JPS6233593A - Biological treatment of waste water - Google Patents

Abstract

PURPOSE:To efficiently remove nitrogen and org. matter in org. waste water by adding grains deposited with microbes and having >=1 sp.gr. into a treating vessel, charging org. waste water contg. ammoniacal nitrogen into the treating vessel, and intermittently aerating the water. CONSTITUTION:In the biological treatment of org. waste water contg. ammoniacal nitrogen, grains 12 deposited with microbes and having >=1 sp.gr. are added into the treating vessel 11 and org. waste water contg. ammoniacal nitrogen is charged into the treating vessel 11 through a line 14. Then the water is intermittently aerated through an air inlet pipe 15 to remove the nitrogen and org. matter in the org. waste water. Since such constitution is adopted, sewage can be biologically treated with high efficiency in removing nitrogen even with such compact equipment.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for treating organic wastewater containing ammonia nitrogen. This relates to sewage treatment methods.

[Prior Art] Biological denitrification methods are widely used to remove ammonia nitrogen contained in organic wastewater. Biological denitrification method converts ammonia nitrogen (NHaN) into nitrate nitrogen (NHaN) in an aerobic atmosphere by the action of nitrifying bacteria.
The nitrate nitrogen generated at the same time as being oxidized to Ox-N) is transferred to the next denitrification tank and reduced to N2 gas in an anaerobic atmosphere by the action of denitrifying bacteria. - To allow the inferior reaction to proceed, hydrogen is supplied in an amorous atmosphere! It is necessary to add F-form (methanol, etc.). Therefore, as a system to solve this uneconomical problem and economically implement the biological denitrification method, a method using the BOD component in organic wastewater (sometimes called raw water) as a hydrogen donor was proposed and put into practical use. has been done. Figure 2 is a flow explanatory diagram showing an example of such a sewage treatment system, in which a denitrification tank 1° is provided on the upstream side and a nitrification tank 2 is provided on the downstream side, and both are connected by a downflow line 3 and a return line 4. This removes nitrogen. To explain the logistics in this flow, if the amount of organic wastewater flowing into denitrification tank I is Q, then if we want to increase the most effective treatment efficiency (balance between total treatment and fraud rate), , about four times the amount (4Q) of wastewater is sent from the denitrification tank 1 to the nitrification tank 2 through the downflow line 3, while about three times the amount (3Q) of wastewater is sent from the nitrification tank 2 to the denitrification tank l via the return line 4. equal to the inflow amount (
The treated water in Q) is discharged from the nitrification tank 2 and introduced into the sedimentation separation tank 6, where it is separated into sludge M and supernatant liquid W. A part of the former is returned to the denitrification tank 1, and the remaining part is treated by incineration, etc. At the same time, the latter is released.

That is, organic wastewater is nitrified in nitrification tank 2 while circulating between nitrification tank 2 and denitrification tank 1, and is returned to denitrification tank 1 where it is denitrified using the BOD component in the organic wastewater as a hydrogen source. After undergoing the reaction, the water is further returned to the nitrification tank 2 via the downstream line 3 and discharged as treated water.

[Problems to be solved by the invention] However, in the above system, in order to advance the nitrification reaction in the nitrification tank 2, dissolved oxygen (DO) in the tank is
It is necessary to maintain the concentration above mg/n, and DO is inevitably present in the circulating liquid from the nitrification tank 2. Therefore, if you try to increase the nitrogen removal rate by increasing the circulation ratio, a large amount of nitrogen will accumulate in the denitrification tank 1.

This will consume part of the organic matter that should be used as a hydrogen donor, which will reduce the reaction rate in the denitrification tank 1, and furthermore, the presence of DO will impair the anaerobic function. Therefore, there are restrictions on increasing the circulation ratio. The normal circulation ratio is about 3, and the nitrogen removal rate in such cases is at most 75 to 80.
%11], and it must be said that there is a lot of room for improvement.

On the other hand, the present inventors added fine solid particles with a particle size of 0.2 to 0.5 mm into a treatment tank, and introduced the solid particles into the tank by an appropriate stirring operation, with the aim of making wastewater treatment facilities more compact. For many years, we have conducted research on aerobic treatment or aerobic treatment using the action of microbial films that are dispersed and grown on the surface of solid particles. The principle of this method is the same as that used for fluidized bed treatment of wastewater, but since it is possible to treat wastewater with at least five times the volume load compared to the activated sludge method, it has the characteristic that the equipment is extremely compact. ing.

The disadvantage of the fluidized bed method is that some solid particles with excessive growth of biofilm migrate to the upper part of the fluidized bed due to their apparent specific gravity, and this often flows out of the tank, making stable operation impossible. have.

The present inventors have studied methods using mechanical stirring or gas stirring operations using aeration air, and have overcome the problems of the fluidized bed method by preventing biofilm particles from flowing into the tank.

As part of these studies, we conducted experiments to remove nitrogen by circulating nitrified water to a denitrification tank, similar to the activated sludge method described above, and demonstrated that nitrogen removal is possible with a high volumetric load. (16th Sewerage Research Conference Lectures P320-322.'79).

By this method, a nitrogen removal apparatus for organic wastewater containing ammonia nitrogen such as sewage can be shown as shown in FIG. In this equipment, in order to prevent the biofilm particles in the reaction tank from flowing out of the tank, a sedimentation separation section is formed between the biofilm particles and the treated water, and the water area load is usually 120 ta3/
s2. Design with da7.

For example, if nitrified water is circulated in an amount three times the amount of inflow water (Q), 75 to 80% of nitrogen can be removed very efficiently. However, at this time, the amount of water in the denitrification φ nitrification tank becomes 4Q, and in order to create a sedimentation separation section corresponding to that amount, an area four times as large as that in the case where no circulation is performed is required. Due to these tank structure constraints, there is a limit to the amount of water that can be processed per line, and the maximum amount of water that can be processed when treating normal sewage is approximately 800 m3/da.
y is a drawback of this device. Also, like the conventional method using activated sludge, the nitrogen removal rate is usually about 75 to 80%. If even more efficient nitrogen removal is desired, a second tank where methanol is added after the nitrification tank is used.
Similar to the conventional method shown in FIG. 2, it is necessary to install a denitrification tank and then a reaeration tank for removing methanol remaining in the treated water in the second denitrification tank.

The present invention has been made focusing on these circumstances,
The present invention aims to provide a biological wastewater treatment method that can make the equipment more compact and improve the nitrogen removal rate without adding organic chemicals such as methanol.

[Means for Solving the Problems] The method of the present invention that achieves the above object is to add particles with a specific gravity greater than 1 to which microorganisms are attached into a treatment tank, and to treat organic wastewater containing ammonia nitrogen. The gist of this method is to remove nitrogen and organic matter from organic wastewater by charging the organic wastewater into the treatment tank and performing aeration intermittently.

[Operation] The biofilm particles may be appropriately selected from those on which microorganisms can grow attached to their surfaces, such as sand and activated carbon.

Coke, zeolite, chamotte, lightweight aggregates.

The zero particle size, which can be exemplified by vinyl chloride resin, varies depending on the material, and sand with a relatively large specific gravity has a diameter of 0.1 to 0.5 m.
s, 0.5 to 2 for vinyl chloride resin with relatively low specific gravity.
■Use later. The amount added is 5 to 20%, preferably 10 to 20%. The aeration time is 2 to 10 minutes, and the aeration stop time is 5 to 10 minutes. The residence time of wastewater is 1 to 2 hours' in the case of sewage. If the aeration time is 5 minutes and the aeration stop time is 5 minutes, one cycle time of the nitrification and denitrification reactions is 10 minutes. If the residence time is now 80 minutes, the number of cycles of nitrification and denitrification will be eight times during this time. This corresponds to the case where the circulation rate of the nitrification treated water is 8 times the inflow water rate, and a much larger fI ring effect is achieved compared to the usual case where the circulation rate is 3 times the inflow water rate, and even chemical-free injection is possible. Since the nitrogen removal rate is improved to over 90% and this is carried out in a single tank, the structural constraints caused by the sedimentation and separation tank described above can be eliminated.

As described above, the present invention solves the problems of the conventional method at once, and not only makes it possible to make the device even more compact, but also makes it possible to make the device extremely simple and easy to manage.

[Example] An implementation IE of the present invention will be explained with reference to FIG.

FIG. 1 is a schematic explanatory diagram of a processing tank 11 to which the present invention is applied. Wastewater is introduced into the wastewater introduction line 14 by the wastewater pump Pt.
The water is sent to the bottom of the processing tank 11 through the tank 11. The processing tank 1
Air is fed into the processing tank 11 by a blower 18 through an air introduction pipe 15, and is aerated for a time set by a timer 19. After a pause of 1 to 5 minutes after the aeration stops (depending on the setting of the timer 19), the circulation pump P2 operates for the time set on the timer 19, and water is circulated from the top of the tank to the bottom of the tank through the circulation line 16. Processing 11
Then, the blower 18 is operated again by the timer 19, and air is sent from the air introduction pipe 15 to the bottom of the treatment tank 11 for aeration, and the same process is performed automatically. This cycle is repeated. The treated water is separated from biofilm particles in the sedimentation separation section 13,
The treated water is discharged from the discharge line 20.

In the draft pipe 17 for air agitation, air rises inside the pipe during aeration, and an L countercurrent is generated inside the pipe due to the air lift effect.
Since a downward flow occurs on the outside of the air lift pipe 17 for air agitation, biofilm particles and the treatment tank ll are generated throughout the treatment tank 11.
This is to ensure that the wastewater inside is well mixed. Note that, instead of the draft pipe 17, other stirring means may be used to create an aerobic atmosphere (dissolved oxygen concentration of 2 to 3 mg/l) in the processing tank 11, or the draft pipe 17 for air stirring may be removed. Simply aerating can accomplish this goal.

During the downtime after the aeration stops, the treatment tank 11
up to the water surface (over the entire area except for the settling section 13)
Dispersed biofilm particles begin interfacial sedimentation. That is,
The period of 1 m during the pause is a waiting time for the biofilm particle interface 12 to descend to a position below the height of the suction port 21 above the circulating water introduction line 16.

The operation of the circulation pump P2 is effective when sand or the like with a relatively high specific gravity is used as the biofilm particles, but it is not necessarily necessary when using something with a relatively low specific gravity such as vinyl chloride resin particles. The reason for this is that the particle sedimentation rate is relatively slow and the biofilm particle interface 1 during the aeration stop time.
This is because the volume under 2 remains at the same level as the reaction tank volume, and the biological reaction by biofilm particles proceeds smoothly. In summary, the downtime after the aeration stops, and whether or not the circulation pump P2 needs to be operated and installed after that, may be determined based on the interfacial sedimentation velocity of the biofilm particles and the aeration stop+h time.

It is efficient to introduce wastewater continuously as described above, but if there are large fluctuations in the introduction time of wastewater, it is also possible to treat it in batches or introduce wastewater intermittently. The sedimentation separation section 13 is not necessary. In addition, when treating a relatively small amount of wastewater, biofilm particles are present in a continuous mechanical stirring tank using an agitator, the wastewater is allowed to flow into this, intermittent aeration is performed, and the treated water is placed in a continuous mechanical stirring tank. A system in which the water flows out through a sedimentation separation tank may be used, and if necessary, it is also possible to use a multi-stage tank.

The present inventors conducted experiments as described below using a processing apparatus as shown in FIG.

BOD: 198 g/l, T-N: 31.5
sg/u.

NH4-N: 26mg/i, T-P: 3.5
First sedimentation pond overflow water at the sewage treatment plant in Kog/Ko 28.41
/h was injected into a JIII tank with a volume of 27 mm (excluding the volume of the sedimentation tank). BOD transplantation load is 5.0 k
It is g-BOD/m3 meeting day. The particle size is 0.
A light aggregate powder of 2 to 0.5+em was added with an apparent volume of 5.4 grams.

A greening operation was performed continuously for 20 days with an aeration time of 5 minutes, a rest time of 1 minute, and a circulation pump P2 operation time of 4 minutes to ensure that the biofilm particles were sufficiently loaded with microorganisms.

The amount of air is such that after 5 minutes of aeration, the dissolved element concentration (DO) is 2~2.
Adjustment was made so that there were 3 tags/intersection. D after aeration stop F
o decreased rapidly and reached almost 0 in 1.5 minutes. The water temperature was adjusted to 20°C. The circulation pump water amount was set so that the water rising speed in the tank was 15 m/h. The treated water was analyzed after SS separation, and the analysis value was BOD: 3.0 layer g/view.
, NH4-N: 0.8 1g/statement.

T-N: 1.5 g/b, T-P: 1.8 g/b. The removal rates of BOD, TN, and TP were θ8.5%, 35.2%, and 54.2%, respectively.

Comparing the examples of the present invention with the experimental values using activated sludge compared to the above, the volume load indicating each treatment capacity is 5.5% in the present invention. [ζ'g/l13・da7, the comparative experimental value is 0.47 kg/intestine 3・day, which shows a processing capacity of more than 10 times. This means that the device can be made more compact. Furthermore, the nitrogen removal rates were greatly improved to 95.2% and 79.1%, respectively.

The reason why such a large processing capacity can be achieved in the method of the present invention is not only because MLSS can be maintained at a higher concentration in the tank, but also because nitrifying bacteria and denitrifying bacteria are present at a higher concentration in the biofilm. It is thought that this is because of this. In addition, the equipment is simple, the single tank eliminates the need for circulation of nitrified water as shown in Figure 3, which eliminates the tank structure constraints, and it can also be used in batches depending on changes in the amount of water required. Another advantage of the present invention is that it can be handled using various methods such as formulas.

[Comparative Example] In comparison to this example, experimental results using a system similar to that shown in FIG. 3 are shown below.

The overflow sewage from the primary sedimentation tank with the same water quality as in the previous example was added to an experimental apparatus consisting of a denitrification tank (volume 5 cubic meters), a nitrification tank (volume if 1.5 cubic meters), and a settling tank at 1.14 cubic meters/h. was injected into the denitrification tank. The amount of circulation from the nitrification tank is four times this, or 4.58 Li.
/h. MLSS is 3800-4000m at this time
Activated sludge was regularly withdrawn from the sedimentation tank every day so that the amount of activated sludge was 1.5 g/min. The water temperature was adjusted to 20°C. The volumetric load calculated from the total volume of the denitrification tank and nitrification tank of 11.5 cm is 0.
It is 47 kg・day 00/proverb 3・day. As a result, T
-N removal rate was 79.1%.

[Effects of generation] As described above, according to the present invention, by adopting the above-described configuration, a biological wastewater treatment method with high nitrogen removal efficiency was realized despite the compact equipment. .

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a schematic explanatory diagram of a treatment tank 11 to which the present invention is applied;
FIGS. 2 and 3 are flow explanatory diagrams showing a typical conventional sewage treatment system. 1101. Treatment tank 12... Biofilm particle interface 13... Sedimentation separation section 14... Wastewater introduction line 15... Air introduction pipe 16... Circulation line 18
...Timer Pl...Waste water pump P2...Circulation pump Figure 1

Claims (1)

[Claims] In a method of biologically treating organic wastewater containing ammonia nitrogen, particles with a specific gravity greater than 1 to which microorganisms are attached are added into a treatment tank, and the organic wastewater containing ammonia nitrogen is transferred into the treatment tank. 1. A biological treatment method for wastewater, characterized in that nitrogen and organic matter are removed from organic wastewater by charging the organic wastewater into water and performing intermittent aeration.