JPH032040B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a biological nitrification and denitrification treatment apparatus for wastewater that includes a nitrification section and a denitrification section in a single tank and circulates the liquid between them.

Generally, in biological nitrification and denitrification treatment of organic wastewater, _NH4 -N generated from the biodecomposition of organic nitrogen in wastewater is converted into nitrite bacteria, which are aerobic bacteria, in the nitrification section.
NO _x −N (NO ₂ −N and NO ₃ −
Nitrogen is removed by nitrifying the NO x -N to N2 gas and then reducing the NO _x -N to N ₂ gas using denitrifying bacteria, which are facultative anaerobic bacteria, in the denitrification section. In the circulation treatment method in which denitrification is carried out by mutually circulating the liquid in the nitrification part and the liquid in the denitrification part, organic substances in the raw water are used as an organic carbon source in place of the methanol etc. normally used in the denitrification part. It has the advantage of neutralizing the nitrification part by generating alkali, and nitrification and denitrification treatment can be performed without chemical injection. In particular, this can also be done in a single tank.

The present invention provides a nitrification and denitrification apparatus that has a nitrification section and a denitrification section in a single tank, and effectively uses the pumping force of an aerator and the water flow generated by an agitator to effectively force circulation of the liquid in the tank. The purpose of this system is to reduce equipment costs and power costs. Specifically, the wastewater nitrification and denitrification apparatus of the present invention has a tank equipped with a mechanical surface aerator divided into upper and lower parts by a partition wall, with the upper part being a nitrification part and the lower part being a denitrification part, and the aerator rotating shaft. A stirring blade is installed in the denitrification section by extending it downward, and a downward flow circulation channel is provided in the center of the partition wall for sucking the nitrified liquid into the stirring blade. The feature is that an upward flow circulation channel is provided to send denitrification liquid to the upper part of the tank.

Furthermore, in the nitrification and denitrification treatment method using liquid circulation described above, assuming that complete nitrification and complete denitrification are performed, the nitrogen removal rate R = n + γ / 1 + n + γ × 100 (where n: circulation amount / raw water amount, γ : amount of returned sludge/amount of raw water), the nitrogen removal rate should increase as the amount of circulation increases. However, in reality, there is a limit to the residence time of the liquid in the tank, so as the circulation rate increases, the amount of dissolved oxygen brought in from the nitrification section increases, and an anaerobic state is maintained in the denitrification section. If denitrification becomes impossible or the organic carbon source necessary for denitrification is consumed by dissolved oxygen, the denitrification effect decreases and reaches a breaking point. This process is also greatly influenced by the quality of the raw water and the amount of oxygen supply.

In this regard, the apparatus of the present invention further includes a configuration in which the amount of oxygen supply and the amount of liquid circulation can be automatically adjusted in response to fluctuations in the quality of raw water so that a good denitrification effect can always be maintained in the denitrification section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below with reference to embodiments shown in the accompanying drawings.

This device consists of a tank 1 with an open top, which is equipped with a mechanical surface aerator 3 having two rows of rotating blades partially submerged below the liquid surface.
Inside this tank 1, a partition wall 4 sloped so that the center part is lower is provided at an intermediate height (in this example, the top-to-bottom ratio is about 2:1) to divide the tank into upper and lower parts, and the upper part is for aerobic nitrification. section 5, the lower part of which is used as an anaerobic denitrification section 6.

In the nitrification section 5, a draft pipe 7 is provided for the aerator 3, and the upper end of the draft pipe surrounds the blade 2 of the aerator, and the lower end is close to the lowered center of the partition wall 4, so that the rotating blade 2 of the aerator 3 The liquid is projected outward above the liquid surface as shown by arrow a, supplying oxygen by dissolving oxygen in the air, and the draft pipe is drawn in the area of the nitrification section 5 by the lifting force of the blade 2 as shown by arrow b. A general circulation flow is generated inside and outside of the tube 7, preventing liquid stagnation and sludge accumulation.

For agitation in the denitrification section 6, an extension shaft 8, which is an extension of the rotating shaft 8 of the aerator 3 downward into the denitrification section 6, is used. The blades 10 are attached so that the aerator blades 2 and the stirring blades 10 share a driving source.

As one means for circulating the liquid between the nitrification section 5 and the denitrification section 6, the central part of the partition wall 4 is opened and a downward flow circulation channel 11 is provided adjacent to the stirring blade 10. 12 is a guide plate above the opening. By doing so, a part of the nitrified liquid in the nitrification unit 5 passes between the guide plate 12 and the partition wall 4 as shown by the arrow c, and descends through the downward flow circulation channel 11 to absorb the suction force of the stirring blade 10. It flows into the denitrification section 6 due to this.

In order to supply raw water together with return sludge, a descending channel 13 is provided on the side wall of the tank 1. Raw water and returned sludge are supplied into the denitrification section 6 through the water channel 13 as shown by arrow d. In the denitrification section 6, strong stirring is applied by the stirring blades 10, and the raw water, returned sludge, and circulating nitrification liquid are mixed well, and sludge accumulation and stagnation of _N2 gas generated by denitrification are prevented. .

As another means for circulating the liquid from the denitrification section 6 to the nitrification section 5, an upward flow circulation channel 1 is provided on the side wall of the tank 1.
4 is provided, and a weir 15 is provided at the upper end near the liquid level.
is provided. By doing this,
A part of the denitrification liquid in the denitrification section 6 flows upward through the upward circulation channel 14 as shown by the arrow e by a strong radial discharge flow from the stirring blade 10 and is sent to the upper part of the tank and passes through the weir 15. and flows into the nitrification section 5. In this way, a circulating flow between the nitrification section 5 and the denitrification section 6 is generated together with the circulating flow c. It is noteworthy that this liquid circulation is accomplished by a single drive source, without any other circulation pump or external piping. Reference numeral 16 denotes a baffle plate that prevents the flow condition of the nitrification section 5 from being disturbed by overflow water from the weir 15.

A liquid outlet 17 is provided in the nitrification section 5 . In the process of nitrification and denitrification by repeatedly circulating in tank 1,
A part of the nitrification liquid is sent as treated water through the liquid outlet 17 to a settling tank for the next process, as shown by arrow f.

The basic nitrification-denitrification process of the apparatus of the present invention constructed as described above is clarified by the explanation related to the construction. In particular, in the device of the present invention, since the aerator blades 2 and the stirring blades 10 are directly connected by the same rotating shafts 8, 8', the amount of oxygen supplied can be adjusted by changing the rotation speed of a single drive motor. The amount of liquid circulated can be changed at the same time.
This makes it easier to match the nitrification and denitrification effects in response to wide variations in raw water conditions, and as a result is effective in making it possible to maintain stable optimal operation. In other words, the required amount of oxygen supply depends on the loading amount of raw water (the amount of BOD components and HN ₄ -N),
In order to always maintain a good denitrification effect in the denitrification section, it is necessary to adjust the load amount of raw water and the amount of liquid circulation.

When the raw water load is high, in order to maintain the target treated water quality, it is necessary to increase the amount of oxygen supplied and at the same time increase the amount of liquid circulation to increase the absolute amount of nitrogen removed. The need for tobacco is satisfied. In this case, sufficient
Since there is usually a BOD component, much of the dissolved oxygen brought in from the nitrification section is quickly consumed and does not adversely affect denitrification.

On the other hand, when the raw water load decreases, it is necessary to reduce the oxygen supply amount and liquid circulation amount to ensure the necessary BOD amount in the denitrification section, but this invention satisfies this need. be done. in this case,
Although the denitrification rate will decrease, the quality of the treated water will remain almost constant, and the required power will decrease in proportion to the cube of the rotational speed, allowing efficient operation.

In normal aerobic treatment, the dissolved oxygen concentration is reduced to 2mg/
It is maintained and operated to a certain level. On the other hand, in the apparatus of the present invention, both the nitrification section 5 and the denitrification section 6 are in a state of almost complete mixing, resulting in a strong circulating flow, and most of the BOD components in the raw water are removed in the denitrification section 6. Therefore, the dissolved oxygen concentration in the nitrification section 5 is
Sufficient nitrification and denitrification is possible even if the amount is kept at about 0.5 to 1.0 mg/d.

Furthermore, the device of the present invention includes a DO meter in the nitrification section 5,
That is, a dissolved oxygen concentration meter 18 is provided to measure the dissolved oxygen concentration of the nitrifying solution, and a rotation speed changing means 19 such as a frequency converter is used to adjust the aeration machine 3 and the stirring blade 1.
By controlling the rotational speed of the 0-drive motor, efficient automatic operation that can accommodate fluctuations in the raw water load becomes possible.

Furthermore, the device of the present invention has NO _x in the denitrification section 6.
- Since the reduction reaction from N to N ₂ gas can be confirmed by the oxidation-reduction potential of the liquid, the weir 15 at the upper end outlet of the upward flow circulation channel 14 is constructed as a movable weir that can be raised and lowered, and an ORP meter is installed at the upper end of this channel. That is, an oxidation-reduction potential meter 20 is provided to measure the oxidation-reduction potential of the denitrification liquid, and when this exceeds -150mV, the weir plate 15' is raised to reduce the amount of liquid circulation and prevent the denitrification effect from decreasing. It is also possible to drive this weir plate 15' by a motor and automatically control its height according to the oxidation-reduction potential.

As described above, according to the present invention, the installation area is small, the drive system is simple, and the drive system is relatively inexpensive as a wastewater nitrification-denitrification device.Moreover, it can cope with a wide range of changes in the load of raw water, and has good performance in nitrification and denitrification. It is possible to maintain excellent denitrification effects and reduce power consumption, and automatic control operation is also possible, resulting in various effects such as easy energy and labor savings. It will be done.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional side view in FIG. 2 of a wastewater nitrification-denitrification apparatus according to an embodiment of the present invention, and FIG. 2 is a plan view of the cross-section in FIG. 1. 1... Tank, 2... Blade, 3... Mechanical surface aerator, 4... Partition wall, 5... Nitrification section, 6... Denitrification section, 7... Draft pipe, 8... Rotating shaft, 8 ′...
Extension shaft, 9... Bearing, 10... Stirring blade, 11...
Downward flow circulation channel, 12... Guide plate, 13... Downward flow channel, 14... Upward flow circulation channel, 15... Weir,
15'...Weir board, 16...Bassful board, 17...
Liquid outlet, 18... Dissolved oxygen concentration meter, 19... Rotation speed changing means, 20... Redox potential meter, a, b,
c, d, e, f...water flow arrows.

Claims (1)

[Claims] 1. The inside of a tank equipped with a mechanical surface aerator is divided into upper and lower parts by partition walls, with the upper part being a nitrification part and the lower part being a denitrification part,
The aerator rotating shaft is extended downward and a stirring blade is installed inside the denitrification section, and a downward flow circulation channel is installed in the center of the partition wall to suck the nitrified liquid into the stirring blade, and the denitrification section is installed on the side wall of the tank. A nitrification and denitrification device for wastewater, characterized in that an upward flow circulation channel is provided for sending the denitrification liquid to the upper part of the tank using a stirring water flow. 2. A patent characterized in that the nitrification section is equipped with a dissolved oxygen concentration meter to control the rotational speed of the aerator in order to simultaneously adjust the oxygen supply amount and liquid circulation amount according to the dissolved oxygen concentration in the nitrification section. A nitrification-denitrification device for wastewater according to claim 1. 3. In order to adjust the liquid circulation amount according to the redox potential of the denitrifying liquid, a movable weir is provided at the upper end outlet of the upward flow circulation channel, and a redox potentiometer is provided for this part to control the movable weir. A wastewater nitrification and denitrification device according to claim 1, characterized in that the wastewater nitrification and denitrification device is configured as follows.