JPH0240400B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for treating organic wastewater with activated sludge. [Prior art] In the activated sludge method, compared to the method of aeration using air (hereinafter referred to as aeration),
The pure oxygen aeration method, which uses pure oxygen (hereinafter abbreviated as _O2 ), can supply oxygen at a high rate and has practical advantages such as improving the settling properties of activated sludge. It originated in the United States and is also used in Japan. In addition, there is a case in which O ₂ aeration was performed only in the latter stages of a biological treatment tank to improve the settling properties of activated sludge (Proceedings of the 14th Sewerage Research Conference, October 1972). Published on the 4th,
(pp. 233-235). [Problems to be Solved by the Invention] In wastewater treatment, reducing treatment costs is the most important issue. Unlike the air aeration method, the O ₂ aeration method uses valuable gas that is expensive to produce, and the most important point is to use O ₂ at the highest possible rate. However, with the treatment technologies developed so far, the O ₂ utilization rate is low due to the high concentration of oxygen in the exhaust gas and dissolved oxygen in the effluent.
It remains at around 70% (Water Treatment Engineering 254-256
Page Published June 1975). The present invention partially utilizes O ₂ to improve the sedimentation properties of activated sludge, and also utilizes nearly 100% of O ₂ .
This is a method of improving O ₂ usage efficiency and reducing power costs. Further, since the ability to thicken the settled sludge is improved, sludge treatment becomes easier and dewatering ability is also improved. [Means for solving the problem] Returned sludge from the settling tank is brought into contact with oxygen or oxygen-enriched gas in a closed water tank before being mixed with raw water, and then mixed with raw water to eliminate excess in the returned sludge. Aeration is performed after oxygen is used to oxidize some of the organic matter in raw water. One embodiment of the present invention will be described with reference to FIG. The returned sludge 2 from the settling tank 6 flows into the reforming tank 3, where the gas phase section 9 is sealed and O ₂ or oxygen-enriched gas 8 is supplied, and the sludge returns to the reforming tank 3, where the gas phase section 9 is sealed and O 2 or oxygen-enriched gas 8 is supplied.
After contacting with the liquid, the communication port 1 located below the liquid surface
0 to the raw water mixing tank 4. The DO in the activated sludge that flows into the injected raw water 1
It is used to oxidize BOD components or other oxidizable substances. The raw water 1 flows down to the next aeration tank 5 via the communication port 10', and after the oxidation of pollutants is completed by air aeration, activated sludge is separated in the settling tank 6, and most of the sludge is reformed. The sludge tank 3 is returned, and the remainder is treated and disposed of as surplus sludge 7.
The supply amount of O ₂ or oxygen-enriched gas 8 is such that the oxygen concentration in the gas phase 9 is 30% or more, or the DO in the liquid phase is 10% or more.
It is best to automatically control the amount to be at least mg/mg. It is preferable that the communication ports 10, 10' be arranged at a shallow position, about 50 to 300 mm below the water surface, and the communication port 10 should be arranged about 50 mm below the communication port 10'. This can prevent a drop in the liquid level and damage to the tank wall due to an increase in pressure in the gas phase section 9. When the pressure in the gas phase section 9 is reduced, O ₂ or oxygen-enriched gas may be supplied, and when the pressure in the gas phase section 9' is reduced, the pressure regulating valve 11 may be opened to introduce air. Therefore, pressure can be adjusted. The volumes of the reforming tank and raw water mixing tank will vary depending on the concentration of returned sludge and the type of wastewater, but it is recommended that the influent remains in each tank 3 and 4 for about 2 to 3 hours, or about 0.5 hour. . In the present invention, in addition to O ₂ gas, an oxygen-enriched gas containing 50% or more oxygen gas (a gas with a higher oxygen concentration than air) may be used. Example Table 1 shows the results of treating food wastewater under the following conditions using the treatment apparatus shown in FIG.

【table】

[Table] [Effects of the Invention] When the food wastewater shown in the Examples was subjected to the conventional standard activated sludge method, the SVI was as high as 300 to 1000 ml/g, and problems often occurred in which SS overflowed from the settling tank.
However, according to the present invention, the settling properties of sludge could be significantly improved. Moreover, it is economically advantageous because 100% oxygen can be used. Furthermore, the same effect could be achieved by using oxygen-enriched gas with an oxygen concentration of 50% or more instead of O ₂ gas.

[Brief explanation of drawings]

FIG. 1 is a schematic flow diagram for explaining the method of the present invention. 1...Raw water, 2...Return sludge, 3...Reforming tank,
4... Raw water mixing tank, 5... Aeration tank, 6... Sedimentation tank, 12... Oxygen generator.

Claims (1)

[Claims] 1. In a method of treating organic wastewater by the activated sludge method, the returned sludge is brought into contact with oxygen gas or oxygen-enriched gas fed into the gas phase in a closed water tank, and then mixed with the organic wastewater. A method for treating organic wastewater with activated sludge, which is characterized by removing dissolved oxygen in returned sludge and then aerating it with air.