JPS61118198A - Biological treatment of waste water - Google Patents

Abstract

PURPOSE:To separate simultaneously the nitrogen and phosphorus of waste water by executing anaerobic stirring in an aerator during the inflow of the waste water into the aerator, regulating the treated liquid of an aerobic stage to a specific pH value and controlling the stagnation time of the activated sludge in the aerator to a specific number of days or above. CONSTITUTION:The anaerobic stirring is executed in the aerator during the inflow of the waste water into the aerator; at the same time the pH of the treating liquid in the aerobic stage is regulated to 6.5-7.8 and the stagnation time of the activated sludge in the aerator is controlled to at least 16 days in the biological treatment method of the waste water by a batch type activated sludge method including an anaerobic stage and aerobic stage. The simultaneous and efficient treatment of the nitrogen and phosphoru-s in the waste water is made possible by using the conventional batch type installation as it is without requiring intricate and costly equipment in the above-mentioned method.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a biological treatment method for wastewater using a batch activated sludge method including an anaerobic process and an aerobic process, and in particular to The present invention relates to a method for simultaneously biologically treating and removing wastewater from wastewater.

(Prior art) In recent years, the progression of eutrophication due to nitrogen and phosphorus in water bodies such as inner bays, inland seas, and lakes has become a major social problem as a main cause of water pollution. Strict regulations have been put in place for factory wastewater, particularly regarding nitrogen and phosphorus contained in the wastewater, and various wastewater treatment methods have been proposed.

The most common method for wastewater treatment is the biological treatment method using activated sludge.This method uses BOD oxidation 1 and nitrifying bacteria under aerobic conditions to remove various types of nitrogen from wastewater. It consists of two steps: a step in which nitrogen compounds are oxidized to nitrous acid or nitric acid, and a denitrification step in which nitric acid or nitrous acid produced in the nitrification step is reduced to nitrogen gas using denitrifying bacteria under anaerobic conditions.

In addition, a method for removing phosphorus that utilizes microbial reactions using the activated sludge method is called a biological phosphorus removal method, in which excess phosphorus released in the anaerobic process of biological treatment is transferred to microbial cells in the aerobic process. The microorganisms that have taken in this phosphorus are removed from the treatment system in the form of surplus sludge, and the excess phosphorus taken in by the microorganisms is released again under anaerobic conditions to become a concentrated phosphorus solution. It is broadly divided into methods that involve chemically coagulating and separating and removing.

(The problem that the invention is trying to solve) However,
Attempting to simultaneously remove nitrogen and phosphorus using the conventional activated sludge method as described above utilizes mutually contradictory microbial metabolic mechanisms of anaerobic treatment and aerobic treatment.

It is extremely difficult to efficiently remove nitrogen and phosphorus from wastewater at the same time using the conventional activated sludge method, which combines an anaerobic process and an aerobic process.
Only 60% could be removed, and only about 30-50% of phosphorus was removed.

Therefore, there is a strong demand for a biological treatment method for wastewater that is as simple and efficient as possible.

7 In order to solve the above-mentioned drawbacks of the conventional technology and meet the above-mentioned needs, the present inventor has conducted extensive research into biological treatment methods for wastewater, and has found that by simply controlling the treatment conditions of each step, the conventional technology can be improved. It was discovered that nitrogen and phosphorus in wastewater can be easily and inexpensively treated and removed at the same time with a high efficiency that could not be achieved using conventional methods, by using the same batch-type wastewater biological treatment equipment as is. The present invention was completed.

(Means for Solving the Problems) That is, the present invention provides a biological treatment method for wastewater using a batch activated sludge method including an anaerobic process and an aerobic process. anaerobic stirring is carried out in the wastewater treatment process, the pH of the treated liquid in the aerobic process is adjusted to 6.5 to 7.8, and the residence time of activated sludge in the aeration tank is controlled at least 16 days. It is a biological treatment method.

To explain the present invention in more detail, the first main feature of the present invention is that anaerobic stirring is performed in the aeration tank while the wastewater to be treated is flowing into the aeration tank, and the second feature is that , the pH of the treated liquid in the subsequent aerobic step is adjusted to 6.5 to 7.8, and the third feature is to control the residence time of activated sludge in the aeration tank for at least 16 days. These features have primarily achieved the object of the present invention.

That is, according to the detailed ζ research conducted by the present inventor, by anaerobically stirring the raw wastewater to be treated in the aeration tank while it is flowing into the aeration tank, the hydrolysis of ATP proceeds rapidly and phosphorus is released. In the aeration process, which is the aerobic process that follows the release, 1. By adjusting the pH of the mixed liquid of raw wastewater and activated sludge to the specified range as described above, it is possible to achieve very efficient results.
ATP is produced and taken up by the activated sludge, which is always retained for more than 16 days during the aeration process, and therefore remains highly biologically active, allowing for excessive uptake of phosphorus; Under anaerobic conditions during the subsequent denitrification process, polyphosphate-accumulating microorganisms are able to maintain normal respiratory metabolism due to the presence of nitrogen in the form of nitrite or nitrate, and the ingested phosphorus is not released. Through a series of biological treatment steps, the phosphorus content of the sludge is maintained at a high concentration,
As a result, it was discovered that the phosphorus removal effect remained extremely high.

In the present invention, wastewater that can be treated with nitrogen and phosphorus at the same time includes: 1. Industrial wastewater including food factory wastewater, organic wastewater such as human waste and sewage, and wastewater that contains excessive amounts of nitrogen and phosphorus. If so, any wastewater can be treated. In particular, the treatment effect of the present invention is most remarkable when the BOD concentration is 100 mg/l or more and 5,000 g/l or less and the BOD/nitrogen ratio is 3 or more.

The method of the present invention has the above points as main features, and the other biological treatment steps may be conventionally known steps. To explain more specifically with reference to FIG. 1, raw wastewater to be treated is led from an inflow path 1 to a storage tank 2, where it is temporarily stored. The capacity of this storage tank can be arbitrarily selected based on the inflow pattern of the wastewater so that the inflow of wastewater into the aeration tank satisfies the time schedule of single-batch treatment.The capacity of this storage tank can be arbitrarily selected based on the inflow pattern of the wastewater, especially considering the residence time of the wastewater. It is not necessary to do this, but it is preferable that the waste water from the storage tank is agitated and mixed by aeration or mechanical stirring to homogenize the waste water.

Next, the vertical drainage in the storage tank is carried out by the vertical drainage pump 3.
It flows into the aeration tank 5 via the inflow path 4.

As mentioned above, the first feature of the present invention is that while this vertical wastewater is flowing into the aeration tank, aeration is not performed in the aeration tank, and stirring and mixing, that is, anaerobic stirring, is performed as it is, and this anaerobic Thoroughly mix the vertical wastewater and activated sludge by stirring.

This anaerobic stirring hydrolyzes ATP in the raw wastewater and releases sufficient phosphorus. Such anaerobic stirring may be performed by mechanical stirring using a stirring pump or the like, or by any stirring method that utilizes the inflow velocity of vertical drainage water.

After the vertical drainage has finished flowing in, aeration begins in the aeration tank. Aeration may be carried out by any conventionally known method, for example by air blown through conduit 8 by blower 7. Through this aeration process, the nitrification reaction of the nitrogen components in the inflowing raw wastewater progresses, and most of the nitrogen components are oxidized to nitrite or nitrate nitrogen. Once the oxidation of nitrogen components is completed,
It is preferable to terminate the aeration, and therefore, it is preferable to set the loading amount, aeration amount, etc. so that the oxidation is exactly completed within a predetermined aeration time.Also, since the nitrification reaction is an acid production reaction, If the pH drops too much, it is preferable to add an alkaline agent into the aeration tank from the chemical injection path 9.The pH of the positive air liquid at the end of the treatment must be maintained at 6.5 to 7.8. It is.

After the nitrification reaction is finished and the aeration process is finished.

Anaerobic stirring is performed by adding a hydrogen donor into the aeration tank from the chemical injection path 10 and using the stirring pump 6 in the aeration tank to perform anaerobic stirring without aeration to advance the denitrification reaction. to separate nitrogen as nitrogen gas. The hydrogen donors used in this anaerobic process include methanol,
Industrial chemicals such as ethanol, acetic acid, isopropyl alcohol, or waste fluids similar to the influent wastewater composition but not containing excessive amounts of nitrogen and phosphorus can be used. The amount of hydrogen donor added in this anaerobic stirring step is sufficient to remove nitrogen in the form of nitrous acid and nitrate produced by the nitrification reaction from the system as nitrogen gas by the denitrification reaction. Also, the anaerobic stirring time is set to be the time required to complete the denitrification reaction.

When the above denitrification reaction is completed, the added hydrogen donor is not consumed and some portion may remain, so a short reaeration process is performed to remove this hydrogen donor. After completion of the stirring, the stirring is stopped and the activated sludge is separated by sedimentation. Once the precipitation process is completed for the specified time,
The supernatant water is discharged through the discharge channel 11 as treated water.

This treated water is preferably sterilized and disinfected using a disinfectant such as chlorine or hypochlorites.

Excess sludge that has taken in too much phosphorus through the above treatment is transferred to the aeration tank 5.
A predetermined amount of sludge is removed from the sludge pipe 12 to the sludge storage tank 13 at the same time as, or before or after, the treated water is discharged from the pipe 14.
From this activated sludge, it is either subjected to dewatering or other treatment or taken out and disposed of as is. However, it is preferable to control the remaining activated sludge so that it stays in the aeration process for at least 16 days at all times. As a result, the activity of the activated sludge toward phosphorus can be maintained at a high level, and phosphorus can be taken up by the activated sludge with high efficiency in the primary cycle. Such control can be easily carried out by any method, such as by controlling the amount of activated sludge discharged and the draining time, or by detecting the activated sludge interface with an interface meter. Excess sludge can be dewatered using a commonly used method using iron salt as a dewatering aid, and phosphorus can be effectively fixed in the sludge, so no special dewatering method is required.

(Function/Effect) In the method of the present invention as described above, conventionally known comparatively low-cost batch-type wastewater treatment equipment is used as is, and during the treatment of wastewater, aeration is performed while vertical wastewater is flowing into the aeration tank. By performing anaerobic stirring without performing anaerobic stirring, the release of phosphorus by hydrolysis of ATP is effectively carried out, and then AT-P is produced under aerobic conditions by aeration in a specific pH range, and the activity is sufficiently increased. The sludge is maintained in a state where it can efficiently absorb excess phosphorus. In addition, even in the anaerobic state of the denitrification reaction, nitrite or nitrate nitrogen is present, so microorganisms that have ingested an excessive amount of phosphorus can carry out normal respiratory metabolism. is not released,
Therefore, in the present invention, the phosphorus content of the sludge can be maintained higher until the end compared to the conventional method, so that phosphorus can be removed stably and to a high degree simply by disposing of the excess sludge at the end.

Furthermore, the method of the present invention not only removes phosphorus as described above, but also does not have any adverse effect on biological nitrogen nitrification and denitrification reactions even under the above-mentioned specific conditions.

Therefore, in the method of the present invention, nitrogen and phosphorus in wastewater can be efficiently treated and separated simultaneously using conventional batch-type equipment without requiring complicated and expensive equipment.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Glucose 700 mg/l, starch 400 g using a batch type activated sludge oil experimental device with an aeration tank capacity of 8041
/AC, peptone 320 mgl, potassium dihydrogen phosphate 60rag/text, urea 200g/test, BODI, 00
Experiments were performed using synthetic wastewater containing 0 tag/n, 120 sg/fL of total nitrogen, and 25 tag/n of total phosphorus.

The time schedule for the experimental treatment is: inflow of wastewater (anaerobic agitation) and 2 hours of aeration at the mountain pass! The schedule is as follows: 5 hours → denitrification 3 hours → reaeration 1 hour, mountain pass sedimentation 2 hours → discharge 1 hour, and one treatment is completed in 24 hours.

In the experiment, eight experimental apparatuses having the same aeration tank were used, and parallel operation was performed under the following processing conditions.

Experiment 1 Experiment 2 Plant No., pH5TR (Japan) P) I
5TR (Sun) 1' 7.0 2
B, 0 182 7.0 4 8.5
1B3 7.0 8 7.0 184
7.0 12 7.4 1B5 7
．． 0 1B 7.8 186 7.0
24 8.0 1B7 7.0
32 8.3 1B8
7.0 B4 8.7
The experiment was conducted by keeping the temperature of the activated sludge mixture constant at 20° C. by immersing the aeration tank No. 18 in a constant temperature water tank. For replacing the wastewater, after 2 hours of static sedimentation, 40fL of supernatant water, which is equivalent to half of the aeration tank capacity in addition to the sludge measurement, is discharged, and then 401 artificial sewage is quantitatively added at a rate of 400mjL per minute. While injecting into the solution, gentle mechanical stirring was performed for 100 minutes without aeration. In the denitrification step, isopropyl alcohol was used as a hydrogen donor, and 400 ml of a 1% solution was added at the beginning of the denitrification step, followed by gentle stirring in the same manner as when the wastewater was introduced. In the @ air process and the re-aeration process, aeration was performed using bubble aeration, and the air flow rate was kept constant at 301/min. The pH of the aeration tank mixture is adjusted using a sulfuric acid solution or a sodium hydroxide solution.
In addition, the sludge retention time (SRT) was adjusted using a predetermined amount of activated sludge while the activated sludge mixture was being aerated in the re-aeration process. This was done by drawing out the mixture.

Under the conditions of Experiment I shown in the table above, the experimental equipment was operated for 90 days, and the first 70 days were regarded as the acclimatization period of activated sludge.
The average value of the treated water quality for 20 days from the 71st to the 90th day was determined, and from this result, the relationship between the phosphorus removal rate, nitrogen removal rate, and sludge retention time (SRT) was determined and shown in Figure 2. showed a value of 95% or more when the SRT was 16 days or more, and when the SRT was 12 days, the removal rate rapidly decreased to 35%. The nitrogen removal rate showed a value of 95% or more when the SRT was 8 days or more, and a sharp decrease in the nitrogen removal rate was observed when the SRT was 4 days or less.

As mentioned above, under the conditions of keeping the pH of the aeration tank mixture at 7,
Both phosphorus and nitrogen are reduced by 95% by SRT for 16 days or more.
We were able to obtain an extremely good removal rate of over %.

Next, under the treatment conditions of Experiment 2, a continuous treatment experiment was carried out for 50 days, and the average value of the treated water quality for 20 days was determined from the 31st in-house treatment and the 50th in-house treatment, and based on the results, the phosphorus removal rate and nitrogen removal rate Figure 3 shows the relationship between the pH of the activated sludge mixture and the phosphorus removal rate of 95% at pH 7 and 8 or below.
It shows a high value of more than %, and decreases rapidly at pH 8 or more,
The value was around 30%. Regarding the nitrogen removal rate,
p) At pH 1115, 5 or higher, it showed a good result of 90% or higher, and at pH 6,0, it decreased to 20%, and it was found that sufficient nitrogen removal could not be achieved.Sludge retention time (SRT) However, under the conditions of 16 days, extremely good simultaneous removal of phosphorus and nitrogen was achieved by adjusting the pH of the activated sludge mixture between 6.5 and 7.8.

Comparative Example Using the same experimental equipment and method as in Example 1, the pH of the activated sludge mixture was set to 7, and the sludge retention time (SRT) was set to 24.
The treatment experiment was carried out for 50 days in 8 rows without stirring the wastewater at the time of inflow.The average value of the treated water quality for 10 days from day 41 to day 50 was BOD
(mg/view), 9 (99%), total nitrogen (-87 sentences); 5
．． 5 (95%), total phosphorus (187 sentences); 3.8. (85%
), and as a result, it was confirmed that the phosphorus removal rate was clearly lower than in Example 1, in which mechanical stirring was performed during the inflow of wastewater.

Example 2 Instead of using the pHwRM machine in the experimental method of Example 1, 10 g of sodium bicarbonate was added at the beginning of the aeration process, and the sludge retention time (SRT) was adjusted to 16 days, and the other treatment conditions were as in Example 1. I did the same thing.

As a result, the pH of the activated sludge mixture in the aeration process was 8.4 at the beginning of the addition of sodium bicarbonate, and then pH 8.
pif rose to 7, then gradually decreased to pif7,0 at the end of the aeration process. In the denitrification process, the pH gradually decreases.
rose to reach pH 8.0, but at the end of the reaeration process it showed pH 7.7. Total nitrogen in treated water is 4mg/l
, total phosphorus was 0.8 mg/cross, achieving good simultaneous treatment of nitrogen and phosphorus.・Deafness was achieved.

[Brief explanation of the drawing]

FIG. 1 schematically shows the treatment process of the present invention, and FIG. 2 shows the relationship between the phosphorus removal rate and nitrogen removal rate in wastewater and the sludge retention time according to an embodiment of the present invention. Moreover, FIG. 3 shows the relationship between the phosphorus removal rate and nitrogen removal rate in wastewater and the pH of the sludge mixture according to an embodiment of the present invention. 1...Inflow channel 2...Storage tank 3...Pump 4...Flow channel 5
...Aeration tank 6 ...Stirring pump 7 ...Blower 8 ...Pipe line 9 ...Medicine injection path 10 ... - Chemical injection channel 11...Discharge channel 12...Sludge drainage pipe 13...Sludge storage tank 14...Pipe patent applicant Kankyo Engineering Co., Ltd. No. 1 figure

Claims (1)

[Claims] (1) In a biological treatment method for wastewater using a batch activated sludge method that includes an anaerobic process and an aerobic process, anaerobic stirring is performed in the aeration tank while the wastewater is flowing into the aeration tank, and the treated liquid in the aerobic process is A biological treatment method for wastewater, which comprises adjusting the pH to 6.5 to 7.8 and controlling the residence time of activated sludge in an aeration tank for at least 16 days.