JPH0994596A - Removal and recovery of phosphorus from organic sewage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new system capable of stably and highly removing phosphorus even when a BOD/P ratio of raw water is low and markedly reducing the generation amt. of excessive sludge by establishing new technique, by which the defect of a conventional biological dephosphrization method is solved. SOLUTION: In a biological dephosphorization method by an anaerobic/ aerobic method having an anaerobic process and an aerobic process in this order, a part of sludge returned to the anaerobic process from an activated sludge sedimentation process succeeding to the aerobic process or the sludge drawn out of the aerobic process is oxidized by ozone to be solubilized and, thereafter, metal ions generating the sedimentation forming reaction with phosphate ions are added to recover phosphorus, and soluble sludge free from phosphorus is supplied to the anaerobic process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for highly purifying phosphorus-containing wastewater such as sewage, and in particular, it can remove phosphorus more stably than the prior art, and can reduce the amount of surplus biological sludge generated significantly. Regarding removal technology.

[0002]

2. Description of the Related Art The most typical technique for removing phosphorus from wastewater such as sewage is biological dephosphorization. This technology supplies organic sewage to the anaerobic process, discharges phosphorus from the activated sludge (which coexists with dephosphorizing bacteria) in the returned sludge, and then supplies it to the aerobic process to ingest phosphorus to the dephosphorizing bacteria. After being carried out, the activated sludge is precipitated and separated, and the precipitated sludge is recycled to the anaerobic process.

However, the conventional biological dephosphorization method has the following drawbacks. When the BOD / P ratio of the raw water decreases, the phosphorus discharge from the dephosphorization bacteria in the anaerobic process becomes insufficient, and as a result, the phosphorus intake to the dephosphorization bacteria in the aerobic process also deteriorates. Since phosphorus is not removed except by being incorporated into biological sludge, the substance balance of phosphorus cannot be established unless the sludge incorporating phosphorus is discharged to the outside of the system. Processing becomes a burden.

[0004]

The present invention has established a new technique that solves the drawbacks of the conventional biological dephosphorization method.
It is an object of the present invention to provide a new system capable of stably removing phosphorus at a high level even when the OD / P ratio is small, and capable of significantly reducing the amount of excess sludge generated.

[0005]

Means for Solving the Problems The present inventor has solved the above problems by reforming the process structure of the biological phosphorus removal method and further combining chemical phosphorus removal and sludge solubilization by ozone in a novel manner. I found that I can achieve. That is, the present invention is a method of biologically dephosphorizing phosphorus-containing wastewater by an anaerobic aerobic method having at least an anaerobic step aerobic step in this order, from the activated sludge precipitation step to the anaerobic step subsequent to the aerobic step. Part of the sludge returned to the plant or sludge extracted from the aerobic process is oxidised by ozone and solubilized, and then phosphate ions and metal ions that cause a precipitation-forming reaction are added to recover phosphorus and remove it. The solubilized sludge is supplied to the anaerobic process.

With the above-described structure of the present invention, the sludge in the aerobic tank or the precipitation tank is ozone-oxidized and solubilized, and metal ions that react with phosphate ions and precipitate are added to the sludge to achieve a stable high degree of phosphorus removal. It is possible to reduce the amount of excess sludge generated. In the present invention, the phosphorus-containing water is, for example, municipal wastewater (sewage or human waste) and organic industrial wastewater containing phosphorus.

In the biological dephosphorization method, the anaerobic process is a process that does not aerate with an oxygen-containing gas, and the aerobic process is a process that aerates with an oxygen-containing gas and supplies dissolved oxygen. Ozone oxidation of sludge is carried out by providing an ozone oxidation tank capable of generating ozone.

The solubilized sludge refers to sludge after ozone oxidation treatment. In addition, since the solution is rich in soluble organic matter (BOD) due to ozone oxidation and sludge has increased biodegradability, it is possible to increase the BOD / P ratio of the anaerobic tank by introducing them into the anaerobic tank. Discharge of phosphorus from the dephosphorizing bacteria is improved, and phosphorus intake to the dephosphorizing bacteria in the aerobic tank is also improved.

Further, conventionally, a large amount of non-dehydrating surplus biological sludge generated during treatment has been a problem in sludge treatment, but in the present invention, the sludge is oxidized by ozone to be solubilized, and phosphorus is recovered from the solution. By introducing sludge that has not been further solubilized (however, sludge whose biodegradability is increased by ozone oxidation) into the anaerobic tank, the solubilized sludge decomposes into CO ₂ and H ₂ O,
No increase in surplus sludge.

As described above, the present invention is the first to break the stereotype that "it is impossible to make the surplus sludge biomass almost zero in the biological dephosphorization method in terms of the mass balance of phosphorus". is there. Furthermore, paying attention to the fact that solubilized liquid (suspension form) containing a large amount of phosphorus, nitrogen, and organic matter is generated when ozone oxidation of activated sludge that is rich in phosphorus is generated. The idea of using it to promote the unleashing of barefoot has never been seen before.

[0011]

FIG. 1 shows a configuration example of the present invention. The anaerobic process and the aerobic process are performed in an anaerobic tank and an aerobic tank, respectively.
Raw water 2 and return sludge 4 from the settling tank 3 are made to flow into the anaerobic tank 1 of FIG. 1, and phosphorus is discharged from the dephosphorization bacteria in the sludge.
Next, the activated sludge is aerated in the aerobic tank 5, so that the dephosphorizing bacteria absorb more phosphorus than the exhaled phosphorus. Most of the returned sludge 4 of the sludge 6 settled in the settling tank 3 is recycled to the anaerobic tank 1.

The remaining sludge 7 of the sludge 6 settled in the settling tank 3
Is guided to the ozone oxidation tank 8, and the sludge rich in phosphorus is oxidatively decomposed and solubilized by ozone, and soluble organic matter, colloidal organic matter, ammonia nitrogen, and phosphate ions are eluted from the solubilized sludge 7. As the sludge supplied to the ozone oxidation tank 8, a part of the sludge may be extracted from the aerobic tank 5 and ozone-oxidized. Residual sludge that has not been solubilized by ozone oxidation is subjected to solid-liquid separation, and to the separated liquid 9 is added metal ions 10 that cause a chemical precipitation reaction with phosphorus such as magnesium, calcium, aluminum, and iron to add phosphorus. It is separated and recovered as magnesium acid ammonium ammonium (abbreviated as MAP), calcium phosphate, aluminum phosphate, and iron phosphate. Of these, magnesium ions are preferable because both ammonia and phosphorus in the ozone oxidation solubilizing solution can be recovered as MAP. Ideally, MAP is a well-known valuable as a slow-acting fertilizer.

Since the BOD component is abundantly contained in the effluent 12 from the phosphorus recovery tank 14 after the precipitation product of the phosphate ion and the metal ion is recovered, this is taken as the anaerobic tank 1.
BOD / P ratio of raw water can be increased by adding to
Phosphorus discharge from dephosphorizing bacteria occurs actively. Since the residual sludge that has not been solubilized by ozone oxidation is also highly biodegradable, it is supplied to the anaerobic tank 1 and decomposed into CO ₂ and H ₂ O in the biological treatment process.

The activated sludge grown by removing the BOD of the raw water is the ozone oxidation tank 8, the anaerobic tank 1 and the aerobic tank 5.
By circulating (in some cases, passing through the settling tank 5) in this order, the excess sludge that is decomposed into carbon dioxide and water almost completely and should be discharged to the outside of the system becomes almost zero. The amount of sludge supplied to the ozone oxidation tank 8 is M in the anaerobic tank 1 or the aerobic tank 5.
It suffices to install an LSS measuring device and control so that the activated sludge MLSS falls within a certain range (for example, a range of 3000 to 4000 mg / l).

As another preferred embodiment, as in the process incorporating the present invention shown in FIG. 2, a denitrification tank and a nitrification tank are provided subsequent to the anaerobic tank 1 for biological dephosphorization and biological denitrification. It is a method to do at the same time. The circulating slurry reduces NO ₃ ⁻ and NO ₂ ⁻ generated in the nitrification tank to N ₂ gas in the denitrification tank.

In FIG. 2, when ozone-solubilized sludge is supplied to the anaerobic tank 1, not only the biological dephosphorization reaction can be promoted, but also the BOD / N ratio in the denitrification tank is increased, the denitrification rate is improved, and the denitrification rate is also increased. There is an important effect.
Since biological dephosphorization and biological denitrification can be performed simultaneously, raw water can be treated better.

[0017]

EXAMPLE A verification test of the present invention was conducted on sewage (average water quality is shown in Table 1) according to the process shown in FIG. Table 2
Shows the test conditions.

[0018]

[Table 1] Table 1 Water temperature 22 degrees pH 7.1 SS 135 mg / l BOD 116 mg / l Phosphorus 5.4 mg / l

[0019]

[Table 2] Table 2 Sewage treatment amount 24 l / d Anaerobic tank volume 1 l Aerobic tank volume 5 l Floating activated sludge MLSS concentration 3000 to 4000 mg / l Sedimentation tank water area load 25 mm / min Return sludge from sedimentation layer Amount 20 l / d (those not passing through ozone oxidation tank) Ozone oxidation tank volume 500 cc Ozone oxidation sludge amount 1.5 to 1.7 g-ss / d Ozone addition amount 0.2 to 0.3 g Ozone / d Magnesium ion addition amount 0.12-0.15 g / d (using magnesium hydroxide)

As a result of the experiment, as shown in Table 3, the average quality of treated water from the settling tank after the treatment condition became stable two months after the start of treatment showed that phosphorus and BOD were highly removed. Also, excess sludge was not drawn out during the one-year test, but the MLSS of the aerobic tank was maintained at 4000 mg / l or less, which revealed that the generation of excess sludge was negligible.

[0021]

[Table 3] Table 3 SS 5 mg / l BOD 4 mg / l Phosphorus 0.8 mg / l

[0022]

【The invention's effect】

1. As a result of newly combining the biological dephosphorization method, the chemical phosphorus removal method, and the sludge solubilization method using ozone, the amount of excess sludge generated can be reduced to almost zero, and phosphorus removal can be performed stably. 2. Phosphorus ingested by dephosphorization bacteria can be recovered as a valuable resource such as MAP.

3. Since the organic matter generated by ozone solubilization was used for phosphorus discharge in the anaerobic tank of dephosphorization bacteria, a stable phosphorus discharge effect is performed. 4. When the ozone-solubilized sludge is supplied to the anaerobic tank 1, not only the biological dephosphorization reaction can be promoted but also the BO in the denitrification tank
The D / N ratio is increased, the denitrification rate is improved, and the denitrification rate is also increased.

[Brief description of drawings]

FIG. 1 is a flowchart of a method for removing and recovering phosphorus from organic wastewater, which is an embodiment of the present invention.

FIG. 2 is a flowchart of another embodiment of the present invention, a method for removing and recovering phosphorus from organic wastewater.

[Explanation of Codes] 1 Anaerobic tank 2 Raw water 3 Precipitation tank 4 Return sludge 5 Aerobic tank 6 Sludge 7 Remaining sludge of precipitated sludge 6 Ozone oxidation tank 9 Separation liquid 10 Metal ion 11 Phosphorus precipitated by addition of metal Separation and recovery 12 Effluent from phosphorus recovery tank 14 Part of sludge from aerobic tank 14 Phosphorus recovery tank

Claims (1)

[Claims] 1. A method of biologically dephosphorizing phosphorus-containing wastewater by an anaerobic aerobic method having at least an anaerobic step and an aerobic step in this order, from a step of precipitating activated sludge following the aerobic step to an anaerobic step. After solubilizing some of the returned sludge or sludge drawn from the aerobic process by ozone oxidation,
A method comprising adding phosphorous ions and metal ions that cause a precipitation-forming reaction to recover phosphorus, and supplying the solubilized sludge from which phosphorus has been removed to an anaerobic process.