WO2003101896A1 - Apparatus and method for waste water treatment - Google Patents

Abstract

An apparatus for waste water treatment wherein sludge is circulated between an anaelobic tank and an aeration tank, and thereby waste water is biologically treated, characterized in that in the step of sending a sludge from the aeration tank to the anaelobic tank, the sludge is withdrawn from a position lower than that of an aeration device arranged at the lowest position among such devices provided in the aeration tank. The apparatus allows, for example, the removal of both nitrogen and phosphorus by the use of only two treatment tanks of an anaelobic tank and an aeration tank without the use of a coagulating agent.

Description

 Description Wastewater treatment device and wastewater treatment method

 The present invention relates to an apparatus and a method for efficiently treating wastewater containing organic matter. Background art

 As a dephosphorization method in the wastewater treatment method, there is a so-called AO method in which an anaerobic tank, an aeration tank, and a sedimentation tank are provided, and sludge in the sedimentation tank is returned to the anaerobic tank. This method utilizes the fact that phosphorus storage bacteria accumulate phosphoric acid as polyphosphate in cells by continuously repeating a cycle in which activated sludge is put into an anaerobic state and then into an aerobic state. However, although dephosphorization was possible with this method, denitrification could not be performed.

 As a denitrification method in the wastewater treatment method, the sludge in the anoxic tank and the aeration tank is circulated, the ammonia gas is oxidized to nitrate nitrogen in the aeration tank, and the nitrate nitrogen is reduced in the anoxic tank to reduce the nitrogen gas. The activated sludge circulation method that discharges the wastewater from the system has been widely used. However, this method could remove nitrogen efficiently but did not remove phosphorus sufficiently. This is because dissolved oxygen, nitric acid nitrate, and nitrite nitrogen contained in the circulating water from the aerobic tank do not sufficiently increase the anaerobicity of the anoxic tank and do not sufficiently release phosphorus from phosphorus-accumulating bacteria. That's why.

 For this reason, when it is necessary to simultaneously perform denitrification and phosphorus removal, an inorganic coagulant is added to the anoxic tank or aeration tank of the modified activated sludge circulation method to insolubilize phosphate ions and to remove excess sludge together with excess sludge. Before the anoxic tank of the activated sludge circulation method,

Full arranged anaerobic tank performs a biologically denitrifying the dephosphorization called A ₂ 0 methods have been found using.

However, the method of adding the coagulant has a problem that the cost of the coagulant is increased and the amount of excess sludge generated is increased, so that the processing cost of the excess sludge is also increased. In addition, the A., 〇 method requires a (complete) anaerobic tank compared to the activated sludge circulation method. However, there is a problem that a large equipment installation area is required.

 The present invention has been made to solve such a problem, and a wastewater treatment method capable of removing nitrogen and phosphorus without using a coagulant in only two treatment tanks, an anoxic tank and an aeration tank. And a wastewater treatment method. Disclosure of the invention

 In order to achieve the above object, the present invention relates to a wastewater treatment apparatus configured to circulate sludge between an anoxic tank and an aeration tank to biologically treat wastewater. Provided is a wastewater treatment apparatus configured to take out circulating fluid sludge from under an aeration device located at the lowest position in an aeration tank when sending circulating fluid sludge to an oxygen tank. The wastewater treatment apparatus of the present invention can remove nitrogen and phosphorus in only two treatment tanks, an anoxic tank and an aeration tank, without using a coagulant.

 In the above wastewater treatment apparatus, it is preferable that the position for taking out the sludge, which is the circulating liquid, be at least 20 cm below the lowest aeration device.

 Further, in order to achieve the above object, the present invention relates to a wastewater treatment method using activated sludge for biologically treating wastewater by circulating sludge between an anoxic tank and an aeration tank. The dissolved oxygen concentration (hereinafter abbreviated as DOC) at the site where the sludge to be sent enters the anoxic tank is set to 0. SmgZL or less, and / or the DOC at the site where the sludge is removed from the aeration tank is set to 0.5. Provided is a wastewater treatment method characterized by being not more than mgZL. According to the wastewater treatment method of the present invention, nitrogen and phosphorus can be removed using only two treatment tanks, an anoxic tank and an aeration tank, without using a coagulant.

 In the above treatment method, it is preferable that the oxygen utilization rate () of the sludge in the aeration tank is maintained at 15 mg / L -hour or more, more preferably 25 mgZL * hour or more. Thereby, phosphorus can be removed more efficiently.

 In the above treatment method, it is preferable to maintain the sludge concentration in the aeration tank (hereinafter, referred to as MLSS concentration) at 500 OmgZL or more. This makes it possible to more reliably remove phosphorus.

In the above treatment method, maintain the DOC in the aeration tank in the range of l ~ 3mgZL Thus, phosphorus can be removed more reliably.

 In the treatment method, when circulating the sludge from the aeration tank to the oxygen-free tank, it is preferable to take out the sludge from the sludge accumulating portion in the aeration tank. Among them, it is preferable to take out the sludge from below the lowest position of the aeration device, and it is more preferable to take out the sludge from below at least 20 cm below the lowest position of the aeration device. This makes it possible to more reliably remove phosphorus.

 In the above treatment method, it is preferable to maintain the concentration of the soluble phosphate ion-form phosphorus in the oxygen-free tank at 10 mg / L or more.

 In the above treatment method, it is preferable to maintain the oxidation-reduction potential (hereinafter abbreviated as ORP) of the oxygen-free tank at −150 mV (based on silver-silver chloride). This makes it possible to remove phosphorus more reliably.

 Further, in the above treatment method, it is preferable to take out the treated water out of the system using a membrane separation device immersed in an aeration tank. Thereby, treated water containing no solid content can be obtained, and the MLSS concentration in the aeration tank can be kept high. BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a schematic diagram showing an example of an embodiment of the present invention.

 FIG. 2 is a schematic diagram showing an example of another embodiment of the present invention.

 FIG. 3 is a schematic diagram showing an example of another embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

 Hereinafter, the present invention will be described in detail, but the present invention is not construed as being limited thereto.

FIG. 1 is a schematic diagram showing an example of an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an anoxic tank, and reference numeral 2 denotes an aeration tank. The wastewater (raw water) enters the anoxic tank 1 (arrow a), then enters the aeration tank 2 by overflow (arrow d), and is pumped from the pipe 9 through the pipe 9 at a location 6 below the aeration device 3 in the tank 2. The liquid is sent as a suction flow (arrow b), and enters the oxygen-free tank 1 from the discharge unit 5 and circulates (as indicated by the arrow). The raw wastewater a is biologically purified by activated sludge in the anoxic tank 1 and the aeration tank 2. Nitrogen is removed by circulating sludge between the anoxic tank 1 and the aeration tank 2 by a so-called nitrification denitrification reaction. Organic substances converted into BOD are aerobically oxidized and decomposed mainly by air discharged from the air discharge part of the aeration device 3 disposed in the aeration tank 2.

 In the present invention, the removal of phosphorus is carried out by being taken up as polyphosphoric acid into the microorganisms by the action of microorganisms (phosphorus accumulating bacteria) in the sludge. This microorganism takes up phosphorus in an aerobic state and releases phosphorus stored in the body in an anaerobic state. Phosphorus-accumulating bacteria, when repeatedly exposed to anaerobic and aerobic conditions, aerobically absorb more phosphorus than the amount released during anaerobic conditions.

 The sludge is circulated between the anoxic tank 1 and the aeration tank 2 by using a pump 4 to send liquid from one tank to the other tank, and to flow in from the other tank by overflow. At this time, it is not necessarily limited from which tank the liquid is sent using a pump, but sending the liquid from the aeration tank 2 to the oxygen-free tank 1 is preferable from the viewpoint of energy cost because the amount of the liquid sent can be reduced.

 In the present invention, the DOC at the part 5 where the circulating fluid from the aeration tank 2 enters the anoxic tank 1 is set to 0.2 mg or less, and the DOC at the part 6 where the circulating fluid is removed from the aeration tank 2 is reduced to 0%. By controlling the concentration to 5 mg / L or less, the flow of dissolved oxygen into the anaerobic tank 1 is suppressed, and the anaerobic degree in the anaerobic tank 1 is sufficiently maintained, thereby promoting the release of phosphorus.

 If dissolved oxygen, nitrate ions and nitrite ions are not substantially present in the anoxic tank 1, organic matter is anaerobically decomposed, and polyphosphoric acid accumulated in the bacteria is released outside the cells as phosphoric acid. Is done.

 In the present invention, the DOC at the site 5 where the circulating liquid (sludge) from the aeration tank 2 enters the anoxic tank 1 needs to be 0.2 mgZL or less, and if it is 0.1 mg / L or less, phosphorus is removed. Is more preferable because the stability is more stable, and further preferably 0.05 mg / L or less.

The DOC of the circulating fluid (sludge) from the aeration tank 2 at the part 5 entering the anoxic tank 1 is determined by the length of the pipe 9 from the part 6 taking out from the aeration tank 2 to the part 5 entering the anoxic tank 1. By increasing the length, the dissolved oxygen can be reduced in the piping by consuming it. In addition, it can be reduced by providing a deaeration means in the piping. Although not necessarily limited, by providing a portion where dissolved oxygen becomes low in the aeration tank 2 and removing the circulating fluid (sludge) therefrom, DOC at the portion entering the anoxic tank 1 can be reduced with a simple device configuration .

 It has been experimentally confirmed that the DOC at the part 6 for removing the circulating fluid from the aeration tank 2 should be 0.5 mgZL or less in order to reduce the DOC at the part 5 entering the anoxic tank 1 to 0.2 mg / L or less. Was done. It is preferable that the DOC of the site 6 from which the circulating fluid is removed from the aeration tank 2 is set to 0.3 mgZL or less, since the removal of phosphorus is more stable.

 The DOC can be measured using an ordinary D〇 meter based on the diaphragm electrode method.

 In order to reduce the DOC at the site 6 where the circulating fluid (sludge) is removed from the aeration tank 2 to 0.5 mgZL or less, it is preferable to remove the sludge from the aeration tank 2 into the oxygen-free tank 1 from the sludge accumulation part. . The sludge accumulating part means a part that is not easily affected by sludge flow due to aeration. For example, if a space is provided between the aeration device 3 and the bottom of the aeration tank 2, the sludge present in the lower part of the aeration device 3 will not be sufficiently stirred, and will be a stagnant portion.

 Therefore, by extracting sludge from below the position of the aeration device 3 as shown in Fig. 1, the DOC at the site 6 where the circulating fluid (sludge) is extracted from the aeration tank 2 can be reduced to 0.5 mg ZL or less. . When a plurality of aeration devices 3 are provided in the aeration tank 2, a portion for extracting circulating fluid (sludge) is provided below the lowest aeration device. Further, the distance from the aeration device 3 to the site 6 to be taken out is preferably 20 cm or more downward, more preferably 30 cm or more.

 In addition, as shown in FIG. 3, as another embodiment, the aeration liquid (sludge) is taken out from the aeration tank 2 by providing a partition plate 7 inside the aeration tank 2 and providing a part 6 where the sludge is not well stirred. You may make it take out sludge.

The flow of sludge in the aeration tank 2 is not aerated, mainly due to the rise of air bubbles from the air outlet at the aeration part by the aerator 3 The sludge descends in the part, whereby the whole is stirred. At this time, if the oxygen utilization rate (ι \) of the sludge in the aeration tank 2 is maintained at a high level, the oxygen is rapidly consumed in the non-aerated area, so that the portion where the dissolved oxygen becomes low in the aeration tank 2 is reduced. It is easy to form. As a specific example, it is preferable to maintain the rate at 15 mg / L · h or more, and it is more preferable to maintain the rate at 25 mgZL · h or more because the phosphorus removal property becomes more stable.

Oxygen utilization rate of the sludge in the aeration tank 2 (r _f), the adjustment of the aeration intensity by adjustment of the MLS S concentration can be maintained at or above 1 5mgZL.

 The oxygen utilization rate () of the sludge in the aeration tank 2 refers to the i of the sludge taken from the aerated part of the aeration tank 2, and the measuring method is a sewer test method (1997, Japan Sewage Works Corporation). Association).

 The MLSS concentration in the anoxic tank 1 and the aeration tank 2 can be controlled by SRT (solid matter retention time), but for more stable dephosphorization, the MLS S concentration must be increased. It is preferable to maintain. This is because if the MLSS concentration is high, oxygen is rapidly consumed in the non-aerated portion, so that it becomes easier to form a portion in the aeration tank 2 where the DOC becomes low. When the MLSS concentration is high, the number of denitrifying bacteria per unit volume is large, so that the denitrification rate is high and an anaerobic state free of dissolved oxygen and bound oxygen easily occurs in the anoxic tank 1. Specifically, the MLSS concentration in the aeration tank 2 is preferably maintained at 500 OmgZL or more, more preferably 800 OmgZL or more. If the MLSS concentration is too high, the dissolution efficiency of oxygen is extremely reduced due to a decrease in sludge fluidity. Therefore, the upper limit is preferably 2000 OmgZL or less.

 The MLSS concentration can be measured according to a sewer test method (1997, Japan Sewer Association).

D〇C in the aeration section in the aeration tank 2 needs to be maintained at a concentration higher than that required for the organic matter decomposition treatment and the nitrification treatment, and is preferably maintained at lmg / L or more. However, if the concentration is too high, the phosphorus removal performance is reduced, so it is preferable to keep the concentration at 3 mgZL or less. D〇C in the aeration section can be adjusted by adjusting the amount of aeration, changing the dissolving efficiency of the aeration apparatus 3, and the like. If the phosphate-accumulating bacteria release more phosphorus in the anoxic tank 1, more phosphorus can be taken up in the aeration tank 2. Therefore, when the treatment is performed in a state in which the concentration of the soluble phosphorus phosphate in the oxygen-free tank 1 is high, the performance of removing phosphorus can be enhanced. The concentration of the soluble phosphate ion form phosphorus in the anoxic tank 1 is preferably maintained at 10 mg ZL or more, more preferably at 15 mg ZL or more.

 In order to release a large amount of phosphorus in the anoxic tank 1, it is also effective to keep the ORP of the anoxic tank 1 low. The ORP of the oxygen-free tank 1 is preferably maintained at -150 mV (based on silver-silver chloride), more preferably at 120 OmV or less.

 ORP is an indicator of whether a substance is easy to oxidize or reduce another substance.The larger the number, the more it is likely to participate in other substances. This means that the more the other substances are, the more easily they can be reduced. The ORP is measured by a metal electrode method using a saturated silver chloride electrode as a reference electrode.

 A part of the sludge treated in the aeration tank 2 by the wastewater treatment method of the present invention is solid-liquid separated, disinfected if necessary, and then discharged. The solid-liquid separation means is not particularly limited, and a conventional precipitation separation method can be used.However, when the membrane separation device 8 is immersed in the aeration tank 2 as shown in FIG. This is preferable because high-quality treated water that is substantially not contained can be obtained. When solid-liquid separation is performed using the membrane separation device 8, the MLSS concentration can be easily maintained at a high level, and the efficiency of phosphorus removal can be increased. The membrane separation device 8 is not particularly limited, and a known device such as a flat membrane, a hollow fiber membrane, a tubular ceramic membrane, and a rotating disk membrane can be used. The treated water separated by the membrane is discharged out of the system by the arrow e. Of course, as shown in FIG. 2, the membrane separation device 8 may not be provided.

In the treatment method of the present invention, a microorganism-immobilized carrier can be added to the oxygen-free tank 1, the aeration tank 2, or both. As a result, the actual MLSS concentration increases, and in the aeration tank 2, nitrifying bacteria having a low growth rate are fixed to the carrier, so that the nitrification rate in the tank is increased, and the nitrogen removal treatment can be performed in a short time. Will be able to do so. The carrier used is not particularly limited, and a polyolefin hollow foam, a urethane foam carrier, or the like can be used. Add carrier In this case, a screen, mesh, etc. should be provided at the sludge discharge port, overflow port, etc. from each tank so that the carrier does not flow out. Further, the specific gravity of the carrier is preferably 1 or less in order to avoid sedimentation or the like in the stagnant portion.

 In addition, during operation during rainfall, rainwater may enter the wastewater and the concentration of phosphorus in the treated water may temporarily increase, as in the case of a decrease in the concentration of wastewater. A coagulant may be added to the raw water, the oxygen-free tank 1, or the aeration tank 2 to reduce the phosphorus concentration in the treated water. Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1

 Using the equipment shown in Fig. 1, effluent from municipal sewage was treated for about 450 days. The tank size and the like were configured as follows.

(1) Sludge capacity of anoxic tank 1 and aeration tank 2 (size): 6.75 m ^{: i} (L 150 cmXW 100 cmXH600 cm, water depth 450 cm)

 (2) Aeration device: Installed at a height of 60 cm from the bottom of the aeration tank

 (3) Circulating fluid outlet from aeration tank 2: Installed at a height of 20 cm from the bottom of the aeration tank

(4) amount of treated water: 54m ³ Z Date

(5) Sludge extraction amount from the aeration tank 2 to the anoxic tank 1: 6. 75 m ³ Bruno Date

(6) excess sludge withdrawal amount: 0. 48~ 96 m ³ days

(7) Aeration amount: 40 ~ 70Nm ³ Zhr

Furthermore, a membrane separation device 8 using a hollow fiber membrane (membrane area: 126 m ² ; manufactured by Mitsubishi Rayon Co., Ltd .; using a polyethylene hollow fiber membrane; product name: EX 540 V) was installed at a position 50 cm above the aeration device. The filtrate was taken out as treated water.

表 2 Table 1 shows the raw water quality and sludge properties, and Table 2 shows the treated water quality.

Table 2

なお、 各測定方法は下水道試験方法 （1 9 9 7年、 社団法人日本下水道協会） に従い以下のように行った。

In addition, each measurement method was performed as follows according to the sewer test method (1997, Japan Sewerage Association).

 (1) BOD: BOD was measured without adding a nitrification inhibitor.

 (2) C〇D: COD was measured by the so-called Mangan method determined from the consumption of potassium permanganate.

 (3) Total nitrogen: Total nitrogen was measured by the summation method.

 (4) Total phosphorus: Total phosphorus was measured by a complete degradation assay.

 (5) DOC: DOC was measured using a dissolved oxygen meter (a dissolved oxygen sensor (model number: DO30G) and a dissolved oxygen converter (model number: DO402G) manufactured by Yokogawa Electric Corporation).

(6) ORP (silver-silver chloride standard): For ORP, use an ORP meter (ORP sensor (model number: OR8 EFG) manufactured by Yokogawa Electric Corporation) and an ORP converter (model number: OR400G). Use Measured. As the electrode, a saturated silver chloride electrode was used, and a direct reading value was used.

 (7) Soluble phosphate ion phosphorus concentration: The concentration of soluble phosphate ion phosphorus is determined by filtering a non-oxygen tank sludge sample with dry filter paper Type 5 B and then filtering the filtrate with molybdenum blue (ascorbic acid reduction). It was measured using the method.

 (8) Solid content and MLSS concentration: Measured by centrifugation. That is, take an appropriate amount of sludge sample in a sedimentation tube, perform centrifugation for 2 to 3 minutes at "3000 to 4000]" 13171, discard the supernatant, add water to the sedimentation tube, stir, and centrifuge again in the same manner. The liquid was discarded, the precipitate was washed in an evaporating dish, dried at 105 to 110 ° C for 2 hours, the mass was measured, and calculated by the following formula.

 MLS S concentration = Dry sludge mass (mg) Z sample amount (L)

 (9) r in the aeration section of the aeration tank 1 L of sludge was taken from the aeration section of the aeration tank into a small-mouthed bottle, allowed to stand for 10 to 20 minutes, and the supernatant was siphoned into the small-mouthed bottle. When the MLS S concentration was high, there was almost no sedimentation by standing, so the sludge was separated into the supernatant by centrifugation. Then, the supernatant of the narrow-mouthed bottle was vigorously aerated for 5 to 10 minutes using an air diffuser so that the DOC was about 5 mg / L or more, and the mixture was stirred well with the precipitated sludge. Into an Erlenmeyer flask, and use a DO meter to prevent air from entering.

A part of the sensor (Central Chemical Co., UC 101) was inserted and the decrease in oxygen concentration was recorded. The oxygen utilization rate was calculated from the following equation using the initial linear part of the recorded decrease curve.

Oxygen utilization rate (r _r ) (mgZL ') = oxygen reduction (mgZL) Z elapsed time (time) As shown in Table 2, good removal performance can be achieved for all water quality items during the treatment period. In particular, with regard to phosphorus, an extremely high removal rate of about 96% was achieved, even though no coagulant was added. Industrial applicability

As described in detail above, according to the present invention, phosphorus can be removed in addition to removing nitrogen and BOD using only two tanks, an anoxic tank and an aeration tank. You. Furthermore, since no coagulant is added, the amount of excess sludge generated can be kept low.

Claims

The scope of the claims  1. A wastewater treatment device configured to circulate sludge between an anoxic tank and an aeration tank to biologically treat wastewater, and to send sludge as circulating liquid from the aeration tank to the anoxic tank. A wastewater treatment apparatus characterized in that sludge, which is circulating liquid, is taken out from below the lowest aeration device disposed in the aeration tank when the solution is liquefied. 2. The wastewater treatment system according to claim 1, wherein a position where sludge as circulating liquid is removed from the aeration tank is at least 20 cm below the lowest aeration device. 3. Biological treatment of wastewater by circulating sludge between an anoxic tank and an aeration tank This is an activated sludge wastewater treatment method, in which the circulating sludge sent from the aeration tank is oxygen-free. Wastewater characterized by having a dissolved oxygen concentration (DOC) of 0.2 mgZL or less at the part entering the tank, and a dissolved oxygen concentration (DOC) of 0.5 m2 at the part where the sludge is removed from Z or the aeration tank. Processing method. 4. waste water treatment method according to claim 3, wherein that you keep the oxygen utilization rate of the sludge in the aeration tank (r _f) above at 15 mg. 5. The wastewater treatment method according to claim 4, wherein the sludge oxygen utilization rate () in the aeration tank is maintained at 25 mg hour or more. 6. The wastewater treatment method according to claim 3, wherein the sludge concentration (MLS S concentration) in the aeration tank is maintained at 500 OmgZL or more. 7. The wastewater treatment method according to claim 3, wherein the dissolved oxygen concentration (DOC) of the aeration tank is maintained in a range of 1 to 3 mgZL. 8. The sludge circulating from the aeration tank to the anoxic tank is stored in the aeration tank. 4. The wastewater treatment method according to claim 3, wherein the wastewater is taken out of the section. 9. The wastewater treatment method according to claim 8, wherein the sludge retaining portion is located below a lowest aeration device provided in an aeration tank. 10. The wastewater treatment method according to claim 9, wherein the sludge accumulating portion is separated from the lowest aerator by 20 cm or more. The wastewater treatment method according to claim 3, wherein the concentration of the soluble phosphate ion-form phosphorus in the oxygen-free tank is maintained at 1 OmgZL or more. 12. The wastewater treatment method according to claim 3, wherein the oxidation-reduction potential (〇RP) of the oxygen-free tank is maintained at 15 OmV or less (based on silver / silver chloride). 13. The wastewater treatment method according to claim 3, wherein the treated water is taken out of the system using a membrane separator immersed in the aeration tank.