JP2006181445A - Waste water treatment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a waste water treatment apparatus in which scale is hardly stuck to the surface of a reverse osmosis membrane when waste water is separated into permeated water and concentrated water by using the reverse osmosis membrane even when waste water contains an inorganic ion. <P>SOLUTION: This waste water treatment apparatus is provided with; a supplying means 5 for supplying waste water containing an organic nitrogen compound and/or ammonia nitrogen and the inorganic ion; an aeration tank 32 in which the waste water from the supply means 5 is received and the organic nitrogen compound is biodegraded and nitrified by aeration; a solid-liquid separating means 33 for subjecting a liquid mixture in the aeration tank 32 to solid-liquid separation; a water softening means 2 for softening the water separated by the solid-liquid separating means 33; a reverse osmosis membrane-used separating means 3 for separating the liquid discharged from the water softening means 2 into permeated water and concentrated water by using the reverse osmosis membrane; and a denitrifying means 4 for denitrifying the concentrated water biologically to obtain denitrified water. According to this constitution, the problem that scale is stuck to the surface of the reverse osmosis membrane can be solved. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a treatment apparatus for wastewater containing organic nitrogen compounds and / or ammonia nitrogen, and more specifically, a treatment apparatus for treating wastewater containing inorganic ions in addition to organic nitrogen compounds and / or ammonia nitrogen. It is about.

  In semiconductor manufacturing processes and liquid crystal manufacturing processes in the electronics industry, amines and ammonium such as monoethanolamine (MEA) and tetramethylammonium hydroxide (TMAH) are often used, so these organic nitrogen compounds and / or ammonia states are used. Wastewater containing nitrogen is discharged.

The above organic nitrogen compounds such as MEA and TMAH are decomposed by aerobic microbial treatment that is mixed with activated sludge and aerated to oxidize the nitrogen content into nitric acid or nitrous acid. And in order to remove nitrate nitrogen and nitrite nitrogen from wastewater containing nitrogen oxides such as nitric acid, it is separated into permeated water and concentrated water by a separation means using a reverse osmosis membrane, A method of biologically denitrifying the separated concentrated water using a biological treatment apparatus has been conventionally performed (see, for example, Patent Document 1).
JP 2000-70986 A

  However, in the above-described method, the wastewater contains divalent or trivalent inorganic ions such as calcium ions, aluminum ions, iron ions, etc. in addition to nitrate nitrogen and nitrite nitrogen caused by organic nitrogen compounds. In some cases, the reverse osmosis membrane separates the permeated water and the concentrated water (hereinafter, “separating the permeated water and the concentrated water by the reverse osmosis membrane” may be referred to as “membrane separation”). Inorganic ion scales are deposited and deposited on the membrane surface of the reverse osmosis membrane. For this reason, there has been a problem that the phenomenon of the amount of permeated water permeating through the reverse osmosis membrane gradually proceeds and membrane separation becomes difficult.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to treat wastewater in which scale does not adhere to the membrane surface of the reverse osmosis membrane even if the wastewater contains inorganic ions. Is to provide.

  The wastewater treatment apparatus of the present invention for solving the above-mentioned problems includes a softening means for softening wastewater containing nitrate nitrogen or nitrite nitrogen and containing inorganic ions, and reverse osmosis of the effluent from the softening means. A reverse osmosis membrane separating means for separating permeated water and concentrated water by a membrane; and a denitrifying means for biologically denitrifying the concentrated water to obtain denitrified treated water ( Claim 1).

  The softening means softens the ion by exchanging inorganic ions in the wastewater with sodium ions or the like. For this reason, when the effluent from the softening means is separated into permeated water and concentrated water by the reverse osmosis membrane separation means, the scale of inorganic ions does not precipitate on the membrane surface of the reverse osmosis membrane, preventing scale adhesion. can do. Accordingly, separation of the permeated water and concentrated water by the reverse osmosis membrane (membrane separation) can be performed smoothly, and after biological denitrification treatment by supplying the separated concentrated water to the denitrification means, Can be released.

  The wastewater treatment apparatus of the present invention for solving the above-mentioned problems is a wastewater supply means containing an organic nitrogen compound and / or ammonia nitrogen and inorganic ions, and accepts the wastewater from the supply means, and aeration treatment An aeration tank for microbial decomposition of organic nitrogen compounds and nitrification, solid-liquid separation means for solid-liquid separation of the liquid mixture in the aeration tank, and softening means for softening the separated water separated by the solid-liquid separation means And reverse osmosis membrane separation means for separating the effluent from the softening means into permeate and concentrated water using a reverse osmosis membrane; and denitrification treatment by biologically denitrifying the concentrated water to obtain denitrified water. Nitrogen means. (Claim 2).

  In the aeration tank, organic nitrogen compounds such as MEA and TMAH are microbially decomposed into nitrate nitrogen and nitrite nitrogen, and the solid-liquid separation means performs solid-liquid separation. The water separated by solid-liquid separation contains inorganic ions in addition to nitrate nitrogen and nitrite nitrogen, but in the softening means that performs the subsequent treatment, the inorganic ions are softened by ion exchange with sodium ions, etc. Therefore, even if the effluent from there is separated into permeated water and concentrated water by a reverse osmosis membrane, the scale of inorganic ions does not precipitate on the membrane surface, and scale adhesion can be prevented. Therefore, separation of the permeated water and concentrated water by the reverse osmosis membrane (membrane separation) can be performed smoothly, and biological separation is performed by supplying the separated concentrated water to the denitrification means. Denitrification water can be discharged.

  In the wastewater treatment apparatus of the present invention, it is preferable to have a feeding means for feeding the denitrification treated water to the aeration tank. In this invention, denitrification water can be used as a means for assisting the pH adjuster in the aeration tank.

  In the wastewater treatment apparatus of the present invention, the aeration tank is preferably filled with a carrier supporting microorganisms (Claim 4), and the regeneration includes inorganic ions discharged from the softening means. It is preferable to further have a regeneration drainage feeding means for feeding a part or all of the wastewater to the denitrification means (Claim 5), and in the denitrification means, the denitrification bacteria form sludge particles. A denitrification tank is preferred (claim 6).

  As described above, according to the wastewater treatment apparatus of the present invention, since the softening means softens by exchanging inorganic ions such as calcium ions, aluminum ions, iron ions, etc. with sodium ions, etc., the outflow from the softening means. Even if the liquid is separated into permeated water and concentrated water by a reverse osmosis membrane, the scale of inorganic ions does not precipitate on the membrane surface, and scale adhesion can be prevented. For this reason, the separation (membrane separation) of the permeated water and the concentrated water by the reverse osmosis membrane can be performed smoothly.

  Hereinafter, the waste water treatment apparatus of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing a first wastewater treatment apparatus according to the present invention. The processing apparatus 1 shown in FIG. 1 is characterized by comprising a softening means 2, a reverse osmosis membrane separation means 3, and a denitrification tank 4 as a denitrification means.

  Waste water is supplied from the supply means 5 to the softening means 2. The wastewater contains nitrate nitrogen and nitrite nitrogen derived from organic nitrogen compounds such as MEA and TMAH, and also contains divalent and / or trivalent inorganic ions such as calcium ion, aluminum ion, iron ion, etc. is doing. The softening means 2 softens inorganic ions in the waste water by ion exchange, and the reaction tower is filled with a cation exchange resin. Therefore, by introducing waste water from the upper part of the softening means 2 and passing through the reaction tower, the waste water is ion-exchanged into sodium ions and then discharged from the lower part of the softening means 2. The effluent is introduced into the reverse osmosis membrane separation means 3.

  Here, in the softening means 2, the concentration of inorganic ions is adjusted to 1/10000 to 1/1 of the saturated concentration, more preferably 1/10000 to 9/10, depending on the concentration ratio in the reverse osmosis membrane separation step. It is removed as follows.

  The reverse osmosis membrane separation means 3 separates the ion-exchanged waste water into permeated water 6 and concentrated water 7 using a reverse osmosis membrane. The permeated water 6 is reused as recovered water, and the concentrated water 7 is introduced into the denitrification tank 4. The concentrated water 7 is introduced into the denitrification tank 4 together with an organic substance such as methanol, and the introduced concentrated water 7 is subjected to biological denitrification treatment to become denitrification treated water 8, which is aerated and precipitated as necessary. And then released.

  As biological denitrification treatment in the denitrification tank 4, a floating activated sludge method or an upflow sludge bed (USB) method can be used. The USB method is a method for performing a denitrification process using sludge grains formed by denitrifying bacteria. That is, a denitrification process is performed by forming granules having a diameter of 1 to several millimeters using a carrier or calcium carbonate as a core, and concentrated water 7 from the reverse osmosis membrane separation means 3 is introduced from the lower part of the denitrification tank 4 Then, by bringing the concentrated water 7 into contact with the granules, the nitrate nitrogen and the nitrite nitrogen in the concentrated water 7 are decomposed, and the denitrified treated water 8 is taken out from the upper part of the denitrification tank 4. . This USB method has an advantage that the installation area is smaller than that of the floating activated sludge and the load can be increased.

  According to the above processing apparatus 1, even if the waste water contains inorganic ions, the inorganic ions are removed by ion exchange by passing through the softening means 2. For this reason, in the subsequent separation of the permeated water and the concentrated water (membrane separation) in the reverse osmosis membrane separation means 3, these inorganic ions become scales and deposit on the membrane surface of the reverse osmosis membrane. Nothing will happen. Therefore, separation of the permeated water and the concentrated water by the reverse osmosis membrane (membrane separation) can be performed smoothly, so that the waste water can be treated quickly and efficiently.

  FIG. 2 is a block diagram showing a second wastewater treatment apparatus 11 according to the present invention. The processing apparatus 11 shown in FIG. 2 includes a regenerated waste water supply means 9 in addition to the structure of FIG. The regeneration drainage supply means 9 has one end connected to the upper part of the softening means 2 and the other end connected to the denitrification tank 4. The reclaimed waste water supply means 9 includes a reclaimed waste water storage tank 10 that stores reclaimed waste water.

  2 includes the softening means 2, the reverse osmosis membrane separation means 3, and the denitrification tank 4, and thus can operate in the same manner as the processing apparatus 1 of FIG. In addition to this, the treatment apparatus 11 of FIG. 2 includes the regenerative waste water supply means 9 to introduce backwash water 12 such as a sodium chloride aqueous solution from the lower part of the reaction tower in the softening means 2. Inorganic ions trapped in the ion exchange resin can be separated from the cation exchange resin. The separated water containing inorganic ions becomes reclaimed wastewater and is stored in the reclaimed wastewater storage tank 10. A part or all of the stored reclaimed water is supplied to the denitrification tank 4 together with the concentrated water 7 from the reverse osmosis membrane separation means 3.

  In general, the biological denitrification treatment in the denitrification tank 4 requires a small amount of inorganic ions. In particular, in the USB method, adhesion of the generated nitrogen gas and floating / outflow of granules due to inclusion are problematic, so formation of granules with high sedimentation is important for maintaining the nitrogen treatment load. For this purpose, it is effective to increase the specific gravity by incorporating inorganic ions into granules or sludge.

  On the other hand, since the softening means 2 uses a sodium chloride aqueous solution, the recycled wastewater contains inorganic ions such as calcium ions, magnesium ions, and iron ions at a high concentration. Since the regenerated waste water supply means 9 supplies regenerated waste water containing such inorganic ions at a high concentration to the denitrification tank 4, the specific gravity of the granules and sludge in the denitrification tank 4 can be increased. Thereby, the denitrification process in the denitrification tank 4 can be performed with high efficiency.

FIG. 3 is a block diagram showing a third wastewater treatment apparatus 21 in the present invention. The processing apparatus 21 shown in FIG. 3 includes the softening means 2, the reverse osmosis membrane separation means 3, and the denitrification tank 4 as in FIGS. In addition to this, the processing apparatus 21 has a structure capable of supplying inorganic ions such as calcium compounds (CaCl ₂ ) to the denitrification tank 4. Inorganic ions are introduced into the denitrification tank 4 by being mixed into the concentrated water 7 from the reverse osmosis membrane separation means 3. Thereby, like the processing apparatus 11 of FIG. 2, the specific gravity of the granule and sludge in the denitrification tank 4 can be increased, and the denitrification process in the denitrification tank 4 can be performed with high efficiency.

  FIG. 4 is a block diagram showing a fourth wastewater treatment apparatus 31 in the present invention. The processing apparatus 31 shown in FIG. 4 includes an aeration tank 32, a solid-liquid separation means 33 comprising a precipitation tank, a softening means 2, a filter 34, a reverse osmosis membrane separation means 3, and a denitrification tank 4. Yes. In the aeration tank 32, air is aerated from the air diffuser 35. The supply means 5 supplies waste water to the aeration tank 32. The waste water is introduced into the aeration tank 32 in a state containing organic nitrogen compounds such as MEA and TMAH and / or ammonia nitrogen and the above-described inorganic ions.

  In the aeration tank 32, the waste water is aerated by the air aerated from the aeration means 35. In this aeration treatment, the organic nitrogen compound is oxidized and decomposed by microorganisms, and the nitrogen component is nitrified to become nitrate nitrogen or nitrite nitrogen. The solid-liquid separation means 33 performs solid-liquid separation on the processing liquid that has been aerated in the aeration tank 32. A sludge return line 36 is provided between the solid-liquid separation means 33 and the aeration tank 32, and the separated sludge separated by the solid-liquid separation means 33 is returned to the aeration tank 32 via the sludge return line 36. Is done. On the other hand, the separated supernatant water is supplied to the softening means 2.

  In the softening means 2, the supernatant water from the solid-liquid separation means 33 is introduced from above and ion exchanged while passing through the reaction tower. Thereby, the inorganic ion contained in the supernatant water is ion-exchanged with sodium ions, and the supernatant water is softened.

  The ion-exchanged supernatant water passes through the filter 34 to remove fine solids. As the filter 34, sand filtration, microfiltration, ultrafiltration, and other means can be used.

  After passing through the filter 34, it is supplied to the reverse osmosis membrane separation means 3 and separated into the permeated water 6 and the concentrated water 7. The permeated water 6 is reused as recovered water, and the concentrated water 7 is introduced into the denitrification tank 4 with an organic substance such as methanol added thereto, and is biologically denitrified in the denitrification tank 4. The denitrified water 8 that has been denitrified is re-aerated as necessary and subjected to precipitation, and then discharged.

  In the processing apparatus 31, a feeding unit 37 that feeds a part of the denitrification water from the denitrification tank 4 to the aeration tank 32 is provided. Thus, the denitrification water 8 fed to the aeration tank 32 by the feeding means 37 acts as a pH adjuster, and the pH of the waste water from the supply means 5 can be adjusted smoothly.

  In the fourth treatment apparatus 31, even if the wastewater contains organic nitrogen compound and / or ammonia nitrogen and inorganic ions, the organic nitrogen compound is oxidized and decomposed and nitrified by the aeration tank 32, so that nitrate nitrogen or Since it becomes nitrite nitrogen, the denitrification tank 4 can effectively perform denitrification. In addition, since the softening means 2 for ion exchange of the supernatant water from the solid-liquid separation means 33 is provided, inorganic ions can be removed, and inorganic ions are present on the membrane surface of the reverse osmosis membrane in the reverse osmosis membrane separation means 3. It does not adhere as a scale. Thereby, separation (membrane separation) of permeated water 6 and concentrated water 7 by a reverse osmosis membrane can be performed efficiently.

  Although not shown, as in FIG. 2, inorganic ions captured by the cation exchange resin of the softening means 2 are separated into reclaimed wastewater, and a part or all of this reclaimed wastewater is supplied to the denitrification tank 4. You may make it do. Thereby, the specific gravity of the granule and sludge in the denitrification tank 4 can be enlarged, and the denitrification process in the denitrification tank 4 can be performed with high efficiency.

  FIG. 5 is a block diagram showing a fifth wastewater treatment apparatus 41 according to the present invention. In the processing apparatus 41 shown in FIG. 5, a carrier 42 holding nitrifying bacteria is used with respect to the processing apparatus 31 of FIG. 4, and this carrier 42 is introduced into the aeration tank 32. As the carrier 42 for holding nitrifying bacteria, a carrier having a large specific surface area such as foamed resin is used. By applying the carrier 42 holding nitrifying bacteria to the aeration tank 32 in this manner, nitrification in the aeration tank 32 can be performed more efficiently.

  In addition to this, the processing apparatus 41 of FIG. 5 uses a coagulation reaction tank 43 and a coagulation sedimentation tank 44. The agglomeration reaction tank 43 is an agglomeration agent added to the solid matter such as sludge and flocculent suspended cells separated from the carrier 42 in the aeration tank 32 to cause aggregation, and the floc after aggregation is supplied to the aggregation precipitation tank 44. Then, solid-liquid separation is performed in the coagulation sedimentation tank 44. Thus, by using the agglomeration reaction tank 43 and the agglomeration sedimentation tank 44, solid-liquid separation can be reliably and rapidly performed.

  FIG. 6 is a block diagram showing a sixth waste water treatment apparatus 51 of the present invention. The processing apparatus 51 shown in FIG. 6 uses an immersion membrane type aeration tank 52 instead of the aeration tank 32 of the processing apparatus 31 in FIG. The immersion membrane type aeration tank 52 uses an immersion membrane 53, and the immersion membrane 53 is immersed in the waste water in the aeration tank 52 and is decomposed and nitrified in the aeration tank 52. The treated water generated by is filtered by the immersion film 53 and then supplied to the softening means 2. Therefore, in this processing apparatus 51, the solid-liquid separation means 33 in the processing apparatus 31 of FIG. 4 becomes unnecessary, and the installation area can be reduced.

  In this case, the inside of the aeration tank 52 is in an aerated state by the aeration means 35, and by placing the immersion film 53 here, deposits on the film surface can be removed by aeration from the lower part. Therefore, the immersion film 53 can act stably over a long period of time. As the immersion membrane 53, an ultrafiltration membrane, a microfiltration membrane or the like can be used, and as a material thereof, polyolefin, cellulose acetate, ceramic, or the like can be selected. Such an immersion film 53 can be used repeatedly by washing and can be economical.

The present invention will be specifically described with reference to Examples and Comparative Examples. In the following Examples and Comparative Examples, wastewater having a Ca ion concentration of 45 mg / L and a NO ₃ —N concentration of 80 mg / L was used as raw water, and water was passed at a flow rate of 200 L / d to perform nitrogen removal treatment. In addition, the operation with the target wastewater was started when the processing capacity became a steady state after the apparatus of each process was started up. The operating conditions for each processing step are as follows.

(1) Softening treatment process: Weakly acidic cation exchange resin (manufactured by Bayer, trade name “Lewatit CNP80”), SV70hr- ¹
(2) Membrane separation step: reverse osmosis membrane (RO membrane) (manufactured by Nitto Denko Corporation, trade name “NTR759 HR-S2”)
(3) Denitrification step: USB method (upflow sludge bed method: Upflow Sludge Balnket method, denitrification tank volume 3.5 L, pH 7.5, temperature 35 ° C., methanol 240 mg / L added

(Comparative example)
Waste water was treated according to the flow shown in FIG. That is, the raw water not subjected to the softening treatment step was separated into the permeated water 6 and the concentrated water 7 by the reverse osmosis membrane, and the separated concentrated water 7 was denitrified in the denitrification tank 4. After the operation is started, the scale gradually adheres to the reverse osmosis membrane, and as shown in Table 1, the amount of permeated water separated by the reverse osmosis membrane (hereinafter referred to as flux) is 1 day compared with the time of the operation start. It decreased by 26% on the eyes and 42% on the third day.

(Example 1)
Waste water was treated according to the flow shown in FIG. That is, the waste water is subjected to ion exchange treatment by the softening means 2 and then passed through the reverse osmosis membrane separation means 3 to be separated into permeated water 6 and concentrated water 7, and then the concentrated water 7 is introduced into the denitrification tank 4. The denitrification process was performed. The results are shown in Table 2.

As shown in Table 2, in Example 1, the flux reduction rate on the first day from the start of the operation is only 2.1% lower than that at the start of the operation. Also, in each sample, it decreased only 3.1% and 4.3%, respectively, and was maintained at 5% or less, and it was confirmed that separation of permeated water and concentrated water by the reverse osmosis membrane was continued. In the denitrification process, the concentration of nitrate nitrogen in the treated water gradually increased from the start of operation, but nitrate nitrogen on the 30th day from the start of operation was 86.5%, and the removal rate was 85. % Could be maintained. Note that the removal rate of nitrate nitrogen, shows the percentage removal of nitrate nitrogen (NO 3 _-N) from the inflow water flowing into the denitrification process.

(Example 2)
Waste water was treated according to the flow shown in FIG. That is, the waste water is subjected to ion exchange treatment by the softening means 2 and then passed through the reverse osmosis membrane separation means 3 to be separated into permeated water 6 and concentrated 7 water, and then the concentrated water 7 is introduced into the denitrification tank 4. The denitrification process was performed. In the denitrification treatment, the regenerated wastewater from the regenerated wastewater feeding means 9 was mixed with the concentrated water 7 and introduced into the denitrification tank 4. Sodium chloride (NaCl) was used as the regenerant. The results are shown in Table 3.

  As shown in Table 3, in Example 2, even after 30 days from the start of operation, no significant increase was observed in the rate of flux decrease, maintaining 5% or less, and the removal rate of nitrate nitrogen was also reduced. There was no noticeable variation and the total was about 95%. Therefore, both the reverse osmosis membrane separation treatment and the denitrification treatment were able to maintain the same treatment performance and treated water quality as at the start of operation.

(Example 3)
Waste water was treated according to the flow shown in FIG. That is, the waste water is subjected to ion exchange treatment by the softening means 2 and then passed through the reverse osmosis membrane separation means 3 to separate into permeated water 6 and concentrated water 7, and then the concentrated water 7 is introduced into the denitrification tank 4. At the same time, a calcium compound was added to the denitrification tank 4 for denitrification treatment. Calcium chloride was used as the calcium compound. The results are shown in Table 4.

  As shown in Table 4, in Example 3, even after 30 days from the start of operation, the decrease rate of the flux was not significantly increased and maintained at 5% or less, and the removal rate of nitrate nitrogen was also reduced. There was no noticeable variation and the total was about 95%. Therefore, both the reverse osmosis membrane separation treatment and the denitrification treatment were able to maintain the same treatment performance and treated water quality as at the start of operation.

  FIG. 8 is a graph showing transition of the sedimentation rate of granules in Examples 1 to 3. In Example 1 in which calcium ions were not included in the water introduced into the denitrification tank 4, the granule sedimentation rate, which was 50 m / hr at the start of operation, decreased to 40 m / hr on the 30th day after the start of operation. It was. On the other hand, in Example 2 and Example 3 to which calcium ions were added, the granule sedimentation rate could be maintained at 50 m / hr even 30 days after the start of operation.

  From the above results, it can be seen that the reverse osmosis membrane separation treatment and the denitrification treatment can be stably performed by introducing the softening treatment step. Moreover, by adding calcium ions as inorganic ions to the denitrification tank, the denitrification treatment could be performed stably with a higher load.

It is a block diagram which shows the 1st waste water treatment apparatus of this invention. It is a block diagram which shows the 2nd waste water treatment apparatus of this invention. It is a block diagram which shows the processing apparatus of the 3rd waste_water | drain of this invention. It is a block diagram which shows the processing apparatus of the 4th waste_water | drain of this invention. It is a block diagram which shows the processing apparatus of the 5th waste_water | drain of this invention. It is a block diagram which shows the 6th waste water treatment apparatus of this invention. It is a block diagram of a comparative example. It is a characteristic view which shows the sedimentation rate of the granule of Examples 1-3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 11, 21, 31, 41, 51 Processing apparatus 2 Softening means 3 Reverse osmosis membrane separation means 4 Denitrification tank 5 Supply means 6 Permeated water 7 Concentrated water 8 Denitrification treated water 9 Reclaimed waste water feeding means 10 Regeneration waste water storage tank DESCRIPTION OF SYMBOLS 12 Backwash water 32 Aeration tank 33 Solid-liquid separation means 34 Filter 35 Diffusion means 36 Sludge return line 37 Feeding means of denitrification water 42 Carrier 43 Aggregation reaction tank 44 Aggregation precipitation tank 52 Immersion membrane type aeration tank 53 Immersion film

Claims (6)

Softening means for softening waste water containing nitrate nitrogen or nitrite nitrogen and containing inorganic ions;
Reverse osmosis membrane separation means for separating the effluent from the softening means into permeate and concentrated water by a reverse osmosis membrane;
Denitrification means for biologically denitrifying the concentrated water to obtain denitrified water;
A wastewater treatment apparatus comprising: Means for supplying wastewater containing organic nitrogen compounds and / or ammonia nitrogen and inorganic ions;
An aeration tank that receives the waste water from the supply means, microbially decomposes organic nitrogen compounds by aeration treatment, and nitrifies;
Solid-liquid separation means for solid-liquid separation of the mixed liquid in the aeration tank;
A softening means for softening the separated water separated by the solid-liquid separation means;
Reverse osmosis membrane separation means for separating the effluent from the softening means into permeate and concentrated water by a reverse osmosis membrane;
Denitrification means for biologically denitrifying the concentrated water to obtain denitrified water;
A wastewater treatment apparatus comprising:   The wastewater treatment apparatus according to claim 2, further comprising a feeding unit that feeds the denitrification water to the aeration tank.   The waste water treatment apparatus according to claim 2 or 3, wherein the aeration tank is filled with a carrier supporting microorganisms.   5. The reclaimed wastewater feeding means for feeding a part or all of the reclaimed wastewater containing inorganic ions discharged from the softening means to the denitrification means. The waste water treatment apparatus as described.   The wastewater treatment apparatus according to any one of claims 1 to 5, wherein the denitrification means is a denitrification tank in which denitrifying bacteria form sludge particles.

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