JP2005238084A - Wastewater treatment system and wastewater treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve recovery of phosphorus from surplus sludge, to reduce the volume of the sludge, and to enable procurement of organic carbon sources for an aerobic process in the processes. <P>SOLUTION: A wastewater treatment system 10 has a wastewater treatment tank 12 for removing phosphorus and nitrogen from wastewater, and a phosphorus recovery means 13 for recovering the phosphorus from the sludge in the wastewater treatment tank 12. The wastewater treatment tank 12 comprises an anaerobic tank 15 for the anaerobic process, an aerobic tank 16 for an aerobic process, and an oxygen-free tank 17 for an oxygen-free process. The phosphorus recovery means 13 has an ozone tank 21 for solubilizing the sludge from the oxygen-free tank 17, a second sedimentation tank 22 for recovering the residual sludge from the sludge solubilized liquid passing through the ozone tank 21, and a dephosphorization tank 23 for recovering phosphorus from the sludge solubilized liquid passing through the second sedimentation tank 22. The sludge solubilized liquid after the recovery of phosphorus is returned to the aerobic tank 16 to feed the organic carbon sources required for the aerobic process. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wastewater treatment system and a wastewater treatment method, and more particularly to a wastewater treatment system and a wastewater treatment method for removing nitrogen and phosphorus contained in wastewater using denitrifying phosphorus accumulating bacteria.

In stagnant closed water areas such as lakes, inner bays, and inland seas, nitrogen and phosphorus cause the occurrence of blue sea urchins and red tides.To create a healthy water environment in the water areas, domestic wastewater that flows into the water areas Nitrogen and phosphorus need to be sufficiently removed from the water. Therefore, various biological treatments using predetermined bacteria are known as wastewater treatment techniques for removing nitrogen and phosphorus from wastewater. As this biological treatment, anaerobic / anoxic / aerobic methods (A ₂ O method) is known (see Patent Document 1). The A ₂ O method is a method of removing nitrogen components from wastewater using nitrifying bacteria and denitrifying bacteria and removing phosphorus from wastewater using phosphorus accumulating bacteria.

However, in the A ₂ O method, since effective nitrogen removal cannot be performed due to a shortage of a carbon source, the present inventors can perform denitrification and dephosphorization that can simultaneously perform denitrification and phosphorus uptake under carbonless and oxygen-free conditions. An anaerobic / aerobic / anoxic method (AOA method) using phosphorus-accumulating bacteria has already been proposed (see Patent Document 1). In this AOA method, first, ingestion of organic matter and release of phosphorus by phosphorus accumulating bacteria and denitrifying phosphorus accumulating bacteria are performed in an anaerobic process. Next, excessive phosphorus uptake by phosphorus accumulating bacteria is performed in the aerobic process. At this time, as it is, it becomes difficult to take up nitrate nitrogen in the subsequent oxygen-free process due to the physiological properties of the denitrifying phosphorus accumulating bacteria. Limit phosphorus uptake by nitrifying phosphorus accumulating bacteria. In the oxygen-free process, denitrification and phosphorus uptake by denitrifying phosphorus accumulating bacteria are performed.
JP 2003-285096 A

By the way, it is said that phosphorus ore on the earth will be depleted in about 100 years from now on, and there is a social demand for recovery and reuse of phosphorus from wastewater and waste. Therefore, as a result of intensive studies by the present inventors based on such social demands, in the A ₂ O method, the phosphorus content in the excess sludge is as low as 3 wt%, from the viewpoint of reuse of phosphorus. Although not useful, the AOA method has found that the excess sludge contains a large amount of phosphorus that is about 5 times (15 wt%) of the A ₂ O method. This phosphorus content is a value that exceeds the phosphorus content (14 wt%) in the phosphate ore, and is a value that can be an effective phosphorus resource. In this way, the reason why the excess sludge in the AOA method contains a large amount of phosphorus component is that the denitrifying phosphorus-accumulating bacteria that take in phosphorus using nitrate-bound oxygen in the oxygen-free process are excellent in the wastewater treatment tank. It can be considered that the amount of denitrifying bacteria and heterotrophic bacteria decreases and the phosphorus content in the sludge is dramatically increased because it can be occupied.

  In addition, some of the excess sludge generated in the wastewater treatment process is sent to the anaerobic process, but the rest is discarded in the environment, so that the volume of sludge is also socially demanded.

  Furthermore, the AOA method requires the addition of an organic carbon source in an aerobic process, and there is a problem that the organic carbon source must be procured separately.

  The present invention has been devised based on the above social demands and the inventor's knowledge, and its purpose is to provide a wastewater treatment system and a wastewater treatment method capable of increasing the phosphorus recovery rate from excess sludge. There is to do.

  Another object of the present invention is to provide a wastewater treatment system and a wastewater treatment method that can procure an organic carbon source in an aerobic process in the process and can reduce the volume of sludge. It is in.

(1) In order to achieve the above object, the present invention provides an anaerobic process, an aerobic process in the presence of sludge containing denitrifying phosphorus accumulating bacteria and / or a biofilm on which the denitrifying phosphorus accumulating bacteria are immobilized. In a wastewater treatment system including a wastewater treatment tank that removes phosphorus and nitrogen in wastewater by performing wastewater treatment in the order of the process and the oxygen-free process,
A configuration is adopted in which a sludge recovery means for solubilizing sludge at the time of the oxygen-free process and recovering phosphorus from the sludge solubilizing solution is provided.

  (2) Here, it is preferable that the phosphorus recovery means is configured to be provided so that the sludge solubilized liquid after phosphorus recovery can be returned into the wastewater treatment tank in the aerobic process.

(3) The present invention also provides an anaerobic process, an aerobic process, and an anaerobic process in the presence of sludge containing denitrifying phosphorus accumulating bacteria and / or a biofilm on which the denitrifying phosphorus accumulating bacteria are immobilized. In a wastewater treatment system including a wastewater treatment tank that removes phosphorus and nitrogen in wastewater by treating wastewater in the order of steps,
The wastewater treatment tank includes an anaerobic tank that performs the anaerobic process, an aerobic tank that performs the aerobic process, and an anaerobic tank that performs the anaerobic process,
A configuration may be adopted in which a sludge recovery means for solubilizing sludge in the oxygen-free tank and recovering phosphorus from the sludge solubilizing solution is provided.

  (4) Here, it is preferable that the phosphorus recovery means is configured to be provided so that the sludge solubilized liquid after phosphorus recovery can be returned to the aerobic tank.

(5) Further, the present invention provides an anaerobic process, an aerobic process, and an anaerobic process in the presence of sludge containing denitrifying phosphorus accumulating bacteria and / or a biofilm in which the denitrifying phosphorus accumulating bacteria are immobilized. In the wastewater treatment method for removing phosphorus and nitrogen in wastewater by treating wastewater in the order of the process,
A technique is employed in which sludge is extracted and solubilized during the oxygen-free process, and phosphorus is recovered from the sludge solubilized liquid.

  (6) Here, the sludge solubilized liquid after phosphorus recovery may be used as an organic carbon source necessary for the aerobic process.

According to the above (1), (3) and (5), from the excess sludge containing phosphorus significantly exceeding the excess sludge of the conventional anaerobic / anoxic / aerobic method (A ₂ O method), As a result, the phosphorus recovery rate from surplus sludge can be increased compared to the conventional A ₂ O method, which can contribute to securing phosphorus resources.

  In addition, according to the above (2), (4) and (6), the sludge solubilized liquid after phosphorus recovery is reused as the organic carbon source added in the aerobic process, and the organic in the aerobic process The carbon source can be procured in the process, and sludge volume can be reduced by solubilization of the sludge.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a schematic configuration diagram of a wastewater treatment system according to the present embodiment. In this figure, a wastewater treatment system 10 includes a wastewater treatment tank 12 that removes phosphorus and nitrogen from wastewater, and a phosphorus recovery means 13 that is attached to the wastewater treatment tank 12 and collects phosphorus from sludge in the wastewater treatment tank 12. It is prepared for.

  The waste water treatment tank 12 is substantially the same as the configuration described in Japanese Patent Application Laid-Open No. 2003-285096, and sludge and / or denitrifying phosphorus accumulating bacteria containing denitrifying phosphorus accumulating bacteria are immobilized. In the presence of a biofilm, phosphorus and nitrogen in the wastewater are removed by performing wastewater treatment in the order of an anaerobic process, an aerobic process, and an oxygen-free process.

  That is, the waste water treatment tank 12 of this embodiment is an anaerobic tank 15 for an anaerobic process in which organic matter is ingested and phosphorus is released using phosphorus accumulating bacteria and denitrifying phosphorus accumulating bacteria with respect to waste water (raw water); An aerobic tank 16 for an aerobic process in which excess phosphorus is taken up using phosphorus accumulating bacteria with respect to the wastewater that has passed through the anaerobic tank 15, and denitrifying phosphorus accumulation with respect to the wastewater that has passed through the aerobic tank 16 Oxygen-free anaerobic tank 17 that performs denitrification and phosphorus uptake using bacteria, and wastewater that has passed through oxygen-free tank 17 is separated into sludge containing phosphorus and treated water that has been drained. The first settling tank 18 is provided.

  The anaerobic tank 15 contains sludge containing denitrifying phosphorus accumulating bacteria, and is supplied with waste water containing nitrogen and phosphorus to be treated. A part of the sludge separated in the first sedimentation tank 18 is returned to the anaerobic tank 15 so that the MLSS concentration in the anaerobic tank 15 is maintained.

  Here, the wastewater to be treated is not particularly limited, but when it contains a water-insoluble suspended substance, it may be subjected to a primary treatment for physically removing it. preferable. Moreover, it is preferable to adjust pH value of waste water to 6.5-8.5 by the compound which can be used for normal pH adjustment, such as hydrochloric acid and sodium hydroxide, and is especially adjusted to 7.0-7.5. Good. Furthermore, although it does not specifically limit about the temperature of waste_water | drain, The range of 15-40 degreeC is desirable.

  The sludge put in the anaerobic tank 15 may be any sludge containing denitrifying phosphorus accumulating bacteria. Preferably, the collected sludge containing denitrifying phosphorus accumulating bacteria is conditioned under anaerobic / anoxic conditions to predominate the denitrifying phosphorus accumulating bacteria. In this acclimatization, an appropriate amount of a nitrate ion source such as sodium nitrate must be added at the end of anaerobic conditions depending on the activity state of the microorganism. These steps may be repeated until the denitrifying phosphorus-accumulating bacteria dominate for each condition. In addition, whether denitrifying phosphorus accumulating bacteria in the sludge is dominant depends on organic matter uptake and phosphorus release in the anaerobic process, and denitrification reaction and phosphorus uptake amount in the oxygen-free process without organic matter. Can be confirmed by examining by a known measuring method such as chromatograph.

  Further, in the anaerobic tank 15, a biofilm in which the denitrifying phosphorus accumulating bacteria are immobilized may be placed instead of the sludge containing the denitrifying phosphorus accumulating bacteria or together with the sludge. The biofilm may be any biofilm obtained by immobilizing denitrifying phosphorus-accumulating bacteria on a known carrier such as activated carbon, cement ball, organic polymer, and the like. It may be a known method such as an immobilization method or a comprehensive immobilization method, and is not limited. This biofilm has an ecological structure in which slow-growing nitrifying bacteria are localized inside the biofilm and denitrifying phosphorus-accumulating bacteria are located outside the biofilm. Since it is a denitrifying phosphorus accumulating bacterium, an effect of increasing the phosphorus content in the extracted sludge can be expected as compared with the case where the sludge containing the denitrifying phosphorus accumulating bacterium is used.

  The initial input amount of the sludge or biofilm is not particularly limited, but is preferably 3000 mg / l to 6000 mg / l in MLSS concentration.

  The treatment time in the anaerobic tank 15 is preferably until the uptake of organic substances by the phosphorus accumulating bacteria and denitrifying phosphorus accumulating bacteria is completed.

In the aerobic tank 16, the oxidation of ammonia nitrogen to nitrate nitrogen by nitrifying bacteria and the uptake of phosphorus by phosphorus accumulating bacteria are performed by feeding air. Here, as will be described later, the aerobic tank 16 is supplied with the sludge solubilized liquid after phosphorus recovery from the phosphorus recovery means 13. In this solution, an organic carbon source is contained, and when the organic carbon source is supplied to the aerobic tank 16, the uptake of phosphorus by the denitrifying phosphorus accumulating bacteria present in the aerobic tank 16 is achieved. Be regulated. As a result, nitrate nitrogen can be sufficiently taken up by denitrifying phosphorus-accumulating bacteria in the subsequent oxygen-free process. Here, the supply of the organic carbon source from the phosphorus recovery means 13 is controlled to be performed at the initial stage of the aerobic process, and the optimal amount of the organic carbon source should be determined by appropriately examining the conditions. However, it is preferably 20 to 50 mg-TOC · L ⁻¹ , more preferably 30 to 45 mg-TOC · L ⁻¹ .

  The amount of air fed into the aerobic tank 16 may be an amount that can maintain a dissolved oxygen concentration of 0.3 to 3 mg / l in the range where the nitrification reaction occurs, and is appropriately determined depending on the apparatus shape and the amount of microorganisms. However, it is preferably 50 to 2000 ml / min, and more preferably 100 to 500 ml / min.

  The treatment time in the aerobic tank 16 is preferably until the oxidation of ammonia nitrogen to nitrate nitrogen is completed.

  In the oxygen-free tank 17, denitrification reaction and phosphorus uptake using denitrifying phosphorus accumulating bacteria are performed while stirring by a stirring means (not shown). At this time, as described above, in the previous aerobic process, an organic carbon source is added from the phosphorus recovery means 13 and the phosphorus uptake by the denitrifying phosphorus accumulating bacteria is regulated. Accumulated bacteria and denitrifying phosphorus-accumulating bacteria efficiently incorporate nitrate-bound oxygen as an electron acceptor at the same time as phosphorus, and the treatment solution is efficiently denitrified and dephosphorized. Here, a part of the sludge distributed substantially uniformly in the liquid by stirring in the oxygen-free tank 17 is extracted from the oxygen-free tank 17 to the phosphorus recovery means 13.

  The first settling tank 18 is separated into sludge and treated water from which the sludge has been removed by a known solid-liquid separation method such as a sedimentation method or a membrane separation method, and the treated water is discharged to the outside. ing. A portion of the sludge separated in the first sedimentation tank 18 is returned to the anaerobic tank 15, while the rest is discarded.

  In addition, although the waste water treatment tank 12 of a present Example employ | adopts the continuous type which uses the different processing tanks 15-18 for every processing process, this invention is not restricted to this, Each processing process is the same processing tank. You may make it applicable to the batch type which performs. In this case, after the anaerobic process is completed, air is fed by an air pump to perform the aerobic process. Then, the supply of air is stopped to perform an oxygen-free process, and then the sludge is extracted during stirring immediately before the end of the oxygen-free process, and the sludge is supplied to the waste water treatment tank 12 in the next anaerobic process, and phosphorus recovery means 13 The sludge may be extracted from the drain through a step of settling sludge after the end of the oxygen-free process.

  The phosphorus recovery means 13 includes a pump 20 that partially extracts sludge from the oxygen-free tank 17, an ozone tank 21 that feeds sludge from the oxygen-free tank 17 extracted by the pump 20 and solubilizes the sludge, A second sedimentation tank 22 for recovering residual sludge contained in the sludge solubilization liquid that has passed through the ozone tank 21; and a dephosphorization tank 23 for recovering phosphorus from the sludge solubilization liquid that has passed through the second precipitation tank 22. Configured.

The amount of sludge withdrawn by the pump 20 greatly affects the phosphorus recovery rate and sludge volume reduction rate, and therefore, excess sludge volume reduction is used as an index. Here, it is said that the volume reduction efficiency of sludge, that is, the ratio of sludge reduced in the amount of sludge used for ozone treatment in the ozone tank 21 is generally 30%. For this reason, it is necessary to extract 3.3 times the amount of sludge to be reduced in volume.
Therefore, if the total organic carbon (TOC) load flowing into the wastewater treatment equipment is X (g-TOC / day) and the sludge generation rate is 0.7 (g-MLSS / g-TOC), one day The amount of generated sludge is 0.7X (g-MLSS). When aiming to achieve a sludge volume reduction rate of Y%, the amount of extracted sludge R (g-MLSS) required is
R = (0.7X) × 3.3 × Y × 0.01
It is expressed. In principle, Y can be freely set in the range of 0 to 100%.

Ozone is injected into the ozone tank 21 and the sludge from the anoxic tank 17 is solubilized. Here, the ozone injection conditions are determined by the ozone concentration and the ozone injection amount. Examples of the ozone concentration range include 1 to 100 (mg-O ₃ / L), preferably about 10 to 50 (mg-O ₃ / L). On the other hand, the ozone injection amount per sludge amount (MLSS) can be 1 to 500 (mg-O ₃ / g-MLSS), preferably 20 (mg-O ₃ / g-MLSS) or more.
The gas injection amount required from the above two points is suitably in the range of 0.01 to 500 (L / g-MLSS).
Specifically, the amount of gas injected per day can be calculated by determining the amount of extracted sludge per day R (MLSS conversion) set as described above and multiplying the amount of ozone injected per amount of sludge (MLSS). . Then, it is selected whether the gas is continuously injected or intermittently injected, and the gas flow rate (L / hr) is appropriately set according to the injection time (hr).

  In the second sedimentation tank 22, the sludge remaining in the sludge solubilized liquid discharged from the ozone tank 21 is recovered in the same manner as the first sedimentation tank 18. The residual sludge collected here is sent to the anaerobic tank 15 together with the sludge from the first sedimentation tank 18.

  The dephosphorization tank 23 is filled with a granular adsorbent, and has a structure in which the sludge solubilizing liquid from the second settling tank 22 passes therethrough. That is, in the dephosphorization tank 23, the phosphorus component in the sludge solubilizing solution is adsorbed and recovered by the adsorbent.

Here, as the adsorbent, a zirconium ferrite adsorbent that is a cubic inorganic compound is used. The adsorbent has a spherical shape with a particle size of 0.7 to 2.0 mm, a surface area of about 150 m ² / g, and a packing density of 1.0 to 1.2 g / cm ³ . The ion exchange action of zirconium ferrite is derived from a large number of hydroxyl groups present on the surface, and the surface hydroxyl groups act as anion exchangers in acidic and neutral solutions and as cation exchangers in alkaline solutions. That is, zirconium ferrite exerts a trapping (adsorption) action on phosphate ions in acidic and neutral solutions, while releasing (desorbing) action in an alkaline solution. The adsorbent has been confirmed to have an adsorption capacity of about 10 g-P · l-resin ⁻¹ . Furthermore, studies have been conducted on phosphorus adsorption in the presence of various ions, and it has been confirmed that the present adsorbent can maintain high phosphorus adsorption capacity without being affected by nitrate ions and ammonia ions.

  The removal of phosphoric acid adsorbed on the adsorbent is usually carried out in an aqueous sodium hydroxide solution. In addition, the adsorbent after desorbing phosphoric acid can be regenerated to a state in which phosphoric acid can be adsorbed by being immersed in an acidic solution such as dilute hydrochloric acid or dilute sulfuric acid. As described above, the present adsorbent can repeatedly perform adsorption, desorption, regeneration, and adsorption of phosphoric acid, and recover the desorbed phosphate ions as phosphates for reuse as resources. Is possible.

  Further, in order to efficiently desorb phosphorus from the present adsorbent, about 7% sodium hydroxide aqueous solution is required about 10 times the amount of adsorbent. Furthermore, if excess sodium hydroxide is added to the alkaline solution, phosphate ions are precipitated as sodium salts, and these can be recovered by filtration.

  As the adsorbent in the present invention, it is also possible to use yttrium carbonate, activated alumina, chelate resin, pyrolite, hydrotalcite, etc. in addition to other zirconium-based carriers.

  The sludge solubilized liquid after the phosphorus is removed by the dephosphorization tank 23 contains organic carbon sources such as organic acids, sugars, and amino acids, and the sludge solubilized liquid can be returned to the aerobic tank 16. It has become a structure.

  When the wastewater treatment tank 12 is batch-type, the phosphorus recovery means 13 operates so as to extract sludge by the pump 20 immediately before or after the end of the oxygen-free process, and is removed during the aerobic process. The sludge solubilizing solution that has passed through the phosphorus tank 23 may be returned to the wastewater treatment tank 12.

  Therefore, according to such an embodiment, the sludge is extracted in the oxygen-free process, the phosphorus present in the sludge with a high content is recovered, and the sludge solubilized liquid after the phosphorus recovery is returned to the aerobic process. Since the supply of the organic carbon source during the aerobic process is covered within the process, the phosphorus recovery efficiency can be increased and the sludge volume can be reduced. .

  The configuration of each part of the apparatus in the present invention is not limited to the illustrated configuration example, and various modifications are possible as long as substantially the same operation is achieved.

The schematic block diagram of the waste water treatment system which concerns on a present Example.

Explanation of symbols

10 Wastewater treatment system 12 Wastewater treatment tank 15 Anaerobic tank 16 Aerobic tank 17 Anoxic tank

Claims (6)

Wastewater is treated by wastewater treatment in the order of anaerobic process, aerobic process, and oxygen-free process in the presence of sludge containing denitrifying phosphorus accumulating bacteria and / or a biofilm with immobilized denitrifying phosphorus accumulating bacteria. In a wastewater treatment system including a wastewater treatment tank that removes phosphorus and nitrogen in the interior,
A wastewater treatment system comprising a phosphorus recovery means for solubilizing sludge during the oxygen-free process and recovering phosphorus from the sludge solubilized liquid.   2. The waste water treatment system according to claim 1, wherein the phosphorus recovery means is provided so that the sludge solubilized liquid after phosphorus recovery can be returned to the waste water treatment tank during the aerobic process. Wastewater is treated by wastewater treatment in the order of anaerobic process, aerobic process, and oxygen-free process in the presence of sludge containing denitrifying phosphorus accumulating bacteria and / or a biofilm on which denitrifying phosphorus accumulating bacteria are immobilized. In a wastewater treatment system including a wastewater treatment tank that removes phosphorus and nitrogen in the interior,
The wastewater treatment tank includes an anaerobic tank that performs the anaerobic process, an aerobic tank that performs the aerobic process, and an anaerobic tank that performs the anaerobic process,
A wastewater treatment system comprising a phosphorus recovery means for solubilizing sludge in the oxygen-free tank and recovering phosphorus from the sludge solubilized liquid.   The wastewater treatment system according to claim 3, wherein the phosphorus recovery means is provided so that the sludge solubilized liquid after phosphorus recovery can be returned to the aerobic tank. In the presence of sludge containing denitrifying phosphorus accumulating bacteria and / or a biofilm in which denitrifying phosphorus accumulating bacteria are immobilized, wastewater treatment is performed in the order of anaerobic process, aerobic process, and oxygen-free process. In a wastewater treatment method for removing phosphorus and nitrogen in wastewater,
A wastewater treatment method characterized by extracting and solubilizing sludge from the oxygen-free process and recovering phosphorus from the sludge solubilized liquid.   6. The wastewater treatment method according to claim 5, wherein the sludge solubilized liquid after phosphorus recovery is used as an organic carbon source necessary for the aerobic process.

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