JPS61125495A - Method and device for biological denitrification treatment of organic waste water - Google Patents

Abstract

PURPOSE:To decrease the carry over of the dissolved oxygen by circulation of a nitrifying liquid into a denitrification tank and to execute efficient denitrification reaction by aerating the nitrifying liquid with the gaseous nitrogen generated from the denitrification tank of a hermetic type and removing the dissolved oxygen in the denitrifying liquid down to a low level. CONSTITUTION:Org. waste water contg. a nitrogen compd. is subjected to the denitrification treatment by sludge contg. denitrifying bacteria in the denitrification tank 1, then the nitrifying liquid is circulated to the tank 1 in the process of subjecting the org. waste liquid to the denitrification treatment by the sludge contg. the nitrifying bacteria in a nitrification tank 2 to remove biologically the nitrogen. The gas contg. nitrogen generated from the denitrification stage in the above-mentioned method is blown into a gas lifter 12 installed to the circulating system of the nitrifying liquid to transfer forcibly the nitrifying liquid in the nitrification state to the denitrification part 1 and to decrease the concn. of the dissolved oxygen in the nitrifying liquid in the lifter 12. As a result, the carry over of the dissolved oxygen by the circulation of the nitrifying liquid into the denitrification tank is prevented and stable and efficient denitrification reaction is effected.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. The present invention relates to a method and apparatus for biological denitrification treatment of organic wastewater containing nitrogen compounds, and in particular, to a method and apparatus for biological denitrification treatment of organic wastewater containing nitrogen compounds, and in particular, to a method and apparatus for biological denitrification treatment of organic wastewater containing nitrogen compounds. This invention relates to a biological denitrification treatment method using a nitrifying solution circulation method.

The conventional denitrification process using a nitrification solution circulation method consists of a denitrification process in which nitrate or nitrite nitrogen is reduced to nitrogen gas under anaerobic conditions, and a denitrification process in which ammonia nitrogen is reduced to nitrate under aerobic conditions. Alternatively, it consists of a nitrification process that oxidizes to nitrite nitrogen. In this method, the denitrifying solution is allowed to flow from the No. 1 denitrifying tank to the nitrifying tank, and the nitrifying solution is circulated to the denitrifying tank using a pump. This nitrification liquid circulation type biological denitrification treatment uses BOD in wastewater as an organic carbon source consumed in the denitrification reaction, and is therefore attracting attention as an economical treatment method with low operating costs.

However, when circulating the nitrification solution, as mentioned above, the circulation pump is used to suck the nitrification solution from the nitrification tank that follows the denitrification tank and discharge it into the denitrification tank. No particular consideration is given to the removal of dissolved oxygen in the nitrifying solution, which is a prerequisite for smooth denitrification, and the dissolved oxygen is simply removed by natural reduction within the denitrification tank. In particular, in the nitrification liquid circulation system, the amount of nitrification liquid circulated is 3 to 5 times that of wastewater (and the denitrification efficiency decreases due to the incorporation of dissolved oxygen from the nitrification liquid).

Therefore, an object of the present invention is to provide a biological denitrification treatment method and apparatus that can reduce the amount of dissolved oxygen brought into the denitrification tank by circulating the nitrifying solution and perform a stable and efficient denitrification reaction. shall be.

According to the present invention, dissolved oxygen in the nitrification solution can be removed to an extremely low level in a short time by aerating the nitration solution with nitrogen gas generated from a closed denitrification tank. Furthermore, the above-mentioned problem has been solved by making it possible to circulate the nitrifying liquid by the lifting force of the nitrogen gas blown into the tank.

That is, in the method of the present invention, the nitrogen-containing gas generated from the denitrification process is blown into a gas lift device installed in the nitrification liquid circulation system, and the nitrification liquid in the nitrification process is forcibly transferred to the denitrification part, while It is characterized by reducing the dissolved oxygen concentration in the nitrification liquid within the gas lift device.

In addition, the apparatus for carrying out the method of the present invention has a denitrification tank, a nitrification tank, and a precipitation tank connected by a communication pipe, and further includes a nitrification liquid circulation pipe that circulates the nitrification liquid from the nitrification tank to the denitrification tank, and A gas lift device installed midway, a gas holder that stores the gas generated in the denitrification tank, a gas blowing pipe that blows gas from the gas holder into the nitrification liquid circulation pipe, and a sludge return that returns sludge from the settling tank to the denitrification tank. It is characterized by the fact that it is equipped with piping.

Next, the present invention will be explained in detail based on the drawings.

FIG. 1 is a flow sheet of a processing apparatus according to the present invention.

In this apparatus, the liquid to be treated flows from a liquid to be treated inlet pipe 6 into a sealed denitrification tank 1, and flows into a nitrification tank 2 under gravity flow. In the denitrification tank 1, nitrate or nitrite nitrogen in the liquid to be treated is reduced to nitrogen gas by the action of nitrification under anaerobic conditions, and nitrogen gas is generated. Air is blown into the solution to oxidize the ammonia nitrogen in the liquid to be treated to nitrate or nitrite nitrogen under aerobic conditions. The treated wastewater is separated into solid and liquid in settling tank 3.
The treated water is discharged from the treated water pipe 8, and a part of the precipitated sludge is introduced into the nitrification liquid circulation pipe 4 through the gate valve 14, or through the gate valve 13 and sent to the membrane chamber rosewood 1 by the return sludge pump 5. It will be sent back. It is also possible to set the flow rate 6 using the gate valve 14 and transfer the return sludge from the settling tank 3 to the denitrification tank 1 using the gas lift device 12. In this case, the return sludge pump 5 becomes unnecessary.

Nitrogen gas generated in the denitrification tank 1 is stored in a gas holder 10 and supplied to the lower part of a gas lift device 12 via a blower 11. The nitrified liquid from the nitrated liquid circulation pipe 4 is forcibly fed into the denitrification tank 1 by the lifting force of this blown nitrogen gas. At the same time, dissolved oxygen in the nitrification solution is efficiently removed in a short time by the gas-liquid contact between the nitrogen gas and the nitrification solution.

The gas lift device 12 is preferably installed perpendicularly to the nitrification liquid circulation path, and porous partition plates are preferably installed in multiple stages within the device in order to promote gas-liquid contact. This embodiment is particularly effective when dissolved oxygen in the nitrification solution is high.

When nitrogen gas is blown into the circulating nitrifying solution according to the present invention,
According to Henry's law, the oxygen partial pressure in the gas phase decreases significantly, so the dissolved oxygen concentration in the nitrifying solution also decreases relatively. In this way, the dissolved oxygen concentration in the nitrifying solution is reduced, and the anaerobic conditions in the denitrification tank are maintained well. Furthermore,
The nitrification liquid is circulated by the lifting force of the blown nitrogen gas.

EXAMPLES Next, the present invention will be described in detail based on Examples, but the present invention is not limited thereto.

Example 1 Ammonia nitrogen approximately 400 ■/l and BOD 850 ■/l
Chemical factory wastewater containing No. 1 was treated for 40 days using the treatment apparatus of the present invention shown in FIG. At that time, the amount of circulating nitrification liquid was increased to 5 times that of the raw water, and the nitrogen load in the nitrification tank was increased to 0.1 kg.
The nitrogen load in the denitrification tank was increased stepwise while keeping it constant at N/rd·d.

The nitrogen load in the denitrification tank, the dissolved oxygen concentration at the inlet of the denitrification tank, and the denitrification rate were measured, and the results are shown in Figure 2.

Furthermore, for comparison, the same wastewater was denitrified using a conventional treatment device without a gas lift device under the same conditions (conventional method) except that nitrogen gas was not blown, and the results were compared to the second one.
As shown in the figure.

As is clear from Fig. 2, according to the present invention, the dissolved oxygen concentration at the inlet of the denitrification tank is 1 to 2 ppm, and the maximum nitrogen load is 0.5 kg-N/i-d, whereas in the conventional method According to the method, the dissolved oxygen concentration at the inlet of the denitrification tank is 5 to 7 ppm, and the maximum nitrogen load is 0.35 kg-N/rr?・It was d. That is, according to the present invention, the dissolved oxygen in the nitrifying solution at the inlet of the denitrifying tank can be stably kept at an extremely low level for a long period of time, and the denitrifying efficiency can be improved.

According to the present invention, the nitrogen gas generated from the denitrification tank, which has conventionally been dissipated into the atmosphere and has not been used for any purpose, is used to reduce the amount of nitrogen gas in the nitrification liquid that is circulated to the denitrification tank. dissolved oxygen can be reduced to extremely low concentrations, and therefore high denitrification efficiency can be achieved over a long period of time. Furthermore, since the nitrification liquid can be circulated by the lifting force when nitrogen gas is supplied, a nitrification liquid circulation pump can be omitted, and operating costs can be reduced.

[Brief explanation of drawings]

Fig. 1 is a flow sheet of a denitrification treatment apparatus showing one embodiment of the present invention, and Fig. 2 shows the nitrogen load of the denitrification tank and the denitrification tank inlet when denitrification treatment is performed by the method of the present invention and the conventional method. FIG. 2 is a diagram of changes in dissolved oxygen and denitrification rate over time.

Claims (3)

[Claims] (1) In the process of denitrifying organic wastewater containing nitrogen compounds using sludge containing denitrifying bacteria, and then nitrifying using sludge containing nitrifying bacteria, the nitrifying solution is circulated to the denitrifying process. In the method of biologically removing nitrogen, the nitrogen-containing gas generated from the denitrification process is blown into a gas lift device installed in the nitrification liquid circulation system, and the nitrification liquid in the nitrification process is forced into the denitrification section. 1. A biological denitrification treatment method for organic wastewater, which comprises reducing the dissolved oxygen concentration in the nitrification liquid within the gas lift device while transporting the nitrification liquid. (2) The denitrification tank, nitrification tank, and sedimentation tank are connected by a communication pipe, and the nitrification liquid circulation pipe that circulates the nitrification liquid from the nitrification tank to the denitrification tank is also installed, and a gas lift device installed in the middle of the pipe. , a gas holder for storing gas generated in the denitrification tank, a gas blowing pipe for blowing gas from the gas holder into the nitrification liquid circulation pipe, and a sludge return pipe for returning sludge from the settling tank to the denitrification tank. A biological denitrification treatment device for organic wastewater, characterized by: (3) Biological denitrification of organic wastewater according to claim 2, wherein the gas lift device is installed vertically in the nitrification liquid circulation pipe, and the inside of the device is divided into multiple stages by porous partition plates. Processing equipment.