exceeds 20,000, intermittent aeration is performed as a countermeasure, with the ratio of aeration time / aeration stop time in the biological treatment process being 2 to 10.

[0018] [9] The method for treating wastewater containing organic matter according to any one of [5] to [8], wherein the measures are continued until the number of microscopic animals per mL of total volume is reduced to 10,000 or less.

[0019]

[10] The BOD volume load of the biological treatment tank in which the biological treatment step is performed is 0.2 to 2.0 kg / m 3 [1] A method for treating wastewater containing organic matter.

[0020]

[11] A method for treating wastewater containing organic matter according to [1], in which the correlation between the number of microscopic animals attached to the fluidized bed carrier and the number of microscopic animals in the biologically treated water from the biological treatment process is obtained in advance, the number of microscopic animals attached to the fluidized bed carrier is estimated from the measured value of the number of microscopic animals in the biologically treated water and the correlation, and this estimated value is used as the number of microscopic animals. [Effects of the Invention]

[0021] In the present invention, when organic matter-containing wastewater is subjected to aerobic biological treatment using a fluidized bed carrier, followed by coagulation treatment and then membrane separation, the number of microscopic animals adhering to the fluidized bed carrier can be appropriately controlled, thereby enabling stable membrane separation. For example, it becomes possible to operate the membrane separation means at a normal membrane cleaning frequency. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a flow diagram of a method for treating wastewater containing organic matter according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] The method for treating organic wastewater of the present invention includes a biological treatment step in which organic wastewater is subjected to aerobic biological treatment using a fluidized bed carrier; a coagulation treatment step in which a coagulant is added to the biologically treated wastewater from the biological treatment step to perform coagulation treatment; and a solid-liquid separation step in which the coagulated wastewater from the coagulation treatment step is separated into solid and liquid forms by membrane separation. Examples of organic wastewater to be treated in the present invention include, but are not limited to, wastewater from electronic, liquid crystal, and semiconductor factories and chemical factories. The organic matter concentration in the organic wastewater is preferably, but not limited to, about 20 to 1,000 mg / L, particularly about 50 to 500 mg / L, in terms of TOC.

[0024] The present invention will now be described in more detail with reference to Figure 1. Figure 1 shows an example of the present invention.

[0025] Wastewater containing organic matter undergoes aerobic biological treatment in a biological treatment tank (aeration tank) 1. 1a denotes an aeration pipe, and 1b denotes a carrier. A flocculant is added to the biologically treated water in a first flocculation tank 2, where it is subjected to flocculation treatment, and then slowly stirred in a second flocculation tank 3 to allow the flocculation reaction to proceed. After that, it is subjected to sedimentation treatment in a sedimentation tank 4, where the precipitate containing solids resulting from the biological treatment is separated into solid and liquid.

[0026] Examples of inorganic flocculants used in the flocculation treatment include iron-based flocculants such as ferric chloride and polyiron sulfate, and aluminum-based flocculants such as aluminum sulfate, aluminum chloride and polyaluminum chloride, with iron-based flocculants being preferred in terms of flocculation effect. These inorganic flocculants may be used alone or in combination of two or more.

[0027] During the coagulation treatment, a pH adjuster is added as needed to adjust the pH to a suitable level for the inorganic coagulant used. For example, with iron-based coagulants, it is effective to react at a pH of 5 to 7, preferably 5.5 to 6.5, while with aluminum-based coagulants, it is effective to react at a pH of 4.5 to 5.5 and then adjust the pH to 6 to 7. Examples of pH adjusters include acids such as hydrochloric acid (HCl) and sulfuric acid (H2SO4), and alkalis such as sodium hydroxide (NaOH). The polymer flocculant may be either anionic or nonionic, but when increasing the amount of inorganic flocculant, it is necessary to conduct a flocculation test and adjust the amount added.

[0028] The separated water (supernatant water) obtained in the settling tank 4 is filtered in a filtration device 5, and the filtered water is subjected to membrane separation treatment in an RO membrane separation device 6 as an advanced treatment means, and the permeate water is used as treated water.

[0029] Instead of the settling tank 4, a pressure flotation device, an ultrafiltration (UF) membrane device, or the like may be used as solid-liquid separation means.

[0030] If a UF (ultrafiltration) membrane device is used instead of an RO (reverse osmosis) membrane device, the filtration device 5 can be omitted, but it is preferable to perform a sterilization treatment before the UF membrane treatment. Depending on the intended use of the treated water, the UF membrane permeate may also be used as the treated water, in which case the UF membrane treatment is the final treatment. In this case, the UF membrane device, like the RO membrane, is also a device that is affected by organic matter remaining in the biologically treated water.

[0031] When an RO membrane separator is used as the advanced treatment means, it is preferable to remove SS from the water by providing a filtration device 5 upstream of the RO membrane separator 6 as shown in Figure 1. The filtration device 5 may be a packed bed type filtration device filled with a filter material such as sand, anthracite, or activated carbon.

[0032] In this embodiment, the biological treatment tank 1 is a fluidized bed type, and treatment is performed by a pass-through method (without returning sludge). The shape of the fluidized bed carrier may be any shape, such as spheres, pellets, hollow cylinders, filaments, or plates, and the size preferably has an average diameter of about 0.1 to 10 mm. The material may be any material, such as natural materials, inorganic materials, or polymeric materials, and gel-like substances may also be used.

[0033] Particularly preferred is a polyurethane sponge carrier consisting of cubes of about 3 to 10 mm square, with a cell count of 30 cells / 25 mm or more and a specific surface area of ​​2000 m² from the viewpoint of sludge retention. 2 / m 3 In order to maintain the fluidity of the carrier even when the sludge settles at a high concentration, the density of the polyurethane sponge carrier should be 20 to 60 kg / m 3 Furthermore, in order to prevent the sludge from peeling off due to excessive deformation of the carrier, the volume expansion rate of the polyurethane sponge carrier is preferably about 100 to 120%.

[0034] By filling the carrier, the BOD volume load of the biological treatment tank 1 is reduced to 0.75 kg / m 3 / d or more (0.3kg / m at TOC load 3 The carrier loading rate is preferably 50% or less, and more preferably 20 to 40%.

[0035] Unlike the flotation method, this fluidized bed treatment method does not require management of sludge retention volume, is capable of high-load operation, and has been considered an easy-to-operate treatment method.Furthermore, when treating and recovering wastewater, it is possible to operate at high loads compared to the flotation method, and is therefore widely adopted.

[0036] However, with fluidized bed treatment, if adherent sludge is not properly managed, depending on the operating conditions, higher microorganisms known as microorganisms (metazoans and protozoans) can rapidly grow, and the metabolites they produce can increase the organic matter concentration after biological treatment, affecting the advanced treatment that follows (RO membrane treatment in the case of Figure 1).With a flotation treatment method, the number of microorganisms can be controlled by managing the SRT, but with a fluidized bed treatment method, as mentioned above, if adherent sludge is not properly managed, the number of microorganisms in the fluidized bed carriers will periodically increase sharply, requiring management specific to fluidized beds.

[0037] In the present invention, the number of microscopic animals, including metazoans, attached to the carrier is measured, and the number of microscopic animals is maintained at 20,000 or less per mL of tank volume.

[0038] Among microorganisms, protozoa, which prey on fewer bacteria per individual, have a smaller impact than metazoans, so management may be based solely on the number of metazoan individuals. However, it is preferable to also measure the number of protozoans, which have a relatively small impact, and multiply the counted number of protozoan individuals by a predetermined coefficient and add the result to the number of metazoans to determine the number of microorganisms.

[0039] That is, in the present invention, the "number of microscopic animals" does not simply refer to the total number of microscopic animals (metazoans and protozoans). Taking into consideration the magnitude of the impact on downstream processing, it is preferable to define the number of microscopic animals as the sum of the number of metazoans and the number of protozoans multiplied by a predetermined coefficient (a value selected from 0.01 to 0.5). The coefficient multiplied by the count of protozoans is set in the range of 0.01 to 0.5, preferably 0.05 to 0.2. For example, when the coefficient is set to 0.1, the number of microscopic animals is expressed as "number of metazoans + number of protozoans × 0.1." Note that, as mentioned above, when managing only the number of metazoan individuals, the predetermined coefficient is set to 0. Incidentally, including this case, the number of microscopic animals is defined as the sum of the number of metazoans and the number of protozoans multiplied by a predetermined coefficient (a value selected from 0 to 0.5).

[0040] The method for measuring the number of microscopic animals is to collect 1 to 10 carriers, for example, 5 carriers, from the fluidized bed biological treatment tank. Then, each carrier is immersed in 1 mL of pure water, and the adhering solid matter is removed. The number of microscopic animals per carrier is calculated from the number of microscopic animals in the liquid. number If the carrier is a sponge, crush the carrier and push out the sludge inside to measure it. It is desirable to count the number of microorganisms using a hemocytometer under a microscope. After that, calculate the amount of carrier per liter of biological treatment tank and convert it to the number of microorganisms per mL of biological treatment tank. The frequency of this should be at least once every four weeks, especially once every two weeks or more, and most especially 1 to 4 times every two weeks.

[0041] Furthermore, such measurement of the number of microscopic animals takes time, and depending on the site, frequent measurement may be difficult. In such cases, the number of microscopic animals leaked into the treated water may be measured at least once a month, preferably at least once every two weeks, and particularly preferably 1 to 4 times every two weeks, and the number of microscopic animals attached to the carrier may be measured only if the number of microscopic animals per mL of treated water is confirmed to be 1,000 or more. Note that if a correlation is observed between the number of microscopic animals in the treated water and the number of microscopic animals in the carrier, the number of microscopic animals in the treated water may be used as a management indicator.

[0042] The microscopic animals that grow in fluidized-bed biological treatment are not aggregate-feeding animals that break down sludge, but rather filter-feeding animals that create water currents and suck up and prey on microscopic bacteria. The microscopic animals that affect the quality of treated water are primarily aggregate-feeding animals, and the impact of filter-feeding animals on the growth of conventional wastewater treatment has not been taken into consideration. However, in wastewater reclamation systems equipped with advanced treatment at a later stage, the sludge is rapidly consumed by microscopic animals, and even an increase of just 1 mg-TOC / L in the organic matter concentration produced during this process can have an impact on the advanced treatment at the later stage. For this reason, in this invention, the number of microscopic animals is measured without distinguishing between filter-feeding and aggregate-feeding animals.

[0043] When the number of microscopic animals per 1 mL of tank volume exceeds 20,000, one of the following measures (1) to (4) is taken to reduce the amount of sludge adhering to the carrier to 80 to 90% of normal levels and reduce the number of microscopic animals.

[0044] Countermeasure (1): The amount of flocculant added during solid-liquid separation is increased by 1.2 times or more, preferably 1.2 to 3.0 times, more preferably 1.2 to 3.0 times, to reduce the organic matter in the flocculated water.

[0045] Countermeasure (2): The aeration volume in the biological treatment tank is temporarily increased to 1.2 to 2.5 times, preferably 1.5 to 2.0 times, the normal treatment volume (e.g., the weekly average aeration volume), and this is continued for at least one week, preferably two to three weeks, to push out the microorganisms attached to the carriers. However, care must be taken not to excessively reduce the amount of attached sludge. When the amount of sludge attached to the carriers falls to 70% or less of the normal amount, the aeration volume should be returned to normal treatment. Therefore, it is preferable to periodically measure not only the number of microorganisms but also the amount of attached sludge on the carriers. Methods for measuring the amount of attached sludge include drying the SS detached from the carriers and measuring it, or eluting the sludge with sodium hydroxide, measuring the protein content, and converting it to the volume of sludge (VSS).

[0046] Countermeasure (3): Ensure that the aeration volume is 0.7 to 0.9 times that during normal treatment (for example, the average weekly aeration volume) and that DO is 2 mg / L or more.

[0047] Countermeasure (4): Use intermittent aeration with aeration time / aeration stop time = 2 to 10.

[0048] It is desirable to continue these measures (1) to (4) until the number of microscopic animals per mL of tank volume is reduced to 10,000 or less, particularly 5,000 or less.

[0049] In addition, when multiple transient fluidized bed aerobic treatment tanks are installed, it is preferable to apply the present invention to the second and subsequent biological treatment tanks. In addition, the rapid increase in microorganisms is prevented by a relatively low BOD volumetric load of 2.0 kg / m. 3 / d or less, especially 1.0 kg / m 3 This is likely to occur when the load is less than 1 / d, so the present invention is suitable for operation under such a load. [Example]

[0050] <Initial operation> The organic wastewater treatment system shown in Figure 1 was operated for two months under the following conditions.

[0051] Raw water: IPA, TMAH, MEA mixed raw water. CODcr=500mg / L, BOD=250mg / L, TOC=200mg / L Nutrients: Urea, phosphate, and sulfate were added to achieve a BOD:N:P:S ratio of 100:5:1:0.1. Minerals: Ca, Mg, and K are added as elements to raw water to a concentration of 1 mg / L or more. Trace metals: Fe should be added as an element to the raw water to a concentration of 0.1 mg / L or more, and Cu, Zn, Mo, Mn, Ni, and Co should each be added as an element to the raw water to a concentration of 0.005 mg / L or more. Water amount: 1000L / d Aeration tank (fluidized bed type): 500L BOD volumetric load: 0.5kg / m 3 / d Carrier: 3mm square polyurethane sponge carrier. Filling rate: 40% Aeration tank DO: 4mg / L Aeration amount: 50L / min 1st coagulation tank: 120L (stirring speed 150rpm) Coagulant: 38% ferric chloride aqueous solution 300mg / L added Coagulation pH:6.0 Second flocculation tank: 20L (stirring speed 50rpm) Polymer flocculant: Anionic flocculant 1mg / L added Sedimentation tank: Lv=20m / d Filtration device: Filled with activated carbon as filter material. Lv=1m / hr RO membrane separation equipment: Nitto Denko RO membrane equipment

[0052] After two months of operation under the above conditions, Bdelloid rotifers (metazoans) multiplied in the carriers, reaching 25,000 per mL of tank volume, and the S.TOC of the treated water reached 10 mg / L.

[0053] [Comparative Example 1] The initial operation was continued as described above. As a result, the RO flux declined by 17% after 5 days, 24% after 15 days, and over 30% after 30 days, necessitating cleaning. The flux decline continued even after cleaning. Cleaning was continued once a month for three months, and the number of microfauna naturally decreased, after which the flux decline slowed.

[0054] [Example 1] After the second month of initial operation, the amount of 38% ferric chloride aqueous solution added to the first coagulation tank was increased by 1.5 times (450 mg / L). As a result, the flux reduction rate after 30 days was only 11%, and unlike Comparative Example 1, operation was possible without cleaning. However, it was necessary to continue adding 1.5 times the amount of coagulant until the number of microfauna naturally decreased.

[0055] [Example 2] In the second month of the above treatment operation, the amount of 38% ferric chloride aqueous solution added to the first coagulation tank was increased by 1.5 times (450 mg / L), and the aeration volume of the biological treatment tank was increased by 1.3 times for two weeks, resulting in a decrease in the number of microscopic animals per mL of tank volume of less than 10,000, and the S.TOC of the treated water falling to 5 mg / L. After that, the aeration volume and coagulant addition volume were returned to their original levels, and the RO flux decline after 30 days was limited to about 12%, and the system was able to operate for another three months without cleaning, but the amount of sludge generated increased by 1.1 times.

[0056] [Example 3] In the second month of the above treatment operation, the amount of 38% ferric chloride aqueous solution added to the first coagulation tank was increased by 1.5 times (450 mg / L), and the aeration volume of the biological treatment tank was reduced to DO = 2 mg / L. After 10 days, the number of microscopic animals had decreased to below 10,000 / ml-tank volume, and the S.TOC of the treated water had dropped to 6 mg / L. After that, the aeration volume and coagulant addition volume were returned to their original levels, and the decrease in RO flux after 30 days was limited to about 10.5%, and the system could be operated for three months without cleaning. [Explanation of symbols]

[0057] 1 Biological treatment tank 2 1st coagulation tank 3 Second flocculation tank 4 Settling tank 5 Filtration device 6 RO membrane separation equipment

Claims

1. A biological treatment process in which organic matter-containing wastewater having a TOC of 20 mg / L or more is subjected to aerobic biological treatment using a fluidized bed carrier; a flocculation treatment step in which a flocculant is added to the biological treatment water from the biological treatment step to perform flocculation treatment; a solid-liquid separation step of separating the coagulated water from the coagulation treatment step into solid and liquid form by membrane separation; A method for treating wastewater containing organic matter, comprising: A method for treating wastewater containing organic matter, characterized in that the number of microorganisms, including metazoans (including aggregate-feeding microorganisms) attached to the fluidized bed carrier is maintained at 20,000 or less per mL of tank volume.

2. 2. The method for treating wastewater containing organic matter according to claim 1, further comprising an advanced treatment step downstream of said solid-liquid separation step for removing dissolved substances contained in the water by membrane separation.

3. 2. The method for treating wastewater containing organic matter according to claim 1, wherein said fluidized bed carrier is a sponge carrier.

4. The method for treating wastewater containing organic matter according to claim 1, wherein the number of microscopic animals is the sum of the number of metazoans and the number of protozoans multiplied by a predetermined coefficient (a value selected from the range of 0.01 to 0.5).

5. The method for treating wastewater containing organic matter according to claim 1, wherein when the number of microscopic animals per mL of the tank volume exceeds 20,000, the amount of flocculant added in the flocculation step is increased to 1.2 to 3.0 times the average amount added up to that point.

6. 2. The method for treating wastewater containing organic matter according to claim 1, wherein when the number of microscopic animals per mL of tank volume exceeds 20,000, aeration volume in the biological treatment step is increased to 1.2 to 2.5 times the average aeration volume up to that point.

7. 2. The method for treating wastewater containing organic matter according to claim 1, wherein when the number of microscopic animals per mL of tank volume exceeds 20,000, the aeration amount in the biological treatment step is set to 0.7 to 0.9 times the average aeration amount up to that point, and measures are taken to make the dissolved oxygen concentration 2 mg / L or more.

8. 2. The method for treating wastewater containing organic matter according to claim 1, wherein, when the number of microscopic animals per mL of tank volume exceeds 20,000, intermittent aeration is performed in the biological treatment step with a ratio of aeration time / aeration stop time set to 2 to 10 as a countermeasure.

9. 9. The method for treating wastewater containing organic matter according to claim 5, wherein the countermeasure is continued until the number of microscopic animals per mL of total volume is reduced to 10,000 or less.

10. The BOD volume load of the biological treatment tank in which the biological treatment step is carried out is 0.2 to 2.0 kg / m ３ 2. The method for treating wastewater containing organic matter according to claim 1, wherein the organic matter content is 0.1 to 0.5 wt %.

11. A method for treating wastewater containing organic matter according to claim 1, wherein the correlation between the number of microscopic animals attached to the fluidized bed carrier and the number of microscopic animals in the biologically treated water from the biological treatment process is obtained in advance, the number of microscopic animals attached to the fluidized bed carrier is estimated from the measured value of the number of microscopic animals in the biologically treated water and this correlation, and this estimated value is used as the number of microscopic animals.

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