JP3442204B2 - Organic wastewater phosphorus removal and recovery method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for highly purifying phosphorus-containing wastewater such as sewage, and more particularly to a technique for removing phosphorus more stably than conventional techniques, The present invention relates to a novel phosphorus removal technology that can significantly reduce sludge generation. [0002] The most typical technique for removing phosphorus from sewage or other wastewater is a biological phosphorus removal method. This technology supplies organic sewage to the anaerobic process and discharges phosphorus from activated sludge (in which dephosphorylated bacteria coexist) in the returned sludge, and then supplies it to the aerobic process to ingest phosphorus from the dephosphorylated bacteria. After that, the activated sludge is settled and separated, and the settled sludge is recycled to the anaerobic process. However, the conventional biological phosphorus removal method has the following disadvantages. When the BOD / P ratio of the raw water decreases, the phosphorus discharge from the dephosphorylated bacteria in the anaerobic step becomes insufficient, and as a result, the phosphorus intake to the dephosphorylated bacteria in the aerobic step also worsens. Since phosphorus is not removed except in the form taken up by biological sludge, the material balance of phosphorus is not established unless the sludge containing phosphorus is discharged out of the system. Processing becomes a burden. [0004] The present invention has established a new technique which has solved 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 further reducing the amount of generated excess sludge. SUMMARY OF THE INVENTION The present inventors have changed the process configuration of the biological phosphorus removal method to further combine chemical phosphorus removal and sludge solubilization with ozone in a novel manner. It has been found that the above-mentioned problem can be achieved by the above. That is, the present invention relates to a method for biologically dephosphorizing phosphorus-containing wastewater by an anaerobic aerobic method having at least an anaerobic step and an aerobic step in this order. After ozone oxidation and solubilization of a part of the sludge returned to the sludge or sludge extracted from the aerobic process, phosphate ions and metal ions that cause a precipitation reaction are added to recover phosphorus, and phosphorus is removed. And supplying the solubilized sludge to the anaerobic step. According to the structure of the present invention, the sludge in the aerobic tank or the sedimentation tank is ozone-oxidized and solubilized, and the metal ions which react with and precipitate with the phosphate ions are added to stably remove the phosphorus at a high level. And the amount of excess sludge generated can be significantly reduced. The phosphorus-containing water in the present invention is phosphorus-containing municipal wastewater (sewage or human waste) and organic industrial wastewater. In the biological dephosphorization method, the anaerobic step is a step in which aeration is not performed with an oxygen-containing gas, and the aerobic step is a step in which aeration is performed with an oxygen-containing gas and dissolved oxygen is supplied. Ozone oxidation of sludge is performed by providing an ozone oxidation tank capable of generating ozone. [0008] Solubilized sludge refers to sludge after ozone oxidation treatment. Also, due to ozone oxidation, the solution contains abundant soluble organic matter (BOD), and the sludge has increased biodegradability, so by introducing these into the anaerobic tank, the BOD / P ratio of the anaerobic tank can be increased. The expulsion of phosphorus from the dephosphorylated bacterium is improved, and the intake of phosphorus to the dephosphorylated bacterium in the aerobic tank is also improved. [0009] Conventionally, the amount of surplus biological sludge which is difficult to dehydrate due to the treatment is large and sludge treatment is problematic. However, the present invention oxidizes sludge with ozone to solubilize it, and recovers phosphorus from the solution. By introducing sludge that has not been solubilized (sludge that has increased biodegradability due to ozone oxidation) into the anaerobic tank, the solubilized sludge is decomposed into CO ₂ and H ₂ O.
There is no increase in excess sludge. Thus, the present invention for the first time breaks the stereotype that "it is impossible to reduce the amount of surplus sludge biomass to almost zero in the biological dephosphorization method in terms of the material balance of phosphorus". is there. Focusing on the fact that activated sludge containing a large amount of phosphorus is oxidized with ozone, a solubilized solution (suspension-like) containing a large amount of phosphorus, nitrogen and organic substances is generated. The idea of using it for the promotion of a new one has never been seen before. FIG. 1 shows a configuration example of the present invention. The anaerobic step and the aerobic step are performed in an anaerobic tank and an aerobic tank, respectively.
Raw water 2 and return sludge 4 from the sedimentation tank 3 are allowed to flow into the anaerobic tank 1 in FIG. 1 to discharge phosphorus from the dephosphorylated bacteria in the sludge.
Next, the activated sludge is aerated in the aerobic tank 5 to absorb phosphorus in an amount equal to or greater than the exhaled phosphorus to the dephosphorus bacteria. 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 led to an ozone oxidation tank 8, where sludge rich in phosphorus is oxidized and decomposed by ozone to be solubilized, and soluble organic matter, colloidal organic matter, ammonia nitrogen and phosphate ions are eluted from the solubilized sludge 7. As the sludge to be supplied to the ozone oxidizing tank 8, a part of the sludge may be extracted from the aerobic tank 5 and oxidized with ozone. Residual sludge not solubilized by ozone oxidation is solid-liquid separated, and to the separated liquid 9 is added a metal ion 10 which chemically reacts with phosphorus such as magnesium, calcium, aluminum, iron, etc. to remove phosphorus. It is separated and collected as magnesium ammonium phosphate (abbreviated as MAP), calcium phosphate, aluminum phosphate, and iron phosphate. Among them, magnesium ions are preferable because both ammonia and phosphorus in the ozone oxidation solubilizing solution can be recovered as MAP. MAP is also ideally a valuable resource as a slow-acting fertilizer. The effluent 12 from the phosphorus recovery tank 14 after the precipitation of phosphate ions and metal ions is recovered contains abundant BOD components.
To increase the BOD / P ratio of raw water,
Phosphorus exhalation from dephosphorus bacteria occurs actively. Residual sludge that has not been solubilized by ozone oxidation is also supplied to the anaerobic tank 1 because of its increased biodegradability, and is decomposed into CO ₂ and H ₂ O in the biological treatment step. [0014] The activated sludge that has grown due to the BOD removal of the raw water is supplied to the ozone oxidation tank 8, the anaerobic tank 1, and the aerobic tank 5
By circulating (which may pass through the sedimentation tank 5) in this order, surplus sludge almost completely decomposed into carbon dioxide and water and to be discharged out 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 is sufficient that an LSS measuring device is installed and the activated sludge MLSS is controlled so as to be within a certain range (for example, 3000 to 4000 mg / l). As another preferred embodiment, a denitrification tank and a nitrification tank are provided following the anaerobic tank 1 as in the step incorporating the present invention shown in FIG. It is a method that is performed simultaneously. By the circulation slurry, NO ₃ ⁻ and NO ₂ ⁻ generated in the nitrification tank are reduced to N ₂ gas in the denitrification tank. In FIG. 2, when the 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 increases, the denitrification rate increases, and the denitrification rate increases. There is an important effect.
Since biological dephosphorization and biological denitrification can be performed at the same time, raw water can be more favorably treated. EXAMPLE A proof 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. Table 1 Water temperature 22 degree pH 7.1 SS 135 mg / l BOD 116 mg / l Phosphorus 5.4 mg / l Table 2 Sewage treatment amount 24 l / d Anaerobic tank Volume 1 l Aerobic tank volume 5 l Floating activated sludge MLSS concentration 3000-4000 mg / l Sedimentation tank water area load 25 mm / min Sludge amount returned from the sedimentation layer 20 l / d (Those not passing through the ozone oxidation tank) Ozone Oxidation tank volume 500 cc Ozone oxidized sludge amount 1.5 to 1.7 g-ss / d Ozone added amount 0.2 to 0.3 g ozone / d Magnesium ion added amount 0.12 to 0.15 g / d ( As a result of the experiment, the average water quality of the treated water from the sedimentation tank after the treatment condition became stable two months after the start of the treatment was as shown in Table 3, and phosphorus and BOD were highly removed. It had been. Although the surplus sludge was not extracted during the one-year test, the occurrence of surplus sludge was found to be negligible since the MLSS of the aerobic tank was maintained at 4000 mg / l or less. [Table 3] SS 5 mg / l BOD 4 mg / l Phosphorus 0.8 mg / l As a result of newly combining the biological dephosphorization method, the chemical phosphorus removal method, and the sludge solubilization method with ozone, the amount of excess sludge generated can be reduced to almost zero, and the phosphorus removal can be performed stably. 2. The phosphorus ingested by the dephosphorus bacteria can be collected as valuable resources such as MAP. 3. Since the organic matter generated by ozone solubilization is used for discharging phosphorus in the anaerobic tank for dephosphorus bacteria, a stable phosphorus discharging action is performed. 4. When the ozone-solubilized sludge is supplied to the anaerobic tank 1, not only can the biological dephosphorization reaction be promoted, but also the BO in the denitrification tank can be improved.
The D / N ratio increases, the denitrification rate increases, and the denitrification rate also increases.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flowchart of a method for removing and recovering phosphorus from organic wastewater according to an embodiment of the present invention. FIG. 2 is a flowchart of a method for removing and recovering organic sewage phosphorus according to another embodiment of the present invention. [Description of Signs] 1 Anaerobic tank 2 Raw water 3 Sedimentation tank 4 Returned sludge 5 Aerobic tank 6 Sludge 7 Remaining sludge of precipitated sludge 8 Ozone oxidation tank 9 Separation liquid 10 Metal ions 11 Addition of metal to phosphorus Separation and recovery 12 Effluent from phosphorus recovery tank 13 Part of sludge from aerobic tank 14 Phosphorous recovery tank

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Claims (1)

(57) [Claim 1] In a method for biologically dephosphorizing phosphorus-containing wastewater by an anaerobic-aerobic method having at least an anaerobic step and an aerobic step in this order, the method follows the aerobic step. After a part of the sludge returned from the activated sludge settling process to the anaerobic process or the sludge extracted from the aerobic process is solubilized by ozone oxidation,
A method comprising adding a phosphate ion and a metal ion causing a precipitation reaction to recover phosphorus, and supplying the solubilized sludge from which the phosphorus has been removed to an anaerobic step.