JP2010069413A - Organic waste water treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new organic waste water treatment method which can reduce the influence of organic waste water on treated water while remarkably reducing the generation of surplus sludge generated with biological treatment for the organic waste water. <P>SOLUTION: The organic waste water treatment method treats waste water by subjecting organic waste water to biological treatment in a biological treatment tank, thereafter, subjecting a mixture produced by the biological treatment to solid-liquid separation into treated water and sludge, subjecting a part or the whole of the sludge subjected to the solid-liquid separation to solubilizing treatment of solubilizing organic matter in the sludge, and subsequently, returning the produced solubilized liquid to the biological treatment tank. In the method, (1) phosphoric aid in the treated water obtained by subjecting the mixture produced by the biological treatment to the solid-liquid separation is adsorbed on an adsorbent, (2) the phosphoric acid adsorbed on the adsorbent is desorbed from the adsorbent with an alkali aqueous solution, (3) alkaline-earth metal is added to the alkali aqueous solution containing the phosphoric acid to separate the phosphoric acid as a phosphate, and (4) the solubilization treatment is performed using the alkali aqueous solution after the separation of the phosphoric acid. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wastewater treatment method such as an activated sludge method for biologically treating organic wastewater, and more specifically, organic wastewater that incorporates phosphorus recovery and sludge solubilization treatment into the biological treatment of the organic wastewater. It relates to the processing method.

The activated sludge method used for organic wastewater treatment generates a lot of excess sludge. As a reduction method, the excess sludge is reduced by solubilizing the excess sludge and returning it to the activated sludge tank for processing. A method to do this has been proposed previously. However, by reducing the excess sludge, phosphorus that was conventionally extracted out of the system together with the sludge is included in the activated sludge treated water and goes out of the system as it is. There is a case where an increase is seen.
Thus, while it is required to suppress the discharge of phosphorus, which is a cause of eutrophication in wastewater treatment, since phosphorus is a depleted resource, it is also required to recover from wastewater.
For this reason, a combination of solubilization treatment and phosphorus recovery technology has been proposed as a countermeasure for total phosphorus in the treated water.

  Patent Document 1 discloses a method in which Ca or Mg ions are added to a solution after solubilization treatment and phosphoric acid is recovered by a crystallization method. However, in the above method, it is necessary to accurately control the concentration and pH of the precipitation product at the time of phosphorus recovery.

  Patent Document 2 discloses a method of combining a sludge reduction method and phosphorus recovery by adsorption. Specifically, a method is described in which phosphoric acid, which is a phosphorus compound, is selectively adsorbed and removed from the treated water of the activated sludge process, and then phosphorus is desorbed from the adsorbent and then phosphorus is recovered. Yes. When desorbing phosphoric acid from the adsorbent, an alkali agent, particularly sodium hydroxide, is generally used. In the above method, a large amount of alkali is required for the desorption of phosphoric acid from the adsorbent, and most of the alkali after phosphorus separation is reused repeatedly for desorption in the process. Periodic replacement and partial replacement were required, and waste alkali treatment was also necessary. Furthermore, it was necessary to strictly control the amount of alkaline earth metal ions added with respect to the phosphoric acid concentration in the alkali.

  Furthermore, in Patent Document 3, phosphoric acid in the supernatant obtained by solid-liquid separation of the solubilized solution treated with alkali is guided to a chemical phosphoric acid precipitation step to precipitate and separate phosphorus, and the supernatant is used again for the solubilization treatment. It is disclosed. The above method requires the solid-liquid separation of the alkali solubilizing solution, and further, there is a large amount of impurities in the collected phosphate because the phosphoric acid precipitates in the solubilizing solution, and the solubilized in the alkaline solution after phosphorus separation. Since many components remain, it was necessary to take measures when circulating.

JP 2003-71487 A JP 2006-346555 JP 2002-361277 A

  The present invention eliminates the above-described problems of the prior art and significantly reduces the amount of excess sludge generated during biological treatment of organic wastewater, while reducing the effect of organic wastewater on treated water. It aims at providing the processing method of the novel organic waste water which can be reduced.

  As a result of intensive studies in view of such circumstances, the present inventor reduced the phosphoric acid in the discharged treated water with an adsorbent, desorbed the phosphoric acid contained in the adsorbent with an alkaline aqueous solution, Excess sludge generated with biological treatment of organic wastewater by recovering phosphoric acid from alkaline aqueous solution containing acid by precipitation separation and solubilizing sludge using alkaline aqueous solution from which phosphoric acid has been removed The present inventors have found that the generation amount of water can be remarkably reduced, the concentration of phosphoric acid in the treated water discharged out of the system can be remarkably reduced, and phosphorus can be easily and efficiently recovered.

In order to achieve the above object, the present invention provides the following processing method.
(1) After biologically treating organic wastewater in a biological treatment tank, the mixture produced by the biological treatment is solid-liquid separated into treated water and sludge, and the part or all of the solid-liquid separated sludge In the method for treating organic wastewater, after the solubilization treatment to solubilize the organic matter in the sludge is performed, the generated solubilized liquid is returned to the biological treatment tank.
1) Adsorb the phosphoric acid in the treated water obtained by solid-liquid separation of the biological treatment mixture to an adsorbent;
2) The phosphoric acid adsorbed on the adsorbent is desorbed from the adsorbent with an alkaline aqueous solution,
3) Separating phosphoric acid as a phosphate by adding an alkaline earth metal to the alkaline aqueous solution containing phosphoric acid,
4) The solubilization treatment is performed using an aqueous alkaline solution after separation of phosphoric acid.
A method for treating organic wastewater.
(2) The organic wastewater treatment method according to (1), wherein the 1) adsorption step and 2) the desorption step are performed by swinging the adsorption step and the desorption step in two or more adsorption tanks.
(3) The organic wastewater treatment method according to the above (2), wherein the adsorption process and the desorption process are alternately swung, and the 1) adsorption process and 2) the desorption process are continuously processed.
(4) The organic wastewater treatment method according to any one of the above (1) to (3), wherein the alkaline aqueous solution in the 2) desorption step is a 1 to 20% by weight aqueous sodium hydroxide solution.
(5) The organic wastewater treatment method according to any one of the above (1) to (4), wherein an alkali agent addition and physical crushing means are used in combination as solubilization treatment.
(6) The organic wastewater treatment method according to (5), wherein the physical crushing means uses treatment by a homogenizer, a mixer, a mill, or treatment by high pressure and instantaneous decompression expansion.

  According to the organic wastewater treatment method of the present invention, it is possible to remarkably reduce the amount of surplus sludge generated with the biological treatment of organic wastewater, and the concentration of phosphoric acid in the treated water discharged out of the system. As a result, phosphorus can be easily and efficiently recovered. Moreover, the required amount and discard amount of alkali used for phosphorus recovery and solubilization can be reduced.

  The organic wastewater treatment method of the present invention can be applied to biological treatment of various organic wastewater that generates excess sludge, and this biological treatment may be aerobic biological treatment using a biological treatment tank, Moreover, anaerobic biological treatment may be used. Examples of the aerobic biological treatment include an activated sludge method and a biofilm method. The activated sludge process is an aerobic biological treatment of organic wastewater in the presence of activated sludge. Organic wastewater is mixed with activated sludge in an aeration tank and aerated, and the mixture is concentrated with a concentrator. A standard activated sludge method is generally used in which a part of the concentrated sludge is returned to the aeration tank. However, a modified treatment method may be used. The biofilm method is a treatment method in which a biofilm is formed on a carrier and brought into contact with organic waste water under aerobic conditions. Examples of the anaerobic biological treatment include an anaerobic digestion method and a high-load anaerobic treatment method. Among the biological treatments of the above various organic wastewaters, the activated sludge method that is frequently used for the treatment of organic wastewaters can be suitably applied.

  A general flow of a conventional standard activated sludge process system is as shown in FIG. In the flow of the treatment system of FIG. 1, organic waste water (raw water) is supplied from the line 1 to the aeration tank 2, aerated in the aeration tank 2, subjected to aerobic biological treatment with activated sludge, and then sludge through the line 3. It is sent to the settling tank 4. Then, the supernatant liquid of the sludge settling tank 4 is discharged and discharged from the line 5 as treated water, while the precipitated sludge in the sludge settling tank 4 is returned to the aeration tank 2 via the line 6 as return sludge. After the part is separated and passed through line 7 as surplus sludge, it is supplied to sludge concentration process 8 as necessary to further increase the solids concentration, and then led to sludge dewatering process 10 via line 9 for dewatering. The dehydrated excess sludge 11 obtained is discharged out of the system.

  The flow of the processing system when an example of the embodiment of the present invention is applied is shown in FIG. The present invention will be described with reference to FIG.

In the flow of the treatment system of the embodiment of the present invention shown in FIG. 2, the organic waste water is supplied from the line 1 to the aeration tank 2 and is aerated in the aeration tank 2 (biological treatment tank) and is subjected to aerobic biological treatment with activated sludge. To produce a mixture. Subsequently, the mixture is sent to the sludge settling tank 4 (sludge settling step) via the line 3.
Then, the mixture is solid-liquid separated into treated water (supernatant liquid) and precipitated sludge in the sludge settling tank 4, and the supernatant liquid is discharged and discharged from the line 5 as treated water, while the precipitated sludge is returned as sludge. It returns to the aeration tank 2 through the line 6.
Further, a part of the returned sludge is collected and passed through the line 7 as surplus sludge and supplied to the sludge concentration step 8 as necessary to concentrate, and in particular, the solids concentration is concentrated to about 0.5 to 5% by weight. After that, a part of the excess sludge is guided to the sludge dewatering step 10 via the line 9 and dehydrated, and the obtained dehydrated surplus sludge 11 is discharged out of the system.
The flow up to this point is the same as the flow of the conventional standard activated sludge process.

Then, a part or all of the sludge separated into solid and liquid is subjected to a solubilization treatment for solubilizing organic matter in the sludge by being guided to a solubilization process 17 via line 6, line 7 and then line 13. A solubilized product (also referred to as a solubilized solution) is returned to the aeration tank 2 via a line 16 and biologically treated with activated sludge.
In the solubilization treatment step, the excess sludge discharged out of the system can be reduced or eliminated by solubilizing sludge that is about 2 to 4 times the amount of surplus sludge generated under the condition that the solubilization treatment is not performed.

  In this way, when excess sludge is reduced or eliminated, the amount of phosphorus contained in the organic wastewater (raw water) in line 1 is contained in the excess sludge and decreases out of the system. A large amount is contained in the treated water (supernatant liquid) flowing from the outlet 4 to the line 5. Moreover, since the phosphorus compound contained in the treated water of this line 5 is biologically treated, most of it is in the form of phosphoric acid.

  In the adsorption step of the adsorption / desorption step 18, the treated water (supernatant liquid) flowing from the sludge settling tank 4 passes through the inside (adsorbent) of the adsorption tank 19 and is discharged out of the system as discharge water through the line 12. It is released. At this time, phosphoric acid contained in the treated water is adsorbed by the adsorbent and removed from the treated water (supernatant liquid), so that the concentration of phosphoric acid in the treated water can be reduced.

  Furthermore, after the operation of the adsorption tank 19 is switched from the adsorption process to the desorption process, in the desorption process of the adsorption / desorption process 18, if necessary, a solid substance adhering to the adsorbent surface is poured with backwash water, Phosphoric acid adsorbed by flowing (mainly sodium hydroxide aqueous solution) through the line 20 to the adsorption tank 19 is desorbed from the adsorbent so that the phosphoric acid is contained in the alkaline aqueous solution and contains this phosphoric acid. The alkaline aqueous solution is transferred to the phosphate precipitation separation step 21 through the line 14.

Here, switching from the adsorption process to the desorption process measures the concentration of phosphoric acid (total phosphorus (TP) value) in the effluent water, so that the operation according to the regulation value or control value can be performed. It is preferable to switch to the desorption step. Moreover, it is preferable to implement a desorption process by distribute | circulating a prescribed amount of aqueous alkali solution. At this time, the phosphate ion concentration in the alkaline aqueous solution that has undergone the desorption step may be measured to determine the completion of the desorption of phosphate ions.
The adsorbent from which phosphoric acid has been desorbed in the desorption step can be neutralized with an acid, washed with water as necessary to regenerate the adsorption power of phosphoric acid, and then used again in the adsorption step. The liquid used at this time is preferably discharged out of the system.

Since the alkaline aqueous solution transferred to the phosphate precipitation separation step 21 (phosphate precipitation separation tank) via the line 14 is in a state in which phosphoric acid is dissolved, a polyvalent metal (preferably in the alkaline aqueous solution containing phosphoric acid) Alkaline earth metal, more preferably alkaline earth metal compound, more preferably alkaline earth metal hydroxide, mainly calcium hydroxide is preferably used as it is in the form of a suspension or aqueous solution via line 22. Added. Thus, by adding a polyvalent metal, a phosphate (for example, alkaline earth metal phosphate (such as Ca phosphate)) is precipitated in the alkaline aqueous solution, and the alkaline aqueous solution and the phosphate (phosphorus) are added. Compound) to reduce phosphorus in the aqueous alkali solution. The precipitated alkaline earth metal phosphate is taken out of the system via the line 23 and collected.
Then, the aqueous alkaline solution after the phosphoric acid separation is led to the solubilization step 17 through the line 15 and used for the sludge solubilization treatment. The subsequent steps are the same as the above-described solubilization process.

  In the present invention, conventionally used biological treatment tank (aeration tank 2) and solid-liquid separation means (sludge settling tank 4) can be appropriately used. Further, as a concentration means in the sludge concentration step 8, a conventionally used concentration means, for example, a gravity sedimentation separator, a flotation separator, a centrifugal separator, a membrane separator, a screw dehydrator or the like can be appropriately used. Further, as the dewatering means of the sludge dewatering step 10, a conventionally used dewatering means such as a centrifugal separator, a belt filter dehydrator, a screw press dehydrator, or the like can be used as appropriate.

In the solubilization treatment step 17 of the present invention, the solubilization treatment method in the sludge solubilization tank is not particularly limited, but a solubilization treatment method using an alkaline agent or a solubilization treatment method by physical crushing is suitable. In particular, a solubilization method by physical crushing with an alkali agent is suitable.
As the alkaline agent used for the solubilization treatment, at least an alkaline aqueous solution in which a phosphorus compound is desorbed from the adsorbent, preferably an alkaline aqueous solution after separation of phosphoric acid is used, but an unused alkaline agent may be additionally added thereto. Good. Thus, since the aqueous alkali solution used in the adsorption / desorption step is used for the solubilization treatment, the required amount and waste amount of alkali used as the entire system can be reduced.

Examples of the main component of the alkali agent include alkali metal compounds such as sodium and potassium, and alkali metal compounds such as sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate. Among these, sodium hydroxide, Alkali metal hydroxides such as potassium hydroxide, particularly sodium hydroxide are preferred.
The amount of the alkali agent added is not particularly limited, but the alkali agent may be added so as to be 0.005 to 0.15 N with respect to the excess sludge to be solubilized, and is preferably 0.01 to 0.10 N. Especially preferably, it is 0.02-0.07N.
Examples of the physical crushing means include a homogenizer, a mixer, a mill, a high pressure and a momentary decompression treatment, and a pipeline mixer and a pipeline mill are preferable.
The solubilization treatment time is 1 minute to 300 minutes, preferably 10 minutes to 250 minutes, and more preferably 20 minutes to 200 minutes. When a physical crushing means is used in combination, the contact efficiency with the alkaline agent is improved. From the viewpoint of adding a crushing effect, 10 minutes to 180 minutes is preferable.

  Further, in the solubilization treatment step 17, the solubilized solution after the solubilization treatment may be subjected to neutralization treatment or decolorization treatment with an oxidizing agent as necessary. By performing the decoloring treatment, it is possible to reduce the coloration of the solubilized product that occurs when reducing the volume of excess sludge and the adverse effect on the hue of the treated water resulting therefrom. Although this decoloring process and neutralization process can be used together, it is preferable to perform a decoloring process before performing a neutralization process in that case. For the neutralization treatment, mineral acids such as hydrochloric acid and sulfuric acid, spent waste acid, and the like can be used. The oxidizing agent is preferably hydrogen peroxide, sodium peroxide, sodium percarbonate, etc., which have strong oxidizing power and change itself to be harmless to activated sludge after decomposition, and hydrogen peroxide is particularly preferable.

In the adsorption / desorption process 18 of the present invention, the number of adsorption tanks (towers) 19 may be one, but a part of the adsorption tanks are used as the adsorption process and the other adsorption tanks are used as the desorption process. In consideration of continuous treatment that can be used by swinging regularly, two or more are usually preferred.
As an example of the embodiment, the adsorption tank 19 includes an adsorption tank 19a and an adsorption tank 19b, and the line 5, line 12, line 14, and line 20 are connected to the adsorption tank 19a and the adsorption tank 19b, respectively. (Not shown).

  Specifically, as shown in FIG. 3, the treated water (supernatant liquid) passes through the adsorption tank 19a and is discharged and discharged out of the system as discharged water with reduced phosphoric acid, while the alkaline aqueous solution is phosphorus After passing through the adsorption tank 19b that has adsorbed the acid, it is transferred to the phosphate precipitation separation step 21 as an alkaline aqueous solution containing phosphoric acid. Next, the adsorption tank 19a in the adsorption process is swung to the desorption process, and the adsorption tank 19b in the desorption process is swung to the adsorption process. As shown in FIG. 4, after switching from the regenerated adsorption tank 19b to the adsorption tank 19a that adsorbs phosphoric acid, the alkaline aqueous solution was swung through the adsorption tank 19a to be adsorbed by the adsorption tank 19a. Phosphoric acid is desorbed and contained in the alkaline aqueous solution, and is led to the phosphate precipitation separation step 21 through the line 14, while the adsorption tank 19a that has adsorbed phosphoric acid is switched to the regenerated adsorption tank 19b. The treatment water (supernatant liquid) is swung through the adsorption tank 19b to remove the phosphoric acid contained in the treatment water from the treatment water (supernatant liquid) while adsorbing the adsorption water to the adsorption tank 19b. Is discharged and discharged through the line 12 as discharged water. Further, the above-described processing is continuously performed by swinging the adsorption tank 19a to the adsorption process and the adsorption tank 19b to the desorption process.

The adsorbent filled in the adsorption tank 19 is not particularly limited as long as it can selectively adsorb phosphoric acid and can be desorbed with an alkali, and a commercially available adsorbent can be used. Examples include adsorbents containing metal elements such as iron, titanium, zirconium, calcium, and magnesium, and oxides such as zeolite and silica gel. In particular, adsorbents containing zirconium have adsorption selectivity for phosphoric acid. Highly preferred. The adsorbent is preferably a porous material having a high adsorbability.
If such an adsorbent is used, phosphorus in the treated water can be easily and efficiently recovered, and the required amount and waste amount of alkali used for recovery and solubilization of phosphorus can be reduced.

Moreover, the alkaline aqueous solution used in the desorption step may be any alkaline solution used in the solubilization step. However, in order to easily and efficiently recover phosphorus in the treated water, an alkali metal such as sodium or potassium is used. An aqueous solution is preferred. Among the alkali agents, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkali metal compounds such as alkali metal carbonates such as sodium carbonate and sodium bicarbonate are preferable. Metal hydroxides are preferred, and sodium hydroxide is particularly preferred.
Further, the alkaline aqueous solution may be an alkaline aqueous solution after the phosphoric acid separation in the phosphate precipitation separation step 21, and an unused alkali may be additionally added thereto.

  In the desorption step, the concentration of the alkaline aqueous solution used for the desorption of phosphoric acid from the adsorbent is preferably in the range of 1 to 20% by weight in consideration of the desorption time, the liquid flow rate, and utilization in the solubilization process More preferably, it is 2 to 15% by weight, particularly preferably 3 to 10% by weight.

  The acid used for regenerating the adsorbent is not particularly limited, but mineral acids such as hydrochloric acid, nitric acid and sulfuric acid and used waste acids are preferred, and sulfuric acid is particularly preferred.

  Examples of the polyvalent metal used in the phosphate precipitation step 21 of the present invention include aluminum, calcium, and magnesium. Then, in the phosphate precipitation step, the alkaline earth metal such as calcium hydroxide, calcium chloride, calcium sulfate, magnesium hydroxide, magnesium chloride, magnesium sulfate or the compound thereof is used as it is, as a suspension or as an aqueous solution. It is preferable to add to the alkaline aqueous solution containing phosphoric acid in the tank. These alkaline earth metals or compounds thereof are easily combined with phosphoric acid to precipitate, and become alkaline earth metal phosphates that are phosphorus compounds in a form that is easy to use after separation. Furthermore, considering that it can be reused as a fertilizer and the production cost is low, it is preferable to add calcium compounds such as calcium hydroxide and calcium chloride, especially calcium hydroxide and calcium chloride.

  When the alkaline earth metal is added to the alkaline aqueous solution containing phosphoric acid, the alkaline earth metal concentration may be higher than the phosphoric acid concentration. Depending on the acid concentration, it is preferable to add 1.5 to 10 times more alkaline earth metal ions, preferably 1.5 to 5 times more alkaline earth metal ions as the number of moles relative to phosphate ions. . When using the entire amount of the alkaline aqueous solution used in the desorption step for solubilization, the alkaline earth metal ion concentration may be excessive. However, when a part of the alkaline aqueous solution is used again for desorption, the alkaline earth metal ion is used again. It is preferable to control the amount of ions to be close to an equal amount by 1.5 to 2 times. Of the alkaline earth metal ions, Ca ions are particularly desirable.

  Moreover, the temperature at the time of phosphate precipitation separation is not particularly limited as long as it is a temperature at which phosphoric acid and an aqueous alkali solution can be separated, but a range of 5 to 60 ° C. is preferable, considering economic efficiency and work efficiency. The range of 10-40 degreeC is still more preferable.

The application of the wastewater treatment method of the present invention is preferable in a wastewater treatment load in a range of 0.05 to 1.0 kg / (m ³ · day) of BOD volume of the biological treatment tank, and 0.1 to 1.0 kg / (m ³ is more preferable in the wastewater treatment load in the range of ³ · day), and particularly preferable in the wastewater treatment load in the range of 0.2 to 0.8 kg / (m ³ · day).

The CODs in the present invention all represent COD (Mn). The measurement of COD (Mn) is a value measured by either a measurement method defined in JIS or a method based on the measurement method of JIS.
All BODs represent BOD5. The measurement of BOD5 shall be the value measured by the measuring method defined in JIS.
The total phosphorus (TP) value represents the total sum of phosphorus contained in inorganic phosphoric acid, organic phosphoric acid, and organic phosphorus compound contained in water. The measurement of the total phosphorus (TP) value is a value measured by either a measurement method defined in JIS or a method based on the measurement method of JIS.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention in more detail, this invention is not limited to these Examples.

<Example 1>
Simulated factory wastewater (BOD = 120mg / L, TP = 1.0mg / L) in a 40L aeration tank (BOD volumetric load 0.36 (kg-BOD / m ³ / day)) with aeration time 8hr, activated sludge MLSS = 3000mg / L After the supply, the activated sludge was settled and separated in a 20 L settling tank to obtain a precipitated sludge having a solid concentration of 0.5 to 1.0% by weight. In the simulated factory wastewater treatment, the wastewater treatment amount is 0.12 m ³ / day, 1.5 to 3.5 L / day (dry-base = 17.4 g / day) of the precipitated sludge is extracted, and the remaining precipitated sludge is put into the aeration tank. I returned it. Next, this extracted sludge is introduced into a batch-type sludge solubilization tank, and the peripheral speed of the rotary blade is set to 15 m / sec using an in-line mixer (IKA laboratory pilot), and phosphoric acid described later After separation, sodium hydroxide was added to 0.05 N and the treatment was performed for 1 hour to solubilize sludge. The solubilized solution was added to the aeration tank at a constant rate to perform aerobic biological treatment. As a result of continuing the operation according to the above conditions for 30 days, the water quality of the settling tank effluent was COD = 8 mg / L (average) and SS = 2 mg / L (average). During the 30 days during the test, the MLSS in the activated sludge tank was almost constant, and there was no increase or decrease in the amount of sludge.

  The TP value of the settling tank effluent during this test period is 0.9 mg / L (average), and the TP value after passing through the phosphoric acid recovery device (using zirconium-based adsorbent) is 0.1 mg / L or less. there were. The phosphoric acid recovery apparatus was composed of two adsorption towers, and the adsorption tower was switched when the TP value after passing through was 0.1 mg / L or more. In the desorption process, phosphoric acid was desorbed by passing 140 ml of 4 wt% NaOH. Thereafter, 0.46 g of calcium hydroxide was added to and stirred with phosphoric acid-containing sodium hydroxide, and calcium phosphate crystals were precipitated at 20 to 30 ° C. and recovered by solid-liquid separation. Moreover, sodium hydroxide after phosphoric acid separation was used for the above-mentioned solubilization.

The adsorbent treated with sodium hydroxide was then treated with sulfuric acid and used again for adsorption.
As a result of performing the above operation for 30 days, 29 g was obtained as calcium phosphate. This amount was 81% of the amount of phosphorus contained in the raw water.
The NaOH weight used for desorption was 180 g. This total amount of NaOH was used for solubilization, and no NaOH was added during solubilization. For this reason, the total amount of NaOH used for 30 days was 180 g.

<Example 2>
Simulated factory wastewater (BOD = 120mg / L, TP = 1.0mg / L) in a 40L aeration tank (BOD volumetric load 0.36 (kg-BOD / m ³ / day)) with aeration time 8hr, activated sludge MLSS = 3000mg / L After the supply, the activated sludge was settled and separated in a 20 L settling tank to obtain a precipitated sludge having a solid concentration of 0.5 to 1.0% by weight. In the simulated factory wastewater treatment, the wastewater treatment amount is 0.12 m ³ / day, 1.5 to 3.5 L / day (dry-base = 17.4 g / day) of the precipitated sludge is extracted, and the remaining precipitated sludge is put into the aeration tank. I returned it. Next, this extracted sludge is introduced into a batch-type sludge solubilization tank, and the peripheral speed of the rotary blade is set to 15 m / sec using an in-line mixer (IKA laboratory pilot), and phosphoric acid described later After separation, sodium hydroxide was added to 0.05 N and the treatment was performed for 1 hour to solubilize sludge. The solubilized solution was added to the aeration tank at a constant rate to perform aerobic biological treatment. As a result of continuing the operation according to the above conditions for 30 days, the water quality of the settling tank effluent was COD = 8 mg / L (average) and SS = 2 mg / L (average). During the 30 days during the test, the MLSS in the activated sludge tank was almost constant, and there was no increase or decrease in the amount of sludge.

The TP value of the settling tank effluent during this test period is 0.9 mg / L (average), and the TP value after passing through the phosphoric acid recovery device (using zirconium-based adsorbent) is 0.1 mg / L or less. there were. The phosphoric acid recovery apparatus is composed of two adsorption towers, and the adsorption tower is switched when the TP value after passing through is 0.1 mg / L or more. In the desorption process, phosphoric acid was desorbed by passing 140 ml of 8 wt% NaOH. Thereafter, 0.46 g of calcium hydroxide was added to and stirred with phosphoric acid-containing sodium hydroxide, and calcium phosphate crystals were precipitated at 20 to 30 ° C. and recovered by solid-liquid separation. Moreover, about half of sodium hydroxide after phosphoric acid separation was used for the solubilization described above.
The adsorbent treated with sodium hydroxide was then treated with sulfuric acid and used again for adsorption.
As a result of performing the above operation for 30 days, 30 g was obtained as calcium phosphate. This amount was 83% of the amount of phosphorus contained in the raw water.
The amount of NaOH used for 30 days was 210 g. This was the amount used for solubilization of 180 g of NaOH used at the time of phosphate ion desorption, and the remaining 30 g was an additional amount of NaOH when reused for phosphate ion desorption.

<Comparative Example 1>
In Example 1, operation was carried out under the condition that NaOH used for recovery of phosphorus by the adsorbent was not used for solubilization treatment.
Simulated factory wastewater (BOD = 120mg / L, TP = 1.0mg / L) in a 40L aeration tank (BOD volumetric load 0.36 (kg-BOD / m ³ / day)) with aeration time 8hr, activated sludge MLSS = 3000mg / L After the supply, the activated sludge was settled and separated in a 20 L settling tank to obtain a precipitated sludge having a solid concentration of 0.5 to 1.0% by weight. In the simulated factory wastewater treatment, the wastewater treatment amount is 0.12 m ³ / day, 1.5 to 3.5 L / day (dry-base = 17.4 g / day) of the precipitated sludge is extracted, and the remaining precipitated sludge is put into the aeration tank. I returned it. Next, the extracted precipitated sludge is introduced into a batch-type sludge solubilization tank, and the peripheral speed of the rotary blade is set to 15 m / sec using an in-line mixer (IKA laboratory pilot). Was solubilized by adding 1 to 0.05 N and treating for 1 hour. The solubilized solution was added to the aeration tank at a constant rate to perform aerobic biological treatment. As a result of continuing the operation according to the above conditions for 30 days, the water quality of the settling tank effluent was COD = 8 mg / L (average) and SS = 2 mg / L (average). During the 30 days during the test, the MLSS in the activated sludge tank was almost constant, and there was no increase or decrease in the amount of sludge.
The TP value of the settling tank effluent during this test period is 0.9 mg / L (average), and the TP value after passing through the phosphoric acid recovery device (using zirconium-based adsorbent) is 0.1 mg / L or less. there were. The phosphoric acid recovery apparatus is composed of two adsorption towers, and the adsorption tower is switched when the TP value after passing through is 0.1 mg / L or more. In the desorption process, phosphoric acid was desorbed by passing 140 ml of 4 wt% NaOH. Thereafter, 0.35 g of calcium hydroxide was added to phosphoric acid-containing sodium hydroxide and stirred, and crystals of calcium phosphate were precipitated at 20 to 30 ° C. and recovered by solid-liquid separation. Moreover, sodium hydroxide after phosphoric acid separation was used again for phosphoric acid desorption from the adsorbent.

The adsorbent treated with sodium hydroxide was then treated with sulfuric acid and used again for adsorption.
As a result of performing the above operation for 30 days, 24 g was obtained as calcium phosphate. This was an amount equivalent to 67% of the amount of phosphorus contained in the raw water.
The weight of sodium hydroxide used for the solubilization treatment was 180 g, and the weight of sodium hydroxide used for phosphate ion desorption was 36 g. This is an additional portion when reused for desorption among those used during desorption. For this reason, the total amount of sodium hydroxide used for 30 days was 216 g.

  The results of Examples 1 and 2 and Comparative Example 1 are shown in Table 1 below.

  From the above, both Examples 1 and 2 can reduce the amount of sodium hydroxide required and the amount of waste compared to Comparative Example 1 by using the alkali used for desorption during phosphorus recovery for the solubilization process. It was. Further, since fresh (unused) sodium hydroxide was used for desorption of phosphorus recovery, the amount of phosphorus recovered from the adsorbent was higher than that of Comparative Example 1. Furthermore, in both Examples 1 and 2, since the strict control for the addition of alkaline earth metal when separating phosphoric acid from sodium hydroxide was not necessary, the operation was simple.

It is a general flow sheet of a conventional standard activated sludge process system. It is a flow sheet of a processing system of an example of an embodiment of the present invention. It is a flow sheet of a processing system of an example of an embodiment of an adsorption / desorption process in a plurality of adsorption tanks of the present invention. It is a flow sheet of a processing system of an example of an embodiment of an adsorption / desorption process in a plurality of adsorption tanks of the present invention.

Explanation of symbols

2 Aeration tank 4 Sludge sedimentation tank 8 Sludge concentration process 10 Sludge dewatering process 11 Dehydrated surplus sludge 17 Solubilization process 18 Adsorption / desorption process 19 Adsorption tank 19a Adsorption tank 19b Adsorption tank 21 Phosphate precipitation separation process

Claims (6)

After biologically treating organic wastewater in a biological treatment tank, the mixture produced by the biological treatment is solid-liquid separated into treated water and sludge, and a part or all of the solid-liquid separated sludge is mixed in the sludge. In the organic wastewater treatment method of returning the generated solubilized liquid to the biological treatment tank after performing solubilization treatment to solubilize organic matter,
1) Adsorb the phosphoric acid in the treated water obtained by solid-liquid separation of the biological treatment mixture to an adsorbent;
2) The phosphoric acid adsorbed on the adsorbent is desorbed from the adsorbent with an alkaline aqueous solution,
3) Separating phosphoric acid as a phosphate by adding an alkaline earth metal to the alkaline aqueous solution containing phosphoric acid,
4) The solubilization treatment is performed using an aqueous alkaline solution after separation of phosphoric acid.
A method for treating organic wastewater.   The organic wastewater treatment method according to claim 1, wherein the 1) adsorption step and 2) desorption step are performed in two or more adsorption tanks by swinging the adsorption step and the desorption step.   The organic wastewater treatment method according to claim 2, wherein the adsorption process and the desorption process are alternately swung, and the 1) adsorption process and 2) the desorption process are continuously processed.   The method of treating organic waste water according to any one of claims 1 to 3, wherein the aqueous alkali solution in the 2) desorption step is a 1 to 20 wt% aqueous sodium hydroxide solution.   The organic wastewater treatment method according to any one of claims 1 to 4, wherein the solubilization treatment is performed by using an alkali agent addition and physical crushing means in combination.   6. The organic wastewater treatment method according to claim 5, wherein the physical crushing means uses treatment by a homogenizer, a mixer, a mill, or treatment by high pressure and instantaneous decompression expansion.

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