JPH0476757B2 - - 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. Only 60% could be removed, and only 30-50% 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 needs, the present inventor has conducted intensive research into a biological treatment method for wastewater, and found that it is possible to simply control the properties of the wastewater to be treated. By using the batch-type wastewater biological treatment equipment of 2015 as is, nitrogen and phosphorus in wastewater can be easily and inexpensively treated at the same time with high efficiency that could not be achieved with conventional methods.
The present invention was completed based on the finding that it can be removed. (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 wastewater introduced into an aeration tank is stored in an anaerobic storage system. After staying in the tank for over 1 hour and controlling the redox potential to -150mV or less, the wastewater is introduced into the aeration tank, and anaerobic stirring is performed while the wastewater is flowing into the aeration tank to remove nitrogen and nitrogen from the wastewater. This is a biological treatment method for wastewater that is characterized by the simultaneous removal of phosphorus. To explain the present invention in more detail, the first main feature of the present invention is that when wastewater to be treated is treated by the conventional batch activated sludge method,
The oxidation-reduction potential is adjusted to below a certain value before treatment, and the second feature is that while the wastewater thus adjusted is flowing into the aeration tank, anaerobic stirring is performed in the aeration tank. , These features have mainly achieved the object of the present invention. That is, according to detailed research by the present inventor, raw wastewater to be treated is maintained under aeration conditions of −150 mV or less, and the anaerobic state at the time of flow into the aeration tank is maintained, and the anaerobic state is maintained in the aeration tank. By stirring,
Hydrolysis of ATP proceeds quickly and phosphorus is released, and under aerobic conditions due to subsequent aeration, ATP
is produced, allowing microorganisms to take in excess phosphorus, while under anaerobic conditions during the subsequent denitrification process, polyphosphate-accumulating microorganisms maintain normal respiratory metabolism due to the presence of nitrite or nitrate nitrogen. It was found that the ingested phosphorus is not released, and therefore the phosphorus content of the sludge is maintained at a high concentration through a series of biological treatment steps, and as a result, the phosphorus removal effect remains extremely high. It is something. In the present invention, a preferable method for keeping the redox potential of the raw wastewater to be treated below a certain value, that is, below -150mV, is to keep the raw wastewater to be treated in an anaerobic state for a certain period of time before injecting it into the aeration tank. It's a method. Such methods include maintaining an anaerobic state for a certain period of time in a storage tank before injecting the raw wastewater into the aeration tank, controlling aeration during mixing and stirring of the raw wastewater in the storage tank, or controlling the aeration while stirring the raw wastewater in the storage tank. It is preferable not to do so. Generally, by maintaining the anaerobic state for about one hour or more, the oxidation-reduction potential of raw wastewater is reduced to -
It can be 150mV or less. Such measurement of the redox potential of raw wastewater can be easily carried out using an ordinary redox potentiometer. 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. Such organic wastewater can usually be easily maintained in an anaerobic state unless it is kept in an oxidized state by aeration or the like. To give a specific example, when various amounts of wastewater from domestic sewage A, 20-fold diluted human waste digested liquid B, pharmaceutical factory C, and brewing factory D are aerated, the change in DO during aeration and the redox potential change. The relationship is as shown below, and therefore, by easily selecting the DO value in the waste water, the oxidation-reduction potential of the waste water can be easily controlled to -150 mV or less.

[Table] In addition, when the above wastewater A to D is aerated to bring its redox potential to +100 mV, and then the aeration is stopped and only stirring is performed, the change in redox potential over time is shown in Figure 1. As shown. Therefore,
The oxidation-reduction potential of the waste water as described above can be reduced to -150 mV or less within about 60 minutes after stopping the aeration. 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. 1 to a storage tank 2, where it is temporarily stored. It is preferable to stir and mix the raw wastewater in this storage tank for the purpose of homogenization, but as mentioned above, the oxidation-reduction potential of this raw wastewater is -
Since it is necessary to maintain the voltage below 150 mV, it is preferable to perform mixing and stirring using mechanical stirring or a stirring pump. When stirring and mixing by aeration, the redox potential of the raw wastewater is monitored and the redox potential of the raw wastewater is monitored. Care must be taken to ensure that the potential does not exceed -150mV. In addition, the capacity of this storage tank is preferably set so that the residence time of the raw wastewater is always at least 1 hour, and in this way, it is easier to control the redox potential of the raw wastewater to -150 mV or less. becomes. Next, the raw wastewater in the storage tank is caused to flow into the aeration tank 5 via the inflow path 4 by the raw wastewater pump 3 . As mentioned above, the second 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 method 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 raw wastewater flowing in 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. The pH of the mixed solution at the end of the treatment should normally be maintained at 6.5 to 9.5. 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 aeration 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 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 the completion of the process, the stirring is stopped and the activated sludge method moves to the sedimentation step where the activated sludge method 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
Simultaneously with or before or after discharging the treated water from the pot bag tank 5, a predetermined amount of sludge is removed from the sludge pipe 12 into the sludge storage tank 13, and either subjected to treatment such as dewatering from the pipe 14, or carried out as is. Dispose of it. As for the dewatering method of excess sludge, phosphorus can be effectively fixed in the sludge by a commonly used method using iron salt as a dewatering aid, so no special dewatering method is necessary. (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, raw wastewater is maintained in an anaerobic state during wastewater treatment, and in particular, the oxidation and reduction ATP
The hydrolysis of phosphorus effectively releases phosphorus, and then ATP is produced under aerobic conditions through aeration, and the sludge is maintained in a state where it can efficiently uptake phosphorus in excess. In addition, even in the anaerobic state of denitrification reactions, nitrite or nitrate nitrogen is present, so microorganisms that have ingested too much phosphorus can carry out normal respiratory metabolism.
Even under such anaerobic conditions, phosphorus 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 by simply disposing of the excess sludge at the end. In addition, the method of the present invention not only removes phosphorus as described above, but also maintains the redox potential of raw wastewater in an anaerobic state of -150 mV or less during the wastewater inflow process. It does not have any adverse effect on the nitrogen reaction. 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 Using a bench scale experimental device with an aeration tank of 80,
Glucose 180mg/, Starch 100mg/, Peptone 80mg/, Potassium dihydrogen phosphate 16mg/, Urea 50mg/, BOD 250mg/, Total nitrogen 35mg/,
Experiments were conducted using synthetic wastewater containing 6.5 mg of total phosphorus and varying the redox potential of the wastewater flowing into the aeration tank. The time schedule for processing the experiment is
Inflow of wastewater for 1 hour → Aeration for 5 hours → Addition of methanol
The process was as follows: 0.25 hours → 3 hours of anaerobic stirring → 1 hour of re-aeration → 1 hour of precipitation → 1 hour of discharge, one treatment was completed in 12 hours, and half of the wastewater was replaced, and the treatment was performed in two cycles a day. In this experiment, we determined and compared the treatment effects of changing the redox potential of wastewater flowing into the aeration tank in the range of +100mV to -300mV by adjusting the amount of aeration stirring in the storage tank. The processing results are as shown in Table 1 below,
The treatment effect of BOD and total nitrogen is constant regardless of the redox potential of the inflowing wastewater, and BOD10
mg/, total nitrogen is less than 10 mg/. On the other hand, total phosphorus has a redox potential of -
0.5 only when adjusted below 150mV
mg/or less, and if the redox potential of the wastewater is -150mV or more, the total phosphorus is 0.5
mg/ or more, demonstrating the effectiveness of the present invention. Example 2 A continuous water flow treatment test for soy sauce manufacturing factory wastewater was carried out using a pilot plant with a treatment capacity of 2 m ³ /day. The properties of the sample wastewater during this continuous water flow treatment test period are as follows: BOD during the treatment period,
No major changes were observed in the composition of nitrogen and phosphorus in the wastewater, and since nitrogen and phosphorus were excessive (BOD: nitrogen: phosphorus = 100:12:1.5), treatment using the normal activated sludge method The composition of the wastewater is such that nitrogen and phosphorus remain in the wastewater. x σn−1 PH 7.0 0.2 SS (mg/) 230 114 TOC (mg/) 210 80 COD (mg/) 206 62 BOD (mg/) 606 183 Total nitrogen (mg/) 70 18 Total phosphorus (mg/) 9.2 1.9 Chromaticity (degrees) 142 26 The processing time schedule is as follows.
That is, wastewater was allowed to flow into the aeration tank in one hour from a storage tank that had a storage capacity for one day's worth of wastewater. The storage tank was stirred by aeration and controlled using an oxidation-reduction potentiometer to constantly maintain an anaerobic state of -150 mV during the inflow process. Anaerobic stirring was performed during the wastewater inflow process, and aeration was started after the inflow was completed. The nitrification process by aeration is for 12 hours, and once the nitrification process is finished,
Isopropyl alcohol is added as a hydrogen donor, and denitrification treatment is performed by an anaerobic stirring process for 6 hours.
After the denitrification process, 2 hours of re-aeration process, precipitation process 2
The treated water is discharged for 1 hour, and one treatment takes 24 hours.
It is a schedule that can be completed within a certain amount of time. The results of the above treatment are as shown in FIG. 3, and the removal rate of BOD component A during the treatment period was 98 to 99%, and did not exceed 20 mg/at maximum.
The removal rate for nitrogen component B is also 93-98%.
The maximum dose never exceeded 10mg/. In addition, the removal rate of phosphorus component C was 97 to 98%, and the amount did not exceed 0.5 mg/at maximum. From the above results, it is clear that the method of simultaneously treating nitrogen and phosphorus by biological treatment according to the method of the present invention exhibits an extremely stable treatment effect. Comparative Example 1 In Example 2, everything else was the same as in Example 2, except that the storage tank was agitated by aeration and the redox potential of the wastewater was always controlled to -150 mV or higher using a redox potentiometer. I processed it. The results are shown in FIG. As shown in Figure 4, BOD components during the treatment period
The removal rate of A′ is 98-99%, and the removal rate of nitrogen component B′ is
Although the removal rate of phosphorus component C' was 45 to 97%, it was necessary to stabilize the treatment effect regarding the removal of phosphorus component. was difficult. From the above, the oxidation-reduction potential of wastewater is -
It is clear that the object of the present invention cannot be achieved at 150 mV or more.

【table】 [Brief explanation of the drawing]

FIG. 1 shows changes over time in the oxidation-reduction potential of various wastewaters caused by anaerobic stirring, FIG. 2 schematically shows the treatment process of the present invention, and FIG. 3 shows Example 2 of the present invention. Fig. 4 shows the removal effect of BOD (mg/), total nitrogen (mg/), and total phosphorus (mg/) in wastewater in wastewater by the method, and Fig. 4 shows the removal effect of the above by a comparative example. 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, A...BOD
(mg/), B...Total nitrogen (mg/), C...Total phosphorus (mg/), A'...BOD (mg/), B'...Total nitrogen (mg/), C'... Total phosphorus (mg/).

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,
After the wastewater to be introduced into the aeration tank is allowed to stay in the anaerobic storage tank for at least one hour and the redox potential is controlled to -150mV or less, the wastewater is introduced into the aeration tank, and while the wastewater is flowing into the aeration tank. is a biological treatment method for wastewater that is characterized by the simultaneous removal of nitrogen and phosphorus from wastewater through anaerobic agitation.