JPH0476758B2 - - Google Patents

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, 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 how to remove it 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 oxidizing bacteria 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 phosphorus are taken out of the treatment system in the form of surplus sludge, and the excess phosphorus taken up by the microorganisms is released again under anaerobic conditions to form a concentrated phosphorus solution.
There are two main types of methods: chemically agglomerating the particles and separating and removing them. (Problem to be solved by the invention) 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. Because it is a thing,
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. In addition, only 30 to 50% of phosphorus was removed. Therefore, the reality is that there is a strong demand for a biological treatment method for wastewater that is as simple and efficient as possible. In order to solve the above-mentioned drawbacks of the conventional technology and meet the above-mentioned demands, the present inventor has conducted intensive research into a biological treatment method for wastewater. We discovered that by using a batch-type biological treatment system for wastewater as is, it is possible to simultaneously treat and remove nitrogen and phosphorus from wastewater easily and at low cost with a high efficiency that could not be achieved with conventional methods. The invention has been 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, in which the wastewater is not aerated while flowing into the aeration tank. Perform anaerobic stirring in the tank, adjust the pH of the treated solution in the aerobic process to 6.5 to 7.8, and control the residence time of activated sludge in the aeration tank for at least 16 days to simultaneously remove nitrogen and phosphorus from the wastewater. This is a biological treatment method for wastewater that is characterized by: 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: Adjusting the pH of the treatment liquid in the subsequent aerobic process 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 largely achieved the objectives of the present invention. In other words, according to detailed research conducted by the present inventor, by subjecting the raw wastewater to be treated to anaerobic agitation in the aeration tank while it flows 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 after ATP is released, ATP can be produced very efficiently by adjusting the pH of the mixed liquid of raw wastewater and activated sludge to a predetermined range as described above. The activated sludge is always retained for more than 16 days during the aeration process, and therefore the biological activity remains high, allowing for an excessive uptake of phosphorus; Due to the presence of nitrite or nitrate nitrogen under anaerobic conditions in the denitrification process, polyphosphate-accumulating microorganisms can maintain normal respiratory metabolism, and the ingested phosphorus is not released, so that a series of organisms It was discovered that the phosphorus content of sludge was maintained at a high concentration throughout the chemical treatment process, and as a result, the phosphorus removal effect was maintained at a significantly high level. In the present invention, wastewater that can be treated with nitrogen and phosphorus at the same time includes 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. Especially when the BOD concentration is 100 mg/ to 5000 mg/
When wastewater has a BOD/nitrogen ratio of 3 or more, the treatment effect of the present invention is most significant. The method of the present invention has the above-mentioned main features, and the other biological treatment steps may be conventionally known steps. The method of the present invention having the above characteristics will be explained in more detail with reference to the accompanying drawings showing one embodiment of the present invention.As schematically shown in FIG. It is guided from channel 1 to 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 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. do not have to. 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 raw wastewater in the storage tank is transferred to the raw wastewater pump 3.
As a result, the water 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 raw 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 raw wastewater and activated sludge by stirring. This anaerobic agitation 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 raw wastewater. After the raw wastewater has finished flowing in, aeration begins in the aeration tank. Aeration may be carried out by any conventionally known method, for example by air sent through pipe 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. It is preferable to terminate the aeration when the oxidation of the nitrogen component is completed, and therefore it is preferable to set the load amount, aeration amount, etc. so that the oxidation is exactly completed within a predetermined aeration time. Further, since the nitrification reaction is an acid production reaction, it is preferable to add an alkaline agent into the aeration tank through the chemical injection path 9 if the pH drops too much during aeration. It is necessary to maintain the pH of the aeration liquid at 6.5 to 7.8 at the end of the treatment. After the nitrification reaction is completed and the aeration process is completed,
Perform anaerobic stirring. In this anaerobic stirring, a hydrogen donor is added into the aeration tank from the chemical injection path 10, and the stirring pump 6 in the aeration tank performs anaerobic stirring without aeration to advance the denitrification reaction and convert nitrogen into nitrogen. Separate it as a gas. As the hydrogen donor used in this anaerobic process, industrial chemicals such as methanol, ethanol, acetic acid, isopropyl alcohol, etc., or waste liquids having a composition similar to the influent wastewater but not containing excessive amounts of nitrogen and phosphorus, etc. can be used. The amount of hydrogen donor added in this anaerobic stirring step is sufficient to remove nitrogen in the form of nitrite 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 a time necessary for the denitrification reaction to complete. 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 the completion of the stirring, the stirring is stopped and the process moves on to the sedimentation step in which the activated sludge is separated by sedimentation. After the settling process for a predetermined period of time is completed, the discharge channel 1
1, the supernatant water is discharged as treated water. This treated water is usually preferably sterilized and disinfected using a disinfectant such as chlorine or hypochlorites. Surplus sludge that has taken in excessive phosphorus through the above treatment is
At the same time as the treated water is discharged from the aeration tank 5, or before or after, a predetermined amount of sludge is removed from the sludge pipe 12 into the sludge storage tank 13, and then subjected to treatment such as dewatering from the pipe 14, or carried out as is. Although most of the remaining activated sludge is disposed of, it is preferable to control the activated sludge so that it remains in the aeration process for at least 16 days at all times.By doing this, the activated sludge's activity toward phosphorus can be maintained at a high level. This allows for highly efficient phosphorus uptake by activated sludge in the next cycle. Such control can be easily performed by any method, such as by controlling the amount of activated sludge drained and the draining time, or by detecting the activated sludge interface with an interface meter. The method for dewatering excess sludge is
Since phosphorus can be effectively fixed in sludge by the commonly used method of using iron salts as a dewatering aid, 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 when raw wastewater is flowing into the aeration tank, aeration is performed during wastewater treatment. By performing anaerobic stirring without performing anaerobic stirring, the release of phosphorus by hydrolysis of ATP is effectively carried out, and then ATP 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. Furthermore, 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. 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 by simply 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 700mg/, starch 400mg/
, peptone 320mg/, potassium dihydrogen phosphate 60
Experiments were conducted using synthetic wastewater containing urea 200mg/, BOD 1000mg/, total nitrogen 120mg/, and total phosphorus 25mg/. The treatment time schedule for the experiment was: 2 hours of inflow of wastewater (anaerobic stirring) → 15 hours of aeration → 3 hours of denitrification → 1 hour of re-aeration → 2 hours of precipitation → 1 hour of discharge, and one treatment was completed in 24 hours. This is the schedule to be completed. In the experiment, eight experimental apparatuses having the same aeration tank were used, and parallel operation was performed under the following processing conditions.

[Table] The experiment was conducted by keeping the temperature of the activated sludge mixture constant at 20°C by immersing the aeration tank in a constant temperature water tank. After 2 hours of static sedimentation, the wastewater is exchanged at 40°C, which is equivalent to half the capacity of the aeration tank, including the volume of the sludge tank.
Drain the supernatant water, then 40 artificial sewage per minute
While quantitatively injecting 400 ml, gentle mechanical stirring was performed for 100 minutes without aeration. In addition, isopropyl alcohol is used as a hydrogen donor in the denitrification process, and 1%
400 ml of the solution was added and gently stirred in the same way as when the waste water was flowing in. In the aeration process and reaeration process, aeration was performed using bubble aeration, and the air flow rate was kept constant at 30/min. The PH of the aeration tank mixture was adjusted using a sulfuric acid solution or a sodium hydroxide solution using an ON-OFF type PH regulator. In addition, adjustment of sludge retention time (SRT) is necessary to facilitate experimental operations.
This was carried out by withdrawing a predetermined amount of the activated sludge mixture while the activated sludge mixture was being aerated in the reaeration step. Under the conditions of Experiment 1 shown in the table above, the experimental equipment was
The first 70 days are regarded as the acclimatization period for activated sludge, and the average value of the treated water quality for 20 days from the 71st to the 90th is calculated. From this result, the phosphorus removal rate, nitrogen removal rate, and sludge retention time ( Figure 2 shows the relationship between
On the 12th, the removal rate dropped sharply to 35%.
Nitrogen removal rate is 95 when SRT is 8 days or more.
% or more, and a rapid decrease in nitrogen removal rate was observed when the SRT was 4 days or less. As described above, under conditions where the pH of the aeration tank mixture was maintained at 7, an extremely good removal rate of 95% or more for both phosphorus and nitrogen could be obtained by increasing the SRT to 16 days or more. Next, under the treatment conditions of Experiment 2, a continuous treatment experiment was carried out for 50 days, the average value of the treated water quality for 20 days from the 31st day to the 50th day was determined, and the phosphorus removal rate and nitrogen removal rate were determined from the results. The relationship between PH and activated sludge mixed liquid PH is summarized and shown in Figure 3. Phosphorus removal rate, PH
Shows a high value of 95% or more at 7.8 or below, PH8
In the above cases, it decreased rapidly and reached a value of around 30%.
The nitrogen removal rate is 90 at pH 6.5 or above.
% or more, but at pH 6.0, it decreased to 20%, indicating that sufficient nitrogen removal could not be achieved. As mentioned above, the sludge retention time (SRT)
Under the conditions on the 16th, 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 activated sludge mixture pH was set to 7, the sludge retention time (SRT) was adjusted to 24 days, but the wastewater was not stirred when it entered, and the experiment was carried out for 50 days. A treatment experiment was conducted.
The average values of treated water quality for 10 days from day 41 to day 50 were BOD (mg/); 9 (99%), total nitrogen (mg/
); 5.5 (95%), and total phosphorus (mg/); 3.8 (85%). 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 In the experimental method of Example 1, 10 g of sodium bicarbonate was added at the beginning of the aeration process without using the PH regulator, and the sludge retention time (SRT) was adjusted to 16 days, and the other treatment conditions were as in Example I did the same as 1. As a result, the pH of the activated sludge mixture during the aeration process
The pH was 8.4 at the beginning of the addition of bicarbonate of soda, and then increased to 8.7 and then gradually decreased to 7.0 at the end of the aeration process. In the denitrification process,
The pH gradually increased and reached PH8.0, but at the end of the reaeration process it was PH7.7. The total nitrogen in the treated water was 4 mg/, and the total phosphorus was 0.8 mg/, indicating that good nitrogen and phosphorus simultaneous treatment could be 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 example of the present invention. 1...Inflow path, 2...Storage tank, 3...Pump,
4... Channel, 5... Aeration tank, 6... Stirring pump,
7...Blower, 8...Pipeline, 9...Medicine injection channel, 10
...Medical injection channel, 11...Discharge channel, 12...Sludge drainage pipe,
13...sludge storage tank, 14...pipe line.

Claims (1)

[Claims] 1. In a biological treatment method for wastewater using a batch activated sludge method including an anaerobic process and an aerobic process,
While the wastewater is flowing into the aeration tank, perform anaerobic stirring in the aeration tank, adjust the pH of the treated liquid in the aerobic process to 6.5 to 7.8, and control the residence time of activated sludge in the aeration tank for at least 16 days. A biological treatment method for wastewater, characterized by simultaneously removing nitrogen and phosphorus from the wastewater.